The cohomology rings of the orbit spaces of free transformation groups of the product of two spheres

Let , a prime (resp. , act freely on a finitistic space with (resp. rational) cohomology ring isomorphic to that of . In this paper we determine the possible cohomology algebra of the orbit space .

     

Three-halves harmonic emission from a laser filament in a plasmachannel

A self-trapped laser filament is susceptible to decay-producing radially localized Langmuir waves. A nonlinear interaction of the pump wave with the density oscillation at the Langmuir frequency gives rise to three-halves harmonic emissions. Using a basis-function expansion technique, the emitted power in the backward direction is obtained. It decreases with the increasing size of the filament     

Stimulated Brillouin scattering of obliquely propagatingextraordinary electromagnetic waves off ion-Bernstein waves in plasmas

The parametric decay of an obliquely propagating extraordinary electromagnetic wave into another extraordinary electromagnetic wave and a low-frequency electrostatic ion-Berstein wave via the stimulated Brillouin scattering process is considered. Explicit expressions for the growth rate and threshold power for this instability are presented. Applications of the present investigation to fusion plasmas in the end cells of tandem mirrors and the magnetospheric and ionospheric plasmas to explain wave phenomena are pointed out. The dependence of threshold power on the pump wave angle is studied. The general expressions for the growth rate and threshold derived here can also be useful to explain future experimental data     

High-frequency emissions during the propagation of an electron beamin high-density plasma

A relativistic annular electron beam passing through a high-density plasma excites Langmuir waves via Cerenkov interaction. The Langmuir waves are backscattered off ions via nonlinear ion Landau damping. At moderately high amplitudes these waves are parametrically up-converted by the beam into high-frequency electromagnetic radiation, as observed in some recent experiments. A nonlocal theory of this process is developed in a cylindrical geometry. It is seen that the growth rate of the Langmuir wave scales as one-third the power of beam density. The growth rate of parametric instability scales as one-fourth the power of beam density and the square root of beam thickness     

Filamentation of laser radiation in DC biased GaAs

In this paper, we have examined the filamentation instability of laser radiation in a GaAs sample in the negative differential resistivity region. A dc electric field is applied to assist the laser beam transferring electrons in the conduction band from the lower valley to upper satellite valleys, i.e. in increasing the effective mass of electrons. The instability causes the space charge perturbations in the microwave range of frequencies. The nonlinearity arises through the energy dependence of the effective mass and the ponderomotive force on the electrons. The instability has finite frequency and possesses large growth rate which is greatly influenced by the dc electric field.     

Nonlinear electromagnetic propagation in plasma filled cylindrical waveguides

Using an appropriate expression for the field-dependent dielectric constant of a collisionless plasma, we have studied the field distribution of the TM₀₁ mode in a cylindrical waveguide. The wave equation has been solved by a Runge Kutta technique. It is seen that on account of redistribution of carriers from the high-field regions to low-field regions a beam of frequency lower than the average plasma frequency can be transmitted if its power is high. Work supported by NSF     

Selfconsistent equation of state

We investigate the effects of a selfconsistent single-particle potential and the Pauli principle on the equation of state for dense systems at low temperatures. It is found that the selfconsistent potential plays an extremely important role for the equation of state near nuclear matter density.     

Comparison of eikonal-Born series and modified Gluaber approach for the study of elastic electron-hydrogen scattering

Elastic electron-hydrogen scattering at medium and high energies has been analysed in eikonal-Born series and modified Glauber approach forE _i ≥ 50 eV. We have used closed form expressions for evaluating the second Born term in the fixed scatterer approximation and for higher order terms of Glauber-eikonal series. The exchange effect has also been included via Glauber-Bonham-Ochkur type procedure. The fixed scatterer approximation calculations are compared with results obtained using other approximations for the second Born term available in the literature. The results compare fairly well with experimental data.     

Partition functions and dissociation constants for HeH+

Partition functions and dissociation equilibrium constants for HeH⁺ have been computed for temperatures between 2,000 and 16,000 K in steps of 100 K.