Devraj Singh

Ultrasonic wave propagation in rare-earth monochalcogenides

The ultrasonic attenuation in thulium monochalcogenides TmX (X=S, Se and Te) has been studied theoretically with a modified Mason’s approach in the temperature and range 100 K to 300 K along 〈100〉, 〈110〉 〈111〉 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second- and third-order elastic constants. These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time, and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic parameters with available theoretical/experimental physical parameters gives information about classification of these materials.

Elastic and Acoustic Properties of Heavy Rare-Earth Metals

In this paper, ultrasonic properties like ultrasonic attenuation, sound velocities, acoustic coupling constants and thermal relaxation time have been studied in hexagonal structured metals Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and Thulium (Tm) along unique axis at room temperature. For the evaluations of ultrasonic properties, secondand thirdorder elastic constants have been computed also. The peculiar behavior of these metals is found at 55° due their least thermal relaxation time and highest Debye average velocity. Dy is more ductile, stable, perfect metal in comparison to other chosen metals due to its lowest value of attenuation. So we predict that Dy is most suitable lanthanide metals for material science and engineering.

Ultrasonic Attenuation in Lanthanum Monochalcogenides

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation are studied in Lanthanum Monochalcogenides in direction at different higher temperatures. For evaluation of ultrasonic absorption coefficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along propagation direction with polarized along and the attenuation increases at higher temperatures. Thermo-elastic loss is very small compared to phonon-viscosity loss. Behavior of temperature dependence of the absorption is the same as in case of pure metals and dielectric crystals.

A study of ZnO nanoparticles and ZnO-EG nanofluid

This study deals with the synthesis and characterisation of ZnO nanoparticles and suspension of ZnO-ethylene glycol (EG) nanofluid. Crystalline ZnO nanoparticles are synthesised using the chemical method. The nanofluids were synthesised by the dispersion of ZnO nanoparticles in EG solution using an ultrasonicator. The prepared ZnO nanoparticles are characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-Vis absorption spectrum. The particle size distribution and ultrasonic parameters of the synthesised nanofluid are measured with the help of acoustic particle sizer (APS-100) and ultrasonic interferometer. The observed features of ZnO nanoparticles and ZnO-EG nanofluids are discussed in correlation with known properties of other nanofluids.

Study of Copper/Palladium Nanoclusters Using Acoustic Particle Sizer

Department of Physics, University of Allahabad, Allahabad-211002, India In the present study polyvinylpyrrolidone (PVP) stabilised copper/palladium bimetallic nanoclusters were synthesised through chemical routes. The prepared Cu/Pd bimetallic nanoparticles were characterised by ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-vis absorbance band confi rmed the formation of complex metal ions triggered by the complexing agent trisodium citrate. The XRD pattern indicated the formation of bimetallic nanoparticles. The TEM images of the synthesised bimetallic Cu/Pd nanoparticles showed that the size distribution of the particles was in the range 5–15 nm. An acoustic particle sizer was then used to analyse the size distribution. The results obtained by the acoustic particle sizer were consistent with the XRD and TEM analyses. These results demonstrate the potential usefulness of the acoustic particle sizer for quick and easy characterisation of nanoparticles in various catalytic, sensor and fuel cell applications.

MECHANICAL AND THERMAL PROPERTIES OF PRASEODYMIUM MONOPNICTIDES: AN ULTRASONIC STUDY

We have computed ultrasonic attenuation, acoustic coupling constants and ultrasonic velocities of praseodymium monopnictides PrX(X: N, P, As, Sb and Bi) along the 〈100〉, 〈110〉, 〈111〉 in the temperature range 100–500 K using higher order elastic constants. The higher order elastic constants are evaluated using Coulomb and Born–Mayer potential with two basic parameters viz. nearest-neighbor distance and hardness parameter in the temperature range of 0–500 K. Several other mechanical and thermal parameters like bulk modulus, shear modulus, Youngs modulus, Poisson ratio, anisotropic ratio, tetragonal moduli, Breazeales nonlinearity parameter and Debye temperature are also calculated. In the present study, the fracture/toughness (B/G) ratio is less than 1.75 which implies that PrX compounds are brittle in nature at room temperature. The chosen material fulfilled Born criterion of mechanical stability. We also found the deviation of Cauchys relation at higher temperatures. PrN is most stable material as it has highest valued higher order elastic constants as well as the ultrasonic velocity. Further, the lattice thermal conductivity using modified approach of Slack and Berman is determined at room temperature. The ultrasonic attenuation due to phonon–phonon interaction and thermoelastic relaxation mechanisms have been computed using modified Masons approach. The results with other well-known physical properties are useful for industrial applications.

Temperature Dependent Heat Transfer Performance of Multi-walled Carbon Nanotube-based Aqueous Nanofluids at Very Low Particle Loadings

Aqueous suspensions of multi-walled carbon nanotubes (MWCNTs + deionised water) have been synthesised. Carbon nanotubes (CNTs) were derived by chemical vapour deposition (CVD). Transmission electron microscopy (TEM) measurements show the formation of MWCNTs. Three samples of CNT-based aqueous nanofluids having MWCNT concentrations of 0.01 vol%, 0.03 vol% and 0.05 vol% were prepared with the help of ultrasonic irradiation. A very small amount of sodium dodecyl sulfate (SDS) was used as a surfactant to minimise the agglomeration of the MWCNTs. An effective enhancement in thermal conductivity was observed at different temperatures. The obtained results are explained with percolation theory.

Temperature Dependence of Elastic and Ultrasonic Properties of Sodium Borohydride

We present the temperature dependent elastic and ultrasonic properties of sodium borohydride. The second and third order elastic constants of NaBH4 have been computed in the temperature range 0-300K using Coulomb and Born-Mayer potentials. The sodium borohydride crystallizes into NaCl-type structure. The computed values of second order elastic constants have been applied to evaluate the temperature dependent mechanical properties such as bulk modulus, shear modulus, tetragonal modulus, Poisson’s ratio and Zener anisotropy factor and ultrasonic velocity to predict futuristic information about sodium borohydride. The fracture to toughness ratio (bulk modulus/shear modulus) in sodium borohydride varied from 1.91 to 1.62, which shows its behavioral change from ductile to brittle on increasing the temperature. Then, ultrasonic Grüneisen parameters have been computed with the use of elastic constants in the temperature regime 100300K. The obtained results have been discussed in correlation with available experimental and theoretical results.

Ultrasonic Investigations on Polonides of Ba, Ca, and Pb

Abstract The temperature-dependent mechanical and ultrasonic properties of barium, calcium, and lead polonides (BaPo, CaPo, and PbPo) were investigated in the temperature range 100–300 K. The second- and third-order elastic constants (SOECs and TOECs) were computed using Coulomb and Born-Mayer potential and these in turn have been used to estimate other secondary elastic properties such as strength, anisotropy, microhardness, etc. The theoretical approach followed the prediction that BaPo, CaPo, and PbPo are brittle in nature. PbPo is found to be the hardest amongst the chosen compounds. Further the SOECs and TOECs are applied to determine ultrasonic velocities, Debye temperature, and acoustic coupling constants along <100>, <110>, and <111> orientations at room temperature. Additionally thermal conductivity has been computed using Morelli and Slack’s approach along different crystallographic directions at room temperature. Finally ultrasonic attenuation due to phonon–phonon interaction and thermoelastic relaxation mechanisms has been computed for BaPo, CaPo, and PbPo. The behaviour of these compounds is similar to that of semi-metals with thermal relaxation time of the order 10−11 s. The present computation study is reasonably in agreement with the available theoretical data for the similar type of materials.

Working with JIT requires a Flexible Approach

Flexibility in management is essential today to survive in the most changing and turbulent environment, especially in the global changing international trade scenario and competitiveness in the world market. More transparency and a greater sense of participative decision-making at different levels of management decisions are vital. Decisions made with an open mind without any presumptions or constraints help in sustaining conducive atmosphere with respect to encouraging innovation in the organization. Flexibility in manufacturing ensures customization of products, which have maximum customer satisfying capability. JIT is an innovative management philosophy which evolved in Japan. Flexibility in organizational management as well as manufacturing management is essentially required to accelerate the pace of JIT implementation. This is possible because of improved communication and cordial working atmosphere among the people, which helps them to coordinate their activities effectively to achieve their common organizational goal of becoming the best and number one in the market by producing the customized products. This is what JIT asks for. In this paper, an attempt has been made to explore how the two flexibilities are critical for JIT and to what extent they affect its implementation.