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Cappa CD Smith JD Wilson KR Messer BM Gilles MK Cohen RC Saykally RJ 《The journal of physical chemistry. B》2005,109(15):7046-7052
Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network. 相似文献
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Cappa CD Drisdell WS Smith JD Saykally RJ Cohen RC 《The journal of physical chemistry. B》2005,109(51):24391-24400
The microscopic events engendering liquid water evaporation have received much attention over the last century, but remain incompletely understood. We present measurements of isotope fractionation occurring during free molecular evaporation from liquid microjets and show that the isotope ratios of evaporating molecules exhibit dramatic differences from equilibrium vapor values, strong variations with the solution deuterium mole fraction, and a clear temperature dependence. These results indicate the existence of an energetic barrier to evaporation and that the evaporation coefficient of water is less than unity. These new insights into water evaporation promise to advance our understanding of the processes that control the formation and lifetime of clouds in the atmosphere. 相似文献
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Summary Sea wave measurements have been carried out in the Sicilian Channel using a navigational radar for the lower-frequency component
and a teflon-coated wire (Goubau line) for the high-frequency component. The results are discussed and the continuity of the
complete spectrum is clearly proved.
Riassunto Mediante nuove tecniche elettromagnetiche è stata misurata l'ondosità del mare nel Canale di Sicilia. è stato ottenuto lo spettro completo del mare, dalla banda di gravità a quella capillare, grazie all'impiego congiunto di un radar di navigazione che fornisce la componente a bassa frequenza, e di un nuovo ondametro a microonde a filo che misura in modo assoluto la componente a bassa frequenza. Si discutono i risultati ottenuti e si dimostra la validità dei sistemi impiegati.相似文献
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The thread load distribution has been examined, as is known, in literature both theoretically and experimentally. in the present paper the load distribution is validated by strain-gage measurements. Starting from the theoretical load distribution the stresses on the outer surface of the female member of a threaded connection are calculated. The theoretical and experimental stress values obtained are reasonably close. 相似文献
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Summary Two SAR marine images taken one hour and half apart over the same Western Mediterranean area are used for testing a model
able to produce the wind field in gale weather conditions. 相似文献
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Computer-controlled data-acquisition systems are being used extensively for gathering strain-gage data. This paper explores the relative merits of using modern solidstate digital multi-meters (DDM) to measure the strain-gage resistance directly rather than using a conventional Wheatstone bridge. Both a direct-resistance measurement scheme and a reversed current scheme are compared over long measurements terms of 6 and 12 days using a 6 1/2-digit multimeter. The results show that the reversed current method is superior in maintaining the zero-gage resistance reading at the cost of using several meters. Possibly the direct-resistance method can be improved so that the operation and equipment can be simplified.Paper was presented at the 1990 SEM Spring Conference on Experimental Mechanics held in Albuquerque, NM on June 4–6. 相似文献
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Faulstich FR Castro HV de Oliveira LF Neumann R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,80(1):102-105
In this investigation, Raman spectroscopy with 1064 and 632.8 nm excitation was used to investigate real mineral samples of bauxite ore from mines of Northern Brazil, together with Raman mapping and X-rays diffraction. The obtained results show clearly that the use of microRaman spectroscopy is a powerful tool for the identification of all the minerals usually found in bauxites: gibbsite, kaolinite, goethite, hematite, anatase and quartz. Bulk samples can also be analysed, and FT-Raman is more adequate due to better signal-to-noise ratio and representativity, although not efficient for kaolinite. The identification of fingerprinting vibrations for all the minerals allows the acquisition of Raman-based chemical maps, potentially powerful tools for process mineralogy applied to bauxite ores. 相似文献
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Cappa CD Smith JD Messer BM Cohen RC Saykally RJ 《The journal of physical chemistry. B》2006,110(11):5301-5309
Oxygen K-edge X-ray absorption spectra (XAS) of aqueous chloride solutions have been measured for Li(+), Na(+), K(+), NH(4)(+), C(NH(2))(3)(+), Mg(2+), and Ca(2+) at 2 and 4 M cation concentrations. Marked changes in the liquid water XAS are observed upon addition of the various monovalent cation chlorides that are nearly independent of the identity of the cation. This indicates that interactions with the dissolved monovalent cations do not significantly perturb the unoccupied molecular orbitals of water molecules in the vicinity of the cations and that water-chloride interactions are primarily responsible for the observed spectral changes. In contrast, the addition of the divalent cations engenders changes unique from the case of the monovalent cations, as well as from each other. Density functional theory calculations suggest that the ion-specific spectral variations arise primarily from direct electronic perturbation of the unoccupied orbitals due to the presence of the ions, probably as a result of differences in charge transfer from the water molecules onto the divalent cations. 相似文献