Morphological instabilities in thin films: Evolution maps

We consider morphological instabilities in binary multilayers and the post-instability evolution of the system. The alloys with and without intermediate phase are considered, as well as the cases with stable and meta-stable intermediate phase.Using the Galerkin finite element formulation for coupled Cahn–Hilliard – elasticity problem, maps of different evolution paths are developed in the parameter space of relative thicknesses of initial phases. We consider the relative importance of elastic and chemical energy of the system and develop maps for different cases.The systems exhibit rich evolution behavior. Depending on the initial configuration (which determines the mass conservation condition), the final equilibrium varies, but even greater variety is observed in evolution paths. The paths may consist of multiple evolution steps, which may proceed at different rates.Except for few special circumstances, the instabilities are to perturbations non-homogeneous in the film plane. Post-instability evolution is essentially two-dimensional, and cannot be reduced to the one-dimensional model.     

An hourly diffuse fraction model with correction for variability and surface albedo

The paper presents an improved version of a previously published model for the diffuse fraction of hourly global irradiance. In addition to hourly solar elevation and clearness index, an hour-to-hour variability index and regional surface albedo are included among the input parameters. Moreover, to prevent excessively high normal incidence beam irradiances at very low solar elevations, the model does not allow a solar elevation dependent maximum beam transmittance to be exceeded. This new model is tuned to 32 years of data from Bergen, Norway. Moreover, a test against independent data from four European stations showed that the model performs better than the models of Erbs et al. (1982), Maxwell (1987) and Perez et al. (1992).     

Prediction of welding buckling distortion in a thin wall aluminum T joint

In this paper, local and global welding buckling distortion of a thin wall aluminum T joint is investigated. A thermo-elastic–viscoplastic model is employed to determine longitudinal residual stresses; analysis of thermal model and elastic–viscoplastic (Anand) model are uncoupled. Molten puddle motion (speed of welding) is modeled by using time dependent birth and death element method. Three dimensional nonlinear-transient heat flow analysis has been used to obtain the temperature distribution, and then by applying thermal results and using three dimensional Anand elastic–viscoplastic model, stress and deformation distributions are obtained during welding and after cooling. Local buckling is investigated by analyzing the history of stress and strain relations. Local buckling is assumed to occur at a point if a small change in the magnitude of stress causes large deformation during of the welding process. By applying residual stresses on a structural model and using eigenvalue methods, global buckling instability of the welded structure is determined.     

Spatially continuous mapping of solar resources in a complex high latitude topography

The annual number of hours with low sun is highest at 60–70° latitude, making the scope for horizon screening effects particularly wide there. The present paper presents a technique for spatially continuous mapping of local screening effects. The method requires a digital topographical map, and radiation data from a site with free horizon. Screening effects are found to introduce local spatial variations in the solar radiation field, amounting to a factor of more than two within a 10 × 10 km area around Bergen (69°24′N, 5°19′E).     

On the estimation of atmospheric radiation from surface meteorological data

A large number of simple formulae for the estimation of total longwave atmospheric irradiance have been compared to both measured data and to output from the spectral model MODTRAN. MODTRAN predictions under cloudless sky agree well with the average of 38 profile-based models, and observed irradiances on the average agree with MODTRAN predictions within some 5 Wm⁻². It was also found that for “normally” stratified cloudfree atmospheres, the formulae of Berdahl and Fromberg (1982) and of Frank and Püntener (1986), both expressing the emittance as a linear function of dew point temperature, adequately reflect the radiation physics over a wide range of temperature and humidity. Besides, the formulae of Swinbank (1963) and of Czeplak and Kasten (1987), which both express the emittance as a quadratic function of dry bulb temperature, turned out to reflect the radiation physics of “normally” stratified not too dry atmospheres. For “abnormally” stratified atmospheres, a correction to empirical formulae was found. For overcast situations, the increase in atmospheric emittance beyond its cloudless value showed up to be a function of the fractional cloud cover, the cloud emittance, and the surface minus cloud base temperature difference, as phrased by Martin and Berdahl (1984). Except for a coarser spectral resolution and a slight underestimation, the simple spectral model of Berger (1988) conforms well with spectral irradiances derived from observed spectral radiances.     

A model for the diffuse fraction of hourly global radiation

Hourly values of diffuse and beam irradiance are often required in cases where, at best, only global irradiance is available. For use in the evaluation of the climatological potential for solar energy utilization in Norway, an analytical model is proposed expressing the hourly diffuse fraction of global irradiance in terms of hourly solar elevation and clearness index. This model, developed for average snow-free close to sea level conditions in Norway, fairly well fits the average picture of an extensive independent data base.     

Effect of the Compositional Strain on the Diffusive Interface Thickness and on the Phase Transformation in a Phase-Field Model for Binary Alloys

A Cahn-Hilliard phase-field—elasticity model was used to study the effect of compositional strain on the diffusive interface thickness and on the solid state phase transformations in binary alloys. Compositional strain was introduced using the Vegard’s law. Mixed order finite element analyses and analytical solutions of an infinite diffusion couple with a flat interface were used to track the phase-field interface morphology. Both analytical and numerical calculations showed a substantial rate-increasing effect of compositional strain on the interface thickness, especially for low energy barrier values. Compositional strain was found to cause substantial patterning of single precipitates during their evolution in a parent matrix and significantly change the equilibrium size of the precipitates. Results show a considerable influence of compositional strain on the coarsening kinetics of coherent precipitates.     

Simulation and Design of Biological Shield for the 115 kJ IR-MPF-100 Plasma Focus Device Using MCNP Code

The paper reports on the design of biological neutron shielding for IR-MPF100 plasma focus device which recently has been designed and constructed in plasma physics and nuclear fusion research institute. Plasma focus devices are known as pulsed intense sources of ionizing radiations such as hard X-ray and fast neutrons as a result of the formation of a hot dense plasma column then acceleration of energetic ions and electrons in the opposite directions. Therefore, taking into account a biological shield particularly for the operators of the PF device as radiation workers is crucial. Analytical calculations on the maximum permissible effective dose for radiation workers (for whole-body exposure) allow below 200 shots/year for IR-MPF100 operating at its nominal 115 kJ capacitor bank energy without any shielding wall. In order to decrease the personnel absorbed radiation dose and increase the maximum allowed shot per year the design considerations for a biological shield has been recognized using MCNP4C code. Our calculations was based on the effect of ordinary concrete, polyethylene mixed with 30 % natural boron and solid boric acid on the decrement of the absorbed dose. These calculations represent that using a double layer shield consists of 30 cm width of pure polyethylene as well as 10 cm lead, ends in appropriate decrement of the effective dose per shot from 0.1 mSv to 1.2 µSv, therefore increases the allowed usage of the device up to 15,600 annual shots.