Existence of the gravitomagnetic interaction

The point of view expressed in the literature that gravitomagnetism has not yet been observed or measured is not entirely correct. Observations of gravitational phenomena are reviewed in which the gravitomagnetic interaction—a post-Newtonian gravitational force between moving matter—has participated and which has been measured to 1 part in 1000. Gravitomagnetism is shown to be ubiquitous in gravitational phenomena and is a necessary ingredient in the equations of motion, without which the most basic gravitational dynamical effects (including Newtonian gravity) could not be consistently calculated by different inertial observers.     

Observers in spacetime and nonlocality

Characteristics of observers in relativity theory are critically examined. For field measurements in Minkowski spacetime, the Bohr‐Rosenfeld principle implies that the connection between actual (i.e., noninertial) and inertial observers must be nonlocal. Nonlocal electrodynamics of non‐uniformly rotating observers is discussed and the consequences of this theory for the phenomenon of spin‐rotation coupling are briefly explored.     

Commutator Green's functions for a spin Hamiltonian

All the commutator Green's functions are calculated for the Heisenberg spin Hamiltonian in the Hartree-Fock approximation. It is shown further that the Tyablikov transverse commutator Green's function corresponds to the Hartree—Fock approximation only for the longitudinal part of the Heisenberg spin Hamiltonian, and to obtain the longitudinal part of the commutator Green's function to the same accuracy as the Tyablikov transverse commutator Green's function it is necessary to go over to the Hartree—Fock approximation only with respect to the transverse part of the Heisenberg spin Hamiltonian.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 62–65, December, 1980.     

Synthesis,Structural and Magnetic Resonance Studies of YxEr2-xCu2O5 Compounds

Polycrystalline samples of Y_xEr_2—xCu₂O₅ compound, where x = 2.0, 1.75, 1.5, 1.25. 1.0,0.75.0.25, and 0.0, have been synthesized by the solid state reaction technique. The XRD measurements have shown that the obtained samples were single-phase and belong to the orthorhombic space group Pna2₁. The measured lattice constants of Y_xEr_2-xCu₂O₅ compounds scaled linearly with the itrium index x. The TGA/DSC measurements allowed to establish the temperature range of stability for the samples and enabled the observation of their decomposition. EPR studies at room temperature showed that the integral intensity of the resonance line decreases nonlinearly with the increasing erbium content and that the Er₂Cu₂O₅ compound is EPR inactive. A broad copper EPR line has been analyzed in order to establish the contributions of different spin—spin relaxation mechanism. The observed resonance linewidth has been explained by the action of the dipole—dipole, anisotropic exchange, and Dzialoshinky—Moriya (DM) interactions.     

Magnetic properties of two complex ferric paramagnetics

The magnetic susceptibility of two complex ferric compounds in both the solid state and solution — ferric ammonium citrate and potassium (hexa)cyanoferrate (III) — was measured. On the basis of measurements of other physical constants the magnetic moments were calculated from the susceptibility and with citrate also from the longitudinal relaxation time of nuclear magnetic resonance. Some magnetic measurements of these substances made hitherto were verified and missing data were found. The results show that for citrate the magnetic moment from both the solid state and solution is smaller than purely spin moment, which confirms the opinion that it is a mixture of several components having different values of the Weiss constant. With potassium ferricyanide the opposite is the case, which indicates that the orbital moment, the contribution of which in the solid state is relatively larger than in solutions, is not quite suppressed. In both materials an excess of carriers of relatively larger magnetic moments appears in dilute solutions than in concentrated ones. The results obtained for a solution of potassium ferricyanide differed from the earlier measurements of Collet.     

OPTESIM, a versatile toolbox for numerical simulation of electron spin echo envelope modulation (ESEEM) that features hybrid optimization and statistical assessment of parameters

Electron spin echo envelope modulation (ESEEM) is a technique of pulsed-electron paramagnetic resonance (EPR) spectroscopy. The analyis of ESEEM data to extract information about the nuclear and electronic structure of a disordered (powder) paramagnetic system requires accurate and efficient numerical simulations. A single coupled nucleus of known nuclear g value (g_N) and spin I = 1 can have up to eight adjustable parameters in the nuclear part of the spin Hamiltonian. We have developed OPTESIM, an ESEEM simulation toolbox, for automated numerical simulation of powder two- and three-pulse one-dimensional ESEEM for arbitrary number (N) and type (I, g_N) of coupled nuclei, and arbitrary mutual orientations of the hyperfine tensor principal axis systems for N > 1. OPTESIM is based in the Matlab environment, and includes the following features: (1) a fast algorithm for translation of the spin Hamiltonian into simulated ESEEM, (2) different optimization methods that can be hybridized to achieve an efficient coarse-to-fine grained search of the parameter space and convergence to a global minimum, (3) statistical analysis of the simulation parameters, which allows the identification of simultaneous confidence regions at specific confidence levels. OPTESIM also includes a geometry-preserving spherical averaging algorithm as default for N > 1, and global optimization over multiple experimental conditions, such as the dephasing time (τ) for three-pulse ESEEM, and external magnetic field values. Application examples for simulation of ¹⁴N coupling (N = 1, N = 2) in biological and chemical model paramagnets are included. Automated, optimized simulations by using OPTESIM lead to a convergence on dramatically shorter time scales, relative to manual simulations.     

聚对苯撑中杂质诱导的磁性缺陷

本工作研究了掺FeCl₃和掺碘聚对苯撑(PPP)样品中与极化子相互转化有关的电子顺磁共振(EPR)谱特性.在掺碘的样品中,我们观测到一种新的实验现象:室温线宽△H_pp(RT)、自旋浓度N_spin对掺碘浓度的特有依赖关系,即随碘浓度N (Ⅰ)的增大,△H_pp首先减小又增大,然后再次减小重又增大.与此对应,自旋浓度首先升高又下降,然后再次升高又下降.然而,在掺FeCl₃的样品中,△H_pp和N_spin没有出现象在掺碘的样品中那种变化现象,而是随掺FeCl₃浓度增大,△H_pp,首先减小而后增大.相对应地,N_spin首先升高而后下降.本文着重探讨了产生上述差别的原因.由于聚合物链上的自旋和掺杂分子相互作用,观测到的g因子数值接近自由基g值,并且基本上不随掺杂种类、温度的变化而变化.     

Preparation-limited predictions in Einstein-Podolsky-Rosen experiments

It is shown that unavoidable uncertainties arising from the experimental conditions in which systems are prepared for Einstein-Podolsky-Rosen experiments severely limit the possibilities for prediction. In the example originally proposed by EPR, time measurements are necessary for precise position predictions. If the preparation is designed to make the timing errors negligible, the parameters chosen for the preparation fix minimum uncertainties in the predictions leaving the observer no choice in the matter. In the case of correlated spin measurements, the preparation leaves the observer no control over the effect of the detector on the particles; the uncertainty of the previous condition of any one particle is so large that no (classical) prediction of the response of another detector is possible. Thus, there are as yet no proposed experiments which satisfy the conditions required by EPR—i.e., precise predictions which violate the uncertainty principle.     

Electromagnetic waves in a rotating frame of reference

We discuss the electromagnetic measurements of rotating observers and study the propagation of electromagnetic waves in a uniformly rotating frame of reference. The phenomenon of helicity‐rotation coupling is elucidated and some of the observational consequences of the coupling of the spin of a particle with the rotation of a gravitational source are briefly examined.     

Spin — lattice relaxation in chlorofluorocarbon liquids

We have used the spin — echo method to measure spin — lattice relaxation times in liquid chlorofluorocarbons over a wide range of temperatures, frequencies, and molecular weights. Analysis of the experimental data shows that to determine the kinetic parameters of viscous liquids it is necessary to use the theory of nuclear magnetic relaxation by translational diffusion. We describe a method for the computer calculation of these parameters and discuss the results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 46–51, March, 1976.     

Spin-dependent transport in a magnetic two-dimensional electron gas

Magneto-transport and magneto-optical probes are used to interrogate spin-dependent transport in magnetic heterostructures wherein a two dimensional electron gas (2DEG) is exchange-coupled to local moments. At low temperatures, the significant s–d exchange-enhanced spin splitting in these “magnetic” 2DEGs is responsible for the observation of unusual transport properties such as a complete spin polarization of the gas at large Landau level filling factors and a pronounced, non-monotonic background magneto-resistance. Magneto-transport measurements of gated samples performed in a parallel field geometry are used to systematically study the variation of the magneto-resistance with sheet concentration, yielding new insights into the dependence of spin transport on the Fermi energy of the majority spin carriers.     

On Jacobi fields

We define curves on a Riemannian manifold as integrals of generalized Jacobi fields. We show that the force term that deviates the trajectory from the geodesic motion can be constructed as a functional of the metric tensor. These curves can be interpreted as particles (observers) coupled nonminimally with gravitation that can provide a class of residual observers for the inevitable singularity—as shown in the text.This essay received an honorable mention (1976) from the Gravity Research Foundation-Ed.     

A lattice test of strong coupling behaviour in QCD at finite temperature

We propose a set of lattice measurements which could test whether the deconfined, quark–gluon plasma, phase of QCD shows strong coupling aspects at temperatures a few times the critical temperature for deconfinement. The measurements refer to twist-two operators which are not protected by symmetries and which in a strong-coupling scenario would develop large, negative, anomalous dimensions, resulting in a strong suppression of the respective lattice expectation values in the continuum limit. Special emphasis is put on the twist-two operator with lowest spin (the spin-2 operator orthogonal to the energy–momentum tensor within the renormalization flow) and on the case of quenched QCD, where this operator is known for arbitrary values of the coupling: this is the quark energy–momentum tensor. The proposed lattice measurements could also test whether the plasma constituents are pointlike (as expected at weak coupling), or not.     

Intensity of Cross-Peaks in Hyscore Spectra of S = 1/2, I = 1/2 Spin Systems

The cross-peak intensity for a S = 1/2, I = 1/2 spin system in two-dimensional HYSCORE spectra of single-crystals and powders is analyzed. There is a fundamental difference between these two cases. For single crystals, the cross-peak intensity is distributed between the two (+, +) and (+, −) quadrants of the hyperfine sublevel correlation (HYSCORE) spectrum by the ratio c²:s² (C. Gemperle, G. Aebli, A. Schweiger, and R. R. Ernst, J. Magn. Reson. 88, 241 (1990)). However, for powder spectra another factor becomes dominant and governs cross-peak intensities in the two quadrants. This factor is the phase interference between modulation from different orientations of the paramagnetic species. This can lead to essentially complete disappearance of the cross-peak in one of the two (+, +) or (+, −) quadrants. In the (+, +) quadrant, cross-peaks oriented parallel to the main (positive) diagonal of the HYSCORE spectrum are suppressed, while the opposite is true in the (+, −) quadrant where cross-peaks nearly perpendicular to the main (negative) diagonal of HYSCORE spectra are suppressed. Analytical expressions are derived for the cross-peak intensity profiles in powder HYSCORE spectra for both axial and nonaxial hyperfine interactions (HFI). The intensity is a product of two terms, one depending only on experimental parameter (τ) and the other only on the spin Hamiltonian. This separation provides a rapid way to choose τ for maximum cross-peak intensity in a region of interest in the spectrum. For axial HFI, the Hamiltonian-dependent term has only one maximum and decreases to zero at the canonical orientations. For nonaxial HFI, this term produces three separate ridges which outline the whole powder lineshape. These three ridges have the majority of the intensity in the HYSCORE spectrum. The intensity profile of each ridge resembles that observed for axial HFI. Each ridge defines two principal values of the HFI similar to the ridges from an axial HFI.     

Emergence of Objectivity for Quantum Many-Body Systems

We examine the emergence of objectivity for quantum many-body systems in a setting without an environment to decohere the system’s state, but where observers can only access small fragments of the whole system. We extend the result of Reidel (2017) to the case where the system is in a mixed state, measurements are performed through POVMs, and imprints of the outcomes are imperfect. We introduce a new condition on states and measurements to recover full classicality for any number of observers. We further show that evolutions of quantum many-body systems can be expected to yield states that satisfy this condition whenever the corresponding measurement outcomes are redundant.     

Entropy in Kerr–de Sitter Black Holes with Spin Fields

Generalized master equations due to spin fields are given. We obtain the entropy of electromagnetic, gravitational, Dirac, and scalar fields in a unified form by using the improved brick-wall method—membrane model. The results show that, as the cutoff is properly chosen, the entropy in the black hole satisfies the Bekenstein–Hawking area formula.     

Saturation recovery EPR and ELDOR at W-band for spin labels

A reference arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) [J.W. Sidabras, R.R. Mett, W. Froncisz, T.G. Camenisch, J.R. Anderson, J.S. Hyde, Multipurpose EPR loop-gap resonator and cylindrical TE₀₁₁ cavity for aqueous samples at 94 GHz, Rev. Sci. Instrum. 78 (2007) 034701]. The high efficiency parameter (8.2 GW^−1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE. Free induction decay (FID) signals for small nitroxides at W-band are also reported. Results are compared with multifrequency measurements of T_1e previously reported for these molecules in the range of 2–35 GHz [J.S. Hyde, J.-J. Yin, W.K. Subczynski, T.G. Camenisch, J.J. Ratke, W. Froncisz, Spin label EPR T₁ values using saturation recovery from 2 to 35 GHz. J. Phys. Chem. B 108 (2004) 9524–9529]. The values of T_1e decrease at 94 GHz relative to values at 35 GHz.     

EPR oximetry in three spatial dimensions using sparse spin distribution

A method is presented to use continuous wave electron paramagnetic resonance imaging for rapid measurement of oxygen partial pressure in three spatial dimensions. A particulate paramagnetic probe is employed to create a sparse distribution of spins in a volume of interest. Information encoding location and spectral linewidth is collected by varying the spatial orientation and strength of an applied magnetic gradient field. Data processing exploits the spatial sparseness of spins to detect voxels with nonzero spin and to estimate the spectral linewidth for those voxels. The parsimonious representation of spin locations and linewidths permits an order of magnitude reduction in data acquisition time, compared to four-dimensional tomographic reconstruction using traditional spectral-spatial imaging. The proposed oximetry method is experimentally demonstrated for a lithium octa-n-butoxy naphthalocyanine (LiNc–BuO) probe using an L-band EPR spectrometer.     

Higher spin fields and the Gelfand-Dickey algebra

We show that in 2-dimensional field theory, higher spin algebras are contained in the algebra of formal pseudodifferential operators introduced by Gelfand and Dickey to describe integrable nonlinear differential equations in Lax form. The spin 2 and 3 algebras are discussed in detail and the generalization to all higher spins is outlined. This provides a conformal field theory approach to the representation theory of Gelfand—Dickey algebras.Supported in part by the NSF Grant PHY-84-04931