Dynamical fluctuations in classical adiabatic processes: General description and their implications

Dynamical fluctuations in classical adiabatic processes are not considered by the conventional classical adiabatic theorem. In this work a general result is derived to describe the intrinsic dynamical fluctuations in classical adiabatic processes. Interesting implications of our general result are discussed via two subtopics, namely, an intriguing adiabatic geometric phase in a dynamical model with an adiabatically moving fixed-point solution, and the possible “pollution” to Hannay’s angle or to other adiabatic phase objects for adiabatic processes involving non-fixed-point solutions.     

Evaluation of an edge-based registration method: application to magnetic resonance first-pass myocardial perfusion data

Purpose

Quantification of cardiac magnetic resonance (CMR) myocardial perfusion remains time consuming since it requires manual interventions to compensate for motion. Thus, the aim of this study was to evaluate a semiautomated registration method.

Materials and Methods

A rigid edge-based registration algorithm was applied on 10 patients who had rest and stress CMR acquisitions on three slice levels (apical, midventricular and basal slices). Registration efficiency was assessed qualitatively by evaluating the quality of k-means maps in terms of symmetry and heart structures identification before and after registration and quantitatively by estimating noise amplitude within the myocardium. Finally, residual registration errors were manually estimated.

Results

Before registration, k-means maps were satisfactory for 15 of 30 slices at rest and for only 5 of 30 slices during stress. After registration, the k-means maps quality was satisfactory for 29 of 30 slices at rest and for 30 of 30 slices during stress. Moreover, registration reduced noise amplitude from 49±26 to 29±11 at rest (P<.01) and from 52±14 to 30±10 during stress (P<.01). The residual horizontal and vertical shifts were 0.06±0.12 and 0.04±0.08 mm at rest and 0.32±0.69 and 0.28±0.53 mm at stress.

Conclusion

The registration was successfully tested on rest and stress CMR perfusion data. It provides a valuable basis for quantitative evaluation of myocardial perfusion.     

Order and membrane stability from magnetic resonance measurements: an application of statistical thermodynamics

Summary This paper compares different approaches, reported in the literature, for obtaining thermodynamic statistical information from ESR and NMR measurements on the conformations of lipid bilayers. A statistical approach recently proposed by the authors has been employed to reexamine several literature values of order parameters and to calculate Helmholtz free energy and entropy. This approach was applied to eggphosphatidylcholine, cerebroside and gangliosoyds, spin labelled at different acyl chain positions, and to bilayered membranes containing phosphatidylcholine and different gangliosides (GM1, GD1a and GT1b) at increasing glycolipid mole percent. The variation of the stability of the membrane with the peroxidation is also reexamined at different intramembrane locations by various probes. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

High-order harmonic generation: A quantum-mechanical description and the effects of propagation

A theoretical investigation of the generation of high-order harmonics in an ensemble of atoms interacting with femtosecond laser pulses of high intensity is conducted. It is shown that the cut-off frequency of the photoemission spectra is saturated in a laser field of subatomic strength. A model of the effect dispersion has on the radiation of high-order harmonics in extended environments is proposed.     

Mössbauer and magnetic resonance experiments on amorphous iron-silicon films

Mössbauer measurements at room temperature and 4.2 K, and room temperature magnetic resonance measurements on a series of amorphous Fe_xSi_1-x thin films (0.23?x?0.81) are presented. The concentration dependence of the isomer shifts and quadrupole splittings provides information on the nature of the local coordination in these amorphous materials. Analysis of the distributions of magnetic hyperfine splitting combined with the presence of multiple resonances in the magnetic resonance data indicates that magnetoanisotropy plays a dominant role in determining the magnetic behaviour of these films.     

Berry's phase in the presence of a non-adiabatic environment with an application to magnetic resonance.

We consider a two-level system coupled to an environment that evolves non-adiabatically. We present a non-perturbative method for determining the persistence amplitude whose phase contains all the corrections to Berry's phase produced by the non-adiabatic motion of the environment. Specifically, it includes the effect of transitions between the two energy levels to all orders in the non-adiabatic coupling. The problem of determining all non-adiabatic corrections is reduced to solving an ordinary differential equation to which numerical methods should provide solutions in a variety of situations. We apply our method to a particular example that can be realized as a magnetic resonance experiment, thus raising the possibility of testing our results in the laboratory.     

"Learn on the fly": a hybrid classical and quantum-mechanical molecular dynamics simulation

We describe and test a novel molecular dynamics method which combines quantum-mechanical embedding and classical force model optimization into a unified scheme free of the boundary region, and the transferability problems which these techniques, taken separately, involve. The scheme is based on the idea of augmenting a unique, simple parametrized force model by incorporating in it, at run time, the quantum-mechanical information necessary to ensure accurate trajectories. The scheme is tested on a number of silicon systems composed of up to approximately 200 000 atoms.     

A Bayesian approach to characterising multi-phase flows using magnetic resonance: application to bubble flows

Magnetic Resonance (MR) imaging is difficult to apply to multi-phase flows due to both the inherently short T?* characterising such systems and the relatively long time taken to acquire the data. We develop a Bayesian MR approach for analysing data in k-space that eliminates the need for image acquisition, thereby significantly extending the range of systems that can be studied. We demonstrate the technique by measuring bubble size distributions in gas-liquid flows. The MR approach is compared with an optical technique at a low gas fraction (～2%), before being applied to a system where the gas fraction is too high for optical measurements (～15%).     

Real-time animal functional magnetic resonance imaging and its application to neuropharmacological studies

In pharmacological magnetic resonance imaging (phMRI) with anesthetized animals, there is usually only a single time window to observe the dynamic signal change to an acute drug administration since subsequent drug injections are likely to result in altered response properties (e.g., tolerance). Unlike the block-design experiments in which fMRI signal can be elicited with multiple repetitions of a task, these single-event experiments require stable baseline in order to reliably identify drug-induced signal changes. Such factors as subject motion, scanner instability and/or alterations in physiological conditions of the anesthetized animal could confound the baseline signal. The unique feature of such functional MRI (fMRI) studies necessitates a technique that is able to monitor MRI signal in a real-time fashion and to interactively control certain experimental procedures. In the present study, an approach for real-time MRI on a Bruker scanner is presented. The custom software runs on the console computer in parallel with the scanner imaging software, and no additional hardware is required. The utility of this technique is demonstrated in manganese-enhanced MRI (MEMRI) with acute cocaine challenge, in which temporary disruption of the blood-brain barrier (BBB) is a critical step for MEMRI experiments. With the aid of real-time MRI, we were able to assess the outcome of BBB disruption following bolus injection of hyperosmolar mannitol in a near real-time fashion prior to drug administration, improving experimental success rate. It is also shown that this technique can be applied to monitor baseline physiological conditions in conventional fMRI experiments using blood oxygenation level-dependent (BOLD) contrast, further demonstrating the versatility of this technique.     

Determination of the defining boundary in nuclear magnetic resonance diffusion experiments

While nuclear magnetic resonance diffusion experiments are widely used to resolve structures confining the diffusion process, it has been elusive whether they can exactly reveal these structures. This question is closely related to x-ray scattering and to Kac's "hear the drum" problem. Although the shape of the drum is not "hearable," we show that the confining boundary of closed pores can indeed be detected using modified Stejskal-Tanner magnetic field gradients that preserve the phase information and enable imaging of the average pore in a porous medium with a largely increased signal-to-noise ratio.     

On the hydrodynamic theory of a magnetic liquid I. General description

Using Zubarev's method of nonequilibrium statistical operator, the generalized hydrodynamic equations are obtained for a model of magnetic liquid in an inhomogeneous external field. In this model the “liquid” subsystem is treated as a classical one and the “magnetic” subsystem is described by quantum mechanical methods. The properties of the transport equations are analysed in the case of a weak nonequilibrium. The equations for time correlation functions and collective mode spectrum are also found in the same manner. It is shown that the generalized hydrodynamic equations reduce to the well-known results in the limiting cases when the dynamic variables of one subsystem are formally neglected. As an illustration, a simple model of spin relaxation is considered, and the frequency matrix and the matrix of memory functions are calculated. A comparison with previous works is made.     

Techniques of non-orthogonal magnetic resonance imaging and its clinical application

A technique to obtain non-orthogonal magnetic resonance (MR) images in the body has been developed using a simple three-dimensional model (3-DM). Images were obtained with multiple non-orthogonal planes, without subjecting patients to uncomfortable oblique positions. Eighty-two patients were studied using non-orthogonal planes. Euler angle determinations (EAD) were developed for different anatomical locations as well as for multiple clinical situations. One or all three Euler angles were changed using the EAD to define any plane of orientation relative to reference orthogonal frame. In a series of 12 patients for postoperative evaluation of Mustard and Senning procedure, the demonstration of anastomotic site was superior with angled coronal planes when compared to the routine coronal views in 83% of the studies. With the use of EAD, acquisition time for non-orthogonal planes can be reduced. 3-DM aids in the understanding of the Euler angles and leads to multiple non-orthogonal planes.     

Extreme statistics in Raman fiber amplifiers: From analytical description to experiments

In this work, we investigate the emergence of rare and intense events during the Raman fiber amplification of a continuous wave. We highlight how dispersive properties and pump depletion can strongly influence the statistical properties of the amplified signal and its optical spectrum. Under certain conditions, the probability density functions of the amplified signal are calculated analytically and compared with the results of the numerical simulations. The conclusions are qualitatively validated by experiments carried out at telecommunication wavelengths.     

Use of lasers to study magnetic resonance and magnetic relaxation

Optical methods of recording ESR, which were developed in the early 1950s to record magnetic resonance of excited atoms, are extensively used at present in investigations of ESR of the ground and excited states of atoms and paramagnetic centers in condensed media [1]. Attention is called in the present communication to additional capabilities of optical ESR and of paramagnetic relaxation methods, which are realizable through the use of laser sources.S. I. Vavilov State Optical Institute, Leningrad. Translated from Primenenie Lazerov v Atomnoi, Molekulyarnoi i Yadernoi Fiziki — Trudy II Vsesoyuznoi Shkoly, pp. 3–11, 1981.     

Deep inelastic collisions: A classical description with friction and deformation

A simple classical model with frictional forces and deformation degrees of freedom is presented which reproduces the deep inelastic cross sections, angular distributions and energy losses in a wide range of nuclei. A quantitative fit to the fusion cross sections can also be obtained.