1,505 research outputs found
Application of Bragg superlattice filters in low temperature microrefrigerators
We propose to use the Bragg interference filter technology for fabrication of
microrefrigerators. The idea of using superconductor-insulator-superconductor
(SIS) or normal metal-insulator-superconductor (SIN) tunnel junctions as
cooling elements in micro-refrigerators is attractive because of the absence of
(micro-) refrigerators operating below 150 K. The microscopic approach to
cooling is based on the "phonon deficit effect" in nonequilibrium regime of
tunnel junctions. This effect can be improved by use of phonon filters placed
between the tunnel junction and the heath-bath. Such a filter can be the Bragg
interference superlattice (Bragg's grating) which is well studied for problems
of optical communications. Bragg interference filters are used also for
detection of phonons emitted by tunnel junctions. To enhance the refrigeration
process one needs filters with very broad spectral transmission properties or a
large transmission band with one or two narrow stop bands. The type of the
needed filter will depend on the types of the used tunnel junction.
Corresponding discussion is presented.Comment: 9 pages, International Conference of Applied Photonic Technologies
(ICAPT), Quebec, 200
The application of passive sampler (DGT) technology for improved understanding of metal behaviour at a marine disposal site
Metal behaviour and availability at a contaminated dredge material disposal site within UK waters has been investigated using Diffusive Gradient in Thin films (DGT) passive sampling technology. Three stations representing contrasting history and presence of maintenance dredge disposal, including a control station outside the disposal site, have been studied and depth profiles of fluxes of different metals (Fe, Mn, Pb, Cu, Cd, Cr, Ni, Zn) to the binding gel (Chelex 100) have been derived. Higher flux rates and shallower mobilisation of metals (Mn and Fe) to the binding gel were observed at the disposal stations compared to the control station. Here we describe metal mobilization at different depths, linking the remobilization of Fe2+ and Mn2+ to the sediment (re)supply of other heavy metals of interest with a focus on Cd, Ni and Pb and as they are on the Water Framework Directive (WFD) list of priority substances and OSPAR list of priority pollutants. Results showed that Cd, Pb and Ni exhibited signs of resupply at the sediment-water interface (SWI). There was a potential increased mobilisation and source to the water column of Pb and Ni at the disposal site stations, but there was no Cd source, despite higher total loadings. This information has the potential to improve our current understanding of metal cycles at disposal sites. This work can be used as an indication of likely metal bioavailability and also assist in determining whether the sites act as sources or sinks of heavy metals. This information could assist disposal site monitoring and dredge material licensing
The agrin gene codes for a family of basal lamina proteins that differ in function and distribution
We isolated two cDNAs that encode isoforms of agrin, the basal lamina protein that mediates the motor neuron-induced aggregation of acetylcholine receptors on muscle fibers at the neuromuscular junction. Both proteins are the result of alternative splicing of the product of the agrin gene, but, unlike agrin, they are inactive in standard acetylcholine receptor aggregation assays. They lack one (agrin-related protein 1) or two (agrin-related protein 2) regions in agrin that are required for its activity. Expression studies provide evidence that both proteins are present in the nervous system and muscle and that, in muscle, myofibers and Schwann cells synthesize the agrin-related proteins while the axon terminals of motor neurons are the sole source of agrin
Air-cooled heat exchangers and cooling towers : thermal-flow performance evaluation and design
Thesis (PhD)--Stellenbosch University, 2004.ENGLISH ABSTRACT: During the last 30 years I have been involved in the theory and practice of thermal engineering and
in particular, in the areas of air-cooled heat exchangers and cooling towers for the power,
refrigeration, process and petrochemical industries in South Africa and internationally. During this
period, I have authored and co-authored more than 120 papers that were published in technical
journals or presented at conferences nationally or internationally. Most of these papers are included
in a manuscript entitled "Air-cooled Heat Exchangers and Cooling Towers", in which Ipresent a
systematic approach to the thermal performance evaluation and design of industrial air-cooled heat
exchangers and cooling towers. This original publication also includes the relevant practice
applicable to the design of cooling systems, based on my experience as a consultant to industry.
Design offices throughout the world presently follow our design methods, or at least employ many
of our research results. Our work has furthermore contributed to the development of improved
cooling system designs (e.g. new dephlegmator header designs), components (e.g. single-row
flattened finned tubes) and product improvement and quality control (e.g. performance testing and
measurement of thermal contact resistance between fin and tube during production). Many of our
research findings have found application in the modification of existing cooling systems. The
manuscript has also been used as reference work during the presentation of short courses to
practising engineers and consultants in industry and to engineering graduates at the University of
Stellenbosch.
A two-volume edition of this manuscript was published by PennWell Corp., Tulsa, Oklahoma, USA
in 2004.AFRIKAANSE OPSOMMING: Gedurende die laaste 30 jaar was ek betrokke by die teorie en praktyk van lugverkoelde warmteoordraers
en koeltorings vir die kragopwekkings-, verkoelings-, proses- en petro-chemiesenywerhede
in Suid-Afrika sowel as in die buiteland. Gedurende hierdie periode was ek outeur en
mede-outeur van meer as 120 publikasies wat in tegniese tydskrifte, of by plaaslike of oorsese
konferensies aangebied is. Die meeste van hierdie publikasies vorm deel van 'n manuskrip getiteld
"Air-cooled Heat Exchangers and Cooling Towers" waarin ek 'n sistematiese benadering tot die
bepaling van die termiese vermoë en ontwerp van industriële lugverkoelde warmteoordraers en
koeltorings aanbied. Hierdie oorspronklike publikasie bevat ook die relevante praktyk wat van
toepassing is op verkoelingsaanlegte. Ontwerpkantore wêreldwyd volg tans hierdie
ontwerpsmetodes, of gebruik ten minste baie van ons navorsingsresultate. Ons werk het verder
bygedra tot die ontwikkeling van verbeterde verkoelingsaanlegte (bv. nuwe deflegmatore),
komponente (bv. enkelbuisry platvinbuise ) en verbeterde produkte en kwaliteitskontrole
(bv. toetsing van verkoelingsvermoë oftermiese kontakweerstand tussen vin en buis gedurende
produksie). Baie van ons bevindinge het toepassing gevind in die modifikasie van
verkoelingsaanlegte. Die manuskrip is ook as verwysing gebruik gedurende die aanbieding van
kort kursusse aan ingenieurs in die praktyk en aan nagraadse studente aan die Universiteit van
Stellenbosch.
'n Twee-volume uitgawe van die manuskrip is deur PennWell Corp., Tulsa, Oklahome, VSA in
2004 gepubliseer
The effectiveness of axial flow fans in a-frame plenums
Thesis (PhD (Mechanical and Mechatronic Engineering)--University of Stellenbosch, 1990.ENGLISH ABSTRACT: The ultimate goal of this project is to ensure a better understanding of the governing
mechanisms present when flow distorting components are installed in close proximity of
an axial flow fan.
The effect of different parameters on the operation of axial flow fans is investigated. These
parameters are divided into flow enhancing and flow reduction effects. The performance
of an axial flow fan can be enhanced by changing the tip clearance, by adding a solid
disc to the hub of the fan or by varying the number of fan blades. Flow reductions are
caused by components such as inlet grids, walkways and their supporting structures, heat
exchangers and windwalls.
The effects of flow enhancing components are measured and compared to the results of
other authors. The sensitivity of these effects to parameters such as the type of fan rotor
and the specific system in which the rotor is installed is highlighted.
The system effect (the interaction between the fan rotor and flow resistances in close
proximity of each other) of individual components, as well as the combination of different
components, is predicted both theoretically and experimentally. These predictions are
compared to measured data relevant to the components in an installation where the system
effects are present. The results are correlated to the kinetic energy flux coefficient of the
flow at different locations within the installation.
Experimental data obtained from a full scale unit (inlet shroud diameter of 9,216 m) are
used to compare to scaled data from the model (inlet shroud diameter of 1,542 m). The
hub to tip ratio of the axial flow fans investigated is 0,15.
The most important conclusions are that the performance of the type of axial flow fan
under investigation can be improved by reducing its tip clearance and by installing a solid
disc to the downstream side of the rotor. An increase in the number of blades of the fan
leads to only marginal improvements in the fan performance. The overall performance of
the system can also be improved by removing some of the flow resisting components, or
by changing their relative positions. All these conclusions are based on the assumption
that the power input to the fan rotor remains constant.AFRIKAANSE OPSOMMING: Die uiteindelike doel van hierdie projek is om te verseker dat die beherende meganismes wat
teenwoordig is wanneer vloeiversteurende komponente in die nabyheid van 'n aksiaalwaaier
geinstalleer word, beter verstaan word.
Die effek van verskillende parameters op die werkverrigting van aksiaalwaaiers word ondersoek.
Hierdie parameters word verdeel in vloeiverbeterings- en vloeiverminderingseffekte.
Die werkverrigting van 'n aksiaalwaaier kan verbeter word deur die lempuntspeling te verstel,
deur 'n soliede skyf aan die naaf van die waaierrotor te installeer, of deur die aantal
lemme te verander. Die vloeiverminderings word veroorsaak deur inlaatsiwwe, loopvlakke
en hul ondersteuningsstrukture, warmteruilers en windwande.
Die effekte van vloeiverbeteringskomponente word gemeet en vergelyk met die resultate
van ander outeurs. Die sensitiwiteit van hierdie effekte op parameters soos die tipe rotor
en die spesifieke stelsel waarin die rotor geinstalleer is, word uitgelig.
Die stelseleffek (die interaksie tussen die rotor van die waaier en vloei weerstande wat
naby mekaar geinstalleer is) van individuele, sowel as 'n kombinasie van verskillende
komponente, word teoreties en eksperimenteel voorspel. Hierdie voorspellings word dan
vergelyk met eksperimentele data wat van toepassing is op die komponente in 'n installasie
waar stelseleffekte voorkom. Die resultate word gekoppel aan die kinetiese energievloedkoeffisient
van die vloei by verskillende posisies binne die installasie.
Eksperimentele data, verkry vanaf 'n volskaaleenheid (inlaatmondstukdiameter van 9,216 m),
word met die geskaleerde data van die model (inlaatmondstukdiameter van 1,542 m) vcrgelyk.
Die naaf- tot hulsverhouding van die aksiaalwaaiers wat ondersoek word is 0,15.
Die belangrikste gevolgtrekkings is dat die werkverrigting van die tipe aksiaalwaaier wat
ondersoek word verbeter kan word deur die lempuntspeling te verminder en deur 'n soliede
skyf te installeer by die stroomaf kant van die rotor. 'n Toename in die aantal lemme
van die waaier lei slegs tot marginale verbeterings in die werkverrigting van die waaier.
Die totale werkverrigting van die stesel kan ook verbeter word deur sommige vloeiweerstandskomponente
te verwyder, of deur hulle relatiewe posisies te verander. Al hierdie gevolgtrekkings is gebasseer op die aanname dat die drywingsinset na die waaierrotor konstant
bly.260 leaves printed single pages, preliminary pages i-xxi and numbered pages Chapter 1/1.1-1.3, Chapter 2/2.1-2.17, Chapter 3/3.1.1-3.10, Chapter 4/4.1-4.18, Chapter 5/5.1-5.3, References pages R.1-R.7, Appendix A pages A.1-A.34, Appendix B pages B.1-B.34, Appendix C pages C.1-C.26, Appendix D pages D.1-D.16, Appendix E pages E.1-E.30, Appendix F pages F.1-F.39. Includes bibliography, list of tables, figures and symbols
Food activities and identity maintenance in old age: a systematic review and meta-synthesis
This article has been made available through the Brunel Open Access Publishing Fund.Objectives: Services provided to older people should be developed based on active ageing policies. Nutrition is one aspect of active ageing, but little is known about how food activities contribute to psychological well-being in later life. This is a systematic review of qualitative and quantitative research that answers the question ‘What is known about the relationship between food activities and the maintenance of identities in old age?’
The Fractal Geometry of Critical Systems
We investigate the geometry of a critical system undergoing a second order
thermal phase transition. Using a local description for the dynamics
characterizing the system at the critical point T=Tc, we reveal the formation
of clusters with fractal geometry, where the term cluster is used to describe
regions with a nonvanishing value of the order parameter. We show that,
treating the cluster as an open subsystem of the entire system, new
instanton-like configurations dominate the statistical mechanics of the
cluster. We study the dependence of the resulting fractal dimension on the
embedding dimension and the scaling properties (isothermal critical exponent)
of the system. Taking into account the finite size effects we are able to
calculate the size of the critical cluster in terms of the total size of the
system, the critical temperature and the effective coupling of the long
wavelength interaction at the critical point. We also show that the size of the
cluster has to be identified with the correlation length at criticality.
Finally, within the framework of the mean field approximation, we extend our
local considerations to obtain a global description of the system.Comment: 1 LaTeX file, 4 figures in ps-files. Accepted for publication in
Physical Review
Starting from scratch: patient-reported outcome questionnaires & their role in an integrative medicine primary care minimum-dataset
Aim This research explored the use of patient questionnaires for evaluating integrative medicine (IM) clinics in the primary care setting. Background Integrative medicine (IM) combines traditional, complementary, and alternative medicine with conventional biomedicine. With more clinics in Australia offering IM, it is important to evaluate outcomes. Methods Mixed methods were used. This included a case study of an IM clinic in Sydney, Australia; interviews with 20 patients and 13 staff at the clinic; and a systematic literature review of patient questionnaires. Results Challenges for meausring IM outcomes limitations with routine clinical data collection, selecting appropriate questionnaires able to measure the wide range of IM outcomes whilst minimizing responder burden, patient recruitment and practitioner support. Electronic questionnaires have many advantages. Alternative formats such as paper are still needed. Not all interviewees were interested in cohort results or research and instead wanted to access their individual patient results. Discussion The results from the studies were synthesised and a set of recommendations are offered. Conclusions Patient questionnaires could be used to establish a minimum dataset for use in research, health service development, and informing and improving individual patient care. A bottom-up approach that adresses stakeholders’ needs for a dataset is essential
Rabbit ATG/ATLG in preventing graft-versus-host disease after allogeneic stem cell transplantation: consensus-based recommendations by an international expert panel
This collaborative initiative aimed to provide recommendations on the use of polyclonal antithymocyte globulin (ATG) or anti-T lymphocyte globulin (ATLG) for the prevention of graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (HSCT). A comprehensive review of articles released up to October, 2018 was performed as a source of scientific evidence. Fourteen clinically relevant key questions to the domains indication, administration, and post-transplant management were developed and recommendations were produced using the Delphi technique involving a Panel of 14 experts. ATG/ATLG was strongly recommended as part of myeloablative conditioning regimen prior to matched or mismatched unrelated bone marrow or peripheral blood allogeneic HSCT in malignant diseases to prevent severe acute and chronic GvHD. ATG/ATLG was also recommended prior to HLA-identical sibling peripheral HSCT with good but lesser bulk of evidence. In reduced intensity or nonmyeloablative conditioning regimens, ATG/ATLG was deemed appropriate to reduce the incidence of acute and chronic GvHD, but a higher risk of relapse should be taken into account. Recommendations regarding dose, application, and premedication were also provided as well as post-transplant infectious prophylaxis and vaccination. Overall, these recommendations can be used for a proper and safe application of polyclonal ATG/ATLG to prevent GvHD after allogeneic HSCT
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