Measurement of dielectric constant of conducting liquids

A ratio transformer method suitable for the measurement of the dielectric constant of highly conducting liquids is described. The resistance between the two plates of the capacitor can be as low as 2 k Omega . In this method variations in this low resistance will not give any error in capacitance measurement. One of the features of this method is the simplicity in balancing the resistance, using a LDR (light dependent resistor), without influencing the independent capacitance measurement. The ratio transformer enables the ground capacitances to be eliminated. The change in leakage inductance of the ratio transformer while changing the ratios is also taken into account. The capacitance of a dielectric cell of the order of 50 pF can be measured from 1000 Hz to 100 kHz with a resolution of 0.06 pF. The electrode polarisation problem is also discussed.

Propagation of ion-acoustic waves in a multi-component plasma

The authors derive the Korteweg-de Vries equation in a multicomponent plasma that includes any number of positive and negative ions. The solitary wave solutions are also found explicitly for the case of isothermal and non-isothermal electrons.

On the determination of energy eigenvalues and coupling strengths using duality

The Shifman-Vainshtein-Zakharov method of determining the eigenvalues and coupling strengths, from the operator product expansion, for the current correlation functions is studied in the nonrelativistic context, using the semiclassical expansion. The relationship between the low-lying eigenvalues, and the leading corrections to the imaginary-time Green function is elucidated by comparing systems which have almost identical spectra. In the case of an anharmonic oscillator it is found that with the procedure stated in the paper, that inclusion of more terms to the asymptotic expansion does not show any simple trend towards convergence to the exact values. Generalization to higher partial waves is given. In particular for the P-level of the oscillator, the procedure gives poorer results than for the S-level, although the ratio of the two comes out much better.

Investigation of biferroic properties in La0.6Sr0.4MnO3/0.7Pb(Mg1/3Nb2/3)O3â0.3PbTiO3 epitaxial bilayered heterostructures

Epitaxial bilayered thin films consisting of La0.6Sr0.4MnO3 (LSMO) and 0.7Pb(Mg1/3Nb2/3)O3â0.3PbTiO3 (PMN-PT) layers of relatively different thicknesses were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by pulsed laser ablation technique. The crystallinity, ferroelectric, ferromagnetic, and magnetodielectric properties have been studied for all the bilayered heterostructures. Their microstructural analysis suggested possible StranskiâKrastanov type of growth mechanism in the present case. Ferroelectric and ferromagnetic characteristics of these bilayered heterostructures over a wide range of temperatures confirmed their biferroic nature. The magnetization and ferroelectric polarization of the bilayered heterostructures were enhanced with increasing PMN-PT layer thickness owing to the effect of lattice strain. In addition, evolution of the ferroelectric and ferromagnetic properties of these heterostructures with changing thicknesses of the PMN-PT and LSMO layers indicated possible influence of several interfacial effects such as space charge, depolarization field, domain wall pinning, and spin disorder on the observed properties. Dielectric properties of these heterostructures studied over a wide range of temperatures under different magnetic field strengths suggested a possible role of elastic strain mediated magnetoelectric coupling behind the observed magnetodielectric effect in addition to the influence of rearrangement of the interfacial charge carriers under an applied magnetic field.

A probabilistic approach to the problem of electron localization in disordered systems and sharpness of the mobility edge

By applying the theory of the asymptotic distribution of extremes and a certain stability criterion to the question of the domain of convergence in the probability sense, of the renormalized perturbation expansion (RPE) for the site self-energy in a cellularly disordered system, an expression has been obtained in closed form for the probability of nonconvergence of the RPE on the real-energy axis. Hence, the intrinsic mobility mu (E) as a function of the carrier energy E is deduced to be given by mu (E)= mu 0exp(-exp( mod E mod -Ec) Delta ), where Ec is a nominal 'mobility edge' and Delta is the width of the random site-energy distribution. Thus mobility falls off sharply but continuously for mod E mod >Ec, in contradistinction with the notion of an abrupt 'mobility edge' proposed by Cohen et al. and Mott. Also, the calculated electrical conductivity shows a temperature dependence in qualitative agreement with experiments on disordered semiconductors.

ESR study of copper diethyldithiophosphate

ESR investigations are reported in single crystals of copper diethyldithiophosphate, magnetically diluted with the corresponding diamagnetic nickel complex. The spectrum at normal gain shows hyperfine components from 63Cu, 65Cu, and 31P nuclei. At much higher gain, hyperfine interaction from 33S nuclei in the ligand is detected. The spin Hamiltonian parameters relating to copper show tetragonal symmetry. The measured parameters are g = 2.085, g =2.025, A63Cu = 149.6 × 10−4 cm−1, A65Cu = 160.8 × 10−4 cm−1, BCu = 32.5 × 10−4 cm−1 and QCu 5.5 × 10−4cm−1. The 31P interaction is isotropic with a coupling constant AP = 9.6 × 10−4 cm−1. Angular variation of the 33S lines shows two different hyperfine tensors indicating the presence of two chemically inequivalent Cu S bonds. The experimentally determined hyperfine constants are A =34.9×10−4 cm−1, B =26.1×10−4 cm−1, A =60.4×10−4 cm−1, B =55.5×10−4 cm−1. The hyperfine parameters show that the hybridization of the ligand orbitals is very sensitive to the symmetry around the ligand. The g values and Cu hyperfine parameters are not much affected by the distortions occurring in the ligand. The energies of the d-d transitions are determined by optical absorption measurements on Cu diethyldithiophosphate in solution. Using the spin Hamiltonian parameters together with optical absorption results, the MO parameters for the complex are calculated. It is found that in addition to the bond, the bonds are also strongly covalent. ©1973 The American Institute of Physics

NMR investigation of certain hydrated fluorosilicates

Proton and fluorine NMR were investigated in the temperature range 90–425 °K in the hexahydrated fluorosilicates of Zn, Cu, Mn, Co, and Ni and in the tetrahydrated CuSiF6 to obtain information about the internal motions in these solids. Second moment transitions were observed at widely different temperatures for the different substances, and these are ascribed to the onset of reorientation of the M(H2O) and SiF octahedra. The correlation frequency and the potential barrier hindering the motion were calculated in all the cases. Apart from the narrowing taking place at higher temperatures, the Co salt showed a change in the line structure at 248 °K, where a phase transition was reported from magnetic susceptibility measurements. Studies on the single crystals of ZnSiF6 • 6H2O and NiSiF6 • 6H2O showed that there are three nonequivalent p-p vectors, and after the transition they all become equivalent, with the M(H2O) octahedron reorienting about the fourfold axes. ©1973 The American Institute of Physics

Vibration of generally orthotropic skew plates

Vibration problem of generally orthotropic plates with particular attention to plates of skew geometry is studied. The formulation is based on orthotropic plate theory with arbitrary orientation of the principal axes of orthotropy. The boundary conditions considered are combinations of simply supported, clamped, and free-edge conditions. Approximate solution for frequencies and modes is obtained by the Ritz method using products of appropriate beam characteristic functions as admissible functions. The variation of frequencies and modes with orientation of the axes of orthotropy is examined for different skew angles and boundary conditions. Features such as "crossings" and "quasi-degeneracies" of the frequency curves are found to occur with variation of the orientation of the axes of orthotropy for a given geometry of the skew plate. It is also found that for each combination of skew angle and side ratio, a particular orientation of the axes gives the highest value for the fundamental frequency of the plate.

Dispersion of the stress-optic coefficient in glasses

The stress-optic coefficient (n3/2)(q11-q12) has been determined for a series of 18 optical glasses of different compositions in the wavelength range 5700-3200 Å. The coefficients are negative for all the glasses except for a high-lead-content glass of density 6·7 and refractive index 1·89. The numerical value of the coefficient decreases as one proceeds to the ultraviolet. This behaviour is just the opposite of what is observed in fused silica. By applying Mueller's theory, the strain polarizability constant and its dispersion have been evaluated.

Delay characteristics of a simple triggered vacuum gap

Firing delays of a simple triggered vacuum gap are reported in this paper. The effects of insulating materials in the auxiliary gap, auxiliary gap current, main gap current and electrode separation on the delay have been investigated. The presence of insulating material in the auxiliary gap having low auxiliary gap resistance appears to exhibit large delay. Delay decreases considerably with increase of current in the auxiliary and the main gaps, but it increases with increase of electrode separation. The scatter in the delay is less than 25 ps and 500 ps with supramica (Mycalex Corporation of America) and silicon carbide respectively at lower values of auxiliary gap current and it becomes negligible for supramica at auxiliary gap currents greater than 6A. This investigation appears to indicate that the simple device can be used as a fast switch.

An accurate method for the experimental evaluation of the acoustical impedance of a black box

Among different methods, the transmission-line or the impedance tube method has been most popular for the experimental evaluation of the acoustical impedance of any termination. The current state of method involves extrapolation of the measured data to the reflecting surface or exact locations of the pressure maxima, both of which are known to be rather tricky. The present paper discusses a method which makes use of the positions of the pressure minima and the values of the standing-wave ratio at these points. Lippert's concept of enveloping curves has been extended. The use of Smith or Beranek charts, with their inherent inaccuracy, has been altogether avoided. The existing formulas for the impedance have been corrected. Incidentally, certain other errors in the current literature have also been brought to light.Subject Classification: 85.20.

Singular perturbation analysis of spherical and cylindrical N waves

Using a singular perturbation analysis the nonplanar Burgers' equation is solved to yield the shock wave-displacement due to diffusion for spherical and cylindrical N waves, thus supplementing the earlier results of Lighthill for the plane N waves. Physics of Fluids is copyrighted by The American Institute of Physics.

High-pressure magnetic susceptibility of the intermediate valence system EuPd2Si2

The pressure dependence (0-7 kbar) of the magnetic susceptibility is reported for the intermediate valence system EuPd2Si2 in the temperature interval 77-300K. It is found that the thermally induced valence transition becomes more gradual on application of pressure The characteristic fluctuation temperature Tf, also seems to be pressure dependent.

Measurements of partial discharges-corrections to erroneous counts occurring in a cumulative pulse-counting system

The discharge pulse rates at different magnitude levels are often used as criteria for monitoring the partial-discharge aging of insulation systems. Use of suggested corrections for errors in cumulative probability counting leads to better use of available counters.

An electron spectroscopic study of the surface oxidation of glassy and crystalline Cu-Zr alloys

Surface oxidation of three metglasses in the Cu-Zr system has been investigated by employing X-ray photoelectron spectroscopy and Auger electron spectroscopy with a view to comparing their oxidation behaviour with that of the corresponding crystalline states of the alloys. Surface oxidation of pure Zr metal has also been examined in detail using these techniques. Sub-oxides of Zr are formed during the initial stages of oxidation of Zr (at oxygen exposures <10L), while at higher exposures, ZrO2 is formed together with the highest possible sub-oxide which the authors designate as 'ZrO'. The relative proportion of 'ZrO' goes through a maximum in the range 25-50 L. Both the glassy and the crystalline states of the Cu-Zr alloys exhibit preferential oxidation of Zr. The glassy alloys exhibit a higher rate of oxidation at intermediate exposures compared with the crystalline states of the alloys; the extent of oxidation at higher oxygen exposures is, however, higher for crystalline alloys. Interatomic Auger transitions have been found in the Zr+O2 system as well as in Cu-Zr alloys.