Change In Total Current Research Articles

Large magnetoresistance in a Co/MoS2/graphene/MoS2/Co magnetic tunnel junction

We demonstrate a large magnetoresistance (MR) in a $\mathrm{Co}/\mathrm{Mo}{\mathrm{S}}_{2}/\mathrm{graphene}/\mathrm{Mo}{\mathrm{S}}_{2}/\mathrm{Co}$ magnetic tunnel junction by means of ab initio transport calculations. A Co electrode turns out to be an excellent spin injector for a $\mathrm{Mo}{\mathrm{S}}_{2}/\mathrm{graphene}/\mathrm{Mo}{\mathrm{S}}_{2}$ barrier. The transmission spectrum, current-voltage characteristics, spin injection efficiency, and magnetoresistance are calculated for the modeled device at various bias voltages in the parallel and antiparallel magnetic configurations. A remarkable change in the transmission spectrum and a subsequent change in total current through the junction have been observed, when the relative magnetic orientations of the electrodes are altered. The huge change in current due to the change in the relative magnetic orientation of the Co electrodes produces a high magnetoresistance up to $1270%$. The obtained values of the device parameters clearly indicate that a $\mathrm{Mo}{\mathrm{S}}_{2}/\mathrm{graphene}/\mathrm{Mo}{\mathrm{S}}_{2}$ heterostructure would be an excellent compound for highly efficient spin-valve device applications.

EXPERIMENTAL STUDY OF DISTRIBUTION OF PERTURBATIONS FROM THE LITHOSPHERE TO IONOSPHERE AT THE EXAMPLE OF UNDERGROUND NUCLEAR EXPLOSIONS AND EARTHQUAKES

Lithosphere-atmospheric-ionospheric relations have been investigated at the example of the perturbations propagation from the lithosphere to ionosphere during underground nuclear explosions at the Semipalatinsk test site and two earthquakes (Mb = 3.5 and Mb = 3.6) near Almaty. Simultaneously, seven days prior to the earthquake the abnormal effects in variations of intensity of a gamma-ray flux, temperatures, acoustic impulses and the Doppler frequency shift of ionospheric signal are registered by a complex of the measuring equipment installed in the mountain area. A retrospective analysis of the recordings of the Doppler frequency shift of ionospheric signal variations during the UNEs at the Semipalatinsk test site detected disturbances in the DFS records 15–18 minutes after the explosion and the response of ionosphere to the acoustic wave. The anomalous effects recorded in ionosphere when UNE radioactive products penetrated the atmosphere and when gamma-ray flux increased prior to earthquake, apparently have a common mechanism for disturbances perturbation to ionosphere, namely, the ionization change of the atmospheric boundary layer leading to the total current change between the ionosphere and the Earth.

Multi-amplification of the signal of voltammetric immunosensors: Highly sensitive detection of tumor marker

For sandwich-type voltammetric immunosensor, immunoprobe contains redox species, antibody (as recognition element) and protein (as blocking agent). These proteins on the immunoprobe possess poor conductivity, which is not benefit to the improvement of current response. Herein, a novel way that the redox species was fixed on the substrate was proposed to solve this issue. Redox species (methylene blue) and hemin (a catalyst for H2O2) were immobilized on the substrate. Non-conductive CaCO3 nanoparticles were used to construct the immunoprobe (glucose oxidase as blocking agent), which was regarded as impedance enhancer to hinder the electron transfer for current change (ΔI1). In addition, when immunosensor was immersed in the glucose solution, methylene blue can be degraded by the synergism of glucose oxidase and hemin, which further increased current change (ΔI2). The total current change (ΔI) of this immunosensor was the sum of ΔI1 and ΔI2. Under optimum conditions, the developed immunosensor was able to determine carbohydrate antigen 199 with good selectivity, high sensitivity and reproducibility.

Comparison of gate and drain current detection of hydrogen at room temperature with AlGaN∕GaN high electron mobility transistors

Pt-gated AlGaN∕GaN high electron mobility transistors can be used as room-temperature hydrogen gas sensors at hydrogen concentrations as low as 100ppm. A comparison of the changes in drain and gate current-voltage (I-V) characteristics with the introduction of 500ppm H2 into the measurement ambient shows that monitoring the change in drain-source current provides a wider gate voltage operation range for maximum detection sensitivity and higher total current change than measuring the change in gate current. However, over a narrow gate voltage range, the relative sensitivity of detection by monitoring the gate current changes is up to an order of magnitude larger than that of drain-source current changes. In both cases, the changes are fully reversible in <2–3min at 25°C upon removal of the hydrogen from the ambient.

Current transients in extrinsic photoconductors: comprehensive analytical description of initial response

We revisit the theory of the transients in low-temperature extrinsic photoconductors, with emphasis on the initial fast component response. Application of a photon-generation step launches a traveling zone boundary between part of the device where, in the short term, a quasi-equilibrium has been reached and a part where the carrier concentration is still growing. As the boundary passes, the exponentially slowing growth of carriers is abruptly terminated. The time to reach this quasi-equilibrium depends on the sample length and the carrier drift velocity rather than on the carrier lifetime. We note restricting errors in earlier analyses and produce an improved formula for the subsequent slow fraction of the total current change by including carrier diffusion. Comparison of numerical and analytical results suggests that measurement of the fast or slow fraction of the response can provide a highly accurate measure of the mobility-lifetime (μτ) product.

Ionic diffusion in transverse tubules of cardiac ventricular myocytes.

We have estimated the rate of diffusion of calcium ions in the transverse tubules of isolated cardiocytes by recording changes in peak calcium current (ICa) caused by rapid changes of the extracellular calcium concentration ([Ca]o) at various intervals just preceding activation of ICa. Isolated ventricular cells of guinea pig heart and atrial cells from rabbit heart were voltage-clamped (whole cell patch), superfused at a high flow rate, and stimulated continuously with depolarizing pulses (0.5 Hz, 200- or 20-ms pulses from a holding potential of -45 or -75 mV to 0 mV). In ventricular cells, the change in peak ICa following a sudden change of [Ca]o increased rapidly as the delay between the solution change and depolarization was increased, up to a delay of approximately 75 ms [time constant (tau) approximately 20 ms, 30-40% of total current change), and then increased more slowly (tau approximately 200 ms, 60-70% of total current change); 400-500 ms were needed to achieve 90% of the total current increase. In atrial cells, a clear separation into two phases was not possible and 90% of the current change occurred within 85 ms. The slow phase of current change, which was unique to the ventricular cells, presumably reflects the slow equilibration of ions between the bulk perfusate and the lumina of the transverse tubules. If the lengths of the transverse tubules were equal to the cell thickness, the slow rate of change of current would be consistent with an apparent diffusion coefficient for calcium ions of 0.95 x 10(-6) cm2/s, considerably smaller than the value in bulk solution (7.9 x 10(-6) cm2/s). Most likely, this discrepancy is due to a high degree of tortuosity in the transverse tubular system in guinea pig ventricular cells or possibly to ion binding sites within the tubular membranes and glycocalyx.

Application of an ionization chamber as a gas sensor

A potentially promising approach to using an ionization chamber as a gas sensor is operating it in an alternating electric field. The resulting selectivity can hardly be compared to that of an ion mobility spectrometer, but significantly simpler construction of the chamber and operating principle itself deserve attention and offer possibilities for further optimization. It is shown that by using suitable operating conditions, the chamber will operate in a mode that produces the greatest change in total current after formation of less mobile product ions. Theoretical results are also experimentally verified. The response is fast and reversible. Partial selectivity of the sensor is due to high proton or electron affinity of measured compounds.