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61.
Christensen KE Shi L Conradsson T Ren TZ Dadachov MS Zou X 《Journal of the American Chemical Society》2006,128(44):14238-14239
Open-framework germanates with extra-large channels are built from two different types of clusters. The two different clusters are connected in such a way to form a pseudo-body-centered cluster aggregate (PBCCA). The different packing of PBCCAs resulted in different 3D open-framework germanates. 相似文献
62.
Various free radicals formed during UV.-irradiation of aliphatic dicarboxylic acids in aqueous and methanolic solution are identified by ESR.-spectroscopy. Their structures point to α-cleavage and photoreduction as the dominant primary photochemical decay processes. The relative contributions of these reactions to the overall photodecomposition depend on solvent and degree of α-alkylation of the acid. Emission ESR.-spectra are found for radicals formed by C, CO-bond cleavage of α-dimethyl substituted acids. The polarization is referred to the triplet mechanism of CIDEP. and indicates this cleavage reaction occurs from a triplet molecular state. 相似文献
63.
We consider random subgraphs of a fixed graph with large minimum degree. We fix a positive integer k and let Gk be the random subgraph where each independently chooses k random neighbors, making kn edges in all. When the minimum degree then Gk is k‐connected w.h.p. for ; Hamiltonian for k sufficiently large. When , then Gk has a cycle of length for . By w.h.p. we mean that the probability of non‐occurrence can be bounded by a function (or ) where . © 2016 Wiley Periodicals, Inc. Random Struct. Alg., 50, 143–157, 2017 相似文献
64.
Aromatization of cyclohexadienes by TEMPO electro-mediated oxidation: Kinetic and structural aspects
Cyclohexadienes are easily converted into the corresponding aromatics in excellent yield (>90%) in the presence of 2,2,6,6-tetramethyl-1-oxopiperidinium ion (TEMPO+). The TEMPO radical was used in catalytic amount and was electrochemically regenerated in the presence of 2,6-lutidine as a base in hydro-organic medium (AcCN/H2O 95/5). This work has been focused on the kinetic aspects. We have demonstrated that the reactivity of different cyclohexadienes is strongly dependent on the configuration of the double bonds and on the nature of the substituents. Competition between allylic functionalization and aromatization has been observed during the oxidation of 1,2-dihydro-4-phenylnaphthalene. 相似文献
65.
A new method for probing the equilibrium structures and folding states of proteins utilizing electrospray ionization mass spectrometry is described. Protein structure is explored as a function of side-chain availability as determined by a specific interaction between lysine and 18-crown-6 ether (18C6). Various intramolecular interactions are competitive with the lysine/18C6 interaction and can prevent noncovalent attachment of 18C6. Changes to protein structure modify these inhibiting intramolecular interactions, which leads to a change in the number of 18C6s that attach to the protein. Experiments conducted with cytochrome c, ubiquitin, and melittin reveal that the method is sensitive to changes in both tertiary and secondary structure. In addition, the structure of each charge state can be examined independently. Experiments can be performed under conditions where the pH and amount of organic cosolvent are varied. Control experiments conducted with pentalysine, which lacks structural organization, are also presented. 相似文献
66.
Summary.
We consider two level overlapping Schwarz domain decomposition methods
for solving the finite element problems that arise from
discretizations of elliptic problems on general unstructured meshes
in two and three dimensions. Standard finite element interpolation
from
the coarse to the fine grid may be used. Our theory requires no
assumption on the substructures
that constitute the whole domain, so the
substructures can be of arbitrary shape and of different
size. The global coarse mesh is allowed to be non-nested
to the fine grid on which the discrete problem is to be solved, and
neither
the coarse mesh nor the fine mesh need be quasi-uniform.
In addition, the domains defined by the fine and coarse grid need
not be identical. The one important constraint is that the closure
of the coarse grid must cover any portion of the fine grid boundary
for which Neumann boundary conditions are given.
In this general setting, our algorithms have the same optimal
convergence rate as the usual two level overlapping domain decomposition
methods on structured meshes.
The condition number of the preconditioned system depends only on the
(possibly small)
overlap of the
substructures and the size of the coarse grid, but is independent of
the sizes of the subdomains.
Received
March 23, 1994 / Revised version received June 2, 1995 相似文献
67.
Unraveling of all of the information contained in proteomes poses a tremendous chemical challenge, which is balanced by the promise of potentially transformational knowledge. Mass spectrometry offers an unprecedented arsenal of tools for diverse proteomic investigations. Recently, it was demonstrated that ultraviolet light can be utilized to initiate unique and potentially useful fragmentations in peptides and proteins. Either nonspecific dissociation or highly specific dissociation at engineered chromophoric sites is possible following photon absorption. The level of specificity and control over fragmentation in these experiments is greater than with other fragmentation methods. Novel techniques made possible by this technology are poised to make substantial contributions to the field of proteomics. 相似文献
68.
69.
We consider the problem of sampling a Boltzmann‐Gibbs probability distribution when this distribution is restricted (in some suitable sense) on a submanifold Σ of ?n implicitly defined by N constraints q1(x) = ? = qN(x) = 0 (N < n). This problem arises, for example, in systems subject to hard constraints or in the context of free energy calculations. We prove that the constrained stochastic differential equations (i.e., diffusions) proposed in [7, 13] are ergodic with respect to this restricted distribution. We also construct numerical schemes for the integration of the constrained diffusions. Finally, we show how these schemes can be used to compute the gradient of the free energy associated with the constraints. © 2007 Wiley Periodicals, Inc. 相似文献
70.
Novel regioisomers of 2′-methyl-branched nucleosides were designed and synthesized to mimic potent anti-viral drugs like Valopicitabine. The short and efficient synthesis of the targets involves a one-pot tosylation/cyclization step that leads to an activated furan scaffold on which the isonucleosides were built. 相似文献