Formation of ultrashort microwave pulses in coaxial cavities

We describe shaper cavities for the production of ultrashort microwave pulses with a minimum duration of one period of the high-frequency field and a power of several tens of megawatts. Experimental results are presented.Scientific and Research Insititute for Nuclear Physics at S. M. Kirov Polytechnical Institute, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 12, pp. 1250–1256, December, 1995.     

2H NMR spectra of 2-(p-heptylbenzoyloxy)-5-(p-heptylbenzenazo)tropone. A new sigmatropic liquid crystal

Liquid crystals incorporating in their molecular framework a seven-membered ring are still relatively rare [1]. Recently the synthesis and thermal behaviour of a series of liquid crystal materials having a tropone moiety in their mesogenic core have been reported [2-4]. These mesogens, based on a 2-(acyloxy)tropone core structure, show intramolecular migration of the acyl substituents between the two oxygen atoms at C-1 and C-2, an effect already known for simple 2-(acyloxy)tropones in their isotropic solutions [5]. This migration involves a concerted [1, 9]-sigmatropic rearrangement [2]. This rearrangement could play a major role in determining the properties of the mesophases: it has been suggested in fact that, because of this rearrangement, the mesogenic molecules acquire a mean rod-like shape which can sustain the mesophase formation [2].     

Numerical solution of the electron distribution function for ECRheating in magnetic mirror

The Fokker-Planck equation is solved with electron cyclotron resonance heating in a magnetic mirror with a fixed electrostatic potential on a loss-cone boundary and ECR heating. A self-consistent calculation of the plasma concentration justifies the fact that the degree of ionization of the ECR plasma is about 10%. The high values of the total electron energy (15-30 eV) are achieved. The electron concentration and the EVDF anisotropy degree are the nonmonotonic functions of the applied MW electric field. The basis for such dependencies is discussed. A linear perturbation analysis of the Vlasov equation together with with Maxwell's equations is briefly reviewed. The criteria for the start of unstable whistler oscillation growth are proposed. Using the simulated distribution function, the regimes where the unstable oscillations should to be taken into account are considered     

Studies on solution cast perfluorocarbonsulfonic acid ionomers

The thermal properties of perfluorocarbonsulfonic acid ionomer films cast from solution and their temperature-dependent far infrared spectra have been investigated. In addition to the endotherms and spectral changes associated with the loss of solvent as the films were heated, a significant exotherm has been observed and assigned to the relaxation associated with rearrangements resulting in partially crystallized phases in insoluble thermally treated membranes. © 1993 John Wiley & Sons, Inc.     

Measurement of the spin and temperature dependence of ddµ molecule formation rate in solid and liquid deuterium

The ddµ molecule formation rate is experimentally measured for the two hyperfine states of the dµ-atom in the temperature range of 5–30 K. Results are consistent with a preliminary measurement by the TRIUMF group and contradict theoretical predictions. The work has been performed on the JINR phasotron (Dubna).     

Electron transfer at lanthanum endohedral fullerenes

The aim of this contribution is to study lanthanum containing fullerenes produced and treated under different conditions. The work was done using solid soot extract giving poorly resolved ESR spectra or separated lanthanofullerenes in solution showing well resolved ESR spectra. ESR experiments in connection with the mass spectrometry give information on the electronic states due to the electron transfer from the endohedral metal to the fullerene cage and the influence of oxygen on endohedral lanthanofullerene. The analysis of ESR spectra indicates the presence of up to nine octets of lanthanum containing fullerenes. These species have different stabilities. Furthermore, a very narrow single ESR line in the lanthanofullerene spectrum was detected having a linewidth ΔB=0.008 mT and ag-factor 2.0025. The electron transfer to the endohedral La@C₈₂ molecule studied by voltammetry and electrochemicalin situ ESR experiments is described. The interaction of the lanthanofullerene with oxygen in solution is also studied. In different solvents the influence of oxygen on line broadening in the ESR spectra of La@C₈₂ was observed.     

Exciton molecules and exciton liquids in semiconductors

Excitons in many-valley semiconductors form molecules consisting of four and more excitons. The degeneracy factor g of the conduction band in germanium is 8, and in silicon g=12. As in acceptors, the hole ground state in excitons is fourfold degenerate. The same is valid for exciton molecules, because they are quantum objects with spherical symmetry. The exciton binding energy in molecules is close to that in exciton-liquid droplets. Experimental evidence is considered for the existence, besides biexcitons, of stable exciton molecules consisting of three and four, and, possibly, 11 and 12 excitons. Molecules containing from five to ten excitons are apparently unstable. Fiz. Tverd. Tela (St. Petersburg) 40, 929–931 (May 1998)