Electric Current Fluctuations Research Articles

Исследование долговременных флуктуаций тока в электролитических ячейках и туннельных диодах

The paper presents long-term measurement results concerning the Kullback --- Leibler divergence variations for electric current fluctuations in electrolytic cells and relative dispersion variations for electric current fluctuations in tunnel diodes. It is possible to transition from investigating current fluctuations in electrolytic cells to measuring similar fluctuations in tunnel diodes due to the charge carrier mass in diodes being considerably lower than masses of electrolyte ions. This decrease in mass leads to an increase in the sensitivity of the experimental installation. We found that the magnitude spectrum of Kullback --- Leibler divergence variations has a maximum corresponding to a period of 25.25 days (606 h). As for the magnitude spectrum of relative dispersion variations, its maximum is observed at the signal period of 25.88 days (621 h). These periods are close to the sidereal period of the Sun, that is, 25.38 days (609 h). We propose to use tunnel diodes with high peak current values and high direct forward voltage applied in order to increase the sensitivity of the experimental installation

Application of Fractional-Order PI Controllers and Neuro-Fuzzy PWM Technique to Multi-Rotor Wind Turbine Systems

In recent years, the methods of controlling electrical machines have been witnessing increasing development to reduce torque and electric current fluctuations in electrical power generation systems from renewable sources such as wind energy. The generation of electric power from wind plants imposes the need for an efficient and more robust method in order to obtain fewer ripples in active and reactive power. In this work, a new fractional-order proportional-integral (FOPI) controller and intelligent PWM (IPWM) technique are proposed to control an existing asynchronous generator (AG) in variable-speed multi-rotor wind turbines (VSMRWTs). This proposed method depends on combining or using two methods, namely nonlinear area and fractional calculus, to obtain a more robust method and to reduce current and torque ripples. In the framework of this study, the electric power generation system consists of a 1.5 MW AG and VSMRWTs. The AG is controlled using a simpler and easily accomplished method called direct vector control, based on FOPI controllers and the IPWM technique (DVC-FOPI-IPWM). The maximum power point tracking (MPPT) method is used to generate the maximum energy from the VSMRWTs. The proposed DVC-FOPI-IPWM technique is modeled in the Matlab/Simulink platform to obtain good quality current and active power. Simulation results show that the proposed strategy reduces the ripples of torque, current, and active power compared to the classical technique. Moreover, the reduction ratio is about 85%, 99%, and 93.33% for the current, active power, and torque, respectively.

Single-spin qubit magnetic spectroscopy of two-dimensional superconductivity

A single-spin qubit placed near the surface of a conductor acquires an additional contribution to its $1/T_1$ relaxation rate due to magnetic noise created by electric current fluctuations in the material. We analyze this technique as a wireless probe of superconductivity in atomically thin two dimensional materials. At temperatures $T \lesssim T_c$, the dominant contribution to the qubit relaxation rate is due to transverse electric current fluctuations arising from quasiparticle excitations. We demonstrate that this method enables detection of metal-to-superconductor transitions, as well as investigation of the symmetry of the superconducting gap function, through the noise scaling with temperature. We show that scaling of the noise with sample-probe distance provides a window into the non-local quasi-static conductivity of superconductors, both clean and disordered. At low temperatures the quasiparticle fluctuations get suppressed, yet the noise can be substantial due to resonant contributions from collective longitudinal modes, such as plasmons in monolayers and Josephson plasmons in bilayers. Potential experimental implications are discussed.

Electron Waiting Times in a Strongly Interacting Quantum Dot: Interaction Effects and Higher-Order Tunneling Processes.

Distributions of electron waiting times have been measured in several recent experiments and have been shown to provide complementary information compared with what can be learned from the electric current fluctuations. Existing theories, however, are restricted to either weakly coupled nanostructures or phase-coherent transport in mesoscopic conductors. Here, we consider an interacting quantum dot and develop a real-time diagrammatic theory of waiting time distributions that can treat the interesting regime, in which both interaction effects and higher-order tunneling processes are important. Specifically, we find that our quantum-mechanical theory captures higher-order tunneling processes at low temperatures, which are not included in a classical description, and which dramatically affect the waiting times by allowing fast tunneling processes inside the Coulomb blockade region. Our work paves the way for systematic investigations of temporal fluctuations in interacting quantum systems, for example close to a Kondo resonance or in a Luttinger liquid.

INVESTIGATION OF COMPRESSOR START-UP OF CONE DRILLING RIG WITH CURRENT LIMITING FUNCTION

The article deals with the problem of investigation of the system "soft starter- induction motor" for compressing equipment of cone drilling machine. Also refined mathematical model of the system, taking into account the behavior of compressor load, as well as existing working algorithm of the stator current control block is developed. The problems of choice of starting mode of compressing equipment are considered, the necessity of full research of the electric drive system with the methods of numerical modeling is determined. The basic parameters which have to be specified and corrected by the designer of the electromechanical system of the compressor during equipment commissioning are determined. Further, an algorithm for firing angle control of power thyristors, which used in modern soft starters, produced by WEG Company, is implemented. After that, the simulation of the procedure for starting the compressor induction motor using thyristors soft starter with the stator current limiting function is performed. As a result of modeling using application Simulink of software environment ATLAB, the graphs of transients for the most important working parameters, such as stator windings current, shaft rotation speed, load torque and firing angle for thyristors are obtained. The analysis of the obtained results, as a result of which formulated the conclusions on the possibility of using soft starters for the cone drill rig compressors is made. It has been determined that in the case of almost linear behavior of compressor load, the motor starts with a smooth change of speed without significant fluctuations of electric motor stator currents. It is proposed to use the current limiting function for easy starting modes and current control functions with an initial kick of torque.

Different Anomeric Sugar Bound States of Maltose Binding Protein Resolved by a Cytolysin A Nanopore Tweezer.

Conformational changes of proteins are essential to their functions. Yet it remains challenging to measure the amplitudes and time scales of protein motions. Here we show that the cytolysin A (ClyA) nanopore was used as a molecular tweezer to trap a single maltose-binding protein (MBP) within its lumen, which allows conformation changes to be monitored as electrical current fluctuations in real time. In contrast to the current two state binding model, the current measurements revealed three distinct ligand-bound states for MBP in the presence of reducing saccharides. Our analysis reveals that these three states represented MBP bound to different isomers of reducing sugars. These findings contribute to the understanding of the mechanism of substrate recognition by MBP and illustrate that the nanopore tweezer is a powerful, label-free, single-molecule approach for studying protein conformational dynamics under functional conditions.

Effect of specimen size on natural vibration of open hole copper/glass-reinforced epoxy laminate composites

Composite material has attractive applications in electronic devices; glass fiber/copper reinforced epoxy is one completive material in Micro–Electro–Mechanical-Systems (MEMS). Upon operation, mechanical vibration arises from the electrical current fluctuations causing damage and consequently affect its performance. On the other hand, size effect in the strength of a material is referred to as a decrease in the nominal strength of a scaled open hole structure. Therefore, this work aims to study the scaling phenomenon concerning dynamic and vibration for a composite structure used in MEMS devices. At this end, a matrix of specimens with 2, 4, 6, 8, 10, and 12 mm diameter circular holes of copper/laminated glass fiber reinforced epoxy plated have subjected to simple vibration test modal analysis using the free-fallen hammer. A simple finite element model is built to obtain different shape modes which revealed the different mode shapes and Mises stress effect regions, moreover the frequency factor at each mode. The response of the material to free vibration has given different trends with holes. With increasing specimen size, the natural frequencies increase, this is opposite results when increasing the static load. The Finite element results are in good agreement with the published ones. The cantilever boundary condition is reported to be the most satisfied for the lower two modes.

Electrical conductivity and relaxation via colored noise in a hadronic gas

Motivated by the theory of relativistic hydrodynamic fluctuations we make use of the Green-Kubo formula to compute the electrical conductivity and the (second-order) relaxation time of the electric current of an interacting hadron gas. We use the recently developed transport code SMASH to numerically solve the coupled set of Boltzmann equations implementing realistic hadronic interactions. In particular, we explore the role of the resonance lifetimes in the determination of the electrical relaxation time. As opposed to a previous calculation of the shear viscosity we observe that the presence of resonances with lifetimes of the order of the mean-free time does not appreciably affect the relaxation of the electric current fluctuations. We compare our results to other approaches describing similar systems, and provide the value of the electrical conductivity and the relaxation time for a hadron gas at temperatures between T=60 MeV and T=150 MeV.

Non-equilibrium Majorana fluctuations

Non-equilibrium physics of random events, or fluctuations, is a unique fingerprint of a given system. Here we demonstrate that in non-interacting systems with dynamics driven essentially by Majorana states the effective charge , characterizing the electric current fluctuations, is fractional. This is in contrast to non-interacting Dirac systems with the trivial electronic charge . In the Majorana state, however, we predict two different fractional effective charges at low and high energies, and , accessible at low and high bias voltages, respectively. We show that while the low-energy effective charge is sensitive to thermal fluctuations of the current, the high-energy effective charge is robust against thermal noise. A unique fluctuation signature of Majorana fermions is therefore encoded in the high-voltage tails of the electric current noise easily accessible in experiments on strongly non-equilibrium systems even at high temperatures.

Application of Electrical Measurements to Investigation of Solar Cell Microstructure Defects

The research is aimed to the investigation of the microstructure defects in the silicon and the thin-film CIGS solar cells. These defects have their origin mainly in the technological process of a production but they can be caused by an accidental mechanical stress during a normal operation, too. That leads to a formation of the micro-cracks and the fractures, which have a significant effect on a device efficiency and reliability. The reverse-bias conditions are usually used for the defects charac- terization purposes. The mechanical induced defects increase a reverse current which leads to a strong overheating in the local breakdowns and the surroundings areas, thus for the defects localization pur- poses an infrared imaging and an electroluminescence method is used. Beyond these commonly used methods the results from the electrical current noise fluctuations observed in a frequency domain are presented in this work. The noise fluctuations measurement is a reliable indicator of a device quality and allow us to qualify the device damage extent. Using combination of these methods it is possible to localize the particular defects, assess the degree of a damage and classify the elimination process of the particular defects.

Fluctuational electrodynamics for nonlinear media

We develop fluctuational electrodynamics for media with nonlinear optical response. In a perturbative manner, we amend the stochastic Helmholtz equation to describe fluctuations in a nonlinear setting, in agreement with the fluctuation dissipation theorem, and identify the local (Rytov) fluctuations of electric currents. We show how the linear response (the solution of the scattering problem) of a collection of objects is found from the individual responses, as measured in isolation. As an example, we compute the Casimir force acting between nonlinear objects which approaches the result for linear optics for large separations, and deviates for small distances.

Variations in the specific charge of saltating sand in a windsand flux over a desertified area

The probability distribution of specific charge of saltating sand over a desertified area has been obtained for the first time. The specific charge of the saltating sand varied between 10 and 150 μC/kg (48.5 μC/kg on the average) according to measurements over a desertified area in Kalmykia (July 2014). An original setup has been designed whereby the saltating sand concentrations, electric current fluctuations, and turbulent pulsations of the wind velocity have been measured over the desertified area in Kalmykia. Regularities in transformations of the statistical parameters from the wind speed to the sand grain concentration and further to the electric current of the saltation due to nonlinear processes in a windsand flux have been ascertained for the first time, including variations in the empirical distribution functions and fluctuation power spectra.

Hot spot dynamics in carbon nanotube array devices.

We report on the dynamics of spatial temperature distributions in aligned semiconducting carbon nanotube array devices with submicrometer channel lengths. By using high-resolution optical microscopy in combination with electrical transport measurements, we observe under steady state bias conditions the emergence of time-variable, local temperature maxima with dimensions below 300 nm, and temperatures above 400 K. On the basis of time domain cross-correlation analysis, we investigate how the intensity fluctuations of the thermal radiation patterns are correlated with the overall device current. The analysis reveals the interdependence of electrical current fluctuations and time-variable hot spot formation that limits the overall device performance and, ultimately, may cause device degradation. The findings have implications for the future development of carbon nanotube-based technologies.

Superstatistical view of stress-induced electric current fluctuations in rocks

The concepts of non-extensive statistical physics, which have recently been applied in the study of complex systems, have been used here to analyse stress-induced electric current data in triaxially deformed Carrara marble samples. The fluctuations of electric current appear to follow a q-Gaussian distribution, with the PDF exhibiting ‘fat tails’. The application of super-statistical techniques to these electric current fluctuations shows to good approximation that they can be described by local Gaussian processes with fluctuating variance.

Facets of Decoherence: Chiral Magnetic Effect in Heavy Ion Collisions

We discuss the effect of anisotropy for fluctuations of electric currents in magnetic field using the quantum measurements theory language. Possible interpretation of parity-odd phenomena like Chiral Magnetic Effect in this framework is given. It is advocated that quantum-to-classical transition caused by decoherence plays crucial role. The talk is based on papers [1–3].

Non-stationary measurements of Chiral Magnetic Effect

We discuss the Chiral Magnetic Effect from the quantum theory of measurements point of view for non-stationary measurements. The effect of anisotropy for fluctuations of electric currents in a magnetic field is addressed. It is shown that anisotropy caused by nonzero axial chemical potential is indistinguishable in this framework from anisotropy caused by finite measurement time or finite lifetime of the magnetic field, and in all cases it is related to abelian triangle anomaly. Possible P-odd effects in central heavy-ion collisions (where the Chiral Magnetic Effect is absent) are discussed in this context. This paper is dedicated to the memory of Professor Mikhail Polikarpov (1952–2013).

Spin-orbit interactions in a helical Luttinger liquid with a Kondo impurity

The combined effect of Rashba and Dresselhaus spin-orbit interactions on the physics of a helical Luttinger liquid coupled to a Kondo impurity is studied. A Rashba coupling can potentially destroy the Kondo singlet formation in certain parameter regimes [Phys. Rev. B 86, 161103(R) (2012)]. This effect is here shown to vanish for sufficiently strong Dresselhaus interaction. The transport properties of the system are investigated by calculating electrical conductance, current and current fluctuations, and thermal conductance.

Quantum measurements and chiral magnetic effect

The effect of anisotropy for fluctuations of electric currents in magnetic field is addressed within framework of quantum measurements theory. It is shown that for free fermions in uniform magnetic field the anisotropy is of the same sign as one expects for chiral magnetic effect and is related to triangle anomaly. The corresponding decoherence functional contains anomalous off-diagonal terms leading to correlation of fluctuations between observables of opposite P-parity.

An experimental artificial-neural-network-based modeling of magneto-rheological fluid dampers

A static model for a magneto-rheological (MR) damper based on artificial neural networks (ANNs) is proposed, and an intensive and experimental study is presented for designing the ANN structure. The ANN model does not require time delays in the input vector. Besides the electric current signal, only one additional sensor is used to achieve a reliable MR damper structure. The model is experimentally validated with two commercial MR dampers of different characteristics: MR1 damper with continuous actuation and MR2 damper with two levels of actuation. The error to signal ratio (ESR) index is used to measure the model accuracy; for both MR dampers, an average value of 6.03% of total error is obtained from different experiments, which are designed to explore the nonlinearities of the MR phenomenon at different frequencies by including the impact of the electric current fluctuations. The proposed ANN model is compared with other well known parametric models; the qualitative and quantitative comparison among the models highlights the advantages of the ANN for representing a commercial MR damper. The ESR index was reduced by the ANN-based model by up to 29% with respect to the parametric models for the MR1 damper and up to 40% for the MR2 damper. The force–velocity diagram is used to compare the modeling properties of each approach: (1) the Bingham model cannot describe the hysteresis of both MR dampers and the distribution function of the modeled force varies from the experimental data, (2) the algebraic models have complications in representing the nonlinear behavior of the asymmetric damper (MR2) and, (3) the ANN-based MR damper can model the nonlinearities of both MR dampers and presents good scalability; the accuracy of the results supports the use of this model for the validation of semi-active suspension control systems for a vehicle, by using nonlinear simulations.

Magnetorheological damper—an experimental study

A magnetorheological damper is evaluated under exhaustive experimental scenarios, generating a complete database. The obtained database includes classical tests and new proposals emphasizing the frequency contents. It also includes the impact of the electric current fluctuations. The variety of the performed experiments allows us to study the magnetorheological damper force dynamics. A brief description of the damper behavior and a categorization of experiments based on driving conditions and target applications on vehicle dynamics are discussed. The identification of two magnetorheological damper models and their cross validation emphasize the importance of the persistence of experimental inputs and the combinations of rod displacement and electric current sequences for better modeling. New findings in design of experiments for model identification are presented.