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This review addresses tremor, which is among the maladaptive and difficult-to-treat symptoms of Parkinson's disease (PD). Along with classical resting tremor, patients with PD may experience postural and kinetic types of tremor, reflecting the multimodal mechanism of its formation, which involves multiple neurotransmitter systems. Unpredictable therapeutic responses and mixed responses to levodopa also reflect the roles of multiple underlying pathophysiological processes. Among medication-based methods for tremor correction, preference is given to dopamine receptor agonists because of their wide range of pharmaceutical effects and high efficacy in relation to the major motor and various non-motor manifestations. Evidence of the efficacy of advanced neurosurgical and non-invasive treatment methods is not always convincing; there have been no large-scale comparative studies assessing their efficacy in patients with tremor-dominant forms of PD. [ABSTRACT FROM AUTHOR]

The efficiency of preparing donor platelet concentrates using the MCS+ apparatus (Haemonetics, USA) using the Leukodepleted Platelet (LDP) protocol and the Universal Platelet Protocol (UPP) was evaluated. Reinfusion is carried out intermittently in the LDP protocol and continuously in the UPP protocol. A total of 40 consecutive donors were alternately assigned to the LDP (LDP group, n = 20) and UPP (UPP group, n = 20) protocols and donor platelet concentrate was prepared. The UPP protocol, with continuous plasma return during apheretic preparation of two therapeutic doses of donor platelet concentrates on the MCS+ device, was found to provide greater speed and volume of blood processing and, thus, a 15% greater platelet collection efficiency as compared with procedures using the LDP protocol. [ABSTRACT FROM AUTHOR]

The conductance of a trench-type quantum point contact (QPC) with side gates has been experimentally investigated over a wide range of gate voltages. The performed measurements, in which the asymmetric gate bias modifies the confinement potential while the sum of the gate voltages populates it with electrons, made it possible to scan the electron states in the QPC. Analysis of the experimental data revealed an unusual four-well shape of the confining potential in a single QPC. The rather complicated transconductance plot measured can be divided into its component parts—the contributions of the four separate conducting channels. Different electron states observed in the experiment have been associated with a certain number of filled one-dimensional (1D) subbands belonging to different channels. A whole network of degeneration events of 1D subbands in parallel channels has been found. Almost every such event was experimentally manifested by anticrossings observed both for small and large numbers of filled 1D subbands. [ABSTRACT FROM AUTHOR]

Objective. To study tremor and olfactory function in patients with Parkinson's disease and essential tremor and essentially healthy people for differential diagnosis and to test the hypothesis that there is an inverse relationship between the severity of tremor and the extent of olfactory impairment. Materials and methods. Olfactory function was assessed in 45 patients with Parkinson's disease, 40 people with essential tremor, and 64 presumptively healthy people (control group). Olfactory functional diagnosis was run using the Sniffin' Sticks test. Tremor was analyzed in 90 people: 30 presumptively healthy people, 30 patients with Parkinson's disease, and 30 patients with essential tremor. Tremor parameters were determined using a wireless electrophysiological signal monitoring system and three main parameters were recorded: the surface electromyogram, gyrometry and accelerometry (frequency and amplitude of each of three measures). Data were analyzed in IBM SPSS Statistics 2.3 using classical statistical methods: the Shapiro–Wilk test and the Spearman correlation coefficient. In addition, data were processed by nonlinear methods using the elastic map method in ViDaExpert software. Results and conclusion. The elastic map including the selected measures of tremor and olfactory test data showed that patients with different diseases are clearly distinguished from each other, forming three separate clusters. Analysis of the resulting clusters showed that patients with essential tremor had better olfaction than Parkinson's disease patients. Measures of tremor in Parkinson's disease patients were higher, supporting the hypothesis that there is an inverse relationship between tremor severity and the magnitude of the reduction in olfaction. [ABSTRACT FROM AUTHOR]

A physical mechanism has been proposed to explain the appearance of the multichannel electron transport regime in trench quantum point contacts. It has been shown that the redistribution of electrons in a two-dimensional electron gas, which is due to the Coulomb interaction between them and with charged donors and X-valley electrons, results in the experimentally observed multichannel regime. The numerical simulation of the redistribution of electrons and its comparison with the measurements of the conductance of trench quantum point contacts based on a GaAs/AlGaAs heterostructure demonstrate the formation of a multiwell confining potential. [ABSTRACT FROM AUTHOR]

Objectives. To assess the dynamics of cognitive impairment (CI) in patients with Parkinson's disease (PD) during L-DOPA treatment. Materials and methods. A randomized clinical trial included 41 patients with confirmed diagnoses of PD at stage 2.5–3.5 on the Hoehn and Yahr scale, mainly of the akinetic-rigid and mixed forms, who were taking levodopa and had PD-associated CI syndrome. Mean duration of illness was five years. The design included randomization of study participants to two groups. The dynamics of CI were assessed using neuropsychological investigations on two occasions separated by six months: group 1 in the on and off phases of L-DOPA therapy and group 2 in the off and on phases of levodopa therapy, respectively. The state of CI was assessed on the Mini Mental State Examination (MMSE), the Montreal Cognitive Assessment Scale (MoCA), the Frontal Assessment Battery (FAB), the Scales for Outcomes in Parkinson's Disease – Cognition (SCOPA-Cog), and the Geriatric Depression Scale (GDS). Results. A statistically significant improvement in cognitive status was seen at the on phase of levodopa action, along with degradation in the off phase of L-DOPA therapy in the form of increased cognitive deficit (p < 0.05). Conclusions. CI in PD may to some extent be dependent on L-DOPA therapy, as well as on motor signs. The most dynamic functions on the background of L-DOPA therapy were attention, language, and executive and visuospatial functions. [ABSTRACT FROM AUTHOR]

The conductance of a suspended quantum point contact fabricated on the basis of GaAs/AlGaAs heterostructures with a two-dimensional electron gas and equipped with side gates separated from the constriction using lithographical trenches is investigated. The gate dependences of the conductance of such structures correspond to the unusual double-channel mode with independent quantization of the conductance of two channels, and the conductance of separate channels can be independently controlled using two side gates. The electrostatic-formation mechanism of a two-channel structure inside a single constriction associated with the lateral redistribution of low-mobility X-valley electrons containing superlattice heterostructure layers, which leads to the formation of a potential barrier separating the conductivity electrons into two channels symmetrically shifted towards the lithographic trenches, specifying the nanostructure geometry, is considered. [ABSTRACT FROM AUTHOR]

A multichannel electron transport mode with independent conductance quantization in individual channels is implemented and studied in quantum point contacts with side gates. Simulation of the total conductance as the sum of quantized individual conductances reproduces the experimentally observed complex conductance dependence on the sum and difference of gate voltages in this regime. The considered model reproduces the following experimentally observed features of conductance quantization: the absence of some of the plateaus, the conductance steps equal to 4e2/h and other values different from 2e2/h, the plateaus appearing at nonmultiples of 2e2/h, the evolution of the anomalous plateaus with a change in gate voltage difference, and the low visibility of some plateaus. The study shows that a non-trivial experimentally observed conductance behaviour in quantum point contacts may originate from channel multiplicity which may not be obvious in advance. [ABSTRACT FROM AUTHOR]

This paper demonstrates the applicability of nanoindentation technique using atomic-force microscope cantilever for studying the elastic properties of suspended semiconductor structures on the basis of relatively thick GaAs/AlGaAs membranes in the case when their stiffness significantly exceeds that of the cantilever of atomic-force microscope, which is confirmed by the agreement between the experimentally determined values of both relative and absolute stiffness measured at different points of the investigated structure with theoretical predictions. [ABSTRACT FROM AUTHOR]

The magnetoresistance of suspended semiconductor nanostructures with a two-dimensional electron gas structured by periodic square antidot lattices is studied. It is shown that the ballistic regime of electron transport is retained after detaching the sample from the substrate. Direct comparative analysis of commensurability oscillations of magnetoresistance and their temperature dependences in samples before and after suspension is performed. It is found that the temperature dependences are almost identical for non-suspended and suspended samples, whereas significant differences are observed in the nonlinear regime, caused by direct current passage. Commensurability oscillations in the suspended samples are more stable with respect to exposure to direct current, which can be presumably explained by electron-electron interaction enhancement after detaching nanostructures from the high-permittivity substrate. [ABSTRACT FROM AUTHOR]

The nonequilibrium state of a two-dimensional electron gas in the quantum-Hall-effect regime is studied in Hall bars equipped with additional inner contacts situated within the bar. The magnetic-field dependence of the voltage drop between different contact pairs are studied at various temperatures. It was found that the voltage between the inner and outer contacts exhibits peaks of significant amplitude in narrow magnetic-field intervals near integer filling factors. Furthermore, the magnetic-field dependence of the voltage in these intervals exhibits a hysteresis, whereas the voltage between the outer contacts remains zero in the entire magnetic-field range. The appearance of the observed voltage peaks and their hysteretic behavior can be explained by an imbalance between the chemical potentials of edge and bulk states, resulting from nonequilibrium charge redistribution between the edge and bulk states when the magnetic field sweeps under conditions of the quantum Hall effect. The results of the study significantly complement the conventional picture of the quantum Hall effect, explicitly indicating the existence of a significant imbalance at the edge of the two-dimensional electron gas: the experimentally observed difference between the electrochemical potentials of the edge and bulk exceeds the distance between Landau levels by tens of times. [ABSTRACT FROM AUTHOR]

The nonequilibrium state of a two-dimensional electron gas (2DEG) in the quantum Hall effect (QHE) regime, manifested in the hysteresis of magnetoresistance of a 2DEG with a constriction, has been experimentally studied. The large amplitude of the hysteresis enabled us to make the consistent phenomenological description of the hysteresis. We performed minor loop measurements, recovered the anhysteretic curve, and studied the time dependence. We showed that the hysteresis has significant phenomenological similarities with that of magnetization of ferromagnets, showing multistability, jumps of relaxation, and having the anhysteretic curve. The difference is manifested itself in an unusual inverted (anti-coercive) behavior of the hysteresis. The time relaxation of the hysteresis has fast and slow regimes, similar to that of non-equilibrium magnetization of a 2DEG in QHE regime pointing to their common origin. We studied the dependence of the hysteresis loop area on the lithographic width of the constriction and found the threshold value of width ∼1.35 μm. This points to the edge nature of the nonequilibrium currents (NECs) and allows us to determine the width of the NECs area (∼0.5 μm). We suggest the qualitative picture of the observed hysteresis, based on non-equilibrium redistribution of the electrons among the Landau level states and assuming huge imbalance between the population of bulk and edge electronic states. [ABSTRACT FROM AUTHOR]

One of the most important signs of parkinsonism is gait impairments, which often largely determine the severity of the patient's condition and quality of life. Development of methods for correction of gait abnormalities, including non-medication-based methods, is therefore very relevant. This article describes a method of identifying gait characteristics and correcting them in patients with parkinsonism (Parkinson's disease and vascular parkinsonism; the method is accessible for out-patient use. Patients with Parkinson's disease and vascular parkinsonism were characterized by decreases in step length and increases in length variability. Preliminary determination of patients' individual optimum sound signal frequencies for tuning the gait rhythm increased treatment efficacy. The audio stimulation method used here, based on use of portable audio players, can maintain the resultant positive effects. [ABSTRACT FROM AUTHOR]

Extraordinary piecewise parabolic behavior of the magnetoresistance has been experimentally detected in the two-dimensional electron gas with a dense triangular lattice of antidots, where commensurability magnetoresistance oscillations are suppressed. The magnetic field range of 0-0.6 T can be divided into three wide regions, in each of which the magnetoresistance is described by parabolic dependences with high accuracy (comparable to the experimental accuracy) and the transition regions between adjacent regions are much narrower than the regions themselves. In the region corresponding to the weakest magnetic fields, the parabolic behavior becomes almost linear. The observed behavior is reproducible as the electron gas density changes, which results in a change in the resistance by more than an order of magnitude. Possible physical mechanisms responsible for the observed behavior, including so-called 'memory effects,' are discussed. [ABSTRACT FROM AUTHOR]