Axial Structure of the Field Intensity in Diffusion-Controlled Surface-Wave Produced Plasmas

Surface-wave gas discharges sustained under the conditions of a diffusion controlled regime are studied on the basis of the fluid plasma model. The self-consistent behaviour of the plasma density and of the field intensity along the discharge length is obtained. It is shown that the nonlinearity in the particle balance equation due to stepwise ionisation determines the plasma density in terms of the field intensity and ensures self-consistent behaviour of the wave ? discharge characteristics in a diffusion controlled regime.     

Gasdynamic aspects of a modified expansion-shock tube for nucleation and condensation studies

A modified expansion-shock tube for nucleation and condensation studies in a supersaturated vapour is described. An analysis is made of the gas-dynamical properties of the new tube configuration and numerical simulations with the Random Choice Method are compared with experiments. It is shown that with the modified configuration one single nucleation pulse can be realized.     

Determination of low level85Kr and133Xe concentrations in the environment

This study was performed under the joint TRMC/INER program for the determination of low level⁸⁵Kr and¹³³Xe concentrations in the environmental air samples. Based on cryogenic adsorption of krypton and xenon on charcoal followed by chromatographic separation from other gases, the⁸⁵Kr and¹³³Xe recovered from 200 liters of atmospheric air can be determined by either on-line gas flow proportional counter or liquid scintillation counting. The recovery yields of krypton and xenon examined by using⁸⁵Kr and¹³³Xe tracers were nearly 100%. The minimum detectable activity of⁸⁵Kr and¹³³Xe by gas flow proportional counting is about 7.40 Bq. The method is satisfactory for environmental monitoring applications under abnormal conditions of nuclear facilities. However, for lower level environmental⁸⁵Kr and¹³³Xe measurements, the liquid scintillation counting method can be applied due to their extremely low detection limits (i.e. 0.107 Bq and 0.093 Bq for⁸⁵Kr and¹³³Xe, respectively). Using this method, the measurable limits of concentrations are 0.535 Bq/m³ and 0.466 Bq/m³ for⁸⁵Kr and¹³³Xe, respectively.     

Electron diffraction investigation of PPTA/nylon 3T blends from shear-oriented anisotropic solutions

Nematic solutions of PPTA and nylon 3T were prepared in H₂SO₄ Optical microscopy was used to ascertain the phase behaviour of the blends. In the studied concentration range, no phase separation was observed. The solutions were shear-oriented and coagulated, and the resulting samples were studied by x-ray and electron diffraction. Nylon 3T crystallised even at a low concentration, which is indicative of a phase separation. Electron diffraction investigations of the oriented samples showed that well-oriented areas, which were predominantly composed of PPTA, adjoined areas where the major component, nylon 3T, showed no orientation. The relative proportion of the unoriented areas increased with increasing nylon concentration. It was concluded that, upon coagulation, the nylon was segregated into separate phases and crystallised unoriented, whereas for PPTA, crystallisation proceeded with very little chain rearrangement therefore preserving the orientation.     

Critical evaluation of gas standards based on hydrogen

Summary Six commercial hydrogen standards containing helium, oxygen, nitrogen, methane and carbon dioxide at trace levels were analyzed by gas chromatography, for periods up to 105 days. The concentrations, in the range of 0–120 μmol mol⁻¹, were stable (with the exception of oxygen) but often significantly different from the certified values provided by the suppliers, especially for helium, oxygen and nitrogen. Concurrently, some experiments were carried out to verify the stability of gas mixtures based on hydrogen stored in cylinders submitted to different chemical and physical treatments. The causes that led to the deviations observed, as well as the decreases in oxygen, are discussed. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

Time‐integrated energy domain measurements with synchrotron radiation

A new time integrated method for the study of resonant nuclear scattering of synchrotron radiation in the forward direction or in Bragg directions is introduced. This method gives in principle similar information as the well known time differential method. A brief comparison of both methods is presented. The idea is to excite coherently the nuclei incorporated in two absorbers, one moving with respect to the other. The fields radiated by the nuclei from both absorbers interfere and each time the nuclear energy in one absorber matches, by Doppler modulation, the nuclear energy of the other, an extremum in the time integrated intensity is observed. The results of the first experiments at the Advanced Photon Source at the Argonne National Laboratory will be presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anisotropy of optical phonons in semiconductor superlattices: Raman scattering experiments

Experiments on Raman scattering in the “forward” geometry, permitting observation of anisotropy of the optical phonons, are performed on specially prepared short-period GaAs/AlAs superlattice structures with the substrates removed and the surfaces covered with an antireflective layer. The experimental data agree well with the computational results obtained for the angular dispersion of optical phonons in superlattices on the basis of a modified continuum model. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 50–55 (10 July 1998)     

Difference Sets and Recursion Theory

There is a recursive set of natural numbers which is the difference set of some recursively enumerable set but which is not the difference set of any recursive set.     

On the nature of the γ-α transition in cerium

In 1964 Davis and Adams established that the large increase of the thermal expansion and compressibility in the critical region of the γ-to α-Ce phase transition occurs predominantly in the α phase. This provides strong evidence that a tricritical point is realized in Ce. This also means that the aforementioned transition is not isomorphic and that α-Ce should have a distorted fcc structure. A careful examination of Jayaraman’s data (1965) shows that a second-order transition line continues beyond the tricritical point to the vicinity of a triple point on the melting curve. The phase boundary with the tricritical point and the minimum of the melting curve are reconstructed within the framework of Landau theory. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 111–117 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.