Studies on elemental tellurium under high pressure

A non-linear behaviour in the resistance of tellurium as a function of pressure has been observed. At each pressure the resistance shows a time variation. At lower pressures, the normalized resistance increases with time, and at higher pressures, the normalized resistance decreases exponentially as a function of time. This change in behaviour with respect to time occurs in the region of the steepest descent in the resistance versus pressure plot. However, the magnitude of the change in the resistance with time is small compared to a change in the resistance with pressure. The origin of this behaviour is suggested to be linked with the generation and annealing of localized charged defects. This revised version was published online in November 2006 with corrections to the Cover Date.     

Radiometric studies of transportation of water vapour over Calcutta

A characteristic feature of the lingering of post-rain attenuation over Calcutta, India, has been observed by 22·235 GH_z radiometer. This feature is presumably due to the injection of extra water vapour during the post-rain period in the presence of large ambient humidity and low wind activity. Experimentally observed post-rain attenuation was found to be mostly due to the vertical diffusion of water vapour into the raining zone, the contribution due to horizontal diffusion being small compared to that of the vertical diffusion.     

DIELECTRIC PROPERTIES of RICE BRAN

The dielectric properties of rice bran have been of interest because of their correlation with moisture content and because to a large extent they determine the absorption of energy in dielectric heating applications. the dielectric properties, namely, dielectric constant, loss tangent, dielectric loss factor and a.c. conductivity of rice bran were measured experimentally at a frequency of 13.56 MHz by a resonance method using a Q-meter along with a coaxial, cylindrical sample holder. In order to study the effects of various factors, namely, the moisture content, temperature and bulk density of rice bran, the experiments were designed and performed based on Response Surface Methodology. the dielectric constant, dielectric loss factor and a.c. conductivity were found to have positive nonlinear relationships, while the loss tangent had a positive linear relationship within the ranges of factors studied, namely 3.95 to 14.05% (w.b.) moisture content, 26.5 to 53.5°C temperature, and 299.5 to 400.5 kg/m³ bulk density.     

Relook on fitting of viscosity with undercooling of glassy liquids

The present approach is on the modification of viscosity fitting of undercooled liquid as a function of undercooling. The method consists of finding analytical solution of three arbitrary constants of the Vogel–Fulcher–Tamman (VFT) equation by choosing three viscosity data at three critical temperatures for an undercooled liquid. Three critical temperatures are liquidus temperature (T _l), crystallization onset temperature (T _x) and glass transition temperature (T _g). The experimental viscosity data at or very near to these three critical temperatures (depending on the availability in literature) have been utilized to achieve the analytical solution. The analytical solution of VFT equation is further examined by selecting the experimental data points away from the critical temperatures in order to check their (T _l,T _x and T _g) significance towards the solution. Total absolute error (TAE) and total squared error (TSE) values obtained from the present method with respect to the experimental viscosity data in the temperature range between T _l and T _g are very much comparable and in most of the cases lower than that of existing ‘best-fit’ cited in the literature for a number of glassy alloys. Moreover, this method interestingly enables us to find the fragility parameters for a number of glassy alloys and convincingly explain their true glass forming abilities (GFA).     

Uneven (and Divergent) Technological Accumulation among Advanced Countries: Evidence and a Framework of Explanation

We present evidence for the advanced OECD countries of unevenand divergent patterns of technological accumulation. We showthat ‘global’ firms will not smooth out the differences,since their technological activities are strongly influencedby conditionsin their own countries. We suggest that—in addition to diversity in cumulative technological trajectories7— the divergent patterns reflect international differencesin the capacities of management, financial and training institutionsproperly to evaluate— and exploit— the learningbenefits of technological investments. For these reasons, weconclude that technological gaps among the advanced OECD countriesare here to stay.     

A DESIGN OPTIMIZATION PROCEDURE FOR MINIMIZING DRIVE SYSTEM WEIGHT OF HIGH SPEED PROP-ROTORS

An optimization procedure is developed to address the problem of minimizing the drive system weight of high speed prop-rotor aircraft which are required to demonstrate fixed-wing-like efficiencies in high speed forward flight and maintain acceptable hover figure of merit similar to helicopters. The optimization is performed using the method of feasible directions. A hybrid approximate analysis procedure is also used to reduce the computational effort of using exact analysis for every function evaluation necessary within the optimizer. The results compared to a reference rotor show significant weight reductions. The aerodynamic performance of the optimized rotor, analyzed at “off-design” points to judge the strength of the optimization problem formulation and the validity of the resulting design, shows considerable improvements. The results are compared to the reference values and significant reduction in the weight is achieved.     

Integrated water vapour content by scanning radiometry

Abstract

Radiometry at the water vapour line with a scanning antenna beam from horizon to horizon through the zenith, in the vertical plane, was shown to be useful in estimating the integrated water vapour content from the zenith angle variation of radiometric temperature. The beam scanning may be made at a rate slower than the radiometer time constant using a Dicke type radiometer. Alternatively, a fast scanning beam may be used in a total power radiometer with a synchronous detection of the radiometer output at the scanning frequency to obtain a space domain Dicke switching for the measurements. A simultaneous scanning beam with 22.235 and 31.4GHz radiometers would allow us to separate the liquid water, if any, from the integrated water vapour content. Theoretical studies of the scanning beam radiometer performance in the estimation of integrated water vapour content from radiosonde data is presented and some typical results of Dicke type scanning beam radiometers at 22.235 and 31.4 GHz are also presented in this paper.     

HEAT TRANSFER DURING FLUIDIZED BED PUFFING of RICE GRAINS

A pneumatic rice puffing machine was developed for increasing the production capacity of puffed rice for which a knowledge of the heat transfer process during puffing was required. the physical properties of the rice grains and other fluidization parameters, necessary for this study was experimentally determined. the surface heat transfer coefficient in case of hot air fluidized bed puffing was found to be 155.39 W/m²K. the calculated grain surface temperature for puffing was about 170°C and this did not vary significantly for experimental puffing air temperatures ranging from 200°C to 270°C. the air temperature ranging from 240°C to 270°C with corresponding exposure time of 9.7 s to 7s was found to be optimum for higher expansion ratio (8.5 to 10) and better color of the product. the temperature differentials between surface and center temperatures and between surface and average temperatures of the grains at the time of puffing were found to vary linearly with various puffing air temperatures and their ratios remained almost constant at 2.056.