共查询到20条相似文献,搜索用时 10 毫秒
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E. D. Skakovskii A. I. Stankevich S. A. Lamotkin L. Yu. Tychinskaya G. S. Avrinskii S. V. Rykov 《Journal of Applied Spectroscopy》2000,67(5):770-777
On the basis of the effects of chemically induced dynamic nuclear polarization of 1H and 13C and the yields of reaction products, the photolysis of methanol-d
4 solutions of acetylpropionyl peroxide is investigated within the temperature interval 193–333 K. Polarization of all the protons of ethylethanoate is detected; it is shown that the latter is formed in several chemical reactions. The role of different excited states of the peroxide in the mechanism of its photolysis is discussed. 相似文献
3.
The laws governing polarization of luminescence in the nanostructure Si/CaF2 upon polarization of the spins of the fluorine nuclei by means of optical excitation of charge carriers are considered theoretically.
The possibility of studying experimentally the properties of nuclear spins in analyzing luminescence is shown. The polarization
of luminescence is most informative in the range of excitation rates of charge carriers from 3⋅107 to 3⋅ 108 sec−1 with the CaF2 layer of thickness from 0.6 to 0.8 nm and optical excitation polarization degree of 0.1.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 524–529, July–August, 2005. 相似文献
4.
We discuss the dynamic properties of the square-lattice spin-1/2 XY model obtained using the two-dimensional Jordan-Wigner fermionization approach. We argue the relevance of the fermionic picture for interpreting the neutron scattering measurements in the two-dimensional frustrated quantum magnet Cs2CuCl4. 相似文献
5.
Momota S. Nojiri Y. Fukuda M. Matsuta K. Minamisono T. 《Hyperfine Interactions》2002,142(3-4):513-548
In order to disclose the polarization mechanism of the tilted-foil technique, systematic experimental studies were performed through direct observations of the nuclear polarization of short-lived beta-emitters. The present studies concentrated on the mechanisms of the following processes: (1) production of atomic polarization in the beam–tilted-foil interaction, (2) polarization transfer between an atom and a nucleus, and (3) enhancement of nuclear polarization by the beam multi-tilted-foil interaction. The present results have confirmed the plausibility of a previous model in which the atomic-polarization process in the tilted-foil technique is attributed to the right–left asymmetry of the electron-capture process at the final surface of a tilted foil. The enhancement effect of nuclear polarization by the multi-tilted-foil technique could be consistently explained by a model proposed by Goldring and Niv. Further information on atomic processes is required to make a definite statement on hyperfine interactions and atomic configurations, which contribute to polarization transfer. 相似文献
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微波诱导光学核极化(Microwave-Induced Optical Nuclear Polarization,MIONP)技术利用光激发三重态样品来极化电子,再用微波将处于非热平衡态的电子极化转移到待检测原子核,将原子核的检测灵敏度提高几个量级甚至更多.这种灵敏度极化增强方法可以用来进行蛋白质结构和动力学检测、光化学和光物理进程的基础研究、量子计算和低场核磁共振(Low-field Nuclear Magnetic Resonance,Low-field NMR)与磁共振成像(Magnetic Resonance Imaging,MRI)应用研究.该文简要分析了MIONP的物理原理及其在核极化增强中的优势,结合实验条件综述了一些重要的成果.最后,对微波诱导光学核极化的前景作了展望. 相似文献
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The behavior of nuclear polarization in a substance, i.e., a solution of the complex HMBA(CrV)Na+ in 1,2-propylene glycol used in polarized nuclear targets is experimentally investigated by magnetic spectroscopic methods
under conditions of dynamic nuclear polarization at hvS/kT=≈1.5−3.2. Nuclear polarization is measured and analyzed as a function of time at different values of the saturating microwave
signal and temperature. It is shown that the process of decreasing the nuclear polarization involving free nuclear relaxation
is described by a nonmonoexponential law with two damping decrements, which determine the time of reaching equilibrium between
the Zeeman nuclear subsystem, the dipole-dipole pool, and the lattice. Specific features of dynamic processes proceeding in
the electronic-nuclear system of the substance investigated are discussed.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 363–366, May–June, 1997. 相似文献
9.
Burkhard Luy Steffen J. Glaser 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,153(2):210-214
Analytical coherence transfer functions are presented for spin systems consisting of two spins 1 under planar mixing conditions. Compared to isotropic mixing experiments, larger transfer amplitudes are found and differences in the multiplet patterns are discussed. 相似文献
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The dynamic phase transition has been studied, within a mean-field approach, in the kinetic spin-3/2 Ising model Hamiltonian
with arbitrary bilinear and biquadratic pair interactions in the presence of a time dependent oscillating magnetic field by
using the Glauber-type stochastic dynamics. The nature (first- or second-order) of the transition is characterized by investigating
the behavior of the thermal variation of the dynamic order parameters and as well as by using the Liapunov exponents. The
dynamic phase transitions (DPTs) are obtained and the phase diagrams are constructed in the temperature and magnetic field
amplitude plane and found nine fundamental types of phase diagrams. Phase diagrams exhibit one, two or three dynamic tricritical
points, and besides a disordered (D) and the ferromagnetic-3/2 (F3/2) phases, six coexistence phase regions, namely F
3/2+ F
1/2, F
3/2+ D, F
3/2+ F
1/2+ FQ, F
3/2+ FQ, F
3/2+ FQ + D and FQ + D, exist in which depending on the biquadratic interaction.
PACS number(s): 05.50.+q, 05.70.Fh, 64.60.Ht, 75.10.Hk 相似文献
12.
Rollin S. Armour Jr. 《Foundations of Physics》2004,34(5):815-842
Requiring covariance of Maxwell's equations without a priori imposing charge invariance allows for both spin-1 and spin-1/2 transformations of the complete Maxwell field and current. The spin-1/2 case yields new transformation rules, with new invariants, for all traditional Maxwell field and source quantities. The accompanying spin-1/2 representations of the Lorentz group employ the Minkowski metric, and consequently the primary spin-1/2 Maxwell invariants are also spin-1 invariants; for example,
2–A
2, E
2–B
2+2i
EB–(0
+A)2. The associated Maxwell Lagrangian density is also the same for both spin-1 and spin-1/2 fields. However, in the spin-1/2 case, standard field and source quantities are complex and both charge and gauge invariance are lost. Requiring the potentials to satisfy the Klein–Gordon equation equates the Maxwell and field-potential equations with two Dirac equations of the Klein–Gordon mass, and thus one complex Klein–Gordon Maxwell field describes either two real vector fields or two Dirac fields, all of the same mass. 相似文献
13.
A.N.Behkami M.N.Nasrabadi 《理论物理通讯》2002,37(4):457-460
The level densities of even-odd and even-even isotopes^161,162Dy,^166Er and ^171,172Yb were calculated using microscopic theory of interacting fermions and compared with experiments.It is found that the data can be well reproduced with level density formalism for nuclei with static deformation.The nuclear temperature as well as the reproduced with level density formalism for nuclei with static deformation.The nuclear temperature as well as the entropy of nuclear system as a function of excitation energy has been extracted from the BCS theory.It is shown that the entropy exhibits an S-formed shape as a function of excitation energy.This is interpreted as a phase transition.Procedure of treating the even-odd and even-even nuclear systems has been presented and discussed. 相似文献
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Recent trends in Low-Temperature Nuclear Orientation (LTNO) and its site-selective derivative, Nuclear Magnetic Resonance
on Oriented Nuclei (NMRON), are reviewed. Traditional areas of endeavour using elemental ferromagnetic hosts remain strong
with significant improvements in methodology since last reviewed [1]; but there are new emphases emerging in solid-state physics
and especially magnetism. Exotic single crystals hosts and MBE-grown multi-layers are gaining increased prominence as the
principal focus of LTNO study. Increasingly, in off-line work and very recent on-line implantation into insulators [2], the
radioactive probes are often chosen to be isoelectronic with an abundant chemical species within the host, rather than representing
an extremely dilute, electronic impurity spy. Recent NMRON on a heavy rare earth, isoelectronic probe in an ordered rare earth
halide opens up new dimensions.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
15.
We examine the dynamic phase transitions and the dynamic compensation temperatures, within a mean-field approach, in the mixed
spin-3/2 and spin-5/2 Ising system with a crystal-field interaction under a time-varying magnetic field on a hexagonal lattice
by using Glauber-type stochastic dynamics. The model system consists of two interpenetrating sublattices with σ=3/2 and S=5/2. The Hamiltonian model includes intersublattice, intrasublattice, and crystal-field interactions. The intersublattice
interaction is considered antiferromagnetic and to be a simple but interesting model of a ferrimagnetic system. We employ
the Glauber transition rates to construct the mean-field dynamic equations, and we solve these equations in order to find
the phases in the system. We also investigate the thermal behavior of the dynamic sublattice magnetizations and the dynamic
total magnetization to obtain the dynamic phase transition points and compensation temperatures as well as to characterize
the nature (continuous and discontinuous) of transitions. We also calculate the dynamic phase diagrams including the compensation
temperatures in five different planes. According to the values of Hamiltonian parameters, five different fundamental phases,
three different mixed phases, and six different types of compensation behaviors in the Néel classification nomenclature exist
in the system. 相似文献
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We develop a Radon-like transformation, in which P quasiprobability distribution for spin-1/2 states is written in terms of the tomographic probability distribution w. 相似文献
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本文设想了一个相互作用淬火后在 时刻开启的海森堡反铁磁模型,并对其进行了解析分析.在低温近似下,通过求解海森堡方程给出该系统随时间演化的自旋算符的解析形式.主要推算并讨论了自旋传播子,通过对传播子的讨论发现这个新体系的自旋波谱发生了变化.文末对此现象进行了讨论. 相似文献
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针对目前传统稻种发芽率检测方法周期长、精度低的问题,提出新颖的基于连续偏振光谱技术实现稻种发芽率快速、无损检测的方法。以不同老化天数稻种为检测目标,10 min为检测时间点,使用起偏器将光纤准直光源调制成线偏振光垂直入射稻种浸出液,而后以5°为间隔旋转检偏器,并通过光纤光谱仪检测透射的光谱,对检测的偏振光谱通过归一化预处理后,根据不同发芽率稻种检测时偏振角及波长的贡献给出特征偏振角和特征波长,特征偏振角为0°,5°和25°,特征波长为576,620和788 nm,将获取的连续偏振光谱以特征偏振角和特征波长处的透射率为输入,构建稻种发芽率检测模型。分别比较运用偏最小二乘法回归(partial least squares regression,PLSR)、BP神经网络(back propagation neural network,BPNN)、径向基神经网络(radial basis function neural network,RBFNN)三种建模方法建立稻种发芽率检测模型。分别用老化天数为0,2,4,6 d的稻种,在不同的偏振角共测量1 520组实验数据,其中912组数据作为校正集,608组数据作为预测集,建模结果表明三种模型预测精度较高,其中RBFNN模型预测精度最高,其相关系数r为0.976,均方误差RMSE为0.785,平均相对误差MRE为0.85%。表明利用连续偏振光谱技术通过多维度光谱信息能够有效实现稻种发芽率的快速、准确检测。 相似文献
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A mixed spin-1/2 and spin-1 Ising ferrimagnet with a layered honeycomb structure is studied within the framework of an effective-field theory with correlations. The effect of interlayer interactions and a single-ion anisotropy on the existence of the compensation temperature and tricritical point is investigated. In particular, it is pointed out that the tricritical point may be only possible if interlayer interactions are nonzero. 相似文献
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WEI Guo-Zhu MIAO Hai-Ling 《理论物理通讯》2009,51(4):756-760
The magnetic properties of a mixed spin-3/2 and spin-2 and a mixed spin-3/2and spin-5/2 Ising ferromagnetic system with different anisotropies are studied by means of mean-field theory (MFT). The dependence of the phase diagram on single-ion anisotropy strengths is studied too. In the mixed spin-3/2 and spin-2 Ising model, besides the second-order phase transition, the first order-disorder phase transition and the tricritical line are found. In the mixed spin-3/2 and spin-5/2 Ising model, there is no first-order transition and tricritical line. 相似文献