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61.
Charlotte G. Monsour Abegail C. Tadle Bliss J. Tafolla-Aguirre Nidhi Lakshmanan Jin Hyeok Yoon Rhemrose B. Sabio Matthias Selke 《Photochemistry and photobiology》2023,99(2):672-679
We investigated the singlet oxygen quenching ability of several derivatives of trans-resveratrol which have been reported to have significant antioxidant ability, including photoprotective activity. We measured the total rate constants of singlet oxygen removal (kT) by the methylated resveratrol derivative 1,3-dimethoxy-5-[(E)-2-(4-methoxyphenyl)ethenyl]benzene, and the partially methylated resveratrol derivatives 4-((E)-2-(3,5-dimethoxyphenyl)ethenyl)phenol (pterostilbene), 5-[(E)-2-(4-methoxyphenyl)ethenyl]benzene-1,3-diol and (2R,3R)-3,5,7-trihydroxy-2-(3,4,5-trihydroxyphenyl)-2,3-dihydrochromen-4-one (dihydromyricetin). A protic solvent system results in higher kT values, except for the completely methylated derivative. We also investigated the ability of trans-resveratrol to directly act as a photosensitizer (rather than via secondary photoproducts resulting from other primary photochemical reactions) for the production of singlet oxygen but found that neither resveratrol nor any of its derivatives are able to do so. We then studied the chemical reactions of the methylated derivative with singlet oxygen. The main pathway consists of a [4 + 2] cycloaddition reaction involving the trans-double bond and the para-substituted benzene ring similar to what has been observed for trans-resveratrol. Unlike trans-resveratrol, the primary singlet oxygen product undergoes a second [4 + 2] cycloaddition with singlet oxygen leading to the formation of diendoperoxides. A second reactivity pathway for both trans-resveratrol and the methylated derivative leads to the formation of aldehydes via cleavage of a transient dioxetane. 相似文献
62.
The point of departure for this analysis is Bjørndal and Lindroos [2012], who developed an empirical bioeconomic model to analyze cooperative and noncooperative management of Northeast Atlantic cod. In their analysis, only constant strategies were analyzed for noncooperative games. In this paper, nonconstant strategies are considered. Moreover, the fishery in question is characterized by cooperative management. What may happen in the real world is that one nation breaks the cooperative agreement by fishing in excess of its quota. Often, it takes time for the other agent to detect this and respond. In this paper, we allow this kind of delayed response into a two‐agent noncooperative game so that, if country 2 exceeds its quota, there will be a time lag before this is detected by country 1; moreover, there may also be a delay until country 1 is able to respond. Results show that the outcome critically depends on the length of these two lags as well as initial conditions. 相似文献
63.
Kuo PS Vodopyanov KL Fejer MM Yu X Harris JS Bliss DF Weyburne D 《Optics letters》2007,32(18):2735-2737
We demonstrate an optical parametric oscillator (OPO) based on GaAs pumped with linearly polarized and circularly polarized light and show that the relative OPO thresholds agree with theoretical expectations. For the circularly polarized pump, the threshold was as low as for the [111]-linearly polarized pump case. The pump was also passed through a Lyot depolarizer to produce pseudo-depolarized light, and the OPO threshold in this case was only 22% higher than that for [001]-linearly polarized pump. 相似文献
64.
Sanford TW Jennings CA Rochau GA Rosenthal SE Sarkisov GS Sasorov PV Stygar WA Bennett LF Bliss DE Chittenden JP Cuneo ME Haines MG Leeper RJ Mock RC Nash TJ Peterson DL 《Physical review letters》2007,98(6):065003
Axial symmetry in x-ray radiation of wire-array z pinches is important for the creation of dynamic hohlraums used to compress inertial-confinement-fusion capsules. We present the first evidence that this symmetry is directly correlated with the magnitude of the negative radial electric field along the wire surface. This field (in turn) is inferred to control the initial energy deposition into the wire cores, as well as any current shorting to the return conductor. 相似文献
65.
L. W. Winkler E. Ekman A. Samyschlayewa W. Zimmermann K. Bodendorf N. Prileshajew L. Kofler F. Krämer P. HOrkheimer J. Reilly N. Noonan P. J. Drumm W. Peyer H. Iffinger S. Kroll W. J. Blackie J. F. Clevenger M. L. Pabst A. R. Bliss jun R. W. Morrison und E. O. Prather jun 《Fresenius' Journal of Analytical Chemistry》1935,102(3-4):141-146
Ohne Zusammenfassung 相似文献
66.
M. Snure J. Jiménez V. Hortelano S. Swider M. Mann V. Tassev C. Lynch D. Bliss 《Journal of Crystal Growth》2012,352(1):258-261
Orientation-patterned GaAs (OP-GaAs) has shown promise as an efficient frequency-shifted laser source over the range of 2–12 μm. In order to make OP-GaAs a viable source, efficiency and output power must be significantly increased, which requires minimizing major sources of loss. Low pressure HVPE has been adopted as the most suitable technique for regrowth of thick high quality GaAs layers on OP templates. We have explored process parameters in bulk and OP material to identify and control the sources of point defects, a key contributor to optical losses. Growth on OP templates with periodic [001] and [00?1] domains results in domain specific surface orientation, which should have inhomogeneous defect incorporation. Hall measurements, SIMS depth profiling, and cathodoluminescence (CL) were used to identify point defects in bulk and OP-GaAs. It was found that Si impurities are the primary source of donors, while VGa were identified as the primary source of acceptors. In order to study the incorporation of impurities in OP-GaAs samples, we intentionally doped samples with Si to increase CL and SIMS detectability. Spatially resolved CL and SIMS revealed regions with significant differences in the defect concentration, which can affect device output. 相似文献
67.
Buguo Wang Michael Suscavage David F. Bliss J. Jimenez 《Journal of Crystal Growth》2010,312(18):2507-2513
Macro-defects such as twins, inversion domains, crevices, and columnar growth occasionally appear in ammonothermally grown GaN crystals. Twinning mechanisms and parallel growth are proposed to explain the formation of these defects. As a polar crystal with wurtzite structure, GaN can have several different kinds of twins depending on the polarity arrangement of each individual twin. Inversion domains are formed in one of the twinning mechanisms. Parallel growth is used to explain the formation of pits on the nitrogen face and the columnar growth on the gallium face. Etching in hot H3PO4 is used to reveal the polarities and defects of GaN crystals when they are indistinguishable. Optical microscopy, scanning electron microscope, and cathodoluminescence are also employed to study these defects. In addition, seed quality, avoidance of macro-defect formation, and impurity effects are also discussed. 相似文献
68.
69.
The lasing outputs and lifetime constants are reported for the fluorinated azacoumarin dyes, AC2F, AC3F, and AC4F, in a variety of solvents. Most of the tests were made under both air and argon. The best results were obtained using solvents such as ethanol mixed with water or ethylene glycol under air. The dyes AC2F or AC4F gave results that were comparable or superior to those of AC3F. These dyes represent the longest lived of the presently known coumarin laser dyes when used with a solvent capable of hydrogen bonding. 相似文献
70.
Laser dye stability. Part 5 总被引:6,自引:0,他引:6
Aaron N. Fletcher Dan E. Bliss 《Applied Physics A: Materials Science & Processing》1978,16(3):289-295
Photodegradation parameters that relate bleaching and absorption at the lasing wavelength λl have been examined for over 30 different coumarin and quinolone laser dyes in a number of solvents. Quinolone dyes were found
to bleach faster than the coumarin dyes. The effect of chemical substituents was found to affect bleaching of the coumarin
dyes only to a small (20%) extent in ethanol. The major effect of chemical substituents was in the conversion of a dye to
products absorbing at λl. Effects of solvent, cover gas, and changes in fluorescent quantum yields are discussed. Of particular interest is the photodegradation
parameterA, the ratio of the percent absorption at λl to the total input energy per dm3. Combined with τ, the total input energy per dm3 required for a laser to reach half its original intensity, it was found thatAτ=1.2±0.9 for all of the dyes independent of dye concentration in all of the solvents tested. It appears that where bleaching
of the dye is only of the order of 10–20%, the absorption at λl is 1.2% when our dye laser has reached one-half of its initial output. It is consequently possible to estimate τ values of
new dyes by the use ofA terms through the relationshipA
1τ1=A
2τ2 where τ1 of Dye 1 has been calibrated in the same dye laser system. 相似文献