Van Vleck's polarization-paramagnetism of several diamagnetic substances of elements of the first and fifth principal subgroups

Magnetic susceptibilities, indices of refraction and densities of diamagnetic substances of the Ist and Vth principal subgroups are determined. From them, by means of the Kirkwood's formula, the temperature independent Van Vleck's polarization-paramagnetism was calculated. Its dependence on the electric polarizability, or on the number of electrons of the molecule, is a decreasing function for the carbonates of elements of the Ist principal subgroup. Its analysis shows that the substances Li₂CO₃, Na₂CO₃, K₂CO₃ have an ionic bond with a certain portion of covalency.The polarization-paramagnetism of perchlorates of the Ist principal subgroup has the character of a rising function of the polarizability and of the number of electrons. This is in connection with the fixation of the electron cloud of the [ClO₄]^1– anion and, probably, also with the fact that for ions of those substances the energy difference of the normal and excited states in zero field decreases progressively with increasing number of electrons in a molecule.The measurements show a considerable value of the polarization-paramagnetism of oxides of the Vth principal subgroup of elements, increasing with the number of electrons in a molecule. This phenomenon is also interpreted.     

Electromagnetic radiation of relativistic channeling particles (the Kumakhov effect)

A new type of electromagnetic radiation characteristic for channeling in single crystals relativistic particles which has been recently predicted by Kumakhov and proved experimentally is reviewed. It is observed as one or several strong peaks in the soft part of the Bremsstrahlung, surpassing it by a factor of nearly one hundred. At moderate electron energies sharp peaks corresponding to spontaneous transitions between quantum eigenstates of the channeling particles were detected. But for high energy channeling electrons these peaks merge into one broad classical peak with the frequency determined by the collective potential of an atomic row or plane. This radiation also strongly depends on the charge sign, velocity and mass of the particle.     

Modelling the thermal quenching mechanism in quartz based on time-resolved optically stimulated luminescence

This paper presents a new numerical model for thermal quenching in quartz, based on the previously suggested Mott-Seitz mechanism. In the model electrons from a dosimetric trap are raised by optical or thermal stimulation into the conduction band, followed by an electronic transition from the conduction band into an excited state of the recombination center. Subsequently electrons in this excited state undergo either a direct radiative transition into a recombination center, or a competing thermally assisted non-radiative process into the ground state of the recombination center. As the temperature of the sample is increased, more electrons are removed from the excited state via the non-radiative pathway. This reduction in the number of available electrons leads to both a decrease of the intensity of the luminescence signal and to a simultaneous decrease of the luminescence lifetime. Several simulations are carried out of time-resolved optically stimulated luminescence (TR-OSL) experiments, in which the temperature dependence of luminescence lifetimes in quartz is studied as a function of the stimulation temperature. Good quantitative agreement is found between the simulation results and new experimental data obtained using a single-aliquot procedure on a sedimentary quartz sample.     

On glancing scattering of light ions from tungsten single crystal surfaces

A computer calculation of light ion (200–800 keV protons and helium) scattering from a tungsten single crystal model with a (110)-type surface is presented. An axis (100) is considered. Thermal vibrations in 3 dimensions have been incorporated. The number, i.e. fraction, and spatial distribution of reflected ions for some angular scans are presented in an appendix. The importance of trajectory histories is demonstrated. 3 regimes of scattering behaviour as a function of the incidence angle ψ in to the string in the surface are found:

(i) for very small ψ_in surface-semi-proper-channelling of all ions;

(ii) for intermediate ψ_in mainly planar channelling and dechannelling resulting in a decreasing reflective index for increasing ψ _in;

(iii) axial channelling and transverse plane focussing are mainly of importance leading to a small reflective index, and surface semi-channelling like for (ii) occurs for very few ions.

The importance of the scattering potential is demonstrated and an expression is discussed.     

Stark Effect of Polarons in Parabolic Quantum Wells

We report the study of Stark effect of polarons in infinite parabolic quantum wells under an electric field, taking into account the effects of interaction with bulk LO-phonons. The electron-phonon interaction and the.effective mass in the plane perpendicular to the growth direction for excited states of free polarons have been calculated as functions of the degree of confinement. The general behavior of the excited states is found to be in agreement with previous works on the ground state. It is shown that in the limit of strong confinement the differences in electron-phonon interaction and effective mass between the ground state and excited states vanish. Although the applied electric field has no effect on the electronphonon interaction or the effective mass of a free polaron system, our numerical results for an AlGaAs parabolic quantum well have demonstrated its significance in determining the coupling of electrons with bulk LO-phonons of bound polaron systems.     

Retardation of the relaxation over quantum-well energy levels in CdSe/ZnS quantum dots with increasing number of excited carriers

The differential transmission spectra of CdSe/ZnS quantum dots are investigated. It is revealed that the differential transmission spectra measured upon resonant excitation of electrons into the first excited state 1P(e) exhibit a number of specific features, such as a decrease in transmission at the pump frequency, bleaching in the course of the pump pulse at frequencies corresponding to the fundamental optical transition 1S _3/2(h)-1S(e) and transitions between excited hole states and the 1S(e) electron ground state, and retardation of this process with an increase in the energy of the pump pulse. The observed specific features can be explained by the following factors: (i) the absence of a “phonon bottleneck” for electrons due to the energy transfer from hot electrons to rapidly relaxing holes, (ii) relaxation through intermediate quantum-well energy levels of holes, and (iii) retardation of relaxation with increasing number of excited charge carriers in a quantum dot.     

Experimental consequences of a small mixture of cc̄ in the η′ and η mesons

We show that a small but significant mixing of η and η′ with the pseudoscalar cc? state may explanin the large η and η′ masses, the small mass of the new 2.8 GeV state, the large rates for ψ′ → ψη, ψ → η′γ and ψ → ηψ, the large number of photons in ψ decay, some of the missing decay modes of ψ′ and ψ and the small K/π ratio in ψ′ and ψ decays. We predict that 20–30% of all ψ and ψ′ decays contain an η′. Other tests and one important difficulty are also discussed.     

球壳量子点中极化子和量子比特的声子效应

采用求解能量本征方程、LLP幺正变换、变分相结合的方法研究 球壳量子点中极化子和量子比特的声子效应. 数值计算表明: 声子效应使极化子的基态(或激发态)能量小于电子的基态(或激发态)能量, 使量子比特的振荡周期减小, 且内径给定时, 随着外径的增大声子效应对极化子和量子比特振荡周期的影响越大; 声子效应不改变量子比特内电子概率密度分布的幅值, 量子比特内中心球面处概率密度幅值最大, 界面处概率密度为零, 其它处的概率密度幅值介于最大和最小之间, 且各个空间点的概率密度随半径和方位角的变化而变化, 随时间做周期性振荡.     

Al高掺杂浓度对ZnO导电性能影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法,在同等环境条件下,建立了未掺杂和三种不同浓度的Al原子取代Zn原子的Zn_1-xAl_xO模型,然后分别对模型进行了几何结构优化、总态密度分布和能带分布的计算.结果表明:ZnO高掺杂Al的条件下,随掺杂Al原子浓度增大,进入导带的电子增多,电子迁移率减小,电导率减小,导电性能减弱;但是随高掺杂Al的浓度减小,反而使电子迁移率增大,电导率增大,导电性能增强.计算得到的结果与实验中Al原子 关键词： Al高掺ZnO 电导率 浓度 第一性原理     

Influence of radiation cross section uncertainties on shock wave structure

This numerical study investigates the sensitivity of non-equilibrium shockwave structure to uncertainties in (a) the ground and excited state continuum radiative cross section and (b) the bound-bound radiative cross section in a three level (ground, excited, and free electronic states considered) argon-like gas at Mach 18 and a pressure of 1 cm Hg. Changing the values of the radiative cross sections by an order of magnitude does not significantly influence the relaxation region; however, a large change occurs in not only the magnitude but also the extent of both the electron and excited state precursors. Increasing either the ground state continuum or the bound-bound cross section decreases the number of free electrons in front of the shock wave. These cross sections also influence the extent of the electron precursor through their influence on the ratio of the electrons produced by ground state photoionization to those produced by ground state photoexcitation followed by excited state photoionization. The bound-bound cross section also controls the excited state precursor, because the production of excited states is entirely due to line radiation. Increasing the excited state photoionization cross section increases both the magnitude and extent of the electron precursor, because the cross section influences the ratio of the two processes that compete to produce free electrons, and at the same time it influences the magnitude of the excited state precursor.     

Interaction of dielectrics with femtosecond laser pulses: application of kinetic approach and multiple rate equation

We calculate the transient free-electron density in laser-irradiated dielectrics with two different approaches, both considering the energy distribution of excited electrons. The kinetic approach solves a system of complete Boltzmann collision integrals describing different excitation and relaxation processes in detail. The multiple rate equation (MRE) is an approximative way to keep track of the energy distribution of excited electrons with reduced numerical effort. Both methods are applied to trace dielectric breakdown, considering the changing optical parameters during irradiation with a high-intensity laser pulse. In the MRE approach we include also fast recombination, leading to a delay of the increase of the electronic density and to a decrease of the maximum number of free electrons.     

Transient convective burning of interactive fuel droplets in single-layer arrays

The transient convective burning of n-octane droplets interacting within single-layer arrays in a hot gas flow perpendicular to the layer is studied numerically, with considerations of droplet surface regression, deceleration due to the drag of the droplets, internal liquid motion, variable properties, non-uniform liquid temperature and surface tension. Infinite periodic arrays, semi-infinite periodic arrays with one row of droplets (linear array) or two rows of droplets, and finite arrays with nine droplets with centers in a plane are investigated. All arrays are aligned orthogonal to the free stream direction. This paper compares the behavior of semi-infinite periodic arrays and finite arrays with the behavior of previously studied infinite periodic arrays. Furthermore, it identifies the critical values of the initial Damköhler number for bifurcations in flame behavior at various initial droplet spacing for all these arrays. The initial flame shape is either an envelope flame or a wake flame as determined by the initial Damköhler number, the array configuration and the initial droplet spacing. The critical initial Damköhler number separating initial wake flames from initial envelope flames decreases with increasing interaction amongst droplets at intermediate droplet spacing (when the number of rows in the array increases or the initial droplet spacing decreases for a specific number of rows in the array). In the transient process, an initial wake flame has a tendency to develop from a wake flame to an envelope flame, with the moment of wake-to-envelope transition advanced for the increasing interaction amongst droplets at intermediate droplet spacing. For the array with nine droplets with centers in a plane, the droplets at different types of positions have different critical initial Damköhler number and different wake-to-envelope transition time for initial wake flame.     

Theory of Faraday rotation beats in quantum wells with large spin splitting

Spin dynamics of conduction electrons in a quantum well with a zinc blende structure is considered theoretically for the case where spin splitting exceeds the collisional broadening of energy levels. It is shown that, under certain conditions, the spin density component normal to the quantum well plane may oscillate with time even in the absence of an external magnetic field. These oscillations can be excited and detected using nonlinear two-pulse spectroscopy. Contrary to the case of small spin splitting, the external transverse magnetic field strongly affects spin dynamics in this regime.     

Multidimensional Instability of Dust‐Acoustic Solitary Waves in a Magnetized Hot Dusty Plasma with Superthermal Electrons and Ions

Multidimensional instability of dust‐acoustic solitary wave (DASW) in magnetized dusty plasma with superthermal electrons and ions and micron size hot dust particles is investigated. The Zakharov‐Kuznetsov (ZK) equation, describing the small but finite amplitude DASW, was derived using the reductive perturbation method and its solitary answers was introduced. Effects of electrons and ions superthermality as well as the external magnetic field on the nature of DASW are discussed in detail. Dispersion relation, threshold condition, and growth rate of multidimensional instability of DASW were derived using small‐k (long wavelength plane wave) perturbation expansion method. We found that the direction and strength of external magnetic field extremely affect the growth rate and instability criterion. Results show that growth rate of instability decreases with increasing the number of superthermal electrons and increases with increasing the number of superthermal ions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zur Lumineszenz des Zinkoxyds

The temperature dependance of efficiency and decay of the ultraviolet and green luminescence bands at UV- and cathode ray-excitation is investigated. In addition to earlier results the Riehl-effect is only observed when excited by cathode rays. The UV-band decays hyperbolically at all temperatures while the decay of the green band depends on kind and intensity of the excitation as well as on temperature. The results can be interpreted by considering the increasing number of electrons in the conduction band under different kinds of excitation and the variation of conductivity with temperature. Furthermore, the glow curves of various ZnO-samples (untreated and annealed in reducing atmosphere) show one or two peaks respectively, thus revealing two trap depths. As the light sum increases with the efficiency it is assumed that by reduction both activators and traps are created. The occurrence of thermoluminescence with many conduction electrons being present leads to the assumption of hole traps.     

Large scale structures in Rayleigh-Bénard convection at high Rayleigh numbers

Direct numerical simulations of Rayleigh-Bénard convection in a plane layer with periodic boundary conditions at Rayleigh numbers up to 10(7) show that flow structures can be objectively classified as large or small scale structures because of a gap in spatial spectra. The typical size of the large scale structures does not always vary monotonically as a function of the Rayleigh number but broadly increases with increasing Rayleigh number. A mean flow (whose average over horizontal planes differs from zero) is also excited but is weak in comparison with the large scale structures. The large scale circulation observed in experiments should therefore be a manifestation of the large scale structures identified here.     

Shortened equations for the elliptically polarized wave

The field of an elliptically polarized wave is represented for the convenient solution of practical problems. The wave amplitude is written in terms of four parameters: magnitude E, phase φ, angle ψ of the polarization plane, and ellipticity ? (|?| is the ratio of the ellipse axes). The shortened equations are derived using these parameters and the solution of the shortened equations is obtained for a linear medium.     

The effect of excited atomic states on the harmonic generation in a photoionized plasma

Owing to the conservation by the electrons of the memory of their intra-atomic states, a photoionized plasma arising in the mode of suppression of the ionization barrier exhibits a pronounced dependence of the efficiency of generation of the third and fifth harmonics of the pumping field on such states of electrons. For the maximal values of generation efficiency, this dependence is directly proportional to the tenth power of the principal quantum number of excited ns states of electrons.