Photon-Assisted Heat Generation by Electric Current in a Quantum Dot Attached to Ferromagnetic Leads

Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the nonequilibrium Green function technique.Spin-polarized current is generated owing to the Zeeman splitting of the dot level.The current's strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads.We find that the associated heat by this spinpolarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon.It is also found that both the strength and the resonant peaks' position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads,and then provides an effective method to generate large spin-polarized current with weak heat.Such a result may be useful in designing low energy consumption spintronic devices.

Evolution of melt convection in a liquid metal driven by a pulsed electric current

Gain refinement in metal alloy can be achieved by applying an electric current pulse(ECP)in solidification process.Forced flow inside the melt has been proved to be a key role in grain refinement.In this paper,the fluid flow inside Ga 20 wt%-In 12 wt%-Sn alloy induced by a damping sinusoidal ECP flowing through two parallel electrodes into the cylindrical melt was investigated by both experimental measurements and numerical simulations.Experimental results showed that a strong descending jet was induced beneath the bottom of electrodes under the application of ECP.Besides,it was found that flow intensity increases with the increase of amplitude,frequency,and pulse width,respectively.In order to unlock the formation mechanism of flow pattern and the relevance of flow intensity varied with electrical parameters,a three-dimensional numerical model under the application of ECP was established.Meanwhile,a comparative study was conducted by numerical simulations to reveal the distributions of electromagnetic fields and forced flow.Numerical results showed that the downward Lorentz force induced by ECP was concentrated beneath the bottom of electrodes.This downward Lorentz force induces a descending jet and provokes a global forced flow.According to numerical simulations,the evolution of flow intensity with electrical parameters under the application of ECP can be understood by the time averaged impulse of Lorentz force.

Evolution of Vertical Electric Currents and Flares in An Active Region

In this paper, solar active region (AR) 6891 is studied. The long term temporal (over a 8 day period) relationahip between vertical current evolution and flare are examined. We found that the day to day variation of the flare number in the active region is more closly associated with the variation of net current intensity than that of total current intensity. The increase in negative current in the weak following polarity area is due to the reduction in negative current in the strong preceding area.

Altering the Residual Stress in High-Carbon Steel through Promoted Dislocation Movement and Accelerated Carbon Diffusion by Pulsed Electric Current

Residual stress in high-carbon steel affects the dimensional accuracy, structural stability, and integrity of components. Although the evolution of residual stress under an electric field has received extensive attention, its elimination mechanism has not been fully clarified. In this study, it was found that the residual stress of high-carbon steel could be effectively relieved within a few minutes through the application of a low density pulse current. The difference between the current pulse treatment and traditional heat treatment in reducing residual stress is that the electric pulse provides additional Gibbs free energy for the system, which promotes dislocation annihilation and carbon atom diffusion to form carbides, thus reducing the free energy of the system. The electroplastic and thermal effects of the pulse current promoted the movement of dislocations under the electric field, thus eliminating the internal stress caused by dislocation entanglement. The precipitation of carbides reduced the carbon content of the steel matrix and lattice shrinkage, thereby reducing the residual tensile stress. Considering that a pulsed current has the advantages of small size, small power requirement, continuous output, and continuously controllable parameters, it has broad application prospects for eliminating residual stress.

Removing prior particle boundaries in a powder superalloy based on the interaction between pulsed electric current and chain-like structure

The chain-like prior particle boundaries(PPBs)as a kind of stubborn harmful precipitate will hinder atomic diffusion and particle connection.They can only be broken into nanoscale through thermal deformation(1160–1200℃).Here,treated by the pulsed electric current at 800℃,PPBs were dissolved quickly as a result of the interaction between the pulsed electric current and the chain-like structure.According to the electromigration theory and the calculation results,the high current density regions will be mainly produced at the gaps due to the conductivity difference between the precipitates and the matrix.The atomic diffusion flux caused by the pulsed electric current is proportional to the current density.Therefore,the existence of a large number of gaps in the chain-like PPBs will make the high current density regions play a more positive role in fast-dissolution.

Influence of direct electric current on wetting behavior during brazing

The wetting behavior of liquid metals is of great importance for many processes. For brazing, however, a targeted modification beyond the adjustment of conventional process parameters or the actual set-up was not possible in the past. Therefore, the effect of direct electric current along the surface of a steel substrate on the wetting behavior and the formation of the spreading pattern of an industrial nickel-based filler metal was investigated at a temperature above T = 1000 °C in a vacuum brazing furnace. By applying direct current up to I = 60 A the wetted surface area could be increased and the spreading of the molten filler metal could be controlled in dependence of the polarity of the electric current. The electric component of the Lorentz force is supposed to be feasible reasons for the observed dependence of the electrical polarity on the filler metal spreading direction. To evaluate the influence of the electric current on the phase formation subsequent selective electron microscope analyses of the spreading pattern were carried out.

Suggestions on the Current Electricity Price Level and Policies in China

The State Council decided to raise the retail electricity price by 0.25 Yuan/kWh from July, 2008. This will, to some extent, relieve the conflicts between power supply and demand, and decrease the economic losses in

The Effect of Micro-Pulsatile Electrical and Ultrasound Stimulation on Cellular Biosynthetic Activities Such as Cellular Proliferation, Endogenous Nitrogen Oxide and Collagen Synthesis

The skin barrier poses an ongoing challenge for the cosmetics industry. Its penetration, by non-invasive means, can readily be achieved with currents and ultrasound or radiofrequency devices through electroporation, sonophoresis, iontophoresis or cavitation. When several types of energy are applied simultaneously, we expect the effects to be magnified and all the more effective. Although the mechanism of action of each technology on the skin is not entirely controlled, and is even less so when multiple technologies are applied concurrently, some studies demonstrate that nitric oxide (NO) plays a pivotal role in skin wound-healing and regeneration. With regard to wound healing, one of the key functions of NO appears to be its permissive effect on keratinocyte and fibroblast proliferation, which helps promote wound re-epithelialization. The objective of the actual research is to gain an in-depth understanding of the mechanisms generated by NO through the application of a specific combination of technologies.

A Pulsed Electromagnet for Laser Wakefield Electron Acceleration Experiments

Laser Wakefield plasma acceleration of electrons to energies above 10 GeV, may be possible in the new high power Laser beam facilities. The design of an Electron Spectrometer with an electro-magnet with adjustable magnetic field is proposed for the characterization of electron energy spectrum with a precision better than 10% for the entire energy range from 0.5 GeV to 38 GeV. The expected precision in the measurement of the electron energy is calculated as a function of the magnetic field, of the electron energy and of the magnet length. To outline the advantages offered by a pulsed electromagnet with high magnetic fields, the mass and the electric power lost in the coils of a 4 m long electromagnet with continuous current and Iron yoke are calculated.

Weak Wavefront Solutions of Maxwell’s Equations in Conducting Media

We analyze the propagation of electromagnetic fronts in unbounded electric conductors. Our analysis is based on the Maxwell model of electromagnetism that includes the displacement current and Ohm’s law in its simplest forms. A weak electromagnetic front is a propagating interface at which the electromagnetic field remains continuous while its first- and higher-order derivatives experience finite jump discontinuities. Remarkably, analysis of such fronts can be performed autonomously, i.e. strictly in terms of the quantities defined on the front. This property opens the possibility of establishing exact analytical solutions of the exact Maxwell system along with the evolution of the front.

Comprehensive Experimental Study on the Migration Law of the Floor at the Mining Face

Under the circumstance that deep mining is increasingly vulnerable to underlying limestone water, accurate detection of floor failure depth ranges at a mining face becomes rather critical to coal mine production in safety. Underground borehole fiber optic sensing technology is combined with 2-D parallel electrical surveying to comprehensively monitor and analyze development laws of floor deformation and failure. Moreover, a working face 1022 in a mine of Huaibei Mining Area was taken, for example, introducing the layout of monitoring borehole and installation of relevant sensing units. Based on the stope progress of a working face, data related to strain and geoelectric fields were collected regularly to analyze relationships of field source variation characteristics and strata deformation failures. In this way, the development mechanism of the floor deformation failure can be revealed. As demonstrated by results, the depth failure of the floor at coal seam 10 is calculated to be 15 m, while its disturbance depth turns out to be 22 m. Due to advanced stress, concentrated stope load and post-mining pressure relief, the floor experienced elastic deformation, shear deformation and swelling deformation successively. Without a doubt, testing results obtained have scientific guiding significance for mines with similar geological conditions.

Modeling of Residential Photovoltaic (PV) System Connected to Low Voltage (LV) Network: Application to Public Distribution Network of Burkina Faso

Residential photovoltaic (PV) systems connected to the grid are used for self-consumption. Any surplus production is fed into the grid and contributes to improving the voltage. Several techniques are developed to model their connection. However, studies on methods of injecting energy production into the Low Voltage (LV) network are nowadays a problem. This paper proposes a mathematical model to determine the current to be injected and calculate each node’s voltage. The current equation is a recurrence relation with an initial condition. This initial condition is for the case of a single PV system connected to the LV grid. The equation can also be written in matrix form. Similarly, the voltage solution is a recurrence relation. It also has an initial condition for the first node. Both mathematical formulae with the proposed initial conditions are consistent and can be used for the determination of the current and voltage of the different nodes in the grid.

Shock Fronts in Non-Polar Electro-Conducting Media

We analyze the propagation of electromagnetic fronts in unbounded electric conductors. Our model is based on the Maxwell model of electromagnetism, which includes the displacement current and Ohm’s law in its simplest forms. The shock-like electromagnetic front is a propagating surface, across which the electric and magnetic fields, as well as their higher temporal and spatial derivatives, experience finite jumps. The shock-like fronts are essentially different as compared with the weak fronts;in particular, the bulk Maxwell equations are essentially insufficient for the analysis of the shock-like fronts, and they should be amended we the physical jump conditions. We choose these additional conditions by using conditions similar to those suggested by Heaviside. We derive the basic shock intensity relationships implied by this model.

Statistical Study of foF2 Diurnal Variation at Dakar Station from 1971 to 1996:Effect of Geomagnetic Classes of Activity on Seasonal Variation at Solar Minimum and Maximum

The statistical study of F2 layer critical frequency at Dakar station from 1971 to 1996 is carried out. This paper shows foF2 statistical diurnal for all geomagnetic activities and all seasons and that during solar maximum and minimum phases. It emerges that foF2 diurnal variation graphs at Dakar station exhibits the different types of foF2 profiles in African EIA regions. The type of profile depends on solar activity, season and solar phase. During solar minimum and under quiet time condition, data show?the signature of a strength electrojet that is coupled with intense counter electrojet in the afternoon. Under disturbed conditions,?mean intense electrojet is observed in winter?during fluctuating and recurrent activities. Intense counter electrojet is seen under fluctuating and shock activities in all seasons coupled with strength electrojet in autumn. In summer?and spring under all geomagnetic activity condition, there is intense counter electrojet. During solar maximum, in summer and spring there is no electrojet under geomagnetic activity conditions.?Winter shows a mean intense electrojet. Winter and autumn are marked by the signature of the reversal electric field.

Modelisation and Optimization of a Microbial Desalination Cell System

In this work, we used a hybrid system composed of a Microbial Desalination Cell (MDC). This system allows, at the same time, the treatment of wastewater and the production of electrical energy for the desalination of saltwater. MDC is a cleaning technology used to purify wastewater. This process has been driven by converting organic compounds contained in wastewater into electrical energy through biological, chemical, and electrochemical processes. The produced electrical energy was used to desalinate the saline water. The objective of this work is the desalination or pre-desalination of seawater. For this, we have established a theoretical model consisting of differential equations describing the behavior of this system. Subsequently, we developed a program on MAT-LAB software to simulate and optimized the operation of this system and to promote the production of electrical energy in order to improve the desalination efficiency of the MDC. The theoretical result shows that the electrical current production is maximal when the methanogenic growth rate equal to zero, increases with the increasing of influent substrate concentration and the efficiency of desalination increased with flow rate of saline water.

Electric field tunable strong transverse light current from nanoparticles embedded in liquid crystal

We present an exact solution to the problem of electromagnetic scattering by nanosphere clusters embedded in a liquid crystal cell, based on the Mie theory. The dependence of the scattering property on the structure parameters is investigated in detail. It is shown that strong transverse light currents at the optical frequency can be obtained from these complex structures. Furthermore, we find that sign reversal of the transverse light current can be realized by changing frequency and voltage. The physical origins of these phenomena have been analyzed.The transverse light current for subwavelength nanoscale dimensions is of practical significance. Thus, the application of these phenomena to optical devices is

Grain nucleation and growth behavior of a Sn-Pb alloy affected by direct current： An in situ investigation

In situ synchrotron X-ray radiography was used to study the effect of direct current(DC) on the grain nucleation and growth of Sn-50 wt.%Pb alloy. The results showed that applying DC adequately during solidification could effectively enhance the grain nucleation and inhibit its growth. Imaging of comparative experiments with varying DC intensity indicated that the final grain size, determined by the competition between grain nucleation and growth, was sensitively dependent on the DC intensity. It was found that the average grain size was decreased from 1632 to 567 μm with DC density of 1.5 A/mm^2 compared to the case without DC. Beyond this value, raising the current density may cause a significant decrease in the nucleation rate, and thus lead to a coarsening of the grain structure.

Effect of High Density Current Pulses on Microstructure and Mechanical Properties of Dual-Phase Wrought Superalloy

In this study,high density electric current pulse(ECP)treatment was introduced instead of the conventional solution treatment,and theγ′phase was completely dissolved under the ECP treatment within only several milliseconds at 1148°C.Due to the extremely short treatment time and high cooling rate,the growth ofγ-phase matrix grain andγ′phase precipitate was effectively retarded.By comparing with the conventional heat process,the grain size of ECP treated sample was controlled to about 15μm,the size of the re-precipitatedγ′phase reduced from 65 to 35 nm,and the number density ofγ′precipitate increased from 1.46×108 to 3.03×108/mm2.The Vickers hardness,ultimate tensile strength and yield strength of the ECP treated sample were significantly improved.According to the theoretical derivation of kinetics,the ECP treatment introduces an extra electrical free energy which promoted the dissolution ofγ′phase.The ECP treatment may provide a new method for solution treatment of the Ni-based superalloy.

Ultrafast regulation of nano-scale matrix defects using electrical property discrepancies to delay material embrittlement

Nano-scale phases can enhance or reduce the mechanical properties of materials,so it is very important to control the size of the phases.Copper-rich nanoclusters as matrix defects will significantly reduce the performance of materials for key nuclear power components,while traditional heat treatment method has a technical bottleneck for the dissolution of nanoclusters.A new method of using the inherent electrical property discrepancies between the matrix material and the nanoclusters to effectively dissolve the nanoclusters through pulsed electric current to realize the recovery of material aging degradation performance is proposed.The performance evolution of simulated steel in the aging-external field repair cycle was studied,and it was found the dislocations as the preferred nucleation sites of nanoclusters were regulated in virtue of the non-thermal effect of current,resulting in a decrease in dislocation density and entanglement release.In the subsequent thermal aging process,the embrittlement rate of the aged and tempered material trained by the electric pulse was slower than that of the untreated sample.When moving dislocations are pinned by nanoclusters under high stress,nano-scale dislocations can be induced into the clusters.The dislocations near the nanoclusters and the newly formed nano-scale dislocations in the nanoclusters act as fast diffusion channels,which can further accelerate the dissolution of the nanoclusters.

Mechanical Manipulation of Electrical Behaviors of Piezoelectric Semiconductor Nanofibers by Time-Dependent Stresses

We study electric currents in a piezoelectric semiconductor fiber under a constant voltage and time-dependent axial stresses applied locally.From a nonlinear numerical analysis based on a one-dimensional phenomenological model using the commercial software COMSOL,it is found that pulse electric currents can be produced by periodic or time-harmonic stresses.The pulse currents can be tuned by the amplitude and frequency of the applied stress.The result obtained provides a new approach for the mechanical control of electric currents in piezoelectric semiconductor fibers and has potential applications in piezotronics.