Necessary conditions for STDP-based pattern recognition learning in a memristive spiking neural network.

This work is aimed to study experimental and theoretical approaches for searching effective local training rules for unsupervised pattern recognition by high-performance memristor-based Spiking Neural Networks (SNNs). First, the possibility of weight change using Spike-Timing-Dependent Plasticity (STDP) is demonstrated with a pair of hardware analog neurons connected through a (CoFeB)x(LiNbO3)1-x nanocomposite memristor. Next, the learning convergence to a solution of binary clusterization task is analyzed in a wide range of memristive STDP parameters for a single-layer fully connected feedforward SNN. The memristive STDP behavior supplying convergence in this simple task is shown also to provide it in the handwritten digit recognition domain by the more complex SNN architecture with a Winner-Take-All competition between neurons. To investigate basic conditions necessary for training convergence, an original probabilistic generative model of a rate-based single-layer network with independent or competing neurons is built and thoroughly analyzed. The main result is a statement of "correlation growth-anticorrelation decay" principle which prompts near-optimal policy to configure model parameters. This principle is in line with requiring the binary clusterization convergence which can be defined as the necessary condition for optimal learning and used as the simple benchmark for tuning parameters of various neural network realizations with population-rate information coding. At last, a heuristic algorithm is described to experimentally find out the convergence conditions in a memristive SNN, including robustness to a device variability. Due to the generality of the proposed approach, it can be applied to a wide range of memristors and neurons of software- or hardware-based rate-coding single-layer SNNs when searching for local rules that ensure their unsupervised learning convergence in a pattern recognition task domain.

Self-adaptive STDP-based learning of a spiking neuron with nanocomposite memristive weights.

Neuromorphic systems consisting of artificial neurons and memristive synapses could provide a much better performance and a significantly more energy-efficient approach to the implementation of different types of neural network algorithms than traditional hardware with the Von-Neumann architecture. However, the memristive weight adjustment in the formal neuromorphic networks by the standard back-propagation techniques suffers from poor device-to-device reproducibility. One of the most promising approaches to overcome this problem is to use local learning rules for spiking neuromorphic architectures which potentially could be adaptive to the variability issue mentioned above. Different kinds of local rules for learning spiking systems are mostly realized on a bio-inspired spike-time-dependent plasticity (STDP) mechanism, which is an improved type of classical Hebbian learning. Whereas the STDP-like mechanism has already been shown to emerge naturally in memristive devices, the demonstration of its self-adaptive learning property, potentially overcoming the variability problem, is more challenging and has yet to be reported. Here we experimentally demonstrate an STDP-based learning protocol that ensures self-adaptation of the memristor resistive states, after only a very few spikes, and makes the plasticity sensitive only to the input signal configuration, but neither to the initial state of the devices nor their device-to-device variability. Then, it is shown that the self-adaptive learning of a spiking neuron with memristive weights on rate-coded patterns could also be realized with hardware-based STDP rules. The experiments have been carried out with nanocomposite-based (Co40Fe40B20) х (LiNbO3-y )100-х memristive structures, but their results are believed to be applicable to a wide range of memristive devices. All the experimental data were supported and extended by numerical simulations. There is a hope that the obtained results pave the way for building up reliable spiking neuromorphic systems composed of partially unreliable analog memristive elements, with a more complex architecture and the capability of unsupervised learning.

[Nuclear activation analytical methods and X-ray fluorescence analysis in application to determination of pollutants and trace elements in food and for studying biokinetics of nanoparticles].

For assurance of food quality and safety, it is necessary to control routes of food pollutants, including toxic trace elements in all stages of handling, ranging from the production of agricultural products, including the processing, storage, transportation, and ending with cooking and consumption. For this control the nuclear activation analytical methods (NAAMs) and X-ray fluorescence analysis (XRFA) are studied and developed for the detection of chemical elements in different environments. NAAMs involve two stages: the activation of nuclear isotopes with thermal neutrons or fast charged particles and gamma spectrometry. XRFA technique is based on detecting characteristic fluorescent X-rays of elements. Interest in these methods is due to the relative simplicity of the analysis, the ability to provide the required sensitivity and accuracy of detection of chemical elements. The main objective of the research work is to demonstrate the potential of these techniques for controlling the quality and safety of food products and for research of trace elements' biokinetics with achieving the required accuracy (no worse than 15%) and sensitivity (below the permissible concentrations of harmful substances) and to prepare them for the practical application. Both methods complement each other in terms of expanding the list of detected chemical elements and choosing the best option in the analysis depending on the type of the test sample and readiness of technical means. In addition to the analysis of NAAMs and XRFA capabilities two different but partly connected research options were performed using NAAMs: 1) control of food quality and safety; 2) research of biokinetics of nanoparticles (NPs), incoming with food and water into laboratory animals with special attention to overcoming biological barriers. One of the important result is the demonstration of overcoming the blood/brain barrier by silver NPs when they are ingested into the animals with food or water, and possibility of their accumulation in brains with extremely low excretion (≈6% per month).

Bilayered graphene as a platform of nanostructures with folded edge holes.

The stability and the electronic properties of new AB-stacking and moiré bilayer graphene superlattices with closed edge nanoholes are studied using DFT calculations. The closing of the edges is made of C-C bonds that form after folding the borders of the holes. Superlattices with periodic hexagonal symmetry are considered in more detail. The electronic band structure of the nanomeshes has metallic to semiconductor characteristics, depending not only on the size of the holes and the distance between them, but also on the hole shape. Bilayered graphene is considered as a platform for the engineering of nanostructures with folded edge holes.

Band gaps in jagged and straight graphene nanoribbons tunable by an external electric field.

Band gap control by an external field is useful in various optical, infrared and THz applications. However, widely tunable band gaps are still not practical due to a variety of reasons. Using the orthogonal tight-binding method for π-electrons, we have investigated the effect of the external electric field on a subclass of monolayer chevron-type graphene nanoribbons that can be referred to as jagged graphene nanoribbons. A classification of these ribbons was proposed and band gaps for applied fields up to the SiO2 breakdown strength (1 V nm(-1)) were calculated. According to the tight-binding model, band gap opening (or closing) takes place for some types of jagged graphene nanoribbons in the external electric field that lies on the plane of the structure and perpendicular to its longitudinal axis. Tunability of the band gap up to 0.6 eV is attainable for narrow ribbons. In the case of jagged ribbons with armchair edges larger jags forming a chevron pattern of the ribbon enhance the controllability of the band gap. For jagged ribbons with zigzag and armchair edges regions of linear and quadratic dependence of the band gap on the external electric field can be found that are useful in devices with controllable modulation of the band gap.

Transfer of Silver Nanoparticles through the Placenta and Breast Milk during in vivo Experiments on Rats.

Silver nanoparticles (NPs), widely used in the manufacture of various types of consumer products and for medical applications, belong to novel types of materials that pose potential risks to human health. The potential negative effects of the influence of these NPs on reproduction are insufficiently researched. A quantitative assessment of the transfer of metallic silver nanoparticles through the placenta and breast milk was carried out during an in vivo experiment. We used 34.9 ± 14.8 nm in size silver NPs that were stabilized by low-molecularweight polyvinylpyrrolidone and labeled with the (110m)Ag radioactive isotope using thermal neutron irradiation in a nuclear reactor. [(110m)Ag]-labeled NPs preparations were administered intragastrically via a gavage needle to pregnant (20(th) day of gestation) or lactating (14-16th day of lactation) female rats at a dose of 1.69-2.21 mg/kg of body weight upon conversion into silver. The accumulation of NPs in rat fetuses and infant rats consuming their mother's breast milk was evaluated using a low-background semiconductor gamma-ray spectrometer 24 and 48 hours following labeling, respectively. In all cases, we observed a penetration of the [(110m)Ag]-labeled NPs through the placenta and ther entry into the mother's milk in amounts exceeding by 100-1,000 times the sensitivity of the utilized analytical method. The average level of accumulation of NPs in fetuses was 0.085-0.147% of the administered dose, which was comparable to the accumulation of the label in the liver, blood, and muscle carcass of adult animals and exceeded the penetration of NPs across the hematoencephalic barrier into the brain of females by a factor of 10-100. In lactating females, the total accumulation of [(110m)Ag]-labeled NPs into the milk exceeded 1.94 ± 0.29% of the administered dose over a 48 h period of lactation; not less than 25% of this amount was absorbed into the gastrointestinal tract of infant rats. Thus, this was the first time experimental evidence of the transfer of NPs from mother to offspring through the placenta and breast milk was obtained.

[Use of systems approach to solving regional problems of renewal of the stock of ultrasound scanners (the case of the Smolensk Region)]. / O primenenii sistemnogo podkhoda k rezheniiu regional'noi problemy obnovleniia parka ul'trazvukovykh skanerov (na primere Smolenskoi oblasti).

The Smolensk Region (Russian Federation) was used to assess how ultrasound diagnosis is made in the therapeutical and prophylactic institutions. Requirements for the diagnosis are worded in terms of regional, organizational, and other features. At the same time the paper gives main criteria for assessing the obsolescence of equipment; data on the level of organization of service; a share of brands of equipment; and characteristics of manufacturers in the ultrasound equipment market of the Smolensk Region.

[Clinico-roentgenological diagnosis of dumping syndrome in expert medical evaluation of work capacity]. / Kliniko-rentgenologicheskoe issledovanie pri demping-sindrome v praktike vrachebno-trudovoi ékspertizy.

The authors conducted complex clinical and X-ray examination of 80 patients suffering from the dumping syndrome of various degree. They were sent to the Central Scientific Research Institute of Expert Medical Assessment of Working Capacity for establishing the degree of severity of morphological and functional disorders affecting their capacity for work. The method of examination of such patients, including X-ray and other clinical methods, is described. The main clinical and roentgenosemeiotic signs characteristic of the mild, moderately severe, and severe forms of the dumping syndrome are pointed out. Clinical cases are described in illustration of the diagnostic possibilities and the expert approach to the results of the examination of such patients.

[Clinico-roentgeno-functional studies during expert evaluation of work capacity of patients with neurotrophic disorders after war-time neck injuries]. / Kliniko-rentgenofunktsional'noe issledovanie pri ékspertize trudosposobnosti lits s neirotroficheskimi narusheniiami vsledstvie voennoi travmy oblasti shei.

The paper is concerned with a clinico-roentgeno-functional++ study into sequelae of fighting injury to the osseous and soft tissue structures of the neck with the aid of testometric stereoroentgenogrammetry, a method of x-ray topical diagnosis used in fragmentation effects and gunshot injuries, as well as a method of color reading of limb roentgenograms to identify pathomorphological alterations and neurotrophic disorders of the osseous tissue. The pathofunctional alterations related to derangement of the radix structures can be verified by means of using the current methods of functional research: echoosteometry, rheovasography, etc.