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.

Inductively-Coupled Plasma Optical Emission Spectrometry (ICP-OES) is evaluated as a method for the selective determination of several non-metals which emit light in the Vacuum Ultraviolet (VUV) region of the spectrum. In this study, emphasis is placed on those elements which are totally unobservable with standard techniques or have very weak lines in the UV-VIS region of the spectrum. The sensitivity and accuracy of the apparatus and methods devised allows the determination of empirical formulas of gas chromatographic effluents. The results of this study indicate that the background emission of the ICP in the VUV is low level and nearly constant over the entire spectral region investigated (125 - 185 nm.). Promising analytical lines for oxygen, nitrogen, chlorine, bromine, and carbon are also observed in this region. A progression of four experimental configurations were constructed, employing a purged optical path and a unique coolant tube design. The last of these configurations has the capability of spatial resolution of individual portions of the discharge so that emission maps and profiles could be constructed. The results of the maps generated indicate that the region of highest emission intensity is always centered in the discharge. However, the vertical position of this region is found to be dependent upon r.f. power and argon flow rates. Detection limits in the low nanogram region are observed for each non-metal. The dynamic range for each element is in excess of 10⁴ and the selectivity ratio versus carbon is above 100 in each case. A method was developed for determining the elemental composition of the effluents of a GC. Using internal standards, the method is independent of the weight of each component eluted thus sampling errors are eliminated. The average relative errors in multielement analysis are 0.89%, 0.75%, 2.1%, 0.55%, and 0.64% for the percent carbon, oxygen, nitrogen, chlorine, and bromine, respectively.

Chronic exposure to solar UVA plays a causative role in skin photoaging and photocarcinogenesis. Guided by exploratory difference-in-gel-electrophoresis (DIGE)-proteomics, we identified the thiol-dependent cysteine-proteases cathepsin B and cathepsin L as novel UVA-targets undergoing photo-oxidative inactivation upstream of autophagic-lysosomal dysfunction. In human skin fibroblasts, exposure to noncytotoxic doses of chronic UVA (9.9 J/cm ², twice a week, 3 weeks) caused pronounced photooxidative impairment of cathepsin B and L enzymatic activity suppressed by antioxidant intervention. Western blot analysis revealed extensive 4-hydroxy-2-trans-nonenal (4-HNE) modification of cathepsin B in UVA-exposed fibroblasts. Consistent with lysosomal impairment, accumulation of cellular autofluorescent material colocalizing with lysosomes was observed by confocal fluorescence microscopy, and extensive deposition of lipofuscin was detectable by transmission electron microscopy (TEM). Lysosomal expansion was further evidenced by increased immunodetection of lysosomal associated membrane protein-1 (Lamp-1) and Lysotracker-based flow cytometric analysis. While lysosomal membrane integrity remained intact, autophagic blockade was suggested by accumulation of cellular protein levels of LC3-II and p62 (sequestosome 1) in UVA-exposed fibroblasts. Furthermore, UVA-exposure modulated transcriptional levels of p62 (sequestosome 1, SQSTM1), α-synuclein (SNCA), and transglutaminase-2 (TGM2). Strikingly, pharmacological cathepsin B/L inhibition using CA074Me mimicked UVA-induced accumulation of lipofuscin and autophagic-lysosomal proteins (Lamp-1, LC3-II, and p62), as well as changes at the transcriptional levels. In order to determine if UVA-induced lysosomal impairment requires single or dual inactivation of cathepsin B and/or L, we used a genetic approach (siRNA) to selectively downregulate enzymatic activity of these target cathepsins. Monitoring protein levels of Lamp-1, LC3-II, and p62, we observed that only dual genetic antagonism (targeting both CTSB and CTSL expression) could mimic UVA-induced autophagic-lysosomal alterations, whereas single knockdown (targeting CTSB or CTSL only) did not reproduce the UVA-induced phenotype. Similarly, TEM revealed massive accumulation of lipofuscin-containing lysosomal vesicles in fibroblasts only after CTSB/CTSL-double knockdown. Taken together, our data indicate for the first time that UVA impairs lysosomal function causing autophagic-lysosomal alterations downstream of cathepsin B/L enzymatic inactivation. This work provides evidence for a heretofore unrecognized 'double-hit' mechanism of UVA skin photodamage where primary photo-oxidative insult occurs simultaneously with impaired clearance of damaged molecules and organelles downstream of dual inactivation of cathepsin B and L.

Human peripheral blood monocytes provide a model for the in vivo exposure to, and immune functional damage caused by chronic UVB exposure at the skin surface. Retinoids and carotenoids are known immune function enhancers; they can also prevent cellular toxic product formation caused by UVB exposure. Application of these compounds in vitro may prevent functional damage to monocytes. Monocytes were exposed in vitro to UVB, then assayed for cytotoxic, phagocytic, and antigen presenting abilities. Phagocytic activity was protected from UVB damage by exposure to these compounds; cytotoxic activity was not altered by UVB exposure, but increased by retinoid or carotenoid exposure. Antigen presentation was not affected by either the UVB or these compounds. Protection of phagocytic function was not due to release of activating monokines or prostaglandins. Instead, the cell membrane antioxidant properties of these retinoids or carotenoids were the factors that protected the monocyte from phagocytic damage caused by UVB exposure.

No description available.

Protection against the harmful effects of ultraviolet radiation is of increasing importance due to the depletion of stratospheric ozone, which shields the earth from harmful UVC rays (in the range 200-280 nm) and some UVB rays (in the range 280-290 nm). In addition, as the skin is repeatedly exposed to solar radiation, the possibility exists that the incidence of skin cancer is enhanced. This has led to the increased use of commercial sunscreens, which apart from their benefits, also have undesirable effects such as photodegradation and skin penetration. We therefore studied the photodegradation of two sunscreen absorbers that are used in most sunscreen formulations. The combination of the UVB filter, 2-ethylhexyl-p-methoxycinnamate (EHMC), and the UVA filter, avobenzone (AVO), are commonly used in sunscreen products. These two filters are known to exhibit differing photostabilities in different media. The aim of this project was to investigate their photochemical behaviour in a polar and a non-polar solvent and to identify the UV-induced breakdown products. Methanol was chosen as the polar medium and cyclohexane as the non-polar medium. The sunscreen filters were irradiated either singly or in combination in the two solvents with wavelengths greater than 300 nm. The irradiated samples were analysed by UV-spectrophotometry, high performance liquid chromatography (HPLC) and gas chromatography (GC). The effects of direct irradiation with UVB and UVA light, quenchers and photosensitisers were also examined. EHMC is supplied commercially as the trans-isomer and upon irradiation photoisomerises, in both methanol and cyclohexane, to its cis-isomer. AVO is photostable in methanol but photodegrades in cyclohexane. This behaviour is also evident when mixtures of the two filters are irradiated. The loss in absorbance of both EHMC and AVO was monitored by UV-spectrophotometric analysis. Since EHMC does not absorb UV light at the wavelength of maximum absorbance of AVO, a method to quantify the amount of EHMC and AVO present in the mixture was devised. In order to identify the degradation products, HPLC and GC techniques were implemented. The photoproducts formed in the polar methanolic medium were separated and quantified by HPLC analysis. Gas chromatography with flame ionisation detection (GC-FID) was used to separate the photoproducts formed in the non-polar cyclohexane medium. Gas chromatography with mass-spectral detection (GC-MS) was used to identify the photoproducts formed upon irradiation of AVO and to show that UVA irradiation of AVO photosensitises the isomerisation of EHMC. The rate of a photochemical reaction depends upon a number of factors including the number of photons absorbed by sunscreen absorbers. Chemical actinometry was used to determine the number of photons absorbed by EHMC, AVO and the mixture of the two in methanol and cyclohexane. The number of photons absorbed by AVO in cyclohexane was used to determine the quantum yield for the photodegradation of AVO. We also determined the rate constants for EHMC photoisomerisation and AVO photodegradation. Finally, we investigated the effect of sunlight on commercial sunscreens containing EHMC and AVO. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

Typical CCD digital imaging sensors are insensitive to ultraviolet ( UV ) radiation by virtue of the very shallow ( 2 nm ) penetration depth in silicon. This warrants the use of a post-packaging coating to up-covert the UV radiation to longer wavelengths. In this thesis, A light-converting inorganic coating has been developed to improve the responsivity of gated CCD image sensors in the UV ( from 250 - 400 nm ). The coating consists of a plastic acrylic layer doped with inorganic phosphors. The coating is deposited using a spin-coater typically used by the IC fabrication industry. Inorganic phosphors were selected over organic phosphors since they are quite well established and are typically used to coat light bulbs, an application that requires a long lifetime. In contrast, organic phosphors rapidly degrade upon exposure to UV radiation. The parameters associated with the coating and coated sensor are presented here. They include coating conversion effciency, penetration depth, photostability; and coated sensor quantum effciency, contrast transfer function and photo-response non-uniformity. The coatings presented here are a viable, cost-effective alternative to other UV response CCD designs.

Cardiovascular disease (CVD) such as hypertension and stroke are serious illnesses that impact on the lives of millions all over the world, with 972 million (26% of the world’s population) suffering from hypertension in year 2000, and an estimated 1.56 billion to be affected by 2025. Hypertension, being one of the most common CVD is associated with the development of stroke, peripheral vascular diseases, myocardial infarction, renal failure as well as cardiac failure. Several studies have shown a seasonal correlation for both the systolic and diastolic blood pressure in mankind. A hypertension trial done by the Medical Research Council in the 1980s showed the average blood pressure being lower in summer than winter, and this difference was more significant in the elderly than the younger population. Other than seasonal variation, blood pressure (including hypertension prevalence) is also noted to correlate with latitude, being higher at places further away from the equator. Other cardiovascular related diseases such as stroke and acute coronary syndrome are also shown occur more frequently in winter. The morbidity and mortality of CVD could be due to various factors including diet, culture, race and social status, but within the United Kingdom, all cause mortality (with cerebral-vascular disease being the major one) correlates with latitude even after accounting for all known risk factors, with CVD risks highest in the north. We propose that this difference in cardiovascular mortality is caused by variations in ultraviolet exposure other than temperature. Known mechanisms of sunlight exposure that affect cardiovascular health include temperature and the ultraviolet B (UVB) mediated photolysis of 7-dehydrocholesterol in the skin to produce 1,25 dihydroxycholecalciferol (Vitamin D). UVB is however a potent skin carcinogen, and calculating risk-benefit ratios for exposure will be important. We believe that independently of vitamin D, nitric oxide plays an important role in blood pressure regulation and cardiovascular health, accounting for seasonal and latitude variation. In 1961, Furchgott demonstrated relaxation of rabbit aorta by irradiating them with ultraviolet light, and in later research he noted this effect is most significant in the ultraviolet A (UVA) spectrum. Recently, Mowbray showed a rich store of various nitro-species within human skin and Oplander showed a reduction of blood pressure in human after giving whole body UVA irradiation. We therefore hypothesize that independently of vitamin D, NO mediates the UVA induced beneficial effects on cardiovascular health. To support our hypothesis, in vivo as well as in vitro studies were conducted. We recruited a total of 63 healthy volunteers and monitored blood pressure, forearm blood flow as well as other cardiovascular parameters before and after UVA irradiation. Blood samples were also taken for the measurement of circulatory nitro-species. We have noted a significant reduction of blood pressure (from 84.5±1.76 to 81.33±1.37 mmHg) and increased forearm blood flow (1.95±0.28 to 2.94±0.47 mL/100mL of tissue/min) after UVA irradiation of human skin; simultaneously, we also noted a rise in circulatory nitrite (0.5±0.04 μM before irradiation to 0.72±0.04 μM) and a drop in circulatory nitrate (11.79±0.64 μM before irradiation and 8.99±0.4 μM). For us to further clarify the role of nitric oxide in different latitude, a monochromator machine that generates specific wavelength of light was been used to irradiate aqueous nitrite solution, and the total amount of nitric oxide release at different latitude was then calculated according to the irradiance of various wavelength across the globe. The results of our studies provide evidence suggesting that nitric oxide release induced by UVA irradiation of the skin can account for the difference in cardiovascular mortality and morbidity by latitude. The current public health advice of avoiding sun exposure to reduce the risk of developing skin cancer may need to be modified.

The intrinsic colors of Type Ia supernovae (SNe Ia) are important to understanding their use as cosmological standard candles. Understanding the effects of reddening and redshift on the observed colors are complicated and dependent on the intrinsic spectrum, the filter curves, and the wavelength dependence of reddening. We present ultraviolet and optical data of a growing sample of SNe Ia observed with the Ultraviolet/Optical Telescope on the Swift spacecraft and use this sample to re-examine the near-UV (NUV) colors of SNe Ia. We find that a small amount of reddening (E(B - V) = 0.2 mag) could account for the difference between groups designated as NUVblue and NUV-red, and a moderate amount of reddening (E(B - V) = 0.5 mag) could account for the whole NUVoptical differences. The reddening scenario, however, is inconsistent with the mid-UV colors and color evolution. The effect of redshift alone only accounts for part of the variation. Using a spectral template of SN2011fe, we can forward model the effects of redshift and reddening and directly compare those with the observed colors. We find that some SNe are consistent with reddened versions of SN2011fe, but most SNe Ia are much redder in the uvw1 - v color than SN2011fe reddened to the same b - v color. The absolute magnitudes show that two out of five NUV-blue SNe Ia are blue because their near-UV luminosity is high, and the other three are optically fainter. We also show that SN. 2011fe is not a "normal" SN Ia in the UV, but has colors placing it at the blue extreme of our sample.

Dissertation submitted in compliance with the requirements for Master's Degree in Technology: Electrical Engineering (Light Current), Technikon Natal, 2002. / M