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101.
The electronic absorption and emission spectra of large molecules reflect the extent and timescale of electron-vibration coupling and therefore the extent and timescale of relaxation/reorganization in response to a perturbation. In this paper, we present a comparison of the calculated absorption and emission spectra of NADH in liver alcohol dehydrogenase (LADH), using quantum mechanical/molecular mechanical methods, in which we vary the QM component. Specifically, we have looked at the influence of basis set (STO-3G, 3-21G*, 6-31G*, CC-pVDZ, and 6-311G**), as well as the influence of applying the DFT TD-B3LYP and ab initio TD-HF and CIS methods to the calculation of absorption/emission spectra and the reorganization energy (Stokes shift). The ab initio TD-HF and CIS methods reproduce the experimentally determined Stokes shift and spectral profiles to a high level of agreement, while the TD-B3LYP method significantly underestimates the Stokes shift, by 45%. We comment on the origin of this problem and suggest that ab initio methods may be naturally more suited to predicting molecular behavior away from equilibrium geometries. 相似文献
102.
CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
103.
T. Ouchterlony I.V. Zozoulenko C.-K. Wang K.-F. Berggren C. Gould A.S. Sachrajda 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):361-370
We study the conductance of a square quantum dot, modeling the potential with a self-consistent Thomas-Fermi approximation.
The resulting potential is characterized by level statistics indicative of mixed chaotic and regular electron dynamics within
the dot in spite of the regular geometry of the gates defining the dot. We calculate numerically, for the case of a quantum
dot with soft confinement, the weak localization (WL) correction. We demonstrate that this confining potential may generate
either Lorentzian or linear lineshapes depending on the number of modes in the leads. Finally, we present experimental WL
data for a lithographically square dot and compare the results with numerical calculations. We analyze the experimental results
and numerical simulations in terms of semiclassical and random matrix theory (RMT) predictions and discuss their limitations
as far as real experimental structures are concerned. Our results indicate that direct application of the above predictions
to distinguish between chaotic and regular dynamics in a particular cavity can not always lead to reliable conclusions as
the shape and magnitude of the WL correction can be strongly sensitive to the geometry-specific, non-universal features of
the system.
Received 13 May 1998 相似文献
104.
Stephan Brandt Guantao Chen Ralph Faudree Ronald J. Gould Linda Lesniak 《Journal of Graph Theory》1997,24(2):165-173
For any positive integer k, we investigate degree conditions implying that a graph G of order n contains a 2-factor with exactly k components (vertex disjoint cycles). In particular, we prove that for k ≤ (n/4), Ore's classical condition for a graph to be hamiltonian (k = 1) implies that the graph contains a 2-factor with exactly k components. We also obtain a sufficient degree condition for a graph to have k vertex disjoint cycles, at least s of which are 3-cycles and the remaining are 4-cycles for any s ≤ k. © 1997 John Wiley & Sons, Inc. 相似文献
105.
106.
Alexander J. Blake Robert O. Gould Wan-Sheung Li Vito Lippolis Simon Parsons Christian Radek Martin Schrder 《Angewandte Chemie (International ed. in English)》1998,37(3):293-296
The cations [Pd 2 Cl 2 L] 2+ and [KL 2 ′ + (L = [18]aneN2S4, L′ =[15]aneO5) have been used as templates for the synthesis of unique three-dimensional polyiodide networks. The metal cations in [Pd2Cl2L]1.5I5(I3)2 are linked into infinite chains by pairwise hydrogen bonding; the resulting cationic polymers run through channels formed by the extended polyiodide network. [KL2′]I9 shows a three-dimensional network of puckered cubic cages of I9− ions whose cavities are occupied by the metal cations (section from the structure shown on the right). 相似文献
107.
108.
Michel J. Dayd Jrme P. Dcamps Nicholas I. M. Gould 《Numerical Linear Algebra with Applications》1999,6(3):213-234
We consider the iterative solution of symmetric positive‐definite linear systems whose coefficient matrix may be expressed as the outer product of low‐rank terms. We derive suitable preconditioners for such systems, and demonstrate their effectiveness on a number of test examples. We also consider combining these methods with existing techniques to cope with the commonly‐occuring case where the coefficient matrix is the linear sum of elements, some of which are of very low rank. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
109.
Je Kyun Lee George L. Gould Wendell Rhine 《Journal of Sol-Gel Science and Technology》2009,49(2):209-220
Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and
supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure
by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity
of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and
equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO2) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity
values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature
to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity
values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property
and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated
with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications
and as a thermal insulation component of spacesuits. 相似文献
110.
We consider the question of membership of A ∨ G, where A and G are the pseudovarieties of finite aperiodic semigroups, and finite groups, respectively. We find a straightforward criterion
for a semigroup S lying in a class of finite semigroups that are weakly abundant, to be in A ∨ G. The class of weakly abundant semigroups contains the class of regular semigroups, but is much more extensive; we remark
that any finite monoid with semilattice of idempotents is weakly abundant. To study such semigroups we develop a number of
techniques that may be of interest in their own right. 相似文献