Large scale particle simulations in a virtual memory computer

Virtual memory computers are capable of executing large-scale particle simulations even when the memory requirements exceed the computer core size. The required address space is automatically mapped onto slow disc memory by the operating system. When the simulation size is very large, frequent random accesses to slow memory occur during the charge accumulation and particle pushing processes. Accesses to slow memory significantly reduce the execution rate of the simulation. We demonstrate in this paper that with the proper choice of sorting algorithm, a nominal amount of sorting to keep physically adjacent particles near particles with neighboring array indices can reduce random access to slow memory, increase the efficiency of the I/O system, and hence, reduce the required computing time.     

Development of training syllabi for radiation protection and quality assurance of dual-energy X-ray absorptiometry (DXA) systems

The use of dual-energy X-ray absorptiometry (DXA) scanners for measuring bone mineral density (BMD) is on the increase. A single DXA scan is a relatively low-dose diagnostic X-ray examination; however, radiation protection (RP) issues should not be trivialised. One objective of the EU 6th Framework SENTINEL co-ordination action was to develop training syllabi in RP and quality assurance (QA) for BMD, and this study presents the results. An EU-wide survey was carried out which confirmed that there was a need for an accredited DXA RP training course in many EU states. There is also limited published guidance on acceptance testing/QA for DXA. Two training syllabi were developed: one on RP and one on QA of DXA systems. A training course was delivered in Ireland in 2006 by the Medical Physics & Bioengineering Department of St James's Hospital, Dublin. Following the training course, a PC-based training CD was developed and will be made available. A harmonised approach to training will promote consistent approaches to radiation safety across the EU.     

Factor structure of the developmental behavior checklist using confirmatory factor analysis of polytomous items

The Developmental Behavior Checklist (DBC; Einfeld and Tonge, 1995) is a 95 item clinical screening checklist designed to assess the extent of behavioral and emotional disturbance in populations with intellectual deficit (ID). The DBC provides five principal-component derived subscales covering clinically relevant dimensions of psychopathology (i.e., Disruptive, Self-Absorbed, Communication Disturbance, Anxiety, and Social Relating). Validating these subscales for individual differences research requires examinations of the stability of this structure. This study begins a program of psychometric study of the DBC, by utilizing item level data to investigate the DBC's subscale structure in regard to simple-structure restrictions, as well as the implications of factorially complex items for inter-subscale correlations. To accomplish these goals a polytomous confirmatory factor analysis (PCFA) of the DBC was performed, and the pattern of loadings and inter-factor correlations was examined with and without simple-structure restrictions. Our findings provide evidence that the two largest subscales (Disruptive/Antisocial, Self Absorbed) are well behaved in PCFA models and should exhibit little bias under unit-weighted scoring procedures, or in latent factor models. Findings for the three smaller subscales (Communication Disturbance, Social Relating, and Anxiety) do not invalidate their use in individual differences research, but do highlight several issues that should be considered by individual differences researchers.     

Minimizing water utilization in hydrolysis of sodium borohydride: The role of sodium metaborate hydrates

Hydrogen can be obtained from hydrolysis of chemical hydrides, making this an interesting option for hydrogen storage. The gravimetric and volumetric energy densities attainable from hydrolysis of chemical hydrides depend in large measure on the amount of water required for the process. The steam hydrolysis of sodium borohydride produces hydrated metaborate byproducts in which the degree of hydration of the metaborate is closely tied to the amount of water in the reaction. Experimental characterization of these sodium metaborate byproducts indicates that the primary byproduct of steam hydrolysis is _NaBO2·2_H2O${\mathrm{NaBO}}_2·2{\mathrm{H}}_2\mathrm{O}$ under a variety of reaction conditions. A group contribution method is used to estimate the heats and free energies of formation of a variety of hydrated metaborates. This information will be useful in establishing the preferred (stable) hydration state of the byproducts, and in distinguishing these from metastable products.     

The Use of an Objective Index for the Assessment of the Contamination of Surface Water and Groundwater by Acid Mine Drainage

Temporal and spatial comparisons of acid mine-drainage contaminated waters are difficult because of the complex physico-chemical nature of the pollutant, and an objective index has been developed and evaluated for the assessment of such waters. The acid mine-drainage index is calculated using a modified arithmetic weighted index utilizing seven parameters which are most indicative of acid mine-drainage contamination, i.e. pH value, sulphate, iron, zinc, aluminium, copper and cadmium. Weighting is used to express the relative indicator value of each parameter. pH and sulphate are considered to be of greatest indicator value as they are unaffected by sorption processes, while sulphate is also unaffected by natural neutralization processes. The acid mine-drainage index, as proposed, is designed to detect and quantify contamination from acid mine drainage, and to help categorize samples, quantify impact and to monitor the recovery of receiving waters.     

Arc-intersect method for -axis tool paths on a 5-axis machine

An inherent problem with simultaneous 5-axis machining is that it often suffers from dramatic reductions in feed rate when the tool axis is in the vicinity of the singularity point of the machine; during large orientation changes over small distances; during rotary axes reversals and from interpolation of the tool axis vector. $3\frac{1}{2}\frac{1}{2}$-axis machining offers an alternative strategy that can be used to overcome these problems and still maintain some of the salient features of 5-axis machining to improve machining times over 3-axis ballnose machining. In $3\frac{1}{2}\frac{1}{2}$-axis machining, during cutting the machine moves only its three linear axes while the two rotary axes are locked, resulting in a fixed tool orientation. Locking the rotary axes generates fewer fluctuations in the feed rate than simultaneous 5-axis machining and results in a more consistent surface finish with lower variations in cutting force and torque. A new tool positioning strategy called the Arc-Intersect Method (AIM), which can also be applied to simultaneous 5-axis machining, is presented here for $3\frac{1}{2}\frac{1}{2}$-axis machining on simultaneous 5-axis machines using toroidal or flat endmills. A cutting test was performed and the part was measured with a CMM to check for accuracy and to measure the cusp heights. Machining times were compared to 5- and 3-axis tool paths and cutting torque measurements were compared between $3\frac{1}{2}\frac{1}{2}$- and 5-axis machining.     

Inhibition and Promotion of Hydrolysis of Chloride Salts in Model Crude Oil and Heavy Oil

Abstract

The interactions of chloride salts with naphthenic acid and inhibitors during exposure to steam at 100–350°C were investigated in order to understand the release of hydrochloric acid in crude units. Naphthenic acid promoted the release of chlorine from calcium and sodium chlorides by a factor of up to 30 times, forming metal naphthenates in solution. Mitigation of the hydrolysis reactions was achieved with the use of chemical additives in both a model oil and in a Canadian heavy oil.