Mechanism of current flow in alloyed ohmic In/GaAs contacts

A mechanism of current flow in an alloyed ohmic In contact to low-doped gallium arsenide (n = 4 × 10¹⁵ cm^?3) is studied. From the temperature dependence of the contact resistance per unit surface area, it is found that the basic mechanism of current flow is thermionic emission through a potential barrier 0.03 eV in height.     

Charge-changing cross sections of the neutron-rich isotopes8,9,11Li

Total charge-changing cross sections have been measured for⁸Li on C and Pb targets, for⁹Li on C, Al, Cu, Sn and Pb targets, as well as for¹¹Li on C, Sn and Pb targets at about 80 MeV/nucleon. These data are compared to measured total reaction cross sections and Glauber-type calculations using Hartree-Fock density distributions. These comparisons allow to draw conclusions on the proton density distribution of the neutronrich lithium isotopes. The results show that even for the most exotic nucleus¹¹Li the proton distribution is only very weakly influenced by the long tail in the neutron density distribution already established in several experiments.     

Influence of iron-subgroup metals on the atomization of silicon in a graphite furnace

The regime of atomization of Si in the presence of Fe-subgroup metals was investigated with the use of a “Saturn” spectrophotometer and a “Graphit-2” electrothermic atomizer. The optimal operating parameters of the atomizer have been determined. It was established that the optimal value of the ashing and the atomization temperatures are, respectively, 900–1000°C and 2400°C, the optimal rate of temperature rise at the stage of atomization is 1400 K/sec, and the appropriate amount of Fe, Co and Ni additions is 1–2 μg. It was established that the formation of gaseous silicides of the Fe-subgroup metals, the dissociation energies of which are lower than the dissociation energies of Si oxides and carbides, increases the sensitivity for determination of Si. To whom correspondences should be addressed. Institute of Single Crystals, National Academy of Sciences of Ukraine, 60, Lenin Ave., Khar'kov, 310001, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 153–157, March–April, 1999.     

Complete structure determination of the astrophysically important nucleus Na below the proton threshold

The fusion–evaporation reaction ¹⁰B(¹²C, 2n) was used to make the first observation of in-beam γ decays from the astrophysically important nucleus ²⁰Na, lying adjacent to the proton drip-line. All states below the proton threshold in ²⁰Na were populated and identified in the experiment. These include new levels, previously unresolved levels, and states located with improved energy precision. The level structure of ²⁰Na, and its γ transitions, are compared to the mirror partner ²⁰F measured simultaneously in this experiment. In particular, a high degree of energy stability is found for all negative parity states. These results are discussed in the context of the nuclear shell model.     

Elastic properties of ultrahard fullerites

The elastic properties of C₆₀ fullerite samples synthesized under pressure P=13.0 GPa at high temperatures were investigated using acoustic microscopy. The velocities of longitudinal (c _L=17–26 km/s) and transverse (c _T=7.2–9.6 km/s) elastic waves in the samples were measured. It was established that the longitudinal sound velocity of ultrahard fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard samples is higher than that of diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substantial Poisson ratio indicate that the structure of the ultrahard fullerites is fundamentally different from that of diamond. Zh. éksp. Teor. Fiz. 114, 1365–1374 (October 1998)     

On the tensor product of supersingleton representations ofosp(1, 2n)

The tensor product of two supersingleton representations _n of the Lie superalgebraosp (1, 2n) is studied forn2. The main results are as follows: (a) anticommutators and commutators of the odd generators in _{n n} form a skew-symmetric representation of the Lie algebrau(n, n); (b) simple explicit form of all irreducible components of _{n n}, which are labelled by a single parameterJ=0, 1, ..., has been found. Each of them is a^*-representation ofosp (1, 2n) for which assertion (a) is valid. The dimension of its vacuum subspace equals , i.e., the nondegenerate vacuum occurs for J=0 only. Basic property of this family of irreducible^*-representations of osp(1, 2n) are analogous to those of massless representations of osp(1, 4).Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.     

Phosphine-catalyzed intramolecular γ-umpolung addition of α-aminoalkylallenic esters: facile synthesis of 3-carbethoxy-2-alkyl-3-pyrrolines

An array of N-tosylated α-aminoalkylallenic esters was prepared and their cyclization under the influence of nucleophilic phosphine catalysts was explored. The α-aminoalkylallenic esters were prepared through aza-Baylis-Hillman reactions or novel DABCO-mediated decarboxylative rearrangements of allenylic carbamates. Conversion of these substrates to 3-carbethoxy-2-alkyl-3-pyrrolines was facilitated through Ph(3)P-catalyzed intramolecular γ-umpolung addition.     

Use of the mathematical apparatus of two-component spectrophotometry for the simultaneous catalymetric determination of two anions

Previously studied reactions of aluminum(III) with Xylenol Orange and of cobalt(III) with nitroso-R salt in weakly acidic solutions were proposed for the simultaneous catalymetric determination of carbonate and borate ions and carbonate and phosphate ions, respectively. It was demonstrated that the mathematical apparatus of two-component spectrophotometry is suitable for processing the results of analysis.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 7–10.Original Russian Text Copyright © 2005 by Mikhailova, Belikov, Blank.