Time-dependent Current Research Articles

Simulations of processes in the power circuit of VL10 (VL-10W) locomotives with traction motors connected in series

Results of simulations of the processes of changing currents and voltages in power circuits of VL10 (VL-10W) locomotives with traction motors, which are connected in series, in cold insulation have been considered. Taking the thermal state of the insulation structures of traction motors of locomotives into account is a new approach in simulations of electrical processes in power circuits. Such a differentiated approach to simulating the electrical processes in power circuits of locomotives became possible when the capacitive components of anchor and pole windings of traction motors in locomotives were studied and taken into account in the equivalent circuits, as well as their temperature dependences. In this work, the results of simulations of the processes of changing currents and voltages in power circuits of VL10 (VL-10W) locomotives during a start from rest in the case of series connection of traction motors with insulation temperature of their anchor and pole windings equal to 20°C. The results of simulations are shown as graphic time dependences of currents and voltages in the main elements of a locomotive power circuit.

Rapid Oceanic Response to Tropical Cyclone Oli (2010) over the South Pacific

ABSTRACTThe effect of Tropical Cyclone Oli (2010) on the ocean is investigated using a variety of measurements. In situ temperature measurements on the cyclone track are available via the Centre de Recherches Insulaires et Observatoire de l’Environnement (CRIOBE) array of probes. This reflects an extreme fluctuation of the temperature some 18 h after the cyclone, lasting only 12 h and exceeding 3°C in amplitude. This study interprets this extreme fluctuation in terms of enhanced mixing associated with the time-dependent inertial currents due to the cyclonic winds. The authors show, using Lagrangian simulations, that this rapid event is compatible with the severe length-scale shortening observed in Lagrangian simulations.

Momentum conservation in a relativistic engine

In a previous paper we have shown that Newton’s third law cannot strictly hold in a distributed system of which the different parts are at a finite distance from each other. This is due to the finite speed of signal propagation which cannot exceed the speed of light in vacuum, which in turn means that when summing the total force in the system the force does not add up to zero. This was demonstrated in a specific example of two current loops with time-dependent currents, the above analysis led to the suggestion of a relativistic engine. Since the system is affected by a total force for a finite period of time this means that the system acquires momentum, the question then arises if we need to abandon the law of momentum conservation. In this paper we make a detailed calculation and show that any momentum gained by the material part of the system is equal in magnitude and opposite in direction to the momentum gained by the electromagnetic field. Hence the total momentum of the system is conserved.

Leakage current phenomena in Mn-doped Bi(Na,K)TiO3-based ferroelectric thin films

Mn-doped 80(Bi0.5Na0.5)TiO3-20(Bi0.5K0.5)TiO3 thin films were fabricated by chemical solution deposition on Pt/TiO2/SiO2/Si substrates. Steady state and time-dependent leakage current were investigated from room temperature to 180 °C. Undoped and low-doped films showed space-charge-limited current (SCLC) at high temperatures. The electric field marking the transition from Ohmic to trap-filling-limited current increased monotonically with Mn-doping. With 2 mol. % Mn, the current was Ohmic up to 430 kV/cm, even at 180 °C. Modeling of the SCLC showed that all films exhibited shallow trap levels and high trap concentrations. In the regime of steady state leakage, there were also observations of negative differential resistivity and positive temperature coefficient of resistivity near room temperature. Both of these phenomena were confined to relatively low temperatures (below ∼60 °C). Transient currents were observed in the time-dependent leakage data, which was measured out to several hundred seconds. In the undoped films, these were found to be a consequence of oxygen vacancy migration modulating the electronic conductivity. The mobility and thermal activation energy for oxygen vacancies was extracted as μion ≈ 1.7 × 10−12 cm2 V−1 s−1 and EA,ion ≈ 0.92 eV, respectively. The transient current displayed different characteristics in the 1 mol. % Mn-doped films which were not readily explained by oxygen vacancy migration.

Properties of slow traps of ALD Al2O3/GeOx/Ge nMOSFETs with plasma post oxidation

The realization of Ge gate stacks with a small amount of slow trap density as well as thin equivalent oxide thickness and low interface state density (Dit) is a crucial issue for Ge CMOS. In this study, we examine the properties of slow traps, particularly the location of slow traps, of Al2O3/GeOx/n-Ge and HfO2/Al2O3/GeOx/n-Ge MOS interfaces with changing the process and structural parameters, formed by atomic layer deposition (ALD) of Al2O3 and HfO2/Al2O3 combined with plasma post oxidation. It is found that the slow traps can locate in the GeOx interfacial layer, not in the ALD Al2O3 layer. Furthermore, we study the time dependence of channel currents in the Ge n-MOSFETs with 5-nm-thick Al2O3/GeOx/Ge gate stacks, with changing the thickness of GeOx, in order to further clarify the position of slow traps. The time dependence of the current drift and the effective time constant of slow traps do not change among the MOSFETs with the different thickness GeOx, demonstrating that the slow traps mainly exist near the interfaces between Ge and GeOx.

Double relaxation via AdS/CFT

We exploit the AdS/CFT correspondence to investigate thermalization in an N=2 strongly coupled gauge theory including massless fundamental matter (quark). More precisely, we consider the response of a zero temperature state of the gauge theory under influence of an external electric field which leads to a time-dependent current. The holographic dual of the above set-up is given by introducing a time-dependent electric field on the probe D7-brane embedded in an AdS5×S5 background. In the dual gravity theory an apparent horizon forms on the brane which, according to AdS/CFT dictionary, is the counterpart of the thermalization process in the gauge theory side. We classify different functions for time-dependent electric field and study their effect on the apparent horizon formation. In the case of pulse functions, where the electric field varies from zero to zero, apart from non-equilibrium phase, we observe the formation of two separate apparent horizons on the brane. This means that the state of the gauge theory experiences two different temperature regimes during its time evolution.

Time-dependent simulation of particle and displacement currents in THz graphene transistors

Although time-independent models provide very useful dynamical information with a reduced computational burden, going beyond the quasi-static approximation provides enriched information when dealing with terahertz (THz) frequencies. In this work, the THz noise of dual-gate graphene transistors with DC polarization is analyzed from a careful simulation of the time-dependent particle and displacement currents. From such currents, the power spectral density (PSD) of the total current fluctuations are computed at the source, drain and gate contacts. The role of the lateral dimensions of the transistors, the Klein tunneling and the positive–negative energy injection on the PSD are analyzed. Through the comparison of the PSD with and without band-to-band tunneling and graphene injection, it is shown that the unavoidable Klein tunneling and positive–negative energy injection in graphene structures imply an increment of noise without similar increment on the current, degrading the (either low or high frequency) signal-to-noise ratio. Finally, it is shown that the shorter the vertical height (in comparison with the length of the active region in the transport direction), the larger the maximum frequency of the PSD. As a byproduct of this result, an alternative strategy (without length scaling) to optimize the intrinsic cut-off frequency of graphene transistors is envisioned.

(Keynote) Electrochemistry at Regular and Random Arrays of Nano-Disk Electrodes

Electrochemical microdisk arrays provide great analytical improvement essentially by increasing the signal-to-noise (S/N) ratio of electrochemical experiments. Indeed, in electrochemistry the minimum current noise of electrochemical origin mostly stems from the electrode capacitance so that the S/N value is drastically increased upon minimizing the electrode surface area[1]. In an electrochemical array performing under conditions when diffusion occurs over the whole array surface area A array the Faradaic current is proportional to A array while the capacitance of the array is proportional to the surface area of its N disk disk micro- or nanoelectrodes of radius r 0, so that the S/N value increases upon increasing the area of inactive sections relative to that of the active ones: S/N ≈ A array/(N diskπr 0 2)[1]. However, present theories allowing the precise prediction/rationalization of electrochemical responses of electrode arrays rely on a model we developed ca thirty years ago based on hypothetical arrays consisting of cylindrical unit cells[2]. Indeed, at the time numerical capabilities could not allow developing theory covering realistic arrays, so it was intuitively accepted that the “cylindrical unit cell” model was representing an ideal framework describing the behavior of electrochemical arrays despite that it is impossible to pave regularly a plane with unit cells having a circular section. Doing so involves significant overlap between the unit cells and leaves uncovered a non-negligible fraction of the array surface. This is easily evident from basic geometry for the squared and hexagonal arrays but is even worse for irregular or random arrays. Since this seminal work was published, many interesting other ones have followed with the aim of establishing effective conversions between real arrays and their “cylindrical equivalents” but none has been able to proceed beyond reasonable intuition to validate the conversion processes proposed[3]. In the present lecture we will establish quantitatively, based on analytical theory and on the outcome of 3-dimension Brownian simulations that “cylindrical equivalents” models can be developed to account for the behavior of regular arrays[4] as well as of irregular ones[5]. Indeed, these two works establish that in all cases, predictions based on “cylindrical equivalents” are correct within a maximum 10% error on chronoamperometric currents when the time-dependent currents are measured on the plateau of a redox wave and in absence of any ohmic drop. This remains true for any electrochemical method (e.g., voltammetry) even in the presence of ohmic drop but only for regular arrays (hexagonal or squared). Indeed in both arrays, the “cylindrical unit cells equivalents” cross-section surface area are identical so as at any time or potential all disk electrodes experience the same current density which ensures that the events in each unit cell are identical. Conversely, in the case of random arrays each unit cell is specific. This is evident upon considering the outcome of Voronoi construction of unit elements around each disk electrode. Each one has a cross-section surface area which depends on the proximity between the disk electrode it includes and its neighboring ones. As such, when the disk electrodes potential is not extremely rapid (viz., the analyte concentration is not governed by Nernst’s law) and there is possibly ohmic drop the analyte surface concentration depends on the current density in the unit cell, viz., on its cross-section surface area. Conversely, when the disk electrodes potential is poised onto the plateau of the investigated redox wave, the analyte concentration at its surface is nihil which eliminates the influence of the current density. Under such conditions, the dimensionless chronoamperometric response, I Array(t), of the whole array is predicted within a relative accuracy better than a few percent by a simple weighted summation of the responses, I cell(t), of each of its independent equivalent cylindrical unit cells.This allows an easy and quick prediction of I Array(t) since I cell(t) functions are obtained under simple analytical form as a function of r. to afford the real array current value, i Array(t). Indeed, I Array(t) is directly related to this latter one through a simple normalization involving its short-time, i array 0(t), and long-time current limits, i array ∞(t), which are achievable experimentally or can be predicted through an analytical law. References C. Amatore, in Physical Electrochemistry: Principles, Methods and Applications; (Eds: I. Rubinstein), M. Dekker, New York 1995; Chapter 4.C. Amatore, J.-M. Savéant and D. Tessier, J. Electroanal. Chem., 147, 39-51 (1983).For one recent contribution, see e.g.: S.R. Belding and R. G. Compton, J. Phys. Chem. C, 114 , 8309-8319 (2010).O. Sliusarenko, A. Oleinick, I. Svir and C. Amatore, Electroanalysis, 27, 980-991 (2015).O. Sliusarenko, A. Oleinick, I. Svir and C. Amatore, ChemElectroChem, in press.

Electromagnetic processes in power transformers with vector control

One possible circuit of a power transformer with vector control is considered. Initial statements of the electromagnetic analysis of transformers are given. An algorithm for determining the voltage and current time dependences, as well as characteristics ones, is described. The dependences between the power transformer characteristics with vector control and the control parameters are shown by the example of the transformer with a nominal power of 16 MV A and nominal supply voltage of 110 kV. The conclusion is drawn that minimum power losses are present at a certain combination of control parameters. The time dependences of current and voltage power keys involved in the transformer of active converters, which result from the mathematical simulation in MATLAB and Simulink, are presented. The effectiveness of the proposed model is evaluated.

On the front conditions for gravity currents in channels of general cross-section

We consider the propagation of a high-Reynolds-number gravity current in a horizontal channel with general cross-section whose width is \(f(z), 0 \le z\le H\), and the gravity acceleration g acts in \(-z\) direction. (The classical rectangular cross-section is covered by the particular case \(f(z) =\) const.) We assume a two-layer system of homogeneous fluids of constant densities \(\rho _{c}\) (current, of height \(h 0, \alpha \ge 0, 0< z \le H\)). Next, we investigate the connection of the steady-state results with the time-dependent current, and show that in a lock-released current the rate of dissipation of the system is equal to, or larger than, that obtained for Fr corresponding to the conditions at the nose of the current. The results and insights of this study cover a wide range of cross-section geometry and apply to both Boussinesq and non-Boussinesq systems; they reveal a remarkable robustness of Fr as a function of \(\varphi \).

Single Nanoparticle Translocation Through Chemically Modified Solid Nanopore.

The nanopore sensor as a high-throughput and low-cost technology can detect single nanoparticle in solution. In the present study, the silicon nitride nanopores were fabricated by focused Ga ion beam (FIB), and the surface was functionalized with 3-aminopropyltriethoxysilane to change its surface charge density. The positively charged nanopore surface attracted negatively charged nanoparticles when they were in the vicinity of the nanopore. And, nanoparticle translocation speed was slowed down to obtain a clear and deterministic signal. Compared with previous studied small nanoparticles, the electrophoretic translocation of negatively charged polystyrene (PS) nanoparticles (diameter ~100 nm) was investigated in solution using the Coulter counter principle in which the time-dependent nanopore current was recorded as the nanoparticles were driven across the nanopore. A linear dependence was found between current drop and biased voltage. An exponentially decaying function (td ~ e−v/v0) was found between the duration time and biased voltage. The interaction between the amine-functionalized nanopore wall and PS microspheres was discussed while translating PS microspheres. We explored also translocations of PS microspheres through amine-functionalized solid-state nanopores by varying the solution pH (5.4, 7.0, and 10.0) with 0.02 M potassium chloride (KCl). Surface functionalization showed to provide a useful step to fine-tune the surface property, which can selectively transport molecules or particles. This approach is likely to be applied to gene sequencing.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1255-6) contains supplementary material, which is available to authorized users.

Transient currents of a single molecular junction with a vibrational mode

By using a propagation scheme for current matrices and an auxiliary mode expansion method, we investigate the transient dynamics of a single molecular junction coupled with a vibrational mode. Our approach is based on the spinless Anderson–Holstein model and the dressed tunnelling approximation for the electronic self-energy in the polaronic regime. The time-dependent currents after a sudden switching on the tunnelling to leads, an abrupt upward step bias pulse and a step potential on the quantum dot are calculated. We show that the strong electron–phonon interaction greatly influences the nonlinear response properties of the system, and gives rise to interesting characteristics on the time traces of transient currents.

Highly accurate, inexpensive procedures for computing theoretical chronoamperometric currents at single straight electrode edges and at single microband electrodes

Theoretical considerations of potential step chronoamperometry for electrochemical systems involving straight electrode edges lead to a number of analytical or semi-analytical expressions, or special functions, describing current-time dependences. Unfortunately the functions are hard to evaluate accurately on a computer, due to numerical difficulties or high computational costs. In this work computationally inexpensive procedures have been developed, for two special functions describing chronoamperometry at a single straight edge and for one special function expressing chronoamperometric current at a single microband electrode (two straight edges). The concept of the minimax approximation has been employed. The procedures are highly accurate, ensuring relative errors close to, or even smaller than 10− 16, which is the machine accuracy for standard double precision variables. In addition, computing a single function value requires less than a microsecond of the processor time on currently available personal computers. The procedures can be useful for the purposes of experimental data analysis, and for the testing/validation of diverse mathematical and numerical modelling techniques designed for electroanalytical chemistry.

HERG Protein Plays a Role in Moxifloxacin-Induced Hypoglycemia.

The purpose of this study was to investigate the effect of moxifloxacin on HERG channel protein and glucose metabolism. HERG expression was investigated using immunohistochemistry. The whole-cell patch clamp method was used to examine the effect of moxifloxacin on HERG channel currents. A glucose tolerance test was used to analyze the effects of moxifloxacin on blood glucose and insulin concentrations in mice. Results show that HERG protein was expressed in human pancreatic β-cells. Moxifloxacin inhibited HERG time-dependent and tail currents in HEK293 cells in a concentration-dependent manner. The IC50 of moxifloxacin inhibition was 36.65 μmol/L. Moxifloxacin (200 mg/kg) reduced blood glucose levels and increased insulin secretion in wild-type mice at 60 min after the start of the glucose tolerance test. In contrast, moxifloxacin did not significantly alter blood glucose and insulin levels in HERG knockout mice. Serum glucose levels increased and insulin concentrations decreased in HERG knockout mice when compared to wild-type mice. The moxifloxacin-induced decrease in blood glucose and increase in insulin secretion occurred via the HERG protein; thus, HERG protein plays a role in insulin secretion.

Quantum power functional theory for many-body dynamics.

We construct a one-body variational theory for the time evolution of nonrelativistic quantum many-body systems. The position- and time-dependent one-body density, particle current, and time derivative of the current act as three variational fields. The generating (power rate) functional is minimized by the true current time derivative. The corresponding Euler-Lagrange equation, together with the continuity equation for the density, forms a closed set of one-body equations of motion. Space- and time-nonlocal one-body forces are generated by the superadiabatic contribution to the functional. The theory applies to many-electron systems.

Performance change of few layer black phosphorus transistors in ambient

Transistors were fabricated based on mechanical exfoliated few layer black phosphorus (BP) flakes, and performance change of these devices exposed to air was explored systematically. BP devices were found to suffer severe performance degradation in ambient conditions, and the field effect mobility drops to less than 1/10 of the original in no more than 120 hours after fabrication. However the current on/off ratio shows completely different time dependent behavior to the published result, i.e. increases with exposure time in air, since the minimum current decreases with exposure time to air, which is probably originated from the decrease of layer number in BP. A model is developed to estimate the bandgap change of BP according to the time dependent minimum current of the BP device.

Single-electron approach for time-dependent electron transport

We developed a new approach to electron transport in mesoscopic systems by using a particular single-particle basis. Although this basis generates redundant many-particle amplitudes, it greatly simplifies the treatment. By using our method for transport of non-interacting electrons, we generalize the Landauer formula for transient currents and time-dependent potentials. The result has a very simple form and clear physical interpretation. As an example, we apply it to resonant tunneling through a quantum dot where the tunneling barriers are oscillating in time. We obtain an analytical expression for the time-dependent (ac) resonant current. However, in the adiabatic limit this expression displays the dc current for zero bias (electron pumping).

Thalamic neuron models encode stimulus information by burst-size modulation.

Thalamic neurons have been long assumed to fire in tonic mode during perceptive states, and in burst mode during sleep and unconsciousness. However, recent evidence suggests that bursts may also be relevant in the encoding of sensory information. Here, we explore the neural code of such thalamic bursts. In order to assess whether the burst code is generic or whether it depends on the detailed properties of each bursting neuron, we analyzed two neuron models incorporating different levels of biological detail. One of the models contained no information of the biophysical processes entailed in spike generation, and described neuron activity at a phenomenological level. The second model represented the evolution of the individual ionic conductances involved in spiking and bursting, and required a large number of parameters. We analyzed the models' input selectivity using reverse correlation methods and information theory. We found that n-spike bursts from both models transmit information by modulating their spike count in response to changes to instantaneous input features, such as slope, phase, amplitude, etc. The stimulus feature that is most efficiently encoded by bursts, however, need not coincide with one of such classical features. We therefore searched for the optimal feature among all those that could be expressed as a linear transformation of the time-dependent input current. We found that bursting neurons transmitted 6 times more information about such more general features. The relevant events in the stimulus were located in a time window spanning ~100 ms before and ~20 ms after burst onset. Most importantly, the neural code employed by the simple and the biologically realistic models was largely the same, implying that the simple thalamic neuron model contains the essential ingredients that account for the computational properties of the thalamic burst code. Thus, our results suggest the n-spike burst code is a general property of thalamic neurons.

Time-dependent current of interacting quantum capacitors subjected to large amplitude pulses

We investigate the time-dependent response of an interacting mesoscopic capacitor using the Floquet-Green function formalism applied to a single-level Anderson model. We obtain closed expressions for the current and the occupation valid for arbitrary values of the applied ac potential in the limit of small frequencies. In the noninteracting case, we obtain nonsinusoidal responses when the ac amplitude allows crossings between the dot level and the Fermi energy of the attached reservoir. For interacting electrons treated within the Hartree approximation, we self-consistently calculate the capacitor current as a function of time and find a decrease of the peak amplitudes due to the on-site Coulomb repulsion.

The Effect of Atomic Hydrogen on the Kinetics of Iron Passivation in Neutral Solutions

The current–time dependences recorded upon metal transition from the active to the passive state or at the potential jump within the passive range have been repeatedly studied in numerous works1. There is still no general theoretical description of the passivation kinetics of a freshly formed electrode surface2, but it is clear that there should be a time interval between the stages of dissolution without a passive film and repassivation, within which passive film islets appear and begin to grow. As was noted, the hydrogen charging of iron, nickel, and stainless steels increases the rates of their corrosion, decreasing the resistance against pit formation3,4. The transition kinetics of hydrogen charged metal into the passive state is of certain practical importance and necessary for deep understanding of such phenomena as corrosion cracking, pitting corrosion, and corrosion–erosion wear. The object of this work was to study the passivation kinetics of hydrogen charged iron in borate solutions in a broad range of potential values, including passivity, active–passive transition and prepassivity states of the metal. The experiments were carried out on iron (0.009%С) membranes 100 mm thick in a 0.4 M H3BO3 + x ml 0.1M Na2B4O7 10H2O solution (pH 6.7 and 7.3) deaerated with argon at 20 ± 2°С. Experiments were carried out in a Devanathan–Stachurski cell. The cathodic current i(H) was put on the one (hydrogen charging) side of membrane. The value of i(H) corresponded to a certain hydrogen concentration of the other (working) side of membrane5. To the working side of the membrane, a potential step between the potential of cathodic pretreatment of the electrode surface (E pt) and the E value, at which anodic current transients were, was applied. Potentials are given in the standard hydrogen electrode scale (SHE). In the current transients recorded on iron at the potentials of active–passive transition and complete passivation in a neutral borate buffer (Fig.), one can distinguish three time intervals, which correspond to the formation of primary passive film, the growth (the increase in thickness) of the barrier layer, and the quasi-steady-state dissolution. Hydrogen produces nearly no effect on the growth rate of the barrier layer, but increases several times the dissolution rate of the layer and, hence, decreases the time period that is necessary for attaining the steady state. The effect of hydrogen on dissolution rate of iron at prepassivation potentials is dual in nature. Atomic hydrogen, which desorbs from the bulk metal phase to the surface, decelerates the active dissolution of iron, which results in a decrease in the rate of the total anodic process in the initial time period. The effect is almost independent of hydrogen content in the metal. Starting from a certain time, which depends on the potential and hydrogen content in the metal, hydrogen charged iron is dissolved at a higher rate than is non charged metal. An increase in the concentration of hydrogen in the metal results in an increase in its quasi-steady-state dissolution rate and a decrease in the duration of non-steady-state dissolution. This effect is due to the decrease in the surface coverage of the metal with oxygen due to its interaction with atomic hydrogen6. This work was supported by the Russian Foundation for Basic Research, project no. 14-03-00421. REFERENCES 1. D.D. Macdonald, Electrochim. Acta, 56, 1761 (2011). 2. R.W. Staehle, Corros. Sci., 49, 7 (2007). 3. S.I. Pyun, and R.A. Oriani, Corros. Sci., 29, 485 (1989). 4. Y J.G.u, С.S. Zhang, J.L. Luo and P.R. Norton, J. Electrochem. Soc., 150, B68 (2003). 5. A.I. Marshakov, A.A. Rybkina, and T.A. Nenasheva, Protection of metals, 43, 605 (2007). 6. A.I. Marshakov, A.A. Rybkina, M.A. Maleeva, and A.A. Rybkin, Protection of metals and Physical Chemistry of Surfaces, 50, 345 (2014). Figure 1