Capacitance-voltage behaviour inp-type ɛ-GaSe single crystal ∥c at different temperatures

Summary  Capacitance-voltage measurements have been carried out onp-type ɛ-GaSe single crystal ∥c in the temperature range 300 to 360 K, with applied voltages of -1, 0 and +1 V. TheC-V measurements in this temperature range have shown a shift in capacitanceC and conductanceG to the higher values with an increase in temperature. The depletion layer widthW, the Debye length L_D and the doping densityN _α have been worked out and plots ofN _α vs. W have shown a decrease inW with an increase in temperature. The plots of L_D vs. N _α vary as 1/N_α^1/2, which gives N_αL_D ⋍ 3.3 × 10¹¹ charges/m² for doping density of 10¹⁶m⁻³. The values ofG at different temperatures have been used to obtain the activation energies, which are found to be ΔE ⋍ 0.11 eV for -1 and +1 V applied voltages, and ΔE ⋍ 0.06 eV for zero volt. The authors of this paper have agreed to not receive the proofs for correction.     

Self-assembly of Mo<Subscript> 6</Subscript>S<Subscript> 8</Subscript> clusters on the Au(111) surface

The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo₆S₈ on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact. It experiences a strong, mostly non-ionic attraction to the surface at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room temperature. The analysis of the electronic structure reveals a negligible electron transfer and S-Au hybridised states, which indicate that the cluster-surface interaction is dominated by S-Au bonds, with minor contributions from the Mo atom in the surface vicinity. All results indicate that Mo₆S₈ clusters on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within nano-devices. Therefore, a classical potential model was developed on the basis of the DFT data, which allows to study larger cluster assemblies on the Au(111).     

Multi-strange systems in relativistic mean fields

Characteristics of multi- hypernuclei are investigated within the relativistic mean-field theory. Both linear and nonlinear models and a variety of couplings fitted to ordinary hypernuclei have been investigated. All the parametrizations used in the present work predict qualitatively similar dependence of the studied quantities (rms radii, binding energies, densities) on a number of hyperons.Deceased on May 5, 1991     

Large scale magnetic field influence on trap recharging waves in InP:Fe and GaAs:Cr

An impressive linear influence of a magnetic field on optically generated trap-recharging waves (TRW) has been observed in InP:Fe and GaAs:Cr. The phenomenon appears for the particular orientation of parallel to the samples’ surface and orthogonal to the direction of the electric field and wave vector of the TRW . The results are qualitatively explained taking into account the Lorentz force and a pronounced inhomogeneity of the charge transport and of the TRW parameters.     

Magnet design and beam dynamics in computed fields for the DC-350 cyclotron

The DC-350 is an isochronous cyclotron designed in the Flerov Laboratory of Nuclear Reaction (FLNR). It is intended for accelerating ions with a mass-to-charge ratio A/Z within an interval of 5–10 and with an energy of 3–12 MeV/u at the extraction radius. These ion beams will be used in nuclear and applied physics experiments. The paper describes the results of a 3D magnet simulation. The cyclotron magnet and IM90 analiziting-bend magnet of the axial injection channel are studied here. The influence of correction coils on the cyclotron magnet is calculated. All magnet fields were calculated by MERMAID 3D code [1]. The text was submitted by the authors in English.     

Initial state-resolved excited state absorption spectroscopy of ZBLAN:Ho<Superscript>3+</Superscript> glass

Phase-sensitive and frequency-resolved detection techniques are used for the initial state-resolved excited state absorption (ESA) measurements in ZBLAN:Ho³⁺ glass. Both experimental techniques were applied simultaneously in a broad spectral range (550–1750 nm) for the first time. Estimated results are compared and discussed in detail. A simple kinetic model, used for qualitative considerations, is presented and successfully compared with the experimental data. The measured spectra will be useful for identifying new up-conversion excitation channels in the considered system, where ESA transitions originating from several excited levels are observed.     

Finite-size effects on the statistics of extreme events in the BTW model

The BTW Abelian sandpile model is a prominent example of systems showing self-organised criticality (SOC) in the infinite size limit. We study finite-size effects with special focus on the statistics of extreme events, i.e., of particularly large avalanches. Not only the avalanche size probability distribution, but also the mutual independence of large avalanches in the critical state is affected by finite-size effects. Instead of a Poissonian recurrencetime distribution, in the finite system we find a repulsion of extreme events that depends on the avalanche size and not on the respective probability. The dependence of these effects on the system size is investigated and some data collapse is found. Our results imply that SOC is an unsuitable mechanism for the explanation of extreme events which occur in clusters.     

Calculation by plane wave Born approximations of electron-impact ionization of silver and copper

The plane wave Born approximation is used to calculate total electron impact ionization cross section of silver and copper. Wavefunctions of the target and residual ions were modeled by non orthogonal Hartree-Fock and Dirac-Fock orbitals. The wave functions of the atom and residual ion are calculated with allowance for relaxation effects. The one-electron wavefunction of the continuous spectrum for the ejected electron is obtained using single-configuration Hartree-Fock and Dirac-Fock method. The orthogonalization of the ejected electron wave functions to all occupied orbitals of the target atom is performed. Results of calculations are compared to available experimental measurements and theoretical calculations performed by non relativistic one-electron PWBA, where the ejected electrons is modeled by the hydrogenic Coulomb wave function.     

Impurity states of electrons in quantum dots in external magnetic fields

The influence of isolated impurity atoms on the electron energy spectrum in a parabolic quantum dot in quantizing magnetic field is studied. The impurity potential is approximated by a Gaussian separable operator which allows one to obtain the exact solution of the problem. We demonstrate that in the electron energy spectrum there is a set of local levels which are split from the Landau zone boundaries in the upward or downward direction depending on the impurity type. We have calculated the local level positions, the wave functions of electrons in bound states, and the residues of the electron scattering amplitudes by impurity atoms at the poles.     

Investigation of the fusion of heavy nearly symmetric systems

Excitation functions in the vicinity of the Coulomb barrier have been measured for the formation of evaporation residues in¹⁰⁰Mo-induced fusion reactions with^{90, 92, 96}Zr,^{92, 96, 98, 100}Mo,¹⁰⁴Ru and¹¹⁰Pd as well as for the system⁹⁶Zr+⁹⁶Zr. From these data the fusion probability in central collisions was extracted covering a range of 4 orders of magnitude. At the fusion barriers expected from systematics we find that the fusion probability is suppressed by one to three orders of magnitude. It is rising very gradually at higher energies and reaches for the heaviest systems saturation only at energies as high as 30 MeV above the barrier. The observed hindrance of the fusion process increases roughly with the growing Coulomb repulsion between the collision partners, but there is also a distinct influence of their individual nuclear structure. The data are compared to the extra-push model, the surface-friction model and the diabatic fusion model. A parameterisation of the extra-push energy and its fluctuation in terms of a macroscopic quantity like the Coulomb repulsion combined with a microscopic quantity characterizing the nuclear structure is proposed. As a byproduct of this work a new alpha emitter,¹⁹¹Po, could be identified. Its half-life is (15.5 _–2.5 ⁺⁶ ) ms, the alpha energy is (7314±20) keV.     

M1-transitions and the mutual orientation of the unpaired nucleons in odd-odd nuclei

Experimental lifetimes and branching ratiosB(M1)/B(E2) are used to determine reduced M1-transition probabilities between collective-band levels withI=1 in^{102, 104, 106}Ag and in the odd-odd isotopes of La, Pr, Pm and Tl. The extractedB(M1) values are compared with calculations in the framework of the quasiclassical approximation and the model axial rotor+two quasiparticles. The reduced M1-transition probabilities along with the magnetic moments were found to depend on the mutual orientation of the angular momenta of the unpaired nucleons in the odd-odd nuclei.The authors would like to thank the staffs of Cyclotron Laboratory of P.T.I. in St. Petersburg and the Nuclear Moments Laboratory of I.N.R. in Kiev for assistance in the experiments. One of us (A.I.L.) wishes to thank the Sektion Physik of the Ludwig Maximilians Universität München for its hospitality and financial support.     

Modulation control and spectral shaping of optical fiber supercontinuum generation in the picosecond regime

Numerical simulations are used to study how fiber supercontinuum generation seeded by picosecond pulses can be actively controlled through the use of input pulse modulation. By carrying out multiple simulations in the presence of noise, we show how tailored supercontinuum spectra with increased bandwidth and improved stability can be generated using an input envelope modulation of appropriate frequency and depth. The results are discussed in terms of the nonlinear propagation dynamics and pump depletion.     

Excited states populated via nucleon transfer in the reaction32S +208Pb

The population strengths of excited states in nuclei produced via transfer reactions in the 185 MeV³²S +²⁰⁸Pb reaction have been investigated by heavy-ion- coincidence techniques. The cross sections extracted from the spectra, have been analyzed in the framework of the Complex WKB approximation theory.     

Propagation of terawatt laser pulses in the air

One of the problems when increasing the intensity of a femtosecond laser pulse is the propagation of the beam. As the intensity increases nonlinear effects begin to play a significant role. When arriving to the terawatt domain, nonlinear effects and filamentation give rise to a new phenomenology in the propagation. The aim of this paper is to analyze new possibilities to control the beam shape to Taylor the interaction of the beam with the target at large distances.     

The effect of angular-momentum dissipation on fluctuations of excitation functions in heavy-ion collisions

We discuss here the effect of dissipation of relative angular momentum on fluctuations of excitation functions in dissipative heavy-ion collisions. Dissipation and fluctuation of relative angular momentum modify and smooth the time-angle localization of the rotating dinuclear system. The secondary maxima in the energy correlation function of the cross-section shift to smaller values of the energy difference, the shift depending on the relaxation time and the diffusion coefficient for angular-momentum dissipation. The results are illustrated for the collision²⁸Si(E _lab=130 MeV)+⁴⁸Ti.Partly supported by the Alexander von Humboldt Foundation     

Conductance through analytic constrictions

We study the dependence of the intrinsic conductance of a nanocontact on its shape by using the recursion-transfer-matrix method. Hour-glass, torus, and spherical shapes are defined through analytic potentials, the latter two serving as rough models for ring-like and spherical molecules, respectively. The sensitivity of the conductance to geometric details is analyzed and discussed. Strong resonance effects are found for a spherical contact weakly coupled to electron reservoirs.     

Wave localization in two-dimensional periodic systems with randomly disordered size

The expression of the localization factor in the two-dimensional periodic systems is derived based on the plane-wave expansion, transfer matrix and matrix eigenvalue methods. A comprehensive study is performed for the wave localization in the phononic crystal which is composed of steel cylinders embedded in epoxy matrix with the randomly disordered rod size. From the results, it can be observed that with the increase of the disorder degree, the localization phenomenon is strengthened. Furthermore, the filling fraction has significant effects on the wave localization characteristics.     

Non-commutative harmonic oscillator in magnetic field and continuous limit

The spectra of a charged harmonic oscillator minimally coupled to a perpendicular magnetic field in the non-commutative plane are studied by using the path integral formulation. We get the spectra in a mapping-independent way. Interestingly, we find that the spectra have no continuous limit when the dimensionless parameter tends to zero. In order to get a finite result, a truncation is inevitable. Finally, we give a reasonable explanation of truncation from the constrained theory point of view.