Electron-phonon interaction via Pekar mechanism in nanostructures

We consider an electron-acoustic phonon coupling mechanism associated with the dependence of crystal dielectric permittivity on the strain (the so-called Pekar mechanism) in nanostructures characterized by strong confining electric fields. The efficiency of Pekar coupling is a function of both the absolute value and the spatial distribution of the electric field. It is demonstrated that this mechanism exhibits a phonon wavevector dependence similar to that of piezoelectricity and must be taken into account for electron transport calculations in an extended field distribution. In particular, we analyze the role of Pekar coupling in energy relaxation in silicon inversion layers. Comparison with the recent experimental results is provided to illustrate its potential significance

Reverse Doppler effect in backward spin waves scattered on acoustic waves

We report on the observation of reverse Doppler effect in backward spin waves reflected off of surface acoustic waves. The spin waves are excited in a yttrium iron garnet (YIG) film. Simultaneously, acoustic waves are also generated. The strain induced by the acoustic waves in the magnetostrictive YIG film results in the periodic modulation of the magnetic anisotropy in the film. Thus, in effect, a travelling Bragg grating for the spin waves is produced. The backward spin waves reflecting off of this grating exhibit a reverse Doppler shift: shifting down rather than up in frequency when reflecting off of an approaching acoustic wave. Similarly, the spin waves are shifted up in frequency when reflecting from receding acoustic waves.Comment: 4 pages, 3 figure

Sodium-23 Magnetic Resonance Imaging

23Na MRI provides additional biochemical information to 1H MRI in terms of cell integrity and tissue viability. We aimed at determining the sensitivity of 23Na MRS, MRI and MR relaxometry methods available on 7T MR scanner Bruker Biospec 70/30 USR and developing of an optimal MRI protocol for small animal 23Na in vivo visualization. The outcomes include 23Na MR spectra, 23Na MR images with SNRs, and T1 and T2 values of 23Na. It is shown that single-pulse 23Na MR spectroscopy can discriminate different 23Na concentrations, and 3D FLASH pulse sequence adapted for 23Na data acquisition may provide the acceptable quality images. Keywords: Sodium MRI, Sodium MRS, 3D FLASH, MR relaxometr

Alternating current driven instability in magnetic junctions

An effect is considered of alternating (high-frequency) current on the spin-valve type magnetic junction configuration. The stability with respect to small fluctuations is investigated in the macrospin approximation. When the current frequency is close to the eigenfrequency (precession frequency) of the free layer, parametric resonance occurs. Both collinear configurations, antiparallel and parallel ones, can become unstable under resonance conditions. The antiparallel configuration can become unstable under non-resonant conditions, also. The threshold current density amplitude is of the order of the dc current density switching the magnetic junction.Comment: 8 page

SPECIFIC FEATURES OF ELECTROENCEPHALOGRAPHIC PAROXYSMAL ACTIVITY REGISTRATION IN OLD AGE GROUP PATIENTS

The differential diagnosis of epilepsy and other paroxysmal states mimicking this condition is very important in the daily activity of a neurologist (an epileptologist) since diagnostic accuracy directly ensures the efficacy and safety of treatment. According the data available in the literature, both overdiagnosis of epilepsy (20–25 % of all new diagnosed cases) and its underdiagnosis (as high as 10 %) are frequent diagnostic errors. Such errors are most commonly related to the misinterpretation of electrophysiological evidence in both young patients (in whom paroxysmal phenomena are a result of functional immaturity of brain structures) and elderly patients (in whom paroxysmal activity is a consequence of the development of degenerative processes in the neurons).Objective: to show examples of electroencephalographic (EEG) paroxysmal activity in old age group patients suffering from non-epileptic paroxysms.Now EEG investigation is a highly sensitive technique that requires a physician’s knowledge of neuroanatomy and neurophysiology to correct interpretation of the findings. Non-epileptiform paroxysmal events may be detected not only in children who have immature cerebral cortical neurons and median brainstem structures, but also in the elderly in whom their emergence is due to the development of degenerative processes in the neurons. The similarity of these phenomena with typical EEG epileptiform patterns is not coincidental. The basis for their occurrence is the similar mechanism for glutamate excitotoxicity, but, unlike epilepsy, which is triggered by ischemic and hypoxic processes, rather than by the exhausted reserve abilities of nerve cells during overstimulation. Therefore the detection of this pathological EEG paroxysmal activity calls for careful differential diagnosis

Nonlinear acousto-electric transport in a two-dimensional electron system

We study both theoretically and experimentally the nonlinear interaction between an intense surface acoustic wave and a two-dimensional electron plasma in semiconductor-piezocrystal hybrid structures. The experiments on hybrid systems exhibit strongly nonlinear acousto-electric effects. The plasma turns into moving electron stripes, the acousto-electric current reaches its maximum, and the sound absorption strongly decreases. To describe the nonlinear phenomena, we develop a coupled-amplitude method for a two-dimensional system in the strongly nonlinear regime of interaction. At low electron densities the absorption coefficient decreases with increasing sound intensity, whereas at high electron density the absorption coefficient is not a monotonous function of the sound intensity. High-harmonic generation coefficients as a function of the sound intensity have a nontrivial behavior. Theory and experiment are found to be in a good agreement.Comment: 27 pages, 6 figure

Mechanisms of interacting <i>Helicobacter pylori</i> with gastric mucosal epithelium. II. A reaction of gastric epithelium on <i>Helicobacter pylori</i> colonization and persistence

Gastric and duodenal recurrent inflammatory diseases have a high prevalence, but the role played by microbes in its development remained unclear. However, the data published in 1983 by Marshall and Warren about isolating Helicobacter pylori from the stomach mucosa of the patient with gastritis and proposing relevant cultivation methods was the turning point in investigating etiology of the upper digestive tract inflammatory disorders. Moreover, it was shown that the majority of H. pylori spp. are found within the gastric lumen upon colonization, whereas around 20% of them are attached to the epithelial cells in the stomach. In addition, effects of interacting H. pylori with gastric epithelium and activation of some defense mechanisms due to bacterial colonization and spreading were analyzed. It was found that along with triggering pro-inflammatory response induced by proteins VacA as well as phosphorylated/unphosphorylated CagA, wherein the latter is able to induce a set of protective reactions H. pylori disrupts intercellular contacts, affects epithelial cell polarity and proliferation, and activates SHP-2 phosphatase resulting in emerging diverse types of cellular responses. The activation mechanisms for the mitogen-activated protein kinase (MAPK) pathway were discussed. The ability of H. pylori to regulate apoptosis, particularly via its suppression, by expressing ERK kinase and protein MCL1 facilitating bacterial survival in the gastric mucosa as well as beneficial effects related to bacterial circulation on gastric epithelial cell survival elicited by anti-apoptotic factors were also examined. Of note, persistence of H. pylori are mainly determined by activating transcriptional factors including NF-κB, NFAT, SRF, T-cell lymphoid enhancing factor (TCF/LEF), regulating activity of MCL1 protein, in turn, being one of the main anti-apoptotic factors, as well as induced production of the migration inhibitory factor (MIF). The role of VacA cytotoxin in triggering epithelial cell apoptosis via caspase-mediated pathways was also considered. Infection with H. pylori is accompanied by release of proinflammatory cytokine cocktail detected both in vitro and in vivo. In particular, bacterial urease activating transcriptional factor NF-κB was shown to play a crucial role in inducing cytokine production. Moreover, such signaling pathways may be activated after H. pylori is attached to the cognate receptor in the gastric epithelial surface by interacting with CD74 and MHC class II molecules. Finally, a role for various CD4+ T cell subsets, particularly type 17 T helper cells (Th17) in inducing immune response against H. pylori antigens in gastric mucosa was revealed were also discussed