Volume discharge in a gas, excited by an electron beam under conditions of nonuniform ionization

Volume discharge in gases excited by electron beams is discussed. The steady state electric field distribution is derived. The voltage-current and energy characteristics are described

Self-consistent approach for the quantum confined Stark effect in shallow quantum wells

A computationally efficient, self-consistent complex scaling approach to calculating characteristics of excitons in an external electric field in quantum wells is introduced. The method allows one to extract the resonance position as well as the field-induced broadening for the exciton resonance. For the case of strong confinement the trial function is represented in factorized form. The corresponding coupled self-consistent equations, which include the effective complex potentials, are obtained. The method is applied to the shallow quantum well. It is shown that in this case the real part of the effective exciton potential is insensitive to changes of external electric field up to the ionization threshold, while the imaginary part has non-analytical field dependence and small for moderate electric fields. This allows one to express the exciton quasi-energy at some field through the renormalized expression for the zero-field bound state.Comment: 13 pages, RevTeX4, 6 figure

Calculations of exchange interaction in impurity band of two-dimensional semiconductors with out of plane impurities

We calculate the singlet-triplet splitting for a couple of two-dimensional electrons in the potential of two positively charged impurities which are located out of plane. We consider different relations between vertical distances of impurities $h_1$ and $h_2$ and their lateral distance $R$. Such a system has never been studied in atomic physics but the methods, worked out for regular two-atomic molecules and helium atom, have been found to be useful. Analytical expressions for several different limiting configurations of impurities are obtained an interpolated formula for intermediate range of parameters is proposed. The $R$-dependence of the splitting is shown to become weaker with increasing $h_1,h_2$.Comment: 14 pages, RevTeX, 5 figures. Submitted to Phys Rev.

Second Josephson excitations beyond mean field as a toy model for thermal pressure: exact quantum dynamics and the quantum phase model

A simple four-mode Bose-Hubbard model with intrinsic time scale separation can be considered as a paradigm for mesoscopic quantum systems in thermal contact. In our previous work we showed that in addition to coherent particle exchange, a novel slow collective excitation can be identified by a series of Holstein-Primakoff transformations. This resonant energy exchange mode is not predicted by linear Bogoliubov theory, and its frequency is sensitive to interactions among Bogoliubov quasi-particles; it may be referred to as a second Josephson oscillation, in analogy to the second sound mode of liquid Helium II. In this paper we will explore this system beyond the Gross-Pitaevskii mean field regime. We directly compare the classical mean field dynamics to the exact full quantum many-particle dynamics and show good agreement over a large range of the system parameters. The second Josephson frequency becomes imaginary for stronger interactions, however, indicating dynamical instability of the symmetric state. By means of a generalized quantum phase model for the full four-mode system, we then show that, in this regime, high-energy Bogoliubov quasiparticles tend to accumulate in one pair of sites, while the actual particles preferentially occupy the opposite pair. We interpret this as a simple model for thermal pressure

Investigation of LiFeAs by means of "Break-junction" Technique

In our tunneling investigation using Andreev superconductor - normal metal - superconductor contacts on LiFeAs single crystals we observed two reproducible independent subharmonic gap structures at dynamic conductance characteristics. From these results, we can derive the energy of the large superconducting gap $\Delta_L=(2.5 \div 3.4)$ meV and the small gap $\Delta_L=(0.9 \div 1)$ meV at $T = 4.2$ K for the $T_C^{local} \approx (10.5 \div 14)$ K (the contact area critical temperature which deviation causes the variation of $\Delta_L$). The BCS-ratio is found to be $2\Delta_L/k_BT_C = (4.6 \div 5.6)$, whereas $2\Delta_S/k_BT_C \ll 3.52$ results from induced superconductivity in the bands with the small gap.Comment: 7 pages, 5 figures. Published in Pis'ma v ZhETF 95, 604-610 (2012

Two-dimensional quantum interference contributions to the magnetoresistance of Nd{2-x}Ce{x}CuO{4-d} single crystals

The 2D weak localization effects at low temperatures T = (0.2-4.2)K have been investigated in nonsuperconducting sample Nd{1.88}Ce{0.12}CuO{4-d} and in the normal state of the superconducting sample Nd{1.82}Ce{0.18}CuO{4-d} for B>B_c2. The phase coherence time and the effective thickness $d$ of a conducting CuO_2 layer have been estimated by the fitting of 2D weak localization theory expressions to the magnetoresistivity data for the normal to plane and the in-plane magnetic fields.Comment: 5 pages, 4 postscript figure

Oscillons: an encounter with dynamical chaos in 1953?

We present evidences that Ben F. Laposky (1914-2000) might have been the first person who created a family of nonlinear analog circuits that allowed him to observe chaotic attractors and other trademarks of nonlinear science as early as 1953.Comment: accepted to Chao

Methodology of designing an air cascade separator

The calculation technique of industrial cascade separators based on experimental and analytical research process methods for air fractionation of bulk materials is considered. The main technological factors and process defining parameters used in calculation of separator design are presented. It is shown that for the design of an industrial separator, it is necessary to find a relationship between the initial granulometric distribution and the fractional requirements for the finished product from the concentration of the material flow and the air flow velocity to the complete cross-section of the separator. The experiment results of material flow concentration influence on division efficiency for various cascade separator constructions are given. Mathematical relationship of the air flow rate through the apparatus on the separation boundary and bulk concentration is proposed. The correlation of these parameters with the constructive sizes of the separator is shown. The initial particle size distribution of bulk, the set restrictions for fractional characteristics of the received powder and the approximating equations of fractional extraction function of fineness narrow classes in a large or small product based on experimental data are used for calculation of the equipment. © Published under licence by IOP Publishing Ltd

Decay of Quasi-Particle in a Quantum Dot: the role of Energy Resolution

The disintegration of quasiparticle in a quantum dot due to the electron interaction is considered. It was predicted recently that above the energy \eps^{*} = \Delta(g/\ln g)^{1/2} each one particle peak in the spectrum is split into many components ($\Delta$ and $g$ are the one particle level spacing and conductance). We show that the observed value of \eps^{*} should depend on the experimental resolution \delta \eps. In the broad region of variation of \delta \eps the $\ln g$ should be replaced by \ln(\Delta/ g\delta \eps). We also give the arguments against the delocalization transition in the Fock space. Most likely the number of satellite peaks grows continuously with energy, being $\sim 1$ at \eps \sim \eps^{*}, but remains finite at \eps > \eps^{*}. The predicted logarithmic distribution of inter-peak spacings may be used for experimental confirmation of the below-Golden-Rule decay.Comment: 5 pages, REVTEX, 2 eps figures, version accepted for publication in Phys. Rev. Let