Time-dependent Current Research Articles

Time-dependent thermoelectric transport in nanosystems: Reflectionless Luttinger field approach

Recently the Luttinger field approach was proposed by Eich et al. in Phys. Rev. B 90, 115116 (2014). as a way to simulate switching on a temperature gradient across a nanoscale device initially in thermal equilibrium. The time-dependent particle and heat currents can then be calculated by propagating the initial equilibrium state of the system in time. Unfortunately, applying a uniform Luttinger field in the whole of a lead causes a discrepancy between steady-state currents in the long time limit and those predicted by the Landauer-B\uttiker formulas as well as artifacts at short times. Here we propose a modified approach where the Luttinger field gradually reaches its final value across a transition region. If the length of the transition region is sufficient, the electrons move through without reflecting. In this way the correct energy distribution of electrons originating from such a lead, corresponding to the new temperature, is established in the scattering region. Our approach is tested on a single quantum dot and a parallel double quantum dot system.

Non-equilibrium charge and spin transport in superconducting-ferromagnetic-superconducting point contacts.

The conventional Josephson effect may be modified by introducing spin-active scattering in the interface layer of the junction. Here, we discuss a Josephson junction consisting of two s-wave superconducting leads coupled over a classical spin that precesses with the Larmor frequency due to an external magnetic field. This magnetically active interface results in a time-dependent boundary condition with different tunnelling amplitudes for spin-up and -down quasi-particles and where the precession produces spin-flip scattering processes. As a result, the Andreev states develop sidebands and a non-equilibrium population that depend on the details of the spin precession. The Andreev states carry a steady-state Josephson charge current and a time-dependent spin current, whose current-phase relations could be used to characterize the precessing spin. The spin current is supported by spin-triplet correlations induced by the spin precession and creates a feedback effect on the classical spin in the form of a torque that shifts the precession frequency. By applying a bias voltage, the Josephson frequency adds another complexity to the situation and may create resonances together with the Larmor frequency. These Shapiro resonances manifest as torques and, under suitable conditions, are able to reverse the direction of the classical spin in sub-nanosecond time. Another characteristic feature is the subharmonic gap structure in the DC charge current displaying an even-odd effect attributable to precession-assisted multiple Andreev reflections.This article is part of the theme issue 'Andreev bound states'.

Insight of electrolyte-free voltammetry at microelectrodes

Electrode reactions without deliberately adding supporting electrolyte are complicated with electric migrations associated with redox reactions, formation of double layers and ion–ion interactions relevant to electrode reactions. The complications can be realized quantitatively through voltammetry at various sized microelectrodes, partly because of negligibly small solution resistance effects and partly because of steady-state voltammograms, which can be analyzed theoretically without capacitive time-dependent current. The present review deals with (i) techniques of fabrication of many sized microelectrodes, (ii) conditions of keeping low electrolyte concentrations, (iii) ionic contribution of forming double layers, (iv) participation in counter ions for electrode reactions and (v) change in ionic environment by redox reactions.

Strange non-chaotic attractors in spin valve systems

The current-driven magnetization dynamics in spin torque oscillators is investigated because of its high potential for high-frequency applications. The system consists of a pinned layer with a fixed magnetization and a single-domain free layer, such that it is governed by the Landau-Lifshitz-Gilbert-Slonczewski equation. In particular, we study the effect of a time-dependent quasi-periodic current. We numerically characterize the dynamical behavior of the system by monitoring the Lyapunov exponents, and by calculating the Fourier spectra. We find a rather complicated landscape of sometimes closely intermingled chaotic and non-chaotic areas in the parameters space. Finally, we compute a phase diagram of the existence of the strange non-chaotic attractors.

Characterization and Performance of the Cananea Near-infrared Camera (CANICA)

We present details of characterization and imaging performance of the Cananea Near-infrared Camera (CANICA) at the 2.1 m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, México. CANICA has a HAWAII array with a HgCdTe detector of 1024 × 1024 pixels covering a field of view of 5.5 × 5.5 arcmin2 with a plate scale of 0.32 arcsec/pixel. The camera characterization involved measuring key detector parameters: conversion gain, dark current, readout noise, and linearity. The pixels in the detector have a full-well-depth of 100,000 e− with the conversion gain measured to be 5.8 e−/ADU. The time-dependent dark current was estimated to be 1.2 e−/sec. Readout noise for correlated double sampled (CDS) technique was measured to be 30 e−/pixel. The detector shows 10% non-linearity close to the full-well-depth. The non-linearity was corrected within 1% levels for the CDS images. Full-field imaging performance was evaluated by measuring the point spread function, zeropoints, throughput, and limiting magnitude. The average zeropoint value in each filter are J = 20.52, H = 20.63, and K = 20.23. The saturation limit of the detector is about sixth magnitude in all the primary broadbands. CANICA on the 2.1 m OAGH telescope reaches background-limited magnitudes of J = 18.5, H = 17.6, and K = 16.0 for a signal-to-noise ratio of 10 with an integration time of 900 s.

Electrochemistry of surface-confined enzymes: Inspiration, insight and opportunity for sustainable biotechnology

Redox enzymes can generate electricity from sunlight and produce valuable chemicals, including fuels, from low-value materials. When an electrode takes the role of an enzyme's natural redox partner, these properties inspire creative approaches to generate renewable resources. Enzymatic fuel cells produce electricity, enzyme electrosynthesis drives chemical transformations and biophotovoltaics harness solar energy. Underpinning rational development of these applications, time-dependent currents resolved by dynamic electrochemistry provide quantitative insight into the determinants of enzyme activity. This article reviews popular and emerging routes to sequester, study and exploit redox enzymes on two- and three-dimensional electrode materials. Studies are highlighted that draw on synergies of these different aspects of enzyme electrochemistry.

Orchestrating TRANSP Simulations for Interpretative and Predictive Tokamak Modeling with OMFIT

TRANSP simulations are being used in the OMFIT workflow manager to enable a machine-independent means of experimental analysis, postdictive validation, and predictive time-dependent simulations on the DIII-D, NSTX, JET, and C-MOD tokamaks. The procedures for preparing input data from plasma profile diagnostics and equilibrium reconstruction, as well as processing of the time-dependent heating and current drive sources and assumptions about the neutral recycling, vary across machines, but are streamlined by using a common workflow manager. Settings for TRANSP simulation fidelity are incorporated into the OMFIT framework, contrasting between-shot analysis, power balance, and fast-particle simulations. A previously established series of data consistency metrics are computed such as comparison of experimental versus calculated neutron rate, equilibrium stored energy versus total stored energy from profile and fast-ion pressure, and experimental versus computed surface loop voltage. Discrepancies between data consistency metrics can indicate errors in input quantities such as electron density profile or , or indicate anomalous fast-particle transport. Measures to assess the sensitivity of the verification metrics to input quantities are provided by OMFIT, including scans of the input profiles and standardized postprocessing visualizations. For predictive simulations, TRANSP uses GLF23 or TGLF to predict core plasma profiles, with user-defined boundary conditions in the outer region of the plasma. International Tokamak Physics Activity (ITPA) validation metrics are provided in postprocessing to assess the transport model validity. By using OMFIT to orchestrate the steps for experimental data preparation, selection of operating mode, submission, postprocessing, and visualization, we have streamlined and standardized the usage of TRANSP.

Gain-of-Function of TMEM16E/ANO5 Scrambling Activity Caused by a Mutation Associated with the Bone Genetic Disease Gnathodiaphyseal Dysplasia

Members of the TMEM16 or anoctamin membrane protein family are involved in a variety of functions that include ion transport, phospholipid scrambling and regulation of other membrane proteins. In particular, TMEM16A, 16B and 16F have a clear plasma membrane localization but while 16A and 16B work as ‘pure’ ion channels, TMEM16F shows both ion channel and scramblase activities. Recent data suggest that also TMEM16E, the closest relative of TMEM16F, may work as a phospholipid scramblase, although a direct confirmation is missing. TMEM16E is highly expressed in bone tissue and skeletal muscle and different mutations in the human TMEM16E (ANO5) gene are associated with the bone disease gnathodiaphyseal dysplasia (GDD) or to different forms of muscular dystrophy (LGMD2L, limb-girdle muscular dystrophy-2l and distal MMD3, miyoshi muscular dystrophy-3). Our data show that human TMEM16E, when overexpressed in mammalian cell lines, displays partial plasma membrane localization and give rise to phospholipid scrambling as well as non-selective ionic currents with slow time-dependent activation at highly depolarized membrane potentials and in presence of high intracellular Ca2+. We address the effect of the GDD-causing mutation T513I, located in the second extracellular loop, on TMEM16E and we show phospholipid scrambling activity and large time-dependent ion currents even at low cytosolic Ca2+ concentrations. Our data provide the first direct demonstration of Ca2+-dependent current and phospholipid scrambling activity for TMEM16E and suggest a gain-of-function phenotype related to a GDD mutation.

Time-dependent framework for energy and charge currents in nanoscale systems

The calculation of time-dependent charge and energy currents in nanoscale systems is a challenging task. Nevertheless it is crucial for gaining a deep understanding of the relevant processes at the nanoscale. We extend the auxiliary-mode approach for time-dependent charge transport to allow for the calculation of energy currents for arbitrary time dependencies. We apply the approach to two illustrative examples, a single-level system and a benzene ring, demonstrating its usefulness for a wide range of problems beyond simple toy models, such as molecular devices.

Path to the Desensitized State of Ligand-Gated Ion Channels: Why Are Inhibitory and Excitatory Receptors Different?

The family of pentameric ligand-gated ion channels (pLGICs) includes both inhibitory and excitatory receptors. Electrophysiological methods have explored the time-dependent ion currents induced by their neurotransmitter agonists. Kinetic modeling requires a minimum of three conformational states: resting, active, and desensitized. However, current traces of inhibitory and excitatory pLGICs differ substantially. Reproducing their basic features requires different state connectivity: whether the desensitized state is accessed from the resting or active state. It is surprising that a property as fundamental as state connectivity would differ within the same family. So, we explore the possibility that the connectivity is the same, but corresponding states differ in function: Analogous states on the free energy landscape have similar structure, but differ in ion conductivity, free energies, and agonist binding affinities. This hypothesis is tested using a kinetic model in which agonist and anesthetics modulate the receptor free energy landscape by adsorbing to the membrane in which the receptor is embedded. It was previously shown that even with only three states, the complex behavior observed for GABAAR is reproduced, including its response to anesthetics. It is demonstrated here that this hypothesis accounts for an important difference between inhibitory and excitatory receptors: their opposite responses to inhalation anesthetics.

Design and analysis of wave energy buoy integrated with seaweed farming

Farming facilities in offshore face natural disasters caused by tropical storms. Without reliable design of mooring system, the wave load on the structure can easily damage it during a natural disaster event that could lead to unacceptable economic loss. Mooring failure represents the most common reason for the loss of ocean devices due to environmental load action and inappropriate design; because the developers concentrate much of their efforts on optimising the efficiency of the device and not enough attention is paid to the design of the mooring system. Thus, ensuring the security and safe deployment of very large floating structure system is very important issue for industrial marine farm and ocean energy activities. This paper presents design and analysis of wave energy integrated with seaweed farming system. The static model will predict the tension and tilt at each mooring component, including the anchor, for which the safe mass will be evaluated in terms of the vertical and horizontal tensions. Predictions can be saved to facilitate mooring motion correction. Time dependent currents can be entered to predict the dynamic response of the mooring.

Analysis of current drift on p-channel pH-Sensitive SiNW ISFET by capacitance measurement

The mechanism of drift effect in pH-sensitive silicon nanowire (SiNW) ion sensitive field effect transistor (ISFET) is comprehensively studied by measuring the time-dependent drain current (ID) and the gate capacitance (CG) under different liquid-gate biases (VLGs) and pH levels. It was revealed that the origin of the current drift can be divided into three different mechanisms; the bulk ionic diffusion in sensing insulator, the chemical modification of insulator surface, and the oxide etch process induced by hydroxide (OH−) ion. Based on the VLG/pH dependency of current drift and the transient CG variation, it is clearly recognized that the drift of n-type SiNW (n-SiNW) ISFET results from H+ diffusion in the insulator, whereas that of p-type SiNW (p-SiNW) ISFET is caused by temporal chemical modification (hydration) of the insulator, along with the oxide thickness (tox) reduction by OH− ions.

Flow of Deformable Droplets: Discontinuous Shear Thinning and Velocity Oscillations.

We study the rheology of a suspension of soft deformable droplets subjected to a pressure-driven flow. Through computer simulations, we measure the apparent viscosity as a function of droplet concentration and pressure gradient, and provide evidence of a discontinuous shear thinning behavior, which occurs at a concentration-dependent value of the forcing. We further show that this response is associated with a nonequilibrium transition between a "hard" (or less deformable) phase, which is nearly jammed and flows very slowly, and a "soft" (or more deformable) phase, which flows much more easily. The soft phase is characterized by flow-induced time dependent shape deformations and internal currents, which are virtually absent in the hard phase. Close to the transition, we find sustained oscillations in both the droplet and fluid velocities. Polydisperse systems show similar phenomenology but with a smoother transition, and less regular oscillations.

Gain of function of TMEM16E/ANO5 scrambling activity caused by a mutation associated with gnathodiaphyseal dysplasia

Mutations in the human TMEM16E (ANO5) gene are associated both with the bone disease gnathodiaphyseal dysplasia (GDD; OMIM: 166260) and muscle dystrophies (OMIM: 611307, 613319). However, the physiological function of TMEM16E has remained unclear. We show here that human TMEM16E, when overexpressed in mammalian cell lines, displayed partial plasma membrane localization and gave rise to phospholipid scrambling (PLS) as well as non-selective ionic currents with slow time-dependent activation at highly depolarized membrane potentials. While the activity of wild-type TMEM16E depended on elevated cytosolic Ca2+ levels, a mutant form carrying the GDD-causing T513I substitution showed PLS and large time-dependent ion currents even at low cytosolic Ca2+ concentrations. Contrarily, mutation of the homologous position in the Ca2+-activated Cl− channel TMEM16B paralog hardly affected its function. In summary, these data provide the first direct demonstration of Ca2+-dependent PLS activity for TMEM16E and suggest a gain-of-function phenotype related to a GDD mutation.

Quantum transport under ac drive from the leads: A Redfield quantum master equation approach

Evaluating the time-dependent dynamics of driven open quantum systems is relevant for a theoretical description of many systems, including molecular junctions, quantum dots, cavity-QED experiments, cold atoms experiments and more. Here, we formulate a rigorous microscopic theory of an out-of-equilibrium open quantum system of non-interacting particles on a lattice weakly coupled to multiple baths and driven by periodically varying thermodynamic parameters like temperature and chemical potential of the bath. The particles can be either bosonic or fermionic and the lattice can be of any dimension and geometry. Based on Redfield quantum master equation under Born-Markov approximation, we derive a complete set of linear differential equations for equal time two-point correlation functions from which various physical observables, for example, current, can be calculated. Various interesting physical effects, such as resonance, can be directly read-off from the equations. Thus, our theory is quite general gives quite transparent and easy-to-calculate results. We validate our theory by comparing with exact numerical simulations. We apply our method to a generic open quantum system, namely a double-quantum dot coupled to leads with modulating chemical potentials. Two most important experimentally relevant insights from this are : (i) time-dependent measurements of current for symmetric oscillating voltages (with zero instantaneous voltage bias) can point to the degree of asymmetry in the system, and (ii) under certain conditions, time-dependent currents can exceed time-averaged currents by several orders of magnitude, and can therefore be detected even when the average current is below the measurement threshold.

Single-particle emission at finite temperatures

The state of particles injected onto the surface of the Fermi sea depends essentially on the temperature. The pure state injected at zero temperature becomes a mixed state if injected at finite temperature. Moreover the electron source injecting a single-particle state at zero temperature may excite a multi-particle state if the Fermi sea is at finite temperature. Here I unveil a symmetry of the scattering amplitude of a source, which is sufficient to preserve a single-particle emission regime at finite temperatures if such a regime is achieved at zero temperature. I give an example and analyze the effect of temperature on time-dependent electrical and heat currents carried by a single-particle excitation.

A Dual Role for the OsK5.2 Ion Channel in Stomatal Movements and K+ Loading into Xylem Sap.

The roles of potassium channels from the Shaker family in stomatal movements have been investigated by reverse genetics analyses in Arabidopsis (Arabidopsis thaliana), but corresponding information is lacking outside this model species. Rice (Oryza sativa) and other cereals possess stomata that are more complex than those of Arabidopsis. We examined the role of the outward Shaker K+ channel gene OsK5.2. Expression of the OsK5.2 gene (GUS reporter strategy) was observed in the whole stomatal complex (guard cells and subsidiary cells), root vasculature, and root cortex. In stomata, loss of OsK5.2 functional expression resulted in lack of time-dependent outward potassium currents in guard cells, higher rates of water loss through transpiration, and severe slowdown of stomatal closure. In line with the expression of OsK5.2 in the plant vasculature, mutant plants displayed a reduced K+ translocation from the root system toward the leaves via the xylem. The comparison between rice and Arabidopsis show that despite the strong conservation of Shaker family in plants, substantial differences can exist between the physiological roles of seemingly orthologous genes, as xylem loading depends on SKOR and stomatal closure on GORK in Arabidopsis, whereas both functions are executed by the single OsK5.2 Shaker in rice.

The method for detecting defects in movable armature of the signalling relay

Despite significant progress in the development of microelectronic rail automatic systems observed in recent decades, relay-contact devices are still widely used in railway signalling systems, that are fundamental to the safe operation of railways and must perform predictably and reliably.Thus, signalling relays used for safety-critical or safety-related applications in railway signalling systems should be properly maintained and tested to ensure their performing safely and reliably throughout their expected service life.With the purpose of developing a method for detecting defects in movable armature of the signalling relay, the time dependences of transient currents during relays switching have been investigated for relay in various technical conditions: in operable condition, as well as with artificially created defects (bends) of contact springs. The measured data have been analyzed in the time and frequency domain using the wavelet transform modifications (CWT, DWT, DWPT).The analysis of the transient currents was carried out using segmentation of the current characteristics of the relay. The relay transient current at first and third segments which corresponded to unmovable anchor state, increase with time during relay switch-on approximately as the exponential function.The time constants of the relay current were calculated by approximating the measured current-time dependences at the first segment of the current curve by exponential function.The presence of defects in the movable armature of the relay had practically no effect on the values of calculated time constants.However, these values strongly depended on the technical condition of the relay magnetic circuit and the relay coil, as well as on the voltage applied to the coil terminals. This behavior of the relay time constant on the first segment of the relay current characteristic makes it possible to use this parameter to monitor the technical state of the electromagnetic relay system.Defects of the armature and contact springs led to the appearance of additional features at the second segment of the relay transient current, which corresponded to the movement of the armature. The magnitude of these features on the current curve depended on the value of bending of the relay's contact spring. The width and appearance time of the features at the second segment of the current-switching curve correspond to the non-simultaneous switching of the relay contacts. To determine the amplitude (energy) of these features (peaks) on transient current curve, their duration and the times of appearance, the wavelet transform was used. The results of investigations confirmed the possibility of determining the defects of the relay movable armature by using wavelet analysis of the second segment of the relay transient current characteristic.

When can time-dependent currents be reproduced by the Landauer steady-state approximation?

We establish well-defined limits in which the time-dependent electronic currents across a molecular junction subject to a fluctuating environment can be quantitatively captured via the Landauer steady-state approximation. For this, we calculate the exact time-dependent non-equilibrium Green's function (TD-NEGF) current along a model two-site molecular junction, in which the site energies are subject to correlated noise, and contrast it with that obtained from the Landauer approach. The ability of the steady-state approximation to capture the TD-NEGF behavior at each instant of time is quantified via the same-time correlation function of the currents obtained from the two methods, while their global agreement is quantified by examining differences in the average currents. The Landauer steady-state approach is found to be a useful approximation when (i) the fluctuations do not disrupt the degree of delocalization of the molecular eigenstates responsible for transport and (ii) the characteristic time for charge exchange between the molecule and leads is fast with respect to the molecular correlation time. For resonant transport, when these conditions are satisfied, the Landauer approach is found to accurately describe the current, both on average and at each instant of time. For non-resonant transport, we find that while the steady-state approach fails to capture the time-dependent transport at each instant of time, it still provides a good approximation to the average currents. These criteria can be employed to adopt effective modeling strategies for transport through molecular junctions in interaction with a fluctuating environment, as is necessary to describe experiments.

Macro modeling of ion sensitive field effect transistor with current drift

In terms of the application of the ion sensitive field effect transistor (ISFET) fabricated with top-down approached and CMOS-compatible back-end process to integrated circuits, the macro model of the ISFET is required. Although several models have been reported, there is no electrical model that reflects the time-dependent drain current (ID) change (drift effect). We propose the electrical model which can reflect the drift effect and can be expressed by the combination of electrical circuit components. In the proposed model, R1 represents the resistance of the electrolyte and the FET can be approximated by the capacitances C1 (capacitance of pure gate oxide in which hydrogen ions move very slowly) and C2 (capacitance by gate oxide with defects in which hydrogen ions move relatively faster). Furthermore, the movement of hydrogen ions in the defective oxide is represented by R2 and the current drift is modeled as the parallel combination of the C2 and the R2 because the drift effect is strongly related to hydrogen ion movement through defective gate oxide or Helmholtz layer. Consequently, the ISFET with the ID drift can be modeled by the series connection of the R1, the parallel combination of the C2 and the R2, and the C1. Also, The ID calculated by the proposed model is successfully fitted to the measured time-dependent ID of the ISFET.