Spin independence of the strongly enhanced effective mass in ultra-clean SiGe/Si/SiGe two-dimensional electron system

The effective mass at the Fermi level is measured in the strongly interacting two-dimensional (2D) electron system in ultra-clean SiGe/Si/SiGe quantum wells in the low-temperature limit in tilted magnetic fields. At low electron densities, the effective mass is found to be strongly enhanced and independent of the degree of spin polarization, which indicates that the mass enhancement is not related to the electrons' spins. The observed effect turns out to be universal for silicon-based 2D electron systems, regardless of random potential, and cannot be explained by existing theories.

The Chick Embryo and Its Structures as a Model System for Experimental Ophthalmology

The possibilities of using the chick embryo and its individual structures as a model system in experimental ophthalmology are considered. Cultures of the retina and spinal ganglia from chick embryos are used in the development of new methods for the treatment of glaucomatous optic neuropathy and ischemic optic neuropathy. The chorioallantoic membrane is used for modelling vascular pathologies of the eye, screening of anti-VEGF drugs, and assessing biocompatibility of implants. Co-culturing of chick embryo nervous tissue and human corneal cells makes it possible to study the processes of corneal reinnervation. The use of chick embryo cells and tissues in the "organ-on-a-chip" system opens up wide opportunities for fundamental and applied ophthalmological studies.

[Application of the organ-on-a-chip technology in experimental ophthalmology]

Organ-on-chip is a microfluidic device that can reproduce in vitro the minimal functional unit of an organ or system of organs and model various physiological processes and body structures with high accuracy. This review covers the main approaches to the use of the organ-on-chip technology in modern experimental ophthalmology. The analysis of literature sources revealed the following main applications of the organ-on-chip technology in ophthalmology; the technology allows modeling the anterior eye surface and its diseases, such as dry eye syndrome, as well as disorders of the posterior segment of the eye such as age-related macular degeneration, diabetic macular edema, diabetic retinopathy, glaucoma. Culturing of eye tissues in microfluidic systems helps identify the toxic effects and pharmacological activity of new compounds, and provides an opportunity for deeper understanding of the normal physiology of the eye and the pathogenesis of ocular diseases. In addition, the technology can reduce the cost and duration of experiments. Thus, the organ-on-a-chip technology has a great potential in the field of experimental ophthalmology and preclinical trials of new ophthalmic drugs.

[Bioprinting technologies in ophthalmology]

Bioprinting allows additive fabrication of bioengineered constructs with defined two- or three-dimensional organization using live cells, biopolymers and other materials. This article reviews main bioprinting technologies and their capabilities in clinical and experimental ophthalmology. Analysis of literature sources helped reveal and describe the main types of bioprinting technologies: inkjet, laser-assisted, and extrusion. Extrusion bioprinting is the most widely used method, providing the ability to use various types of bioinks and a wide range of cell concentrations. The following materials can be used as the base for bioinks: alginate, collagen, gelatin, hyaluronic acid, chitosan, fibrin, as well as their different combinations. These materials can be modified for best bioprinting properties by adding various functional groups. The major directions of application of bioprinting technologies in ophthalmology are tissue engineering for regenerative medicine and fabrication of model systems for fundamental and preclinical studies. Experiments in creating a bioprinted cornea are being conducted in the field of regenerative medicine. Furthermore, there are studies on fabricating retinal tissue equivalents, although tissue engineering of this structure is a task of great complexity. Model systems, which can be fabricated by bioprinting, are represented by tissue equivalents of ocular structures and the appendages of the eye, as well as by microphysiological organ-on-a-chip systems. Another promising application of bioprinting is fabrication of biocompatible implantable electrode arrays for visual neuroprostheses.

Modern concepts of bionic vision

Loss of vision is a pressing medical and social problem leading to profound disability, loss of ability to work, serious alterations in the psycho-emotional state, and a decline of the quality of life. When conservative or surgical treatment can not help restore vision, the use of visual prosthesis - bionic eye - can be an effective solution. This review covers the main modern approaches to the development of visual prosthetic systems. Analysis of publications revealed that there are several main approaches to visual prosthesis differing primarily by the anatomical structure targeted for stimulation in order to activate visual sensations. The most significant among them are retinal prostheses, optic nerve stimulation, and cortical visual prostheses. Currently, retinal prostheses such as ARGUS II demonstrate the most successful results, since the stimulation of the surviving neural structures of the retina is a relatively easy task, but their field of application is limited to diseases associated with pathological changes in photoreceptors. The development of cortical visual prostheses is more difficult, but in the future they may allow using more stimulation channels to obtain a more detailed visual perception. In addition, cortical visual prostheses are universal, as they do not require preservation of any structures of the visual organ, only the primary visual cortex.

Cytoprotective and Antioxidant Effects of Meconic Acid in Model Systems

We studied the antioxidant and cytoprotective effects of meconic acid in the model systems. Meconic acid, similar to commercial drug Mexidol, reduced the intensity of chemiluminescence in the model system of yolk lipoproteins. Meconic acid also reduced the toxic effect of glutamate on neurons in the primary cerebellar culture, but had no effect on cell viability under normal conditions.

[Antioxidant and anxiolytic effect of Bifidobacterium adolescentis and Lactobacillus acidophilus under conditions of normobaric hypoxia with hypercapnia]

Research in recent years has shown that there is a close connection between the brain and the intestine through neuronal, endocrine and immune pathways. The introduction of probiotics into the diet of animals and humans helps to reduce the level of anxiety and depression, as well as inflammatory processes during emotional stress. The aim of this work was to study the effect of intragastric administration of Bifidobacterium adolescentis and Lactobacillus acidophilus on oxidative processes in the brain tissues and the level of anxiety in rats under conditions of normoxia and acute hypoxia with hypercapnia. Material and methods. The experiment was performed on 64 male Wistar rats aged 2.5 months (body weight from 240 to 270 g). The animals were divided into 4 groups: group 1 - control; 2 - hypoxia; 3 - hypoxia + probiotics; 4 - probiotics. There were 16 animals in each group; half of them participated in the behavioral test, and the other half in the biochemical studies. Rats of groups 3 and 4 were orally administered lyophilized bacteria Bifidobacterium adolescentis MC-42, Lactobacillus acidophilus A-97, and Lactobacillus acidophilus A-630 for 30 days before hypoxia. The daily dose of probiotics was 1×10⁹ CFU per animal, administered in a volume of 1 ml. Acute hypoxia with hypercapnia was simulated by placing rats in airtight vessels with a capacity of 1 L before the first agonal inhalation. A day later, in the brain tissues oxidative processes were assessed by the chemiluminescence method and by the level of malone dialdehyde (MDA). The activity of catalase in brain tissues was also determined. The level of anxiety of rats was investigated in the «elevated plus maze» test. Results. Compared to other groups, more intensive free radical oxidation took place in the brain tissues of hypoxified animals that did not receive B. adolescentis and L. acidophilus. There was a significant increase in chemiluminescence intensity and MDA level by 38 and 15%, respectively, compared with the control. In the brain tissues of these animals, catalase activity was reduced by 10% (p<0.01). Moreover, in the group of rats treated with B. adolescentis and L. acidophilus and subjected to acute hypoxia, the value of the light sum of chemiluminescence was 22% lower (p<0.01) than in the hypoxified group without taking probiotics, while the concentration of MDA and catalase activity remained at the level of physiological norms and did not differ from control. Hypoxified animals receiving biomass of lactobacteria and bifidobacteria had also a lower level of anxiety and a higher exploratory activity, expressed in an increase in the number of entries in the open and closed arms, a longer stay in the open arms and the center of the maze, and more frequent performance of orientation reactions and hanging. Conclusion. Pre-hypoxic administration of B. adolescentis and L. acidophilus reduces the development of oxidative stress in rat brain tissues and reduces anxiety indices in the "elevated plus maze" test, thereby exhibiting antioxidant and anxiolytic effects.

[The efficacy of tes-therapy for treatment of anxiety-like behavior and motor disorders in rats with an experimental model of parkinsonism]

AIM

To assess the efficacy of transcranial electrostimulation TES for treatmnet of anxiety-like behavior and motor disorders in rats with rotenone-induced parkinsonism.

MATERIAL AND METHODS

The study was performed on 30 mature male-rats. Animals were divided into following groups: control, intact rats (group 1); rats with an experimental model of parkinsonism without treatment (group 2); rats with an experimental model of parkinsonism, which had 7 sessions of TES-therapy (group 3), the number of rats in each group was 10. The parkinsonism model was achieved by daily rotenone administration for 28 days. Parkinsonism's markers were assessed using 3-point scale; anxiety-like behavior and motor activity were assessed in the open-field test. TES was performed using TRANSAIR-stimulator for 7 days. Substantia nigra slices were stained with hematoxylin and Lillie's staining for neuromelanin.

RESULTS

The rats of group 3 show less neurological deficits, less anxiety-like behavior and less neurodegeneration in the substantia nigra. There are a decrease in individual total scores of motor disorders by 50%, a decrease in the level of anxiety-like behavior or the absence of its increase in the open-field test.

CONCLUSION

TES-therapy may be used as an additional non-pharmacological treatment of motor and related non-motor damage in Parkinson's disease.

Indication of band flattening at the Fermi level in a strongly correlated electron system

Using ultra-high quality SiGe/Si/SiGe quantum wells at millikelvin temperatures, we experimentally compare the energy-averaged effective mass, m, with that at the Fermi level, m_F, and verify that the behaviours of these measured values are qualitatively different. With decreasing electron density (or increasing interaction strength), the mass at the Fermi level monotonically increases in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behaviour reveals a precursor to the interaction-induced single-particle spectrum flattening at the Fermi level in this electron system.

[Comparative evaluation of mastoidoplasty results in application of various plastic materials]

The results of surgical treatment of 62 patients, suffering chronic purulent middle otitis, were analyzed. The structure of mastoid processus and attic constitutes a base for choice of middle ear surgical sanation. Sanation operation with preservation or reconstruction of external acoustical meatus posterior wall was finished with combined mastoidoplasty using autobone, spongioid bone bioimplant Tutoplast or bioceramic material "Sintekost". Achievement of a steady sanating effect have promoted in late postoperative period a trustworthy lowering of the perception threshold of the bone--conducted sounds as on vocal, and also on high frequencies, while of the air--conducted sounds--on vocal frequencies. This permits in perspective to perform a hearing--improving operations with good functional result.

[Restitution of bioactive ceramic material "Syntekost" by a newly evolved bone in experiment]

Peculiarities of reparative processes of bioactive ceramic material "Syntekost", as well as reaction of structures of internal ear on these material, transplanted on osteal bulla in guinea pigs for experimental model of antromastoidotomy creation, were studied up. The signs of its resorbtion were mild, and these processes not always paralleled the osteal tissue evolvement. A newly formed osteal beams were observed up to 90-th day. In terms up to 12 mo there were preserved practically unchanged groups of granules of ceramic implanted material. New bone have evolved in a kind of foci in a distance from internal surface of osteal bulla. Inflammation or ototoxic impact of the material on structures of internal ear were not observed.

Critical behavior of a strongly interacting 2D electron system

With decreasing density n(s) the thermopower S of a low-disorder two-dimensional electron system in silicon is found to exhibit a sharp increase by more than an order of magnitude tending to a divergence at a finite disorder-independent density n(t) consistent with the critical form (-T/S) is proportional to (n(s)-n(t))(x) with x=1.0±0.1 (T is the temperature). Our results provide clear evidence for an interaction-induced transition to a new phase at low density in a strongly interacting 2D electron system.

Magnetization of a strongly interacting two-dimensional electron system in perpendicular magnetic fields

We measure the thermodynamic magnetization of a low-disordered, strongly correlated two-dimensional electron system in silicon in perpendicular magnetic fields. A new, parameter-free method is used to directly determine the spectrum characteristics (Landé g factor and the cyclotron mass) when the Fermi level lies outside the spectral gaps and the interlevel interactions between quasiparticles are avoided. Intralevel interactions are found to strongly modify the magnetization, without affecting the determined g* and m*.

Pauli spin susceptibility of a strongly correlated two-dimensional electron liquid

Thermodynamic measurements reveal that the Pauli spin susceptibility of strongly correlated two-dimensional electrons in silicon grows critically at low electron densities--behavior that is characteristic of the existence of a phase transition.

Coherent backscattering near the two-dimensional metal-insulator transition

We have studied corrections to conductivity due to the coherent backscattering in low-disordered two-dimensional electron systems in silicon for a range of electron densities including the vicinity of the metal-insulator transition, where the dramatic increase of the spin susceptibility has been observed earlier. We show that the corrections, which exist deeper in the metallic phase, weaken upon approaching the transition and practically vanish at the critical density, thus suggesting that the localization is suppressed near and at the transition even in zero field.

Spin-independent origin of the strongly enhanced effective mass in a dilute 2D electron system

We accurately measure the effective mass in a dilute two-dimensional electron system in silicon by analyzing the temperature dependence of the Shubnikov-de Haas oscillations in the low-temperature limit. A sharp increase of the effective mass with decreasing electron density is observed. We find that the enhanced effective mass is independent of the degree of spin polarization, which points to a spin-independent origin of the mass enhancement and is in contradiction with existing theories.

Metal-insulator transition in a 2D electron gas: equivalence of two approaches for determining the critical point

The critical electron density for the metal-insulator transition in a two-dimensional electron gas can be determined by two distinct methods: (i) a sign change of the temperature derivative of the resistance, and (ii) vanishing activation energy and vanishing nonlinearity of current-voltage characteristics as extrapolated from the insulating side. We find that, in zero magnetic field (but not in the presence of a parallel magnetic field), both methods give equivalent results, adding support to the existence of a true zero-field metal-insulator transition.

Indication of the ferromagnetic instability in a dilute two-dimensional electron system

The magnetic field B(c), in which the electrons become fully spin polarized, is found to be proportional to the deviation of the electron density from the zero-field metal-insulator transition in a two-dimensional electron system in silicon. The tendency of B(c) to vanish at a finite electron density suggests a ferromagnetic instability in this strongly correlated electron system.

Metallic low-temperature resistivity in a 2D electron system over an extended temperature range

We report measurements of the zero-field resistivity in a dilute 2D electron system in silicon at temperatures down to 35 mK. This extends the previously explored range of temperatures in this system by almost an order of magnitude. On the metallic side, the resistivity near the metal-insulator transition continues to decrease with decreasing temperature and shows no low-temperature upturn. At the critical electron density, the resistivity is found to be temperature independent in the entire temperature range from 35 mK to 1 K.

Novel phenomena in dilute electron systems in two dimensions

For the past two decades, all two-dimensional systems of electrons were believed to be insulating in the limit of zero temperature. Recent experiments provide evidence for an unexpected transition to a conducting phase at very low electron densities. The nature of this phase is not understood and is currently the focus of intense theoretical and experimental attention.

[A trial of the use of the multivitamin Multitabs in the combined treatment of patients with a perinatal brain lesion]

Pediatric patients in early childhood presenting with perinatal affection of the nervous system benefit much from incorporation into their combined treatment of multivitamins "Multitabs", as evidenced by improvement in their general health, as well as in the red blood parameters and immunity status. Thus, use of the above multivitamins for children presenting with perinatal cerebral pathology is considered liable to be of benefit making for optimization of the process of treatment.