Thermal expansion of ceramics in the MgO-CaO system

The thermal expansion coefficients of refractory ceramics with different compositions in the MgO-CaO system have been measured, and compared with theoretical values for multiphase composites calculated on the basis of the equations of Turner and of Kerner. Good agreement with the predictions of the Turner equation has been found.     

Preparation and strength of forsterite-zirconia ceramic composites

Forsterite ceramics, toughened with zirconia inclusions, have been prepared by heat treating mixtures of zircon and magnesia. The ceramics have been sintered both with and without applied pressure. The extent of reaction, the fraction of tetragonal zirconia and the density of the product materials have been determined. The strength has been measured in 3 point bend tests. Owing to the fact that the rate of reaction is faster than the rate of pore removal during pressureless sintering, suitable microstructures have not been prepared by this technique. However, hot pressing yields dense, fully reacted, materials with 35% of the zirconia present in the tetragonal form; these materials have strengths (>350 MPa) substantially greater than those of conventional forsterite ceramics     

Minicomputer-based development facility for contract research

With the explosion of interest in microelectronics technology and the lag in matching resourses to meet a new demand there has been a significant increase in the use by industry of contact research organizations for specialist design and development. such organizations have, by the nature of their close involvement with the application of technology, been able to respond to this demand by providing both skilled manpower and sophisticated equipment for their clients. Sira Institute is a typical case in point. Traditionally engaged in measurement and control activities, Sira has equipped itself to apply microelectronics technology in its area of specialization. As a part of its sevices the Institute offers experienced multidisciplinary research, development and engineering teams to solve clients' measurement and control problems. an integral part of this service is now a substantial and well established group of microprocessor experts. This article outlines the history and philosophy behind the development of the equipment resources which support this team, and describes in some detail the facilities which are now in use.     

The professional psychologist as evaluator in a community agency setting.

Describes a process evaluation of an industrial work unit for persons with disabilities and comments on the role of the psychologist as evaluator in an agency of this type. The relationship of process evaluation to other aspects of evaluation is discussed, and reasons are offered for establishing aims before embarking on an outcome evaluation. Suggestions are offered for ways of using ranked aims in every phase of the evaluation, and steps to facilitate the implementation of evaluation results are outlined. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The fracture toughness of Fe-20%Co-15%Cr-5%Mo maraging alloy

The paper describes how the $\text{K}{}_{\mathrm{IC}}$ fracture toughness of a high-purity Fe-20%Co-15%Cr-5%Mo maraging alloy is influenced by other mechanical properties and metallurgical factors. Particular consideration is given to the influence of residual oxygen content and to the strain-hardening characteristics of the material. The Krafft process-zone concept and the Hahm-Rosenfield relationship are validated.Although the heat-treatment parameters have not been optimised, the results show this stainless alloy to be capable of developing a high tensile strength, combined with good fracture toughness and the manner in which certain features of the microstructure influence these properties has been discussed.     

Spreading resistance of multiple-layer cylindrical structures

The potential distributions and spreading resistances of multiple-layer cylindrical structures are analysed. Computed results are compared with the measured thermal impedance of a practical heatsink.     

Association between ozone and asthma emergency department visits in Saint John, New Brunswick, Canada

This study examines the relationship of asthma emergency department (ED) visits to daily concentrations of ozone and other air pollutants in Saint John, New Brunswick, Canada. Data on ED visits with a presenting complaint of asthma (n = 1987) were abstracted for the period 1984-1992 (May-September). Air pollution variables included ozone, sulfur dioxide, nitrogen dioxide, sulfate, and total suspended particulate (TSP); weather variables included temperature, humidex, dewpoint, and relative humidity. Daily ED visit frequencies were filtered to remove day of the week and long wave trends, and filtered values were regressed on air pollution and weather variables for the same day and the 3 previous days. The mean daily 1-hr maximum ozone concentration during the study period was 41.6 ppb. A positive, statistically significant (p < 0.05) association was observed between ozone and asthma ED visits 2 days later, and the strength of the association was greater in nonlinear models. The frequency of asthma ED visits was 33% higher (95% CI, 10-56%) when the daily 1-hr maximum ozone concentration exceeded 75 ppb (the 95th percentile). The ozone effect was not significantly influenced by the addition of weather or other pollutant variables into the model or by the exclusion of repeat ED visits. However, given the limited number of sampling days for sulfate and TSP, a particulate effect could not be ruled out. We detected a significant association between ozone and asthma ED visits, despite the vast majority of sampling days being below current U.S. and Canadian standards.     

Influence of projected complication rates on estimated appropriate use rates for carotid endarterectomy. Appropriateness Project Investigators. Academic Medical Center Consortium

OBJECTIVE: To examine specifically the influence of estimated perioperative mortality and stroke rate on the assessment of appropriateness of carotid endarterectomy. DATA SOURCES/STUDY SETTING: An expert panel convened to rate the appropriateness of a variety of potential indications for carotid endarterectomy based on various rates of perioperative complications. We then applied these ratings to the charts of 1,160 randomly selected patients who had carotid endarterectomy in one of the 12 participating academic medical centers. STUDY DESIGN: An expert panel evaluated indications for carotid endarterectomy using the modified Delphi approach. Charts of patients who received surgery were abstracted, and clinical indications for the procedure as well as perioperative complications were recorded. To examine the impact of surgical risk assessment on the rates of appropriateness, three different definitions of risk strata for combined perioperative death or stroke were used: Definition A, low risk < 3 percent; Definition B, low risk < 5 percent; and Definition C, low risk < 7 percent. PRINCIPAL FINDINGS: Overall hospital-specific mortality ranged from 0 percent to 4.0 percent and major complications, defined as death, stroke, intracranial hemorrhage, or myocardial infarction, varied from 2.0 percent to 11.1 percent. Most patients (72 percent) had surgery for transient ischemic attack or stroke; 24 percent of patients were asymptomatic. Most patients (82 percent) had surgery on the side of a high-grade stenosis (70-99 percent). When the thresholds for operative risk were placed at the values defined by the expert panel (Definition A), only 33.5 percent of 1,160 procedures were classified as "appropriate." When the definition of low risk was shifted upward, the proportion of cases categorized as appropriate increased to 58 percent and 81.5 percent for Definitions B and C, respectively. CONCLUSIONS: Despite the high proportion of procedures performed for symptomatic patients with a high degree of ipsilateral extracranial carotid artery stenosis and generally low rates of surgical complications at the participating institutions, the overall rate of "appropriateness" using a perioperative complication rate of < 3 percent was low. However, the rate of "appropriateness" was extremely sensitive to judgments about a single clinical feature, surgical risk. These data show that before applying such "appropriateness" ratings, it is crucial to perform sensitivity analyses in order to assess the stability of the results. Results that are robust to moderate in variation in surgical risk provide a much sounder basis for policy making than those that are not.     

The effect of investment materials on the surface of cast fluorcanasite glasses and glass–ceramics

Modified fluorcanasite glass–ceramics were produced by controlled two stage heat-treatment of as-cast glasses. Castability was determined using a spiral castability test and the lost-wax method. Specimens were cast into moulds formed from gypsum and phosphate bonded investments to observe their effect on the casting process, surface roughness, surface composition and biocompatibility. Both gypsum and phosphate bonded investments could be successfully used for the lost-wax casting of fluorcanasite glasses. Although the stoichiometric glass composition had the highest castability, all modified compositions showed good relative castability. X-ray diffraction showed similar bulk crystallisation for each glass, irrespective of the investment material. However, differences in surface crystallisation were detected when different investment materials were used. Gypsum bonded investment discs showed slightly improved in vitro biocompatibility than equivalent phosphate bonded investment discs under the conditions used.