Nucleus-nucleus potential in the range -2

S Kailas  A Navin 《Canadian Metallurgical Quarterly》1992,46(2):809-810

Process optimization and kinetic modeling for esterification of propionic acid with benzyl alcohol on ion-exchange resin catalyst

Benzyl propionate, an ester with floral and fruity odor, has significant applications in perfumery and flavor industries. This paper describes the optimization of the synthesis of benzyl propionate catalyzed by Amberlyst-15. The effects of various process parameters such as catalyst loading, alcohol-to-acid molar ratio and reaction temperature on propionic acid conversion and yield of ester were assessed by response surface methodology (RSM). The external and internal mass transfer limitations were found to be absent. Analysis of variance (ANOVA) showed that the acquired quadratic model successfully interpreted the experimental data with the coefficient of determination values, (R²>0.98) and adjusted R² values, (>0.97). The RSM model was validated by good agreement between the model predicted and experimental values for responses. Pseudohomogeneous (PH) kinetic model was used and validated (R²>0.95) with the experimental data. The activation energy and frequency factor were evaluated as 42.07 kJ mol^?1 and 19,874.64 L mol^?1 min^?1, respectively.     

Co-doped ZnO–PVA Nanocomposite for EMI Shielding

The article describes the mechanical properties and electromagnetic shielding of Co-doped ZnO–poly(vinyl alcohol) nanocomposite. Significant improvements in mechanical properties can be obtained by incorporating inorganic nano fillers. The E-modulus and tensile strength were found to be enhanced with the increase in the doping concentration of Co_.05Zn_.95O incorporated in PVA matrix. Further, we have observed that electromagnetic shielding of the composite filled with 2 wt% concentration of Co_.05Zn_.95O in the PVA matrix exhibited utmost reflection loss of ? 47.31 dB in the bandwidth 8–12 GHz which may be attributed to good compatibility of dielectric and magnetic properties of materials.     

Opportunistic large array concentric routing algorithm (OLACRA) for upstream routing in wireless sensor networks

An opportunistic large array (OLA) is a form of cooperative diversity in which a large group of relays or forwarding nodes operate without any mutual coordination, but naturally fire together in response to energy received from a single source or another OLA. When used for broadcast, OLAs form concentric rings around the source, and have been shown to use less transmit energy than conventional multi-hop protocols during broadcasting. The OLA concentric routing algorithm (OLACRA) and its variants, the main contributions of this paper, leverage the concentric ring structure of the OLAs during the initialization phase to limit the node participation on the upstream connection. For the simulation scenarios considered in this paper, OLACRA is shown to save over 80% of the transmit energy relative to other OLA-based schemes. This paper analyzes the performance of OLACRA over ‘deterministic channels’ or non-faded orthogonal channels and on ‘diversity’ or Rayleigh flat-fading channels with limited orthogonality. Enhancements to OLACRA to further improve its energy efficiency by limited broadcasting in the initial upstream level and limiting the downlink ‘step-sizes’ are also considered. A simple contention avoidance scheme for WSNs with multiple flows is also proposed. In addition to this, the robustness of OLACRA over mobile channels is also studied. The protocols are tested using Monte Carlo evaluation.     

Axisymmetric fretting analysis in coated cylinder

Fretting is essentially a contact fatigue phenomenon, although bulk stresses and material properties contribute to final failure. The near surface state of stress developed under oscillatory contact between machine elements plays a major role in deciding the severity of fretting. It is possible to enhance tribological properties by coating the surface. There is rather scanty literature available on fretting analysis of coated components. Presence of such coatings has a large influence on the near surface state of stress. The effect of coatings on the severity of fretting is the focus of this paper. Results obtained for both hard and soft coatings are compared with the results obtained for the homogeneous case. The component geometry and loading are chosen to be cylindrical to enable 3D elastic axisymmetric fretting analysis. The results are compared with 2D models (strip and half-plane) to examine their utility and validity for understanding axisymmetric fretting. Contact pressure and frictional shear loading cases are solved separately and superposed appropriately depending on the coefficient of friction considered. Results for different values of coefficient of friction and elastic mismatch are illustrated through contour plots of stresses and strains. These results are expected to be helpful for identifying fretting failure zones and fracture mechanisms in coated components. Analytical results presented here could serve as useful benchmarks for calibrating numerical codes and experimental techniques.     

Influence of roughness parameters on coefficient of friction under lubricated conditions

Surface texture and thus roughness parameters influence coefficient of friction during sliding. In the present investigation, four kinds of surface textures with varying roughness were attained on the steel plate surfaces. The surface textures of the steel plates were characterized in terms of roughness parameter using optical profilometer. Then the pins made of various materials, such as Al-4Mg alloy, Al-8Mg alloy, Cu, Pb, Al, Mg, Zn and Sn were slid against the prepared steel plates using an inclined pin-on-plate sliding tester under lubricated conditions. It was observed that the surface roughness parameter, namely, R _a , for different textured surfaces was comparable to one another although they were prepared by different machining techniques. It was also observed that for a given kind of surface texture the coefficient of friction did not vary with R _a . However, the coefficient of friction changes considerably with surface textures for similar R _a values for all the materials investigated. Thus, attempts were made to study other surface roughness parameters of the steel plates and correlate them with coefficient of friction. It was observed that among the surface roughness parameters, the mean slope of the profile, Del a(Δ _a ), was found to explain the variations best.     

Friction tensor concept for textured surfaces

Directionality of grinding marks influences the coefficient of friction during sliding. Depending on the sliding direction the coefficient of friction varies between maximum and minimum for textured surfaces. For random surfaces without any texture the friction coefficient becomes independent of the sliding direction. This paper proposes the concept of a friction tensor analogous to the heat conduction tensor in anisotropic media. This implies that there exists two principal friction coefficients μ_1,2 analogous to the principal conductivities k _1,2. For symmetrically textured surfaces the principal directions are orthogonal with atleast one plane of symmetry. However, in the case of polished single crystalline solids in relative sliding motion, crystallographic texture controls the friction tensor.