A new chip-thickness model for performance assessment of silicon carbide grinding

The chip-thickness models, used to assess the performance of grinding processes, play a major role in predicting the surface quality. In the present paper, an attempt has been made to develop a new chip-thickness model for the performance assessment of silicon carbide grinding by incorporating the modulus of elasticities of the grinding wheel and the workpiece in the existing basic chip-thickness model to account for elastic deformation. The new model has been validated by conducting experiments, taking the surface roughness as a parameter of evaluation .     

Chrestenson函数序列的生成方法及其数学分析

本文提出了适于三种序号的Ｃｈｒｅｓｔｅｎｓｏｎ函数序列的复制方法，对其复制过程进行了数学分析，并指出当Ｃｈｒｅｓｔｅｎｓｏｎ函数退化为Ｗａｌｓｈ函数时，此方法即为复制理论中的平移复制方法。     

Noninvasive assessment of regional ventilation in the human lung using oxygen-enhanced magnetic resonance imaging

The imaging of regional ventilation in the lungs is essential for the evaluation of a variety of pathological conditions, such as emphysema, pneumonia and pulmonary embolism. We propose a novel approach for ventilation scanning, using magnetic resonance imaging (MRI) and inhaled molecular oxygen as a contrast agent, that directly depicts transfer of oxygen across the alveolus into the pulmonary vasculature. Molecular oxygen is only weakly paramagnetic but produces substantial signal changes in the lungs because of their large surface area. Ventilation defects were shown in a patient with bullous emphysema, and ventilation-perfusion mismatches were shown in two patients with pulmonary embolism.     

Optimal operation of a multibasin reservoir system

A simulation-optimization procedure is presented for evaluating the extent of interbasin transfer of water in the Peninsular Indian river system consisting of 15 reservoirs on four river basins. A system-dependent simulation model is developed incorporating the concept of reservoir zoning to facilitate releases and transfers. The simulation model generates a larger number of solutions which are then screened by the optimization model. The Box complex nonlinear programming algorithm is used for the optimization. The performance of the system is evaluated through simulation with the optimal reservoir zones with respect to four indices, reliability, resiliency, vulnerability and deficit ratio. The results indicate that by operating the system of 15 reservoirs as a single unit the existing utilization of water may be increased significantly.     

Purification, kinetic characterization and involvement of tryptophan residue at the NADPH binding site of xylose reductase from Neurospora crassa

Xylose reductase (XR) from Neurospora crassa was purified to homogeneity and was found to be specific to NADPH (nicotinamide adenine dinucleotide phosphate). The purified enzyme showed M(r) of 60 and 29 kDa by gel filtration and SDS-PAGE indicating the presence of two subunits. The kinetic mechanism of xylose reductase is 'iso-ordered bi bi'. Inactivation of XR by N-bromosuccinimide (NBS) was found to be biphasic with second-order rate constants of 2.5 x 10(2) and 80 M-1S-1 for the fast (kf) and slow phase (ks), respectively. NADPH protected 90% of XR activity against inhibition by NBS. The fluorescence and circular dichroism (CD) studies revealed that inactivation was not due to gross conformational change in the enzyme. Analysis of the modified Stern-Volmer plot indicated that 49% of the tryptophanyl fluorescence was available for quenching which was completely abolished in the presence of NADPH confirming the involvement of tryptophan at the coenzyme binding site. Experimental evidence presented here serves to implicate the involvement of a tryptophan residue at the low-affinity NADPH binding site and the nature of this site has been assessed by using the hydrophobic probe ANS.     

Precipitation hardening in nickel-copper base alloy monel K 500

The occurrence of a significant amount of age hardening, due to the precipitation of the γ′ phase, has been demonstrated in the nickel-copper base alloy MONEL K 500. The microstructure of the precipitation-hardened and deformed alloy has been examined in peak-aged underaged and overaged conditions. An attempt has been made to compare the observed increments in strength in these three aged conditions to those predicted on the basis of relevant theoretical models.