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A miniature three-component accelerometer balance system for measuring the fundamental aerodynamic force coefficients over blunt bodies has been designed, fabricated and tested in the Indian Institute of Science hypersonic shock tunnel HST2 at a nominal Mach number of 5.75. The model and the balance system are supported by rubber bushes, thereby ensuring unrestrained free-floating conditions of the model in the test section during the flow duration. Exhaustive axisymmetric finite-element simulations are carried out to select appropriate rubber bushes and materials for the model and the balance system. The internally mountable accelerometer balance is used to measure the drag, lift and pitching moment coefficients for a $60^o$ apex angle blunt cone within the effective tunnel test time of $800\hspace{2mm}{\mu}s$. The measured aerodynamic force coefficients match very well with the theoretical values predicted using modified Newtonian theory at moderate specific enthalpy levels of the test gas.

Passive mode locking of lasers using the protein molecule bacteriorhodopsin which acts as a slow saturable absorber is proposed. Based on the self‐consistent approach, expressions for the laser pulse energy and pulsewidth are derived. It is shown that mode‐locked pulses of 64 fs duration and 7 nJ energy could be generated in the visible region by this method.

We describe the generation of ultrashort pulses in semiconductor lasers by means of novel regenerative feedback techniques. These new techniques require only relatively simple off-the-shelf electronic components, and circumvent the need for any external RF oscillators for successful picosecond pulse operation of the semiconductor lasers. Pulsewidths as short as /spl sim/10 ps have been obtained by regenerative mode-locking, and repetition rate tunability of /spl sim/200 MHz has been demonstrated (with pulses of /spl sim/35 ps pulsewidth) by regenerative gain switching, as elaborated below. >

A three-component accelerometer balance system is used to study the drag reduction effect of an aerodisc on large angle blunt cones flying at hypersonic Mach numbers. Measurements in a hypersonic shock tunnel at a freestream Mach number of 5.75 indicate more than 50% reduction in the drag coefficient for a 120degrees apex angle blunt cone with a forward facing aerospike having a flat faced aerodisc at moderate angles of attack. Enhancement of drag has been observed for higher angles of attack due to the impingement of the flow separation shock on the windward side of the cone. The flowfields around the large angle blunt cone with aerospike assembly flying at hypersonic Mach numbers are also simulated numerically using a commercial CFD code. The pressure and density levels on the model surface, which is under the aerodynamic shadow of the flat disc tipped spike, are found very low and a drag reduction of 64.34% has been deduced numerically.

Shock tube is an unique facility to create temperature gradients exceeding million degrees Kelvin per second. We have established two shock tubes for measuring the kinetic reaction rates at high temperatures with two different but complementary detection techniques. The first one is a single pulse shock tube, in which the reflected shock is used to heat the molecules. The equilibrated products are analyzed by gas chromatograph and infrared spectrometer. The second one uses laser-schlieren system for online monitoring of the chemical reactions behind primary shock wave. The details of the shock tubes and some typical results obtained are presented in this paper.

Theoretical analysis of internal frequency doubling in actively mode locked broadband solid state lasers is presented. The analysis is used to study the dependence of mode locked pulsewidth on the second harmonic conversion efficiency, the modulation depth, and the tuning element bandwidth in an AM mode locked Ti: sapphire laser. The results are presented in the form of graphs.

All-optical switching has been demonstrated in bacteriorhodopsin based on excited-state nonlinear absorption. A probe laser beam at 640 nm corresponding to the O-state absorption maximum is switched due to a strong pulsed pump laser beam at 570 nm, that corresponds to the maximum ground state absorption. We have studied the effect of variation in pulse width and in small signal absorption coefficient on the switching characteristics. The switching time decreases as the pulse width of the pump beam decreases and the small signal absorption coefficient increases. The switching contrast depends mainly on the peak pumping intensity.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The generation of a 16 μm laser beam through cascading in a downstream‐mixing CO2 gasdynamic laser is studied. To simulate actual lasing action, a generalized, two‐dimensional, flow‐radiation‐coupled power extraction model for a gasdynamic laser is used. Also, to model the cascade process a new four‐mode CO2‐N2 vibrational kinetic model has been proposed. The steady‐state intensity obtained for an exclusive 9.4 μm transition is of the order of 5×107 W/m2. In the cascade mode of operation the steady‐state intensities for 9.4 and 16 μm transitions of the order of 5×107 W/m2 and 1.0×106 W/m2, respectively, have been obtained.

A comprehensive analysis of the light induced processes in the bacteriorhodopsin (BR) molecule is. presented based on the rate equations approach. A simplified energy level scheme is proposed to represent the complex photochemical cycle of the BR molecule. Light intensity-induced population densities in various states of the molecule at steady-state are computed and used to derive an analytic expression for the absorption coefficient of the modulation beam passing through the medium containing the BR molecules. This coefficient encompasses all possible photochromic transitions of the BR molecule and can be used to analyse various nonlinear processes exhibited by the BR molecules. The analysis is used to study the spatial light modulation and the mode-locking applications of BR molecules. It is shown that for a probe beam at 412 nm upto 82% modulation can be achieved using a modulating laser of intensity 3.2 W/cm2 at 570 nm. For temperatures ~77 K, the transmission at 610 nm can be switched from the initial 13% to 96% for modulating laser intensity of 11 W/cm2. The analysis demonstrates the feasibility of constructing a molecular spatial light modulator using BR molecules with a dynamic range of 0.12 and sensitivity of 0.66 cm^/W for the read beam at 412 nm. The analysis of mode-locking demonstrates the possibility of producing pulses of 64 fs duration and 7 nJ energy by passively mode-locking a laser in the visible region using the BR molecules.

Inflammatory cells release a variety of cytokines, including interleukin (IL)-1 beta, into the airway in asthma. This study examined the effects of human IL-1 beta on the function of the beta-adrenergic receptor (beta AR)-adenylyl cyclase (AC) system in BEAS-2B cells, a human airway epithelial cell line. IL-1 beta markedly increased beta AR density (Bmax; P < 0.001) primarily by increasing the percentage of the beta 2AR subtype (from 67 to 91%; P < 0.001). Bmax increased monotonically over time in response to 200 pM IL-1 beta and was approximately 2.5-fold greater than control cells between 36 and 42 h. In contrast, the concentration response of Bmax to IL-1 beta given for 18 h was biphasic. Bmax increased with IL-1 beta concentrations from 2 to 200 pM, but, at > 200 pM, it decreased progressively toward control values. IL-1 beta-induced increases in Bmax with IL-1 beta were associated with approximately threefold increases in beta 2 AR mRNA and were blocked by the protein synthesis inhibitor cycloheximide. Despite the marked increase in Bmax, however, IL-1 beta depressed adenosine 3',5'-cyclic monophosphate (cAMP) responses to isoproterenol and forskolin, a direct activator of AC (P < 0.001 by analysis of variance for both). The inhibitory effect of IL-1 beta on cAMP production appeared to be explained by increases in the activity of an inhibitory GTP binding protein because IL-1 beta treatment increased the activity of a pertussis toxin ADP-ribosylated Gi alpha protein by approximately 2.5-fold; and pretreatment of intact cells with pertussis toxin inhibited the effect of IL-1 beta on cAMP production. These data indicate that IL-1 beta-mediated changes in the beta AR-AC system function in airway epithelial cells are complex and involve expression of receptor protein, GTP binding protein, and possibly AC itself. Increases in IL-1 beta may contribute to abnormalities in airway function in subjects with asthma.

In this paper, we present the molecular density distribution measurement in turbulent nitrogen jet (Re approximate to 3 x 10(3)), using acetone as molecular tracer. The tracer was seeded in the nitrogen jet by purging through the liquid acetone at ambient temperature. Planar laser sheet of 266 nm wavelength from frequency quadrupled, Q-switched, Nd:YAG laser was used as an excitation source. Emitted fluorescence images of jet flow field were recorded on CMOS camera. The dependence of planar laser induced fluorescence (PLIF) intensity on acetone vapor density was used to convert PLIF image of nitrogen jet into the density image on pixel-by-pixel basis. Instantaneous quantitative density image of nitrogen jet, seeded with acetone, was obtained. The arrowhead-shaped coherent turbulent structures were observed in the present work. It was found that coherent structures were non-overlapping with separate boundaries. Breaking of coherent structures into turbulence was clearly observed above four times jet width.

A simple spectrophotometric method is reported her for the estimation of reserpine in polyherbal formulations. Estimation is based on the reaction with3-methylbenzolinone-2hydrazone (MBTH) reagent in presence of cerric ammonium sulphate to yield a violet coloured chromogen, which exhibits and absorption maxima at 580 nm. The chromogen is stable for 10 minutes.

Probit analysis calculations are highly useful in biology and related sciences. Since the statistical calculations and tests required are quite involved, the use of an automatic computer program is desirable. The description of the computational procedures and use of the computer program with suitable examples from mosquito control programmes are discussed.

Polycrystalline Zn x Cd 1-x S/CuGaSe 2 thin film heterojunction solar cells were prepared by laser evaporating CuGaSe 2 onto sprayed Zn x Cd 1-x S films. The reasons for the low efficiency of the cells were discussed in view of the poor performance of the device for x > 0.6. The photovoltaic properties of the cells were studies using illuminated I - V characteristics. A maximum efficiency of 4.9% was obtained on the cells.

Thin films of pure and silver doped zinc telluride were deposited on well-cleaned Corning glass substrates maintained at temperatures in the range 303 - 598 K by the vacuum evaporation method. The electrical conductivity of the pure films decreased from 1.1 X 10 -5 to 4.4 X 10 -6 ohm -1 cm -1 with the deposition temperature. The activation energy in the high temperature region was 0.33 eV, while at low temperatures it was 0.06 eV above the valence band. In the Ag doped films, the conductivity increased one order of magnitude. The optical band gap reduced from 2.23 eV to 2.18 eV with the Ag doping content.

A generalized two‐dimensional flow‐radiation coupled model to extract power from a gasdynamic laser is proposed. The model is used for the study of power extraction from a 9.4‐μm CO2 downstream‐mixing gasdynamic laser, where a cold CO2+H2 stream is mixed with a vibrationally excited N2 stream at the nozzle exits. This model is developed by coupling radiation with the two‐dimensional, unsteady, laminar and viscous flow modeling needed for such systems. The analysis showed that the steady‐state value of 9.4‐μm intensity as high as 5×107 W/m2 can be obtained from the system studied. The role of H2 relaxant in the power extraction process has also been investigated.

The analysis of propagation of a normal shock wave in CO2‐N2‐He or H2 or H2O system seeded with solid particles is presented. The variation of translational and vibrational temperatures of gas phase and the particle temperatures in the relaxation zone behind the shock front are given in graphical form. These results show that the peak value of population inversion and the width of the inversion zone are highest for He catalyst and lowest for H2O catalyst.

A simplified two-temperature model is presented for the vibrational energy levels of the N2O and N2 molecules of an N2O-N2-He gasdynamic laser (GDL), and the governing equations for the unsteady flow of the gas mixture in a convergent-divergent contour nozzle are solved using a time-dependent numerical technique. Final steady-state distributions are obtained for vibrational temperatures, population inversion, and the small-signal laser gain along the nozzle. It is demonstrated that, for plenum temperatures lower than 1200 K, an N2O GDL such as the present is more efficient than a CO2 GDL in identical operating conditions

The analysis of the characteristics of a synchronously mode-locked and internally frequency-doubled dye laser is presented. Dependence of dye laser pulse characteristics on the cavity length mismatch of the pump laser and dye laser is studied. Variation of the minimum pulsewidth with intracavity bandwidth and the harmonic conversion efficiency is presented in the form of graphs.

In this paper, we prove a modified form of Shanks? conjecture on the stability of planar least square inverse (PLSI) polynomials in 2-D by imposing restriction on the original 2-D polynomial. This restriction on the original polynomial is in fact necessary to stabilize an unstable polynomial eventually by taking double PLSI so as to maintain the magnitude spectrum same. A discussion on the optimization technique of designing 2-D recursive filters is then included and it is indicated that in practice, if the optimization in the frequency domain is done over a very close frequency grid (w1, w2) the resulting filter transfer function will have a denominator polynomial satisfying the restriction imposed while proving the modified form of Shanks? conjecture. Thus we conclude that the testing the 2-D transfer functions of recursive filters for stability can be done once for all at the end of optimization. Even this testing is only an equivalent of one dimensional stability test and can be easily performed. If the filter is found unstable we can stabilize it by taking the double PLSI of the denominator polynomial of the transfer function. ? 1984 IEEE

The theoretical study of the propagation of a bell-shaped light pulse through a saturable absorber having excited-state absorption is presented . Assuming that the pulse-width is longer than the first excited-state lifetime of the absorber, a general expression for the steady-state transmission of the absorber is obtained . It is shown that when the excited-state absorption cross-section is larger than the ground-state absorption cross-section (reverse saturable absorber) the absorber acts as a power limiter . An explicit expression for the change of temporal pulse-width in a single transit through the absorber is obtained, which shows that the pulsewidth increases due to the presence of excited-state absorption . An analytical expression is presented for the optimum pulse intensity at which the maximum pulse broadening occurs .

The third-order elastic moduli of polycrystalline Al-rich Al-Mg and Al-Cu alloys are determined by measuring the changes in ultrasonic wave velocities under applied uniaxial stress. A solid-state pulse interferometer sensitive to a few parts per million for the relative velocity measurement was used. Pressure derivatives of elastic moduli and Gruneisen gamma are evaluated from the measured second- and third-order moduli.

Based on a method proposed by Reddy and Shanmugasundaram, similar solutions have been obtained for the steady inviscid quasi‐one‐dimensional nonreacting flow in the supersonic nozzle of CO2–N2–H2O and CO2–N2–He gasdynamic laser systems. Instead of using the correlations of a nonsimilar function NS for pure N2 gas, as is done in previous publications, the NS correlations are computed here for the actual gas mixtures used in the gasdynamic lasers. Optimum small‐signal optical gain and the corresponding optimum values of the operating parameters like reservoir pressure and temperature and nozzle area ratio are computed using these correlations. The present results are compared with the previous results and the main differences are discussed.

The electrical resistivity, temperature coefficient of resistance (TCR) and thermoelectric power are measured on systematically annealed copper films formed by the vacuum evaporation method. From the measured quantities the scattering coefficient and the bulk mean free path of the conduction electrons are calculated. The electron mean free path is found to be 410+or-100 AA. The energy dependence of mean free path U and the energy dependence of Fermi surface area V are calculated from the thermoelectric power measurements as a function of thickness. Both U and V are found to be negative and thickness-dependent.

The heat capacity of four ferrites with the chemical composition Ni1–xZnxFe2O4 (x = 0.5, 0.64), Mn1–xZnxFe2O4 (x = 0.42), and BaFe12O19 has been measured with a Nernst adiabatic calorimeter in the temperature range 80 to 303 °K. The heat capacity has been found to decrease with decreasing temperature. The Debye temperatures have been calculated and compared with those obtained from elastic data. Die Warmekapazitaten von vier Ferriten mit den chemischen Zusammensetzungen Ni1–xZnxFe2O4 (x = 0.5; 0.64), Mn1–xZnxFe2O4 (x = 0,42) und BaFe12O19 wurden mit einem adiabatischen Nernst-Kalorimeter, im Temperaturbereich 80 bis 303 °sK gemessen. Es wurde gefunden, das die Warmekapazitat mit abnehmender Temperatur abnimmt. Die Debye-Temperaturen wurden berechnet und mit denen aus elastischen Daten verglichen.

CI1H15NS3.AgNO3, Mr=427"3, orthorhombic, Pca2~, a=8.616(1) , b = 10.303(2), c = 16.839 (2) A, V= 1494.8/~3, Z = 4, D,,, = 1.91, Dx = 1.898 M~m-3, F(000) = 856, a(Mo Ka) = 0"71073 A, /z = 1.621 mm-~, T = 293 K. The structure was solved by the heavy-atom method and refined to R = 0-033 and wR = 0.039 for 2094 unique reflections. The Ag + cation sits in the cavity of the macrocycle and coordinates to three S atoms [S(4), S(7) and S(10)] and one N atom, N(1) of the pyridine ring. Ag + also coordinates to an S atom, S(7') ( 0 .5 + x, y , z), from an adjacent ligand. The intermolecular Ag--S interaction [2.498 (1) A] is stronger than the intramolecular Ag--S interactions [2.701 (2), 2-710(2) and 2-856(1)A]. Ag--S distances suggest covalent character of the bonds. The nitrate anion does not interact with the Ag + cation. Introduction. Substitution of N or S for O in cyclic polyethers greatly influences the complexing properties. When S replaces O as a donor atom in the macrocycle the stabilities of Ag ÷ and Hg + complexes increase while those of alkali complexes decrease (Frensdorff, 1971; Izatt, Terry, Hansen, Avondet, Bradshaw, Dalley, Jensen, Christensen & Haymore, 1978). The decrease in stability of alkalimetal complexes of polyether sulfides is probably due to the lower electronegativity, the larger size, and the different bond lengths and bond angles associated with the S atom compared to those of O. These factors tend to weaken the electrostatic attraction for alkali cations. In contrast, covalent bonding plays an important part in the Ag + and Hg + complexes. The crystal structure of the hetero analogue o f ' l 2-crown* Author to whom correspondence should be addressed. 0108-2701/89/121871-04503.00 4', namely 2,5,8-trithia[9](2,6)pyridinophane (1), has been described by Weber, Jones & Sheldrick (1983). This compound was reported to form crystalline complexes with AgNO3, HgC12, HAuC14, PdC12, H2PtC16 and Co(SCN)2 (Weber & Vogtle, 1976). The crystal structure analysis of the title compound was undertaken to study the possible structural changes due to complexing of AgNO3. Experimental. Colourless needle shaped crystals, crystal size 0.1 × 0.1 × 0.4 mm, density measured by flotation, data collection on an automated Stoe fourcircle diffractometer using graphite-monochromated Mo Ka radiation (,~ = 0.71073 A), lattice parameters by least-squares analysis of 0 values of 24 high-angle reflections in the range 20 < 20 < 30°; to/20 scan technique, 20max = 60°; index range: 0 ___ h ___ 12, 0 ___ k ___ 14, 0 _< 1___ 23; three standard reflections monitored every 100 reflections showed no significant variations; 2412 reflections measured of which 2094 reflections with I___ 3o(/) considered observed; empirical absorption correction was applied using O scans (North, Phillips & Mathews, 1968), max. and min. transmission 1.11 and 0.83; Lorentz and polarization corrections applied. Structure was solved by heavy-atom method using SHELX76 (Sheldrick, 1976); Ag and S positions from the Patterson map; rest of the non-H atoms from the subsequent Fourier maps; H-atom positions from difference Fourier maps; anisotropic refinement for non-H atoms and isotropic refinement for H atoms using full-matrix least-squares refinement; the isotropic temperature factors of four of the hydrogens were kept fixed at 0.05 A 2 during refinement. Final R = 0.033 and wR =0.039 for 2094 observed reflections; weighting scheme used, w = 1.O0/[o~(Fo) + 0.012031Fo[2], (shift/ © 1989 International Union of Crystallography 1872 2,5,8-TRITHIA[9](2,6)PYRIDINOPHANE-SILVER NITRATE (1.1) e.s.d.)max in the final cycle of refinement for non-H atoms was 0.039, reflections/parameters refined ratio was 8-87; the minimum and maximum heights in the final difference Fourier map were -0.82 and +0.81 elk -3. Atomic scattering factors for non-H atoms from Cromer & Mann (1968), for H atoms from Stewart, Davidson & Simpson (1965); anomalous-dispersion correction from Cromer & Liberman (1970). Fractional coordinates and equivalent isotropic thermal parameters of the non-H atoms are given in Table 1; bond lengths and angles in Table 2.* The atom labels correspond to Fig. 1.

The governing equations for gas flows in 16-^m CO2-N2-H2 gasdynamic lasers using conical or hyperbolic nozzles have been presented in universal form so that for a given gas composition the solutions depend on a single parameter that combines all other parameters of the laser system. The solutions of these equations are used to compute the optimum values of small signal optical gain, and the corresponding optimum values of the area ratio, the reservoir temperature T'0 and the binary scaling parameter p'0L', which is a product of reservoir pressure p'0 and nozzle shape factor L', for a wide range of gas mixture compositions. The results are presented in graph form. An optimum value of 2.06% cm'1 gain has been calculated for the gas composition of C02:N2:H2 = 15:65:20.

Thin AsSeCd films are studied for switching properties. It is shown that the switching characteristics may be varied by controlling film thickness and concentration of cadmium. Dunne AsSeCd-Schichten werden hinsichtlich der Schalteigenschaften untersucht. Es wird gezeigt, das die Schaltcharakteristiken durch Kontrolle von Schichtdicke und Kadmiumkonzentration geandert werden konnen.

A review with 18 refs. A comprehensive theoretical analysis of optimization of gain in $CO_2-N_2$ gasdynamic laser employing wedge or conical or hyperbolic nozzles with either $H_2O$ or He as the catalyst is presented. After a review of previous woprk, the usual governing equations for the steady inviscid quasi-1-dimensional flow in a supersonic nozzle of a gasdynamic laser are used to obtain similar solutions for the various flow quantities, which variables are subsequently used to optimize the small-signal gain on the P(20) line of the $(001) \rightarrow (100)$ transition of $CO_2$ at wavelength $10.6 \mu m$. The corresponding optimum values like reservoir pressure and temperature and nozzle area ratio also have been predicted and presented in the form of graphs. The analysis predicts that employing of 2D- wedge nozzle results in higher gain values and the $CO_2-N_2-H_2O$ gas dynamic laser employing 2D-wedge nozzle is operationally the best laser system for which the optimum value as high as $3.1 m^{-1}$ gain can be obtained.

Electrical conductivity and Hall effect were studied on vapour phase grown CdSxSe1−x single crystals in the entire range of composition in the temperature range 90–300 K. The conductivities of the as-grown crystals varied significantly. High conducting samples were obtained by annealing either in vacuum or in cadmium vapour. Hall mobilities, carrier concentration and donor activation energies were calculated. No definite variation in mobility with composition was observed. Donor activation energy showed an increasing trend with increase of CdS content.

A pulse interferometer, making use of the phase comparison principle, is described which uses monolithic and discrete solid state devices for determining ultrasonic velocities in solids. The apparatus is easy to construct and operate. The pulsed radio frequency output from the final power amplifier is 60-80 V peak-to-peak. Absolute ultrasonic velocities in solids can be measured to an accuracy of 1 in 104 and relative velocities to 1 in 106. The constructional details of the circuits are discussed.

We present periodic solutions, which are described in terms of Jacobian elliptic functions, for the steady state pulses from a laser system consisting of a pair of amplifiers of unequal relaxation time mode locked by a “fast” saturable absorber. The pulsewidth and the average power in the pulse are expressed interms of the system parameters through two different approaches, where detailed plots are given for one of the approaches. Summary of the characters to be possessed by the amplifier pair to ensure the reliable production of shortest possible pulses is given.

In this paper, the numerical experience gained in solving constrained minimization problems using Conjugate Direction Methods is presented. For this purpose, Dennemeyer's Least Square Algorithm, Sequential Conjugate Gradient-Restoration Algorithm, Reduced Conjugate Gradient Method (RCGM) and an accelerated computer code mikki 2 based on RCGM are described. Numerical implementation of these techniques is presented by solving certain test problems. The results obtained clearly indicate superiority and efficiency of the developed code mikki 2.

A theoretical analysis of a 16-\mu m $CO_2-N_2-H_2$ downstream-mixing gasdynamic laser, where a cold $CO_2$, $H_2$ stream is mixed with a vibrationally excited $N_2$ stream, tangentially downstream of the nozzle exit, is presented. The flowfield is analyzed numerically using 2-dimensional, unsteady, laminar, and viscous flow modeling, including the appropriate finite-rate vibrational kinetic equations. The effect of variation of different flowfield parameters on 16-mm small-signal gain is studied, and results are discussed in detail. The anal. shows that the presence of $H_2$ gas is detrimental to small-signal gain. The velocity ratio 1:1 between the $CO_2$, $H_2$, and $N_2$ mixing streams is the best choice rendering local small-signal gain as high as 21.75 $m^-1$ and corresponding av. small-signal gain of 16.7 $m^-1$ for $N_2$ reservoir temp. of 2000 K. These high values of small-signal gain clearly underscore the high potential which a downstream-mixing scheme has over the conventional methods for a 16-\mu m laser source.

Thermally stimulated current (TSC) measurements in the temperature range 90-400K were carried out on vapour-phase grown CdSxSe1-x single crystals over the full range of x (1.00, 0.90, 0.70, 0.50, 0.30, 0.10 and 0.00) by continuously exciting the crystals from different temperatures while cooling (TEWC) in the range 400-90K. Large changes in the peak currents were observed for different illumination conditions. The existing photochemical models are not able to explain the TSC dependence on TEWC observed in the crystals. A tentative photochemical model which takes into account the variation of photochemical reaction with composition has been proposed.

Elastic moduli of nickel-zinc (two different compositions), manganese—zinc and barium ferrites were determined as a function of temperature from 80 to 303 K. The experimental method employed was the composite piezo-electric oscillator capable of measuring elastic wave velocities to a few parts in 104. The elastic moduli of nickel-zinc ferrites were found to increase with decrease in temperature almost linearly whereas in barium ferrite, the moduli decrease with decreasing temperature showing some sort of hysteresis effect. However, in the case of manganese-zinc ferrite the elastic moduli first decrease with decrease in temperature to about 257 K and from there onwards increase with further decrease in temperature down to the boiling point of liquid air (80 K). The existence of a dip in the moduli versus temperature curves of manganese-zinc ferrite was suspected to be due to stress-induced relaxation at grain boundaries.

The structure and electrical conductivity of thin InAs films, prepared by flash evaporation, are seen to be dependent on the substrate temperature, post-deposition heat treatment and thickness. The structure was found to improve from amorphous → → polycrystalline → preferred orientation as the substrate temperature was increased. The corresponding micrographs showed increasingly bigger grain sizes. The post-deposition heat treatment was successfully employed to improve the structure from amorphous → crystalline, which was reflected in the increased electrical conductivity. An interesting observation was that the room temperature electrical conductivities after heat treatment were the same for all films irrespective of the temperature at which they were prepared. The activation energies increased with increasing temperature but decreased with increasing substrate temperature and increasing thickness. These values throw important light on the conduction mechanism operative in the film in various temperature ranges.

A method of steepest descent first applied by White et al. to the calculation of complex chemical equilibrium was used in this article to compute the equilibrium composition of a mixture resulting in the ammoxidation of propylene. As many as twenty species are likely to be present, some in insignificant quantities. A FORTRAN II Program was written for an IBM 1620 computer and calculations were made varying the feed composition, temperature and pressure. The results were discussed and qualitatively compared with those of the plant practice reported in the literature. The agreement is reasonably good when the oxygenated compounds are excluded from consideration. On a utilise la methode de chute la plus prononcee (steepest descent), laquelle White et al., avaient d'abord appliquee an calcul d'equilibres chimiques complexes, pour calculer la composition d'equilibre d'un melange resultant de l'oxydation ammoniacale du propylene. Il est probable qu'une vingtaine de composes sont presents dont quelques-uns en quantites negligeables. On a prepare un programme FORTRAN II pour une calculatrice IBM-1620 et l'on fait des calculs en faisant varier la composition du produit d'alimentation, la temperature et la pression. On discute les resultats obtenus et les compare qualitativement avec ceux qu'on obtient dans les usines et qu'on lapporte dans la litterature technique. La concordance est raisonnablement bonne, lorsqu'on ne considere pas les composes oxygenes.

The six third-order elastic constants of single crystal ferromagnetic nickel at 80°K were determined by measurement of ultrasonic wave velocities as a function of an applied uniaxial stress. The effect of magnetic domains on the ultrasonic propagation were eliminated by keeping the specimen in a transverse saturation magnetic field. Theoretically predicted constants based on central force model are discussed with experimentally measured constants. Die sechs elastischen Konstanten dritter Ordnung von ferromagnetischen Nickeleinkristallen wurden bei 80°K durch Messung der Ultraschallgesch windigkeit in Abhangigkeit von einer auseren uniachsialen Spannung bestimmt. Der Einflus magnetischer Domanen auf die Ultraschallausbreitung wurde dadurch eliminiert, das sich die Probe in einem transversalen Sattigungsfeld befindet. Theoretisch vorhergesagte Konstanten, die auf einem Zentralkraftmodell basieren, werden mit experimentell gemessenen Konstanten diskutiert.