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Pre-equilibrium helion emission induced by protonsBezuidenhout, Jacques 12 1900 (has links)
Thesis (PhD (Physics))--University of Stellenbosch, 2006. / This thesis is devoted to a study of the 93Nb( p r ,3He) and 59Co( p r ,3He) reactions at incident
energies of 100 MeV, 130 MeV and 160 MeV. Double differential cross sections and
analysing power distributions were measured from a threshold of ~30 MeV up to the
kinematic maximum and at scattering angles between 15º and 120º. The experimental data
were compared with theoretical calculations done by combining a statistical multistep theory
with a deuteron pickup mechanism in the final stage. The contribution of the first three steps
towards the total double differential cross section and analysing power was assessed.
The theory described the experimental double differential cross section and analysing power
data reasonably well over all incident and scattered energies and for both target nuclei. As
the incident energy was increased, the characteristics of the reaction mechanism also
remained consistent. Thus the results supported the underlying multistep-pickup theory. The
two target nuclei demonstrated similar responses, suggesting these two share the same basic
reaction mechanism.
The total double differential cross section for the reaction dropped with an increase in
incident energy. At a fixed emission energy, near the maximum allowed value, the slope of
the double differential cross section increased with an increase in incident energy, resulting in
the dominance of forward peaked reactions at higher incident energies.
The sensitivity of analysing power to the multistep part of the reaction was valuable to the
study. Forward-peaked contributions that were associated with single step direct reactions
resulted in large analysing power values at small scattering angles, and values dropped to
around zero at large angles. The analysing power also appeared to decrease to values
approximating zero as the incident energy was increased to 160 MeV. Furthermore, this
study also confirmed the dominance of higher step mechanisms at high excitation energies,
irrespective of incident energy. In general the results were in agreement with the predicted
properties of the assumed reaction mechanism at all incident and emission energies, which
inspires confidence that the theoretical interpretation is likely to be correct.
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Effective field theories for disordered systems from the logarithmic derivative of the wave-functionVan Biljon, Andrew 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: In this dissertation, we give an overview of disordered systems, where we concentrate on the
theoretical calculation techniques used in this field. We first discuss the general properties of
disordered systems and the different models and quantities used in the study of these systems,
before describing calculation techniques used to investigate the quantities introduced. These
calculation techniques include the phase formalism method used one dimension, as well as the
scaling approach and field theoretic approaches leading to non-linear c-models in higher dimensions.
We then introduce a complementary effective field theoretic approach based on the
logarithmic derivative of the wave-function, and show how the quantities of interest are calculated
using this method. As an example, the effective field theory is applied to one dimensional
systems with Gaussian disorder. The average density of states, the average 2-point correlator
and the conductivity are calculated in a weak disorder saddle-point approximation and in strong
disorder duality approximation. These results are then calculated numerically and in the case of
the density of states compared to the exact result. / AFRIKAANSE OPSOMMING: In hierdie tesis, gee ons 'n oorsig van sisteme met wanorde, waar ons konsentreer op teoretiese
berekeningsmetodes wat in die veld gebruik word. Eerstens bespreek ons die algemene eienskappe
van sisteme met wanorde en verskillende modelle en hoeveelhede wat gebruik word in die studie
van hierdie sisteme, voordat ons die berekeningsmetodes beskryf wat gebruik word om die bogenoemde
hoeveelhede te ondersoek. Hierdie berekeningstegnieke sluit in die fase formalisme wat
in een dimensie gebruik word, asook die skalingsbenadering en veldteoretiese metodes wat lei
tot nie-lineêr u-modelle in hoër dimensies. Ons voer in 'n komplementere effektiewe veldeteorie
gebaseer op die logaritmiese afgeleide van die golffunksie, en wys hoe hoeveelhede van belang
met hierdie metode bereken word. As 'n voorbeeld, word die effektiewe veldetoerie toegepas op
'n een dimensionele sisteem met 'n Gauss verdeling. Die gemiddelde digtheid van toestande,
die gemiddelde 2-punt korrelator en die gemiddelde geleidingsvermoë word bereken in 'n swak
wanorde saalpunt benadering en in 'n sterk wanorde duale benadering. Hierdie resultate word
dan numeries bereken, en in die geval van die digtheid van toestande vergelyk met die eksakte
resultaat.
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Relativistic plane wave description of spin transfer observables for proton knockout reactionsWyngaardt, Shaun Metzler 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: In this dissertation we set out to develop the first relativistic model for calculating complete
sets of (p, 2p) spin transfer observables. In addition to this a new technique has been developed
which allows us to evaluate the transition amplitude, which is used to calculate the scattering
observables for the reaction directly. The influence of various modiuin-modificd parameters ()1I
the scattered wave functions anr] NN interact ion lH-IVC' })('('11 invest igatcd DlIC t,C) (I,llIlJigllitic's
surrounding the nNN coupling we have included both pseudosoalar and pseudovector coupling
into the nucleon-nucleon interaction model. Furthermore we have included two different kinematic
prescriptions to obtain the effective NN laboratory kinetic energy and center of mass
scattering angle, which are used to obtain the NN scattering amplitudes. The aim of this
study is to investigate the effects of the various model parameters on complete sets of scattering
observables.
Our investigation has shown that although the analyzing power is not very sensitive to nuclear
medium effects, and the various other spin transfer observables such as Dnn should provide
valuable insight. Further refinements of the model would be to include nuclear distortions as
well as the IA2 model of the NN interaction. / AFRIKAANSE OPSOMMING: In hierdie tesis ontwikkel ons die eerste relatiwistiese model vir die berekening van 'n volledige
stel (p, 2p) spin waarneembares. Verder word 'n nuwe tegniek ingevoer wat ons toelaat om die
oorgangsamplitude, wat gebruik word in berekening van die verstrooings waarneembares vir
die reaksie, direk te evalueer. Die invloed van verskeie medium-gemodifiseerde parameters op
die verstrooide golffunksies en die NN wisselwerking word bestudeer. As gevolg van onsekerhede
betreffende die лNN koppeling word beide die pseudoskalaar en pseudovektor koppeling
in die nukleon-nukleon interaksie model ingesluit. Ons sluit ook twee verskillende kinematiese
preskripsies in om die effektiewe NN laboratorium kinetiese energie en die massa middelpunt
verstrooiings hoek, wat gebruik word vir die berekening van die NN verstrooiings amplitude,
te bereken. Die doel van hierdie studie is om die effek van verskeie model parameters op 'n
volledige stel spin waarneembares te ondersoek.
Die studie toon dat alhoewel die analiseervermoë nie baie sensitief is vir medium effekte
nie, die ander spin waarneembares soos byvoorbeeld Dnn waardevolle insig lewer. Daar word
voorgestel dat die model verfyn word deur kerndistorsies as ook die meer algemele IA2 model
vir die NN interaksie in te sluit.
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Vacuum ultraviolet laser spectroscopy of CO molecules in a supersonic jetSteinmann, C. M. (Christine Margarete) 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: A tunable narrow-bandwidth laser source combined with a supersonic gas jet as sample is wellsuited
for obtaining high-resolution spectra of cold isolated molecules and complexes. In the
present study such a laser source in the vacuum ultraviolet was applied to the spectroscopic
investigation of rare carbon monoxide (CO) isotopomers and CO-noble gas van der Waals
complexes in supersonic gas pulses seeded with natural CO gas.
Tunable coherent vacuum ultraviolet radiation was generated by two-photon resonant fourwave
sum-frequency mixing of two pulsed dye laser beams in a magnesium vapour medium.
Laser induced fluorescence excitation spectra of the A(v'=3)-X(v"=0) vibronic band of CO
molecules in a noble gas (neon or argon) jet were obtained by measuring the total undispersed
fluorescence from the irradiated sample volume in dependence of the excitation wavelength. The
dynamics of the flow-cooling process in the supersonic jet were investigated and the experimental
parameters optimised using the rotational temperature of 12C160as determined from rotational
line intensities. Rotational temperatures as low as 2 ± I K were observed.
Spectroscopic detection of the rare 12C170and 12C180isotopomers was facilitated by the low
rotational temperature and high spectral resolution. Six rotational lines of 12C170and four of
12C180were detected in the A(v'=3)-X(v"=0) vibronic band. This demonstrates the low detection
limit (circa 3 parts per million) obtained in the experiment. The line wavelengths were
determined to an accuracy of 0.2 pm using the well-documented 12C160and 13C160lines for
calibration. The spectral results on 12C170are, to our knowledge, the first rotationally resolved
laboratory measurements published on the A-X band of this isotopomer. Accurate wavelength
data of the stable isotopomers of CO is of importance in the interpretation of astrophysical
observations of CO in the interstellar medium. The newly determined 12C170wavelengths were
successfully applied to a recent problem in astrophysics (Astrophys. J. Lett. 2003).
The conditions in a supersonic jet facilitate the study of weakly bound van der Waals
complexes, of which CO-noble gas complexes are prototypes. However, there is no experimental
data available on the electronic excitation spectra of the CO-noble gas complexes, lying in the
vacuum ultraviolet region. In the present experiment evidence of extensive complexation of the CO in the noble gas jet has been found, but in the spectral region around the A(v'=3)-X(v"=O)
band of CO no distinct spectral features that could be associated with these complexes were
observed. Having considered the existing knowledge on CO and CO-noble gas complexes and
experimental studies on the excitation and dissociation dynamics of Iz-noble gas complexes, we
regard complex induced inter-system crossing or electronic predissociation as the most likely
causes for these observations.
The results on the rare CO isotopomers demonstrate the potential of our experimental setup
for high-resolution, isotope and state selective spectroscopy in the vacuum ultraviolet with a high
sensitivity for fluorescent species. The availability of the now well-characterised experimental
setup in our laboratory opens the way for further investigation of molecular or complex species
with spectroscopic features in the vacuum ultraviolet region. / AFRIKAANSE OPSOMMING: Vakuum ultraviolet laser spektroskopie van CO
molekules in 'n supersoniese gasstraal:
'n Afstembare smal bandwydte laserbron en 'n supersoniese gasstraal as monster is 'n geskikte
kombinasie vir hoë-resolusie spektroskopie van geïsoleerde afgekoelde molekules en komplekse.
In hierdie studie is so 'n laserbron in die vakuum ultraviolet gebruik in die spektroskopiese
ondersoek van skaars koolstofmonoksied (CO) isotopomere en CO-edelgas van der Waals
komplekse in supersoniese gaspulse wat 'n klein persentasie natuurlike CO gas bevat.
Afstembare koherente vakuum ultraviolet lig is verkry deur twee-foton resonante vier-golf
som-frekwensie vermenging van twee gepulseerde kleurstoflaserbundels in 'n magnesiumdamp
medium. Laser-geïnduseerde fluoressensie opwekkingspektra van die A(v'=3)-X(v"=0)
vibroniese band van die CO molekules in die edelgasstraal (neon of argon) is uitgemeet deur die
totale fluoressensie van die beligte gasmonster, sonder golflengteskeiding, te meet as funksie van
die opwekkingsgolflengte. Die dinamika van die vloeiverkoelingsproses in die supersoniese
gasstraal is ondersoek en die eksperimentele parameters geoptimeer deur gebruik te maak van die
rotasionele temperatuur van 12Cl60 soos bepaal uit die intensiteitsverhoudings van die
rotasielyne. Rotasionele temperature tot so laag as 2 ± 1 K is waargeneem.
Spektroskopiese waarneming van die skaars 12C170 and 12Cl80 isotopomere is moontlik
gemaak deur die lae rotasionele temperatuur en die hoë spektrale resolusie. Ses rotasielyne van
12C170 en vier van 12C180 is waargeneem in die A(v'=3)-X(v"=0) vibroniese band. Dit
demonstreer die lae deteksielimiet (ongeveer 3 dele per miljoen) wat bereik kon word. Die
golflengtes van die lyne is bepaal met 'n akkuraatheid van 0.2 pm deur die bekende lyne van
12C160en 13C160vir kalibrasie te gebruik. Die resultate ten opsigte van 12C170 is sover vasgestel
kon word die eerste rotasioneel-opgeloste laboratorium metings van die A-X band van hierdie
isotopomeer. Akkurate golflengte data vir die stabiele CO isotopomere is van belang vir die
interpretasie van die astrofisiese waarnemings van CO in die interstellêre medium. Die nuwe
12C170 golflengtes is suksesvol aangewend in die oplossing van 'n onlangse
interpretasieprobleem in astrofisika (Astrophys. J. Lett. 2003).
Die toestande in 'n supersoniese gasstraal maak die bestudering van swak-gebonde van der
Waals komplekse moontlik. Hoewel CO-edelgas van der Waals komplekse as prototipes beskou word, is daar geen eksperimentele data beskikbaar oor die elektroniese opwekkingspektra van
hierdie spesies, wat in die vakuum ultraviolet gebied lê, nie. In hierdie studie is daar
eksperimentele getuienis gevind vir uitgebreide kompleksering van CO in die edelgasstraal, maar
in die spektraalgebied rondom die A(v'=3)-X(v"=O) band van CO is geen duidelike spektrale
kenmerke wat met hierdie komplekse geassosieer kan word, waargeneem nie. Na oorweging van
die bestaande kennins oor CO en CO-edelgas komplekse en eksperimentele studies oor die
opwekking en dissosiasie-dinamika van Iz-edelgas komplekse, beskou ons kompleksgeïnduseerde
intersisteemoorgange of elektroniese predissosiasie as die waarskynlikste redes vir hierdie
waarnemings.
Die resultate oor die skaars CO isotopomere toon die potensiaal van ons eksperimentele
opstelling vir hoë-resolusie, isotoop- en toestandselektiewe spektroskopie in die vakuum
ultraviolet met uitstekende sensitiwiteit vir fluoresserende spesies. Die beskikbaarheid van hierdie
nou deeglik gekarakteriseerde eksperimentele opstelling in ons laboratorium maak verdere
ondersoek na molekulêre of kompleks-spesies met spektroskopiese kenmerke in die vakuum
ultraviolet moontlik.
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A duality construction for interacting quantum Hall systemsKriel, Johannes Nicolaas 03 1900 (has links)
Thesis (PhD)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The fractional quantum Hall effect represents a true many-body phenomenon in which the
collective behaviour of interacting electrons plays a central role. In contrast to its integral
counterpart, the appearance of a mobility gap in the fractional quantum Hall regime is due
entirely to the Coulomb interaction and is not the result of a perturbed single particle gap.
The bulk of our theoretical understanding of the underlying many-body problem is based on
Laughlin’s ansatz wave function and the composite fermion picture proposed by Jain. In the
latter the fractional quantum Hall effect of interacting electrons is formulated as the integral
quantum Hall effect of weakly interacting quasiparticles called composite fermions. The composite
fermion picture provides a qualitative description of the interacting system’s low-energy
spectrum and leads to a generalisation of Laughlin’s wave functions for the electron ground
state. These predictions have been verified through extensive numerical tests.
In this work we present an alternative formulation of the composite fermion picture within
a more rigorous mathematical framework. Our goal is to establish the relation between the
strongly interacting electron problem and its dual description in terms of weakly interacting
quasiparticles on the level of the microscopic Hamiltonian itself. This allows us to derive an
analytic expression for the interaction induced excitation gap which agrees very well with existing
numerical results. We also formulate a mapping between the states of the free particle and
interacting descriptions in which the characteristic Jastrow-Slater structure of the composite
fermion ansatz appears naturally. Our formalism also serves to clarify several aspects of the
standard heuristic construction, particularly with regard to the emergence of the effective magnetic
field and the role of higher Landau levels. We also resolve a long standing issue regarding
the overlap of unprojected composite fermion trial wave functions with the lowest Landau level
of the free particle Hamiltonian. / AFRIKAANSE OPSOMMING: Die fraksionele kwantum Hall-effek is ’n veeldeeltjie verskynsel waarin die kollektiewe gedrag
van wisselwerkende elektrone ’n sentrale rol speel. In teenstelling met die heeltallige kwantum
Hall-effek is die ontstaan van ’n energie gaping in die fraksionele geval nie ’n enkeldeeltjie
effek nie, maar kan uitsluitlik aan die Coulomb wisselwerking toegeskryf word. Die teoretiese
raamwerk waarbinne hierdie veeldeeltjie probleem verstaan word is grootliks gebaseer op
Laughlin se proefgolffunksie en die komposiete-fermion beeld van Jain. In laasgenoemde word
die fraksionele kwantum Hall-effek van wisselwerkende elektrone geformuleer as die heeltallige
kwantum Hall-effek van swak-wisselwerkende kwasi-deeljies wat as komposiete-fermione bekend
staan. Hierdie beeld lewer ’n kwalitatiewe beskrywing van die wisselwerkende sisteem se
lae-energie spektrum en lei tot ’n veralgemening van Laughlin se golffunksies vir die elektron
grondtoestand. Hierdie voorspellings is deur verskeie numeriese studies geverifieer.
In hierdie tesis ontwikkel ons ’n alternatiewe formulering van die komposiete-fermion beeld
binne ’n strenger wiskundige raamwerk. Ons doel is om die verband tussen die sterk-wisselwerkende
elektron sisteem en sy duale beskrywing in terme van swak-wisselwerkende kwasi-deeltjies op
die vlak van die mikroskopiese Hamilton-operator self te realiseer. Hierdie konstruksie lei tot ’n
analitiese uitdrukking vir die opwekkingsenergie wat baie goed met bestaande numeriese resultate
ooreenstem. Ons identifiseer ook ’n afbeelding tussen die vrye-deeltjie en wisselwerkende
toestande waarbinne die Jastrow-Slater struktuur van die komposiete-fermion proefgolffunksies
op ’n natuurlike wyse na vore kom. Verder werp ons formalisme nuwe lig op kwessies binne die
standaard heuristiese konstruksie, veral met betrekking tot die oorsprong van die effektiewe
magneetveld en die rol van ho¨er effektiewe Landau vlakke. Ons lewer ook uitspraak oor die
vraagstuk van die oorvleueling van ongeprojekteerde komposiete-fermion golffunksies met die
laagste Landau vlak van die vrye-deeltjie Landau probleem.
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Second light-scattering and Kerr-effect virial coefficients of molecules with linear and lower symmetry.Couling, Vincent William. 01 October 2014 (has links)
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1995.
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Electrostatic waves and solitons in electron-positron plasmas.Gray, Greer Jillian. January 1998 (has links)
The magnetosphere of pulsars is thought to consist of an electron-positron
plasma rotating in the pulsar magnetic field (Beskin, Gurevich & Istomin
1983; Lominadze, Melikidze & Pataraya 1984; Gurevich & Istomin 1985). A
finite, and indeed large, longitudinal electric field exists outside the star, and
may accelerate particles, stripped from the surface, to high energies (Goldreich
& Julian 1969; Beskin 1993). These particles may leave the magnetosphere
via open magnetic field lines at the poles of the pulsar. This depletion
of particles causes a vacuum gap to arise, a double layer of substantial potential
difference. The primary particles, extracted from the star's surface,
are accelerated in the double layer, along the pulsar magnetic field lines,
and so produce curvature radiation. The curvature photons, having travelled
the distance of the double layer may produce electron-positron pairs
above the vacuum gap. These first-generation secondary particles, although
no longer accelerating, may synchroradiate, generating photons which may
then produce further electron-positron pairs. These synchrophoton produced
pairs will be at energies lower than curvature photon produced pairs, since
synchrophoton energies are approximately an order of magnitude less than
that of the parent curvature photon.
An attempt to model the electron-positron pulsar magnetosphere is made.
A four component fluid electron-positron plasma is considered, consisting of a
hot electron and positron species, at temperature Th , and a cool electron and
positron species at temperature Tc . The hot components represent the parent
first-generation curvature-born pairs, and the cooler components represent
the second-generation pairs, born of synchrophotons. The hot components
are assumed to be highly mobile, and are thus described by a Boltzmann
density distribution. The cool components are more sluggish and are thus
described as adiabatic fluids. The model is symmetric in accordance with
pair production mechanisms, so that both species of hot(cool) electrons and
positrons have the same temperature Th(Tc, and number density Nh(Nc ) .
In the interests of completeness, linear electrostatic waves in five different
types of electron-positron plasmas are considered. The dispersion relations
for electrostatic waves arising in these unmagnetized plasmas are derived.
Single species electron-positron plasmas are investigated, considering
the constituents to be: both Boltzmann distributed; both adiabatic fluids;
and finally, one species of each type. Linear electrostatic acoustic waves in
multi-component electron-positron plasmas are then considered, under the
four component model and a three component model (Srinivas, Popel &
Shukla 1996).
Small amplitude nonlinear electron-positron acoustic waves are investigated,
under the four component electron-positron plasma model. Reductive
perturbation techniques (Washimi & Taniuti 1966) and a derivation of the
Korteweg-de Vries equation result in a zero nonlinear coefficient, and a purely
dispersive governing wave equation. Higher order nonlinearity is included,
leading to a modified Korteweg-de Vries equation (Watanabe 1984; Verheest
1988), which yields stationary soliton solutions with a sech dependence rather
than the more familiar sech2.
Arbitrary amplitude solitons are then considered via both numerical and
analytical (Chatterjee & Roychoudhury 1995) analysis of the Sagdeev potential.
The symmetric nature of the model leads to the existence of purely
symmetrical compressive and rarefactive soliton solutions. Small and arbitrary
amplitude soliton solutions are compared, and show good correlation.
Under the assumption of Boltzmann distributed hot particles, severe restrictions
are imposed on the existence domains of arbitrary amplitude soliton
solutions. The Boltzmann assumption places a stringent upper limit on the
cool species number density, in order for the solutions to be physical.
An investigation is made of results obtained for an asymmetric electronpositron
plasma (Pillay & Bharuthram 1992), consisting of cold electrons
and positrons, and hot Boltzmann electrons and positrons at different temperatures
Teh and Tph , and number density Neh and Nph . It is found that
the assumption of Boltzmann particles again places restrictions on the acoustic
soliton existence space, and that the results obtained may be physically
invalid. Valid solutions are obtained numerically, within the boundaries of
allowed cool species density values. / Thesis (M.Sc.)-University of Natal, Durban, 1998.
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Two-dimensional plasma sheath observations in plasma source ion implantation.Meyer, Kevin Alan. January 1996 (has links)
Plasma Source Ion Implantation (PSII) is the process of implanting high energy ions
[10-50 keV] into metallic targets, by pulsing them negatively whilst immersed in a
background plasma. PSII achieves surface hardening, and increased wear and corrosion
resistance.
Numerous papers have been published describing numerical simulations and models
of the PSII process, most of which have been limited to one dimension.
This thesis presents the results of work carried out III the Plasma Processing
Laboratory at the University of Natal, Durban, during 1994-1995. In particular,
measurements of two-dimensional plasma sheath effects due to spherical and complex
shaped targets are compared with a particle-in-cell simulation code.
The simulation results are used to define a relationship between the plasma potential
of the sheath edge and the saturation currents. Thus allowing for the saturation
currents to be used to trace sheath evolution. These results are compared with the
experimental measurements from the spherical target.
Results from the rectangular and complex saw-tooth targets show a lack of sheath
conformality. The ion saturation currents were susceptible to electron swamping,
which occured in localised regions associated with target structure. It is thought that
secondary electrons ejected from the target are focused and accelerated by the high
target potential into these regions, where they swamp the ion current. / Thesis (M.Sc.)-University of Natal, Durban, 1996.
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Assessment of the efficiency of solar radiation concentrating system.Artur, Célia Domingas. January 2009 (has links)
A Solar Radiation Concentrating System for generation of high temperature heat for a
solar oven was developed and evaluated at the University of KwaZulu-Natal, Westville
Campus, Durban - South Africa. The system concentrates direct solar radiation on a small
area receiver which absorbs the radiation and converts it into thermal energy that may be
stored and used for several applications where food preparation and water pasteurization
is the priority.
The concentrator, area 2.2 m², is a half satellite communication dish covered with
trapezoidal acrylic mirror tiles. The receiver/absorber is a spiral coil of blackened
stainless steel pipe. Oil is circulated as heat transfer fluid.
To determine the optimal dimension and position of the receiver, two experimental
methods were used:
(1) The tiles were scanned using a vertical, self adjusting laser beam to get a distribution
of reflected radiation across the focal volume.
(2) A thin, blackened stainless steel plate was placed at appropriate distances in the
focal volume, and temperature distribution scanned using a temperature gun.
The latter method proved to be the more useful.
Results of the analysis of system performance showed that the system has the capability
to produce high temperatures for domestic purposes. The efficiency of the system is
about 35 %. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.
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Measurement of soil in sugar cane using non-destructive techniques.Padayachee, Thavashen. January 2001 (has links)
The soil being delivered with sugar cane consignments. from the cane fields to the
factories, has been a recent cause for concern in the South African sugar industry. The
soil impurities increase the wear of processing machinery reduce extraction
efficiency and represents an unnecessary transport of material. The cost due to soil
was estimated at R63 million (about US $8 million) over the 1996/97-season. The
need to reduce costs, due to the unwanted soil component, has been given a high
priority.
Ashing is currently used by the sugar industry to estimate the amount of soil in cane.
Although simple to implement, the method is destructive, requires long processing
times and limited to small sample sizes.
In fecent times, non-destructive techniques have become more prominent in industry.
Hence, the decision to apply such techniques to the soil in cane-problem. This
dissertation describes an experimental investigation into Dual-Energy Transmission
(DuET) and X-ray lmaging for quantifying the amount of soil in cane.
DuET can determine the relative concentrations of the components of a binary
mixture by measuring the transmission of low- and high-energy gamma photons
through the mixture. The principle of DuET was successfully demonstrated with
aqueous solutions of ferric chloride. Experimentally-determined mass attenuation
coefficients of water and ferric chloride were compared to theoretical values. DuET
was then applied to dried, shredded sugar cane spiked with various amounts of soil.
Results showed large variations in the predicted soil concentrations. These variations were attributed to radiation scatter and incomplete volume sampling by the
radioactive source. However, new experimental arrangements are expected to improve
the technique: initial test results are given of a sample holder that continuously rotates
a sample up and down through the source-detector axis.
An alternative approach to processmg DuET-spectra, using the discrete wavelet
transform coupled with an artificial neural network, is also introduced.
X-ray Imaging was the second technique investigated. A literature survey revealed
that this technique had not previously been applied to the soil in cane-problem. The
present work constituted an initial investigation to determine the feasibility of
applying X-ray imaging to measure the amount of soil in cane. The soil/cane-samples,
that were used for DuET, were imaged us ing a commercial mammography unit, and
the resulting radiographs were analysed using image processing techniques. Although
the results are promising, a more comprehensive investigation is foreseen. / Thesis (M.Sc.)-University of Natal, Durban, 2001.
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