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61.
Heteronuclear magnetic double resonance experiments are used to show that 1J(7Li—13C) is positive in methyllithium tetramer. This is consistent with dominance of the coupling mechanism by the Fermi contact interaction. 相似文献
62.
63.
A UV indicator/dosimeter based on benzyl viologen (BV2+) encapsulated in polyvinyl alcohol (PVA) is described. Upon exposure to UV light, the BV2+/PVA film turns a striking purple colour due to the formation of the cation radical, BV•+. The usual oxygen sensitivity of BV•+ is significantly reduced due to the very low oxygen permeability of the encapsulating polymer, PVA. Exposure of a typical
BV2+/PVA film, for a set amount of time, to UVB light with different UV indices produces different levels of BV•+, as measured by the absorbance of the film at 550 nm. A plot of the change in absorbance at this wavelength, ΔAbs(550), as
a function of UV index, UVI, produces a linear calibration curve which allows the film to be used as a UVB indicator, and
a similar procedure could be employed to allow it to be used as a solar UVI indicator. A typical BV2+/PVA film generates a significant, semi-permanent (stable for >24 h) saturated purple colour (absorbance ~0.8–0.9) upon exposure
to sunlight equivalent to a minimal erythemal dose associated with Caucasian skin, i.e. skin type II. The current drawbacks
of the film and the possible future use of the BV2+/PVA film as a personal solar UV dosimeter for all skin types are briefly discussed.
相似文献
64.
Thomas Borrmann James H. Johnston Andrew J. McFarlane Michael J. Richardson Sean J. OConnor 《Journal of colloid and interface science》2009,339(1):175-182
Nano-structured calcium silicate hydrate can physisorb or chemisorb iodine, making it interesting for medical or materials science applications, where a slow, controlled release of iodine is desired. It was found that iodine can be sorbed and released by applying the elemental halogen in solution, either as a gas or as a solid. At ambient temperatures the sorption and desorption process is quantitative and physical, meaning that the same amount of iodine is taken up and released. At temperatures above 32.5 °C (305.7 K) iodine reacts with the calcium silicate hydrate forming a complex, which is stable above the sublimation temperature of iodine. The formation energy for the iodine calcium silicate hydrate complex was established to be 41.8 ± 0.8 kJ mol−1 by calorimetry and the nature of the complex was investigated using X-ray photoelectron spectroscopy. 相似文献
65.
The purpose of this study was to take a critical look at a voice therapy technique known as the yawn-sigh. The voiced sigh as an approach in voice therapy has had increased use in recent years, particularly with problems of vocal hyperfunction. In this study, the physiology of the yawn-sigh was studied with video nasoendoscopy in eight normal subjects; their taped voices were also studied acoustically for possible fundamental frequency and formant changes in producing selected vowels under normal and sigh conditions. Although each subject was given a model by the examiner of a yawn-sigh, one of the eight subjects could not produce a true yawn-sigh. Endoscopic findings for seven of the eight subjects performing the yawn-sigh demonstrated retracted elevation of the tongue, a lower positioning of the larynx, and a widened pharynx. Acoustic analyses for the seven subjects producing the sigh found a marked lowering of the second and third formants. Implications for using the yawn-sigh in voice therapy are given, such as using a modified “silent” yawn-sigh, as an easy method for producing greater vocal tract relaxation. 相似文献
66.
Mathiazhagan C Molzon WR Cousins RD Konigsberg J Kubic J Melese P Rubin P Slater WE Wagner D Hart GW Kinnison WW Lee DM McKee RJ Milner EC Sanders GH Ziock HJ Arisaka K Knibbe P Urheim J Axelrod S Biery KA Irwin GM Lang K Margulies J Ouimette DA Ritchie JL Trang QH Wojcicki SG Auerbach LB Buchholz P Highland VL McFarlane WK Sivertz M Chapman MD Eckhause M Ginkel JF Hancock AD Joyce D Kane JR Kenney CJ Vulcan WF Welsh RE Whyley RJ Winter RG 《Physical review letters》1989,63(20):2185-2188
67.
Robblee JH Messinger J Cinco RM McFarlane KL Fernandez C Pizarro SA Sauer K Yachandra VK 《Journal of the American Chemical Society》2002,124(25):7459-7471
A key component required for an understanding of the mechanism of the evolution of molecular oxygen by the photosynthetic oxygen-evolving complex (OEC) in photosystem II (PS II) is the knowledge of the structures of the Mn cluster in the OEC in each of its intermediate redox states, or S-states. In this paper, we report the first detailed structural characterization using Mn extended X-ray absorption fine structure (EXAFS) spectroscopy of the Mn cluster of the OEC in the S(0) state, which exists immediately after the release of molecular oxygen. On the basis of the EXAFS spectroscopic results, the most likely interpretation is that one of the di-mu-oxo-bridged Mn-Mn moieties in the OEC has increased in distance from 2.7 A in the dark-stable S(1) state to 2.85 A in the S(0) state. Furthermore, curve fitting of the distance heterogeneity present in the EXAFS data from the S(0) state leads to the intriguing possibility that three di-mu-oxo-bridged Mn-Mn moieties may exist in the OEC instead of the two di-mu-oxo-bridged Mn-Mn moieties that are widely used in proposed structural models for the OEC. This possibility is developed using novel structural models for the Mn cluster in the OEC which are consistent with the structural information available from EXAFS and the recent X-ray crystallographic structure of PS II at 3.8 A resolution. 相似文献
68.
Heinson AP Horvath J Mathiazhagan C Molzon WR Arisaka K Cousins RD Kaarsberg T Konigsberg J Rubin P Slater WE Wagner DL Kinnison WW Lee DM McKee RJ Milner EC Sanders GH Ziock HJ Knibbe P Urheim J Biery KA Diwan MV Irwin GM Lang K Margulies J Ouimette DA Schwartz A Wojcicki SG Auerbach LB Belz J Buchholz P Highland VL McFarlane WK Sivertz M Ritchie JL Yamashita A Chapman MD Eckhause M Ginkel JF Hancock AD Kane JR Kenney CJ Kuang Y Vulcan WF Welsh RE Whyley RJ Winter RG 《Physical review D: Particles and fields》1991,44(1):R1-R5
69.
Robert J. Pirkle Christopher C. Davis Ross A. McFarlane 《Chemical physics letters》1975,36(3):305-307
We have compared the performance of CF3I, CD3I, and CH3I in an atomic iodine photodissociation laser over the pressure range 1–200 torr. At pressures below 5 torr, CD3I produces larger energy outputs, while above 5 torr CF3I gives superior performance. The crossing of the laser energy output versus pressure curves is explained on the basis of collisional quenching of I(2P)(≡I*) by undissociated alkyl iodide. 相似文献
70.
Heinson AP Horvath J Knibbe P Mathiazhagan C Molzon WR Urheim J Arisaka K Cousins RD Kaarsberg T Konigsberg J Melese P Rubin P Slater WE Wagner D Hart GW Kinnison WW Lee DM McKee RJ Milner EC Sanders GH Ziock HJ Axelrod S Biery KA Diwan M Irwin GM Lang K Margulies J Ouimette DA Schwartz AJ Wojcicki SG Auerbach LB Belz J Buchholz P Guss C Highland VL Kettell SH McFarlane WK Sivertz M Hoffmann GW Riley PJ Ritchie JL Yamashita A Chapman MD Eckhause M Ginkel JF Hancock AD Kane JR Kenney CJ Kuang Y 《Physical review D: Particles and fields》1995,51(3):985-1013