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Notes: The resulting temperature distribution of a silicon wafer held by an electrostatic chuck (ESC) in an electron-cyclotron-resonance chemical vapor deposition (ECR-CVD) reactor is characterized and modeled. The effects of the clamping voltage VESC, pressure between the ESC and wafer PHe, and the surface finish and pattern on the ESC are investigated. Heat transfer coefficients between the wafer and various ESCs are determined experimentally. A model is developed to predict the temperature distribution at the surface of the wafer, and used to explain the experimentally observed temperature variations both within wafer and between different chucks. The model is then used to aid in the design of an ESC which provides improved temperature uniformity at the wafer surface. The results of this study indicate: (a) the thermal resistances across the interface between the wafer and ESC control both the absolute wafer temperature and the wafer temperature uniformity; (b) the surface roughness of the ESC and the size of the "contact'' regions are major design factors controlling the absolute temperature of the wafer—the temperature can be adjusted by varying the value of VESC and fine tuned by adjusting the value of PHe; (c) the nonuniform temperature distribution across the wafer surface is dictated by the surface pattern on the ESC, the variation in surface roughness, and the size of the ESC relative to the wafer; (d) wafer temperature variations from chuck to chuck are reduced by controlling the surface finish of the ESC and by ensuring that PHe is a dominant heat transfer mechanism; and (e) maximum uniformity in the temperature of the wafer is obtained when the radius of the ESC is matched as closely as possible to that of the wafer. We have shown that numerical heat transfer models can be used to optimize the geometry of the ESC to provide a uniform distribution of temperature across the surface of the wafer. © 1995 American Institute of Physics.

Notes: Purpose This study determined the fracture toughness of four core buildup materials.Materials and Methods Single-edge notch, bar-shaped specimens conforming to the American Society for Testing Materials standard E-399 were fabricated for a high copper amalgam alloy, two composite resins, and a glass ionomer buildup material. The specimens were stored in air for 1 week and then tested in three-point bending mode with an Instron Universal Testing Machine (Instron Corporation, Canton, MA).Results Fracture toughness values obtained were as follows: Fluorocore (composite resin; Caulk, Milford, DE), 1.54 MN · m−1.5; Ti-Core (composite resin and titanium; Essential Dental Systems, New York, NY), 1.34 MN · m−1.5; Valiant Ph.D. (amalgam; Caulk), 1.29 MN · m−1.5; and Coreshade Glass lonomer Base Cement (Shofu Inc, Kyota, Japan), 0.55 MN · m−1.5.Conclusions Glass ionomer materials are probably unsuitable as core buildup materials because of their relatively low fracture toughness. Fluorocore, Ti-Core, and amalgam all had fracture toughness values significantly greater than the glass ionomer (P 〈 .01).

Notes: Abstract Establishing cooperative relationships between schools of nursing and local education agencies for the delivery of health care services to children from pre-school through the twelfth grade is a process all too often characterized by numerous legal, insurance, and administrative roadblocks. While nursing faculty and their students may wish to cooperate with professional educators and their students to enhance the health care of the children, there are obstacles. Both institutions are represented by attorneys, insurance companies and others who must attend to aspects of the process other than direct health care delivery. A model for joint planning and a list of elements of effective agreements are offered as a way of engaging all parties in a constructive and useful process of collaboration.

Notes: Objective To determine the risk of maternal mortality in immigrants to England and Wales. Design Analysis of death registrations, 1970–1985, by country of birth. Setting England and Wales.Population Women dying in England and Wales during regnancy, childbirth or the puerperium, or dying fiom malignant tumour of the placenta.Main outcome measures The risk of dying in pregnancy, childbirth or the puerperium, adjusted for age and year of death, and the risk of cause-specific death, adjusted for age, in immigrants compared with women born in England and Wales.Results Women born in West Africa (relative risk 10.3; 95% CI 8.0–13.2) and the Caribbean (4.6; 3.8–5.7) were at very elevated risk of maternal death and of the main causes of death. Women from Southern Asia (1.6; 1.3–2.0) and ‘Europe and the USSR’ (1.7; 1.2–2.3) were at moderate risk. Adjustment for year of death increased the estimates of risk and women born in the ‘Rest of the World’ and Scotland were at significantly elevated risk.Conclusions An increased incidence of obstetric conditions in immigrant groups may account for the elevated risk but it is also possible that differences in care may account for some of the additional risk. The pattern of increased risk does not appear to be explicable by the parity or social class distribution of immigrants as far as data are available on these. Research is required into the aetiology of the differential incidence of obstetric disease. The collection of routine mortality data which include maternal reproductive and social factors would elucidate the significance of such factors to maternal health. Further investigation into possible differences in the process of antenatal care between immigrants and non-immigrants is required, and into whether this affects the risk of maternal mortality.

Notes: Objective By combining serial measurements of the circulating concentrations of thromboxane A, and prostacyclin with measurements of venous distensibility (taken during the pregnancies of both normal women and those with pregnancy induced hypertension or pre-eclampsia), to test the following hypotheses: 1. that changes in the venous plasma ratio of thromboxane (TXB2) and 6-keto-PGF1α would correlate with changes in the blood pressure of women developing and recovering from pregnancy induced hypertension or pre-eclampsia and 2. that changes in venous distensibility would correlate with changes in arterial blood pressure in pregnancy induced hypertension or pre-eclampsia.Design Prospective, longitudinal cohort study.Setting John Hunter Hospital clinic, Newcastle, Australia.Subjects One hundred and sixty primiparous women, recruited when presenting for their first routine antenatal visit, were investigated at, or close to, 19, 28 and 37 weeks of gestation; a subgroup was also studied in the postnatal period. The measurements of the patients who developed pregnancy induced hypertension or pre-eclampsia were compared with those of controls selected from the cohort.Main outcome measures Serial measurements of the circulating concentrations of the stable metabolites of thromboxane A2 and prostacyclin (TXB2 and 6-keto-PGFlα, respectively), venous distensibility and immediate (no rest) and resting (for at least 30 min) blood pressures.Results There was no significant difference between the subject and control groups at any time during or after the pregnancy in the concentrations of prostaglandin metabolites, their ratio or venous distensibility. In contrast, there was a significant difference between the groups at 19 weeks for immediate and resting readings of diastolic pressure (6 mmHg (95 % CI 1.5 to 10.5) and 4 mmHg (95% CI 0.1 to 7.9), respectively). These differences increased through the pregnancy but mean postnatal readings for the groups were almost identical suggesting that the subjects were not intrinsically hypertensive compared with controls. Blood pressures for the subject group, both immediate and resting, were significantly different from the 19 week readings at 28 weeks (diastolic) and at 37 weeks (systolic and diastolic). The only significant change from first readings among controls was in postnatal systolic pressure which was significantly higher than 19 week values, probably reflecting the vasodilatation, with accompanying hypotension, of early, normal pregnancy. This difference was not observed in those who subsequently developed pregnancy induced hypertension or pre-eclampsia.Conclusions Our study was unable to demonstrate differences in circulating metabolites or venous distensibility between normotensive women and those with pregnancy induced hypertension or pre-eclampsia. If pregnancy induced hypertension or pre-eclampsia in humans represents not so much the presence of abnormal constrictor influences as a process initiated by failure of normal vasodilatation in early pregnancy, studies carried out later may detect mainly adaptive and secondary changes.