Chirped Bloch oscillations in strain-balanced InGaAs/InGaAs superlattices

Bloch oscillations excited in a strain-balanced In_xGa_1 − xAs/In_yGa_1 − yAs superlattice by fs optical pulses at 1.55 μ m are investigated in time-resolved transmission spectroscopy. The transition from the coherent oscillatory motion to an incoherent drift transport of the electrons is observed via a transient frequency shift of the Bloch oscillations due to the associated screening of the applied electric field. These electric field changes are analyzed quantitatively as a function of the initial field strengths and excitation densities. The incoherent transport can be described by a drift-diffusion model. As a result, the carrier mobility in the superlattice is obtained on a picosecond timescale.     

A fully discrete Galerkin method for high frequency exterior acoustic scattering in three dimensions

Standard Galerkin discretization techniques (with locally- or globally-supported basis functions) for boundary integral equations are inefficient for high frequency three dimensional exterior scattering simulations because they require a fixed number of unknowns per wavelength in each dimension, leading to large CPU time and memory requirements to set up the dense Galerkin matrix, with each entry requiring evaluation of multi-dimensional highly oscillatory integrals. In this work, using globally-supported basis functions, we describe an efficient fully discrete Galerkin surface integral equation algorithm for simulating high frequency acoustic scattering by three dimensional convex obstacles that includes a powerful integration scheme for evaluation of four dimensional Galerkin integrals with high-order accuracy. Such high-order order accuracy for various practically relevant frequencies (k ∈ [1, 100,000]) substantially improves on approximations based on standard asymptotic techniques. We demonstrate the efficiency of our algorithm for spherical and non-spherical convex scattering for several wavenumbers 1 ? k ? 100,000 for low to high order prescribed tolerance. Our fully discrete algorithm requires only mild growth in the number of unknowns and CPU time as the frequency increases.     

Optically stimulated second-order optical susceptibilities of self-assembled multi-layers film samples

In the present paper for the first time we study the influence of simultaneous polarized optical treatment (10 ns Nd: YAG lasers with power density 0.6 GW/cm²) together with electrostatic dc electric field (up to 8 kV/cm) on self-assembled multi-layer films samples. The second-order optical susceptibility (SOS) achieves the maximal values after one minute simultaneous dc-electrical-optical treatment. Further treatment will not enhance the values and even leads to the decrease of SOS. The independent measurement of the local temperature shows that local heating do not excess 8.6 K.     

The investigation of transport properties of mesoscopic graphite in high magnetic field

The electrical transport properties of mesoscopic graphite have been investigated in a gate voltage configuration. Few layer graphene structures made from Kish graphite exhibit Shubnikov-de Haas (SdH) oscillations in magnetic fields up to 33 T, with a strong gate voltage dependence. A two band model can be used to explain the linear dependence of the SdH frequency on the gate voltage. The temperature dependence of the SdH oscillation amplitude allows the determination of the effective masses of the carriers, which remain comparable between mesoscopic and bulk graphite samples. However, mesoscopic graphite thinner than 130 nm does not exhibit the field induced charge density wave transition seen in bulk samples above 25 T at low temperatures.     

Three-dimensional simulation of electric field and space charge in the advanced hybrid particulate collector

The advanced hybrid particulate collector (AHPC) is an efficient hybrid system that combines the electrostatic precipitator (ESP) and the bag filter in a unique approach. In this study, an unstructured finite volume method (FVM) is used to compute the three-dimensional distributions of the electric field and the space charge density in an AHPC setup for two cases: without the perforated plate and with the perforated plate. The current–voltage characteristics of the AHPC setup are measured. The current on the bag plate has a mean value 7.82 μA without the perforated plate and 0.08 μA with the perforated plate for the measured voltages. The total currents are used to calculate the charge density at the corona wire according to the Peek's formula. For both cases, the numerical predictions of the current–voltage relations of the plates of the model AHPC agree well with the measurements. When the AHPC has the perforated plate, numerical results show that the electric field and space charge density distributions on the perforated plate have the same number of peaks corresponding to the holes. The electric field on the bag plate surface is lower than that of the top plate and the perforated plate. Though the bag plate has low current, its surface still has high space charge density. When the AHPC has no perforated plate, the electric field is higher than six times and the space charge density is higher than three times that of the case with the perforated plate on the bag plate surface.     

Modified optical bloch equations in nonlocal systems of two-level atoms interacting with ultrashort light pulses

Modified optical Bloch equations for two-level atoms in the radiation field with the complex polarization vector, the complex amplitude, and the complex wave vector are derived. A specific case is considered in which a field of this kind acts on a separate atom of a nonlocal atomic system. The solution of the modified equations for the interaction of atoms with ultrashort light pulses is obtained.     

Determining the work function of a carbon-cone cold-field emitter by in situ electron holography

Cold-field emission properties of carbon cone nanotips (CCnTs) have been studied in situ in the transmission electron microscope (TEM). The current as a function of voltage, i(V), was measured and analyzed using the Fowler–Nordheim (F–N) equation. Off-axis electron holography was employed to map the electric field around the tip at the nanometer scale, and combined with finite element modeling, a quantitative value of the electric field has been obtained. For a tip-anode separation distance of 680 nm (measured with TEM) and a field emission onset voltage of 80 V, the local electric field was 2.55 V/nm. With this knowledge together with recorded i(V) curves, a work function of 4.8 ± 0.3 eV for the CCnT was extracted using the F–N equation.     

2-D corona field computation in configurations with ionising and non-ionising electrodes

An efficient method is proposed for the computation of the electric field strength and of the space-charge density in configurations of at least three ionising and non-ionising electrodes. The physical model is derived under the assumptions commonly accepted for the study of corona fields. The mathematical model makes use of a conformal mapping that converts the actual boundary-free field zone into a rectangular domain with well-defined boundary conditions. The finite-difference method is then used for solving the differential equations that describe the ionic space-charge and electric field distribution. The computational procedure was employed for studying the simple case of the drift zone of the corona discharge generated between a so-called dual electrode and a grounded plate. The dual electrode consisted of an ionising wire (diameter 0.22 mm) located at 20 mm from a tubular metallic support (diameter 25 mm). The computed current–voltage characteristic and current density distribution at the surface of the collector plate were in good agreement with the experimental data obtained for this combined corona–electrostatics electrode arrangement.     

SELF-CONSISTENT TREATMENT OF PLASMA EXPANSION IN THE PRESENCE OF ELECTRON PLASMA WAVE

The hydrodynamic modification of an expanding plasma near the reflection point of an electron plasma wave is investigated by simultaneously solving the wave equation together with the steady-state hydrodynamic equations.The electric field and electron density fluctuation of the plasma wave are derived in a self-consistently steepened density profile. while the density jump and its dependence on the wave amplitude are also determined.     

Development of a novel electric field-assisted modified hydrodynamic cavitation system for disintegration of waste activated sludge

In this current study, we present a modified hydrodynamic cavitation device that combines an electric field to substitute for the chemical addition. A modified HC system is basically an orifice plate and crisscross pipe assembly, in which the crisscross pipe imparts some turbulence, which creates collision events. This study shows that for maximizing disintegration, combining HC system, which called electric field-assisted modified orifice plate hydrodynamic cavitation (EFM-HC) in this study, with an electric field is important. Various HC systems were compared in terms of disintegration of WAS, and, among them, the EFM-HC system exhibited the best performance with the highest disintegration efficiency of 47.0 ± 2.0% as well as the destruction of WAS morphological characteristics. The experimental results clearly show that a conventional HC system was successfully modified. In addition, electric field has a great potential for efficient disintegration of WAS for as a additional option in a combination treatment. This study suggests continued research in this field may lead to an appropriate design for commercial use.     

Kinetic two-dimensional modeling of inductively coupled plasmasbased on a hybrid kinetic approach

In this paper, we present a two-dimensional (2-D) kinetic model for low-pressure inductively coupled discharges. The kinetic treatment of the plasma electrons is based on a hybrid kinetic scheme in which the range of electron energies is divided into two subdomains. In the low energy range the electron distribution function is determined from the traditional nonlocal approximation. In the high energy part the complete spatially dependent Boltzmann equation is solved. The scheme provides computational efficiency and enables inclusion of electron-electron collisions which are important in low-pressure high-density plasmas. The self-consistent scheme is complemented by a 2-D fluid model for the ions and the solution of the complex wave equation for the RF electric field. Results of this model are compared to experimental results. Good agreement in terms of plasma density and potential profiles is observed. In particular, the model is capable of reproducing the transition from on-axis to off-axis peaked density profiles as observed in experiments which underlines the significant improvements compared to models purely based on the traditional nonlocal approximation     

Prevention criteria of electrostatic ignition by a charged cloud in grounded tanks

In this paper, we present the criteria of space charge density and wall electric field required to prevent incendive discharges between a grounded protrusion and a charged cloud in cylindrical tanks grounded of up to ≈1.5 × 10⁵ m³ in volume obtained by numerical investigations with wide ranges in the dimensions of the protrusions and tanks. To obtain such criteria, the thresholds of the charge densities of uniformly charged clouds for initiating a discharge at the tip of protrusions are numerically obtained. Furthermore, the transferred charges and energies of the discharges are estimated to investigate their incendivity. For evaluating the risk with a field measurement, the criterion of the electric fields at the side wall of the tanks for avoiding incendive discharges is also obtained.     

Nonlinear Evolution of Driven Electron Plasma Oscillations in Inhomogeneous Plasmas

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Derivation and solution of multifrequency radiation diffusion equations for homogeneous refractive lossy media

Starting from the radiation transport equation for homogeneous, refractive lossy media, we derive the corresponding time-dependent multifrequency diffusion equations. Zeroth and first moments of the transport equation couple the energy density, flux and pressure tensor. The system is closed by neglecting the temporal derivative of the flux and replacing the pressure tensor by its diagonal analogue. The radiation equations are coupled to a diffusion equation for the matter temperature. We are interested in modeling heating and cooling of silica (SiO₂), at possibly rapid rates. Hence, in contrast to related work, we retain the temporal derivative of the radiation field. We derive boundary conditions at a planar air–silica interface taking account of reflectivities obtained from the Fresnel relations that include absorption. The spectral dimension is discretized into a finite number of intervals leading to a system of multigroup diffusion equations. Three simulations are presented. One models cooling of a silica slab, initially at 2500 K, for 10 s. The other two are 1D and 2D simulations of irradiating silica with a CO₂ laser, λ = 10.59 μm. In 2D, a laser beam (Gaussian profile, r₀ = 0.5 mm for 1/e decay) shines on a disk (radius = 0.4, thickness = 0.4 cm).     

Bloch oscillations and Wannier-Stark ladder in the coupled LC circuits

We present a new scheme for realizing Bloch oscillations and Wannier-Stark ladder based on a lattice of coupled LC circuits. By converting the second order dynamical ODEs of the system into a first order Schrödinger-like equation, we propose an equivalent tight binding Hamiltonian to describe the circuit. We show that a synthesized electric field is produced by introducing a frequency mismatch into the resonant frequency of the adjacent LC resonators. The Wannier-Stark modes are the normal modes of the circuit and the Bloch oscillations can be observed in a coupled LC lattice. By addition of coupling capacitors between nodes of the circuit, we study the Bloch oscillation in the presence of long-range couplings. We also show that the circuit converts to a transmission line simulating synthetic electric fields in the continuum limit. The coupled LC circuit is, in some sense, amongst the simplest physical systems exhibiting Bloch oscillation and Wannier-Stark Ladder.     

The influence of non-equilibrium defects on the anodic dissolution of a metal into a solid electrolyte

The galvanostatic dissolution of a parent metal Me in an electrochemical cell of the type Me/MeX/Me (MeX = cation-conducting solid electrolyte) causes periodic oscillations of the anodic overvoltage in a certain range of current density, pressure and temperature. The amplitude of these oscillations is a function of the applied mechanical pressure and their frequency depends on the electric current density. In the present study the electrode kinetics of transference cells of the type (+) Cu/AgBr/Ag (−) and (+) Cu/CuBr/Ag (−) have been investigated by galvanostatic measurements and linear sweep voltammetry, in order to obtain a better understanding of the nonlinear kinetics. During anodic dissolution the anode surface develops a porous structure which is correlated to the dislocation density of the anode. Linear sweep voltammetry measurements suggest that the rate-limiting step of anodic copper dissolution is the formation or the diffusion of metal adatoms on the metal electrode surface. A qualitative model for the influence of the processes on the oscillatory kinetics is proposed.     

Resonant interaction of an electromagnetic wave with an inhomogeneous plasma slab

Resonant interaction at oblique incidence of an electromagnetic wave on an inhomogeneous plasma slab is studied. The time evolution of this interaction is solved numerically from two-fluid equations, adiabatic equation for electron pressure and from Maxwell equations. It is shown that the electromagnetic energy of an incident wave is transformed both into the heat energy and into the energy of plasma oscillations in the direction of density gradient. The distribution of the transformed energy between the heat energy and the energy of plasma oscillations is strongly dependent on the plasma temperature. The ratio of heat energy to the energy of plasma oscillations is growing with growing temperature. The plasma oscillations are generated by magnetic induction of the penetrating wave. In a cold plasma they are generated especially in the overdense region and their frequency is equal to local plasma frequency. The electric field in the direction of plasma gradient has a form of a wave packet whose envelope reaches a maximum at resonance. The characteristic wavelength in the wave packet decreases and the amplitude of the packet increases with the time.