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This paper described the behaviours of four divalent metal fluorides ( CaF 2 , SrF 2 , CdF 2 and BaF 2) in terms of their superior elastic, mechanical and thermophysical properties. Initially, higher-order elastic constants of the chosen divalent metal fluorides have been calculated using the Coulomb and Born–Mayer interaction potential in the temperature regime 100–300 K. With the help of these constants, other elastic moduli, such as Young’s modulus (Y), bulk modulus (B), shear modulus (G), Poisson’s ratio (σ) and Pugh’s ratio (B/G) have been computed using Voigt–Reuss–Hill approximation. The Born stability criteria and Vicker’s hardness parameter (H ν) have been used for analysing the nature and strength of the materials. Later on, ultrasonic velocities including Debye average velocities were evaluated using calculated values of second-order elastic constants and density in the same physical conditions. Thermal properties such as the lattice thermal conductivity, thermal relaxation time, thermal energy density and acoustic coupling constant have also been computed at the same physical conditions and along ⟨ 100 ⟩ . The temperature-dependent ultrasonic properties have been correlated with other thermophysical properties to extract important information about the microstructural quality and the nature of the materials. The obtained results have been analysed to explore the inherent properties of the chosen divalent metal fluorides, which are useful for numerous industrial applications. [ABSTRACT FROM AUTHOR]

In the present study, ultrasonic and thermophysical behaviour of thermoelectric hexagonal structured HfX2 (X = S, Se) compounds have been analysed by the theoretical evaluation of second and third order elastic constants (SOECs and TOECs) using many body interaction potential model. The computed SOECs have been used to determine the temperature dependent specific heat, thermal energy density, elastic coupling constants, Grüneisen parameters, ultrasonic velocities, Debye average velocity, ultrasonic attenuation, and thermal relaxation time. We have observed that the temperature dependent ultrasonic attenuation and thermal relaxation time for HfX2 are mainly affected by thermal conductivity. The elastic properties of the material are compared with existing data in literature for the validation of the work. The obtained values of elastic stiffness are found very large in comparison to that of other material from transition metal dichalcogenides of group IVB indicating better mechanical properties than the same group materials. Calculated elastic, thermal, and ultrasonic properties are correlated for better characterization of the materials which are useful for thermoelectric and energy transport applications. [ABSTRACT FROM AUTHOR]

Second and third order elastic constants of GaAs Nanowires (NWs) are calculated using the manybody interaction potential model. The velocities of ultrasonic waves at different orientations of propagation with unique axis are evaluated using the second order elastic constants. The ultrasonic attenuation and thermal relaxation times of the single crystalline GaAs-NW are determined as a function of diameter and surface roughness by means of Mason theoretical approach using the thermal conductivity and higher order elastic constants. The diameter variation of ultrasonic attenuation and thermal relaxation exhibit second order polynomial function of diameter. It is also found that ultrasonic attenuation and thermal relaxation follow the exponential decay with the surface roughness for GaAs-NW due to reduction in thermal conductivity caused by dominance of surface asperities. Finally, the correlations among ultrasonic parameters, thermal conductivity, surface roughness, and diameter for GaAs-NWs are established leading towards potential applications. [ABSTRACT FROM AUTHOR]

The IrxRe1−x (0.1≤ x ≤0.7) alloys are hexagonal structured inclusion material used in an on-orbit communication satellite. The characteristic features of high-temperature alloys IrxRe1−x (0.1≤ x ≤0.7) are investigated by the theoretical evaluation of thermophysical and ultrasonic properties at room temperature. Initially, higher-order elastic constants of the alloys are calculated using the simple interaction potential model approach. With the help of this other elastic moduli, elastic stiffness constants and hardness parameters are estimated at room temperature for elastic and mechanical characterization. Later on, the ultrasonic velocity and thermal relaxation time of chosen alloys are evaluated utilizing calculated values of SOECs and lattice parameters within the same physical conditions. The orientation-dependent ultrasonic velocities and thermal relaxation time have been also evaluated for the determination of anisotropic behaviour and thermophysical properties. The obtained results are analysed to explore the inherent properties of IrxRe1−x alloys. [ABSTRACT FROM AUTHOR]

Application of principal component analysis in developing statistical models for forecasting pigeon-pea yield has been demonstrated. The time series data on pigeon-pea yield and weekly data on eight weather variables viz., Minimum and maximum temperature ,Rainfall and number of Rainy days, Relative Humidity at 7hr and 14hr, Sun-Shine hours and Wind- Velocity pertaining to the period 1990-91 to 2011-12 in Faizabad district of Uttar Pradesh have been used in this study. Weather indices have been constructed using weekly data on weather variables [Agrawal et al. (1983)]. Total six models have been developed using principal component analysis of weather indices. The forecast yields have been found to be very close to the actual yield except in one or two cases. The per cent standard errors of forecast yield obtained from the model-2 and 5 have been found below 5.50 per cent in comparison to other models. Therefore, the model-2 and 5 have been found to be most appropriate on the basis of values of R2, per cent deviation of forecast, per cent root mean error (%RMSE) and per cent standard error (PSE) for the reliable forecast of pigeon-pea yield two and half months before the harvest of the crop. [ABSTRACT FROM AUTHOR]