МДП транзистор на основе пленки PbSnTe : In с подзатворным диэлектриком Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=--=SUP=-*-=/SUP=-

Results on the creation and properties of transistor-type MIS structures (MIST) with an Al2O3 thin-film gate dielectric based on PbSnTe:In films obtained by molecular beam epitaxy are presented. The source-drain current-voltage characteristics (CVC) and gate characteristics of the MIST at Т = 4.2 К have been investigated. It is shown that in MIST based on PbSnTe:In films with n ~ 1017 cm-3 the modulation of the channel current reaches 7 – 8 % in the range of gate voltages – 10 V < Ugate < + 10 V. The features of the source-drain CVC and the gate characteristics for a pulsed and sawtooth variation of Ugate are considered.

Electrophysiological Evaluation of an Anticancer Drug Gemcitabine on Cardiotoxicity Revealing Down-regulation and Modification of the Activation Gating Properties in the Human Rapid Delayed Rectifier Potassium Channel

Gemcitabine is an antineoplastic drug commonly used in the treatment of several types of cancers including pancreatic cancer and non–small cell lung cancer. Although gemcitabine-induced cardiotoxicity is widely recognized, the exact mechanism of cardiac dysfunction causing arrhythmias remains unclear. The objective of this study was to electrophysiologically evaluate the proarrhythmic cardiotoxicity of gemcitabine focusing on the human rapid delayed rectifier potassium channel, hERG channel. In heterologous expression system in HEK293 cells, hERG channel current (IhERG) was reduced by gemcitabine when applied for 24 h but not immediately after the application. Gemcitabine modified the activation gating properties of the hERG channel toward the hyperpolarization direction, while inactivation, deactivation or reactivation gating properties were unaffected by gemcitabine. When gemcitabine was applied to hERG-expressing HEK293 cells in combined with tunicamycin, an inhibitor of N-acetylglucosamine phosphotransferase, gemcitabine was unable to reduce IhERG or shift the activation properties toward the hyperpolarization direction. Our results suggest the possible mechanism of arrhythmias caused by gemcitabine revealing a down-regulation of IhERG through the post-translational glycosylation disruption that alters the electrical excitability of cells.

A novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology

In this study, a novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology was fabricated. Sample transistors of different structures and sizes were constructed. Through measurements, it was found that by changing the width of the opening, the threshold voltage of the device could be easily modulated across a larger range. The open-gate device had two working modes with different transconductance. When the gate-source voltage VGS ≤ − 4.5 V, only the open region was conductive, and a new working mechanism modulated the channel current. Corresponding theoretical analysis and calculations showed that its saturation mechanism was related to a virtual gate formed by electron injection onto the surface. Also, the gate-source voltage modulated the open channel current by changing the channel electron mobility through polarization Coulomb field scattering. When used as class-A voltage amplifiers, open-gate devices can achieve effective voltage amplification with very low power consumption.

Compact artificial neuron based on anti-ferroelectric transistor

Neuromorphic machines based on spiking neural networks (SNNs) provide a more fascinating platform over traditional computers on building energy-efficient intelligent systems, in which spiking neuron are pivotal components. Recently, memristive neurons, with promising bio-plausibility and density, have been developed, but with limited reliability or bulky capacitors for integration or additional circuits for reset. Here, we propose a novel anti-ferroelectric field-effect transistor (AFeFET) neuron based on the inherent polarization and depolarization of Hf0.2Zr0.8O2 anti-ferroelectric film to meet these challenges. In this neuron, the intrinsic polarization accumulation effect in the Hf0.2Zr0.8O2 film increases the channel current of AFeFET gradually, which implements the integration feature of the neuronal membrane and avoids using external capacitors. Also, the spontaneous depolarization effect in AFeFET emulates the leaky behavior of neurons, saving the hardware overhead of neuron circuits by getting rid of external reset circuits. Moreover, the AFeFET neuron exhibits other comprehensive merits, such as low energy consumption (37 fJ/spike), excellent endurance (>1012), high uniformity and high stability. Using such an AFeFET neuron, we further construct a two-layer fully ferroelectric (784×400×10) SNN combining established FeFET synapse, achieving 96.8% recognition accuracy on MNIST datasets. This work opens the way to emulate spiking neurons with anti-ferroelectric materials and provides a more competitive approach to build high efficient neuromorphic hardware systems.

Bifurcation Analysis on a Generation of Early Afterdepolarization in a Mathematical Cardiac Model

Electrical activity occurs in the cell membrane of cardiomyocytes. This electrical activity forms the action potential that generates pumping of the heart. An abnormality in the action potential turns into arrhythmia, which may cause sudden death. Studies of arrhythmias using mathematical models are important to reduce the risk of sudden death. In this study, we investigate bifurcations related to the generation of early afterdepolarizations (EADs) in a mathematical model. We clarify the transition process from a normal state to a persistent EAD through a transient EAD while changing only one parameter (multiple of conductance of L-type calcium channel current) value. The dependence of the transient EAD generation on parameters is shown through bifurcation analysis in a [Na]i-parameterized system.

Development of an automated system to measure ion channel currents using a surface-modified gold probe

Artificial lipid bilayer single-channel recording technique has been employed to determine the biophysical and pharmacological properties of various ion channels. However, its measurement efficiency is very low, as it requires two time-consuming processes: preparation of lipid bilayer membranes and incorporation of ion channels into the membranes. In order to address these problems, we previously developed a technique based on hydrophilically modified gold probes on which are immobilized ion channels that can be promptly incorporated into the bilayer membrane at the same time as the membrane is formed on the probes’ hydrophilic area. Here, we improved further this technique by optimizing the gold probe and developed an automated channel current measurement system. We found that use of probes with rounded tips enhanced the efficiency of channel current measurements, and introducing a hydrophobic area on the probe surface, beside the hydrophilic one, further increased measurement efficiency by boosting membrane stability. Moreover, we developed an automated measurement system using the optimized probes; it enabled us to automatically measure channel currents and analyze the effects of a blocker on channel activity. Our study will contribute to the development of high-throughput devices to identify drug candidates affecting ion channel activity.

Energy-induced resonance synchronization in neural circuits

Biological neurons can be approached by using some functional neural circuits, and the biophysical mechanism for signal processing can be explained. Chemical stimulus can adjust the intracellular and extracellular ions concentration, and thus the channel current can be regulated to trigger appropriate firing modes in the neural activities. A physical stimulus often injects kinds of energy, and the energy can be encoded in the components for generating a certain channel current. The energy driving on the cell can be effective to enhance the pumping of ions and mode transition is induced. Based on a simple neural circuit exposed to the external magnetic field, the mode selection is investigated to explore the biophysical mechanism of energy absorption by applying periodic, and stochastic magnetic fields, respectively. The external field energy is encoded in the induction coil of the neural circuit, and the channel current is induced. Two identical neural circuits are exposed to the same magnetic field and the synchronization approach is investigated without synapse coupling. It is found that two neurons in periodic firings can be synchronized under the same periodic or noise-like magnetic field even applying different initials, while intermittent phase lock is induced between two chaotic neurons. Stochastic variation in the external magnetic field can induce noisy induced electromotive force (IEF) and the firing mode is regulated effectively. When both noisy IEF and periodic stimulus are applied, synchronization stability between periodic neurons with initials diversity is enhanced while synchronization approach between chaotic neurons becomes difficult. In addition, the Hamilton energy in each neuron can keep pace with another neuron when complete synchronization is stabilized within a finite transient period. These results provide new insights to know the energy encoding mechanism in neural circuits and neurons exposed to external magnetic field.

Time-dependent expression of ryanodine receptors in sea urchin eggs, zygotes and early embryos

Summary In this work, the presence of calcium-dependent calcium channels and their receptors (RyR) has been investigated in Paracentrotus lividus eggs and early embryos, from unfertilized egg to four-blastomere stages. Electrophysiological recordings of RyR single-channel current fluctuations showed that RyRs are functional during the first developmental events with a maximum at zygote stage, c. 40 min after fertilization, corresponding to the first cleavage. The nature of vertebrate-like RyRs active at this stage was established by specific activation/blockade experiments.