A CFD model for the PECVD of silicon nitride

This work describes the methodology used to develop a computational fluid dynamic (CFD) model for the plasma-enhanced chemical vapor deposition (PECVD) of silicon nitride (SiN_x) for an N ₂SiH₄-NH₃ process. The model has been developed for the Applied Materials Precision 5000 single-wafer reactor, and has the reaction chamber geometry, thermal characteristics, and reactant delivery system incorporated into it. A one-dimensional simulator was used to investigate the initial reaction mechanisms. An experimental design was carried out using physically-based transformations in order to provide model calibration data. The reaction rates were then optimized using the experimental data and the one-dimensional simulator in conjunction with a nonlinear optimizer. A two-dimensional model has been developed using FLUENT, a commercially available computational fluid dynamics program. A simplified plasma modeling technique has been developed which permits the incorporation of electron-initiated reactions generated by the radio-frequency (RF) plasma. This model provides the capability to predict the film composition and deposition rates across the substrate surface. A comparison to the nominal point experimental data has been performed and is reported as well     

Risk factors for lack of detectable antibody following hepatitis B vaccination of Minnesota health care workers

OBJECTIVE: To assess the presence of antibody to hepatitis B surface antigen (anti-HBs) at postvaccination testing in Minnesota health care workers receiving recombinant hepatitis B vaccines, and to identify risk factors for lacking anti-HBs following hepatitis B vaccination. DESIGN: Retrospective cohort study. SETTING: Ten acute care hospitals in Minnesota. PARTICIPANTS: A total of 595 health care workers who had received hepatitis B vaccine (Recombivax HB or Engerix-B) between June 1987 and December 1991 and who underwent postvaccination testing for anti-HBs within 6 months after receiving the third dose of vaccine. MAIN OUTCOME MEASURE: Presence or absence of anti-HBs following hepatitis B vaccination. RESULTS: Five variables were independently associated with lacking anti-HBs by multivariate analysis: vaccine brand, smoking status, gender, age, and body mass index. Stratifying by vaccine brand demonstrated that age (P = .01), body mass index (P < .01), and smoking status (P < .01) were associated with lacking anti-HBs only for Recombivax HB recipients; and gender (P = .03) was associated with lacking anti-HBs only for Engerix-B recipients. After controlling for smoking status, age, gender, and body mass index, recipients of Recombivax HB were more likely to lack anti-HBs than recipients of Engerix-B (relative risk, 2.3; 95% confidence interval, 1.1 to 4.7; P = .02). CONCLUSIONS: Results indicate that certain populations of health care workers are at increased risk of not responding to hepatitis B vaccination. Further studies evaluating immunogenicity of currently available recombinant hepatitis B vaccines in persons at high risk for primary vaccine failure are needed.     

Determination of DNA damage in F344 rats induced by geometric isomers of tamoxifen and analogues

The transformation of Trypanosoma cruzi epimastigotes to mammal-infective metacyclic trypomastigotes (metacyclogenesis) can be performed in vitro under chemically defined conditions (TAU 3AAG medium). During this process, changes in the nature of cell surface sugar composition and sugar distribution was evaluated using FITC and gold-labeled lectins and observed by flow cytometry and transmission electron microscopy. The pattern of labeling with the lectins from Triticum vulgaris (WGA), Arachis hypogaea (PNA), Limax flavus (LFA), Canavalia ensiformis (Con-A), and Ricinus communis (RCA-I) significantly changed during the metacyclogenic process. The results obtained are discussed in relation to the role played by T. cruzi cell surface carbohydrate residues on the process of parasite-host cell interaction.     

Age and sex as factors influencing spontaneous exploration and object investigation by preadult rats (Rattus norvegicus).

Examined developmental and sex differences in the exploratory and investigatory behaviors of Long-Evans rats. Littermate sextuplets were divided into sex-matched groups (at 30, 60, and 90 days of age) and were individually videotaped on 2 consecutive nights in an arena that contained stimulus objects. Multiple measures of locomotor exploration and object investigation increased significantly with age but were not influenced by sex. Older rats entered more quickly, were more active, spent more time in the arena, and spent more time investigating inanimate stimulus objects than did younger rats. Sex did not significantly affect most measures of open-field behavior; however, the data suggest that the sexes may begin to diverge by 90 days. These results suggest that preadult rats of both sexes are equipped early in development with similar strategies and repertoires for exploration and investigation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute renal failure in blacks and Indians in South Africa--comparison after 10 years

Acute renal failure (ARF) has changed in its aetiology in developed Western countries. This study compares our experiences of the aetiology and incidence of ARF a decade after a previously recorded paper in the literature. The data of 226 patients with a diagnosis of ARF during a 3-year period from 1986 to 1988 was analysed. ARF in our study occurred at a younger age. Medical causes of ARF remain the dominant subgroup. There were female patients presenting with ARF associated with self-induced abortions. Toxins of a herbal variety and infections remain the commonest aetiological factors in the medical subgroup. Infections have replaced nephrotoxins as being the principal medical cause. There has been no major change in the incidence or aetiology of ARF over a decade. The prevention of ARF in blacks in sub-Saharan Africa is primarily concerned with the eradication of nephrotoxins and infections and a laxity in the abortion laws of the country. Only by an improvement in education, nutrition, socio-economic status and sanitation can one eradicate or diminish ARF in developing countries.     

Popliteal venous aneurysm: report of two cases and review of the world literature

Two new cases of popliteal venous aneurysm are reported and added to the 22 other cases of popliteal venous aneurysm available for review. Both patients were first seen with acute pulmonary embolism and were treated with thrombolytic therapy followed by anticoagulation. Each had recurrent venous thromboembolism before discovery of the popliteal venous aneurysm. One popliteal venous aneurysm was diagnosed with phlebography and the second with venous duplex imaging, confirmed with phlebography. Both were surgically corrected with tangential aneurysmectomy and lateral venorrhaphy. Twenty-four cases of popliteal venous aneurysm are now available for review. Seventy-one percent (17 of 24) presented with pulmonary embolism, 88% (21 of 24) were saccular, and 96% (23 of 24) were located in the proximal popliteal vein. All but two were diagnosed by ascending phlebography. Three patients received no treatment: in two of these the outcome was not documented and the third had occasional pain. Two patients received anticoagulation without subsequent operative repair and both died of recurrent pulmonary emboli. Operative correction resulted in a 75% patency rate with 21% complications, most of which were related to postoperative anticoagulation. No patient who was operated on had subsequent pulmonary embolism, and there were no operative deaths. We suggest that all patients who have pulmonary embolism have lower-extremity venous duplex imaging. All popliteal venous aneurysms should be surgically repaired, inasmuch as nonoperative therapy results in recurrent thromboembolism and an unacceptably high mortality rate. Tangential aneurysmectomy with lateral venorrhaphy is the recommended procedure.     

Choroidal metastasis from primary mucinous cystadenocarcinoma of the ovary

Central nervous system metastases are uncommon in epithelial carcinoma of the ovary; and metastases to the eye are even more rare. This article describes what is believed to be only the third case reported of epithelial carcinoma of the ovary metastatic to the eye.     

Effects of localized pontine lesions on auditory brain-stem evoked potentials and binaural processing in humans

Potassium channels are involved in the control of neuronal excitability by fixing the membrane potential, shaping the action potential, and setting firing rates. Recently, attention has been focused on identifying the factors influencing excitability in second-order auditory and vestibular neurons. Located in the brainstem, second-order auditory and vestibular neurons are sites for convergence of inputs from first-order auditory or vestibular ganglionic cells with other sensory systems and also motor areas. Typically, second-order auditory neurons exhibit two distinct firing patterns in response to depolarization: tonic, with a repetitive firing of action potentials, and phasic, characterized by only one or a few action potentials. In contrast, all mature vestibular second-order neurons fire tonically on depolarization. Already, certain fundamental roles have emerged for potassium currents in these neurons. In mature auditory and vestibular neurons, I(K), the delayed rectifier, is required for the fast repolarization of action potentials. In tonically firing auditory neurons, I(A), the transient outward rectifier, defines the discharge pattern. I(DS), a delayed rectifier-like current distinguished by its low threshold of activation, is found in phasically firing auditory and some developing vestibular neurons where it limits firing to one or a few spikes, and also may contribute to forming short-duration excitatory postsynaptic potential (EPSPs). Also, I(DS) sets the threshold for action potential generation rather high, which may prevent spontaneous discharge in phasically firing cells. During development, there is a gradual acquisition and loss of some potassium conductances, suggesting developmental regulation. As there are similarities in membrane properties of second-order auditory and vestibular neurons, investigations on firing pattern and its underlying mechanisms in one system should help to uncover fundamental properties of the other.