Thesis (Ph. D.)--Institute of Paper Chemistry, 1941. / Bibliography: leaves 91-93.

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [51]-54).

The "DNA Damage Hypothesis" pertaining to the evolution of sex was tested using Hydra littoralis. DNA damage was produced by irradiating whole live hydra with ultraviolet light. A curve of uv light dosage vs. survival was constructed. Estimations of threshold fluence and LD50 were made from the survival curve. In four separate experiments, using various combinations of environmental temperatures, uv doses, and number of doses, frequencies of asexual and sexual reproduction were observed and compared. The hydra that received uv treatments did not show an increase in the consequent amount of sexual reproduction, and actually showed a decrease. An increase in the amount of sexual reproduction following DNA damage is predicted by the DNA damage hypothesis, therefore these results do not support this theory. The data was also used to make contradictory observations regarding the "stress hypothesis" for the occurrence of sexual reproduction in hydra.

The effect of increased stratospheric dust on the polarization and intensity of sunlight scattered by the terrestrial atmosphere in the spectral region near the ultraviolet transmission cutoff is examined. Particular interest is given to radiation reflected to space or transmitted to the surface in the direction perpendicular to the incident solar beam in a plane containing the sun and the local vertical. Theoretical results are presented from radiative transfer calculations using a simple single scattering model and a four layer model in which ground reflection and multiple scattering were treated. Results show that the polarization state of transmitted radiation of .2975 μ for an incident solar zenith angle of 70° is sensitive to dust loading above 50 mb. The depolarization caused by a moderate increase in stratospheric dust loading is found to be roughly comparable to that caused by ground reflection and tropospheric aerosol. The polarization of light reflected to space is found to be very sensitive to high altitude dust scattering while being much less sensitive to other sources of depolarization. Results show that increasing the amount of stratospheric dust can cause either an increase or a decrease in the daily dosage of ultraviolet radiation at the surface, depending on the altitude profile of the dust, the latitude and the season. Preliminary experimental results or polarization monitoring by a ground-based instrument are presented and discussed. Sky light polarization ratios in the direction normal to the solar beam at .2975 μ and .300 μ based on data collected in the spring and summer of 1980 from the roof of the Physics-Atmospheric Sciences building on the campus of The University of Arizona are presented and discussed. The stratospheric dust problem is considered in terms of stratospheric aerosol enhancement resulting from volcanic activity.

Stratospheric ozone plays an important role in absorbing ultraviolet radiation. The well-known depletion of the ozone layer has raised several concerns in terms of an expected increase in surface ultraviolet radiation. South Africa, situated in the southern mid-latitude regions, has experienced a general downward trend in total column ozone since 1979, As a result of this negative trend in total column ozone, the ultraviolet flux at the earth's surface is expected to increase. Excessive exposure to ultraviolet radiation is known to have acute and chronic effects on human health, including erythema and skin cancer. Numerous studies have acknowledged a relationship between childhood ultraviolet radiation exposure and the risk of contracting skin cancer, namely malignant melanoma, during adulthood. The aim of this study is to investigate the ultraviolet radiation dose and exposure of children and adolescents in Durban, South Africa. Polysulphone film badges were used to quantify the daily erythemal ultraviolet radiation dose of 30 individuals of varying ages and skin types, engaged in different activities, over a one-week period during summer. The results highlight the diversity of childrens' and adolescents' behavioural patterns, with behaviour being found to play an important role in determining an individual's ultraviolet radiation dose. The mean daily erythemal ultraviolet radiation dose of the children and adolescents was 1.03 MED units with a median of 0.57 MED units and a 95% range of 0.22 - 7.22 MED units. The most striking finding was that the median value was below the critical value of 1 MED unit. An explanation for the unexpectedly low erythemal ultraviolet radiation doses recorded in this study was sought in the prevailing climatic conditions. Ambient erythemal ultraviolet radiation levels recorded during the study period were high, ranging between 20.57 - 30.60 MED units. However, high temperatures (>27°C), coupled with high humidity values, may have encouraged the children and adolescents to avoid direct sunlight and find shade while outdoors. The daily erythemal ultraviolet radiation doses of the children and adolescents were also compared to the ambient erythemal ultraviolet radiation levels received on a horizontal surface by a YES UVB-l pyranometer located at the University of Natal (Durban). Children and adolescents in Durban received approximately 4.58% of the total daily ambient erythemal ultraviolet radiation incident upon a horizontal surface. This was found to be similar to a study (5 - 6%) conducted by Diffey et al. (1996) in England, as well as a study (4 - 8%) by Gies et al. (1998) in Brisbane, Australia. The personal ultraviolet radiation exposure journals of the children and adolescents were used to determine the timing of exposures, duration of exposures and nature of outdoor activities and these were then related to their daily ultraviolet radiation doses. Of all the factors considered, the nature of an individual's activity was found to have the strongest influence in determining their ultraviolet radiation dose. An activity model was derived in order to investigate the effect of activity on ultraviolet radiation dose, where three activity factors, namely swimming, walking and tennis, were calculated for a South African context and compared with those from previous international studies. It was found that the activity factors derived in this study were similar to Holman et al. (1983) and Herlihy et al. (1994) and may be used in an activity model to estimate individual erythemal ultraviolet radiation dose for a particular activity. The value of this innovative activity model lies in its ability to predict individual ultraviolet radiation dose and this may help to emphasise the importance of responsible outdoor behaviour. A mannequin was used to quantify the anatomical distribution of erythemal ultraviolet radiation under clear sky and overcast conditions. It was found that the vertex of the head and shoulders received the highest erythemal ultraviolet radiation doses under both conditions. This was then related to the erythemal ultraviolet radiation doses of the children and adolescents as recorded by the polysulphone film badges in order to identify anatomic sites susceptible to high erythemal ultraviolet radiation doses. Behaviour alternatives and ultraviolet radiation protective mechanisms were discussed and recommendations made for children and adolescents residing in Durban. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

No description available.

Ultraviolet radiation causes an alteration in DNA by modifying neighboring thymine bases resulting in the formation of a dimer. These dimers block the processes of transcription and translation and ultimately no protein is synthesized and the cell dies. However, DNA repair mechanisms correct this damage by excising the dimer from the DNA strand and inserting replacement bases which are joined to the original strand by DNA ligase. This allows transcription to resume and ultimately protein synthesis to take place.This research focused on determining the DNA damage and subsequent repair levels in a connective tissue disorder, namely Marfan syndrome. This information is important in understanding the clinical expression and management of life threatening conditions in Marfan syndrome individuals.Preliminary results indicate that at 20-25J/m2 UV dose (254nm) Marfan syndrome skin cells show a mean reduced survival value of 12% compared to normal human skin cells. Gel electrophoresis indicates a reduced DNA repair level 24h post UV irradiation for Marfan syndrome skin cells compared to normal human skin cells. These results suggest Marfan syndrome skin cells have reduced survival and DNA repair levels compared to normal human skin cells. / Department of Biology

Messenger ribonucleic acid (mRNA) turns out to be an increasingly important molecule in forensic analysis of biological samples. Because of the specific role of mRNA in all living cells to transfer genetic information from DNA to proteins, mRNA is able to provide cell-specific information and regulate control of gene expression. mRNA analysis performed on an extracted mRNA sample isolated from a biological stain of a crime scene can be used to identify the nature of the tissue(s) comprising the stain. In this research, the effects of a couple of mRNA storage conditions such as cold temperature and ultraviolet light exposure on mRNA integrity from human saliva have been evaluated. Human saliva samples have been sampled and exposed to UV light and freezing temperature (-20°C) for varying lengths of time. Extracted mRNA from each sample has been quantified spectrophotometrically and subjected to real time RT-PCR to evaluate stability and integrity of one of the saliva marker transcripts, KRT13 mRNA, of treated samples compared to untreated samples. The results of this study indicated that UV light and freezing temperature don’t have a significant effect on the integrity of KRT13 mRNA. There is also no apparent correlation between Ct values of treated samples and treating intervals. This research holds important implications for the use of mRNA for applications in forensic science, an area which has not been researched extensively. / Department of Biology

In young coho salmon (Oncorhynchus kisutch), UVR is known to elicit exposure avoidance behavior and suppress aggressiveness. The latter observation has been attributed to the indirect effect of fish seeking shade from solar UVR under rocks consequently losing sight of prospective rivals. The present study quantified the direct impacts of UVR on agonistic (Strikes, Chases, Approaches) and feeding behaviors in juvenile coho salmon by furnishing outdoor aquaria with structural elements (i.e., inverted funnels) that provided habitat complexity without generating shade during midday experimental trials. Frequencies and durations of behaviors were compared between conditions that excluded or included natural solar UVR. Results indicated that hostile pursuits (Chases) persisted significantly longer under UVR illumination. Likewise, the frequencies of more belligerent interactions (Strikes, Chases) tended to increase under UVR, while milder territorial assertions (Approaches) and foraging (Feeding Efforts) tended to decline. However, none of the latter four outcomes tested as significant.

UV radiation can cause harmful effects to human skin, including premature skin ageing and skin cancer. Historically, sunscreens were developed to filter out UVB (290 nm-320 nm), but now the importance of UVA (320 nm-400 nm) sunscreens is realised. The most common UVA sunscreens are based on dibenzoylmethane (1,3-diphenyl propan-l,3-dione, DBM), of which the most common is Parsol 1789 (4'- methoxy 4'-tertiarybutyl DBM). The photochemistry of these materials has, however, been poorly understood. In this work the photophysics and photochemistry of DBM, Parsol 1789, Parsol DAM and ditertiarybutyl DBM have been studied, along with the respective 0-methylated and C-methylated compounds of DBM and Parsol 1789.DBMs exist primarily as an intra-molecularly bonded enol, which absorbs strongly at λ≈340 nm due to a π,π* transition. The absorption spectra of DBMs also exhibit a smaller peak at λ≈250 nm, due to an n,π* transition of the diketone content. At low temperature the main absorption band of DBMs shifts to longer wavelengths and vibrational structure can be observed. The enol form of DBMs fluorescence at low temperature, (v(_0)’→v’’(_0) at λ≈385 nm), and phosphorescence can be observed from both the diketone (λ(_em)≈495 nm,) and enol forms (λ(_em)≈425 nm). Thus the triplet energies of the diketones and enols of the DBMs studied have been measured. 0-methylated DBMs do not possess an intra-molecular H-bond, and the π,π* absorption band falls to lower wavelengths than for chelated DBMs. C-methylated DBMs exist as a diketone structure, and display photophysics typical of an aromatic ketone. It has been suggested that the main process on irradiation of DBM is the formation of a short-lived non-chelated enol, however no direct evidence as to the structure of this species is reported in the literature. Formation of the diketone form of DBM on prolonged irradiation in acetonitrile solution has also been reported, and in this work the quantum yield of this process has been measured; ɸ≈0.01 ± 0.004. In this work, direct (low temperature) IR spectroscopic evidence is presented to prove that the short-lived species produced on irradiation is indeed a non-chelated enol. The infra-red studies also suggest that the non-chelated enol form of DBM form complexes with polar solvents, as has been proposed in the literature. Quantum yields of non-chelated enol formation in cyclohexane at room temperature have been measured to be approximately ɸ=0.5 + 0.07. This work indicates that the rate of transient decay is enhanced by the interaction of the transient molecules with chelated enol molecules or other transient molecules. IR studies of low temperature transient formation confirm the interaction of transient molecules by the observation of inter-molecular hydrogen-bonding. By comparison with the E and Z isomers of 0-methylated DBM it is suggested that at low temperature DBM initially forms a Z-cis non-hydrogen bonded enol, which then converts to an E-trans non-hydrogen bonded enol with further irradiation. The kinetics and the temperature variation of the enol recovery support the theory that there is more than one species formed. The photochemistry of DBM in emulsions has also been studied in this work. It has been shown that the photochemistry occurring on irradiation is similar to that observed in solutions. This indicates that simple solutions are a good model for actual sunscreen formulations. Singlet oxygen is a highly reactive species capable of causing serious biological damage, however this work shows that DBM sunscreens generate singlet oxygen by photosensitisation, with quantum yields ɸ∆≈0.005-0.01. It has also been shown that the lifetime of the excited state of DBM involved in singlet oxygen production is very short, approximately τ <1 µs.