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排序方式: 共有390条查询结果,搜索用时 31 毫秒
61.
William A. Chupka Steven D. Colson Mark S. Seaver Anne M. Woodward 《Chemical physics letters》1983,95(3):171-176
Two-photon resonant multiphoton ionization has been used to prepare rotationally cooled and selected CH3I+ ions with controlled vibrational and electronic distributions. These ions are photodissociated by a second laser. The highly simplified photodissociation spectrum displays a clear dissociation threshold as well as bands hidden in earlier spectra. The data suggests corrections to previously determined vibrational constants. 相似文献
62.
63.
64.
An X-ray investigation of the two uranyl 8-hydroxy-quinolates UO(2).(C(9)H(6)NO)(2).C(9)H(6)NOH (dark red) and [UO(2).(C(9)H(6)NO)(2)](2).C(9)H(6)NOH (orange), has been carried out on the untreated compounds and after recrystallising them from chloroform. The unsolvated compound UO(2).(C(2)H(6)NO)(2) and the residue remaining after dissolving the orange compound in chloroform have also been examined. The investigation shows that the crystals obtained from the red and orange compounds, respectively, after dissolving in chloroform and recrystallising, are identical. The untreated red and orange compounds are different, the latter showing evidence of existing as a polymer, whereas the former is crystalline. On the basis of the results obtained, a structure for the orange compound is proposed. 相似文献
65.
An unusual fragmentation reaction was observed when terramycin is treated with MeI in acetone at room temp. The reaction proceeds with quaternization, loss of trimethylamine, fission of bonds 4a,5 and 12,12a with formation of an aldehydo-lactone derived from rings B, C and D. Additionally some transformations of this lactone are described. 相似文献
66.
A general procedure for creating Markovian interest rate models is presented. The models created by this procedure automatically fit within the HJM framework and fit the initial term structure exactly. Therefore they are arbitrage free. Because the models created by this procedure have only one state variable per factor, twoand even three-factor models can be computed efficiently, without resorting to Monte Carlo techniques. This computational efficiency makes calibration of the new models to market prices straightforward. Extended Hull- White, extended CIR, Black-Karasinski, Jamshidian's Brownian path independent models, and Flesaker and Hughston's rational log normal models are one-state variable models which fit naturally within this theoretical framework. The ‘separable’ n-factor models of Cheyette and Li, Ritchken, and Sankarasubramanian - which require n(n + 3)/2 state variables - are degenerate members of the new class of models with n(n + 3)/2 factors. The procedure is used to create a new class of one-factor models, the ‘β-η models.’ These models can match the implied volatility smiles of swaptions and caplets, and thus enable one to eliminate smile error. The β-η models are also exactly solvable in that their transition densities can be written explicitly. For these models accurate - but not exact - formulas are presented for caplet and swaption prices, and it is indicated how these closed form expressions can be used to efficiently calibrate the models to market prices. 相似文献
67.
A novel speech communications system using a modulated laser beam has been developed for short-range applications in which
high directionality is an exploitable feature. Although it was designed for certain underwater applications, such as speech
communications between divers or between a diver and the surface, it may equally be used for air applications. With some modification
it could be used for secure diver-to-diver communications in the situation where untethered divers are swimming close together
and do not want their conversations monitored by intruders. Unlike underwater acoustic communications, where the transmitted
speech may be received at ranges of hundreds of metres omnidirectionally, a laser communication link is very difficult to
intercept and also obviates the need for cables that become snagged or broken. Further applications include the transmission
of speech and data, including the short message service (SMS), from a fixed installation such as a sea-bed habitat; and data
transmission to and from an autonomous underwater vehicle (AUV), particularly during docking manoeuvres. The performance of
the system has been assessed subjectively by listening tests, which revealed that the speech was intelligible, although of
poor quality due to the speech algorithm used.
PACS 42.55.Px; 42.60.By; 42.62.-b 相似文献
68.
Turesson M Woodward CE Akesson T Forsman J 《The journal of physical chemistry. B》2008,112(16):5116-5125
We have simulated interactions between charged surfaces in the presence of oppositely charged polyelectrolytes by coupling perturbations in the isotension ensemble to a free energy variance minimization scheme. For polymeric systems, this method completely outperforms configurationally biased versions of grand canonical simulations. Proper diffusive equilibrium between bulk and slit has been established for polyelectrolytes with up to 60 monomers per chain. A consequence of imposing diffusive equilibrium conditions, in contrast to previous more restricted models, is the possibility of surface charge inversion; ion-ion correlation and the cooperativity of monomer adsorption drive the formation of a polyion layer close to the surface, that overcompensates the nominal surface charge. This is observed even at modest surface charge densities, and leads to a build up of a long ranged electrostatic barrier. In addition, the onset of charge inversion requires very low bulk polymer densities. Due to screening effects, this leads to a higher and more long-ranged free energy barrier at low, compared to high, bulk densities. Oscillatory forces, reminiscent of those found in simple hard sphere systems, are resolved in the high concentration regime. As a consequence of a second surface charge inversion, the system "stratifies" to form a stable polyelectrolyte layer in the central part of the slit, stabilized by the adsorbed surface layers. 相似文献
69.
Junjie Zhao Dennis T. Lee Robert W. Yaga Morgan G. Hall Heather F. Barton Ian R. Woodward Christopher J. Oldham Howard J. Walls Gregory W. Peterson Prof. Gregory N. Parsons 《Angewandte Chemie (International ed. in English)》2016,55(42):13224-13228
The threat associated with chemical warfare agents (CWAs) motivates the development of new materials to provide enhanced protection with a reduced burden. Metal–organic frame‐works (MOFs) have recently been shown as highly effective catalysts for detoxifying CWAs, but challenges still remain for integrating MOFs into functional filter media and/or protective garments. Herein, we report a series of MOF–nanofiber kebab structures for fast degradation of CWAs. We found TiO2 coatings deposited via atomic layer deposition (ALD) onto polyamide‐6 nanofibers enable the formation of conformal Zr‐based MOF thin films including UiO‐66, UiO‐66‐NH2, and UiO‐67. Cross‐sectional TEM images show that these MOF crystals nucleate and grow directly on and around the nanofibers, with strong attachment to the substrates. These MOF‐functionalized nanofibers exhibit excellent reactivity for detoxifying CWAs. The half‐lives of a CWA simulant compound and nerve agent soman (GD) are as short as 7.3 min and 2.3 min, respectively. These results therefore provide the earliest report of MOF–nanofiber textile composites capable of ultra‐fast degradation of CWAs. 相似文献
70.
Coleman RS Woodward RL Hayes AM Crane EA Artese A Ortuso F Alcaro S 《Organic letters》2007,9(10):1891-1894
Evaluation of the importance of C18/C19 stereochemistry of azinomycin A/B epoxyamide partial structures with respect to DNA alkylation sequence selectivity is reported using a unique assay with a DNA oligomer containing imbedded normal (5'-GGC-3'/3'-CCG-5') and inverted (5'-CGG-3'/3'-GCC-5') azinomycin consensus cross-linking sequences. Both species were found to have unique selectivity profiles and alkylate DNA in a manner distinct from azinomycin B. Computational docking experiments support altered binding modes for the enantiomers. 相似文献