10,300 research outputs found
Development of a Polysilicon Process Based on Chemical Vapor Deposition of Dichlorosilane in an Advanced Siemen's Reactor
Dichlorosilane (DCS) was used as the feedstock for an advanced decomposition reactor for silicon production. The advanced reactor had a cool bell jar wall temperature, 300 C, when compared to Siemen's reactors previously used for DCS decomposition. Previous reactors had bell jar wall temperatures of approximately 750 C. The cooler wall temperature allows higher DCS flow rates and concentrations. A silicon deposition rate of 2.28 gm/hr-cm was achieved with power consumption of 59 kWh/kg. Interpretation of data suggests that a 2.8 gm/hr-cm deposition rate is possible. Screening of lower cost materials of construction was done as a separate program segment. Stainless Steel (304 and 316), Hastalloy B, Monel 400 and 1010-Carbon Steel were placed individually in an experimental scale reactor. Silicon was deposited from trichlorosilane feedstock. The resultant silicon was analyzed for electrically active and metallic impurities as well as carbon. No material contributed significant amounts of electrically active or metallic impurities, but all contributed carbon
Women's experiences of pregnancy, childbirth, and the postnatal period in the Gambia: A qualitative study
Objective: In sub-Saharan African countries, there are unique cultural factors and adverse physical conditions that contribute to women's experiences of pregnancy and birth. The objective of this study was to qualitatively explore women's experiences of pregnancy, childbirth, the postnatal period, and maternal psychological distress in The Gambia.
Design and methods: Semi-structured interviews were carried out with 55 women who had given birth within the previous year.
Results: Thematic analysis identified five themes: (1) transition to adulthood, (2) physical difficulties, (3) value of children in relation to others, (4) children as a strain, and (5) going through it alone. The results suggest that having a child is a defining point in women's lives associated with happiness and joy. However, women also described situations which could lead to unhappiness and distress in the perinatal period. A child conceived out of wedlock or a baby girl can be sources of distress because of negative cultural perceptions. The strain of having a child, particularly the additional financial burden, and minimal support from men were also a concern for women. Finally, women recognized the danger associated with delivery and expressed recurrent worries of complications during childbirth which could result in the death of them or the baby.
Conclusions: Further research is needed to identify women vulnerable to psychological distress so that health services and target interventions can be developed accordingly
ScotPID - a model of collaboration
ScotPID is a national personal development initiative in Scotland, with thirteen higher education institutions taking part in the development of case studies which enhance personal development planning for students. As a model of collaboration, ScotPID involves all stakeholders: each core project group is composed of an academic, IT support manager, careers service adviser and undergraduate student, with support from QAA Scotland. The case study is developed by the contribution of all of the members of the team. The strength of the ScotPID collaboration is the varied background of the team members. However, collaboration between the ScotPID teams should also be encouraged, to strengthen the inter-institutional approach further
On some singularities of the correlation functions that determine neutrino opacities
Certain perturbation graphs in the calculation of the effects of the medium
on neutrino scattering in supernova matter have a nonintegrable singularity in
a physical region. A number of papers have addressed the apparent pathology
through an ansatz that invokes higher order (rescattering) effects. Taking the
Gamow-Teller terms as an example, we display an expression for the spin-spin
correlation function that determines the cross-sections. It is clear from the
form that there are no pathologies in the order by order perturbation
expansion. Explicit formulae are given for a simple case, leading to an answer
that is very different from one given by other authors.Comment: 8 page
Many-Body Corrections to Charged-Current Neutrino Absorption Rates in Nuclear Matter
Including nucleon--nucleon correlations due to both Fermi statistics and
nuclear forces, we have developed a general formalism for calculating the
charged--current neutrino--nucleon absorption rates in nuclear matter. We find
that at one half nuclear density many--body effects alone suppress the rates by
a factor of two and that the suppression factors increase to 5 at
g cm. The associated increase in the neutrino--matter
mean--free--paths parallels that found for neutral--current interactions and
opens up interesting possibilities in the context of the delayed supernova
mechanism and protoneutron star cooling.Comment: 11 pages, APS REVTeX format, 1 PostScript figure, uuencoded
compressed, and tarred, submitted to Physical Review Letter
Cold Molecule Spectroscopy for Constraining the Evolution of the Fine Structure Constant
We report precise measurements of ground-state, -doublet microwave
transitions in the hydroxyl radical molecule (OH). Utilizing slow, cold
molecules produced by a Stark decelerator we have improved over the precision
of the previous best measurement by twenty-five-fold for the F' = 2 F = 2
transition, yielding (1 667 358 996 4) Hz, and by ten-fold for the F' = 1
F = 1 transition, yielding (1 665 401 803 12) Hz. Comparing these
laboratory frequencies to those from OH megamasers in interstellar space will
allow a sensitivity of 1 ppm for over
years.Comment: This version corrects minor typos in the Zeeman shift discussio
Development of high temperature oxidation resistant coatings for chromium-base alloys Final report
High temperature oxidation resistant coatings for chromium-base alloy
Numerical Toy-Model Calculation of the Nucleon Spin Autocorrelation Function in a Supernova Core
We develop a simple model for the evolution of a nucleon spin in a hot and
dense nuclear medium. A given nucleon is limited to one-dimensional motion in a
distribution of external, spin-dependent scattering potentials. We calculate
the nucleon spin autocorrelation function numerically for a variety of
potential densities and distributions which are meant to bracket realistic
conditions in a supernova core. For all plausible configurations the width of
the spin-density structure function is found to be less than the temperature.
This is in contrast with a naive perturbative calculation based on the one-pion
exchange potential which overestimates the width and thus suggests a large
suppression of the neutrino opacities by nucleon spin fluctuations. Our results
suggest that it may be justified to neglect the collisional broadening of the
spin-density structure function for the purpose of estimating the neutrino
opacities in the deep inner core of a supernova. On the other hand, we find no
indication that processes such as axion or neutrino pair emission, which depend
on nucleon spin fluctuations, are substantially suppressed beyond the
multiple-scattering effect already discussed in the literature. Aside from
these practical conclusions, our model reveals a number of interesting and
unexpected insights. For example, the spin-relaxation rate saturates with
increasing potential strength only if bound states are not allowed to form by
including a repulsive core. There is no saturation with increasing density of
scattering potentials until localized eigenstates of energy begin to form.Comment: 14 latex pages in two-column format, 15 postscript figures included,
uses revtex.sty and epsf.sty. Submitted to Physical Review
A Framework to Manage the Complex Organisation of Collaborating: Its Application to Autonomous Systems
In this paper we present an analysis of the complexities of large group
collaboration and its application to develop detailed requirements for
collaboration schema for Autonomous Systems (AS). These requirements flow from
our development of a framework for collaboration that provides a basis for
designing, supporting and managing complex collaborative systems that can be
applied and tested in various real world settings. We present the concepts of
"collaborative flow" and "working as one" as descriptive expressions of what
good collaborative teamwork can be in such scenarios. The paper considers the
application of the framework within different scenarios and discuses the
utility of the framework in modelling and supporting collaboration in complex
organisational structures
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