Townsend's First Ionization Coefficients and Sparking Potentials in Crossed Electric and Magnetic Fields

Townsend's first ionization coefficients have been measured in corssed electric and magnetic fields for values of B/p ranging from 0.013 TESLA. TORR-1 to 0.064 TESLA.TORR-1 and for 103 x 102¿ E/p 331 x 102 V.M-1. TORR-1 in oxygen and for 122 x 102¿ E/pÂ488 x 102 V.M-1.TORR-1 for dry air. The values of effective collision frequencies determined from the equivalent pressure (pe) concept generally increase with E/p at constant B/p and decrease with increasing B/p at constant E/p. Effective collision frequencies determined from measured sparking potentials at high values of E/p increase with decreasing E/pe. The drift velocity and mean energy of electrons in oxygen in crossed electric and magnetic fields have been derived.

Electron Spectroscopic Studies of Oxygen and Carbon Dioxide Adsorbed on Metal Surfaces

Adsorption of oxygen on Ni, Cu, Pd, Ag, and Au surfaces has been investigated by employing UV and X-ray photoelectron spectrscopy as well as electron energy loss spectroscopy (EELS). Molecularly chemisorbed (singlet) oxygen is found on Ni, Cu, Ag, and Au surfaces showing features such as stabilization of the rB* orbital, destabilization of the .nu orbital, higher O(1s) binding energy than the atomic species, and a band 2-3 eV below the Fermi level due to metal d-O(2p)u* interaction. 0-0 and metal-oxygen stretching frequencies have been observed in EELS. Physical adsorption of O2 is found to occur on Pd and Ni surfaces, only at high exposures in the latter case. Physical adsorption and multilayer condensation of CO, on metal surfaces are distinguished by characteristic relaxation shifts in UPS as well as O(1s) binding energies. Adsorption of CO on a Ni surface covered with presorbed atomic oxygen gives rise to C02.

Temperature dependence of chlorine NQR in 2-chloro 5-nitrobenzoic acid and 4-chloro 3-nitrobenzoic acid

Temperature dependence of chlorine nuclear quadrupole resonance in 2-chloro 5-nitrobenzoic acid and 4-chloro 3-nitrobenzoic acid has been investigated in the region 77° K to room temperature. No phase transition has been observed. The results are analysed to obtain the torsional frequencies and their temperature dependence. A nonlinear temperature dependence is obtained for the torsional frequencies.

Infrared and Raman spectra of 2,4-dithiobiuret and its normal vibrations

The infrared spectra of 2,4-dithiobiuret(DTB), N-deuterated dithiobiuret(DTB-d5) and the laser Raman spectrum of DTB are reported. Normal coordinate treatments of DTB and DTB-d5 have been carried out to aid the assignment of the vibrational frequencies. A trans—cis conformation is favoured for DTB molecule in the solid state.

Free vibrations of a reservoir-foundation system

The natural frequencies of a reservoir-foundation system are calculated by treating the foundation as a system of linear springs with inertia. The reservoir is treated as consisting of compressible liquid, and the influence of waves at the free surface is included. It is shown that the natural frequencies decrease monotonically as the depth of foundation participating in the motion increases. The influence of waves at the reservoir surface is negligible for the cases normally occurring in practice. It is also shown that the wavelength of motion along the reservoir has no influence on the frequencies when the foundation depth is large compared to the reservoir depth.

A Raman study of multiferroic LuMnO3

Magnetic and dielectric measurements confirm the multiferroic nature of LuMnO3. Raman spectra of LuMnO3 have been recorded in the 77-800 K range covering both the antiferromagnetic transition at 90 K and the ferroelectric-paraelectric transition at 750 K. The changes in the phonon modes frequencies and band-widths indicate the presence of phonon-spin coupling in the antiferromagnetically ordered phase. The ferroelectric-paraelectric transition is accompanied by the broadening and disappearance of many of the phonon modes. Some of the phonon modes also show anomalies at the ferroelectric transition.

Analysis of vibration of clamped square plates by the Rayleigh-Ritz method with asymptotic solutions from a modified Bolotin method

Estimates of flexural frequencies of clamped square plates are initially obtained by the modified Bolotin's method. The mode shapes in “each direction” are then determined and the product functions of these mode shapes are used as admissible functions in the Rayleigh-Ritz method. The data for the first twenty eigenvalues in each of the three (four) symmetric groups obtained by the (i) Bolotin, (ii) Rayleigh and (iii) Rayleigh-Ritz methods are reported here. The Rayleigh estimates are found to be much closer to the true eigenvalues than the Bolotin estimates. The present product functions are found to be much superior to the conventional beam eigenmodes as admissible functions in the Rayleigh-Ritz method of analysis.

In-plane normal vibrations of 1,2,5-oxa-, thia- and selena-diazoles, 1,3,4-oxa- and thia-diazoles and 1,2,3,4-thiatriazoles

In-plane vibration modes of 1,2,5- and 1,3,4-oxa- and thia-diazoles, and 1,2,5-selenadiazole have been assigned on the basis of detailed normal coordinate analysis employing data on several deuterated species. In-plane vibration frequencies of two 1,2,3,4-thiatriazole derivatives have been calculated and compared with observed values.

Radio frequency emission in electron beam-plasma and beam-beam interaction

A linear excitation of electromagnetic modes at frequencies (n + ı89 in a plasma through which two electron beams are contra-streaming along the magnetic field is investigated. This may be a source of the observed {cote emissions at auroral latitudes.

Magnetoplasmon-type surface polaritons at the interface between two semiconductors

Magnetoplasmon-type surface polaritons are studied at the interfaces of sandwich structures in the configuration with a magnetic field oriented parallel to the interface but perpendicular to the direction of wave propagation. It is shown that the propagation window for the surface polaritons is shifted to higher frequencies in the presence of the magnetic field directed positively. On reversal of the magnetic field an additional low frequency propagation band appears. Irrespective of the direction and strength of the magnetic field there exists a certain frequency range in which interface polaritons cannot propagate. For sandwich structures for which the dielectric constant and the plasma frequency of one medium are simultaneously greater or less than those of the second medium gaps and multiple branches can appear in the propagation window either for n > 0 or n <; 0 waves. A graphical method for the estimation of critical ranges of B0 and dielectric constant ratios for different sandwich structures, within which gaps and multiple branches appear, is given

Finite element analysis of rotors

A finite element formulation for the natural vibration analysis of tapered and pretwisted rotors has been presented. Numerical results for natural frequencies for various values of the geometric parameters and rotational speeds, have been computed for the case of rotors with and without pretwist. A Galerkin solution for the fundamental has also been worked out and has been used to provide a comparison for the finite element results. Charts for rapid estimation of the fundamental frequency parameter of tapered rotors, have been included.

Microwave modulation by amorphous-semiconductor switches

Microwave modulation has been achieved by using thin-film amorphous-semiconductor switches made of ternary chalcogenides. X-band microwaves were modulated by a threshold switch at frequencies varying from 100 Hz to 1 MHz, with modulation efficiencies comparable to siliconp¿i¿n diodes. The insertion loss was 0.5 to 0.6 dB and the isolation was 18 dB at 100 mA operating current. Possible applications this method are discussed.

Characteristics of nonideal operational amplifiers

The departures of the operational amplifiers (OA's) from the ideal performance and their effect on VCV's in the inverting and noninverting mode are discussed. It is found that for the same ideal gain, the bandwidths for the inverting and noninverting modes are different, the former being less. Complete equivalent circuits describing the frequency dependance of the input and output impedances for both modes are given. In particular, the output impedance is shown to be inductive for the frequencies of interest, and this is also confirmed by experimental results.

Experiments on the fine structure of turbulence

Investigations have been carried out of some aspects of the fine-scale structure of turbulence in grid flows, in boundary layers in a zero pressure gradient and in a boundary layer in a strong favourable pressure gradient leading to relaminarization. Using a narrow-band filter with suitable mid-band frequencies, the properties of the fine-scale structure (appearing as high frequency pulses in the filtered signal) were analysed using the variable discriminator level technique employed earlier by Rao, Narasimha & Badri Narayanan (1971). It was found that, irrespective of the type of flow, the characteristic pulse frequency (say Np) defined by Rao et al. was about 0·6 times the frequency of the zero crossings. It was also found that, over the small range of Reynolds numbers tested, the ratio of the width of the fine-scale regions to the Kolmogorov scale increased linearly with Reynolds number in grid turbulence as well as in flat-plate boundarylayer flow. Nearly lognormal distributions were exhibited by this ratio as well as by the interval between successive zero crossings. The values of Np and of the zero-crossing rate were found to be nearly constant across the boundary layer, except towards its outer edge and very near the wall. In the zero-pressure-gradient boundary-layer flow, very near the wall the high frequency pulses were found to occur mostly when the longitudinal velocity fluctuation u was positive (i.e. above the mean), whereas in the outer part of the boundary layer the pulses more often occurred when u was negative. During acceleration this correlation between the fine-scale motion and the sign of u was less marked.

The interference environment of radio Noise froh4 lightning

The paper furnishes a review and air ovendepr "f radio noise *om lightning as rr so~irce of interference to analogue and digital Corn?tunicatioiz. The parameters of fhe different fornls < f, noise necessary .for pssessigth e interfering effect of the rloise are described. 4railublr irfjrncroiun thrr tndevstor71zs, thunder-clouds, convecrion cells and lightning are er ieveadn d their liizitatimsp ointed oui. Thew fol101r.s a descripiicn of how the source, popugafiona nd receiver chaacteristidse termine the sfrticture qf a/rnosplro.ic noise as receiwd at a point of observation. The tratrrral unit for this noise i.s the mise burst rtrising from o w complete lightning.flas4. The pmuneters of the nrise birrst as a 11.hole and its structure ctetennine the inrqfflrrence enrirnniient. A hisforic reriel$. qf t2sophericii oke .studies sho1(5 that it i. wrreirt(v of importance oldy in thc ropicarl egions of' the wr ldf i>rs hichf hc neailable data are wry defective. New data are ficnrished. The contribution of atmospheric noise for backgrouzd interference even in remote places ,for r.adicj astronomy at VHF is firrnished. The imporlance of aimcspizeric nctise cceurring ;vporadiea@ in high values fur slzort inier.als at VHF and higher frequencies in the tropics is brought out.