Anisotropic properties of the layered semiconductor in Te

Anisotropic properties of the Bridgman grown layered semiconductor p-InTe were studied by analyzing the temperature dependence of electrical conductivity and Hall mobility parallel and perpendicular to the layer planes. The mobilities were μamalgamation or coproduct = 50–60 cm2V−1 sec−1 and μperpendicular = 10–15 cm2V−1sec−1 and varied as μ ≈ Tn where n = 1.43 due to impurity scattering. Pressure-induced semiconductor-metal transition occurred at about 50 kbar. The pressure coefficient of resistance was 3 times larger in the direction perpendicular to the layer plane due to the difference between inter and intra-planar bonding.

A sufficient criterion for Rayleigh-Taylor instability of incompressible viscous three-layer flow

Using normal mode analysis Rayleigh-Taylor instability is investigated for three-layer viscous stratified incompressible steady flow, when the top 3rd and bottom 1st layers extend up to infinity, the middle layer has a small thickness δ. The wave Reynolds number in the middle layer is assumed to be sufficiently small. A dispersion relation (a seventh degree polynomial in wave frequency ω) valid up to the order of the maximal value of all possible Kj (j less-than-or-equals, slant 0, K is the wave number) in each coefficient of the polynomial is obtained. A sufficient condition for instability is found out for the first time, pursuing a medium wavelength analysis. It depends on ratios (α and β) of the coefficients of viscosity, the thickness of the middle layer δ, surface tension ratio T and wave number K. This is a new analytical criterion for Rayleigh-Taylor instability of three-layer fluids. It recovers the results of the corresponding problem for two-layer fluids. Among the results obtained, it is observed that taking the coefficients of viscosity of 2nd and 3rd layers same can inhibit the effect of surface tension completely. For large wave number K, the thickness of the middle layer should be correspondingly small to keep the domain of dependence of the threshold wave number Kc constant for fixed α, β and T.

Interdiffusion studies in bulk Au-Ti system

The performance of the contacts, where Au/Ti layers are used in the metallization scheme, largely depends on the product phases grown by interdiffusion at the interface. It is found that four intermetallic compounds grow with narrow homogeneity range and wavy interfaces in the interdiffusion zone. The presence of wavy interfaces is the indication of high anisotropy in diffusion of the product phases. This also reflects in the deviation of parabolic growth from the average. Further, we have determined the relevant diffusion parameters, such as interdiffusion coefficient in the penetrated region of the end members and integrated diffusion coefficients of the intermetallic compounds.

Terahertz Time Domain Spectroscopy to Detect Low-Frequency Vibrations of Double-Walled Carbon Nanotubes

We have measured the frequency-dependent real index of refraction and extinction coefficient (and hence the complex dielectric function) of a free-standing double-walled carbon nanotube film of thickness 200 nm by using terahertz time domain spectroscopy in the frequency range 0.1 to 2.5 THz. The real index of refraction and extinction coefficient have very high values of approximately 52 and 35, respectively, at 0.1 THz, which decrease at higher frequencies. Two low-frequency phonon modes of the carbon nanotubes at 0.45 and 0.75 THz were clearly observed for the first time in the real and imaginary parts of the complex dielectric function along with a broad resonance centred at around 1.45 THz, the latter being similar to that in single-walled carbon nanotubes assigned to electronic excitations. Our experiments bring out a possible application of double-walled carbon nanotube films as a neutral density filter in the THz range.

Characterization of hot deformation behavior of brasses using processing maps: Part II. β Brass and α-β brass

The hot deformation behaviors of β brass in the temperature range of 550°C to 800°C and α-β brass in the temperature range of 450°C to 800°C have been characterized in the strain rate range of 0.001 to 100 s−1 using processing maps developed on the basis of the Dynamic Materials Model. The map for β brass revealed a domain of superplasticity in the entire temperature range and at strain rates lower than 1 s−1, with a maximum efficiency of power dissipation of about 68 pct. The temperature variation of the efficiency of power dissipation in the domain is similar to that of the diffusion coefficient for zinc in β brass, confirming that the diffusion-accommodated flow controls the superplasticity. The material undergoes microstructural instability in the form of adiabatic shear bands and strain markings at temperatures lower than 700°C and at strain rates higher than 10 s−1. The map for α-β brass revealed a wide domain for processing in the temperature range of 550°C to 800°C and at strain rates lower than 1 s−1, with a maximum efficiency of 54 pct occurring at about 750°C and 0.001 s−1. In the domain, the α phase undergoes dynamic recrystallization and controls the hot deformation of the alloy, while the β phase deforms superplastically. At strain rates greater than 1 s−1, α-β brass exhibits microstructural instabilities manifested as flow rotations at lower temperatures and localized shear bands at higher temperatures.

Diffusion coefficients for selected binary liquid systems: cyclohexanes and n-alkyl alcohols

In the present work the integral diffusion coefficients are estimated by using the diaphragm cell technique. The diffusion coefficients are measured at various compositions for two sets binary systems: one of cyclohexane and n-paraffinic alcohols and the other of methylcyclohexane and n-paraffinic alcohols. The alcohols used are seven members of homologous series of n-paraffinic alcohols from ethanol to octanol. The maximum possible error in the experimental diffusion coefficient could be 8% for both the cyclohexane-n-alkyl alcohol system and methylcyclohexane-n-alkyl alcohol system. A correlation for each of the two sets of binary systems is given. The maximum deviation in the correlations was less than 6.5 and 3.5% for cyclohexane-n-alkyl alcohols and methylcyclohexane-n-alkyl alcohols, respectively.

Theoretical gain‐optimization studies in CO2–N2 gasdynamic lasers. II. Results of parametric study

Based on a method presented in detail in a previous work by the authors, similar solutions have been obtained for the steady inviscid quasi‐one‐dimensional nonreacting flow in the supersonic nozzle of a CO2–N2 gasdynamic laser system, with either H2O or He as the catalyst. It has been demonstrated how these solutions could be used to optimize the small‐signal gain coefficient on a specified vibrational‐rotational transition. Results presented for a wide range of mixture compositions include optimum values for the small‐signal gain, area ratio, reservoir temperature, and a binary scaling parameter, which is the product of reservoir pressure and nozzle shape factor.

Dynamics of sheared inelastic dumbbells

We study the dynamical properties of the homogeneous shear flow of inelastic dumbbells in two dimensions as a first step towards examining the effect of shape on the properties of flowing granular materials. The dumbbells are modelled as smooth fused disks characterized by the ratio of the distance between centres (L) and the disk diameter (D), with an aspect ratio (L/D) varying between 0 and 1 in our simulations. Area fractions studied are in the range 0.1-0.7, while coefficients of normal restitution (e(n)) from 0.99 to 0.7 are considered. The simulations use a modified form of the event-driven methodology for circular disks. The average orientation is characterized by an order parameter S, which varies between 0 (for a perfectly disordered fluid) and 1 (for a fluid with the axes of all dumbbells in the same direction). We investigate power-law fits of S as a function of (L D) and (1 - e(n)(2)) There is a gradual increase in ordering as the area fraction is increased, as the aspect ratio is increased or as the coefficient of restitution is decreased. The order parameter has a maximum value of about 0.5 for the highest area fraction and lowest coefficient of restitution considered here. The mean energy of the velocity fluctuations in the flow direction is higher than that in the gradient direction and the rotational energy, though the difference decreases as the area fraction increases, due to the efficient collisional transfer of energy between the three directions. The distributions of the translational and rotational velocities are Gaussian to a very good approximation. The pressure is found to be remarkably independent of the coefficient of restitution. The pressure and dissipation rate show relatively little variation when scaled by the collision frequency for all the area fractions studied here, indicating that the collision frequency determines the momentum transport and energy dissipation, even at the lowest area fractions studied here. The mean angular velocity of the particles is equal to half the vorticity at low area fractions, but the magnitude systematically decreases to less than half the vorticity as the area fraction is increased, even though the stress tensor is symmetric.

Geometrically simple linear weirs using circular quadrants

A detailed theoretical analysis of flow through a quadrant plate weir is made in the light of the generalized theory of proportional weirs, using a numerical optimization procedure. It is shown that the flow through the quadrant plate weir has a linear discharge-head relationship valid for certain ranges of head. It is shown that the weir is associated with a reference plane or datum from which all heads are reckoned.Further, it is shown that the measuring range of the quadrant plate weir can be considerably enhanced by extending the tangents to the quadrants at the terminals of the quadrant plate weir. The importance of this weir (when the datum of the weir lies below its crest) as an outlet weir for grit chambers is highlighted. Experiments show excellent agreement with the theory by giving a constant average coefficient of discharge.

Protonic conductivity of (NH4) 4Fe(CN)6·1.5H2O by complex admittance method

The protonic conductivity of ammonium ferrocyanide hydrate has been studied by the complex admittance method. The admittance plots show departures from ideal Debye behaviour. The values of ionic conductivity (sigma = 3.7 X 10(-5) (OMEGA-cm)-1) and diffusion coefficient (D = 3.8 X 10(-10) cm2/s) obtained at room temperature are consistent with the corresponding values estimated by an earlier NMR study.

Pyroelectric properties of Bi2VO5.5 ceramic

The dielectric, pyroelectric and thermal properties of ferroelectric Bi2VO5.5(Bi4V2O11) ceramic have been studied over a temperature range of 300-780 K. The sign of the pyroelectric coefficient is positive at room temperature. The dielectric constant, pyroelectric coefficient and specific heat exhibit anomalies around the Curie temperature, 725 K. The frequency response of the dielectric constant and tan delta has been studied over a frequency range of 1-100 kHz. It is found that both the dielectric constant and the loss tangent decrease with increasing frequency. The pyroelectric figures of merit from the point of view of different applications have been calculated at 320 K by combining pyroelectric, dielectric and thermal properties.

Nucleosome core histone complex isolated gently and rapidly in 2 M NaCl is octameric

A relatively stable specific complex of the chromatin core histones H2A, H2B, H3, and H4 has been obtained in 2 M NaCl/25 mM sodium phosphate buffer, pH 7.0. The histone core complex has an apparent specific volume of 0.73 ml/g. Its sedimentation coefficient was dependent on rotor speed (angular velocity, omega) and attained different stable values at low and high rotor speeds. The drop in sedimentation coefficient occurred sharply between omega 2 values of about 9 x 10(6) and 1.1 x 10(7) (radians/sec)2. The s020,w corresponding to zero angular velocity (1 atmosphere pressure) was 6.6 S +/- (SEM) 0.1 S. At high rotor speeds the value decreased to 3.8 S +/- 0.1 S. The core complex has a diffusion coefficient, D20,w, of 5.4 x 10(-7) cm2/sec and a molecular weight of 108,000 +/- (SD) 2500.

Spectral element approach to wave propagation in uncertain beam structures

This paper presents a study on the uncertainty in material parameters of wave propagation responses in metallic beam structures. Special effort is made to quantify the effect of uncertainty in the wave propagation responses at high frequencies. Both the modulus of elasticity and the density are considered uncertain. The analysis is performed using a Monte Carlo simulation (MCS) under the spectral finite element method (SEM). The randomness in the material properties is characterized by three different distributions, the normal, Weibull and extreme value distributions. Their effect on wave propagation in beams is investigated. The numerical study shows that the CPU time taken for MCS under SEM is about 48 times less than for MCS under a conventional one-dimensional finite element environment for 50 kHz loading. The numerical results presented investigate effects of material uncertainties on high frequency modes. A study is performed on the usage of different beam theories and their uncertain responses due to dynamic impulse load. These studies show that even for a small coefficient of variation, significant changes in the above parameters are noticed. A number of interesting results are presented, showing the true effects of uncertainty response due to dynamic impulse load.

Unsteady mixed convection flow in stagnation region adjacent to a vertical surface

The unsteady two-dimensional laminar mixed convection flow in the stagnation region of a vertical surface has been studied where the buoyancy forces are due to both the temperature and concentration gradients. The unsteadiness in the flow and temperature fields is caused by the time-dependent free stream velocity. Both arbitrary wall temperature and concentration, and arbitrary surface heat and mass flux variations have been considered. The Navier-Stokes equations, the energy equation and the concentration equation, which are coupled nonlinear partial differential equations with three independent variables, have been reduced to a set of nonlinear ordinary differential equations. The analysis has also been done using boundary layer approximations and the difference between the solutions has been discussed. The governing ordinary differential equations for buoyancy assisting and buoyancy opposing regions have been solved numerically using a shooting method. The skin friction, heat transfer and mass transfer coefficients increase with the buoyancy parameter. However, the skin friction coefficient increases with the parameter lambda, which represents the unsteadiness in the free stream velocity, but the heat and mass transfer coefficients decrease. In the case of buoyancy opposed flow, the solution does not exist beyond a certain critical value of the buoyancy parameter. Also, for a certain range of the buoyancy parameter dual solutions exist.

Varistor property of n‐BaTiO3 based current limiters

Highly stable varistor (voltage-limiting) property is observed for ceramics based on donor doped (Ba1-xSrx)Ti1-yZryO3 (x < 0.35, y < 0.05), when the ambient temperature (T(a)) is above the Curie point (T(c)). If T(a) < T(c), the same ceramics showed stable current-limiting behavior. The leakage current and the breakdown voltage as well as the nonlinearity coefficient (alpha = 30-50) could be varied with the T(c)-shifting components, the grain boundary layer modifiers and the post-sintering annealing. Analyses of the current-voltage relations show that grain boundary layer conduction at T(a) < T(c) corresponds to tunneling across asymmetric barriers formed under steady-state joule heating. At T(a) > T(c), trap-related conduction gives way to tunneling across symmetric barriers as the field strength increases.