A framework for large-scale relativistic simulations in the characteristic approach

We present a new computational framework (LEO), that enables us to carry out the very first large-scale, high-resolution computations in the context of the characteristic approach in numerical relativity. At the analytic level, our approach is based on a new implementation of the ``eth'' formalism, using a non-standard representation of the spin-raising and lowering angular operators in terms of non-conformal coordinates on the sphere; we couple this formalism to a partially first-order reduction (in the angular variables) of the Einstein equations. The numerical implementation of our approach supplies the basic building blocks for a highly parallel, easily extensible numerical code. We demonstrate the adaptability and excellent scaling of our numerical code by solving, within our numerical framework, for a scalar field minimally coupled to gravity (the Einstein-Klein-Gordon problem) in 3-dimensions. The nonlinear code is globally second-order convergent, and has been extensively tested using as reference a calibrated code with the same boundary-initial data and radial marching algorithm. In this context, we show how accurately we can follow quasi-normal mode ringing. In the linear regime, we show energy conservation for a number of initial data sets with varying angular structure. A striking result that arises in this context is the saturation of the flow of energy through the Schwarzschild radius. As a final calibration check we perform a large simulation with resolution never achieved before.Comment: RevTeX4, 22 pages, 21 figures, to appear in Phys. Rev.

Variation in Periodontal Diagnosis and Treatment Planning Among Clinical Instructors

Consistency in clinical decision making may be necessary for reliable assessment of student performance and teaching effectiveness, yet little has been done to examine variation in periodontal diagnosis and treatment planning among dental school faculty. The purpose of this investigation was to examine variation among faculty in diagnosis and management of common periodontal diseases. Twenty-seven clinical instructors (periodontists, general dentists, dental hygienists, and first- and second-year periodontal graduate students) reviewed three web-based cases and answered a brief questionnaire focusing on radiographic interpretation, periodontal diagnosis, and treatment planning. Response rates for the three cases ranged from 62 percent to 70 percent. Clinical instructors’ rating of percent bone loss in the majority of cases varied between three descriptive categories for the same tooth. Greater consistency in periodontal diagnosis was noted within the graduate student group as compared to periodontal and dental hygiene faculty groups. Diagnoses offered for one of the three patients varied between gingivitis and chronic and aggressive periodontitis. Six to nineteen different treatment plans (many with subtle differences) were submitted for each of the three cases. Inter-rater variation was qualitatively more prevalent than intra-rater variation. To our knowledge, this is the first study to document substantial variation among instructors in radiographic interpretation, diagnosis, and treatment planning for common periodontal diseases. Qualitative judgments speculating on the impact of variability among dental school faculty on student performance and patient care can be made but as yet remain unknown. Consistent use of accepted practice guidelines and greater consensus-building opportunities may decrease variation among faculty and enhance dental education

Potential Health Impacts From Range Fires at Aberdeen Proving Ground, Maryland.

This study uses atmospheric dispersion computer models to evaluate the potential for human health impacts from exposure to contaminants that could be dispersed by fires on the testing ranges at Aberdeen Proving Ground, Maryland. It was designed as a screening study and does not estimate actual human health risks. Considered are five contaminants possibly present in the soil and vegetation from past human activities at APG--lead, arsenic, trichloroethylene (TCE), depleted uranium (DU), and dichlorodiphenyltrichloroethane (DDT); and two chemical warfare agents that could be released from unexploded ordnance rounds heated in a range fire--mustard and phosgene. For comparison, dispersion of two naturally occurring compounds that could be released by burning of uncontaminated vegetation--vinyl acetate and 2-furaldehyde--is also examined. Data from previous studies on soil contamination at APG are used in conjunction with conservative estimates about plant uptake of contaminants, atmospheric conditions, and size and frequency of range fires at APG to estimate dispersion and possible human exposure. The results are compared with US Environmental Protection Agency action levels. The comparisons indicate that for all of the anthropogenic contaminants except arsenic and mustard, exposure levels would be at least an order of magnitude lower than the corresponding action levels. Because of the compoundingly conservative nature of the assumptions made, they conclude that the potential for significant human health risks from range fires is low. The authors recommend that future efforts be directed at fire management and control, rather than at conducting additional studies to more accurately estimate actual human health risk from range fires

Influences of H on the Adsorption of a Single Ag Atom on Si(111)-7 × 7 Surface

The adsorption of a single Ag atom on both clear Si(111)-7 × 7 and 19 hydrogen terminated Si(111)-7 × 7 (hereafter referred as 19H-Si(111)-7 × 7) surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties). Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111)-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface

Xylella fastidiosa gene expression analysis by DNA microarrays

Xylella fastidiosa genome sequencing has generated valuable data by identifying genes acting either on metabolic pathways or in associated pathogenicity and virulence. Based on available information on these genes, new strategies for studying their expression patterns, such as microarray technology, were employed. A total of 2,600 primer pairs were synthesized and then used to generate fragments using the PCR technique. The arrays were hybridized against cDNAs labeled during reverse transcription reactions and which were obtained from bacteria grown under two different conditions (liquid XDM2 and liquid BCYE). All data were statistically analyzed to verify which genes were differentially expressed. In addition to exploring conditions for X. fastidiosa genome-wide transcriptome analysis, the present work observed the differential expression of several classes of genes (energy, protein, amino acid and nucleotide metabolism, transport, degradation of substances, toxins and hypothetical proteins, among others). The understanding of expressed genes in these two different media will be useful in comprehending the metabolic characteristics of X. fastidiosa, and in evaluating how important certain genes are for the functioning and survival of these bacteria in plants