Liquid target generation techniques in molecular dynamics studies of sputtering

Techniques of generating liquid targets for molecular dynamics studies of sputtering were investigated in systems consisting of 603 Cu atoms. The effects of different boundary conditions on sputtering yield, layer yield ratio, energy distribution, and polar angular distribution of ejected particles were found to be important. A box boundary condition and a semiperiodic boundary condition were considered. The box boundary conditions required the particles to experience pure reflection at the boundaries, while semiperodic boundary conditions demanded position and momentum periodicity in the two dimensions defined by the surface of the target. Sputtering from the target generated with a box boundary condition resulted in a 60% higher total yield, a slightly higher first layer yield ratio, a 60% lower surface binding energy, and a sharper polar angular distribution than from the target generated under a semiperodic boundary condition at the same temperature. Since the results obtained with the semiperiodic boundary conditions are in better agreement with experimental sputtering results, we have concluded that the semiperiodic boundary conditions produces a target that better represents the free surface of real liquid systems.     

On-line gamma-ray data acquisition at the power burst facility

A key component in the monitoring of fission product release tests in the Power Burst Facility (PBF) at the Idaho National Engineering Laboratory is the fission product detection system (FPDS). This system incorporates four high-resolution, germanium gamma-ray spectrometers that operate in real time. These spectrometers, monitoring the effluent produced when a fuel rod test bundle is severely damaged, measure the magnitude and timing of fission product releases. Fission product concentrations are measured at four locations along the PBF sampling system to provide transport data. Two computers, located a kilometer from the two processors that perform the spectrometer function, control and monitor system operation. The FPDS incorporates several unique features designed to respond to the requirements of monitoring a severe fuel damage test or severe accident condition in a nuclear power plant. Included are a high-rate analog electronics package, a variable collimator system, and a unique pulser-based system performance monitor. The system has operated during four PBF severe fuel damage tests, some of which have generated sample line radiation fields of nearly 900 R/h. Using the on-line spectral data accumulated, fission product release rates for a variety of nuclides have been quantified.     

Volatile products from lignite pyrolysis and hydropyrolysis

Samples of three Louisiana lignites were subjected to atmospheric pressure pyrolysis and hydropyrolysis over a temperature range of 400–800 °C. Volatile products were collected in cold traps containing dichloromethane solvent and immersed in a salted ice bath. Volatiles were analysed using coupled gas chromatography/mass spectrometry and approximately 150 separate compounds were noted. Because the product complexity made definite identification of each compound impossible, all components were assigned to one of eleven compound groups and subsequent analysis of results was based upon these groups. The effect of atmosphere, nitrogen versus hydrogen, was found to have a significant impact on volatile composition. Increased concentrations of alkyl benzenes and other single ring compounds were found in the hydrogen product with corresponding reductions in alkanes and alkenes. Only trace concentrations of polyaromatic compounds containing more than two rings were found in either atmosphere. Volatile product composition differences between the three lignites were small. Similarly, the effect of temperature on composition was relatively unimportant.     

Post-dryout heat transfer to Freon in a vertical tube at high subcritical pressures

Studies of the post-dryout heat transfer were made based on experimental data of the heat transfer to Freon 22 flowing upward in a vertical, round tube at nigh subcritical pressures (reduced pressures of 0.68–0.92). A conventional theoretical model failed in part to reproduce the measured wall temperature. A nondimensional parameter Kn was introduced to a model for the post-dryout regime to take account of the thermodynamic nonequilibrium between the vapor and the liquid droplets. A correlation of Kn was developed and a method using this correlation was successful in predicting the wall temperature.     

Convection mixte autour d'un cylindre horizontal. Influence des variations des propriétés physiques avec la température

The effects of variable properties with temperature are considered on a transverse mixed convection problem about an horizontal and isothermal circular cylinder. The problem is supposed laminar and stationary. The Navier-Stokes equations, coupled with the transport energy equation are written in the (Ψ, ω, θ) formulation and solved by a finite difference technique. The results, presented for air and water are compared with those obtained by using the Boussinesq approximation.     

Optical properties of oxidized resinite

Resinite concentrate from a subbituminous coal (R_oil = 0.45%) was oxidized in air for 1 h intervals at fixed temperatures between 50 and 400 °C. The oxidized residues were examined using reflected white and fluorescent light microscopy. Three phases of oxidation were observed. Phase I (50–125°C) was marked by an oxidation rim with lower reflectance than the main mass of resinite, perhaps indicating chemisorption and decomposition of the chemisorbed components. Phase II (150–350°C) was apparent from the development of two oxidation rims, the outer of higher and the inner of lower reflectance than the main mass of resinite, perhaps indicating an ‘oxycoal’ phase. Phase III (〉 350°C) was marked by a sharp increase in reflectance of the outer oxidation rim and a similarity in reflectance between the inner oxidation rim and main mass of resinite, perhaps indicating a ‘combustion phase’. The fluorescence properties (colour, wavelength of maximum intensity and red-green quotient) of the oxidation rims shifted from green towards the red region of the spectrum with increasing oxidation temperature and were a good indicator of the progress of oxidation.     

A subsized fatigue specimen

A subsized fatigue specimen has been designed to overcome the difficulty of machining a full-sized specimen from cast superalloy components. A finite element analysis confirmed that the stress was maximum at the gauge section for any given set of clamping and tensile loads, and that the stresses developed due to clamping forces were negligible compared with those due to tensile or compressive loads. Fatigue data generated using subsized specimens of AISI 4130 steel, 2024-T4 aluminium alloy and 6Al-4V titanium alloy compared well with those available in the literature for full-sized specimens.     

Design and performance of a magnetic spectrometer for the study of πp → ππN reactions near threshold

A measurement of the cross sections of several πp → ππN reaction channels in the region of incident pion momenta of 300 to 460 MeV/c has been performed with Omicron, a multi-arm magnetic spectrometer of large solid angle. This paper describes the apparatus, the trigger, the readout and data-acquisition systems and the off-line analysis. Sample data illustrating the operation of the apparatus are also presented.     

A solar-assisted biogas system: A new approach

In order to increase the production of biogas, particularly in the winter months of northern India, a new design of a collection-cum-storage water heater integrated with the dome of conventional Indian (KVIC) biogas units has been proposed and studied theoretically. During sunshine hours, the biogas system is exposed to solar radiation to increase the slurry temperature, and is covered with movable insulation to avoid night heat losses from the top as well as the sides of the dome. Some interesting conclusions have been drawn.     

A generalized thermal analysis of tubular solar collectors

A generalized thermal analysis of tubular solar collectors such as the CPC, CPC with bare absorber and flat-plate (all having U-tube fluid carriers) is presented. The analysis is applicable for smaller as well as larger size troughs. It has been found that earlier published results of thermal analyses of the CPC collectors are not applicable to all CPC collectors encountered in the literature. The present analysis can, however, be successfully applied to all such collectors.