Energy and flux measurements of laser-induced silver plasma ions by using Faraday cup

Silver(Ag)plasma has been generated by employing Nd∶YAG laser(532 nm,6 ns)laser irradiation.The energy and flux of ions have been evaluated by using Faraday cup(FC)using time of flight(TOF)measurements.The dual peak signals of fast and slow Ag plasma ions have been identified.Both energy and flux of fast and slow ions tend to increase with increasing irradiance from 7 GW cm-2 to 17.9 GW cm-2 at all distances of FC from the target surface.Similarly a decreasing trend of energies and flux of ions has been observed with increasing distance of FC from the target.The maximum value of flux of the fast component is 21.2×1010cm-2,whereas for slow ions the maximum energy and flux values are 8.8 keV,8.2×1012 cm-2 respectively.For the analysis of plume expansion dynamics,the angular distribution of ion flux measurement has also been performed.The overall analysis of both spatial and angular distributions of Ag ions revealed that the maximum flux of Ag plasma ions has been observed at an optimal angle of～15°.In order to confirm the ion acceleration by ambipolar field,the self-generated electric field(SGEF)measurements have also been performed by electric probe;these SGEF measurements tend to increase by increasing laser irradiance.The maximum value of 232 V m-1 has been obtained at a maximum laser irradiance of 17.9 GW cm-2.     

From conventional nuclear power reactors to accelerator-driven systems

Due to many factors, there is again increase in trend to use the nuclear power for energy production. But spent fuel from nuclear power plants has become one of the crucial problems of nuclear energy exploitation. Some problems attributed to the conventional nuclear power reactors along with their solutions and a historical transition from nuclear power reactors to accelerator-driven systems are briefly reviewed in the present work. It is argued that accelerator-driven systems (ADS), for transmutation of nuclear waste and energy production, are good alternatives to the conventional nuclear power plants. Important differences between the conventional nuclear reactors and the ADS along with the ADS physics are discussed. The ADS is considered to be relatively safe as compared to the other nuclear power reactors commonly in use.     

The charge state distribution of B,C, Si,Ni, Cu and Au ions on 5 MV pelletron accelerator

Stripper gas and terminal potential play a key role for the charge state distribution in a tandem pelletron accelerator. The knowledge of this distribution is important for experiments performed on tandem accelerators. The charge state distribution of B, C, Si, Ni, Cu and Au beams is measured by using Ar as stripper gas, and terminal potential is varied from 0.3 to 3.0 MV on 5UDH-2 tandem pelletron accelerator installed at the National Centre for Physics, Islamabad. The individual charge state is measured after the switching magnet at 15° in high-energy portion. It is observed that the higher charge states are stable in the range of lower and middle atomic masses of periodic table, whereas higher atomic mass(Au) shows beam current instability in higher charge states. For carbon,the charge distribution at 1.7 MV terminal potential by varying stripper gas pressure is also studied, which resulted in decreased overall transmission with good current value for higher charge states.     

Models for fiber stress utilization in air jet yarns

Abstract

The coefficient of fiber stress utilization of air jet viscose staple spun yarns was predicted from the experimental specific stress-strain curves of both fiber and yarns. The coefficient of fiber stress utilization was calculated from Gegauff’s model, single integral model (SIM) and double integral model (DIM). Results showed that the single integral model overestimated the coefficient of fiber stress utilization considering actual stress-strain relationship which was not considered by Gegauff’s model. When fiber orientation effect in the air jet yarn was considered in double integral equation, the predicted coefficient of fiber stress utilization was in good agreement with the experimental coefficient of fiber stress utilization before the process of break. Furthermore, the yarn specific stress was also evaluated from the predicted coefficient of fiber stress utilization from double integral model and experimental fiber specific stress-strain curve for all three air jet viscose yarns. The predicted yarn specific stress-strain curves were in good agreement with experimental yarn specific stress-strain curves for all air jet yarns.     

Evaluating the effect of masonry infills on natural period of buildings with moment‐resisting frame

Building design codes generally provide empirical formulas for estimating the fundamental period. These formulas are developed on the basis of observed periods of real buildings during ground motion, and the period is generally expressed as a function of building height, type (frame or shear wall), etc. In this study, the fundamental period of vibration of a series of regular steel‐framed buildings is studied using finite element modelling and modal eigenvalue analysis including the effect of infill. It has been found that when the models do not include infill, the period given by the analysis is significantly longer than that predicted by the codes equation. However, when the effect of infill is included in the models, the time periods determined from eigenvalue analysis were remarkably close to those predicted by the code formulas. The finding of the study has shown us a practical way to determine the fundamental period of steel frames using rational approaches like modal analysis. After an evaluation of the results, a modified formula has been proposed for estimation of natural period of steel buildings with moment‐resisting frame system having infill. Using the proposed formula, we can estimate natural period of this kind of structural systems more accurately than the one approximated by code formula. Copyright © 2009 John Wiley & Sons, Ltd.     

Nonisothermal analysis of a couple stress fluid in blade coating process

In this paper, a nonisothermal analysis for the process of blade coating of an incompressible couple stress fluid is presented using both plane and exponential coaters. The governing system is simplified using lubrication approximation theory (LAT). The interesting quantities from engineering point of view like normalized pressure, maximum pressure, pressure gradient, velocity, and effects of involved parameters on temperature distribution, which influence the coating process are evaluated. It is observed that pressure is at maximum near the edge of the blade whereas fluid velocity and temperature are at maximum near the substrate. An increasing couple stress parameter increases the load and decreases the coating thickness. It is worth mentioning that load and pressure are the most significant outcomes of the present exertion as these two physical quantities ensure thickness and the quality of coating.