V. A. Demin

First steps towards the realization of a double layer perceptron based on organic memristive devices

Memristors are widely considered as promising elements for the efficient implementation of synaptic weights in artificial neural networks (ANNs) since they are resistors that keep memory of their previous conductive state. Whereas demonstrations of simple neural networks (e.g., a single-layer perceptron) based on memristors already exist, the implementation of more complicated networks is more challenging and has yet to be reported. In this study, we demonstrate linearly nonseparable combinational logic classification (XOR logic task) using a network implemented with CMOS-based neurons and organic memrisitive devices that constitutes the first step toward the realization of a double layer perceptron. We also show numerically the ability of such network to solve a principally analogue task which cannot be realized by digital devices. The obtained results prove the possibility to create a multilayer ANN based on memristive devices that paves the way for designing a more complex network such as the double layer perceptron.

Electrochemical model of the polyaniline based organic memristive device

The electrochemical organic memristive device with polyaniline active layer is a stand-alone device designed and realized for reproduction of some synapse properties in the innovative electronic circuits, including the neuromorphic networks capable for learning. In this work, a new theoretical model of the polyaniline memristive is presented. The developed model of organic memristive functioning was based on the detailed consideration of possible electrochemical processes occuring in the active zone of this device. Results of the calculation have demonstrated not only the qualitative explanation of the characteristics observed in the experiment but also the quantitative similarities of the resultant current values. It is shown how the memristive could behave at zero potential difference relative to the reference electrode. This improved model can establish a basis for the design and prediction of properties of more complicated circuits and systems (including stochastic ones) based on the organic memristive devices.

Radiotracer methods and neutron activation analysis for the investigation of nanoparticle biokinetics in living organisms

The physical foundations and methodological issues of nuclear activation methods (radiotracers and neutron activation analysis) have been discussed in regards to a study of assimilation of a number of inorganic nanoparticles (NPs) by living organisms and their distribution in organs and excretion. The methods of activation of NPs within a colloidal solution or biological samples have been analyzed. Advantages of the radioactive tracer method and neutron activation analysis have been compared. A brief overview of a number of successful works using nuclear methods for studying the interaction of silver, gold, selenium, and zinc and titanium oxide NPs with living organisms has been given. As an example, a description and results of the experiment on long-term (28 days) injection of silver NPs into laboratory mice have been given. The abilities of neutron activation analysis to estimate the mass of residual blood (and the NPs in it) in biological samples and to confirm the penetration of the NPs through the blood-brain barrier in quantitative terms have been demonstrated.

EPR diagnostics of the photosensitized generation of singlet oxygen on the surface of silicon nanocrystals

Electron paramagnetic resonance spectroscopy is used to determine the concentration of excited (singlet) molecular oxygen photosensitized by silicon nanocrystals. The generation of singlet oxygen in the porous silicon layers is studied quantitatively at various oxygen pressures and exciting light intensities with the use of the technique proposed. The experimental results indicate that silicon nanoclusters as the photosensitizers of singlet oxygen are promising for biomedical applications.

Tunneling anomalous Hall effect in nanogranular CoFe-B-Al-O films near the metal-insulator transition

We present results of experimental studies of structural, magneto-transport and magnetic properties of CoFe-B-Al-O films deposited onto a glass ceramic substrate by the ion-beam sputtering of the target composed of Co40Fe40B20 and Al2O3 plates. The system consists on the strained crystalline CoFe metallic nanogranules with the size 2-5 nm which are embedded into the B-Al-O oxide insulating matrix. Our investigations are focused on the anomalous Hall effect (AHE) resistivity Rh and longitudinal resistivity R at T=5-200 K on the metallic side of metal-insulator transition in samples with the metal content x=49-56 at.%, that nominally corresponds to (Co40Fe40B20)x(Al2O3)100-x in the formula approximation. The conductivity at T > 15 K follows the lnT behavior that matches a strong tunnel coupling between nanogranules. It is shown that the scaling power-laws between AHE resistivity and longitudinal resistivity strongly differ, if temperature T or metal content x are variable parameters: Rh(T)~R(T)^0.4-0.5 obtained from the temperature variation of R and Rh at fixed x, while Rh(x)/x~R(x)^0.24, obtained from measurements at the fixed low temperature region (10-40 K) for samples with different x. We qualitatively describe our experimental data in the frame of phenomenological model of two sources of AHE e.m.f. arising from metallic nanogranules and insulating tunneling regions, respectively, at that the tunneling AHE (TAHE) source is strongly shunted due to generation of local circular Hall currents. We consider our experimental results as the first experimental proof of the TAHE manifestation.

Neuromorphic elements and systems as the basis for the physical implementation of artificial intelligence technologies

The instrumental realization of neuromorphic systems may form the basis of a radically new social and economic setup, redistributing roles between humans and complex technical aggregates. The basic elements of any neuromorphic system are neurons and synapses. New memristive elements based on both organic (polymer) and inorganic materials have been formed, and the possibilities of instrumental implementation of very simple neuromorphic systems with different architectures on the basis of these elements have been demonstrated.

Extremely low level of Ag nanoparticle excretion from mice brain in in vivo experiments

Silver nanoparticle accumulation in mice organs as well as the excretion processes from them were studied. The investigation included a one-time oral administration of silver nanoparticles and a series of prolonged oral administrations of the same nanoparticles to study the long-term impact of the nanoparticles. In these experiments, the mice had been fed with colloid silver and in these prolonged experiments, administrations lasted for 2 months. The nanoparticle administration was then cancelled for one month. The elemental composition of tissue samples was studied by Nuclear Physical technique, which allowed us to obtain the masses of the key element, namely silver. It was demonstrated that silver concentrations in tissues were redistributed with time. The main result of this work was the discovery of extremely low level of silver nanoparticle excretion from mice brain (just 6% per month) following the cancellation of NP administration. However, the rates of excretion from blood and liver appeared to be rather high (about 80% per month). Thus, the accumulation effect of silver nanoparticles in the mice brain was observed, which is of great practical importance. It changes the approach to the toxicity assessment of silver nanoparticles as a result of the prolonged injection of colloidal silver.

The effect of the memristor electrode material on its resistance to degradation under conditions of cyclic switching

The stability of titanium oxide memristors with gold and platinum electrodes with respect to switching-induced degradation has been studied. It is established that the use of gold instead of platinum as the electrode material significantly increases the resistance of a memristor to degradation in the course of repeated resistance read-write(erase) cycles. The first Russian high-endurance memristor based on titanium oxide has been obtained, which can withstand up to 3000 resistive switching cycles.

Formation of certified reference materials and standard measurement guides for development of traceable measurements of mass fractions and sizes of nanoparticles in different media and biological matrixes on the basis of gamma-ray and optical spectroscopy

Metrological assurance has been developed and formed for a promising technique for measuring the mass fraction and number concentration of nanoparticles containing silver or zinc in different media, including those of a biological nature, i.e., the gamma-ray spectroscopy of neutron-activated samples along with dynamic light scattering. The advantage of this complex measurement technique over other approaches to analytically controlling nanomaterials is discussed. The certified reference materials and standard guides developed in order to ensure the uniformity and traceability of measurements are described. The technique is tested in experiments on the kinetics of accumulation and removal of silver nanoparticles in different organs and excrement of laboratory rats.

Modeling interorgan distribution and bioaccumulation of engineered nanoparticles (using the example of silver nanoparticles)

In this paper we demonstrate the validity of a mathematical chamber model to describe the absorption, distribution, and bioaccumulation of nonmetabolizable nanoparticles (NPs) using the example of silver NPs in the organism of laboratory rat. The model is constructed using experimental data on the bioaccumulation and biodistribution of silver NPs of average diameter of 35 ± 15 nm (M ± SD) radiolabeled with 110mAg. In the minimally acceptable form, the model includes all “chambers” in which NP level in the course of the experiment was no lower than 20–25% of its blood content, namely, the gastrointestinal tract (GIT), blood itself, osteomuscular carcass, liver, and spleen. NP bioaccumulation and biodistribution in these chambers is described by five independent linear differential equations of the 1st order. A numerical solution of this system of equations, with account for the data on timing of NP excretion from the GIT in the content of feces, makes it possible to determine the biokinetic rate constants for the interorgan transfer of NPs. These rate constants are used to establish the dose-dependence of the peak (maximum) and quasi-stationary NP content in critical target organs, respectively, in the case of acute (single) and subchronic (repeated) administration of NP in the gastrointestinal tract. The results justify the value of the method of mathematically modeling the interstitial transport and distribution of NPs to assess their potential toxic effects on a system level using previously obtained in vitro data and results from biokinetic studies.