Optical rectification coefficient of a two-dimensional quantum pseudodot system

Laser-induced nonlinear optical rectification in a two-dimensional quantum pseudodot system

Introduction. When heating with high-frequency currents (HFCs) at high speeds, more significant strengthening effects can be observed compared to using machine generators. Therefore, hardening at high frequencies is more efficient. However, the increase in the generator frequency results in a decrease in the depth of penetration of eddy currents and an increased unevenness of heating across the cross-section. The application of a constant external magnetic field during HFC hardening can increase the depth of eddy current penetration and create more uniform heating. Unfortunately, there is not enough information available on the effect of the external magnetic field on HFC heating processes and phase transformations in steel. Currently, there are no quantitative estimates for the impact of an external magnetic field on changes in the kinetics of electric heating and the penetration depth of eddy currents. In connection with the above, the aim of this paper is to investigate changes in the kinetics of high-frequency heating of iron-carbon alloys when an external constant magnetic field is applied and, and, based on this, to consider the potential for technological applications. Materials and Methods. Theoretical assessment of the influence of an external magnetic field on the change in the kinetics of electric heating and the penetration depth of eddy currents is based on the general theory of induction heating kinetics. An experimental study of the influence of a magnetic field on the kinetics of high-frequency current heating was performed on samples of 45 steel, pearlitic gray (SCh30), and ferritic malleable cast iron (KCh30-6). The temperature distribution over the cross-section of ferromagnetic materials during induction heating with an external magnetic field has been studied using special samples of iron, 45 steel, and SCh30 gray pearlitic cast iron. Electric tempering processes have been investigated on samples of U8A steel using a vacuum tube generator (heating temperature — 450℃, heating rate — 750℃/s). Changes in austenite grain size after high-speed heating with external magnetization have been examined on samples of reduced-hardenability 55PP steel. To study the processes of thermal treatment in a magnetic field during experiments involving heating samples using high-frequency currents, a specially designed electromagnet was created to apply an external constant magnetic field. Results. Theoretical curves were constructed for heating conditions with and without an external constant magnetic field. Experimental data on the effect of an external constant magnetic field on induction heating in the surface layer of various materials were summarized in kinetic diagrams. Evidence that the observed changes were due to increased depth of penetration of eddy currents came from experiments on cylindrical samples of 45 steel with different wall thicknesses. Kinetic curves were provided for estimating the temperature field (at 6 points at different depths) during high-frequency current heating with and without external magnetization. The paper presents experimental data on the micro-hardness distribution across the cross-section of a U8 steel sample after quenching, quenching and electric tempering, quenching and electric tempering with external magnetization, and quenching and bulk tempering. It also includes the results of the study of the austenite grain size of 55PP steel after high-speed heating with external magnetization and conventional (slow) deep heating. Discussion. The application of a high-intensity external constant magnetic field during the first quasi-stationary process resulted in a decrease in the rate of induction heating of the ferromagnetic material and an increase in the depth of its uniform heating. However, above the Curie point, the effect of the magnetic field was negligible due to the low magnetic susceptibility of the material, and the heating rate remained unchanged as if there was no field present. In addition, due to the insignificant difference in the values of magnetic permeability below and above the Curie point during heating in the field, the thermal curve did not exhibit the characteristic inflection typical of kinetic curves observed during the transition of the surface layer to a paramagnetic state. Experiments with electric tempering have demonstrated that by applying an external field, it was possible to temper a material to the desired depth and it could be done on a single high-frequency current setup. The size of the austenite grains after high-speed heating with magnetization was reduced compared to conventional deep heating of steel with low hardenability, eliminating the issue of induction heating for low-hardenability steel. Conclusion. The results of the study demonstrated that the use of an external magnetic field enabled the achievement of strengthening effects during heating at higher frequencies, thereby eliminating the drawbacks of such heating methods.

The nonlinear optical rectification coefficient of quantum dots and rings with a repulsive scattering center

Hydrogenic impurity, external electric and magnetic fields effects on the nonlinear optical properties of a multi-layer spherical quantum dot

Investigation of the nonlinear optical rectification coefficient in a multilayered spherical quantum dot

Non-linear optical response of an impurity in a cylindrical quantum dot under the action of a magnetic field

The effect of an external magnetic field with a flux density of 0.2 T and different configurations relative to the plane of the sample (normal‐to and in‐plane) on the nucleation and growth of CoFe nanostructures has been investigated. CoFe nanostructures were grown on N‐type Si (111) substrate using an e‐beam evaporation system. The samples were subjected to an external magnetic field of 2 T normal‐to and in‐plane to the plane of the samples during the growth period. The influence of the magnetic field on the morphology of the CoFe nanostructures was studied using atomic force microscopy and scanning electron microscopy. Significant changes in the structural characteristics due to the influence of the magnetic fields were evident. Further, the influence of the external magnetic field on the magnetic properties of the materials was analyzed using a vibrating sample magnetometer (VSM) and the composition of the samples was analyzed using energy dispersive X‐ray spectrometry. These results indicate that the easy axis of magnetization in both the samples (normal‐to and in‐plane) is along the direction of the applied magnetic field.

Nonlinear optical rectification effects in an asymmetric quantum well was investigated. Analytical expression of optical rectification coefficient was deduced by using density-matrix method. The larger optical rectification coefficient can be obtained by choosing an appropriate parameter a. The optical rectification coefficient increases with the enhancement of the asymmetry of the quantum well. The larger the asymmetry of quantum well is, the bigger the peak value will be. Moreover, with the increasing of asymmetry of quantum well, the peaks move to the left side of the figure. This is a feasible way to get fine nonlinear materials in experiment.

Influence of magnetic field on photoinduced electron transfer in non-Markovian solvents

Experimental and numerical results on the effect of an external vertical magnetic field on the structure of the flow which occurs when an electric current passes through a conducting medium between two hemispheres are presented. The experiments on the velocity measurement were carried out on the eutectic alloy In-Ga-Sn with the unique fiber-optic transducers. Results on influence of the axial external magnetic field on the flow are presented. The boundary curve separating the one-vortex and two-vortices flow mode depending on the current values through the experimental setup and the external magnetic field was obtained. These results can be used in electrometallurgy for a priori estimates of the flow structure in the direct-current-arc furnaces.

Background. Endothelial cells as participants in angiogenesis choose their phenotype as tip cells (leading, migratory) or stalk cells (following). It has been experimentally found and theoretically modeled that rapid oscillations in intracellular calcium concentration play a key role in controlling phenotype selection and possible vessel architecture. In addition, the intracellular calcium concentration in endothelial cells is known to be regulated by mechanical wall shear stress induced by blood flow, which controls mechanosensitive calcium ion channel gating. Experimental methods of controlling mechanosensitive ion channel gating in external magnetic fields with application of magnetic nanoparticles are developed that affect magnetic nanoparticles artificially attached to cell membranes. Objective. A key question is raised about the possibility of controlled selection of endothelial cell phenotype in external magnetic fields due to the presence of artificial or biogenic magnetic nanoparticles embedded in the cell membrane. Methods. The magnetic wall shear stress is calculated due to the influence of the external magnetic field on the magnetic nanoparticles embedded in the cell membrane, which controls the mechanosensitive calcium ion pathways. Numerical modeling of oscillations in intracellular calcium concentration in endothelial cells and determination of their final phenotype was carried out taking into account intercellular communication. The python programming language and scipy, py-pde, matplotlib packages of the python programming language were used for numerical modeling. Results. The magnetic field flux density and frequency ranges of a uniform rotating magnetic field, as well as the magnitude of the gradient and the frequency of a non-uniform oscillating magnetic field were calculated for controlling the amplitude and frequency of intracellular calcium concentration oscillations in endothelial cells, as well as the selection of their phenotype. It opens the perspective of controlling angiogenesis and vessel architecture. Conclusions. Phenotype selection by endothelial cells can be controlled in a uniform rotating external magnetic field, as well as in a non-homogeneous oscillating magnetic field.

Magnetic fields would affect electrochemical reactions for metallic materials in aqueous solutions. The main effect of a magnetic field applied on an electrochemical system is the introduction of additional forces on the ions in the electrolyte, such as Lorentz-force driven magnetohydrodynamics (MHD) effect and Kelvin-force-driven magnetic field gradient force (MFGF) effect. There are some published reports on the influence of magnetic fields on the pitting corrosion, and apparently contradictory results have been reported. In this work, we focused on the effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride ions. The typical potentiodynamic polarization curves of iron in a 0.2 mol L-1 Na2MoO4 +0.2 mol L-1 NaCl solution at a potential sweep rates of 0.833 mV/s and under 0 T and 0.4 T magnetic field are shown in Fig. 1. Magnetic field decreased the limiting current densities at high potentials. The results in Fig. 1 were confirmed by potentiostatic polarization measurements, which were used to study the effect of magnetic field on the anodic corrosion of iron. After a relatively long period of polarization at 0.4V(SCE) at 0T, imposing a magnetic field will result in a sudden increase and then a slowly decrease of the current density, as shown in Fig. 2(a). The electrode surface morphologies after potentiostatic polarization at 0.4V for 200s under 0T are shown in Fig. 2(b), which are corresponded to the conditions in Fig. 2(a). The pits have propagated deeply. The mass transfer process between occluded pit bottom and the pit mouth would became difficult with the deepening of the pits. The retarding effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride is ascribed to its effect on the mass-transport process between the occluded pit bottom and the pit mouth and finally the resultant disturbance of the autocatalysis process involved in pitting Figure 1

In the current study, we numerically investigate the optical properties of interdiffused GaAs/AlwGa1−wAs multiple quantum well systems under the influence of an external electric field. We solve the resulting Schrodinger equation by using a finite element method and present the algorithm. Here, our motivation was that the interdiffusion effect leads to a non-square more realistic confining potential profile. By using few animations, we show that the effect of the interdiffusion on the optical properties of the mentioned system is not so simple and trivial as has so far been described. These videos can also help experimentalists to select easier their physical parameters. The peak position and amplitude of optical rectification coefficient and probability density can be tuned using parameters such as interdiffusion length Ld, composition amplitude w0, electric field, system length and number of wells.

Nonlinear optical rectification in parabolic quantum dots in the presence of electric and magnetic fields

This study aims to elaborate the influence mechanism of magnetic field on the electrochemical machining (ECM) localization, which is characterized by the ECM drilling technique. Two experiment models are constructed based on the effect of magnetic field on the anodic dissolution: Model 1 is based on the 304 SS│FeCl3 system, in which magnetic field suppresses the anodic dissolution, while Model 2 is based on the Cu│NaCl system, in which magnetic field promotes the anodic dissolution. The experimental results show that the magnetic field improves the ECM localization of the 304 SS│FeCl3 system in ECM drilling, while having no beneficial influence on that of the Cu│NaCl system. It is found through experimental result analysis and comparison that the influence of magnetic field on anodic dissolution is of good correspondence with the influence of magnetic field on the ECM localization. To be specific, when the magnetic field suppresses the anodic dissolution, ECM localization is enhanced by the magnetic field; when the magnetic field promotes the anodic dissolution, ECM localization does not benefit from enhancement by the magnetic field. Such conclusion is of positive significance for the extensive application of magnetic field-assisted ECM.