The physics of strong magnetic fields of magnetars
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带电粒子流的磁聚焦和磁控束英文回答:Magnetic focusing and magnetic confinement are two important techniques used in the control and manipulation of charged particle beams. These techniques are widely employed in various fields, such as particle accelerators, fusion reactors, and electron microscopes.Magnetic focusing is a method used to control the trajectory of charged particles by utilizing the Lorentz force. When a charged particle moves through a magnetic field, it experiences a force perpendicular to both its velocity vector and the magnetic field. This force causes the particle to deviate from its original path and follow a curved trajectory. By carefully designing the magnetic field, it is possible to focus the particle beam to a desired location.One example of magnetic focusing is the use ofquadrupole magnets. These magnets consist of four poles arranged in a specific configuration. When a particle beam passes through the quadrupole magnet, the magnetic field gradient causes the particles to converge or diverge depending on their initial position and velocity. This focusing effect can be used to shape and control the beam, allowing for precise manipulation and control.On the other hand, magnetic confinement is a technique used to confine charged particles within a specific region. This is particularly important in applications such as plasma physics and fusion reactors, where high temperatures and pressures are involved. In these systems, charged particles are confined using strong magnetic fields, preventing them from escaping and interacting with the surrounding environment.One example of magnetic confinement is the tokamak, a device used in fusion research. The tokamak consists of a toroidal chamber surrounded by powerful magnets. The magnetic field created by these magnets forms closed loops, confining the plasma within the chamber. This confinementallows for the sustained fusion reactions required for the production of energy.中文回答:磁聚焦和磁控束是控制和操纵带电粒子束的两种重要技术。
物理的英语physicsPhysics is a branch of science that deals with the properties and interactions of matter and energy. It plays a crucial role in understanding the fundamental principles of the universe and has contributed to the development of various technologies. In this article, we will explore different aspects of physics and discuss its importance in various fields.A. IntroductionPhysics, as a field of study, encompasses a wide range of topics, including classical mechanics, thermodynamics, electromagnetism, quantum mechanics, and relativity. It aims to understand the fundamental laws and principles that govern the behavior of matter and energy. By studying the properties and interactions of objects, physicists provide explanations for various phenomena observed in nature.B. Classical MechanicsClassical mechanics is a branch of physics that deals with the motion of objects and the forces acting on them. It is based on Newton's laws of motion, which describe how the velocity of an object changes when subjected to external forces. Classical mechanics is essential for understanding the motion of everyday objects, from the trajectory of a baseball to the movement of planets in the solar system.C. ThermodynamicsThermodynamics focuses on the study of heat and its transformation into different forms of energy. It explores concepts such as temperature, entropy,and energy transfer. Thermodynamics is crucial in engineering fields, as it helps in the design of efficient engines, refrigeration systems, and power plants. It is also vital in understanding the behavior of gases, liquids, and solids in different physical and chemical processes.D. ElectromagnetismElectromagnetism is the study of electric and magnetic fields and their interactions with charged particles. It is one of the fundamental forces of nature, and understanding electromagnetism is essential in many technological applications. From the generation and transmission of electricity to the operation of electronic devices, electromagnetism plays a significant role in our daily lives.E. Quantum MechanicsQuantum mechanics is a branch of physics that deals with the behavior of matter and energy at the atomic and subatomic level. It provides a framework for understanding the peculiar properties of particles, such as wave-particle duality and quantum superposition. Quantum mechanics has revolutionized various fields, including electronics, telecommunications, and modern computing.F. RelativityRelativity, as proposed by Albert Einstein, revolutionized our understanding of space, time, and gravity. It consists of two major theories: special relativity and general relativity. Special relativity introduces the concept of the speed of light as the maximum velocity for any object, while general relativity describes the curvature of spacetime due to the presence ofmass and energy. Relativity has practical applications in global positioning systems (GPS) and the study of cosmology.G. Importance of Physics in Technology and EngineeringPhysics forms the backbone of technology and engineering. Many technological advancements, such as the development of computers, smartphones, and renewable energy sources, rely heavily on the principles of physics. Engineers and technologists constantly apply physics concepts to innovate and improve existing systems, making our lives more convenient and sustainable.H. ConclusionPhysics is a fascinating field that seeks to understand the fundamental aspects of the universe. It provides a framework to explain the behavior of matter and energy, from the motion of everyday objects to the intricate nature of subatomic particles. The various branches of physics, including classical mechanics, thermodynamics, electromagnetism, quantum mechanics, and relativity, have significant implications in numerous fields, ranging from technology and engineering to medicine and cosmology. By studying physics, we can gain a deeper understanding of the world around us and pave the way for future advancements and discoveries.。
The Principles of Magnetic ResonanceImagingMagnetic Resonance Imaging, or MRI, is a medical imaging technique used to visualize structures inside the body. It does not use any ionizing radiation, and is therefore considered a safe alternative to techniques such as X-ray or CT scan. Instead, MRI relies on the interaction between the magnetic field and the hydrogen atoms in the body. In this article, we will discuss the principles underlying MRI, from the physics of magnetic fields to the practical aspects of image reconstruction.At its core, MRI is based on the ability of certain atomic nuclei to absorb and emit electromagnetic radiation when placed in a magnetic field. Specifically, hydrogen nuclei (protons) are most often used in MRI because they are the most abundant nuclei in the body. When these nuclei are placed in an external magnetic field, they become aligned either with or against the field, depending on their intrinsic properties. This alignment can be thought of as a small magnetic moment, which we can measure by applying a radiofrequency (RF) pulse and detecting the resulting signal.The RF pulse causes the protons to emit their own electromagnetic radiation, which we can detect using a coil placed around the area of interest. By manipulating the RF pulse and the gradient magnetic fields (which vary the magnetic field strength across space), we can create a variety of different measurements that allow us to reconstruct an image of the body. For example, by slightly varying the magnetic field along one direction, we can create a gradient that lets us measure the position of the protons along that direction. This allows us to create a two-dimensional image by encoding both the position and the signal intensity.One important property of MRI is its ability to differentiate between different types of tissue based on their physical properties. This is because different tissues have different magnetic properties, such as their magnetic susceptibility or their T1 and T2 relaxation times. For example, we can distinguish between fat and water because their T1and T2 times are different. By using different sequences of RF pulses and gradients, we can selectively enhance or suppress the signal from different tissues to highlight specific structures in the body.Another key principle of MRI is contrast resolution, or the ability to distinguish between adjacent structures with similar densities. This is often achieved by manipulating the contrast between the signal from the tissue of interest and the background signal. One common method is to use a contrast agent, which is a substance that alters the magnetic properties of the tissue and thus changes the signal intensity. Contrast agents may be injected into the bloodstream or directly into a specific area of the body, depending on the application.Finally, the quality of the MRI image depends on many factors, such as the strength of the magnetic field, the quality of the RF coils, and the skill of the technician. One important consideration is the spatial resolution, which is the smallest object that can be distinguished in the image. This is determined by the size of the voxels, or the three-dimensional pixels that make up the image. Higher resolution requires smaller voxel size, which in turn requires a longer scan time and may require higher magnetic field strength.In conclusion, MRI is a powerful tool for visualizing structures inside the body without using ionizing radiation. Its principles are rooted in the physics of magnetic fields and the behavior of atomic nuclei, and it allows us to differentiate between different types of tissue based on their physical properties. MRI images are reconstructed using complex algorithms that exploit the interactions between RF pulses, gradient magnetic fields, and the magnetic properties of the tissue. To produce high-quality images, careful attention must be paid to factors such as spatial resolution, contrast resolution, and the use of contrast agents. MRI has revolutionized the practice of medicine, from diagnosing neurological disorders to monitoring the growth of tumors.。
弦理论研究取得重大突破《科学》:首次在实物中发现磁单极子的存在推动物理学基础理论研究,书写新的物质基本属性德国亥姆霍兹联合会研究中心的研究人员在德国德累斯顿大学、圣安德鲁斯大学、拉普拉塔大学及英国牛津大学同事的协作下,首次观测到了磁单极子的存在,以及这些磁单极子在一种实际材料中出现的过程。
该研究成果发表在9月3日出版的《科学》杂志上。
磁单极子是科学家在理论物理学弦理论中提出的仅带有北极或南极单一磁极的假设性磁性粒子。
在物质世界中,这是相当特殊的,因为磁性粒子通常总是以偶极子(南北两极)的形式成对出现。
磁单极子这种物质的存在性在科学界时有纷争,迄今为止科学家们还未曾发现过这种物质,因此,磁单极子可以说是21世纪物理学界重要的研究主题之一。
英国物理学家保罗·狄拉克早在1931年就利用数学公式预言磁单极子存在于携带磁场的管(所谓的狄拉克弦)的末端。
当时他认为既然带有基本电荷的电子在宇宙中存在,那么理应带有基本“磁荷”的粒子存在,从而启发了许多物理学家开始了他们寻找磁单极子工作。
科学家们曾通过种种方式寻找磁单极子,包括使用粒子加速器人工制造磁单极子,但均无收获。
此次,德国亥姆霍兹联合会研究中心的乔纳森·莫里斯和阿兰·坦南特在柏林研究反应堆中进行了一次中子散射实验。
他们研究的材料是一种钛酸镝单晶体,这种材料可结晶成相当显著的几何形状,也被称为烧录石晶格。
在中子散射的帮助下,研究人员证实材料内部的磁矩已重新组织成所谓的“自旋式意大利面条”,此名得自于偶极子本身的次序。
如此一个可控的管(弦)网络就可通过磁通量的传输得以形成,这些弦可通过与自身携带磁矩的中子进行反应观察到,于是中子就可作为逆表示的弦进行散射。
在中子散射测量过程中,研究人员对晶体施加一个磁场,利用这个磁场就可影响弦的对称和方向,从而降低弦网络的密度以促成单极子的分离。
结果,在0.6K到2K温度条件下,这些弦是可见的,并在其两端出现了磁单极子。
SuperconductivitySuperconductivity was discovered by a Dutch scientist named Heike K.Onnes. In 1908 he was the first to accomplish the liquefaction of helium. Using liquid helium as a coolant, he then began to study the low-temperature conductive properties of metals. In 1911 he observed that the resistivity of mercury displays a remarkable behavior as it is cooled to a temperature approaching absolute zero.超导性是一位名叫Heike K.Onnes的荷兰科学家发现的。
1908年,他第一次完成了氦的液化。
他利用在液态氦中加入冷冻剂,开始研究低温条件下的金属导电性。
1911年他观察到随着温度冷到接近于绝对零度,水银的电阻率显示出不寻常的性质。
At about 4 K, all electrical resistance of mercury is suddenly lost within a temperature range of 0.01K. In 1913Onnes concluded that "mercury has passed into a new state that, on account of its remarkable electrical properties, may be called the superconducting state." The temperature at which a material enters the superconducting state is now called its superconducting transition temperature, Tc.在开氏度4度的时候,温度在开氏度0.01度范围之内变化时,水银的电阻完全消失了。
中国科技大学物理学院物理学专业英语仅供内部学习参考!2014目录1 Physics 物理学 (1)Introduction to physics (1)Classical and modern physics (2)Research fields (4)V ocabulary (7)2 Classical m echanics 经典力学 (10)Introduction (10)Description of classical mechanics (10)Momentum and collisions (14)Angular momentum (15)V ocabulary (16)3 Thermodynamics 热力学 (18)Introduction (18)Laws of thermodynamics (21)System models (22)Thermodynamic processes (27)Scope of thermodynamics (29)V ocabulary (30)4 Electromagnetism 电磁学 (33)Introduction (33)Electrostatics (33)Magnetostatics (35)Electromagnetic induction (40)V ocabulary (43)5 Optics 光学 (45)Introduction (45)Geometrical optics (45)Physical optics (47)Polarization (50)V ocabulary (51)6 Atomic ph ysics 原子物理 (52)Introduction (52)Electronic configuration (52)Excitation and ionization (56)V ocabulary (59)7 Statistical m echanics 统计力学 (60)Overview (60)Fundamentals (60)Statistical ensembles (63)V ocabulary (65)8 Quantum m echanics 量子力学 (67)Introduction (67)Mathematical formulations (68)Quantization (71)Wave-particle duality (72)Quantum entanglement (75)V ocabulary (77)9 Special r e lativity 狭义相对论 (79)Introduction (79)Relativity of simultaneity (80)Lorentz transformations (80)Time dilation and length contraction (81)Mass-energy equivalence (82)Relativistic energy-momentum relation (86)V ocabulary (89)正文标记说明:蓝色Arial字体(例如energy):已知的专业词汇蓝色Arial字体加下划线(例如electromagnetism):新学的专业词汇黑色Times New Roman字体加下划线(例如postulate):新学的普通词汇1 Physics 物理学Introduction to physicsPhysics is a part of natural philosophy and a natural science that involves the study of matter and its motion through space and time, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy. Over the last two millennia, physics was a part of natural philosophy along with chemistry, certain branches of mathematics, and biology, but during the Scientific Revolution in the 17th century, the natural sciences emerged as unique research programs in their own right. Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry,and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms of other sciences, while opening new avenues of research in areas such as mathematics and philosophy.Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs. For example, advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products which have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.Core theoriesThough physics deals with a wide variety of systems, certain theories are used by all physicists. Each of these theories were experimentally tested numerous times and found correct as an approximation of nature (within a certain domain of validity).For instance, the theory of classical mechanics accurately describes the motion of objects, provided they are much larger than atoms and moving at much less than the speed of light. These theories continue to be areas of active research, and a remarkable aspect of classical mechanics known as chaos was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Isaac Newton (1642–1727) 【艾萨克·牛顿】.These central theories are important tools for research into more specialized topics, and any physicist, regardless of his or her specialization, is expected to be literate in them. These include classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.Classical and modern physicsClassical mechanicsClassical physics includes the traditional branches and topics that were recognized and well-developed before the beginning of the 20th century—classical mechanics, acoustics, optics, thermodynamics, and electromagnetism.Classical mechanics is concerned with bodies acted on by forces and bodies in motion and may be divided into statics (study of the forces on a body or bodies at rest), kinematics (study of motion without regard to its causes), and dynamics (study of motion and the forces that affect it); mechanics may also be divided into solid mechanics and fluid mechanics (known together as continuum mechanics), the latter including such branches as hydrostatics, hydrodynamics, aerodynamics pneumatics.Acoustics is the study of how sound is produced, controlled, transmitted and received. Important modern branches of acoustics include ultrasonics, the study of sound waves of very high frequency beyond the range of human hearing; bioacoustics the physics of animal calls and hearing, and electroacoustics, the manipulation of audible sound waves using electronics.Optics, the study of light, is concerned not only with visible light but also with infrared and ultraviolet radiation, which exhibit all of the phenomena of visible light except visibility, e.g., reflection, refraction, interference, diffraction, dispersion, and polarization of light.Heat is a form of energy, the internal energy possessed by the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy.Electricity and magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th century; an electric current gives rise to a magnetic field and a changing magnetic field induces an electric current. Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest.Modern PhysicsClassical physics is generally concerned with matter and energy on the normal scale ofobservation, while much of modern physics is concerned with the behavior of matter and energy under extreme conditions or on the very large or very small scale.For example, atomic and nuclear physics studies matter on the smallest scale at which chemical elements can be identified.The physics of elementary particles is on an even smaller scale, as it is concerned with the most basic units of matter; this branch of physics is also known as high-energy physics because of the extremely high energies necessary to produce many types of particles in large particle accelerators. On this scale, ordinary, commonsense notions of space, time, matter, and energy are no longer valid.The two chief theories of modern physics present a different picture of the concepts of space, time, and matter from that presented by classical physics.Quantum theory is concerned with the discrete, rather than continuous, nature of many phenomena at the atomic and subatomic level, and with the complementary aspects of particles and waves in the description of such phenomena.The theory of relativity is concerned with the description of phenomena that take place in a frame of reference that is in motion with respect to an observer; the special theory of relativity is concerned with relative uniform motion in a straight line and the general theory of relativity with accelerated motion and its connection with gravitation.Both quantum theory and the theory of relativity find applications in all areas of modern physics.Difference between classical and modern physicsWhile physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions.Albert Einstein【阿尔伯特·爱因斯坦】contributed the framework of special relativity, which replaced notions of absolute time and space with space-time and allowed an accurate description of systems whose components have speeds approaching the speed of light.Max Planck【普朗克】, Erwin Schrödinger【薛定谔】, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales.Later, quantum field theory unified quantum mechanics and special relativity.General relativity allowed for a dynamical, curved space-time, with which highly massivesystems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.Research fieldsContemporary research in physics can be broadly divided into condensed matter physics; atomic, molecular, and optical physics; particle physics; astrophysics; geophysics and biophysics. Some physics departments also support research in Physics education.Since the 20th century, the individual fields of physics have become increasingly specialized, and today most physicists work in a single field for their entire careers. "Universalists" such as Albert Einstein (1879–1955) and Lev Landau (1908–1968)【列夫·朗道】, who worked in multiple fields of physics, are now very rare.Condensed matter physicsCondensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. In particular, it is concerned with the "condensed" phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.The most familiar examples of condensed phases are solids and liquids, which arise from the bonding by way of the electromagnetic force between atoms. More exotic condensed phases include the super-fluid and the Bose–Einstein condensate found in certain atomic systems at very low temperature, the superconducting phase exhibited by conduction electrons in certain materials,and the ferromagnetic and antiferromagnetic phases of spins on atomic lattices.Condensed matter physics is by far the largest field of contemporary physics.Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields. The term condensed matter physics was apparently coined by Philip Anderson when he renamed his research group—previously solid-state theory—in 1967. In 1978, the Division of Solid State Physics of the American Physical Society was renamed as the Division of Condensed Matter Physics.Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering.Atomic, molecular and optical physicsAtomic, molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions on the scale of single atoms and molecules.The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of the energy scales that are relevant. All three areas include both classical, semi-classical and quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view).Atomic physics studies the electron shells of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the nucleus(see, e.g., hyperfine splitting), but intra-nuclear phenomena such as fission and fusion are considered part of high-energy physics.Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light.Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects, but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.High-energy physics (particle physics) and nuclear physicsParticle physics is the study of the elementary constituents of matter and energy, and the interactions between them.In addition, particle physicists design and develop the high energy accelerators,detectors, and computer programs necessary for this research. The field is also called "high-energy physics" because many elementary particles do not occur naturally, but are created only during high-energy collisions of other particles.Currently, the interactions of elementary particles and fields are described by the Standard Model.●The model accounts for the 12 known particles of matter (quarks and leptons) thatinteract via the strong, weak, and electromagnetic fundamental forces.●Dynamics are described in terms of matter particles exchanging gauge bosons (gluons,W and Z bosons, and photons, respectively).●The Standard Model also predicts a particle known as the Higgs boson. In July 2012CERN, the European laboratory for particle physics, announced the detection of a particle consistent with the Higgs boson.Nuclear Physics is the field of physics that studies the constituents and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those in nuclear medicine and magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.Astrophysics and Physical CosmologyAstrophysics and astronomy are the application of the theories and methods of physics to the study of stellar structure, stellar evolution, the origin of the solar system, and related problems of cosmology. Because astrophysics is a broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.The discovery by Karl Jansky in 1931 that radio signals were emitted by celestial bodies initiated the science of radio astronomy. Most recently, the frontiers of astronomy have been expanded by space exploration. Perturbations and interference from the earth's atmosphere make space-based observations necessary for infrared, ultraviolet, gamma-ray, and X-ray astronomy.Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Albert Einstein's theory of relativity plays a central role in all modern cosmological theories. In the early 20th century, Hubble's discovery that the universe was expanding, as shown by the Hubble diagram, prompted rival explanations known as the steady state universe and the Big Bang.The Big Bang was confirmed by the success of Big Bang nucleo-synthesis and the discovery of the cosmic microwave background in 1964. The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the cosmological principle (On a sufficiently large scale, the properties of the Universe are the same for all observers). Cosmologists have recently established the ΛCDM model (the standard model of Big Bang cosmology) of the evolution of the universe, which includes cosmic inflation, dark energy and dark matter.Current research frontiersIn condensed matter physics, an important unsolved theoretical problem is that of high-temperature superconductivity. Many condensed matter experiments are aiming to fabricate workable spintronics and quantum computers.In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost among these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing solar neutrino problem, and the physics of massive neutrinos remains an area of active theoretical and experimental research. Particle accelerators have begun probing energy scales in the TeV range, in which experimentalists are hoping to find evidence for the super-symmetric particles, after discovery of the Higgs boson.Theoretical attempts to unify quantum mechanics and general relativity into a single theoryof quantum gravity, a program ongoing for over half a century, have not yet been decisively resolved. The current leading candidates are M-theory, superstring theory and loop quantum gravity.Many astronomical and cosmological phenomena have yet to be satisfactorily explained, including the existence of ultra-high energy cosmic rays, the baryon asymmetry, the acceleration of the universe and the anomalous rotation rates of galaxies.Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena involving complexity, chaos, or turbulence are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics remain unsolved; examples include the formation of sand-piles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, and self-sorting in shaken heterogeneous collections.These complex phenomena have received growing attention since the 1970s for several reasons, including the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. Complex physics has become part of increasingly interdisciplinary research, as exemplified by the study of turbulence in aerodynamics and the observation of pattern formation in biological systems.Vocabulary★natural science 自然科学academic disciplines 学科astronomy 天文学in their own right 凭他们本身的实力intersects相交,交叉interdisciplinary交叉学科的,跨学科的★quantum 量子的theoretical breakthroughs 理论突破★electromagnetism 电磁学dramatically显著地★thermodynamics热力学★calculus微积分validity★classical mechanics 经典力学chaos 混沌literate 学者★quantum mechanics量子力学★thermodynamics and statistical mechanics热力学与统计物理★special relativity狭义相对论is concerned with 关注,讨论,考虑acoustics 声学★optics 光学statics静力学at rest 静息kinematics运动学★dynamics动力学ultrasonics超声学manipulation 操作,处理,使用infrared红外ultraviolet紫外radiation辐射reflection 反射refraction 折射★interference 干涉★diffraction 衍射dispersion散射★polarization 极化,偏振internal energy 内能Electricity电性Magnetism 磁性intimate 亲密的induces 诱导,感应scale尺度★elementary particles基本粒子★high-energy physics 高能物理particle accelerators 粒子加速器valid 有效的,正当的★discrete离散的continuous 连续的complementary 互补的★frame of reference 参照系★the special theory of relativity 狭义相对论★general theory of relativity 广义相对论gravitation 重力,万有引力explicit 详细的,清楚的★quantum field theory 量子场论★condensed matter physics凝聚态物理astrophysics天体物理geophysics地球物理Universalist博学多才者★Macroscopic宏观Exotic奇异的★Superconducting 超导Ferromagnetic铁磁质Antiferromagnetic 反铁磁质★Spin自旋Lattice 晶格,点阵,网格★Society社会,学会★microscopic微观的hyperfine splitting超精细分裂fission分裂,裂变fusion熔合,聚变constituents成分,组分accelerators加速器detectors 检测器★quarks夸克lepton 轻子gauge bosons规范玻色子gluons胶子★Higgs boson希格斯玻色子CERN欧洲核子研究中心★Magnetic Resonance Imaging磁共振成像,核磁共振ion implantation 离子注入radiocarbon dating放射性碳年代测定法geology地质学archaeology考古学stellar 恒星cosmology宇宙论celestial bodies 天体Hubble diagram 哈勃图Rival竞争的★Big Bang大爆炸nucleo-synthesis核聚合,核合成pillar支柱cosmological principle宇宙学原理ΛCDM modelΛ-冷暗物质模型cosmic inflation宇宙膨胀fabricate制造,建造spintronics自旋电子元件,自旋电子学★neutrinos 中微子superstring 超弦baryon重子turbulence湍流,扰动,骚动catastrophes突变,灾变,灾难heterogeneous collections异质性集合pattern formation模式形成2 Classical mechanics 经典力学IntroductionIn physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces. The study of the motion of bodies is an ancient one, making classical mechanics one of the oldest and largest subjects in science, engineering and technology.Classical mechanics describes the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies. Besides this, many specializations within the subject deal with gases, liquids, solids, and other specific sub-topics.Classical mechanics provides extremely accurate results as long as the domain of study is restricted to large objects and the speeds involved do not approach the speed of light. When the objects being dealt with become sufficiently small, it becomes necessary to introduce the other major sub-field of mechanics, quantum mechanics, which reconciles the macroscopic laws of physics with the atomic nature of matter and handles the wave–particle duality of atoms and molecules. In the case of high velocity objects approaching the speed of light, classical mechanics is enhanced by special relativity. General relativity unifies special relativity with Newton's law of universal gravitation, allowing physicists to handle gravitation at a deeper level.The initial stage in the development of classical mechanics is often referred to as Newtonian mechanics, and is associated with the physical concepts employed by and the mathematical methods invented by Newton himself, in parallel with Leibniz【莱布尼兹】, and others.Later, more abstract and general methods were developed, leading to reformulations of classical mechanics known as Lagrangian mechanics and Hamiltonian mechanics. These advances were largely made in the 18th and 19th centuries, and they extend substantially beyond Newton's work, particularly through their use of analytical mechanics. Ultimately, the mathematics developed for these were central to the creation of quantum mechanics.Description of classical mechanicsThe following introduces the basic concepts of classical mechanics. For simplicity, it oftenmodels real-world objects as point particles, objects with negligible size. The motion of a point particle is characterized by a small number of parameters: its position, mass, and the forces applied to it.In reality, the kind of objects that classical mechanics can describe always have a non-zero size. (The physics of very small particles, such as the electron, is more accurately described by quantum mechanics). Objects with non-zero size have more complicated behavior than hypothetical point particles, because of the additional degrees of freedom—for example, a baseball can spin while it is moving. However, the results for point particles can be used to study such objects by treating them as composite objects, made up of a large number of interacting point particles. The center of mass of a composite object behaves like a point particle.Classical mechanics uses common-sense notions of how matter and forces exist and interact. It assumes that matter and energy have definite, knowable attributes such as where an object is in space and its speed. It also assumes that objects may be directly influenced only by their immediate surroundings, known as the principle of locality.In quantum mechanics objects may have unknowable position or velocity, or instantaneously interact with other objects at a distance.Position and its derivativesThe position of a point particle is defined with respect to an arbitrary fixed reference point, O, in space, usually accompanied by a coordinate system, with the reference point located at the origin of the coordinate system. It is defined as the vector r from O to the particle.In general, the point particle need not be stationary relative to O, so r is a function of t, the time elapsed since an arbitrary initial time.In pre-Einstein relativity (known as Galilean relativity), time is considered an absolute, i.e., the time interval between any given pair of events is the same for all observers. In addition to relying on absolute time, classical mechanics assumes Euclidean geometry for the structure of space.Velocity and speedThe velocity, or the rate of change of position with time, is defined as the derivative of the position with respect to time. In classical mechanics, velocities are directly additive and subtractive as vector quantities; they must be dealt with using vector analysis.When both objects are moving in the same direction, the difference can be given in terms of speed only by ignoring direction.AccelerationThe acceleration , or rate of change of velocity, is the derivative of the velocity with respect to time (the second derivative of the position with respect to time).Acceleration can arise from a change with time of the magnitude of the velocity or of the direction of the velocity or both . If only the magnitude v of the velocity decreases, this is sometimes referred to as deceleration , but generally any change in the velocity with time, including deceleration, is simply referred to as acceleration.Inertial frames of referenceWhile the position and velocity and acceleration of a particle can be referred to any observer in any state of motion, classical mechanics assumes the existence of a special family of reference frames in terms of which the mechanical laws of nature take a comparatively simple form. These special reference frames are called inertial frames .An inertial frame is such that when an object without any force interactions (an idealized situation) is viewed from it, it appears either to be at rest or in a state of uniform motion in a straight line. This is the fundamental definition of an inertial frame. They are characterized by the requirement that all forces entering the observer's physical laws originate in identifiable sources (charges, gravitational bodies, and so forth).A non-inertial reference frame is one accelerating with respect to an inertial one, and in such a non-inertial frame a particle is subject to acceleration by fictitious forces that enter the equations of motion solely as a result of its accelerated motion, and do not originate in identifiable sources. These fictitious forces are in addition to the real forces recognized in an inertial frame.A key concept of inertial frames is the method for identifying them. For practical purposes, reference frames that are un-accelerated with respect to the distant stars are regarded as good approximations to inertial frames.Forces; Newton's second lawNewton was the first to mathematically express the relationship between force and momentum . Some physicists interpret Newton's second law of motion as a definition of force and mass, while others consider it a fundamental postulate, a law of nature. Either interpretation has the same mathematical consequences, historically known as "Newton's Second Law":a m t v m t p F ===d )(d d dThe quantity m v is called the (canonical ) momentum . The net force on a particle is thus equal to rate of change of momentum of the particle with time.So long as the force acting on a particle is known, Newton's second law is sufficient to。
Magnetic resonance imagingSagittal MR image of the kneePara-sagittal MRI of the head, with aliasing artifacts (nose and forehead appear at the back of the head)Magnetic resonance imaging (MRI), or nuclear magnetic resonance imaging (NMRI), is primarily a noninvasive medical imaging technique used in radiology to visualize detailed internal structure and limited function of the body. MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does, making it especially useful in neurological (brain), musculoskeletal, cardiovascular, and oncological (cancer) imaging.Unlike CT, MRI uses no ionizing radiation. Rather, it uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water in the body. Radio frequency (RF) fields are used to systematically alter the alignment of this magnetization. This causes the hydrogen nuclei to produce a rotating magnetic field detectable by thescanner. This signal can be manipulated by additional magnetic fields to build up enough information to construct an image of the body.[1]:36Magnetic resonance imaging is a relatively new technology. The first MR image was published in 1973[2][3] and the first cross-sectional image of a living mouse was published in January 1974.[4] The first studies performed on humans were published in 1977.[5][6] By comparison, the first human X-ray image was taken in 1895.Magnetic resonance imaging is a development of nuclear magnetic resonance. Originally, the technique was referred to as nuclear magnetic resonance imaging (NMRI). However, because the word nuclear was associated in the public mind with ionizing radiation exposure, it is generally now referred to simply as MRI. Scientists still use the term NMRI when discussing non-medical devices operating on the same principles. The term magnetic resonance tomography (MRT) is also sometimes used.Contents[hide]∙ 1 How MRI works∙ 2 Applicationso 2.1 Basic MRI scans▪ 2.1.1 T1-weighted MRI▪ 2.1.2 T2-weighted MRI▪ 2.1.3 T*2-weighted MRI▪ 2.1.4 Spin density weighted MRIo 2.2 Specialized MRI scans▪ 2.2.1 Diffusion MRI▪ 2.2.2 Magnetization Transfer MRI▪ 2.2.3 Fluid attenuated inversion recovery (FLAIR)▪ 2.2.4 Magnetic resonance angiography▪ 2.2.5 Magnetic resonance gated intracranial CSF dynamics (MR-GILD)▪ 2.2.6 Magnetic resonance spectroscopy▪ 2.2.7 Functional MRI▪ 2.2.8 Real-time MRIo 2.3 Interventional MRIo 2.4 Radiation therapy simulation▪ 2.4.1 Current density imaging▪ 2.4.2 Magnetic resonance guided focused ultrasound▪ 2.4.3 Multinuclear imaging▪ 2.4.4 Susceptibility weighted imaging (SWI)▪ 2.4.5 Other specialized MRI techniqueso 2.5 Portable instrumentso 2.6 MRI versus CTo 2.7 Economics of MRI∙ 3 Installation of the MRI unit∙ 4 Safetyo 4.1 Implants and foreign bodieso 4.2 Projectile or missile effecto 4.3 Radio frequency energyo 4.4 Peripheral nerve stimulation (PNS)o 4.5 Acoustic noiseo 4.6 Cryogenso 4.7 Contrast agentso 4.8 Pregnancyo 4.9 Claustrophobia and discomforto 4.10 Guidanceo 4.11 The European Physical Agents Directive∙ 5 Three-dimensional (3D) image reconstructiono 5.1 The principleo 5.2 3D rendering techniqueso 5.3 Image segmentation∙ 6 2003 Nobel Prize∙7 See also∙8 References∙9 Further reading∙10 External links[edit] How MRI worksThis section does not cite any references or sources.Please help improve this article by adding citations to reliable sources. Unsourced materialmay be challenged and removed. (September 2009)Main article: Physics of Magnetic Resonance ImagingThe body is largely composed of water molecules. Each water molecule has two hydrogen nuclei or protons. When a person goes inside the powerful magnetic field of the scanner, the magnetic moments of some of these protons changes, and aligns with the direction of the field.In an MRI machine a radio frequency transmitter is briefly turned on, producing an electromagnetic field. The photons of this field have just the right energy, known as the resonance frequency, to flip the spin of the aligned protons in the body. As the intensity and duration of application of the field increase, more aligned spins are affected. After the field is turned off, the protons decay to the original spin-down state and the difference in energy between the two states is released as a photon. It is these photons that produce the electromagnetic signal that the scanner detects. The frequency the protons resonate at depends on the strength of the magnetic field. As a result of conservation of energy, this also dictates the frequency of the released photons. The photons released when the fieldis removed have an energy — and therefore a frequency — due to the amount of energy the protons absorbed while the field was active.It is this relationship between field-strength and frequency that allows the use of nuclear magnetic resonance for imaging. Additional magnetic fields are applied during the scanto make the magnetic field strength depend on the position within the patient, in turn making the frequency of the released photons dependent on position in a predictable manner. Position information can then be recovered from the resulting signal by the useof a Fourier transform. These fields are created by passing electric currents through specially-wound solenoids, known as gradient coils. Since these coils are within the bore of the scanner, there are large forces between them and the main field coils, producing most of the noise that is heard during operation. Without efforts to dampen this noise, it can approach 130 decibels (dB) with strong fields [7] (see also the subsection on acoustic noise).An image can be constructed because the protons in different tissues return to their equilibrium state at different rates, which is a difference that can be detected. By changing the parameters on the scanner, this effect is used to create contrast between different types of body tissue or between other properties, as in fMRI and diffusion MRI. Contrast agents may be injected intravenously to enhance the appearance of blood vessels, tumors or inflammation. Contrast agents may also be directly injected into a joint in the case of arthrograms, MRI images of joints. Unlike CT, MRI uses no ionizing radiation and is generally a very safe procedure. Nonetheless the strong magnetic fields and radio pulses can affect metal implants, including cochlear implants and cardiac pacemakers. In the case of cardiac pacemakers, the results can sometimes be lethal,[8] so patients with such implants are generally not eligible for MRI.MRI is used to image every part of the body, and is particularly useful for tissues with many hydrogen nuclei and little density contrast, such as the brain, muscle, connective tissue and most tumors.[edit] ApplicationsThis section does not cite any references or sources.Please help improve this article by adding citations to reliable sources. Unsourced materialmay be challenged and removed. (September 2009)In clinical practice, MRI is used to distinguish pathologic tissue (such as a brain tumor) from normal tissue. One advantage of an MRI scan is that it is believed to be harmless to the patient. It uses strong magnetic fields and non-ionizing radiation in the radio frequency range, unlike CT scans and traditional X-rays, which both use ionizing radiation.While CT provides good spatial resolution (the ability to distinguish two separate structures an arbitrarily small distance from each other), MRI provides comparableresolution with far better contrast resolution (the ability to distinguish the differences between two arbitrarily similar but not identical tissues). The basis of this ability is the complex library of pulse sequences that the modern medical MRI scanner includes, each of which is optimized to provide image contrast based on the chemical sensitivity of MRI. For example, with particular values of the echo time (T E) and the repetition time (T R), which are basic parameters of image acquisition, a sequence takes on the property of T2-weighting. On a T2-weighted scan, water- and fluid-containing tissues are bright (most modern T2 sequences are actually fast T2 sequences) and fat-containing tissues are dark. The reverse is true for T1-weighted images. Damaged tissue tends to develop edema, which makes a T2-weighted sequence sensitive for pathology, and generally able to distinguish pathologic tissue from normal tissue. With the addition of an additional radio frequency pulse and additional manipulation of the magnetic gradients, a T2-weighted sequence can be converted to a FLAIR sequence, in which free water is now dark, but edematous tissues remain bright. This sequence in particular is currently the most sensitive way to evaluate the brain for demyelinating diseases, such as multiple sclerosis. The typical MRI examination consists of 5–20 sequences, each of which are chosen to provide a particular type of information about the subject tissues. This information is then synthesized by the interpreting physician.[edit] Basic MRI scans[edit] T1-weighted MRIMain article: Spin-lattice relaxation timeT1-weighted scans use a gradient echo (GRE) sequence, with short T E and short T R. This is one of the basic types of MR contrast and is a commonly run clinical scan. The T1 weighting can be increased (improving contrast) with the use of an inversion pulse as in an MP-RAGE sequence. Due to the short repetition time (T R) this scan can be run very fast allowing the collection of high resolution 3D datasets. A T1 reducing gadolinium contrast agent is also commonly used, with a T1 scan being collected before and after administration of contrast agent to compare the difference. In the brain T1-weighted scans provide good gray matter/white matter contrast; in other words, T1-weighted images highlights fat deposition.[edit] T2-weighted MRIMain article: Spin-spin relaxation timeT2-weighted scans use a spin echo (SE) sequence, with long T E and long T R. They have long been the clinical workhorse as the spin echo sequence is less susceptible to inhomogeneities in the magnetic field. They are particularly well suited to edema as they are sensitive to water content (edema is characterized by increased water content). Inother words, put more simply, T2 weighted images light up liquid on the images being visualized.[edit] T*2-weighted MRIT*2 (pronounced "T 2 star") weighted scans use a gradient echo (GRE) sequence, with long T E and long T R. The gradient echo sequence used does not have the extra refocusing pulse used in spin echo so it is subject to additional losses above the normal T2 decay (referred to as T2′), these taken together are called T*2. This also makes it more prone to susceptibility losses at air/tissue boundaries, but can increase contrast for certain types of tissue, such as venous blood.[edit] Spin density weighted MRISpin density, also called proton density, weighted scans try to have no contrast from either T2 or T1 decay, the only signal change coming from differences in the amount of available spins (hydrogen nuclei in water). It uses a spin echo or sometimes a gradient echo sequence, with short T E and long T R.[edit] Specialized MRI scans[edit] Diffusion MRIMain article: Diffusion MRIDTI imageDiffusion MRI measures the diffusion of water molecules in biological tissues.[9] In an isotropic medium (inside a glass of water for example) water molecules naturally move randomly according to turbulence and Brownian motion. In biological tissues however, where the Reynold's number is low enough for flows to be laminar, the diffusion may be anisotropic. For example a molecule inside the axon of a neuron has a low probability of crossing the myelin membrane. Therefore the molecule moves principally along the axis of the neural fiber. If we know that molecules in a particular voxel diffuse principally inone direction we can make the assumption that the majority of the fibers in this area are going parallel to that direction.The recent development of diffusion tensor imaging (DTI)[3] enables diffusion to be measured in multiple directions and the fractional anisotropy in each direction to be calculated for each voxel. This enables researchers to make brain maps of fiber directions to examine the connectivity of different regions in the brain (using tractography) or to examine areas of neural degeneration and demyelination in diseases like Multiple Sclerosis.Another application of diffusion MRI is diffusion-weighted imaging (DWI). Following an ischemic stroke, DWI is highly sensitive to the changes occurring in the lesion.[10] It is speculated that increases in restriction (barriers) to water diffusion, as a result of cytotoxic edema (cellular swelling), is responsible for the increase in signal on a DWI scan. The DWI enhancement appears within 5–10 minutes of the onset of stroke symptoms (as compared with computed tomography, which often does not detect changes of acute infarct for up to 4–6 hours) and remains for up to two weeks. Coupled with imaging of cerebral perfusion, researchers can highlight regions of "perfusion/diffusion mismatch" that may indicate regions capable of salvage by reperfusion therapy.Like many other specialized applications, this technique is usually coupled with a fast image acquisition sequence, such as echo planar imaging sequence.[edit] Magnetization Transfer MRIMain article: Magnetization transferMagnetization transfer (MT) refers to the transfer of longitudinal magnetization from free water protons to hydration water protons in NMR and MRI.In magnetic resonance imaging of molecular solutions, such as protein solutions, two types of water molecules, free (bulk) and hydration (bound), are found. Free water protons have faster average rotational frequency and hence less fixed water molec ules that may cause local field inhomogeneity. Because of this uniformity, most free water protons have resonance frequency lying narrowly around the normal proton resonance frequency of 63 MHz (at 1.5 teslas). This also results in slower transverse magnetization dephasing and hence longer T2. Conversely, hydration water molecules are slowed down by interaction with solute molecules and hence create field inhomogeneities that lead to wider resonance frequency spectrum.[edit] Fluid attenuated inversion recovery (FLAIR)Main article: Fluid attenuated inversion recoveryFluid Attenuated Inversion Recovery (FLAIR)[11] is an inversion-recovery pulse sequence used to null signal from fluids. For example, it can be used in brain imaging to suppress cerebrospinal fluid (CSF) so as to bring out the periventricular hyperintense lesions, such as multiple sclerosis (MS) plaques. By carefully choosing the inversion time TI (the time between the inversion and excitation pulses), the signal from any particular tissue can be suppressed.[edit] Magnetic resonance angiographyMagnetic Resonance AngiographyMain article: Magnetic resonance angiographyMagnetic resonance angiography (MRA) generates pictures of the arteries to evaluate them for stenosis (abnormal narrowing) or aneurysms (vessel wall dilatations, at risk of rupture). MRA is often used to evaluate the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, and the legs (called a "run-off"). A variety of techniques can be used to generate the pictures, such as administration of a paramagnetic contrast agent (gadolinium) or using a technique known as "flow-related enhancement"(e.g. 2D and 3D time-of-flight sequences), where most of the signal on an image is due to blood that recently moved into that plane, see also FLASH MRI. Techniques involving phase accumulation (known as phase contrast angiography) can also be used to generate flow velocity maps easily and accurately. Magnetic resonance venography (MRV) is a similar procedure that is used to image veins. In this method, the tissue is now excited inferiorly, while signal is gathered in the plane immediately superior to the excitation plane—thus imaging the venous blood that recently moved from the excited plane.[12] [edit] Magnetic resonance gated intracranial CSF dynamics (MR-GILD)Magnetic resonance gated intracranial cerebrospinal fluid (CSF) or liquor dynamics (MR-GILD) technique is an MR sequence based on bipolar gradient pulse used to demonstrate CSF pulsatile flow in ventricles, cisterns, aqueduct of Sylvius and entire intracranial CSF pathway. It is a method for analyzing CSF circulatory system dynamics in patients with CSF obstructive lesions such as normal pressure hydrocephalus. It also allows visualization of both arterial and venous pulsatile blood flow in vessels without use o f contrast agents.[13][14]Diastolic time data acquisition (DTDA). Systolic time data acquisition (STDA).[edit] Magnetic resonance spectroscopyMain article: In vivo magnetic resonance spectroscopyMain article: Nuclear magnetic resonance spectroscopyMagnetic resonance spectroscopy (MRS) is used to measure the levels of different metabolites in body tissues. The MR signal produces a spectrum of resonances that correspond to different molecular arrangements of the isotope being "excited". This signature is used to diagnose certain metabolic disorders, especially those affecting the brain,[15] and to provide information on tumor metabolism.[16]Magnetic resonance spectroscopic imaging (MRSI) combines both spectroscopic and imaging methods to produce spatially localized spectra from within the sample or patient. The spatial resolution is much lower (limited by the available SNR), but the spectra in each voxel contains information about many metabolites. Because the available signal is used to encode spatial and spectral information, MRSI requires high SNR achievable only at higher field strengths (3 T and above).[edit] Functional MRIMain article: Functional magnetic resonance imagingA fMRI scan showing regions of activation in orange, including the primary visual cortex (V1, BA17).Functional MRI (fMRI) measures signal changes in the brain that are due to changing neural activity. The brain is scanned at low resolution but at a rapid rate (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via T*2 changes;[17] this mechanism is referred to as the BOLD (blood-oxygen-level dependent) effect. Increased neural activity causes an increased demand for oxygen, and the vascular system actually overcompensates for this, increasing the amount of oxygenated hemoglobin relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue. While BOLD signal is the most common method employed for neuroscience studies in human subjects, the flexible nature of MR imaging provides means to sensitize the signal to other aspects of the blood supply. Alternative techniques employ arterial spin labeling (ASL) or weight the MRI signal by cerebral blood flow (CBF) and cerebral blood volume (CBV). The CBV method requires injection of a class of MRI contrast agents that are now in human clinical trials. Because this method has been shown to be far more sensitive than the BOLD technique in preclinical studies, it may potentially expand the role of fMRI in clinical applications. The CBF method provides more quantitative information than the BOLD signal, albeit at a significant loss of detection sensitivity. [edit] Real-time MRIMain article: Real-time MRIReal-time MRI refers to the continuous monitoring (―filming‖) of moving objects in real time. While many different strategies have been developed over the past two decades, a recent development reported a real-time MRI technique based on radial FLASH that yields a temporal resolution of 20 to 30 milliseconds for images with an in-plane resolution of 1.5 to 2.0 mm. The new method promises to add important information about diseases of the joints and the heart. In many cases MRI examinations may become easier and more comfortable for patients.[edit] Interventional MRIMain article: Interventional MRIThe lack of harmful effects on the patient and the operator make MRI well-suited for "interventional radiology", where the images produced by a MRI scanner are used to guide minimally invasive procedures. Of course, such procedures must be done without any ferromagnetic instruments.A specialized growing subset of interventional MRI is that of intraoperative MRI in which the MRI is used in the surgical process. Some specialized MRI systems have been developed that allow imaging concurrent with the surgical procedure. More typical,however, is that the surgical procedure is temporarily interrupted so that MR images can be acquired to verify the success of the procedure or guide subsequent surgical work. [edit] Radiation therapy simulationBecause of MRI's superior imaging of soft tissues, it is now being utilized to specifically locate tumors within the body in preparation for radiation therapy treatments. For therapy simulation, a patient is placed in specific, reproducible, body position and scanned. The MRI system then computes the precise location, shape and orientation of the tumor mass, correcting for any spatial distortion inherent in the system. The patient is then marked or tattooed with points that, when combined with the specific body position, permits precise triangulation for radiation therapy.[edit] Current density imagingCurrent density imaging (CDI) endeavors to use the phase information from images to reconstruct current densities within a subject. Current density imaging works because electrical currents generate magnetic fields, which in turn affect the phase of the magnetic dipoles during an imaging sequence. To date no successful CDI has been performed using biological currents, but several studies have been published that involve currents applied through a pair of electrodes.[edit] Magnetic resonance guided focused ultrasoundIn MRgFUS therapy, ultrasound beams are focused on a tissue—guided and controlled using MR thermal imaging—and due to the significant energy deposition at the focus, temperature within the tissue rises to more than 65 °C (150 °F), completely destroying it. This technology can achieve precise ablation of diseased tissue. MR imaging provides a three-dimensional view of the target tissue, allowing for precise focusing of ultrasound energy. The MR imaging provides quantitative, real-time, thermal images of the treated area. This allows the physician to ensure that the temperature generated during each cycle of ultrasound energy is sufficient to cause thermal ablation within the desired tissue and if not, to adapt the parameters to ensure effective treatment.[edit] Multinuclear imagingHydrogen is the most frequently imaged nucleus in MRI because it is present in biological tissues in great abundance. However, any nucleus with a net nuclear spin could potentially be imaged with MRI. Such nuclei include helium-3, carbon-13, fluorine-19, oxygen-17, sodium-23, phosphorus-31 and xenon-129. 23Na, 31P and 17O are naturally abundant in the body, so can be imaged directly. Gaseous isotopes such as 3He or 129Xe must be hyperpolarized and then inhaled as their nuclear density is too low to yield auseful signal under normal conditions. 17O, 13C and 19F can be administered in sufficient quantities in liquid form (e.g. 17O-water, 13C-glucose solutions or perfluorocarbons) that hyperpolarization is not a necessity.Multinuclear imaging is primarily a research technique at present. However, potential applications include functional imaging and imaging of organs poorly seen on 1H MRI (e.g. lungs and bones) or as alternative contrast agents. Inhaled hyperpolarized 3He can be used to image the distribution of air spaces within the lungs. Injectable solutions containing 13C or stabilized bubbles of hyperpolarized 129Xe have been studied as contrast agents for angiography and perfusion imaging. 31P can potentially provide information on bone density and structure, as well as functional imaging of the brain.[edit] Susceptibility weighted imaging (SWI)Main article: Susceptibility weighted imagingSusceptibility weighted imaging (SWI), is a new type of contrast in MRI different from spin density, T1, or T2 imaging. This method exploits the susceptibility differences between tissues and uses a fully velocity compensated, three dimensional, RF spoiled, high-resolution, 3D gradient echo scan. This special data acquisition and image processing produces an enhanced contrast magnitude image very sensitive to venous blood, hemorrhage and iron storage. It is used to enhance the detection and diagnosis of tumors, vascular and neurovascular diseases (stroke and hemorrhage, multiple sclerosis, Alzheimer's), and also detects traumatic brain injuries that may not be diagnosed using other methods[18][edit] Other specialized MRI techniquesMRI is a new and active field of research and new methods and variants are often published when they are able to get better results in specific fields. Examples of these recent improvements are T*2-weighted turbo spin-echo (T2 TSE MRI), double inversion recovery MRI (DIR-MRI) or phase-sensitive inversion recovery MRI (PSIR-MRI), all of them able to improve imaging of the brain lesions.[19][20] Another example is MP-RAGE (magnetization-prepared rapid acquisition with gradient echo),[21] which improves images of multiple sclerosis cortical lesions.[22][edit] Portable instrumentsPortable magnetic resonance instruments are available for use in education and field research. Using the principles of Earth's field NMR, they have no powerful polarizing magnet, so that such instruments can be small and inexpensive. Some can be used for both EFNMR spectroscopy and MRI imaging.[23] The low strength of the Earth's field results in poor signal to noise ratios, requiring long scan times to capture spectroscopic data or build up MRI images.Research with atomic magnetometers have discussed the possibility for cheap and portable MRI instruments without the large magnet.[24][25][edit] MRI versus CTA computed tomography (CT) scanner uses X-rays, a type of ionizing radiation, to acquire its images, making it a good tool for examining tissue composed of elements of a higher atomic number than the tissue surrounding them, such as bone and calcifications (calcium based) within the body (carbon based flesh), or of structures (vessels, bowel). MRI, on the other hand, uses non-ionizing radio frequency (RF) signals to acquire its images and is best suited for non-calcified tissue, though MR images can also be acquired from bones and teeth[26] as well as fossils.[27]CT may be enhanced by use of contrast agents containing elements of a higher atomic number than the surrounding flesh such as iodine or barium. Contrast agents for MRI have paramagnetic properties, e.g., gadolinium and manganese.Both CT and MRI scanners are able to generate multiple two-dimensional cross-sections (slices) of tissue and three-dimensional reconstructions. Unlike CT, which uses only X-ray attenuation to generate image contrast, MRI has a long list of properties that may be used to generate image contrast. By variation of scanning parameters, tissue contrast can be altered and enhanced in various ways to detect different features. (See Applications above.)MRI can generate cross-sectional images in any plane (including oblique planes). In the past, CT was limited to acquiring images in the axial (or near axial) plane. The scans used to be called Computed Axial Tomography scans (CAT scans). However, the development of multi-detector CT scanners with near-isotropic resolution, allows the CT scanner to produce data that can be retrospectively reconstructed in any plane with minimal loss of image quality.For purposes of tumor detection and identification in the brain, MRI is generally superior.[28][29][30] However, in the case of solid tumors of the abdomen and chest, CT is often preferred due to less motion artifact. Furthermore, CT usually is more widely available, faster, less expensive, and may be less likely to require the person to be sedated or anesthetized.MRI is also best suited for cases when a patient is to undergo the exam several times successively in the short term, because, unlike CT, it does not expose the patient to the hazards of ionizing radiation.[edit] Economics of MRIMRI equipment is expensive. 1.5 tesla scanners often cost between $1 million and $1.5 million USD. 3.0 tesla scanners often cost between $2 million and $2.3 million USD.。
电生磁知识点Electromagnetism is a fundamental branch of physics that studies the interactions between electric currents and magnetic fields. 电磁学是研究电流与磁场之间相互作用的物理学基础学科。
This field plays a crucial role in our daily lives, as it is responsible for a wide range of technological devices such as electric motors, generators, and transformers. 这一领域在我们日常生活中扮演着至关重要的角色,因为它负责许多技术设备的运作,比如电动机、发电机和变压器。
One of the key concepts in electromagnetism is electromagnetic induction, which refers to the generation of an electromotive force (EMF) in a conductor when it moves through a magnetic field or when there is a change in the magnetic field around it. 电磁感应是电磁学中的一个关键概念,它指的是当导体穿过一个磁场或磁场的变化时,在导体中产生电动势(EMF)。
This phenomenon is the basis for many important technologies such as power generation and transmission, as well as the operation of electric motors. 这一现象是许多重要技术的基础,比如发电和输电,以及电动机的运作。
强场物理英语English:Strong field physics encompasses the study of physical phenomena that occur under the influence of intense electromagnetic fields or high-energy particles. This field of research delves into fundamental processes like quantum electrodynamics, where the behavior of matter and radiation in extreme conditions is explored. Key areas of interest include laser-plasma interactions, high-intensity laser physics, and the investigation of particle dynamics in strong magnetic fields. Strong field physics is instrumental in advancing our understanding of exotic states of matter, such as plasmas and quark-gluon plasma, which are typically difficult to study under ordinary conditions. The applications of strong field physics extend into diverse areas, including materials science, nuclear physics, and astrophysics, providing insights into phenomena like neutron star magnetospheres and cosmic ray acceleration.中文翻译:强场物理涵盖了在强烈电磁场或高能粒子影响下发生的物理现象的研究。
IntroductionMagnetic attraction, an intriguing and fundamental phenomenon in the realm of physics, is a powerful force that arises between magnets or magnetic materials due to their intrinsic magnetic fields. This force, which underpins numerous technological applications and scientific advancements, is governed by intricate principles that extend beyond simple binary attraction or repulsion. This comprehensive analysis delves into the multifaceted nature of magnetic attraction, examining its underlying principles, factors influencing its strength, its manifestations across various scales, and its profound impact on modern technology and scientific research.I. Fundamentals of Magnetic Attraction: The Role of Magnetic Fields and PolesAt the heart of magnetic attraction lies the concept of magnetic fields, generated by moving electric charges or the inherent arrangement of electrons within atoms. A magnet possesses a north (N) pole and a south (S) pole, with the magnetic field lines emerging from the N-pole and terminating at the S-pole. According to Coulomb's law for magnetic forces, like poles repel each other, while unlike poles attract, giving rise to the familiar behavior of magnets attracting or repelling each other depending on their relative orientations.The strength of magnetic attraction between two magnets is determined by several factors, including:1. **Magnetic Moment**: This quantifies the magnet's overall magnetic strength, proportional to the product of its pole strength and the distance between the poles (magnetic length). A larger magnetic moment translates to a stronger magnetic force.2. **Distance**: Magnetic attraction follows an inverse square law, meaning that as the distance between two magnets increases, the attractive force decreases proportionally to the square of the distance. This is mathematically expressed as F ∝ (magnetic moment of magnet 1 × magnetic moment of magnet 2) / (4π× distance^2 × permeability of the medium).3. **Orientation**: The angle between the magnetic moments of the interacting magnets significantly affects the net attractive force. When the magnetic moments are aligned, the force is maximized; when they are orthogonal, the force is zero.4. **Magnetic Permeability**: The ease with which a material allows magnetic flux to pass through it influences the strength of magnetic interactions. Materials with high permeability, such as iron, enhance magnetic attraction, whereas non-magnetic substances like air or vacuum attenuate it.II. Manifestations of Magnetic Attraction Across Different ScalesA. Molecular and Atomic LevelAt the microscopic level, magnetic attraction is rooted in the quantum mechanical behavior of electrons within atoms. Unpaired electrons in certain elements, such as iron, cobalt, and nickel, possess intrinsic magnetic moments due to their spin and orbital motion. When these atoms align their magneticmoments cooperatively, they create a macroscopic magnetic field, giving rise to ferromagnetism, the strongest form of magnetism observed in nature.B. Macroscopic LevelIn everyday life, magnetic attraction is evident in various forms, from simple fridge magnets to complex industrial machinery. Permanent magnets, such as neodymium magnets, maintain a persistent magnetic field due to their stable internal magnetic structure, enabling strong and consistent magnetic attraction. Electromagnets, on the other hand, generate magnetic fields through the flow of electric current, allowing for controllable magnetic attraction.C. Cosmic ScaleMagnetic attraction also plays a significant role in astrophysical phenomena. Earth's magnetic field, generated by the motion of molten iron in its core, not only protects our planet from harmful solar radiation but also guides migrating animals and steers charged particles, creating stunning auroras. Similarly, magnetic fields in stars, galaxies, and even interstellar space influence the dynamics of celestial bodies and the behavior of plasma.III. Applications and Impact of Magnetic Attraction in Technology and ResearchA. Data StorageMagnetic attraction is crucial in modern data storage technologies, such as hard disk drives (HDDs) and magnetic tape. In HDDs, tiny magnetic domains on a spinning platter are polarized to represent digital bits, with the read/write head utilizing magnetic attraction to both record and retrieve data.B. Energy Generation and ConversionMagnetic attraction is central to the operation of electric generators and motors, where it converts mechanical energy to electrical energy and vice versa. In renewable energy systems like wind turbines and hydroelectric generators, the interaction between moving conductors and magnetic fields generates electricity.C. Medical ApplicationsMagnetic resonance imaging (MRI) relies on the interaction between magnetic fields and atomic nuclei, particularly hydrogen, to produce detailed images of internal body structures. Additionally, magnetic nanoparticles are being explored for targeted drug delivery and hyperthermia therapy in cancer treatment, exploiting magnetic attraction for precise localization and controlled release of therapeutic agents.D. Advanced Research and Emerging TechnologiesMagnetic levitation (maglev) trains employ magnetic attraction and repulsion to achieve frictionless movement and high speeds. Moreover, ongoing research in spintronics seeks to harness electron spin and magnetic interactions for novel electronic devices with enhanced functionality and energy efficiency.ConclusionMagnetic attraction, a seemingly simple yet profoundly intricate phenomenon, is governed by the interplay of magnetic fields, pole orientations,distance, and material properties. Its manifestations span across multiple scales, from atomic structures to cosmic phenomena, and have indelibly shaped the course of technological progress and scientific inquiry. As our understanding of magnetism deepens and new applications emerge, magnetic attraction will undoubtedly continue to play a pivotal role in driving innovation and advancing human knowledge.。
英国物理知识点总结1. Classical MechanicsClassical mechanics is the branch of physics that deals with the motion of objects and the forces that cause them to move. It is based on three fundamental principles: Newton's laws of motion, which describe how objects behave when forces are applied to them; the conservation of energy, which states that energy can neither be created nor destroyed, only transformed from one form to another; and the conservation of momentum, which says that the total momentum of a closed system remains constant over time.One of the most influential figures in the development of classical mechanics was Isaac Newton, an English physicist and mathematician who is widely regarded as one of the most important scientists in history. Newton's three laws of motion laid the foundation for the modern understanding of how objects move, and his law of universal gravitation provided the first coherent explanation of the force that causes apples to fall from trees and the moon to orbit the Earth.2. ElectromagnetismElectromagnetism is the study of the electromagnetic force, which is one of the four fundamental forces of nature. It encompasses both electricity and magnetism, and describes how charged particles interact with each other and with magnetic fields. The principles of electromagnetism were first unified by James Clerk Maxwell, a Scottish physicist who formulated a set of equations that describe how electric and magnetic fields are generated and how they propagate through space.Maxwell's equations have had a profound impact on our understanding of light, as they demonstrate that light is an electromagnetic wave. This discovery has paved the way for the development of numerous technologies, including radio, television, and telecommunications. It also laid the groundwork for the theory of special relativity, as the constancy of the speed of light is a fundamental postulate of that theory.3. ThermodynamicsThermodynamics is the branch of physics that deals with the relationship between heat and other forms of energy. It is concerned with the behavior of systems that exchange heat, work, and energy with their surroundings, and it encompasses concepts such as temperature, entropy, and the laws of thermodynamics.The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another. The second law of thermodynamics, on the other hand, states that the total entropy of an isolated system can never decrease over time, and is always increasing. These two laws have far-reaching implications for our understanding of the behavior of heat andenergy, and they are fundamental to the design and operation of many technologies, such as heat engines and refrigerators.4. Quantum MechanicsQuantum mechanics is the branch of physics that deals with the behavior of matter and energy at the smallest scales, such as atoms and subatomic particles. It is a fundamentally different theory from classical mechanics, as it incorporates the principles of wave-particle duality and the uncertainty principle, which states that the position and momentum of a particle cannot be simultaneously measured with arbitrary precision.One of the key figures in the development of quantum mechanics was Paul Dirac, an English physicist who made numerous contributions to the field. He formulated the Dirac equation, which describes the behavior of relativistic electrons, and he also predicted the existence of antimatter, which was later confirmed through experimental observations.5. RelativityRelativity is the branch of physics that deals with the behavior of objects in the presence of strong gravitational fields or when they are moving at a significant fraction of the speed of light. It encompasses two theories: special relativity, which describes how the laws of physics are the same for all observers in uniform motion, and general relativity, which describes how gravity is a curvature of spacetime caused by the presence of mass and energy.The theory of special relativity was formulated by Albert Einstein, a German-born physicist who became a naturalized British citizen later in his life. It introduces the concept of spacetime, which unifies space and time into a single, four-dimensional continuum, and it provides a new understanding of how time and space are relative to the observer's frame of reference.6. Particle PhysicsParticle physics is the branch of physics that studies the properties and behavior of the fundamental particles that make up the universe. It seeks to understand the forces and interactions that govern these particles, and to uncover the underlying laws of nature that govern their behavior.The United Kingdom has made significant contributions to the field of particle physics, particularly through the research conducted at the CERN laboratory in Switzerland. British physicists have been involved in numerous experiments and discoveries, such as the observation of the Higgs boson, which is the particle that gives mass to other fundamental particles.7. Astrophysics and CosmologyAstrophysics and cosmology are two related branches of physics that deal with the study of the universe at the largest scales. They seek to understand the properties and behavior of celestial objects such as stars, galaxies, and black holes, as well as the structure and evolution of the universe as a whole.The United Kingdom has a strong tradition of research in astrophysics and cosmology, with several leading institutions and research groups dedicated to the study of these topics. British astronomers and astrophysicists have made significant contributions to our understanding of the cosmos, such as the discovery of pulsars, the mapping of the cosmic microwave background, and the identification of dark matter and dark energy.In conclusion, the field of physics encompasses a wide range of topics and disciplines, and the United Kingdom has played a significant role in the development of many of these areas. From classical mechanics to quantum physics, from electromagnetism to relativity, and from particle physics to astrophysics, British physicists have made important contributions to our understanding of the natural world and the fundamental forces that govern it. As our knowledge of the universe continues to expand, it is certain that the UK will remain at the forefront of physics research and discovery.。
【初中英语】中国即将发射太空望远镜研究银河系Many black holes and neutron stars are thought to be hidden in the Milky Way. Since they don’t emit visible light, or are covered by dust, only X-ray telescopes can find them.许多黑洞和中子星等天体被认为隐藏在银河系中,由于它们不能发出可见光,或是隐藏在尘埃后面,只有通过X射线太空望远镜才能观测到。
China will soon launch its first X-ray space telescope, the Hard X-ray Modulation Telescope (HXMT), with the aim of surveying the Milky Way toobserve celestial sources of X-rays.中国很快将发射其第一颗X射线太空望远镜――硬X射线调制望远镜(HXMT),以观察银河系从而监测天体的X射线源。
"Our space telescope has unique capabilities to observe high-energycelestial bodies such as black holes and neutron stars. We hope to use it to resolve mysteries such as the evolution of black holes and the strong magnetic fields of neutron stars," says Zhang Shuangnan, lead scientist of HXMT and director of the Key Laboratory of Particle Astrophysics at the Chinese Academy of Sciences (CAS).中国科学院粒子天体物理实验室的负责人、HXMT的首席科学家张双南表示,“我们的太空望远镜有独特的能力来观察如黑洞和中子星等高能天体,我们希望用它来解决诸如黑洞的演化和中子星的强磁场等问题”。
The Physics of Magnets and MagneticMaterials磁铁和磁性材料的物理学磁铁和磁性材料是我们日常生活中常见的物品,如扫地机器人、手机和电视机等都离不开它们。
磁铁和磁性材料背后的科学原理十分有趣,本文就将介绍一下磁铁和磁性材料的物理学原理。
1. 磁铁的原理首先,我们来了解一下磁铁的原理。
磁铁是由磁性材料制成的,如铁、镍和钴等。
这些材料是由微小的磁性颗粒构成的,这些颗粒称为磁域。
当这些磁性颗粒排列在一个方向上时,它们会产生一个磁场。
这个磁场会吸引其他磁性材料,即产生磁性。
这种现象称为磁化。
磁化后的磁铁具有两个极,南极和北极。
这些极是由磁性颗粒的排列方式所决定的。
当磁铁被切成小片时,每个小片都会有南极和北极,这些极是互相吸引的。
2. 磁性材料的种类现在,我们来了解一下磁性材料的种类。
常见的磁性材料有软磁性材料和硬磁性材料。
软磁性材料是指在外部磁场下易于磁化和消磁的材料。
它们使用在变压器、电感器和电机中,以便在电器中产生磁场。
软磁性材料有铁氧体、镍铁和矢量合金等。
与之相反,硬磁性材料是指在外部磁场下难于磁化和消磁的材料。
硬磁性材料通常用于制作永久磁铁。
硬磁性材料有铁、镍和钴等。
3. 磁电效应除了磁化,磁铁和磁性材料还有另一个有趣的性质,即磁电效应。
磁电效应是指当一些材料被置于磁场中时,它们会产生电势差。
这种效应称为磁电效应。
磁电效应是由于材料中的自旋电荷所引起的。
磁电效应在数据存储器中广泛应用。
磁存储器使用磁场将数据存储在磁性介质中。
当磁性介质中的磁域发生变化时,磁电效应产生的电势差可以用于检测数据。
4. 带电粒子运动的磁效应除了上述的磁电效应外,我们还需要了解一下带电粒子运动的磁效应。
当带电粒子在磁场中运动时,它们会受到磁力的作用。
这种现象称为磁效应。
磁效应是由于带电粒子在磁场中的运动所引起的。
磁效应在核磁共振成像中广泛应用。
核磁共振在医学和化学等领域中有广泛的应用。
全文分为作者个人简介和正文两个部分:作者个人简介:Hello everyone, I am an author dedicated to creating and sharing high-quality document templates. In this era of information overload, accurate and efficient communication has become especially important. I firmly believe that good communication can build bridges between people, playing an indispensable role in academia, career, and daily life. Therefore, I decided to invest my knowledge and skills into creating valuable documents to help people find inspiration and direction when needed.正文:六年级下册第一单元英语作文铁水打花全文共3篇示例,供读者参考篇1English Composition on "To Cast Pearls Before Swine"Wow, can you believe we're already starting the second semester of 6th grade? It feels like just yesterday we werenervously walking through the doors on the first day of school. But now we're practically old pros at this middle school thing!This semester in English class we're diving into some really fascinating stuff - idioms and sayings that have been passed down over hundreds of years. Our first unit is on the idiom "to cast pearls before swine." I have to admit, when I first heard this phrase, I was totally confused. It sounded like some weird poem about jewelry and farm animals. But leave it to our awesome English teacher, Mr. Rodriguez, to make it all make sense!So here's the backstory: This saying actually comes from a famous passage in the Bible talking about holy versus unholy. Basically, it means that you shouldn't share valuable things with people who don't appreciate or understand their worth. Like if you showed a really beautiful pearl necklace to a pig, it wouldn't be able to appreciate how special it is - it would just think it's food and try to eat it! Wild, right?At first, I didn't really get why this old saying was so important for us to learn about. But then Mr. Rodriguez explained how it relates to stuff we deal with every single day as students. He asked us to think about times when we put a ton of hard work into a project or presentation, only to have some people in the class goof off and not pay attention. It's like we'recasting those pearls of effort and knowledge in front of swine who can't be bothered to engage! So frustrating.Or what about when you have a big, exciting piece of news - like making the travel basketball team or getting the lead in the school play - and you tell your best friend excitedly, but they just kind of grunt and stare at their phone? Again, pearls wasted on swine. It's all about sharing meaningful things with the people who will truly appreciate them.I have to say, after exploring this idiom and analyzing examples, I realize how relevant it is to our lives right now. We're at this stage where we're starting to really pursue our passions and care deeply about certain subjects, activities, or interests. And it can be super disappointing when the people around us seem to miss the value in the things that matter so much to us.Like, I may be a total theater nerd who goes overboard memorizing my lines and obsessing over lighting cues. But for me, that's precious - it brings me so much joy and fulfillment. So if I work myself to the bone on a performance only to have people snoring in the audience...well, that's casting pearls before swine, my friends. I need to share that passion with the people who will genuinely appreciate the pearls I'm casting out into the world.This idiom has also made me realize how important it is to be a good audience member myself. I may not always instantly understand or resonate with the things my friends are pouring their heart into - like super complicated coding projects or perfectionist baking experiments. But I should do my best to recognize the pearls they're sharing, rather than snoring like the swine. A little effort to appreciate where people's passions lie can go a long way in being a good friend.Overall, I think this old saying has crazy relevance to our modern middle school experience. It's a reminder that we're getting older and our interests are getting more specific and personal. And in sharing those interests, we need to be discerning about who we're sharing them with to avoid casting our pearls before swine. It's all about finding your tribe of people who will value your pearls as much as you do.So thanks for the wisdom, Mr. Rodriguez! I'll be sure to take this lesson to heart as we progress through 6th grade and my pearls get shinier and shinier. I can't wait to explore more idioms and see how many awesome connections we can make to our daily lives. This semester is already off to a pearl-studded start!篇2A Sprinkling of Iron FilingsWow, can you believe we're already starting the second half of 6th grade? The years just seem to fly by faster and faster. This new unit is all about chemistry and experiments, which is really exciting! I've always loved science class and doing hands-on activities. There's just something so fun about mixing things together and seeing what crazy reactions happen.Our first experiment was super cool. Ms. Jones brought in a big glass bowl filled with water. Then she grabbed this little plastic bottle that had some black powder inside. "Does anyone know what this is?" she asked with a sly grin. A bunch of us shouted out guesses like "Pepper!" and "Sand!" But Emily, who always seems to know everything, rolled her eyes and stated matter-of-factly, "It's iron filings, duh."Ms. Jones nodded approvingly at Emily. "That's right, good job! These are very fine iron particles." She unscrewed the cap and started sprinkling the filings into the bowl of water. At first, nothing happened and I thought it was going to be a pretty lame experiment. But then Ms. Jones pulled out a big U-shaped magnet and started running it around the edge of the bowl.Suddenly, the iron filings started swirling and dancing through the water, following the path of the magnet! It lookedlike a miniature tornado was forming as the filings clustered together into funnel shapes. We all gasped in amazement. Even Emily looked impressed for once."What you're seeing is the magnetic fields of the iron filings aligning with the stronger magnetic field of the bar magnet," Ms. Jones explained. "The filings are so tiny that water is not a strong enough force to hold them in place against the magnet's pull."Over the next few days, we got to take turns playing around with the iron filings and magnets. You could make the most awesome designs and patterns in the water just by moving the magnet around. Whenever the lines of filings would cross each other, they would actually defy gravity for a moment and cling together above the water's surface in these crazy spiky shapes. It was like the filings were high-fiving each other!My personal favorite was making a whirlpool vortex by spinning the magnet rapidly in a circle under the bowl. The filings would get whipped around into a flat disk that spun faster and faster. When I stopped spinning the magnet, the disk would pause for a split second before exploding outward from the center in slow motion. So satisfying to watch!Of course, Jake had to take it too far as usual and see if he could break the laws of physics. During his turn, he grabbed twoof the strong bar magnets instead of one. He put them flat against the bottom of the bowl facing each other, then cranked them in opposite directions as hard as he could. The iron filings went absolutely ballistic, splattering up against the glass in jagged branches. A huge clump even jumped right out of the bowl and landed on Jessica's desk! She shrieked like Ms. Jones had pulled a snake on her. Classic Jake.Apart from being just a blast to play around with, this experiment also taught us some serious science about magnetism, forces, and the behavior of particles. We learned that pretty much everything is magnetic to some degree - it all depends on the arrangement of the atoms and molecules. Iron happens to be one of the most magnetic materials because of how its electrons are organized.That's why the iron filings lined up so obediently along the magnetic field lines of the bar magnet. When opposite poles of two magnets face each other, the lines of force want to join up and cause all kinds of crazy turbulence, like the splattering Jake created.I found it really fascinating how something as small and insignificant as a sprinkle of iron filings could teach us so much about the hidden forces that shape our reality. Makes youwonder what other invisible magnetic fields might be swirling all around us, influencing things we can't even perceive. Kind of mind-blowing when you start thinking about it too deeply!Anyways, this first experiment was just a warmup for more advanced chemistry topics to come, like chemical reactions, States of matter, and even some basic biochemistry. I'm really excited to see what other hands-on activities Ms. Jones has planned for us. Who knows, maybe we'll even get to blow something up! Well, safely in a chemistry lab of course. Although sometimes I wonder if Jake is going to be the one doing the exploding someday. Here's hoping he doesn't take the next experiment as an opportunity to finally get expelled...篇3The Iron Flower Art of ChinaMy name is Xiaoming and I'm a 6th grade student in Chengdu, China. For the first unit in our new English textbook this semester, we learned all about the traditional Chinese folk art of making iron flower patterns. It's called tie shui da hua in Chinese, which means "molten iron stamping" in English. I thought it was really cool to study this ancient craft as part of our English lessons!The art of iron flower stamping goes back over 600 years to the Ming Dynasty. It originated in the small village of Zhongyicun near Chengdu in Sichuan Province. This village was famous for its blacksmiths who made tools and other iron items. One day, a clever blacksmith got the idea to use his iron working skills in a decorative way. By dipping a small iron rod into molten iron and then stamping it onto another piece of hot iron, he could create beautiful flower-like patterns! Other blacksmiths in the village saw what he did and started trying this new artform themselves. That's how the unique folk art of iron flower stamping was born.Over the centuries, the blacksmiths of Zhongyicun perfected their iron stamping skills and developed all kinds of different flower patterns and designs. They would stamp the molten iron to make chrysanthemums, peonies, lotus blossoms, and other auspicious flower shapes. These beautiful floral iron patterns would then be used to decorate windows, doors, furniture, and all sorts of other household items. The iron flower art became an iconic local craft representative of Chengdu culture.In our English class, we learned about the whole process of how iron flower stamping is done. First, the blacksmith heats up a bar of wrought iron in a special furnace until it becomes redhot and molten. Using large tongs, he carefully transfers the molten iron into a smaller furnace called a stove. Inside this stove is a thick iron plate called a dessert that the molten iron is poured onto.Next, the artisan takes a long iron rod with a flower pattern carved into the tip. He dips just the very end of this patterned rod into the molten iron on the dessert plate to pick up a little dollop of the red hot liquid metal. Then working very quickly before the molten iron cools and solidifies, he presses the hot metal dollop down onto another thick iron plate called the soil plate. This stamps the flower pattern onto the soil plate, creating an raised impression of the design in iron.The stamped flower pattern can then be filled in with other molten metals like copper or brass to create a beautiful multicolored effect. Different colors and layers of stamping can be added to make the designs even more intricate and decorative. Once finished, the stamped flower patterns almost look like they are woven out of metal! The colors, textures, and delicate blooms are just breathtaking.Of course, working with scorching hot molten metal is extremely dangerous, so only highly skilled master artisans are allowed to do the actual iron stamping. But we got to watch avideo showing the whole process up close. I was amazed at how quickly they had to work and how precise their movements were. One small mistake and they could badly burn themselves! It gave me a whole new appreciation for just how difficult this traditional craft is to master.In addition to learning the history and stamping process, we also studied the symbolic meanings behind the different flower patterns used in iron stamping art. For example, the chrysanthemum represents vitality and longevity. The peony is a symbol of wealth, prosperity, and feminine beauty. And the lotus flower signifies purity of heart and mind. By stamping these auspicious floral emblems onto household objects, it was thought to bring those positive attributes into the home.We even got to try making our own very simple iron stamping designs using pencils and paper instead of molten iron! We traced flower patterns into one sheet of paper, then placed a piece of aluminum foil on top as the "soil plate." By pressing down firmly with another pencil, we could imprint the raised flower shape into the foil. It was just a tiny taste of the real iron stamping process, but it helped me understand the basic technique a little better.For our unit test at the end, we had to do a research project on iron flower stamping. I collected some pictures and made a poster showing the different stages of the process. I also interviewed my grandpa who has several old stamped iron pieces in his home that have been passed down through generations. He told me about the symbolic meanings behind the specific flower patterns on a antique window grate and decorative fire poker. Putting together the project really deepened my knowledge and appreciation of this unique Chinese cultural art.Overall, I'm really glad we studied the iron flower stamping tradition as part of our English lessons. It opened my eyes to an amazing craft that has been practiced for centuries right here in my home province of Sichuan. The amount of skill, artistry and cultural heritage bound up in each stamped iron bloom is just incredible to me now. I have a much deeper respect for the folk arts and traditional handicrafts that are part of Chinese culture after this unit. I think it's so important to preserve these types of intangible cultural treasures for future generations. Who knows, maybe I'll even take up iron flower stamping as a hobby when I'm older! It seems like the perfect combination of delicate artistry and raw physical effort - a microcosm of the essence of Chinese culture itself.。
Magnetism is a fascinating force of nature that has been utilized by humans for centuries in various forms. The question of whether magnets can be harnessed for practical applications is not only valid but also a testament to the innovative spirit of humankind. Here are several ways in which magnets are being used and their potentialfor future utilization:1. Transportation: Magnetic levitation maglev trains use powerful magnets to levitate above the tracks, reducing friction and allowing for highspeed travel with minimal energy loss.2. Medical Applications: Magnets are used in various medical procedures, such as Magnetic Resonance Imaging MRI, which uses strong magnetic fields to generate detailed images of the bodys internal structures.3. Data Storage: Hard drives in computers use magnetic storage to save data. The development of magnetic tape and floppy disks was a significant step in data preservation.4. Power Generation: Many power plants use magnets in their turbines to generate electricity through the principles of electromagnetic induction.5. Household Appliances: Everyday items like refrigerators, washing machines, and electric motors rely on magnets to function.6. Educational Tools: Magnets are used in educational settings to demonstrate principles of physics, such as the laws of attraction and repulsion.7. Renewable Energy: Research is ongoing into using magnets in wind turbines and other renewable energy technologies to improve efficiency and storage capabilities.8. Space Exploration: Magnets are used in spacecraft for various purposes, including navigation and data storage.9. Art and Crafts: Magnetic paints and materials are used in creative projects, allowingfor the creation of magnetic art and decorations.10. Industrial Separation: In industries, magnets are used to separate ferrous metals from waste materials for recycling purposes.11. Health and Wellness: Some people use magnetic therapy, also known as magnetotherapy, as an alternative treatment for pain relief, though its effectiveness is asubject of debate.12. Security Systems: Magnetic sensors are used in alarm systems to detect when doors or windows are opened.The potential for utilizing magnets is vast, and as technology advances, it is likely that we will find even more innovative ways to harness their power. From improving energy efficiency to enhancing our understanding of the universe, magnets will undoubtedly continue to play a significant role in our lives.。
gamma单词单词:gamma1. 定义与释义1.1词性:名词1.2中文释义:希腊字母表的第三个字母(Γ,γ);伽马(磁场强度单位);灰度(非线性图像编辑术语)。
1.3英文释义:The third letter of the Greek alphabet; a unit of magnetic field strength; in non - linear image editing, it refers to the degree of gray scale.1.4相关词汇:gammon(熏腿;胡说),gammoid(拟阵)。
---2. 起源与背景2.1词源:“gamma”来源于古希腊语。
2.2趣闻:在数学中,伽马函数是一个非常特殊的函数,它与阶乘有密切的关系。
在物理学中,伽马射线是一种高频电磁波,在天体物理等众多领域有重要意义,而这个名字也源于希腊字母“gamma”。
---3. 常用搭配与短语3.1短语:gamma ray(伽马射线)例句:Gamma ray bursts are one of the most energetic events in the universe.翻译:伽马射线暴是宇宙中最具能量的事件之一。
3.2短语:gamma correction(伽马校正)例句:The gamma correction can improve the visual quality of the image.翻译:伽马校正可以提高图像的视觉质量。
---4. 实用片段(1). "Look at this equation, there is a gamma symbol in it. What does it represent?" The student asked the teacher. The teacher replied, "In this context, gamma represents a certain variable."翻译:“看这个方程式,里面有个伽马符号。
The physics of strong magnetic fields of magnetarsDepartment of Astronomy, Nanjing University, Nanjing, 210093, China.Abstract :A phase transition from paramagnetism to ferromagnetism in neutron star interior is explored. Since there is 3P 2 neutron superfluid in neutron star interior, it can be treated as a system of magnetic dipoles. Under the presence of background magnetic field, the magnetic dipoles tend to align in the same direction. Below a critical temperature, there is a phase transition from paramagnetism to ferromagnetism. And this gives a convenient explanation of the strong magnetic field of magnetars. In our point of view, there is an upper limit for the magnetic field strength of magnetars. The maximum field strength of magnetars is about (3.0-4.0) 1015 gauss. This can be tested directly by further investigations.Key words : magnetic fields —stars:neutron —pulsar:general I. IntroductionIt is generally accepted that there are very strong magnetic fields, B > 1012 gauss, for most radio pulsars (e.g. Shapiro and Teukolski 1983). There probably are magnetars with magnetic field strength exceeding the quantum critical threshold, H cr =4.414 1013 gauss (Duncan & Thompson 1992; Paczynski 1992; Usov 1992; Thompson & Duncan 1995, 1996). Anomalous X-ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) are identified as classes of magnetar candidates (e.g. Kouvelliotou et al. 1998, 1999; Hurley et al. 1999; Mereghetti & Stella 1995; Wilson et al. 1999; Kaspi et al. 1999). The magnetic fields of the magnetars, which can be deduced from their long spin periods (P~5-12s) and spindown rate (10131010P --~-) based on the standard magnetic dipolar radiation, are so strong as to reach two orders of magnitude the quantum critical threshold H cr . Moreover, the same estimate of the magnetic field is derived from the observation of an absorption line in the X-ray spectrum of SGR 1806-20 (Ibrahim et al. 2002).A puzzle is what is the origin of strong magnetic field of magnetars. A possible explanation is that the strong magnetic field of neutron stars originates from the collapse of the core of a supernova with the conservation of magnetic flux (e.g. Ostriker & Gunn, 1969)(the fossil field hypothesis); therefore magnetic field of 1000B G of the progenitors is required. Braithwaite & Spruit (2004) analysed the structure of the magnetic fields in A stars and white dwarfs, and demonstrated the formation of stable field configurations according to the fossil field hypothesis. Ferrario & Wickramasinghe (2006) studied the field distribution of the white dwarf progenitors, and they suggested that magnetars are descended from the high magnetic field massive progenitors. However, the detailed calculation about the magnetic field of magnetars have not been carried out directly. Moreover, the progenitors of magnetars have not been identified inobservations.Another popular mechanism is presented by Duncan and Thompson (Duncan & Thompson1992; Thompson & Duncan 1993). They point out that there are violent convection in the process of pro-neutron stars formation, and an efficient α-Ω dynamo can amplify the magnetic field to the field strength of magnetars in several seconds if the initial spin period of the magnetar is less than 3ms and the proto-neutron stars rotate differentially. Nevertheless, as pointed out by Braithwaite & Spruit (2004), the dynamo hypothesis may be difficult to produce enough high field and explain the correlation with rotation. Recently, Vink & Kuiper (2006) studied the remnant energetic of magnetars. They detected that the supernova explosion energy of the magnetars is similar to that of normal radio pulsars. However, if the fields of the magnetars originate from the dynamo hypothesis, millisecond initial spin period should be expected, the explosion should be as energetic as the hypernova since the rotational energy of the millisecond proto-neutron is large enough not to be neglected in powering supernova.The fossil field hypothesis and the dynamo hypothesis are relatively mature models as to the origin of the high magnetic field. Both of them have been employed to interpret some observations successfully, whereas some new observational results may challenge to them. Altogether, the origin of the high magnetic fields of magnetars is an active and absorbing issue which need further work. Several models have already been proposed based on the ferromagnetism of the netron star matter, e.g. Iwazaki (2005) argued that the huge magnetic field of magnetars is some color ferromagnetism of quark matter.In this paper we propose a new idea for the origin of the magnetars. The strong magnetic fields of the magnetars may originate from the induced magnetic moment of the 3P 2 neutron Cooper pairs in the anisotropic neutron superfluid.II. Anisotropic 3P 2 neutron superfluidThere are two relevant regimes of neutron superfluid in the neutron star interior: one is the isotropic 1S 0 neutron superfluid with the critical temperature T ● (1S 0) 1 1010K in a density range 1 1010 < ❒ (g/cm 3) <1.6 1014. The other is the anisotropic 3P 2 neutron superfluid with a wide density range 1.3⨯1014 < ρ (g/cm 3) < 7.2 ⨯1014. The critical temperature 32()T P λ is3382max 2()()/2 2.7810T P P k K λ=∆≈⨯. (1)We note that the energy gap (3P 2) is almost a constant about the maximum with an error less than 3% in a rather wide density region 3.3⨯1014 < ρ (g/cm 3) < 5.2⨯1014 ( see Fig. 2 of Elgagøy et al. 1996, but we neglect the F state of neutron Cooper pair here).A 3P 2 neutron Cooper pair has a spin with quantum number, ♦ =1. The magnetic moment of the 3P 2 neutron Cooper pair is twice that of the abnormal magnetic moment of a neutron, 2 ❍n in magnitude, and its projection on the external magnetic field (z-direction) is ♦z ×(2 ❍n ) , ♦z =1,0,-1, where 230.96610 erg/gauss n μ-=-⨯.It is interesting to note that the behavior of the 3P 2 neutron superfluid is very similar to that of the liquid 3He at very low temperature (Leggett 1975):1) The projection distribution for the magnetic moment of the 3P 2 neutron Cooper pairs in the absence of external magnetic field is stochastic, or “Equal Spin Pair” (ESP) phase similar to the A - phase of the liquid 3He at very low temperature (Leggett 1975). The 3P 2 neutron superfluid is basically isotropic without net magnetic moment in the absence of the external magnetic field. We name it as the A- phase of the 3P 2 neutron superfluid similar to the A phase of the liquid 3He at very low temperature (Leggett 1975).2) However, the projection distribution for the magnetic moment of the 3P 2neutron Cooper pairs in the presence of external magnetic field is not stochastic. The number of 3P 2 neutron Cooper pair with paramagnetic moment is more than the ones with diamagnetic moment. Therefore, the 3P 2 neutron superfluid has a net induced paramagnetic moment and its behavior is anisotropic in the presence of external magnetic field. We name it as the B- phase of the 3P 2 neutron superfluid similar to the B phase of the liquid 3He at very low temperature (Leggett 1975).The full story of anisotropic 3P 2 neutron superfluid is more complicated when magnetic interaction is introduced. We consider this problem from the effective field theory point of view (Feng & Jin 2005). It is possible that the induced magnetic field of the 3P 2 superfluid will boost the neutron star magnetic field to that of magnetars, whenever the stellar internal temperature is below the phase transition temperature. We will discuss this in section V.III. Induced paramagnetic moment of the 3P 2 neutron superfluid in the B-phaseThe induced paramagnetic moment of the 3P 2 neutron superfluid in the B-phase may be simply estimated as follows: the system of the 3P 2 neutron Cooper pairs with spin quantum number , 1σ=, may be treated as a Bose-Einstein system. It obeys the Bose-Einstein statistics.A magnetic dipole tends to align in the direction of the external magnetic field. The 3P 2 neutron Cooper pair has energy ♦Z 2❍nB (♦Z =1,0,-1) in the applied magnetic field due to the abnormal magnetic moment of the neutrons. Here ❍n is the absolute value of the magnetic moment of a neutron, we use this convention from now on. B is the background magnetic field. While in the effective field frame, B is the total magnetic field. Detailed discussion will be presented in section V . We denote the number density of 3P 2 neutron Cooper pairs with spin projection ♦z =1,0,-1 by n 1, n 0 and n -1 respectively. Their relative ratios are2/2/1100, n n B kT B kT n n e e n n μμ--+==, (2)31012()n n n n n P -+++=. (3) The difference of the number density of 3P 2 neutron Cooper pairs with paramagnetic and diamagnetic moment is3112()()n n Bn n n n P f kT μ-+∆=-=, (4)2sin (2)()12cos (2)h x f x h x =+. (5) The Brillouin function, f(❍n B/kT), is introduced to take into account the effect of thermal motion We note that f It is an increasing function, in particular,()4/3, for 1f x x x ≈<<and ()1, when 1f x x →>>. f(❍n B/kT) increase with decreasing temperature. And this is the mathematical formula for the B-phase of the 3P 2 superfluid.A relevant question is how many neutrons have been combined into the 3P 2 Cooper pairs? Thetotal number of neutrons is given by 333202(2)3F k F d k V N V k ππ==⎰ (Here k is a wave vector,p k =, p is the momentum). The neutrons combined into the 3P 2 Cooper pairs are just in a thin layer in the Fermi surface with thickness k ∆, 322()n n k m P ∆=∆. Then we have 32F Fk VN k k δπ∆≈ (k <<k F ). Thus, the fraction of the neutrons that combined into the 3P 2 Cooper pairs is. (6) Here, we would like to emphasize that the energy gap, , is the binding energy of the Cooper pair rather than a variation of the Fermi energy due to a disturbance or due to the variation of particle number density (In the latter case, it is easy to misunderstand to get 33322F F FkE q k E E δδ∆≈== or 338Fq E π∆=). Therefore, we think the eq.(6) is a proper estimation. For the non –relativistic neutron gas (22/2F F n E k m =), the fraction of the neutrons thatcombined into the 3P 2 Cooper pairs is (7). The Fermi energy of the neutron system may be calculated by the formula 3F k N q N k δ∆=≈231/231/22234[2()]()3[](4/3)F n F F p m P P q p E ππ∆∆==2/322/32/32/313()()60()28F A n n nuc E h N Y MeV m ρρπρ=≈. (8)The energy gap of the anisotropic neutron superfluid is (3P 2) ~ 0.05 MeV (Elgagøy et al. (1996)), q ~ 8.7%. Thus, the total number of the 3P 2 Cooper pairs is3322()()/2n A n P qN m P ≈. (9)Therefore, the total difference of the 3P 2 neutron Cooper pair number with paramagnetic and diamagnetic moment is33221()()() ()2n n A BB N n P f N m P q f kT kT μμ∆==. (10)The total induced magnetic moment, of the anisotropic neutron superfluid is()3322()2() (/)in n n A n P N N m P q f B kT μμμμ=⨯∆=. (11) Where 32()m P is the mass of the anisotropic neutron superfluid in the neutron star, N A is the A’vogadro constant. The induced magnetic moment is just the fully magnetized quantity 32()n A N m P μ, with two modification factors. The factor q takes into account the Fermi surface effect. While (/)n f B kT μis the thermal factor taking into consideration the finite temperature effect. For a dipolar magnetic field 3/2NS p NS B R μ= (Shapiro and Teukolski, 1984). Here B p is the polar magnetic field strength and R NS is the radius of the neutron star. The induced magnetic field is then3()3()22332()2() (/)in in n A n NS NSN m P P B q f B kT R R μμμ==. (12) The induced magnetic field for the anisotropic neutron superfluid increases with decreasing temperature (as shown in the Fig.1).Fig 1 only shows the case of paramagnetism, that is no magnetic interaction. Since the problem of magnetism is still an open question in condensed matter physics (Feng & Jin, 2005), we will try to discuss this problem in section V . We will first discuss the upper limit of the magnetic field of magnetars in our theoretical frame. Since this can be tested by observation directly.IV . The upper limit of the magnetic field of magnetars We note that the temperature factor f(❍n B/kT ) tends to 1 when the temperature decreases lowenough. Actually, f(❍n B/kT) ~1 as long as ❍n B/kT >>1. For example, this is true when 710T K if B= 1015 gauss.There is an upper limit for the induced magnetic field of the 3P 2 superfluid according to eq.(12). It corresponds to the maximum value unity of the temperature factor f(❍n B/kT ). This upper limit can be realized when all the magnetic moments of the 3P 2 neutron Cooper pairs are arranged with the paramagnetic direction as the temperature become low enough. The upper limit of the magnetic field for the magnetars in our point of view is3()32max 23142()()2.0210in n A NSN m P B P q gauss R gauss μη=≈⨯ . (13) Here 3331/222,6()()[]0.10.05n NS Sun P m P R m MeVη-∆= is the dimensionless factor describes both the macroscopic and microscopic properties of neutron stars.The maximum magnetic field for magnetars depends on the total mass of the anisotropic neutron superfluid of the neutron star. The upper limit of the mass for the neutron stars is more than 2M (Lattimer & Prakash 2007). It is therefore possible that the mass of the anisotropic neutron superfluid of the heaviest neutron star may be about (1 1.5)M -. Hence, the maximal magnetic field for the heaviest magnetar may be estimated to be (3.0-4.0) 1015 gauss. This can be tested directly by magnetar observations.V . From paramagnetism to ferromagnetism1. High temperature and low BWe have n B kT μ<<when B <1013 gauss and T > 3×106 K, therefore we could make Tailor series 3()237()8 1.93in n A n NS N m P B B q B R kT T μμη≈≈ (14))0()(B B B in += (15) Where B (0) is the applied magnetic field which includes both the initial magnetic field of thecollapsed supernova core and the induced magnetic field produced by the Pauli paramagnetization of the highly degenerate relativistic electron gas in the neutron star interior (Peng & Tong 2007).We may solve the induced magnetic field by combining eq.(14) and eq.(15):)0(17)()19.1(B T B in --=η (16) The induced magnetic field, B (in ) , of the anisotropic neutron superfluid is much weaker than the applied magnetic field , B (0) , when the temperature is very high, 7 1.9T η>>. However, the induced magnetic field of the anisotropic neutron superfluid would exceed the applied magnetic field when the temperature decreases down to 71/(1.9)2T η<<. Therefore B (in) should be calculated by both eq.(12) and eq.(15) when η9.1~7T . This belongs to the domain of ferromagnetism.2. From paramagnetism to ferromagnetismWe will look at this problem in the effective field theory. For general discussion see Pathria (2003), Feng & Jin (2005). It is an effective way dealing with ferromagnetism in terrestrial case. In this frame, the effective magnetic field is proportional to the induced magnetic moment ()0()(0)()eff in B B B B γμ=+=+. (17) Here γis a free parameter related to the microscopic magnetic interaction (Feng & Jin 2005). The background magnetic field is assumed to be homogeneous. Noting that the induced magnetic field is also proportional to the induced magnetic moment()3()232()in in NSP B R μ=, (18) we may set ()()eff in BB =in zero order approximation. Then the whole problem lies on the following two coupled equations3()3()22332()2() (/)in in n A n NS NSN m P P B q f B kT R R μμμ== (19) )0()(B B B in +=.(20) Using the definition of maximum induced magnetic field ()max in Beq.(13), the above equations canbe rewritten in dimensionless form ()b f x = (21) 071.40 ()x b b T η=+. (22)Here ()()maxin in B b B =, (0)0()max in B b B =, 7T is the internal temperature expressed in 710K . The above two equations can be solved graphically. Table 1 gives the numerical results. The numerical result shows that there is an obvious phase transition from paramagnetism to ferromagnetism. The transition temperature is about 7210K ⨯.Following terrestrial treatment of phase transition from paramagnetism to ferromagnetism, the coupled equations can be written in 43b x = (23) 071.40 ()x b b T η=+. (24)Setting 00b = gives the transition temperature 74 1.40 1.873c T ηη=⨯=, 7210c T K η≈⨯. Introducing a dimensionless temperature 77r c T T T =, the coupled equations (21) (22) can be rewritten as ()b f x = (25) 031()4r x b b T =+. (25)After some manipulation, we obtain a convenient form of the above two coupled equations ()b f x =(26) 043r b xT b =-. (27) Figure 2 shows the phase transition from paramagnetism to ferromagnetism.In view of the above discussions we may get a very important conclusion: the strong magnetic field of magnetars may originate from the induced magnetic field by the ferromagnetic moments of the 3P 2 Cooper pairs of the anisotropic neutron superfluid at a moderate low temperature about 710K . VI. Conclusion and discussionThe strong magnetic field of magnetars may originate from the induced magnetic field due to the ferromagnetic moment of the 3P 2 superfluid with significant mass more than 0.1M at temperature about 710K . Here we provide a channel for magnetar formation through normal neutron stars.The evolutionary scenario of the magnetic field of neutron stars may be depicted as follows:1) First, the fossil magnetic field of the collapsed core due to the conservation of magnetic flux during supernova explosion would be greatly boosted up more than 90 times to B (0) by the Pauli paramagnetization of the highly degenerate relativistic electron gas just after the formation of the neutron stars (Peng and Tong 2007).2) The magnetic fields of neutron stars with a significant 3P 2 superfluid(for example, ♒ >1), would increase gradually when the temperature of the cooling star decreases down to 7 1.9T η<. Their long spin periods (P~5-12s) can give us some hints. Here we provide a choice for a normal neutron star to evolve toward a magnetar.3) For some magnetars, their magnetic field seem be so strong as 1 1015 gauss according to the standard magnetic dipole model. The corresponding magnetic field is calculated by the observed period (P ) and its varied rate (dP/dt ) following the standard magnetic dipole model, 193.210eff B PP Gauss ≈⨯ (25) However, the calculated magnetic field strength may be weaker than the standard value above according to our hybrid model for pulsar spin down (Peng et al. 1982). In our opinion, the observed strong magnetic field strength of the magnetars should be re-estimated and the magnetic field of the magnetars may somewhat be lower than 1 1015 gauss.4) The maximal magnetic field for the magnetar is (3.0-4.0) 1015 gauss according to our investigation.5) The core temperature of the magnetars is about 107 K in our model. While observations show that some SGR's and AXP's have high thermal-type-spectrum X-ray flux, being among the hottest neutron stars. We shall discuss this question and give reasonable and consistent explanation in our further paper.AcknowledgmentThe author Q-h Peng is very grateful to Prof. Chich-gang Chou for his help of improving the presentation of the paper. This research is supported by Chinese National Science Foundation through grant no.10573011, grant no.10273006, and grant no. 10773005 and the Doctoral Program Foundation of State Education Commission of China.ReferencesBraithwaite J., Spruit H. C., 2004, Nature, 431, 819Duncan R.C. , Thompson C. 1992, ApJ, 392, L9Elgagøy Ø., Engvik L., Hjorth-Jensen M., et al., 1996, PRL, 77, 1428 Feng D., Jing Guo-Jun, 2005, Word Scientific, Singapore, §17.2 Ferrario L., Wickrammasinghe D.,2006, MNRAS 367, 1323Hurley K., Li P., Kouveliotou C., et al., 1999, ApJ, 510, L111Ibrahin A. I., Safi-Harb S., Swank J. H., et al., 2002, ApJ, L51 Iwazaki A., 2005, Phys. Rev. D, 72, 114003Kaspi V. M., Chakrabarty D., Steinberger J., 1999, ApJ, 525, L33 Kouveliotou C. 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Different curves stand for different background magnetic field. Here we consider the paramagnetism case only.Legend of Figure 2.The induced magnetic field ()()maxin in B b B = as a function of temperature. The thick curve stands for()b f x =. The dashed, dotted, dot-dashed, and thick line corresponds to 043r b xT b =-, when 02.5, b 0r T ==, 01, b 0r T ==, 00.5, b 0r T ==, 00.5, b 0.1r T == respectively. So we see directly from the figure that there is a phase transition when 1r T <, that is c T T <. Therefore, we have a almost fully magnetized system even there is no background magnetic field, provided the temperature is below the critical temperature.Table 1. Induced magnetic field ()()maxin in B b B = for different temperatures and background magnetic field. Here B (in)max is about 14210⨯ Gauss, ηis set to 1. We see that when temperatureis below 7210c T ≈⨯, the 3P 2 system is almost fully magnetized. When the temperature is above T c , high temperature and low B approximation is valid.b 0 T 730.510-⨯ 20.510-⨯ 10.510-⨯ 1.0.92 0.92 0.93 1.50.67 0.68 0.74 2. 3710-⨯ 26.810-⨯ 0.37 5. 4310-⨯ 3310-⨯ 2310-⨯。