5,856 research outputs found
Advanced Techiques for Trace Elements Characterisation of Materials
Modern technology uses high purity materials which have to be characterised by measuring impurities at trace levels. For example, properties of semiconductors are influened by dopants present at parts per trillion (ppt). Nuclear Materials must be free from neutron absorbing elements below parts per million (ppm) or parts per billion (ppb). The distance over which signals can be communicated in an
optical fibre depends on its purity. Characterisation of all such materials requires analytical techniques of adequate sensitivity
NLO-QCD Corrections to Dilepton Production in the Randall-Sundrum Model
The dilepton production process at hadron colliders in the Randall-Sundrum
(RS) model is studied at next-to-leading order in QCD. The NLO-QCD corrections
have been computed for the virtual graviton exchange process in the RS model,
in addition to the usual gamma, Z-mediated processes of standard Drell-Yan.
K-factors for the cross-sections at the LHC and Tevatron for differential in
the invariant mass, Q, and the rapidity, Y, of the lepton pair are presented.
We find the K-factors are large over substantial regions of the phase space.Comment: 24 pages, 12 figure
Students get wise about AIDS - The acceptability, feasibility and impact of an AIDS education programme in a suburban school in Cape Town
Objectives. The study assessed the acceptability and feasibility of an AIDS education programme for South African high-school students.Design, setting and sUbjects. A 'before-after' study was conducted in a suburban high school in Cape Town. All 232 standard 8 students were included, and were exposed to the programme over 9 months.Outcome measures. Students' knowledge about AIDS and sexually transmitted diseases (SIDs), attitudes towards people with AIDS and towards AIDS prevention, perceptions of self-efficacy with regard to risk reduction, self-reported behaviour and opinions on the programme were measured using questionnaires. In addition, teachers' opinions of and experiences with the programme were assessed.Results. After the programme, significantly more students knew how to protect themselves from HIV, could identity the symptoms of STOs and understood why people with STOs had a higher risk of becoming infected with HIV. After the programme, significantly more students believed that they knew how to use a condom (77% at baseline, 88.6% at follow-up; P < 0.01). Prior to the programme only 20.8% of the students reported ever having had sexual intercourse. After the programme, significantly more students (32.8%) reported having had sexual intercourse. Most students (80.5%) reported that the programme had helped them to make plans to protect themselves from HIV infection. Teachers found the programme valuable and easy to use.Conclusions. There are severaJ South African school programmes such as 'Get Wise about AIDS' which have been shown to be acceptable and feasible, and which seem to be effective. Randomised controlled trials are now needed to provide conclusive evidence of their effectiveness
Produccion y comercializacion de la larva de Rhynchophorus palmarum (Coleoptera : Dryophtoridae) en la Amazonia peruana
A path unenvisaged to a destination unintended: A collaborative autoethnographic account of becoming a community of practice in an HEI
In this paper we explore how a disparate group of predominately foundation phase teacher educators unintentionally, over a period of time, came together to form a strong community of practice (CoP). Voluntary involvement in a research project positioned this group of lecturers in unaccustomed roles and necessitated that they engage with each other in a variety of ways to meet project outcomes. New relationships developed as people took on different roles and new responsibilities emerged as the group faced challenges. As this was a subjective interrogation of our experiences, a research method such as autoethnography where we could focus on the experience and processes of becoming a CoP, rather than the outcomes of the research itself, seemed appropriate. We outline our understandings of a CoP and show how, through a critical self-reflective process, we were able to strengthen both our teaching and research practices in a Higher Education Institution (HEI). The strengthening occurred, in part, due to the formation and development of this CoP
Liquid sodium- the heat transport medium in fast breeder reactors
Liquid sodium is used as a coolant in fast breeder reactors on account of its excellent heat transfer properties. It must, however, be in the pure form to be compatible with structural materials. Techniques for its purification to nuclear grade and its characterization had to be developed in our laboratory before we could embark on an R & D programme. It is essential to monitor hydrogen at ppb levels in the sodium circuits of the fast reactor in order to detect water leaks in the steam generator in a timely manner. Similarly it is useful to make on-line measurements of oxygen and carbon at trace levels. Electrochemical sensors have been developed in our laboratory for this purpose. These compact sensors work on the principle of concentration cells and are far superior to devices used elsewhere for this purpose. Corrosion of structural materials in the sodium environment depends on the oxygen content of sodium. In order to understand the mechanism of this corrosion, one must have a good grasp of the thermochemistry of the ternary systems, Na-M-O, where M stands for the alloying constitutents of stainless steels. The phase diagrams of most of these systems were established in our laboratory. A specially designed sodium loop is used in the study of corrosion, activity transport and kinetics of sodium-water reaction
DCO, DCN and ND reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296
The formation pathways of deuterated species trace different regions of
protoplanetary disks and may shed light into their physical structure. We aim
to constrain the radial extent of main deuterated species; we are particularly
interested in spatially characterizing the high and low temperature pathways
for enhancing deuteration of these species. We observed the disk surrounding
the Herbig Ae star HD 163296 using ALMA in Band 6 and obtained resolved
spectral imaging data of DCO (=3-2), DCN (=3-2) and ND
(=3-2). We model the radial emission profiles of DCO, DCN and
ND, assuming their emission is optically thin, using a parametric model
of their abundances and radial excitation temperature estimates. DCO can be
described by a three-region model, with constant-abundance rings centered at 70
AU, 150 AU and 260 AU. The DCN radial profile peaks at about ~60 AU and
ND is seen in a ring at ~160 AU. Simple models of both molecules using
constant abundances reproduce the data. Assuming reasonable average excitation
temperatures for the whole disk, their disk-averaged column densities (and
deuterium fractionation ratios) are 1.6-2.6 cm
(0.04-0.07), 2.9-5.2 cm (0.02) and 1.6-2.5 cm (0.34-0.45) for DCO, DCN and ND, respectively.
Our simple best-fit models show a correlation between the radial location of
the first two rings in DCO and the DCN and ND abundance
distributions that can be interpreted as the high and low temperature
deuteration pathways regimes. The origin of the third DCO ring at 260 AU is
unknown but may be due to a local decrease of ultraviolet opacity allowing the
photodesorption of CO or due to thermal desorption of CO as a consequence of
radial drift and settlement of dust grains
- …