Deuteron dynamics in the γ phase of titanium deuterides as probed by NMR

Titanium deuterides TiD _x (x = 1.92, 1.98, 2.0) and the Ti_0.95Zr_0.05D_1.76 alloy were studied by ²H NMR in magnetic fields of 4.69 and 7.04 T in the temperature range 120–500 K. The correlation coefficients of deuteron self-diffusion calculated from the temperature dependence of the line width were described by the Arrhenius equation. The activation energies E _a and preexponential factors were determined. For the Ti_0.95Zr_0.05D_1.76 alloy, the line width was found to depend on the magnetic field, which was explained by the fact that deuterons are in different environments formed by titanium and zirconium atoms.     

The mobility of charge carriers in a size-quantized coated semiconductor wire

Within the framework of a staircase infinitely deep potential well model, the mobility of charge carriers is calculated for scattering on impurity centers located on the axis of a size-quantized semiconducting coated wire. Calculations are done for the dielectric constant mismatch of the wire, coating and surrounding environment, taking into account the difference of the effective masses in the wire and coating. The effect of a longitudinal magnetic field on mobility is also considered. Numerical results are presented for the GaAs–Ga_1−xAl_xAs system at different values of the wire and coating radii, the alloy concentration x, and magnetic field.     

Critical temperature for the nuclear liquid-gas phase transition (from multifragmentation and fission)

Critical temperature T _c for the nuclear liquid-gas phase transition is estimated from both the multifragmentation and fission data. In the first case, the critical temperature is obtained by analysis of the intermediate-mass-fragment yields in p(8.1 GeV) + Au collisions within the statistical model of multifragmentation. In the second case, the experimental fission probability for excited ¹⁸⁸Os is compared with the calculated one with T _c as a free parameter. It is concluded for both cases that the critical temperature is higher than 15 MeV. The text was submitted by the authors in English.     

Parton energy loss in an inhomogeneous color medium

The contribution of stochastic inhomogeneities to the parton collisional loss in a color medium is considered.     

Extraordinary electron transmission through a periodic array of quantum dots

We study electron transmission through a periodic array of quantum dots (QD) sandwiched between doped semiconductor leads. When the Fermi wavelength of tunneling electron exceeds the array lattice constant, the off-resonant per QD conductance is enhanced by several orders of magnitude relative to the single-QD conductance. The physical mechanism of the enhancement is delocalization of a small fraction of system eigenstates caused by coherent coupling of QDs via the electron continuum in the leads.     

Structure Determination of Binuclear Triple-Decker Phthalocyaninato Complexes by NMR via Paramagnetic Shifts Analysis Using Symmetry Peculiarities

The detailed knowledge about the structure of multinuclear paramagnetic lanthanide complexes for the targeted design of these compounds with special magnetic, sensory, optical and electronic properties is a very important task. At the same time, establishing the structure of such multinuclear paramagnetic lanthanide complexes in solution, using NMR is a difficult task, since several paramagnetic centers act simultaneously on the resulting chemical shift of a particular nucleus. In this paper, we have demonstrated the possibility of molecular structure determination in solution on the example of binuclear triple-decker lanthanide(III) complexes with tetra-15-crown-5-phthalocyanine Ln₂[(15C5)₄Pc]₃ {where Ln = Tb (1) and Dy (2)} by quantitative analysis of the pseudo-contact lanthanide-induced shifts (LIS). The symmetry of complexes was used for the simplification of the calculation of pseudo-contact shifts on the base of the expression for the magnetic susceptibility tensor in the arbitrary oriented magnetic axis system. Good agreement between the calculated and experimental shifts in the ¹H NMR spectra indicates the similarity of the structure for the complexes 1 and 2 in solution of CDCl₃ and the structure in the crystalline phase, found from the data of the X-ray structural study of the similar complex Lu₂[(15C5)₄Pc]₃. The described approach can be useful for LIS analysis of other polynuclear symmetric lanthanide complexes.     

Differences Between Consecutive Primes

Let p_n be the nth prime. Then this paper is concerned with provingthe following result on the distribution of consecutive primes. The exponent of x in this theorem improves on the work of Heath-Brownwho proved (1) with exponent . Under the Riemann hypothesisone can prove (1) with exponent .The proof of the theorem startswith the Heath-Brown–Linnik identity which leads to aformula giving the number of primes in an interval in termsof coefficients of certain Dirichlet series. I then estimatethe coefficients by using, among other things, the informationwhich can be gained from Montgomery's mean value theorem andHuxley's version of the Hal' asz lemma. Furthermore, by usingfamiliar sieve arguments I am able to discard some of the coefficientsallowing us to gain an improvement over the previous resultof Heath-Brown. 1991 Mathematics Subject Classification: 11N05.     

The energy-loss rate via polar-optical phonon scattering in quantum wires

The hot-electron energy-loss rate (ELR) conditioned by confined and interface polar-optical (PO) phonons for a quasi-one-dimensional cylindrical quantum wire embedded in a dielectric medium is investigated analytically. It is shown that the inclusion of the PO-phonon confinement effects is crucial for accurate calculation of the ELR in quantum wire. Taking into account the nonequilibrium phonon populations, the hot-electron ELR is derived by a model, which includes the lowest subband occupation and the phonon confinement effects. The contribution of intersubband transitions to electron ELR for the GaAs quantum wire embedded in Al_xGa_1−xAs is estimated. The extrema on the ELR dependences on electron density are obtained.