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On-Board Spacecraft Time-Keeping Mission System Design and VerificationWickham, Mark E. 10 1900 (has links)
International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / Spacecraft on-board time keeping, to an accuracy better than 1 millisecond, is a
requirement for many satellite missions. Scientific satellites must precisely "time tag"
their data to allow it to be correlated with data produced by a network of ground and
space based observatories. Multiple vehicle satellite missions, and satellite networks,
sometimes require several spacecraft to execute tasks in time phased fashion with
respect to absolute time. In all cases, mission systems designed to provide a high
accuracy on-board clock must necessarily include mechanisms for the determination
and correction of spacecraft clock error. In addition, an approach to on-orbit
verification of these mechanisms may be required. Achieving this accuracy however
need not introduce significant mission cost if the task of maintaining this accuracy is
appropriately distributed across both the space and ground mission segments.
This paper presents the mission systems approaches taken by two spacecraft programs
to provide high accuracy on-board spacecraft clocks at minimum cost. The first,
NASA Goddard Space Flight Center's (GSFC) Extreme Ultraviolet Explorer (EUVE)
program demonstrated the ability to use the NASA Tracking and Data Relay Satellite
System (TDRSS) mission environment to maintain an on-board spacecraft clock to
within 100 microseconds of Naval Observatory Standard (NOS) Time. The second
approach utilizes an on-board spacecraft Global Positioning System (GPS) receiver as
a time reference for spacecraft clock tracking which is facilitated through the use of
Fairchild's Telemetry and Command Processor (TCP) spacecraft Command & Data
Handling Subsystem Unit. This approach was designed for a future Shuttle mission
requiring the precise coordination of events among multiple space-vehicles.
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Molecular diagnostic approach to determine the degree of photoaging of the skinWilcox, Stephany Vanessa 04 1900 (has links)
Thesis (MScMedSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Context: Excessive exposure to ultraviolet radiation (UV) results in the risk of acquiring long-term harmful
effects such as photoaging, which is characterised by deep wrinkles, roughness, dyspigmentation and an
increased loss in elasticity. As a result, the detection of photoaging at an early stage is crucial to improving
morbidity, whilst preventing the advancement of skin cancer.
Aim: The aim of the study was to develop and to validate a diagnostic real-time PCR method in order to
establish the gene expression profiles of potential biomarkers in the skin so as to quantify the degree of
photoaging: this was conducted by retrieving total RNA from cells adherent to tape strips from sun exposed
and non-exposed skin areas.
Materials and methods: Twenty healthy volunteers consisting of seven males and thirteen females aged
25 to 67 years were included in this study. Tape stripping was performed using pre-cut D-Squame® 22 mm
adhesive discs. Samples were collected on the right medial thigh area 20 cm above the patella and 2 cm
below the lateral canthus of the right eye. Total RNA was extracted and relative standard curve method of
gene expression was performed. TGF-β, MMP 9, TNF-α and IL-6 mRNA transcripts were selected as
representative cytokines to determine the relative fold-change in sun exposed and non-exposed areas of the
skin so as to determine extent of photoaging.
Results: Repeatability and reproducibility was determined by the coefficient of variation (CV) was within an
acceptable range. Thirty five percent (n=7) samples displayed down-regulatory effects for TGF-β. Down
regulation of MMP 9 was observed within 30% (n=6) of samples, while 15% (n=3) showed marked up
regulation. Only two samples showed measurable levels of TNF-α in the assay, of which one showed
significant up regulation. Furthermore, we were unable to detect any IL-6 expression in any of the samples
prepared.
Conclusion: we have shown that epidermal cytokines can be retrieved from tape stripped samples and can
be quantified via real-time PCR. However, the choices of cytokine biomarkers reveal that they are as
important as the concentration of starting material. In this study cytokines such as IL-6 is not as informative
in determining the extent of photoaging without high doses of ultraviolet radiation before sample collection
as opposed to the other explored cytokines. / AFRIKAANSE OPSOMMING: Konteks: Oormatige blootstelling aan ultraviolet (UV) bestraling kan tot ‘n risiko van skadelike en
lantermynse nagevolge lei wat gekenmerk word deur foto-veroudering. Dit sluit in diep plooie, growwe vel
en ‘n toenemende verlies in elastisiteit. Die ontdekking van foto-veroudering op ‘n vroeë stadium is van
kardinale belang vir die verbetering van morbiditeit en die voorkoming van velkanker bevordering.
Doelstelling: Die doel van hierdie studie was om ‘n diagnostiese polimerase kettings reaksie (PKR) metode
te ontwikkel om geen uitdrukkings profiele van potensiële bio-merkers te vestig in die vel, om so die graad
van foto-veroudering in areas van vel wat blootgestel word aan die son en beskermde van die son te bepaal
deur totale RNS te versamel van kleeflintskyfies.
Materiale en metodes: Twintig gesonde vrywilligers (sewe mans en dertien vroue), tussen die ouderdom
van 25 en 67 jaar, was ingesluit in hiedie studie. Vel monsters was versamel deur gebruik te maak van Dsquame®
22 mm kleeflintskyfies 20 cm bokant die patella van die regterkanste mediale heup en 2 cm onder
die regter oog. Totale RNS was geisoleer en die relatiewe vlak van geen uitdrukking was bepaal deur
gebruik te maak van die kurwe model. Die boodskapper ribonukleiosier transkripsies van die sitokiene TGF-
β, MMP 9, TNF-α en IL-6 was gekies as verteenwoordigers van foto-veroudering om die relatiewe
verandering van foto-veroudering in die vel te bepaal.
Resultate: Validering metodes was aanvaarbaar. ‘n Afwaarts reguleringseffek in TGF-β en MMP 9 merker
uitdrukking is gevind in vyf en dertig persent (n=7) en dertig persent (n=6) van monsters, onderskuidelik. In
vyftien persent (n=3) van monsters is ‘n opwaarts reguleringseffek in die laasgenoemde gevind. Slegs twee
monsters het meetbare vlakke van TNF-α getoon in die eksperiment, waarvan slegs een ‘n
noemenswaardige opwaartse regulering getoon het. IL-6 uitdrukking is nie gevind in enige van die
monsters.
Gevolgtrekkings: Hierdie studie het bepaal dat sitokiene van die vel geisoleer van kleeflint monsters en
gekwantifiseer deer relatiewe PKR uitdrukking bepaal kan word. Die keuse van bio-merkers is egter net so
belangrik as konsentrasie bepaling van die monsters. Die IL-6 sitokien, in vergelyking met ander, is slegs
informaliet tydens hoë ultraviolet bestraling aan die vel blootgestel is.
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Development and application of tunable VUV laser sourcesNortje, Anton Christiaan 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: A tunable narrow-bandwidth vacuum ultra violet laser source was developed
and characterised. Two-photon resonant four-wave sum-frequency mixing of
two pulsed dye laser beams in magnesium vapour was used to generate the
VUV laser light. A heat pipe oven with a concentric design was incorporated
to provide a magnesium vapour column of around 30 cm in length with a sufficiently stable temperature and appropriate vapour pressure for efficient VUV production. This is a longer nonlinear medium length than previously produced in our laboratory using a crossed heat pipe oven. The longer medium facilitated the production of VUV laser light of higher intensity than was previously obtainable.
High resolution laser induced fluorescence spectra of carbon monoxide in a supersonic gas jet was recorded using the tunable VUV laser light produced in the crossed heat pipe oven. Experimental parameters were optimised and adjusted for the selective detection of the forbidden singlet-triplet transitions which typically have longer lifetimes than singlet-singlet transitions. Transitions from the X¹Σ⁺(v = 0) ground state to the e³Σ⁻( v = 5) triplet state were recorded, and accurate wavelength for the spectral lines were determined. Laboratory wavelengths for these lines have not been measured previously. Accurate wavelength for the weak forbidden spectral lines of CO are important in astrophysical applications, for example determining column densities of interstellar gas clouds. / AFRIKAANSE OPSOMMING: 'n Afstembare smal bandwydte vakuum ultraviolet laser bron is ontwikkel en gekarakteriseer. Twee-foton resonante vier-golf som-frekwensie vermenging van twee gepulseerde kleurstoflaserbundels in 'n magnesium damp is gebruik om die VUV laser lig te produseer. 'n Hittepyp oond met 'n konsentriese ontwerp is in gebruik geneem om a magnesium damp kollom van ongeveer 30 cm in lengte te voorsien waarvan die temperatuur voldoende stabiel is en die dampdruk toepaslik is vir effektiewe VUV produksie. Dit is 'n langer nie-liniêre medium as wat in die verlede deur 'n kruis-hittepyp oond voorsien is. Die langer medium het dit moontlik gemaak om VUV laser lig van hoër intensiteit te produseer as wat tot dusver bereikbaar was. Hoë resolusie laser geinduseerde fluoresensie spektra van koolstof monoksied in a supersoniese gasstraal is opgeneem met die hulp van die afstembare VUV laser lig geproduseer in die kruis-hittepyp oond. Eksperimentele parameters is geoptimeer en verstel vir die selektiewe waarneming van die verbode singlet-triplet oorgange wat tipies langer leeftye besit in vergelyking met singlet-singlet oorgange. Oorgange vanaf die X¹Σ⁺(v = 0) grond toestand na die e³Σ⁻( v = 5) triplet toestand is opgeneem en akkurate golflengtes vir die spektrale lyne is bepaal. Laboratorium golflengtes het tot dusver nie bestaan vir hierdie lyne nie. Akkurate golflengtes vir die swak verbode spektrale lyne van CO het belangrike toepassings in astrofisika soos die bepaling van die kollom digtheid van interstellêre gas wolke.
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Development of VUV tunable laser spectroscopy techniques for characterizing calcium fluorideMatindi, Tresor 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The large band gap (approximately 11.5-12.1 eV) and high transmission of calcium fluoride
(CaF2) crystal in the ultraviolet (UV) and vacuum ultraviolet (VUV) region makes it
an important material for optics for laser applications in UV. However, CaF2 degrades
during long exposure to UV irradiation due to defect generation. The formation of selftrapped
excitons (STE) is considered the first step in defect generation. In this project
the possibility of observing STE states in CaF2 using a narrow bandwidth tunable VUV
laser source is investigated. This is the first spectroscopy study of an alkaline earth fluoride
using VUV tunable laser radiation instead of a fixed wavelength laser. The use of a VUV
tunable laser source has potential for determining the energies of the STE states, which are
unknown. Our main objective is addressed by developing techniques to measure absorption
spectra of pure and doped CaF2 samples, using a VUV scanning monochromator and a
tunable VUV laser, and by doing a literature study. The results obtained with the scanning
monochromator show absorption features in 126-180 nm range of all our samples. These
vary for different samples and correlate with information from the supplier on the samples’
fluorescence spectra. Total absorption of the VUV light by CaF2 in the 115-126 nm range is
observed. With the narrow bandwidth tunable laser light, absorption spectra were obtained
in the range of 143-146.7 nm of all our CaF2 samples. No significance peaks which can be
related to the STE states in CaF2 were observed in the VUV laser absorption spectra, but
the results are valuable to improve the technique. The conclusion is that either a different
spectral range or fluorescence detection can be investigated in future. / AFRIKAANSE OPSOMMING: Die groot bandgaping (ongeveer 11.5-12.1 eV) en hoë transmissie van kalsiumfluoried
(CaF2) kristal in die ultraviolet (UV) en die vakuum ultraviolet (VUV) gebied maak dit
’n belangrike materiaal vir optika vir laser toepassings in die UV. CaF2 degradeer egter
gedurende langdurige blootstelling aan UV lig as gevolg van die generering van defekte.
Die vorming van ’n elektron-holte paar wat deur die kristalstuktuur gestabiliseer word teen
rekombinasie (self-trapped excitons, afgekort STE) word beskou as die eerste stap in defek
generering. In hierdie projek word die moontlikheid ondersoek om STE toestande in CaF2
waar te neem deur die gebruik van ’n afstembare VUV laserbron met emissie in ’n smal
spektrale band. Dit is die eerste spektroskopiese studie van ’n aardalkali-fluoried deur die
gebruik van afstembare VUV laserlig in plaas van ’n vaste golflengte laser. Die gebruik
van ’n afstembare VUV laserbron het potensiaal vir die bepaling van die energieë van die
STE teostande, wat onbekend is. Ons hoofdoel word aangespreek deur die ontwikkeling
van tegnieke vir die meet van absorpsie spektra van suiwer en gedoteerde CaF2 monsters
met behulp van ’n VUV skanderende monochromator en ’n afstembare VUV laser, en
deur ’n literatuurstudie. Die resultate wat behaal is met die skanderende monochromator
toon die absorpsieprofiele van al ons monsters in die 126-180 nm spektrale gebied. Die
absopsieprofiele varieer vir die verskillende monsters en korreleer met die inligting van die
verskaffer oor die fluoressensie spektra van die monsters. Totale absorpsie van die VUV lig
deur CaF2 in die 115-126 nm gebied is waargeneem. Met die smalband afstembare laserlig
is absorpsie spektra in die 143-146.7 nm gebied vir al ons CaF2 monsters verkry. Geen
beduidende pieke wat verband hou met die STE toestande in CaF2 is waargeneem in die
VUV laser absorpsie spektra nie, maar die resultate is waardevol vir die verbetering van
die tegniek. Die gevolgtrekking is dat of ’n ander spektraalgebied of fluoressensiedeteksie
in die toekoms ondersoek kan word.
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Thermal desorption, photodesorption, and photodissociation of water on amorphous ice and lunar surfacesDeSimone, Alice Johnson 13 January 2014 (has links)
The temperature-programmed desorption profiles of water from three lunar analogs were measured. These experiments showed that glassy materials were hydrophobic, that water on multiphase materials occupied a continuum of adsorption sites, and that feldspar exhibited significant chemisorption of water. The competition between photodissociation and photodesorption of amorphous solid water (ASW) was investigated on three substrates: copper with a thin oxide coating, an impact melt breccia from Apollo 16, and a mare basalt from Apollo 17. The rotational temperature of desorbing H₂O did not vary significantly with substrate, but the H₂O time-of-flight spectra were broader on the lunar slabs than on copper. Additionally, the cross sections for water removal at low coverages were higher on the lunar slabs than on copper. O(³PJ) produced by 157-nm irradiation of ASW on the same three substrates was measured as a function of spin-orbit state, H₂O exposure, and irradiation time. The same Maxwell-Boltzmann components were present in each case, with translational temperatures of 10,000 K, 1800 K, 400 K, and the surface temperature, but the relative intensities of these components differed widely between substrates. Evidence for diffusion out of pores in the ASW and in the lunar slabs was observed for H2O exposures of at least 1 Langmuir. Cross sections for H2O and O(3PJ) depletion due to 157-nm irradiation of ASW were applied to icy grains in the rings of Saturn, and corresponding cross sections on the lunar substrates were used to estimate the flux of water desorbing from the Moon and the density of oxygen atoms in the lunar atmosphere.
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Economic valuation of UV disinfection in Hong Kong sewageCheung, Chi-shing, 張志成 January 2004 (has links)
published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management
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DNA repair pathways involved in determining the level of cytotoxicity of environmentally relevant UV radiationCarpenter, Lucy January 2000 (has links)
No description available.
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THE ELECTRONIC STRUCTURE OF ORGANOMETALLIC CARBONYL, NITROSYL, THIONITROSYL, AND CYANIDE COMPLEXES BY GAS PHASE X-RAY AND ULTRAVIOLET PHOTOELECTRON SPECTROSCOPY.HUBBARD, JOHN LEE. January 1982 (has links)
Transition metal-ligand interactions in several groups of closely related organometallic complexes are discussed from the results of both valence and core photoelectron experiments. Particular attention is given to the novel experimental aspects, including a charged particle oscillator He II source, sample introduction and containment, and data collection and spectral analysis procedures not normally associated with gas phase photo-electron spectroscopy. The application of the ionization experiments begins with a reassessment of the bonding in the group VIb metal hexacarbonyls. He I ionization data of unprecedented quality for the predominantly metal d t₂g level of Cr(CO)₆ and W(CO)₆ reveals for the first time the presence of metal-carbon vibrational fine structure. These positive ion M-C stretching frequencies are significantly reduced from neutral ground state values, giving direct evidence of the pi back-bonding nature of the t₂g level. The next chapter focuses on the comparison of the metal-nitrosyl interactions in the trans-X-W(CO)₄NO complexes to the isoelectronic/isostructural metal-carbonyl interactions in the X-Re(CO)₅ complexes (X = Cl,Br,I). A further comparison of carbonyl and nitrosyl bonding, as well as the first photoelectron assessment of metal-thionitrosyl bonding, is addressed in the next chapter by comparing the valence and core ionization data for CpCr(CO)₂NO and CpCr(CO)₂NS (Sp = η⁵-C₅H₅) to the data reported earlier for CpMn(CO)₃ and CpMn(CO)₂CS. The final chapter of the dissertation compares the electronic structure of the CpFe(CO)₂X complexes to their CpCr(NO)₂X analogs (X = Cl,Br,I,CH₃,CN). The essence of this work fully contrasts the Fe(CO)₂ and Cr(NO)₂ functional groups.
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Interfacial Electronic Structure of Dipolar Vanadyl Naphthalocyanine Thin FilmsSteele, Mary P. January 2011 (has links)
The studies presented in this work are aimed towards a better understanding of the fundamental physics of the electrode/organic molecule interface in both the ground and excited state manifolds. Systematic investigations of single systems using two-photon photoemission (TPPE) and ultraviolet photoelectron spectroscopy (UPS) were undertaken in order to assess the evolution of the electronic structure and molecular organization at the interface. The adsorbate molecule vanadyl naphthalocyanine (VONc) was used whose properties are well-suited to this purpose. Interfacial electronic states of thin films of VONc were studied with two different substrates: highly ordered pyrolytic graphite (HOPG) and Au(111).The substrate of HOPG is a surface which does not possess reactive dangling bonds and the electron density close to the Fermi edge is very low, permitting high resolution spectroscopic band analysis of VONc and revealing subtle changes to the electronic structure. From interfacial studies of this weakly interacting substrate/ adsorbate system, it is shown in this work that molecular electronic levels in both the ground and excited state manifolds can shift independently of the vacuum level. Further, electron transfer between close lying electron donor and acceptor energy levels may be influenced by energy level shifts caused by depolarization effects as a function of dipole density.The VONc/Au(111) interface is investigated in order to examine energy level alignment in a system with the additional complexity of molecule/substrate interactions. The electron rich Au(111) surface leads to a strong interface dipole upon addition of VONc. Joint experimental and computational data is presented showing that the underlying cause of this interface dipole is Pauli repulsion. Additionally, investigations of energy level alignment in the excited state manifold are presented and the possibility of quantum interference is discussed.The interfacial electronic structure is quite different among these two model systems. The interfacial alignment observed in the HOPG/VONc system was largely due to depolarization of the intrinsic molecular dipole as a function of density, whereas the Au(111)/VONc interface is dominated by interfacial Pauli repulsion interactions.
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The light activated alkylation of glycineKnowles, Haydn Scott January 2001 (has links)
No description available.
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