Measurement of low-frequency noise in tunnel diodes

Conclusions Our studies have revealed that the spectral density of low-frequency current fluctuations in GaAs tunnel diodes can be described by the relation Wi(u, F)=f² (u)mF^–, where the nonlinear function f²(u) is not proportional to the rms of excess diode current. The flicker nature of the current noise in tunnel diodes derives from conductance fluctuations on the p-n junction, which occur in tunnel diodes as well as in low-noise transistors at frequencies ranging from near zero to a few kiloheriz and produce noise of almost the same absolute intensty in both kinds of devices.Leningrad Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 20, No. 5, pp. 777–784, May, 1977.     

On the Lie-Trotter theorems inL p -spaces

In this paper we consider operatorsH ₀ andV possessing the following properties:

1. H ₀ is a positive self-adjoint operator acting inL ²(M, γ) with γ a probability measure, so that exp(?tH ₀) is a contraction onL ¹(M, γ) for eacht>0.
2. V is a semibounded multiplicative operator acting inL ²(M, γ) {fx379-1}

Under these assumptions theorems of Lie-Trotter type are derived for the operatorsH, H ₀, V, whereH is a self-adjoint extension of the algebraic sumH ₀+V, and is built by the form method. Under the additional assumption thatV(·)∈L ²(M, γ) we prove an essential self-adjointness ofH ₀+V. The results obtained are applicable to non-relativistic quantum mechanics.     

Competition between polyelectrolyte macromolecules and amphiphilic polymer micelles in interaction with copper nanoparticles

Competition between poly(1,2-dimethyl-5-vinylpyridinium methyl sulfate) polycationic macromolecules and micelles of amphiphilic polymers containing hydrophilic and hydrophobic blocks (polyethylene glycol-600 monolaurate and poly-N-vinylpyrrolidone monostearate) for copper nanoparticles was studied by means of electrophoresis and electron microscopy techniques. It was shown that, irrespective of the formation method, almost all copper nanoparticles were bonded to the polycation in polycation-polyethylene glycol-600 monolaurate mixed solutions but were distributed between the polymers in polycation-poly-N-vinylpyrrolidone monostearate mixtures. It was concluded that the stability of the complex of copper nanoparticles with the polycation is higher than that with polyethylene glycol-600 monolaurate and is comparable with that of the copper particle-poly-N-vinylpyrrolidone monostearate complex.     

Structure and ambiphilic reactivity of indolizines. 6. Scope of the isomerizational recyclization of indolizines

The behavior of substituted 6- and 8-nitroindolizines in the isomerizational recyclization reaction has been examined. A novel method of synthesis of 2-acyl-5- and 7-nitroindoles has been developed, by recyclization of 3-acyl-6- and 8-nitroindolizines. The scope of the isomerizational recyclization of indolizines for the synthesis of indoles has been established.For Communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 758–764, June, 1990.     

Interpreting the optical spectra of trace Fe2+ in layer silicates

Estimates have been made of Fe²⁺ term splittings in axial crystalline fields. It is found that all three long-wave bands in the optical spectrum are due to Fe²⁺ Fe³⁺ charge transfer, while the splitting of ⁵T_2g and ⁵E_g occurs in low-symmetry fields. Experimental evidence is presented for these calculations.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 4, pp. 464–468, July–August 1987.     

Asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by nucleophilic addition of triazolethiols to a NiII complex with a chiral dehydroalanine Schiff base

An efficient method was developed for the asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by the addition of 3,4-disubstituted 1,2,4-triazole-5-thiols at the electrophilic C=C bond in a Ni^II complex of a Schiff base of dehydroalanine with (S)-N-(N-benzylprolyl)aminobenzophenone. The stereoselectivity of the formation of diastereomeric complexes with the (S,R) configuration under conditions of thermodynamic control of the nucleophilic addition exceeds 94%. Acid treatment of the reaction mixtures afforded enantiomerically pure (R)-S-hetarylcysteines (ee >98%).     

Enhanced electrical conductivity in chemically modified carbon nanotube/methylvinyl silicone rubber nanocomposite

Chemically modified multiwalled carbon nanotubes/methlyvinyl silicone rubber (m-MWNT/VMQ) nanocomposites with relatively good dispersion of nanotubes were prepared by treating the surface of MWNT using γ-aminopropyltriethoxy silane (KH550). Significant enhanced electrical conductivity was discovered in the m-MWNT/VMQ nanocomposites. The results could be attributed a strong interaction between m-MWNT and VMQ which was from the chemically modification of the surface for MWNT. The electrical property was also discussed in order to understand the percolation and electrical transport mechanism. The m-MWNT/VMQ nanocomposites with high conductivity in this study are promising application as one of novel functional materials.     

Water-methanol-benzene ternary system. Thermochemical experiment and computer simulation

Solution heats have been measured for benzene dissolved in mixtures of water with methanol at 25°C. The resulting values are compared with data for water-methanol-aniline, water-acetonitrile-benzene, and water-acetonitrile-aniline systems. Computer simulations have been performed for binary mixtures of water with methanol and dilute solutions of benzene in these mixtures. Thermodynamic and structural characteristics of solutions were obtained by calculations. The enthalpy of benzene transfer from water into a mixed solvent correlates with the relative deviation of the local composition from the mean composition of the mixture.     

三芳基膦配体的合成研究

从间溴苯酚出发, 利用新的合成方法经五步反应合成了一系列具有不同烷氧基的芳基膦配体. 改进后的方法可方便地通用于在苯环上具有各种不同基团基的膦配体衍生物的合成, 且有原料易得、操作简单、产率较高的优点.     

Diffusion of point defects participating in solid-phase chemical reactions (trap diffusion): Demonstration for the Ti3+ → Ti4+ transition in corundum

A problem of trap diffusion, that is diffusion of point defects in crystals participating in a solid-phase chemical reaction with motionless impurity ions, is solved. Time dependences of the reaction-front displacement, X_f, and its steepness, $\text{(}\text{?C}\text{?X}\text{)}{}_{\mathrm{f}}$ are determined analytically for N₀ ? C₀ and numerically for all relations of N₀ and C₀$\text{x}{}_{\mathrm{f}}{}^2\text{=2}\text{N}{}_0\text{C}{}_0\text{Dt; (}\text{ac}\text{ax}\text{)}{}_{\mathrm{f}}\text{=0.3C}{}_0{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{(}\text{g}\text{D}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2></mtext>}}$where C₀ and N₀ are the initial concentration of impurity and the eqilibrium defect concentration, respectively, D is a diffusion coefficient, and g is a chemical reaction constant. Dependence of X_f vs C₀ and t is confirmed for oxygen annealing of corundum crystals doped with titanium which, reacting with the point defects, changes its valency. The data are obtained for dependence of displacement X_f upon partial oxygen pressure and thermotreatment temperature as well as upon the sign of the constant electric field applied to the sample. From these data we conclude that the reaction of titanium impurity, changing from the three-valent to the tetravalent state at the activation energy of 80 ± 8.5 kcal/mole is due to anisotropic diffusion of charged aluminum vacancy and holes in the valence band. The diffusion coefficient for that process at 1500°C is estimated to be larger than 10^?5 cm²/sec. Using the trap-diffusion features, the concentration of optical centers of the 0.315-μm absorption band in ruby is also estimated.