Multi-scale modelling of silicon nanocrystal synthesis by Low Pressure Chemical Vapor Deposition.

A multi-scale model has been developed in order to represent the nucleation and growth phenomena taking place during silicon nanocrystal (NC) synthesis on SiO2 substrates by Low Pressure Chemical Vapor Deposition from pure silane SiH4. Intrinsic sticking coefficients and H2 desorption kinetic parameters were established by ab initio modelling for the first three stages of silicon chemisorption on SiO2 sites, i.e. silanol Si―OH bonds and siloxane Si―O―Si bridges. This ab initio study has revealed that silane cannot directly chemisorb on SiO2 sites, the first silicon chemisorption proceeds from homogeneously born unsaturated species like silylene SiH2. These kinetic data were implemented into the Computational Fluid Dynamics Fluent code at the industrial reactor scale, by activating its system of surface site control in transient conditions. NC area densities and radii deduced from Fluent calculations were validated by comparison with experimental data. Information about the deposition mechanisms was then obtained. In particular, hydrogen desorption has been identified as the main limiting step of NC nucleation and growth, and the NC growth rate highly increases with run duration due to the autocatalytic nature of deposition

Towards multiscale modeling of Si nanocrystals LPCVD deposition on SiO2: From ab initio calculations to reactor scale simulations

A modeling study is presented involving calculations at continuum and atomistic (DFT, Density Functional Theory) levels so as to better understand mechanisms leading to silicon nanocrystals (NC) nucleation and growth on SiO2 silicon dioxide surface, by Low Pressure Chemical Vapor Deposition (LPCVD) from silane SiH4. Calculations at the industrial reactor scale show that a promising way to improve reproducibility and uniformity of NC deposition at short term could be to increase deposition time by highly diluting silane in a carrier gas. This dilution leads to a decrease of silane deposition rate and to a marked increase of the contribution to deposition of unsaturated species such as silylene SiH2. This result gives importance to our DFT calculations since they reveal that only silylene (and probably other unsaturated species) are involved in the very first steps of nucleation i.e. silicon chemisorption on silanol Si–OH or siloxane Si–O–Si bonds present on SiO2 substrates. Saturated molecules such as silane could only contribute to NC growth, i.e. chemisorption on already deposited silicon bonds, since their decomposition activation barriers on SiO2 surface are as high as 3 eV

Mermaid syndrome: virtually no hope for survival

Abstract.: Sirenomelia, also called the mermaid syndrome is a severe malformation involving multiple organs and characterized by partially or completely developed lower extremities fused by the skin. The birth of a "mermaid” is very rare (1.2-4.2 cases for 100,000 births); most are stillborn, or die at or shortly after birth. The case of a living female neonate with dipodic simelia (fusion of well-developed legs) is presented. No prenatal diagnosis was made and the newborn had an uneventful neonatal course following Cesarean section delivery. The complex and striking malformation was obvious at birth and further evaluation revealed very poorly functioning kidneys, associated with abnormal anorectum, urogenital tract, and external genitalia, as well as a pelvic malformation. Supportive care was applied because of the poor prognosis and the child died at 7weeks of age, due to renal failur

Rabies Postexposure Prophylaxis in Routine Practice in View of the New Centers for Disease Control and Prevention and World Health Organization Recommendations

Under real-life conditions rabies post-exposure prophylaxis is often administered in a suboptimal manner. In this study, 6.7% of previously non-immune patients did not develop adequate antibody levels after 4 doses of rabies vaccin

Occurrence of fever in the first postoperative week does not help to diagnose infection in clean orthopaedic surgery

Postoperative fever is often misinterpreted as a sign of infection, especially when occurring after the third postoperative day. We assessed the epidemiology of postoperative fever in adult orthopaedic patients and its association with infection. Among 1,073 patients participating in a prospective observational study, 198 (19%) had a postoperative fever (>38°C). Thirteen patients (1.2%) had a surgical site infection and 78 patients (7.3%) had remote bacterial infections during their hospital stay. Including asymptomatic bacteriuria, 174 patients were given antibiotic therapy for a median duration of six days. In multivariate analysis, no clinical parameter was associated with fever, including haematoma (odds ratio 0.9, 95%CI 0.6-1.3), infection (1.6, 0.7-3.7), or antibiotic use (1.6, 0.9-3.0). The maximum temperature on each of the first seven postoperative days did not differ between infected and uninfected patients (Wilcoxon rank-sum tests; p > 0.10). We conclude that fever, even up to the seventh postoperative day, is not substantially helpful to distinguish infection from general inflammation in clean orthopaedic surger

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Theme: Postqualitative Research (Voicing Places): Basic Skills and Good Practic

Mantle sources and magma evolution beneath the Cameroon Volcanic Line: Geochemistry of mafic rocks from the Bamenda Mountains (NW Cameroon)

International audienceWe report the mineralogy, geochemistry and geochronology of the mafic rocks from the Bamenda Mountains, part of the Cameroon Volcanic Line (CVL), in order to discuss the origin and evolution of the magmas in this part of the CVL. Mafic rocks in the Bamenda Mountains are basanites, basalts, hawaiites and mugearites with an alkaline affinity. K-Ar ages have been obtained on 10 samples and range from 17.6 Myr to present. Trace element and isotopic compositions (Sr-Nd-Pb) show that some samples among the oldest are slightly contaminated by a crustal component with high La/Nb and 87Sr/86Sr ratios and low Pb isotopic ratios. The mafic rocks strongly resemble OIB in their trace element compositions. Some samples possess a positive Sr and Eu anomaly which cannot be explained by a process of plagioclase accumulation. These anomalies are also observed in some pyroxenites found as xenoliths in the Adamawa volcanic province further north. Furthermore, non-contaminated samples have high Pb isotopic ratios and point towards an HIMU component similar to the St. Helena mantle plume. We propose that the Bamenda mafic magmas with positive Sr and Eu anomalies were formed by hybridization of asthenospheric melts with melts formed by the partial melting of pyroxenites. Samples without these anomalies result from the hybridization of the same asthenopheric melts with melts coming from the metasomatized, amphibole-bearing, lithospheric mantle

Quality of life on chronic dialysis: comparison between haemodialysis and peritoneal dialysis

Background. Quality of life (QOL) assessment in patients on chronic haemodialysis (HD) or peritoneal dialysis (PD) has only rarely been carried out with the generic Euroqol-5D® questionnaire. Methods. All chronic HD and PD patients in the 19 centres of western Switzerland were requested to fill in the validated Euroqol-5D® generic QOL questionnaire, assessing health status in five dimensions and on a visual analogue scale, allowing computation of a predicted QOL value, to be compared with the value measured on the visual analogue scale. Results. Of the 558 questionnaires distributed to chronic HD patients, 455 were returned (response rate 82%). Fifty of 64 PD patients (78%) returned the questionnaire. The two groups were similar in age, gender and duration of dialysis treatment. Mean QOL was rated at 60±18% for HD and 61±19% for PD, for a mean predicted QOL value of 62±30 and 58±32% respectively. Results of the five dimensions were similar in both groups, except for a greater restriction in usual activities for PD patients (P = 0.007). The highest scores were recorded for self-care, with 71% HD and 74% PD patients reporting no limitation, and the lowest scores for usual activities, with 14% HD and 23% PD patients reporting severe limitation. Experiencing pain/discomfort (for HD and PD) or anxiety/depression (for PD) had the highest impact on QOL. Conclusions. QOL was equally diminished in HD and PD patients. The questionnaire was well accepted and performed well. Improvement could be achievable in both groups if pain/discomfort and anxiety/depression could be more effectively treate