Two-temperature channel model of a direct current arc

A relatively simple method is proposed for computing the gas and electron temperatures in an arc plasmotron channel within the framework of the self-consistent two-temperature channel model of an arc discharge. This method affords the possibility of obtaining the gas and electron temperature distribution with good enough accuracy for given discharge parameters (current intensity in the discharge, power inserted in the discharge, etc.) as a function of the radial coordinate in both nonequilibrium (T_e T_ai) and quasi-equilibrium (T_e = T_ai within the current conducting channel) cases. The results obtained can be utilized in model computations to estimate the gas and electron temperatures as well, possibly, as in a number of engineering computations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 80–86, July, 1990.The author is grateful to L. A. Rachevskii for useful discussion of results of the research.     

Direct ion beam deposition of polymeric styrene films and in situ characterization by electron spectroscopy

Polymeric styrene films with thicknesses ranging from about one nm up to a few m have been deposited by means of a direct ion beam deposition (IBD) technique. The deposition energy, which can be chosen independently of the parameters which govern the plasma conditions, has been varied between few eV and 1000 eV. The correlation between the deposition parameters and the resulting film properties in terms of the electronic structure is discussed. The in situ characterization by electron spectroscopy has proved to be a very useful characterization method and ultraviolet photoelectron spectroscopy in particular revealed an extremely high sensitivity to structural differences in the deposited films. The polymeric films have also been characterized by scanning electron microscopy and optical spectroscopy. These techniques have also served to compare films prepared by the direct IBD technique with films obtained by standard rf plasma polymerization (RFPP) in a tubular reactor. Significant differences have been found which are dependent on the deposition parameters; these are discussed in detail.Department of Chemical Engineering, Beijing Institute of Technology, P.O. Box 327 Beijing, 100081 Beijing, P.R. China     

A quasi double-grating grazing incidence pulsed dye laser

Continuous scanning of a 1 GHz pulsed laser line using only one 5-cm grating as an intracavity selective element is obtained from a pulsed dye laser pumped by a Nd: YAG (8 ns-532 nm) laser. Such a single-grating dye laser operates in the same way as a real double-grating grazing incidence laser and provides an appreciable improvement of the resolution (enhancement factor 2), compared with previous grazing incidence ones. The superiority of this laser cavity has been proved for single-longitudinal-mode operation.Laboratoire associé à l'Université de Paris-Sud     

Ultrabroadband laser using prism-based “spatially-dispersive” resonator

An ultrabroadband (up to 35 nm FWHM) generation by a pulsed dye laser is reported. The principle of laser operation is based on a recently proposed cavity configuration, which we have termed spatially-dispersive resonator. By means of a prism pair this spreads the various spectral components into different spatial areas in the active medium and thus reduces the competition between them. A generation of a spectrum containing a number of equally spaced lines is also demonstrated.     

Upper-Branch Instability of Flow in Pipes of Large Aspect Ratio with Three-Dimensional Nonlinear Viscous Critical Layers

We consider the upper-branch neutral stability of flow in pipesof large aspect ratio, basically extending the work of F. T.Smith to the nonlinear regime. The inclusion of weak nonlinearityleads to an eigenproblem whose solution depends on the propertiesof three-dimensional nonlinear critical layers. Two specialcases are considered. The first is for very small amplitude perturbations, where R is a Reynolds numberbased on the height of the tube and which is assumed large.Then a fully analytical solution of the three-dimensional criticallayers is possible, from which the linear results of Smith maybe deduced. The second case studied is that of flow in a rectangularpipe, where a solution of the nonlinear critical layer problemcan be obtained. Further analysis of neutral modes in this lattercase suggests the possible existence, inter alia, of neutralmodes for finite aspect ratio tubes. These modes depend on thescaled amplitude and have O(1) wavespeeds.     

Quantum BRST charge for quadratically nonlinear Lie algebras

We consider the construction of a nilpotent BRST charge for extensions of the Virasoro algebra of the form {T _a ,T _b }=f _ab ^c T _c +V _ab ^cd T _c T _d , (classical algebras in terms of Poisson brackets) and [T _a ,T _b ]=h _ab I+f _ab ^c T _c +V _ab ^cd (T _c T _d )(quantum algebras in terms of commutator brackets; normal ordering of the product (T _c T _d ) is understood). In both cases we assume that the set of generators {T _a } splits into a set {H _i } generating an ordinary Lie algebra and remaining generators {S }, such that only theV _ij are nonvanishing. In the classical case a nilpotent BRST charge can always be constructed; for the quantum case we derive a condition which is necessary and sufficient for the existence of a nilpotent BRST charge. Non-trivial examples are the spin-3 algebra with central chargec=100 and theso(N)-extended superconformal algebras with levelS=–2(N–3).     

Crystal structures of dimethylsuccinate and dimethyloxalate: Carbonyl group orientation for C13 chemical shielding tensor studies

The crystal structures of dimethylsuccinate (DMS) and dimethyloxalate (DMO) have been determined to facilitate the determination of the C-13 chemical shielding tensors of the carbonyl carbon in esters. Crystals of DMS are monoclinic, space groupC2/c,Z=4,a=13.154(4),b=6.156(1),c=9.363(4)Å,=98.53(3)°. The structure was solved by direct methods and refined by leastsquares procedures to giveR=0.071 for 932 observed data. Crystals of DMO are monoclinic space group,P2₁/n,Z=2, witha=3.891(1),b=11.879(2),c=6.213(2) Å,=103.32(2)°. The structure is the same (within experimental error) as that reported by Dougill and Jeffrey (1953) and refined to giveR=0.074 for 395 observed data.     

A modified Tolman mass-energy formula

A modified Tolman mass (energy) formula is derived for spherically symmetric, time-independent systems. In the absence of surfaces of discontinuity, the modified formula has, in contradistinction to the original formula, the following desirable properties: (i) it always gives the correct mass of the system as a whole; (ii) it always gives the correct mass of any portion of the system which is surrounded by vacuum; and (iii) it remains invariant under a rescaling of the time coordinate of the formt Ct, C=constant. In the presence of surfaces of discontinuity the Tolman mass formula is further modified by the addition of the Israel mass associated with each surface. The resulting formula also has the above three properties. A new exact solution of Einstein's equations which is well behaved everywhere and is, in a sense, a generalization of Florides' new interior Schwarzschild solution is also presented.This result explains why, takingT ₁ ¹ =[C] in Section 2, we were able to obtain a solution free of surfaces of discontinuity.     

Pair formation in age-structured populations

The modelling problems associated with pair formation in age-structured populations are discussed in this paper. The author also formulates a class of models for pair formation in human populations and derives some results on persistent distributions.