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Spin Diffusion
Spin diffusion describes a situation wherein the individual nuclear Spin (physics), spins undergo continuous exchange of energy. This permits Spin polarization, polarization differences within the sample to be reduced on a timescale much shorter than relaxation time, relaxation effects. Spin diffusion is a process by which magnetization can be exchanged spontaneously between spins. The process is driven by dipolar coupling, and is therefore related to internuclear distances. Spin diffusion has been used to study many structural problems in the past, ranging from domain sizes in polymers and disorder in glassy materials to high-resolution crystal structure determination of small molecules and proteins. In solid-state nuclear magnetic resonance, spin diffusion plays a major role in Cross Polarization (CP) experiments. As mentioned before, by transferring the magnetization (and thus the population) from nuclei with different values for the spin-lattice relaxation (''T1''), the overa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Spin (physics)
Spin is an Intrinsic and extrinsic properties, intrinsic form of angular momentum carried by elementary particles, and thus by List of particles#Composite particles, composite particles such as hadrons, atomic nucleus, atomic nuclei, and atoms. Spin is quantized, and accurate models for the interaction with spin require relativistic quantum mechanics or quantum field theory. The existence of electron spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which silver atoms were observed to possess two possible discrete angular momenta despite having no orbital angular momentum. The relativistic spin–statistics theorem connects electron spin quantization to the Pauli exclusion principle: observations of exclusion imply half-integer spin, and observations of half-integer spin imply exclusion. Spin is described mathematically as a vector for some particles such as photons, and as a spinor or bispinor for other particles such as electrons. Sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Spin Polarization
In particle physics, spin polarization is the degree to which the spin, i.e., the intrinsic angular momentum of elementary particles, is aligned with a given direction. This property may pertain to the spin, hence to the magnetic moment, of conduction electrons in ferromagnetic metals, such as iron, giving rise to spin-polarized currents. It may refer to (static) spin waves, preferential correlation of spin orientation with ordered lattices (semiconductors or insulators). It may also pertain to beams of particles, produced for particular aims, such as polarized neutron scattering or muon spin spectroscopy. Spin polarization of electrons or of nuclei, often called simply magnetization, is also produced by the application of a magnetic field. Curie law is used to produce an induction signal in electron spin resonance (ESR or EPR) and in nuclear magnetic resonance (NMR). Spin polarization is also important for spintronics, a branch of electronics. Magnetic semiconducto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Relaxation Time
Relaxation stands quite generally for a release of tension, a return to equilibrium. In the sciences, the term is used in the following ways: * Relaxation (physics), and more in particular: ** Relaxation (NMR), processes by which nuclear magnetization returns to the equilibrium distribution ** Dielectric relaxation, the delay in the dielectric constant of a material ** Vibrational energy relaxation, the process by which molecules in high energy quantum states return to the Maxwell-Boltzmann distribution ** Chemical relaxation methods, related to temperature jump ** Relaxation oscillator, a type of electronic oscillator In mathematics: :* Relaxation (approximation), a technique for transforming hard constraints into easier ones :* Relaxation (iterative method), a technique for the numerical solution of equations :* Relaxation (extension method), a technique for a natural extension in mathematical optimization or variational problems In computer science: :* Relaxation (com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Solid-state Nuclear Magnetic Resonance
Solid-state nuclear magnetic resonance (ssNMR) is a spectroscopy technique used to characterize atomic-level structure and dynamics in solid materials. ssNMR spectra are broader due to nuclear spin interactions which can be categorized as dipolar coupling, chemical shielding, quadrupolar interactions, and j-coupling. These interactions directly affect the lines shapes of experimental ssNMR spectra which can be seen in powder and dipolar patterns. There are many essential solid-state techniques alongside advanced ssNMR techniques that may be applied to elucidate the fundamental aspects of solid materials. ssNMR is often combined with magic angle spinning (MAS) to remove anisotropic interactions and improve the sensitivity of the technique. The applications of ssNMR further extend to biology and medicine. Nuclear spin interactions The resonance frequency of a nuclear spin depends on the strength of the magnetic field at the nucleus, which can be modified by isotropic (e.g. c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Gyromagnetic Ratio
In physics, the gyromagnetic ratio (also sometimes known as the magnetogyric ratio in other disciplines) of a particle or system is the ratio of its magnetic moment to its angular momentum, and it is often denoted by the symbol , gamma. Its SI unit is the reciprocal second per tesla (s−1⋅T−1) or, equivalently, the coulomb per kilogram (C⋅kg−1). The -factor of a particle is a related dimensionless value of the system, derived as the ratio of its gyromagnetic ratio to that which would be classically expected from a rigid body of which the mass and charge are distributed identically, and for which total mass and charge are the same as that of the system. For a classical rotating body Consider a nonconductive charged body rotating about an axis of symmetry. According to the laws of classical physics, it has both a magnetic dipole moment due to the movement of charge and an angular momentum due to the movement of mass arising from its rotation. It can be shown that as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Quantum Field Theory
In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines Field theory (physics), field theory and the principle of relativity with ideas behind quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles and in condensed matter physics to construct models of quasiparticles. The current standard model of particle physics is based on QFT. History Quantum field theory emerged from the work of generations of theoretical physicists spanning much of the 20th century. Its development began in the 1920s with the description of interactions between light and electrons, culminating in the first quantum field theory—quantum electrodynamics. A major theoretical obstacle soon followed with the appearance and persistence of various infinities in perturbative calculations, a problem only resolved in the 1950s with the invention of the renormalization procedure. A second major barrier came with QFT's apparent inabili ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |