Machining of Tungsten Heavy Alloy under Cryogenic Environment

AbstractThe machining of tungsten heavy alloy is very difficult as it has high strength and hardness, which requires special cutting tools and cutting process. Though carbide tools are extensively used in conventional cutting, these lead take high machining time and tool failures which cause to decrease in productivity. To overcome the above, special techniques are being practiced in machining of tungsten alloys, one such technique is machining under cryogenic environment. In this paper, liquid nitrogen is used as coolant in machining of tungsten heavy alloys, because it is cost effective, safe, non flammable and environmental friendly gas, in addition to that it cannot contaminate the work piece and no separate mechanism required for disposal. An experimental investigation has been carried out on machining of tungsten heavy alloys by the solid carbide cutting tools under cryogenic and conventional coolants. The material removal rate, surface integrity and cutting forces were studied for both the coolants. The chip morphology also measured for evaluation of shear stress and shear strain. The cryogenic coolant has enhanced the machinability of tungsten heavy alloys. It is observed that the material removal rate was three times higher in cryogenic cooling method when compared with conventional coolant method and the surface finish of the machined surfaces are extremely good and the magnitude of cutting forces are lesser in cryogenic coolant

Theoretical Study of Irradiation Effects in Close Binaries

The effect of irradiation is studied in a close binary systemassuming that the secondary component is a point source, moving in a circularorbit. The irradiation effects are calculatedon the atmosphere of the primary component in a 3-dimensional Cartesiancoordinate geometry. In treating the reflection effect theoretically, the totalradiation $(S_mathrm{T})$ is obtained as the sum of the radiation of 1) the effect ofirradiation on the primary component which is calculated by using onedimensional rod model $(S_mathrm{r})$ and 2) the self radiation of the primarycomponent which is calculated by using the solution of radiative transferequation in spherical symmetry $(S_mathrm{s})$. The radiation field is estimated alongthe line of sight of the observer at infinity. It is shown how the radiationfield changes depending on the position of the secondary component

Linear regression model with generalized new symmetric error distribution

Linear models play a dominant role in analyzing several data sets arising at places like agricultural experiments, space experiments, biological experiments, financial modeling and a wide range other practical problems. One of the major strings in the development of the regression model is the assumption of the error. It is often assumed that the random error of the linear regression model is normally distributed. In numerous situations, however, it is nearly impossible to find a data set that satisfies the normality assumption due to various reasons, such as multivariate skewed and/or heavy-tailed distributions. This problem has been addressed by specifying a different parametric distribution family for the error terms. In this paper, a linear regression model with generalized new symmetric errors is developed and analyzed. The Maximum Likelihood (ML) estimators of the model parameters are derived and their properties with respect to the generalized new symmetric distributed errors are discussed. Simulations were carried out to study the performance of the proposed model with that of Gaussian errors and found that the proposed model perform well when the variables are platykurtic. Some applications of the developed model are also pointed.    Key Words: Generalized new symmetric distribution, Regression model, Simulatio

Formulation and evaluation of ileo-colonic targeted matrix-mini-tablets of Naproxen for chronotherapeutic treatment of rheumatoid arthritis

AbstractIn this present research work, the aim was to develop ileo-colonic targeted matrix-mini-tablets-filled capsule system of Naproxen for chronotherapeutic treatment of Rheumatoid Arthritis. So Matrix-mini-tablets of Naproxen were prepared using microsomal enzyme dependent and pH-sensitive polymers by direct compression method which were further filled into an empty HPMC capsule. The compatibility was assessed using FT-IR and DSC studies for pure drug, polymers and their physical mixtures. The prepared batches were subjected to physicochemical studies, drug content estimation, in-vitro drug release and stability studies. When FTIR and DSC studies were performed, it was found that there was no interaction between Naproxen and polymers used. The physicochemical properties of all the prepared matrix-mini-tablets batches were found to be in limits. The drug content percentage in the optimized formulation F18 was found to be 99.24±0.10%. Our optimized matrix-mini-tablets-filled-capsule formulation F18 releases Naproxen after a lag time of 2.45±0.97h and 27.30±0.86%, 92.59±0.47%, 99.38±0.69% at the end of 5, 8, 12h respectively. This formulation was also found to be stable as per the guidelines of International Conference on Harmonisation of Technical Requirements of Pharmaceuticals for Human Use. Thus, a novel ileo-colonic targeted delivery system of Naproxen was successfully developed by filling matrix-mini-tablets into an empty HPMC capsule shell for targeting early morning peak symptoms of rheumatoid arthritis