Irradiamos amostras de DNA com luz UVA em diferentes condições para estudar os possíveis mecanismos envolvidos na indução de lesões de DNA por essa radiação. As lesões de DNA formadas após as irradiações foram quantificadas com enzimas de reparo de DNA que reconhecem e clivam os sítios contendo bases oxidadas e dímeros de pirimidina (CPDs). Complementando essas análises, foram realizados ensaios com anticorpos e HPLC-ED. NaCl e uma maior concentração de DNA são capazes de diminuir a indução de CPDs. Danos gerados por estresse oxidativo são inibidos na presença de azida de sódio e quelantes de metais, indicando o envolvimento de oxigênio singlete e reações de Fenton, na geração dessas lesões. Água deuterada e DNA mais concentrado aumentaram a indução de bases oxidadas. Quanto maior a quantidade de DNA irradiado, mais oxigênio singlete é formado, o que indica um possível mecanismo de fotossensibilização endógeno. / DNA samples were irradiated with UVA light in different conditions for studying the possible mechanisms involved in the induction of DNA lesions by this radiation. DNA lesions formed after irradiation were quantified with DNA repair enzymes, which recognize and cleave the sites containing oxidized bases and pyrimidine dimers (CPDs). Complementing these analyses, tests were performed with antibodies and HPLC-ED. NaCl and more concentrated DNA are capable of reducing the induction of CPDs. Damage caused by oxidative stress is inhibited in the presence of sodium azide and metal chelators, indicating the involvement of singlet oxygen and Fenton reactions, in the generation of these lesions. Deuterated water and more concentrated DNA increased the induction of oxidized bases. The bigger the amount of irradiated DNA, the more singlet oxygen is formed, which indicates a possible endogenous photosensitization mechanism.

<p>Exposure to ultraviolet radiation (UVR) has been shown to cause cellular damage in cyanobacteria. In response to UVR exposure, some cyanobacteria produce scytonemin, an indole-alkaloid sunscreen capable of absorbing long-wavelength UVA radiation. Previous genomic and transcriptomic analyses have determined that the production of scytonemin is controlled by a two-component regulatory system (TCRS), encoded by Npun_F1277 and Npun_F1278 in the cyanobacterium <i>Nostoc punctiforme </i>ATCC 29133. This TCRS is thought to not only regulate scytonemin biosynthesis, but also other responses to light and UVR stimuli. To better understand the functionality of the sensor kinase (SK) Npun_F1277 and to determine if it could activate alternative UVR protection pathways, the SK was expressed in <i>Escherichia coli.</i> The first objective of this study was to observe and quantify the level of fitness conferred to <i>E. coli</i> expressing Npun_F1277 from <i>N. punctiforme </i>(strain SKE) when exposed to white light, UVA, and UVB stress. Results from these experiments do not indicate that expression of the <i>N. punctiforme</i> SK conferred an advantage to <i>E. coli</i> under white light, UVA, or UVB stress based on growth alone. Therefore, the second objective was to study the expression of regulatory genes, such as response regulators, in <i>E. coli</i> that are homologs to those associated with the SK Npun_F1277 in <i>N. punctiforme </i>using quantitative-PCR. Expression of the selected genes was measured following exposure to white light and UVA after 30 and 60 minutes as well as UVB after 15 and 30 minutes. Comparison of SKE to empty-vector (EV) control cells exposed to the same stress showed that there were significant changes in the expression of important regulatory genes (e.g. <i>recA, spoT, relA</i>) in the SKE strain. Moreover, when comparing SKE cells exposed to the same conditions above to unstressed SKE cells, a similar result was seen for SKE cells exposed to UVA and UVB as was found in the studies comparing SKE to EV cells. These results suggest that the SK Npun_F1277 may play a role in multiple defense mechanisms of <i>N. punctiforme</i> in addition to initiation of the scytonemin biosynthesis pathway. </p>

Deep ultraviolet light emitting diodes (UV LEDs) are an important emerging technology for a number of applications such as water/air/surface disinfection, communications, and epoxy curing. However, as of yet, deep UV LEDs grown on sapphire substrates are neither efficient enough nor powerful enough to fully serve these and other potential applications. The majority of UV LEDs reported so far in the literature are grown on sapphire substrates and their design consists of AlGaN quantum wells (QWs) embedded in an AlGaN p-i-n junction with the n-type layer on the sapphire. These devices suffer from a high concentration of threading defects originating from the large lattice mismatch between the sapphire substrate and AlGaN alloys. Other issues include the poor doping efficiency of the n- and particularly the p-AlGaN alloys, the extraction of light through the sapphire substrate, and the heat dissipation through the thermally insulating sapphire substrate. These problems have historically limited the internal quantum efficiency (IQE), injection efficiency (IE), and light extraction efficiency (EE) of devices. As a means of addressing these efficiency and power challenges, I have contributed to the development of a novel inverted vertical deep UV LED design based on AlGaN grown on p-SiC substrates. Starting with a p-SiC substrate that serves as the p-type side of the p-i-n junction largely eliminates the necessity for the notoriously difficult p-type doping of AlGaN alloys, and allows for efficient heat dissipation through the highly thermally conductive SiC substrate. UV light absorption in the SiC substrate can be addressed by first growing p-type doped distributed Bragg reflectors (DBRs) on top of the substrate prior to the deposition of the active region of the device. A number of n-AlGaN films, AlGaN/AlGaN multiple quantum wells, and p-type doped AlGaN DBRs were grown by molecular beam epitaxy (MBE). These were characterized in situ by reflected high energy electron diffraction (RHEED) and ex situ by x-ray diffraction, scanning electron microscopy, atomic force microscopy, photoluminescence, and reflectivity. Using the primary elements of the proposed design, this research culminated in the MBE growth, fabrication, and characterization of prototype deep UV LED devices emitting below 300 nm.

Green sea turtles (Chelonia mydas) are an endangered species prone to a debilitating disease called fibropapillomatosis (FP). The aim of this study was to determine the influence of UV light on vitamin D levels and immune function in juvenile green sea turtles with FP. Phagocytosis, plasma vitamin D levels and viral load of ChHV5 were measured for FP- and FP+ turtles kept at the Gumbo Limbo Nature Center (GLNC) and for turtles caught at the St. Lucie power plant. Turtles kept at GLNC were housed in tanks exposed to varying amounts of UV light. Turtles brought into GLNC had lower phagocytosis compared to turtles at the St. Lucie power plant. Individuals exposed to greater UV light had higher plasma vitamin D levels and a more successful recovery. The results of this project will provide rehabilitation facilities with a mechanism to improve the recovery of animals with this disease. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

Oligotrophic (sub-)tropical oceans receive intense incident ultraviolet radiation (UV, 280–400 nm) and their water columns are highly transparent due to their nutrient-deficient state. This combination suggests a high potential for adverse effects on organisms, yet only few reports describe the UV exposures received in these waters and the associated impacts on marine biota. Here, we aimed to investigate the UV bio-optics of various open ocean locations and, using the Red Sea as a representative oligotrophic environment, we investigated the pattern of UV attenuation over a wide latitudinal range, quantified UV exposures in the water column, and determined impacts of UVB (280–320 nm) on indigenous phytoplankton and scleractinian corals. Globally, the lowest average downwelling diffuse attenuation coefficients (Kd) in the UV spectrum were recorded in the ultra-oligotrophic Indian Ocean Subtropical Gyre (Kd(313nm): 0.110 m-1) and South Pacific Gyre (Kd(313nm): 0.098 m-1), while aCDOM(λ) was ~1–2 orders of magnitude higher than ap(λ), In the Red Sea, UV attenuation mirrored the prevailing latitudinal gradient in nutrients, with the lowest and highest Kd(313) of 0.130 m-1 and 0.357 m-1 measured in the far north and in the south of the basin, respectively. Central Red Sea waters were most transparent to UV in late summer, i.e., a few weeks after incident irradiances and SSTs reach their annual maximum. Although, the projected increase of SST due to climate change means that extreme UV exposure and temperatures could coincide in the near future. This finding is of particular relevance since we found that Red Sea diatom species such as C. closterium are highly sensitive to UVB-induced photoinhibition and cell decay (LRD50: 11.4 kJ). Water temperature also governed the UVB sensitivity of Synechococcus sp., although this group exhibited a high resistance overall (LRD50: 57 kJ to non-detectable). For corals, we found that UVB-removal generally had little impact on the oxidative stress levels and photophysiology of S. pistillata and P. verrucosa from shallow waters, but considerably accelerated the acclimation of upward transplanted corals, which highlights that UVB is a crucial stressor that governs the photoacclimation capacity of Red Sea corals.

Recent discoveries in geospace science have necessitated the design of compact UV imaging instruments to make space-based observations from multiple vantage points. The miniaturized ultraviolet imager (MUVI) instrument from the Space Sciences Laboratory (SSL) at UC Berkeley is under development to facilitate such discoveries on a wider scale. This thesis documents the design, integration, and characterization of a vacuum compatible manipulator to calibrate the MUVI instrument inside the UV thermal vacuum chamber at SSL. Precision linear and rotation stages were implemented with custom mounting plates to achieve four degrees of freedom. Optical components were installed to imitate the MUVI instrument for testing purposes. A customized PCB was fabricated to control the stages and receive position feedback data. A Graphical User Interface was programmed and utilized to position the manipulator during experimental validation. Field of View sweeps were conducted using visible light and a monochromatic CMOS sensor to track the coordinates of a laser's centroid. An analytical model of the optics assembly was developed and later refined from the experimental results. Using this model, the translation stages successfully compensated for optical misalignments. Analysis of the performance data showed the pointing resolution of the manipulator was less than 1 arcmin, which satisfied the calibration requirement for the MUVI imager.

No description available.

In this dissertation, the design and fabrication of deep-ultraviolet photodetectors were investigated based on gallium oxide and its alloys, through the heterogeneous integration with metallic and other inorganic materials. The crystallographic properties of oxide films grown directly and indirectly on silicon, magnesium oxide, and sapphire are examined, and the challenges that hinder the realization of efficient and reliable deep-ultraviolet photodetectors are described. In recent years, single-crystalline heterojunction photodiodes employing beta-polymorph gallium oxide thin films as the main absorption layers have been studied. However, reports in the literature generally lack a thorough examination of epitaxial growth processes of high-quality single-crystalline beta-polymorph gallium oxide thin films on metals, such as transition metal nitrides. My research was initiated by demonstrating an ultraviolet-C photodetector based on an amorphous aluminum gallium oxide photoconductive layer grown directly on (100)-oriented silicon. The solar-blind photodetector exhibited a peak spectral responsivity of 1.17 A/W. This is the first reported gallium oxide-based photodetector to have been grown and fabricated directly on silicon. The growth of high-quality monoclinic crystals on cubic silicon is a challenging process, which is largely due to the large lattice mismatch that compromises the crystal quality of the oxide layer, and leads to the degradation of device performance. This issue was addressed by growing the material on substrates with metal nitride templates, which resulted in improvements to the oxide crystal quality. Consequently, high optical gain ultraviolet-C photodetectors were fabricated based on a beta-polymorph gallium oxide photoconductive layer grown on magnesium oxide and silicon substrates with titanium nitride templates. The enhanced solar-blind photodetectors exhibited peak spectral responsivity levels as high as 276 A/W. Moreover, thin polymorphic gallium oxide films were grown on c-plane sapphire using pulsed laser deposition for the first time. The stacked thin films, namely epsilon- and beta-polymorph gallium oxide, were sequentially grown under the same conditions. X-ray diffraction measurements and transmission electron microscopy micrographs confirmed a heteroepitaxially grown beta-polymorph gallium oxide on a heterogeneously nucleated epsilon-polymorph gallium oxide polymorphic heterostructure on c-plane sapphire, which had rocking-curve widths of 1.4° (β-Ga2O3 (−603)) and 0.6° (ε-Ga2O3 (006)).

There are many potential areas for the utilization of GaN-based nitride materials, including ultraviolet photodetectors. Ultraviolet photodetectors are used in the military for missile plume detection and space communications. Medically, ultraviolet photodiodes are used in monitoring skin cancer. Schottky barrier metal-semiconductor contacts are choice devices for the manufacture of ultraviolet photodiodes due to higher short wavelength sensitivity and fast response. They also require simple fabrication technology; suffer lower breakdown voltages, and record larger leakage currents at lower voltages as compared to p-n structures of the same semiconductor material. Thus the formation of a Schottky contact with high barrier height, low leakage current, and good thermal stability in order to withstand high temperature processing and operation are some of the most important factors in improving the performance of Schottky barrier photodiodes to be used for ultraviolet detection. The first stage of this study was to establish a chemical cleaning and etching technique. It was found that KOH was suitable in reducing C from the surface and that (NH4)2S further reduced the surface oxides. The next phase of the work was to select a metal that will allow UV light to pass through at a high transmission percentage: a combination of annealed Ni/Au was found to be ideal. The transmission percentage of this alloy was found to be above 80%. The next phase was the fabrication of Ni/Au Schottky barrier diodes on GaN to study the electrical characteristics of the diodes. Electrical characterization of the diodes showed that the dominant current transport mechanism was thermionic emission, masked by the effects of series resistance, which resulted from the condition of the GaN surface. Finally, we fabricated GaN UV photodiodes and characterized them in the optoelectronic station designed and produced during this research. Device responsivity as high as 31.8 mA/W for GaN and 3.8 mA/W for AlGaN were recorded. The calculated quantum efficiencies of the photodiodes were 11 % for GaN and 1.7 % for AlGaN respectively. / Thesis (PhD)--University of Pretoria, 2010. / Physics / unrestricted

Visual features of the wing colour, with special reference to the intensity of UV reflectance of the Green-veined White (Pieris napi) were investigated. Several studies revealed that only females of Pieris napi possess UV reflectance on dorsal wing surface. Based on UV sensitive photography, we analysed correlation between environmental conditions (productivity and climate) and 3 patches on forewing of 347 specimens of P. napi from Palaearctic region. Males significantly differ in level of intensity of UV reflectance from females. UV intensity in females is 25% higher in comparison with males. This phenomenon is explained by different deposition of wing pterins. Further, environment significantly affects UV intensity on the forewings of females, but not males. Moreover, we accomplished the analysis of fluctuating asymmetry. First we subjected the environmental variables to PCA. In females, the first PCA axis (temperature seasonality, temperature annual range and longitude) significantly correlated with UV intensity. In males, the second PCA axis (latitude and altitude) was significantly correlated with FA. Additionally, we performed Two-Block Partial Least- Squares (PLS) analysis to assess co-variation between intraspecific shape...