液氦温度(4.2K)下LaOBr:Ce3+,Tb3+粉末的电子顺磁共振研究

本文研究了LaOBr:Ce+3,Tb3+粉末在液氦温度(4.2K)下的电子顺磁共振,并且进行了晶体场理论计算,理论与实验结果符合得较好,这表明Ce,Tb离子取代了基质中La离子形成发光中心。     

Frequency spectra of beam-plates revisited

Based on Mindlin’s plate theory, the frequency spectra for flexural and thickness-shear vibrations of a finite beam-plate with different combinations of boundary conditions are presented and studied. Comparing them with the dispersion curves of the infinite beam-plate reveals an intrinsic relation between resonant vibration and guided wave propagation. The fundamental frequency spectra, which are for beam-plates with hinged and/or guided edges, are found to play an important role in understanding the spectra of beam-plates with other boundary conditions.     

Bell’s inequality, Einstein, Podolsky, Rosen arguments and von Neumann’s projection postulate

This paper is devoted to analysis of the role of projection postulate in Einstein, Podolsky, and Rosen-EPR [1] argument against completeness of QM. It will be shown that the EPR considerations do not match with von Neumann’s quantum measurement theory (QMT). The root of EPR’s conclusion on incompleteness of QM is the misuse of von Neumann’s projection postulate. EPR applied this postulate to observables with degenerate spectra (which is totally forbidden by von Neumann’s axiomatics of QM). Consequences for Bell’s inequality and quantum information theory are analyzed. This paper might stimulate discussion on the role of projection postulate in quantum information theory, especially quantum cryptography and teleportation.     

Simulation of Lamb wave reflections at plate edges using the semi-analytical finite element method

In typical Lamb wave simulation practices, effects of plate edge reflections are often not considered in order to simplify the wave signal interpretations. Methods that are based on infinite plates such as the semi-analytical finite element method is effective in simulating Lamb waves as it excludes the effect of plate edges. However, the inclusion of plate edges in a finite plate could render this method inapplicable, especially for transient response simulations. Here, by applying the ratio of Lamb mode reflections at plate edges, and representing the reflection at plate edges using infinite plate solutions, the semi-analytical finite element method can be applied for transient response simulation, even when the plate is no longer infinite.     

镱掺杂钼酸铅的光谱和EPR谱的理论研究

该文表达了一个研究Yb³⁺掺杂PbMoO₄晶体的光谱和电子顺磁共振谱(EPR)的理论方法. 采用晶体场理论,推导了有关光谱和电子顺磁共振谱的公式. 基于这些理论公式,构建了4f¹³电子组态在D_2d晶体对称下包括Zeeman磁相互作用的14阶能量矩阵. 通过对角化这一能量矩阵,研究了Yb³⁺掺杂PbMoO₄晶体的光谱和电子顺磁共振谱. 所得的理论结果与实验值很好符合. 而且,相关的晶体场参量也在研究中确定.     

An Analysis of the Effects of Eddy Currents on L-Band EPR Spectra

Recently, impressive results have been obtained with EPR studies of living animals and perfused organs using low-frequency EPR. In many instances in such studies, however, there are apparent distortions of the spectra. The shapes of these spectra and theoretical considerations indicate that these effects are due to eddy currents in the moderately conductive biological materials. Therefore the effects of eddy currents produced in biological samples under typical conditions being employed for in vivo EPR studies have been systematically studied in order to determine the extent of these effects and to develop methods for compensating for these effects. The presence of eddy currents was found to decrease the Q factor and distort the shapes of the EPR spectra. The distortion of the spectra led to linewidth broadening, changes in peak heights, and shifts of the apparent center of the lines. These effects could be corrected instrumentally, but this was effective only when signals have a high S/N. The use of appropriate computer simulations, based on linear combinations of the expected absorption and dispersion signals, can effectively correct for the effects of eddy currents and provide accurate data on the parameters of EPR spectra that are needed for most or all of the analyses used in biological studies of animals and tissues at low frequencies.     

The study of the optical and the EPR spectra of V+4 in zircon-type crystals

It has been believed that the optical and the EPR spectra of V⁺⁴ in zircon-type crystals could not be accounted for by conventional crystal field theory In the present article, this problem is analyzed and a calculation is carried out by using a superposition model The results obtained in the present study are in agreement with the experiment. Now the spectra can be explained reasonably.     

晶体CsMgCl3:Ni2+的局部结构、光谱和EPR谱的理论研究

本文采用半自洽场(semi-SCF) 自由Ni2+的3d轨道波函数、点电荷-偶极子模型和Ni2+-6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgCl3:Ni2+晶体的局部结构参数,统一解释了CsMgCl3:Ni2+晶体的吸收光谱和EPR 谱.此外,还讨论了高阶微扰方法、参量拟合方法等问题.理论计算结果与实验值符合得很好.     

Looking into the Matter of Light-Quark Hadrons

In tackling QCD, a constructive feedback between theory and extant and forthcoming experiments is necessary in order to place constraints on the infrared behaviour of QCD’s β-function, a key nonperturbative quantity in hadron physics. The Dyson–Schwinger equations provide a tool with which to work toward this goal. They connect confinement with dynamical chiral symmetry breaking, both with the observable properties of hadrons, and hence can plausibly provide a means of elucidating the material content of real-world QCD. This contribution illustrates these points via comments on: in-hadron condensates; dressed-quark anomalous chromo- and electro-magnetic moments; the spectra of mesons and baryons, and the critical role played by hadron-hadron interactions in producing these spectra.     

Avoiding Haag’s Theorem with Parameterized Quantum Field Theory

Under the normal assumptions of quantum field theory, Haag’s theorem states that any field unitarily equivalent to a free field must itself be a free field. Unfortunately, the derivation of the Dyson series perturbation expansion relies on the use of the interaction picture, in which the interacting field is unitarily equivalent to the free field but must still account for interactions. Thus, the traditional perturbative derivation of the scattering matrix in quantum field theory is mathematically ill defined. Nevertheless, perturbative quantum field theory is currently the only practical approach for addressing scattering for realistic interactions, and it has been spectacularly successful in making empirical predictions. This paper explains this success by showing that Haag’s Theorem can be avoided when quantum field theory is formulated using an invariant, fifth path parameter in addition to the usual four position parameters, such that the Dyson perturbation expansion for the scattering matrix can still be reproduced. As a result, the parameterized formalism provides a consistent foundation for the interpretation of quantum field theory as used in practice and, perhaps, for better dealing with other mathematical issues.     

EPR studies of photoinduced electron transfer in triad model compounds of photosynthesis

Time-resolved EPR spectra are reported for porphyrin-quinone-quinone and porphyrin-porphyrin-quinone triads obtained after photoexcitation in the nematic and soft glass phase of liquid crystals. Spin-polarized EPR spectra were observed for the triplet states of the porphyrin created by spin-selective intersystem crossing (ISC) from the excited singlet state and those of the charge-separated radical pair states (RP) generated by electron transfer (ET) processes. The EPR polarization patterns of the RP are discussed in terms of the favored decay channel of the photoexcited singlet state of the porphyrin donor. The decay pathway may either be singlet ET to the quinone(s) followed by singlet/triplet mixing to yield RPs with triplet character or triplet ET after ISC from the porphyrin singlet to the triplet state, or a superposition of both pathways. It is demonstrated that the nature of the linking bridge between donor and acceptor, i.e., aliphatic cyclohexylene or aromatic phenylene, significantly influences the ET mechanism and thus the polarization patterns of the RP spectra. Using liquid crystals, information about the orientation of the guest molecules in the liquid crystal matrix with respect to the long axes of the liquid crystal molecules can be obtained. In the porphyrin-porphyrin-quinone triads the energy and ET processes strongly depend on the type of metallation of the porphyrins, specifically, whether the distal, the vicinal or both porphyrins bear a zinc atom.     

用光谱和EPR谱确定CsMgBr3:Ni2+的局域结构

本文采用半自洽场(semi-SCF)自由Ni2 的3d轨道波函数、点电荷—偶极子模型和Ni2 -6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgBr3:Ni2 晶体在77K温度时的局域结构参数,统一解释了CsMgBr3:Ni2 晶体的局域结构、光谱和EPR谱。所得理论结果与实验值符合得很好。此外,还讨论了晶体局域结构发生畸变的原因。     

Topology of the Universe: Background and recent observational approaches

Is the Universe (a spatial section thereof) finite or infinite? Knowing the global geometry of a Friedmann-Lemaître (FL) universe requires knowing both its curvature and its topology. A flat or hyperbolic (‘open’) FL universe is not necessarily infinite in volume. Multiply connected flat and hyperbolic models are, in general, as consistent with present observations on scales of 1–20 h^?1 Gpc as are the corresponding simply connected flat and hyperbolic models. The methods of detecting multiply connected models (MCM’s) are presently in their pioneering phase of development and the optimal observationally realistic strategy is probably yet to be calculated. Constraints against MCM’s on ～1–4 h^?1 Gpc scales have been claimed, but relate more to inconsistent assumptions on perturbation statistics rather than just to topology. Candidate 3-manifolds based on hypothesised multiply imaged objects are being offered for observational refutation. The theoretical and observational sides of this rapidly developing subject have yet to make any serious contact, but the prospects of a significant detection in the coming decade may well propel the two together.     

Family of paramagnetic centers of Ce3+ ions in yttrium aluminum garnet

The electron paramagnetic resonance (EPR) spectra of Ce³⁺ ions in single crystals of yttrium aluminum garnet have been investigated. It has been found that, in addition to the usually observed EPR signals of Ce³⁺ ions located in the regular environment at dodecahedral sites of the crystal lattice, the spectra contain a group of less intense anisotropic lines with g-factors close to the corresponding parameters of Ce³⁺ ions in the regular environment. It has been concluded that the observed satellite lines belong to the family of Ce³⁺ ions in the immediate vicinity of which there are permutation defects that lead to a change in the strength and symmetry of the crystal field in the vicinity of the paramagnetic center.     

The features of the EPR spectrum in the vicinity of accidental coincidence of interacting transitions

The mechanisms of the inhomogeneous broadening of the EPR spectra of exchange-coupled copper dimers, high-spin iron centers in lithium germanate, and off-center Tl²⁺ ions in potassium sulfate are analyzed. It is shown that the additional EPR signals observed for these materials when two EPR lines are nearly coincident can be due to averaging of a portion of the spin packets associated with these lines.     

Electron paramagnetic resonance imaging using magnetic-field-gradient spinning

A novel X-band CW EPR imaging has been developed using magnetic-field-gradient (MFG) spinning to obtain spatial distributions of electron paramagnetic species. Spinning MFG EPR imaging for 65 projection spectra required just 55 s while conventional imaging took 11 min 40 s, that is, the acquisition time for the new system is one order of magnitude shorter than that for conventional EPR imaging. Spinning MFG EPR imaging allows one to measure reconstructed images in an interactive manner where resolution and condition can be changed quickly.     

Direct measurements of anticrossings of the electron-nuclear energy levels in LiYF4∶Ho3+ with submillimeter EPR spectroscopy

The electron paramagnetic resonance (EPR) spectra of impurity Ho³⁺ ions in monocrystals LiYF₄∶Ho³⁺ (0.1 and 1%) with the natural abundance of⁶Li (7.42%) and⁷Li (92.58%) isotopes, and in the sample⁷LiYF₄∶Ho³⁺ (0.1%) isotopically pure in⁷Li were taken at the temperature 4.2 K in the frequency range of 165–285 GHz. Resonance transitions between crystal field sublevels (the ground non-Kramers doublet and the nearest excited singlet) of the⁵I₈ term were detected. The refined set of crystal field parameters and the effective constant of the magnetic hyperfine interaction were determined from the detailed analysis of the recorded spectra at frequencies varied by 0.05 GHz. The fine structure of EPR lines with intervals of about 300 MHz observed in the sample LiYF₄∶Ho³⁺ (0.1%) can be interpreted as a result of the isotopic disorder in the Li sublattices. Direct information about energy gaps at the anticrossing points of the electron-nuclear sublevels of the ground doublet was obtained. These gaps are induced by the hyperfine interaction that mixes doublet and singlet states and by random crystal fields. Weak EPR signals from distorted single ion and pair centers of impurity Ho³⁺ ions were resolved. From a comparison of the measured and simulated spectra, estimates of spectral parameters of the dimer centers have been obtained.     

Unseen Coherences Can Be Felt

Forbidden transitions are not observed in the continuous-wave electron paramagnetic resonance (EPR) spectrum nor in the free induction decay because, unlike allowed transitions, their coherences have no observable magnetic moment and are spectroscopically silent. Yet, the paramagnetic relaxation described by Redfield theory can cause coherence transfer between any types of transitions. Coherence transfer between allowed transitions is now known to cause noticeable changes in EPR spectra, but coherence transfer involving forbidden transitions has long been considered to be negligible because those coherences are silent and unseen. However, our simulations of a simple model system indicate that coherence transfer with silent transitions can introduce new features into EPR spectra. The EPR-silent coherence of a forbidden transition can be transferred to an allowed transition by paramagnetic relaxation. A silent coherence can have consequences felt in the EPR spectrum.     

Evolution of Triplet Paramagnetic Centers in Diamonds Obtained by Sintering of Detonation Nanodiamonds at High Pressure and Temperature

The electron paramagnetic resonance (EPR) spectra of triplet centers in detonation nanodiamonds (DNDs) and diamond single crystals of submicrometer size, synthesized from those DNDs at high pressures and temperatures, are studied. In the EPR spectra of DNDs, signals from negatively charged nitrogen- vacancy centers (NV)/sup(-) with a g factor of g₁ = 4.24 and multivacancies with g₂ = 4.00 are observed. The signals from (NV)/sup(-) centers disappear in the spectra of diamond single crystals, and a quintet signal with g = 4.00 is detected at the position of the signal from multivacancies. Analysis of the shape and position of the quintet’ lines showed that this ESR signal is due to the pairs of nitrogen substitution centers in diamond, separated from each other by distances not exceeding 0.7 nm, between which a strong exchange interaction takes place. A comparison of the experimental data and the simulation results allows determining the spin-Hamiltonian parameters of the exchange-coupled pairs of paramagnetic impurity nitrogen atoms.