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.

No description available.

M.S. / Applied Physics / A noble gas ion laser with strong transitions in the 196-225 nm wavelength region has been developed for use as an illuminator in a photoelectron microscope. The laser is pulsed, and it can be operated at repetition rates up to 200 Hz to produce average output powers up to 5.0 mW at 219 nm. This is comparable to the output of the brightest available incoherent source, a Hg-Xe-Cd arc lamp that produces 2.6 mW of usable light in the 221-226 nm range. The laser has the advantage that it can be focused to produce much higher intensities than the arc lamp, and less total power is necessary. But the pulsed laser has a low duty cycle (~ 10[superscript minus 5]), and the corresponding peak powers (~ 300 watts) result in a space-charge-limited resolution of approximately 500 Å when the laser illuminates a phthalocyanine target. The magnitude of this aberration is proportional to beam current. Consequently, the resolution o can be improved to about 50 Å by decreasing the input power, or increasing the duty cycle, by a factor of 100-1000. Techniques for achieving such an improvement are suggested.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 88-97).

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: protein-DNA crosslinking; UV laser. Includes bibliographical references (p. 73-77).

No description available.

The effects of a newly mapped DNA repair-defective mutant, uvsI, on mutagen sensitivities and mutation were investigated. Results showed that uvsI differs for most of the investigated properties from other uvs mutants of A. nidulans which are known to belong to three different epistatic groups, "UvsF", "UvsC", and "UvsB". Most of these mutants are sterile and many of them alter mitotic recombination frequencies, while uvsI exhibits normal levels of meiotic and mitotic recombination. In addition, uvsI strains are not more sensitive than wild type to MMS (methyl methanesulfonate) to which all other uvs strains are sensitive. However, the uvsI mutant was found to be very sensitive to the killing effects of UV light and the chemical mutagen, 4-NQO (4-nitro-quinoline-N-oxide). In line with the distinct phenotype of uvsI, no epistatic interactions were found for this mutant with any members of the established three epistatic groups. The effects of uvsI on mutagenesis are highly specific and dependent on the mutational test systems. In the uvsI mutant, two types of forward mutation were not affected, but spontaneous and UV-induced reversion frequencies of choA1 and pabaA1 were significantly reduced. Specific effects were further demonstrated in reversion tests of various sC alleles originally isolated as selenate resistant mutants by treatment with EMS (ethyl methanesulfonate), which leads mainly to G:C to A:T transitions. After EMS treatment uvsI mutants showed highly reduced reversion frequencies for all these sC alleles (except one) compared to $uvs sp+$ strains. These results suggest that the uvsI mutation may be defective in AT to GC transition mutagenesis, while increasing transversion(s) from A:T base pairs. In contrast, uvsI affected the frequencies of spontaneous and UV-induced reversions for these sC alleles in a variety of ways. Thus, uvsI may well represent a fourth functional and epistatic group of DNA repair and possibly be involved in a minor mutagenic DN

No description available.

Cataract is the leading cause of blindness in the world and is defined by opacification of the normally transparent lens of the eye. The major avoidable cause of cataract is ultraviolet radiation (UVR), but no current strategies have been developed to prevent the onset of cataract. Apoptosis and internal and external antioxidant systems that inhibit apoptosis have been shown to play a significant role in cataractogenesis. The main purposes of this thesis were to study the time evolution of apoptosis, to develop the concept of a protection factor (PF), and to investigate the effect of thioltransferase (Grx1) and topical caffeine in UVR cataract development. Further, to elucidate pharmacokinetics and influence on iris diameter of topical caffeine. Sprague Dawley rats were exposed to UVR and TUNEL staining of the lens sections was analysed. Grx1+/+ and Grx1-/- mice were exposed to 5 sub-doses of UVR. Based on the difference of light scattering between Grx1+/+ and Grx1-/- mice, the concept of the PF was developed. Topical caffeine and a placebo were applied to the eyes of separate groups of Sprague Dawley rats that were exposed to sub-doses of UVR and protective effect was evaluated. Penetration of topical caffeine in Sprague Dawley rats to lens and blood was analysed by high performance liquid chromatography. Pupil diameter was measured in groups of unilaterally and bilaterally caffeine-treated ketamine/xylazine anesthetized Sprague Dawley rats. TUNEL-labeling peaked between 5 and 120 hours after UVR exposure. The PF of Grx1 was 1.3. Moreover, topically administered caffeine protected against UVR-induced cataract development with a PF of 1.23. Topical caffeine peaked at 30 min in the lens, increased up to 120 min in the blood and antagonized ketamine/xylazine-induced mydriasis. In conclusion, UVR induces apoptosis, which is evidenced by the peak of TUNEL-labeling at 24 hours after UVR exposure. The PF is an objective relative measure of protective properties that allows the comparison of different antioxidant systems and administered antioxidant substances. Grx1 and caffeine are protective against UVR-induced cataract. Topically administered caffeine penetrates to the lens and inhibits UVR-induced apoptosis. Additionally, a miotic effect of caffeine is described for the first time.