Supersolidus liquid-phase sintering of prealloyed powders

A model is derived for the sintering densification of prealloyed particles that form internal liquids when heated over the solidus temperature. The model considers the powder size, composition, and microstructure, as well as the processing conditions of green density, heating rate, maximum temperature, hold time, and atmosphere. Internal liquid forms and spreads to create an interparticle capillary bond that induces densification during sintering. Densification is delayed until the particles achieve a mushy state due to grain boundary wetting by the internal liquid. This loss of rigidity and concomitant densification of the semisolid particles depends on the grain size and liquid quantity. Viscous flow is the assumed densification mechanism, where both viscosity and yield strength vary with the liquid content and particle microstructure. Densification predictions are compared to experimental data, giving agreement with previously reported rapid changes in sintered density over narrow temperature ranges. The model is tested using data from steels and tool steels of varying carbon contents, as well as boron-doped stainless steel, bronze, and two nickel-based alloys.     

Comparison of pediatric hospitalization using the pediatric appropriateness evaluation protocol at three diverse hospitals in Louisiana

The purpose of this study was to compare the number of inappropriate pediatric admissions and hospital days in three hospitals in Louisiana using Pediatric Appropriateness Evaluation Protocol (PAEP) criteria. The hospitals studied included an urban, nontertiary care, teaching hospital with 20 inpatient, pediatric beds (A); a private, tertiary care hospital with 30 beds (B); and a tertiary care, regional referral center with 133 pediatric beds (C). The study prospectively observed all nonintensive care pediatric admissions (> six months of age) between May 1 and June 30, 1993. Admissions and subsequent hospital days were labeled as appropriate or inappropriate based on PAEP criteria. A significantly shorter hospital stay (days) was demonstrated at hospital C (4.41 +/- 1.01, p < .05) compared to A (5.98 +/- 4.95) or B (5.78 +/- 1.21). Similarly, hospital B had significantly more patients admitted electively (19%, p < .05) compared to A (4%) or C (15%). The percentage of inappropriate admissions for hospitals A, B, and C were 11.0, 10.0, and 2.0 (p < .05) and hospital days 18.0, 22.0, and 12.0 (p < .05), respectively. A significant proportion of inappropriate hospital days came from trauma admissions in hospital A (18%, p < .05) and elective admissions in hospital B (36%, p < .05). Hospital A had 99% of patients with either Medicaid or uninsured payor status compared to 35% and 84% at hospital B and C, respectively. Significant differences in the rate of inappropriate admission or subsequent hospital days were demonstrated in the three hospitals studied. Finally, the rates of inappropriate hospitalization demonstrated in this study of Louisiana hospitals were similar to previous studies using the PAEP in other regions.     

Behavior and interactions of children in cooperative groups in lower and middle elementary grades.

The study investigated the behaviors and interactions of children in structured and unstructured groups as they worked together on a 6-week social studies activity each term for 3 school terms. Two hundred and twelve children in Grade 1 and 184 children in Grade 3 participated in the study. Stratified random assignment occurred so that each gender-balanced group consisted of 1 high-, 2 medium-, and 1 low-ability student. The results show that the children in the structured groups were consistently more cooperative and they provided more elaborated and nonelaborated help than did their peers in the unstructured groups. The children in the structured groups in Grade 3 obtained higher reading and learning outcome scores than their peers in the unstructured groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recent progress in ALEGRA development and application to ballistic impacts

ALEGRA is a multi-material, arbitrary-Lagrangian-Eulerian (ALE) code for solid dynamics being developed by the Computational Physics Research and Development Department at Sandia National Laboratories. It combines the features of modern Eulerian shock codes, such as CTH, with modern Lagrangian structural analysis codes. With the ALE algorithm, the mesh can be stationary (Eulerian) with the material flowing through the mesh, the mesh can move with the material (Lagrangian) so there is no flow between elements, or the mesh motion can be entirely independent of the material motion (Arbitrary). All three mesh types can coexist in the same problem, and any mesh may change its type during the calculation. In this paper we summarize several key capabilities that have recently been added to the code or are currently being implemented. As a demonstration of the capabilities of ALEGRA, we have applied it to the experimental data taken by Silsby.     

Ewing's sarcoma masquerading as osteomyelitis

Ewing's sarcoma in the infant and young child is rare, highly malignant, and can be difficult to identify. An erroneous diagnosis of osteomyelitis may be considered first because the presentation may be similar to that of Ewing's sarcoma, and routine laboratory evaluation may not distinguish between these entities. Two such cases are presented, one involving the tibia in a 16-month-old child and another a finger phalanx in a 7-month-old child. In both cases the correct diagnosis of Ewing's sarcoma was delayed because of initial misdiagnosis of osteomyelitis. This diagnostic dilemma is summarized, and the literature reviewed. Special attention is given to recent advances in histochemistry and cytogenetics that assist in tumor identification. The conclusion highlights areas of remaining controversies for which additional study may facilitate distinction between osteomyelitis and Ewing's sarcoma.     

The dynamics of integration and separation: ERP, MEG, and neural network studies of immediate repetition effects.

This article presents data and theory concerning the fundamental question of how the brain achieves a balance between integrating and separating perceptual information over time. This theory was tested in the domain of word reading by examining brain responses to briefly presented words that were either new or immediate repetitions. Critically, the prime that immediately preceded the target was presented either for 150 ms or 2,000 ms, thus examining a situation of perceptual integration versus one of perceptual separation. Electrophysiological responses during the first 200 ms following presentation of the target word were assessed using electroencephalography (EEG) and magnetoencephalography (MEG) recordings. As predicted by a dynamic neural network model with habituation, repeated words produced less of a perceptual response, and this effect diminished with increased prime duration. Using dynamics that best accounted for the behavioral transition from positive to negative priming with increasing prime duration, the model correctly predicted the time course of the event-related potential (ERP) repetition effects under the assumption that letter processing is the source of observed P100 repetition effects and word processing is the source of observed N170 repetition effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)