Ultraviolet (UV) radiation is a potent DNA-damaging agent and a known inducer of mutations and skin cancer. The increasing incidence of skin cancer has emphasised the importance of understanding the mechanistic processes involved in the interaction of UV radiation with DNA. One of the most significant photoproducts, induced by UV light, in the DNA molecule is the cis-syn cyclobutane pyrimidine dimer. These dimers, particularly the cytosinecontaining dimers, have been implicated in the mutagenic and carcinogenic effects of sunlight. Dimerisation of contiguous pyrimidine residues in DNA can result from direct irradiation (A = 295-310 nm) or photosensitised irradiation (A > 300 nm) by endogenous photosensitisers. Direct irradiation of DNA produces a wide range of photoproducts, whereas triplet photosensitisation of DNA by acetone produces only thymine, cytosine and cytosinethymine dimers. Thus, acetone photosensitisation of DNA can be used in the elucidation of the mechanistic processes involved in the formation of photoproducts from the direct irradiation of DNA. Calf thymus DNA was irradiated in the presence of acetone at wavelengths greater than 300 nm, using a high pressure mercury lamp. Experimental conditions investigated were irradiation time, acetone concentration and DNA concentration. Irradiated DNA samples were degraded by hot acid hydrolysis to excise the dimers. The yields of thymine and cytosine-thymine dimers were able to be quantitated by reverse phase high performance liquid chromatography with DV detection.Independent kinetic mechanisms were proposed for thymine and cytosine-thymine dimerisation in calf thymus DNA. Rate constants were assigned from experimentally determined values, values cited in literature and values calculated from Stern-Volmer steady state analysis of the proposed mechanisms. Verification of the proposed kinetic mechanisms was achieved by the comparison of experimental dimer yields with those calculated from the computer simulation of the proposed kinetic mechanism. The computer program CAKE (Computer Analysis of Kinetic Equations) was used to obtain the simulated data. Good agreement between the experimental and simulated data was taken as corroboration of the proposed kinetic mechanism. A section of this work was concerned with the application of spectroradiometry to determine the amount of light intensity absorbed by irradiated solutions. The modification, calibration and operation of a Macam SR 9010 spectroradiometer to achieve this aim is discussed. / Thesis (M.Sc.)-University of Natal, Durban, 1992.

Ultraviolet radiation (UVR) has been associated with various health outcomes, including skin cancers, vitamin D insufficiency, and multiple sclerosis. Measurement of UVR has been difficult, traditionally relying on subject recall. We investigated trends in satellite-derived UVB from 1978 to 2014 within the continental United States (US) to inform UVR exposure assessment and determine the potential magnitude of misclassification bias created by ignoring these trends. Monthly UVB data remotely sensed from various NASA satellites were used to investigate changes over time in the United States using linear regression with a harmonic function. Linear regression models for local geographic areas were used to make inferences across the entire study area using a global field significance test. Temporal trends were investigated across all years and separately for each satellite type due to documented differences in UVB estimation. UVB increased from 1978 to 2014 in 48% of local tests. The largest UVB increase was found in Western Nevada (0.145 kJ/m(2) per five-year increment), a total 30-year increase of 0.87 kJ/m(2). This largest change only represented 17% of total ambient exposure for an average January and 2% of an average July in Western Nevada. The observed trends represent cumulative UVB changes of less than a month, which are not relevant when attempting to estimate human exposure. The observation of small trends should be interpreted with caution due to measurement of satellite parameter inputs (ozone and climatological factors) that may impact derived satellite UVR nearly 20% compared to ground level sources. If the observed trends hold, satellite-derived UVB data may reasonably estimate ambient UVB exposures even for outcomes with long latency phases that predate the satellite record.

No description available.

Correlative and regression analyses of daily ERA-Interim reanalysis data for three separate solarmaximum periods confirm the existence of a temperature response to short-term (mainly ∼27 day) solarultraviolet variations at tropical latitudes in both the lower stratosphere and troposphere. The response,which occurs at a phase lag of 6–10 days after the solar forcing peak, consists of a warming in the lowerstratosphere, consistent with relative downwelling and a slowing of the mean meridional (Brewer-Dobson)circulation, and a cooling in the troposphere. The midtropospheric cooling response is most significant inthe tropical Pacific, especially under positive El Niño–Southern Oscillation conditions and may be relatedto a reduction in the number of Madden-Julian oscillation events that propagate eastward into the centralPacific following peaks in short-term solar forcing.

Die vorliegende Arbeit befasst sich mit der Untersuchung von Metall-Halbleiter-Metall ultravioletten Photodioden basierend auf Dünnschichten der weitbandlückigen Halbleitern Magnesiumzinkoxid (Mg,Zn)O und Galliumindiumoxid (In,Ga)2O3. Die Arbeit behandelt zwei inhaltliche Schwerpunkte. Der erste Schwerpunkt liegt auf Herstellung, Entwicklung und Charakterisierung der wellenlängenselektiven (Mg,Zn)O-Photodioden bei Erhaltung der Wurtzitstruktur in UVA und UVB Spektralbereichen. Dabei wurde eine integrierte optische Filterschicht mit einem höheren Mg-Gehalt verwendet, die einen Teil der von der Rückseite einfallende Strahlung absorbieren kann. Um die Selektivität der Absorptionskante und die Bandbreite des Detektoren abzustimmen, wurden unterschiedliche Kombinationen der Mg-Gehalte in den Schichten untersucht. Weiterhin wurde der Ansatz eines kontinuierlichen Kompositionsgradienten mittels großflächig gepulster Laserabscheidung genutzt, um monolithisch mehrkanalig schmalbandige Photodioden zu realisieren. Dadurch konnten die kontinuierliche Verschiebung der Absorptionskante von beiden Activ- und Filterschichten sowie die Photodetektion mit minimierter und einheitlicher spektraler Auflösung innerhalb von einem 2 inch im Durchmesser Wafer ermöglicht werden. Der zweite Schwerpunkt konzentriert sich auf die Untersuchung der wellenlängenselektiven Photodioden basierend auf Si-dotierten (In,Ga)2O3 Dünnschichten mittels der kontinuierlichen Kompositionsgradienten durch unterschiedliche Variation des Indium-Gehaltes. Die Absorptionskante der (In,Ga)2O3 Dünnschichten konnte von UVA bis zum UVC Spektralbereich abgestimmt werden. Die chemische und strukturelle Eigenschaften der Dünnschichten wurden mittels Kathodolumineszenzmikroskop, energiedispersive Röntgenspektroskopie and Röntgenbeugung studiert. Die elektrischen Eigenschaften der Schottky-Kontakte wurden mit hochpräzisen Strom-Spannungs-Messung bestimmt. Die Untersuchung der Absorptionskante sowie der Effzienz der Photodioden geschieht mittels spektralaufgelöster Photostrommessungen.

TAT peptide is one of the best-characterised cell penetrating peptides (CPPs) derived from the transactivator of transcription protein from the human immunodeficiency virus 1 (HIV-1). TAT peptide is able to cross the cell membrane and deliver various biomolecules into cells with low immunogenicity and no toxicity. However, the exact mechanism of internalization still remains a subject of controversy. Lamellar neutron scattering was used to determine the location of TAT peptide in the negativelycharged phospholipids bilayers. The results reveal two locations, one in the peripheral aqueous phase between the adjacent bilayers and the second one below the glycerol backbone region of the lipid bilayer. A concentrationindependent membrane thinning above a peptide concentration threshold (1mol%) and a contiguous transbilayer water channel at the largest peptide concentration (10mol%) were also found. This evidence led to the suggestion that the toroidal pore model might be involved in the transmembrane mechanism at high peptide concentration. Another set of neutron diffraction experiments examined the interaction between the TAT peptide and neutral phospholipids showed that TAT peptide preferentially intercalated into the hydrophobic core and the glycerol backbone region of the neutral lipid bilayer at the lowest peptide concentration investigated (0.1mol%), indicating that the insertion did not require negatively-charged phospholipids. There was also clear evidence for the concentration-dependent reorientation of TAT peptide. A plasmid containing the human copper-zinc SOD gene linked with the coding sequence for a 11-aa HIV-TAT peptide (pGEX-TAT-SOD, 513bp) was constructed and used to express a recombinant fusion protein in Escherichia coli strain BL21 (DE3). High-level expression of TAT-SOD soluble protein with a GST tag (44-kDa) was achieved under optimal expression conditions and a small-scale glutathione affinity column or large-scale ion-exchange chromatography used for its purification. The potential protective effect of TAT-SOD against UV-induced cell damage was studied on UVC-irradiated MDCK epithelial cells. Before any further clinical study, the UV full-length absorption of TAT-SOD protein was measured. The results showed the potential UV protective effect of TAT-SOD was not due to the physical absorption of UV irradiation. In a preclinical study with five healthy volunteers, the penetration of TAT-SOD through human stratum corneum on the inner upper arm was identified by the tape stripping and specific SOD activity analysis. Significant increases on SOD activity were found on the outer layers of stratum corneum in TAT-SOD treated group, compared to placebo treated control, indicating that the TAT peptide assisted SOD to penetrate into the human stratum corneum . In a clinical study with ten healthy volunteers, eight showed a significant increase of minimal erythema dose (MED) with TAT-SOD pre-treatment. The median blood flow value of ten subjects at the UVB-irradiated site decreased with TAT-SOD pretreatment. Taken together, this evidence showed that TATvi SOD did have a marked protective effect against UVB induced skin damage. In a second clinical study, five healthy volunteers were challenged with a series of UVB doses. Skin punch biopsies were taken from four test sites on the lower back for H&E and immunohistochemical staining analysis. UVB-induced apoptotic sunburn cell (SBC) formation, p53 up-regulation and thymine dimer formation in epidermis were not attenuated by pretreatment with TAT-SOD. These data suggest that transdermal superoxide scavenger TAT-SOD reduced the UVB-induced inflammation, but did not abrogate the direct DNA damage of UVB irradiation on the skin. However, the hope of TAT-SOD could reduce UVA indirect DNA damage remains.

III–V nitride quantum-confined structures embedded in nanowires (NWs), also known as quantum-disks-in-nanowires (Qdisks-in-NWs), have recently emerged as a new class of nanoscale materials exhibiting outstanding properties for optoelectronic devices and systems. It is promising for circumventing the technology limitation of existing planar epitaxy devices, which are bounded by the lattice-, crystal-structure-, and thermal- matching conditions. This work presents significant advances in the growth of good quality GaN, InGaN and AlGaN Qdisks-in-NWs based on careful optimization of the growth parameters, coupled with a meticulous layer structure and active region design. The NWs were grown, catalyst-free, using plasma assisted molecular beam epitaxy (PAMBE) on silicon (Si) substrates. A 2-step growth scheme was developed to achieve high areal density, dislocation free and vertically aligned NWs on Ti/Si substrates. Numerical modeling of the NWs structures, using the nextnano3 software, showed reduced polarization fields, and, in the presence of Qdisks, exhibited improved quantum-confinement; thus contributing to high carrier radiative-recombination rates. As a result, based on the growth and device structure optimization, the technologically challenging orange and yellow NWs light emitting devices (LEDs) targeting the ‘green-yellow’ gap were demonstrated on scalable, foundry compatible, and low-cost Ti coated Si substrates. The NWs work was also extended to LEDs emitting in the ultraviolet (UV) range with niche applications in environmental cleaning, UV-curing, medicine, and lighting. In this work, we used a Ti (100 nm) interlayer and Qdisks to achieve good quality AlGaN based UV-A (320 - 400 nm) device. To address the issue of UV-absorbing polymer, used in the planarization process, we developed a pendeo-epitaxy technique, for achieving an ultra-thin coalescence of the top p-GaN contact layer, for a self-planarized Qdisks-in-NWs UV-B (280 – 320 nm) LED grown on silicon. This process constitutes a significant advancement in simplifying the UV-B and UV-C fabrication process favoring light extraction. Addressing the issue of poor white light quality in the conventional blue laser diode (LD) and YAG:Ce3+ technology, a number of applications related investigations was conducted. Notably, the orange and yellow emitting InGaN/GaN Qdisks-in-NWs LEDs were implemented as an “active phosphor” to achieve intensity- and bandwidth-tunability for high color-quality solid-state lighting.

No description available.

No description available.

<p>Ultraviolet radiation (UV-R) is an environmental factor known to increase the risk of developing an irreversible opacification of the lens (cataract). Increased irradiance of UV-R to the earth because of depletion of stratospheric ozone is of current concern considering cataract formation. Detailed metabolic information from the cornea, lens and aqueous humour might give valuable knowledge on the biochcemical processes occurring in the eye after exposure to UV-R, and thereby a better understanding of the mechanisms by which UV-R induces cataractogenesis. The purpose of this thesis was to study metabolic effects of exposure to UV-R on the anterior part of the eye. Effects of UV-B (280-315 nm) and UV-A (315-400 nm) on the aqueous humour, cornea and the lens from animal models were investigated by ¹H nuclear magnetic resonance (NMR) spectroscopy. Since the lens is composed of functionally distinct anatomical compartments, with different metabolic activity, biochemical changes in various compartments of the lens were analyzed.</p><p>Application of NMR-based metabonomics was effective to analyze metabolic changes in the anterior part of the eye after exposure to UV-R. High-resolution (HR) magic angle spinning (MAS)¹H NMR spectroscopy provided high quality spectra from intact tissue of cornea and lens, and provided important information about metabolic alteration occurring in these tissues after exposure to UV-R. The results from this thesis show that in vivo UV-B radiation affects metabolism of the anterior compartments of the eye. Metabolic changes were observed in aqueous humour, cornea, lens and in the different compartments of the lens. The antioxidants, glutathione and ascorbate, several amino acids, high energetic phosphates, and compounds important for membrane building and osmoregulation were substantially altered after exposure to UV-B radiation. Several biochemical effects such as oxidation, membrane disruption, osmoregulatory problems, lipid peroxidation, problems with cellular signalling and impairment of growth and protein synthesis were suggested. After UV-A exposure, no observable metabolic alterations were found in the anterior part of the eye in the present animal models.</p>