Using Leibbrandt's general prescription for regularizing (n.q)-1 poles in momentum intergrals in axial-type non-covariant gauges we show that the difference between two linearly divergent integrals which arise in ...
Using Leibbrandt's general prescription for regularizing (n.q)-1 poles in momentum intergrals in axial-type non-covariant gauges we show that the difference between two linearly divergent integrals which arise in such gauges yield a surface term which is logarithmically divergent. The form of divergence of this term is shown to be independent of the choice of non-covariant gauge. We show that such a term modifies the expression for the one-loop Yang-Mills self-energy evaluated using a cutoff scheme of adding to it a divergent part.
Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times were determined in order to study the dynamics of t-butyl groups in butylated hydroxytoluene. The results are consistent with a mode...
详细信息
Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times were determined in order to study the dynamics of t-butyl groups in butylated hydroxytoluene. The results are consistent with a model first proposed by Beckmann et al. [J. Magn. Reson. 36, 199 (1979)], where there is an inequivalence between the methyl groups within each t-butyl group. While two methyl groups reorient rapidly relative to the whole t-butyl rotation, the remaining methyl group is more restricted in its motion, reorienting at a rate comparable to that of the t-butyl group itself. The spin-lattice relaxation data show two T1 minima, the high temperature minimum (40-degrees-C) corresponding to the combined t-butyl and "slow" methyl rotations, and the low temperature minimum corresponding to "fast" methyl group rotation. Using an explicitly defined T1 fitting function, the T1 data yield activation energies of 2.2 and 6.0 kcal/mol for the fast methyl and t-butyl rotations, respectively, both in agreement with Beckmann's values obtained from proton T1 experiments. It was also possible to simulate the low temperature deuterium NMR spectra from T = - 160-degrees-C to T = - 80-degrees-C using the aforementioned dynamical inequivalence between the t-butyl methyl groups. While the fast methyl group rotation was in the motional narrowing region for T > - 160-degrees-C, it was possible, from the simulations, to determine the t-butyl exchange rates to within 10%. The jump rates are remarkably close to the values predicted from the T1 results. Above - 80-degrees-C, the spectra could not be simulated, implying that a third motion must be present to further alter the high temperature line shapes. The effective axial asymmetry of the T > - 20-degrees spectra indicates that the additional motion involves a two site exchange.
Molecular-dynamics simulations of 500 particles have been performed to study the icosahedral order and the defects in the supercooled liquid and glass states of metallic Mg3Ca7. Not only are Frank-Kasper polyhedra and...
Molecular-dynamics simulations of 500 particles have been performed to study the icosahedral order and the defects in the supercooled liquid and glass states of metallic Mg3Ca7. Not only are Frank-Kasper polyhedra and Bernal ‘‘hole’’ polyhedra detected, but also a variety of defective icosahedra. Especially, the number of the type of defective icosahedron defined by eight 1551 bonds, two 1661 bonds, and two 1441 bonds is much greater than the number of any kind of Frank-Kasper and Bernal polyhedra. This strongly supports the physical picture of liquids and glasses being a disordered, entangled array of +72° and -72° disclination lines in an icosahedral medium.
IN a confocal scanning laser microscope 1,2 (CSLM), the detector pinhole is confocal with the illuminated spot on the sample, and rejects light reflected from objects that are not in the focal plane. This results in i...
详细信息
IN a confocal scanning laser microscope 1,2 (CSLM), the detector pinhole is confocal with the illuminated spot on the sample, and rejects light reflected from objects that are not in the focal plane. This results in images that contain only sharp or empty areas, as opposed to non-confocal images which contain sharp and blurry areas, and allows the CSLM to perform optical sectioning. Individual optical sections can be used to produce a true three-dimensional image or can be added together to produce an extended-depth-of-focus image. For biological specimens, the intensity of the reflected-light (or fluorescence) signal decreases with increasing penetration into the sample, and self-shadowing also limits the information in the image. Moreover, many biological specimens are only weak reflectors, but produce transmission images with good contrast. The only confocal transmission images reported previously have used scanning-stage microscopes 3,4, although Goldstein 5 has reported a confocal scanning-beam microscope that should in principle work in transmission. Here we describe a microscope that produces true confocal images in transmission, and also forms a reflected-light image from both the top and bottom of the specimen. The optical slices produced in transmission do not change in average intensity with depth in the specimen, and as the microscope can also examine the specimen from the bottom in reflected light, loss of data by self-shadowing is minimized. All of the original contrast modes of the CSLM (reflected light, fluorescence, differential phase contrast and so on) are also available using this new microscope.
It is demonstrated that the specific heat behaves as a monotonically increasing function of temperature with failing temperature for those supercooled metallic liquids, which can be laboratory glasses. This is in cont...
It is demonstrated that the specific heat behaves as a monotonically increasing function of temperature with failing temperature for those supercooled metallic liquids, which can be laboratory glasses. This is in contrast to cases where supercooled metallic liquids do not become laboratory glasses. In addition, a comment is made on the specific heat of a supercooled Lennard-Jones liquid.
13 C-NMR is used to probe the motion and orientation of the car☐yl group in a 70% potassium palmitate/30% water mixture. An increase in Δσ with increasing temperature corresponds to a change of orientation of the ca...
详细信息
13 C-NMR is used to probe the motion and orientation of the car☐yl group in a 70% potassium palmitate/30% water mixture. An increase in Δσ with increasing temperature corresponds to a change of orientation of the car☐yl group. Comparison with 2 H-NMR and lineshape simulations show that near 57°C the molecules exchange between two orientations at a rate between 10–500 Hz.
A generalization of the Landau–de Gennes phenomenological theory of smectic-A liquid crystals is described. The theory is based on a Landau-Ginzburg free energy that includes local and nonlocal parts. The local part ...
A generalization of the Landau–de Gennes phenomenological theory of smectic-A liquid crystals is described. The theory is based on a Landau-Ginzburg free energy that includes local and nonlocal parts. The local part consists of the isotropic-Ising-model free energy and de Gennes’s phenomenological free energy of the nematic phase. The nonlocal part is derived from the form of two-body contributions to the free energy in molecular density-functional theories, expanded in gradients of the number density and orientational order parameter. A mean-field approximation to the theory is analyzed by both Landau expansion and by a full numerical solution, involving Fourier-series representations of the number density and an orientational order parameter with an appropriately large number of Fourier coefficients. The main purpose of the analysis is to show that the smectic phase results from the instability of a uniform phase induced by the gradient terms in the free energy, particularly those that couple modulations in the density and orientational order parameter.
In this paper, a model for water-oil-surfactant mixtures, which we have previously studied on two- and three-dimensional lattices, is now studied on a one-dimensional lattice. In this case we are able to obtain exact ...
In this paper, a model for water-oil-surfactant mixtures, which we have previously studied on two- and three-dimensional lattices, is now studied on a one-dimensional lattice. In this case we are able to obtain exact results, whereas on the higher-dimensional lattices it was necessary to use approximations. This one-dimensional model produces correlation and structure functions that are similar to those obtained for the disordered phase on the two- and three-dimensional lattices. The disorder line is obtained from the water-water correlation function and the Lifshitz line is derived from the water-water structure function. One or the other of these lines is typically used to divide the disordered phase into a region of ordinary disordered fluid and a microemulsion region. Both these lines calculated exactly for the one-dimensional lattice behave similarly to their counterparts on the two- and three-dimensional lattices calculated by various approximations.
Phenomenological constraints due to CP violation in the K−K¯ system and the extent of B−B¯ mixing are used to determine the constraints on the various parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix...
Phenomenological constraints due to CP violation in the K−K¯ system and the extent of B−B¯ mixing are used to determine the constraints on the various parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix given the Ansatz is symmetric. An existing parametrization for the CKM matrix is shown to be the most general parametrization for the symmetric Ansatz. This Ansatz implies that the mass of the t quark is at least 180 GeV.
An elementary discussion of time-dependent correlation functions is presented. These functions are discussed in the context of dielectric relaxation and nuclear magnetic resonance for two forms of decay: Simple expone...
详细信息
An elementary discussion of time-dependent correlation functions is presented. These functions are discussed in the context of dielectric relaxation and nuclear magnetic resonance for two forms of decay: Simple exponential and stretched (Kohlrausch-Williams-Watts) exponential. A guide to the calculation of the stretched exponential fitting parameters using numerical methods is given. Computational notes include comments on the truncation of mathematical series used.
暂无评论