Analysis of the characteristics of DC nozzle arcs in air and guidance for the search of SF6 replacement gas

It is shown that the arc model based on laminar flow cannot predict satisfactorily the voltage of an air arc burning in a supersonic nozzle. The Prandtl mixing length model (PML) and a modified k-epsilon turbulence model (MKE) are used to introduce turbulence enhanced momentum and energy transport. Arc voltages predicted by these two turbulence models are in good agreement with experiments at the stagnation pressure (P 0) of 10 bar. The predicted arc voltages by MKE for P 0  =  13 bar and 7 bar are in better agreement with experiments than those predicted by PML. MKE is therefore a preferred turbulence model for an air nozzle arc. There are two peaks in ρC P of air at 4000 K and 7000 K due, respectively, to the dissociation of oxygen and that of nitrogen. These peaks produce corresponding peaks in turbulent thermal conductivity, which results in very broad radial temperature profile and a large arc radius. Thus, turbulence indirectly enhances axial enthalpy transport, which becomes the dominant energy transport process for the overall energy balance of the arc column at high currents. When the current reduces, turbulent thermal conduction gradually becomes dominant. The temperature dependence of ρC P has a decisive influence on the radial temperature profile of a turbulent arc, thus the thermal interruption capability of a gas. Comparison between ρC P for air and SF6 shows that ρC P for SF6 has peaks below 4000 K. This renders a distinctive arc core and a small arc radius for turbulent SF6, thus superior arc quenching capability. It is suggested, for the first time, that ρC P provides guidance for the search of a replacement switching gas for SF6

Burnt Things and Cinderella Perpetua

Two poems

Burnt Things and Cinderella Perpetua

Two poems

Childhood mortality in children emergency centre of the Lagos University Teaching hospital

Background: Infant and childhood mortality has remained high in developing countries like Nigeria with only marginal reductions achieved over the past two decades despite several interventions to reduce morbidity and mortality from the common causes of death in children. It istherefore important to examine the current pattern of mortality inchildren and compare it with previous reports from this centre so as to determine if newer interventions are needed or if these current interventions need to be strengthened for more effective reduction in childhood mortality. Objective: The aim of this study was to examine the pattern of childhood mortality in the children emergency centre of the Lagos University Teaching Hospital (LUTH). Materials and Methods: Admission and discharge records from October 2007 to November 2008 were reviewed retrospectively, the age, sex, diagnosis and duration of hospital stay before death were analyzed. Results: Four hundred and forty six children (446) out of the 4031 children admitted during the studyPeriod died, giving a mortality of 11.1%. More than half of the deaths(55.4%) occurred within 24hours of arrival in hospital. Neonates accounted for 54.7% of deaths. The common causes of death in the neonates were perinatal asphyxia (36.1%) , neonatal jaundice (21.3%), prematurity (16.3%) and septicaemia (11.5%), while in the older children anaemia , septicaemia, severe malaria and acute respiratory illnesses were thecommonest conditions accounting for 22.6%, 16.3%, 12.1% and 9.9%of deaths respectively. Conclusion: Childhood mortality in LUTH is still high with majority of deaths occurring in infancy especially in the neonatal period. Efforts to prevent perinatal asphyxia, the most common causeof death in the neonatal period, should be intensified and educationon the prevention , early identification and management ofconditions such as neonatal jaundice, malaria, anaemia and acute respiratory illnesses should also be strengthened

Evaluation of radiation-induced changes to parotid glands following conventional radiotherapy in patients with nasopharygneal carcinoma

Objectives: Xerostomia is a common post-radiotherapy (post-RT) complication in nasopharyngeal carcinoma (NPC) patients. This study evaluated the relation of post-RT parotid gland changes with the dose received. Methods: Data from 18 NPC patients treated by radiotherapy between 1997 and 2001 were collected. Parotid gland volumes were measured and compared between their pre-RT and post-RT CT images; both sets of CT were conducted with the same scanning protocol. Doppler ultrasound was used to assess the haemodynamic condition of the glands after radiotherapy. Doppler ultrasound results were compared against 18 agematched normal participants. A questionnaire was used to evaluate the patients'comments of xerostomia condition. Radiotherapy treatment plans of the participants were retrieved from the Eclipse treatment planning system from which the radiation doses delivered to the parotid glands were estimated. The correlations of parotid gland doses and the post-RT changes were evaluated. Results: The post-RT parotid glands were significantly smaller (p<0.001) than the pre-RT ones. They also demonstrated lower vascular velocity, resistive and pulsatility indices (p<0.05) than normal participants. The degree of volume shrinkage and subjective severity of xerostomia demonstrated dose dependence, but such dependence was not definite in the haemodynamic changes. Conclusion: It was possible to predict the gland volume change and subjective severity of xerostomia based on the dose to the parotid glands for NPC patients. However, such prediction was not effective for the vascular changes. The damage to the gland was long lasting and had significant effects on the patients' quality of life. © 2011 The British Institute of Radiology.link_to_subscribed_fulltex

Examining the Connections within the Startup Ecosystem: A Case Study of St. Louis

This paper documents the resurgence of entrepreneurial activity in St. Louis by reporting on the collaboration and local learning within the startup community. This activity is happening both between entrepreneurs and between organizations that provide support, such as mentoring and funding, to entrepreneurs. As these connections deepen, the strength of the entrepreneurial ecosystem grows. Another finding from the research is that activity-based events, where entrepreneurs have the chance to use and practice the skills needed to grow their businesses, are most useful. St. Louis provides a multitude of these activities, such as Startup Weekend, 1 Million Cups, Code Until Dawn, StartLouis, and GlobalHack. Some of these are St. Louis specific, but others have nationwide or global operations, providing important implications for other cities

Post-radiotherapy morphological changes of parotid gland are dose- and radiotherapy technique-dependent

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Characterisation of a block to HIV-1 infection in rabbit cells as a model to study HIV-1 trafficking

This thesis focuses mainly on the analysis of the restriction to HIV-1 infection using rabbit cells as a model. Rabbit cells are poorly permissive to HIV-1 infection and the nature of this block is not well understood. This work shows that the restriction is independent of the cell receptor used by the virus for entry, as shown by infection of cells with HIV-1 pseudotyped with different types of envelopes and that it occurs mainly at the level of reverse transcription. It cannot be effectively saturated with high doses of virus or virus-like particles and has a recessive phenotype in human-rabbit heterokaryons. These results point to the existence of a factor required for HIV-1 infection that is absent in SIRC cells but can be complemented by human cells. The reverse transcription complexes extracted from human and rabbit cells have been analysed biochemically and found to have different densities but to be competent for reverse transcription in both cases in an in vitro endogenous assay. Cell fractionation of infected cells showed that HIV-1 is trafficked in a different way in human and rabbit cells and that correct intracellular trafficking is related to efficient reverse transcription and high infectivity in vivo. It is shown as well that viral DNA accumulates in rabbit cell nuclei only at a later stage of infection and fails to associate with chromatin, suggesting a further block prior to integration in SIRC cells Finally, chimeric viruses are used to determine the viral components responsible for the block. Viral chimeras formed by HIV-1 and SIV or MLV are used to infect the human cell line HeLa and SIRC cells. It is found that HIV-1 capsid is the determinant of the block in SIRC cells. Our data point to the existence of cellular factors regulating the early stages of intracytoplasmic and possibly intranuclear HIV-1 trafficking