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81.
Richard G. Zepp P. F. Schlotzhauer M. S. Simmons G. C. Miller G. L. Baughman N. L. Wolfe 《Fresenius' Journal of Analytical Chemistry》1984,319(2):119-125
Summary Light-induced transformations of organic chemicals have been studied to provide kinetic results concerning the influence of sunlight on pollutant behavior in lakes and rivers. A review of these studies shows that the humus component of the dissolved organic matter in natural water affects aquatic photoreactions in two important ways: by attenuating sunlight and by sensitizing photoreactions. Studies of humus-sensitized photoreactions of furans, sulfides, dienes, nitroaromatic compounds, and other chemicals are discussed. Research concerning effects of aquatic particulates on pollutant photoreaction rates are reviewed. Suspended sediments mainly affect photolysis rates through light attenuation and scattering. Algae, diatoms, and bacteria accelerate light-induced transformations of anilines and phosphorothioate insecticides, suggesting that photobiological processes may play a significant role in the breakdown of certain pollutants in aquatic environments. Evidence is presented that nitrate, iron species, and peroxides may be responsible for sunlight-initiated free radical oxidations of pollutants in some natural waters.
Dynamik der Photoreaktionen von Verunreinigungen in der Hydrosphäre
Zusammenfassung Um kinetische Daten über den Einfluß von Sonnenlicht auf das Verhalten von Verunreinigungen in Seen und Flüssen zu erhalten, wurden licht-induzierte Umwandlungsreaktionen von organischen Chemikalien untersucht. Es ergab sich, daß die Humuskomponente der in natürlichen Wässern gelösten organischen Substanzen auf zwei Arten die aquatischen Photoreaktionen beeinflußt. durch Schwächung des Sonnenlichtes und durch Sensibilisierung der Photoreaktionen. Humus-sensibilisierte Photoreaktionen von Furanen, Sulfiden, Dienen, nitroaromatischen Verbindungen u.a. werden diskutiert. Ein Überblick wird gegeben über die Wirkung aquatischer Partikel auf die Geschwindigkeit der Photoreaktion von Verunreinigungen. Suspendierte Sedimente wirken hauptsächlich durch Lichtabschwächung und Streuung auf die Photolysegeschwindigkeit. Algen, Diatomeen und Bakterien beschleunigen lichtinduzierte Umwandlungen von Anilinen und Phosphorthioat-Insecticiden, was darauf hindeutet, daß photobiologische Prozesse eine bedeutende Rolle beim Abbau gewisser Verunreinigungen in aquatischer Umgebung spielen könnten. Es wird gezeigt, daß Nitrat, Eisenverbindungen und Peroxide für die Sonnenlicht-induzierte Oxidation freier Radikale von Verunreinigungen in natürlichen Wässern verantwortlich sein können.相似文献
82.
W. Hoffmann H. Breitzke C. T. Simmons K. Lüders G. Buntkowsky H. H. Limbach E. V. Antipov A. A. Gippius O. Loebich H. R. Khan M. Paranthaman J. R. Thompson 《Applied magnetic resonance》1995,8(1):57-65
Hg-oxide ceramic high temperature superconductors were studied by199Hg and63,65Cu NMR spectroscopy. Room temperature spectra, spin-spin and spin-lattice relaxation times of samples with different superconducting transition temperatures are presented. A spin-lattice relaxation time ofT 1=35 msec and a spin-spin relaxation time ofT 2=1.6 msec were found for the199Hg NMR. All samples exhibit similar characteristic powder spectra caused by an axially symmetric199Hg spin interaction. The isotropic value and the anisotropy of the tensor relative to solid HgCl2 as a standard substance is estimated. Furthermore, results of63,65Cu NMR measurements at a temperature of 4.2 K which exhibit a typical powder line shape (forI=3/2) are presented. 相似文献
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84.
A M Simmons J J Schwartz M Ferragamo 《The Journal of the Acoustical Society of America》1992,91(5):2831-2844
A population study of auditory nerve responses in the bullfrog, Rana catesbeiana, analyzed the relative contributions of spectral and temporal coding in representing a complex, species-specific communication signal at different stimulus intensities and in the presence of background noise. At stimulus levels of 70 and 80 dB SPL, levels which approximate that received during communication in the natural environment, average rate profiles plotted over fiber characteristic frequency do not reflect the detailed spectral fine structure of the synthetic call. Rate profiles do not change significantly in the presence of background noise. In ambient (no noise) and low noise conditions, both amphibian papilla and basilar papilla fibers phase lock strongly to the waveform periodicity (fundamental frequency) of the synthetic advertisement call. The higher harmonic spectral fine structure of the synthetic call is not accurately reflected in the timing of fiber firing, because firing is "captured" by the fundamental frequency. Only a small number of fibers synchronize preferentially to any harmonic in the call other than the first, and none synchronize to any higher than the third, even when fiber characteristic frequency is close to one of these higher harmonics. Background noise affects fiber temporal responses in two ways: It can reduce synchronization to the fundamental frequency, until fiber responses are masked; or it can shift synchronization from the fundamental to the second or third harmonic of the call. This second effect results in a preservation of temporal coding at high noise levels. These data suggest that bullfrog eighth nerve fibers extract the waveform periodicity of multiple-harmonic stimuli primarily by a temporal code. 相似文献
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88.
Optical pumping of the Hg(0) (6s (1)S(0) --> 6p (3)P(1)) transition at 253.7 nm (in air) leads to extremely fast energy transfer and strong laser-induced-fluorescence (LIF) from the Hg(0) (7s(3)S(1) --> 6p (3)P(2)) green transition at 546.2 nm, which is not directly populated by the laser. Ionization occurs simultaneously and becomes particularly strong at reduced background pressures. These observations are consistent with the existence of a multiphoton process followed by electron collisional excitation. Preliminary studies are made to evaluate these phenomena for detecting elemental airborne mercury by LIF and point monitoring with an ionization detector. Measured sensitivities of 2 and 10 parts in 10(9) (ppb), respectively, at 0.1-Torr air pressure are projected to increase to 1 x 10(-4) and 1 x 10(-5) ppb after relevant system optimization. 相似文献
89.
90.
Rucker VC Havenstrite KL Simmons BA Sickafoose SM Herr AE Shediac R 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7621-7625
Reactive ion etching (RIE) was used to pattern antibodies onto the surfaces of polymer substrates. A low pressure, inductively coupled oxygen plasma was used to anisotropically etch 25-30 mum deep features into poly(methyl methacrylate) (PMMA), Zeonex, and polycarbonate (PC). Scanning electron microscopy and contact angle measurements show that the resulting surfaces exhibit significant microroughness and enhanced hydrophilicity. Fourier transform infrared spectroscopy suggests that, in addition to enhanced surface area, chemical modifications may contribute to antibody immobilization. Polyclonal antibodies preferentially bind to the etched areas in RIE-patterned PMMA and Zeonex substrates but localize in unetched regions of RIE-patterned PC surfaces. Simple immunoassays were performed to demonstrate a potential application for RIE-modified polymer surfaces. Antibodies specific for the capture of fluorescently labeled cholera toxin, S. aureus enterotoxin B, and B. anthracis protective antigen were immobilized onto etched PMMA surfaces and shown to specifically capture their labeled antigen from solution. This work demonstrates a potentially useful fabrication methodology for constructing antibody microarrays on plastic substrates. 相似文献