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101.
102.
AN INVARIANT FOR HYPERGRAPHS 总被引:11,自引:0,他引:11
ANINVARIANTFORHYPERGRAPHSWANGJIANFANG(InstituteofAPPliedMathematics,ChineseAcademyofSciences,Beijing100080,ChinaandAsia-Pacif... 相似文献
103.
We link two phenomena concerning the asymptotical behavior of stochastic processes: (i) abrupt convergence or cut-off phenomenon,
and (ii) the escape behavior usually associated to exit from metastability. The former is characterized by convergence at
asymptotically deterministic times, while the convergence times for the latter are exponentially distributed. We compare and
study both phenomena for discrete-time birth-and-death chains on ℤ with drift towards zero. In particular, this includes energy-driven
evolutions with energy functions in the form of a single well. Under suitable drift hypotheses, we show that there is both
an abrupt convergence towards zero and escape behavior in the other direction. Furthermore, as the evolutions are reversible,
the law of the final escape trajectory coincides with the time reverse of the law of cut-off paths. Thus, for evolutions defined
by one-dimensional energy wells with sufficiently steep walls, cut-off and escape behavior are related by time inversion. 相似文献
104.
Chlorometallates of transition and B subgroup elements are readily prepared and precipitated by reaction of the corresponding metallic salts with 1-methyl-4,4-dimercaptopiperidinium chloride. These chlorometallates investigated were [ZnCl4]2?, [CdCl3]?, [CoCl4]2?, [CuCl5]3? and [FeCl4]2?. Strong SH … Cl interactions, but not NH … Cl, have been evidenced by IR spectroscopy in the zinc, cadmium and cobalt complexes. The SH and NH absorptions are observed at ? 2480 cm?1 and 3060 cm?1, respectively. Partial deuteration of the [ZnCl4]2? complex with d1-methanol, shifted these IR signals to 1800 and 2260 cm?1, clearly evidencing a X-hydrogen type of bond. The SH … Cl interaction is smaller in the [FeCl4]2? complex, and practically nonexistent in the [CuCl53? complex. 相似文献
105.
Tony T Lee 《Journal of Combinatorial Theory, Series A》1981,31(2):136-145
A partial ordering is defined for monotone projections f: N → N, N = {1, 2,…, n}, such that the class of these mappings is a lattice which is isomorphic to the partition lattice. Thus a partition can be uniquely represented by an element of this class of mappings and the partial ordering of partitions is preserved. Algorithms for computing the join and meet of given partitions are presented. 相似文献
106.
107.
Poly-N-acetyllactosamine oligomer is a type-2 glycan core from which a number of important bioactive glycoconjugates are assembled in vivo. Development of an effective synthesis of N-acetyllactosamine oligomers will therefore provide a new chemoenzymatic entry to this class of complex saccharides. This paper describes the design and synthesis of thioglycoside building blocks, determination of their relative reactivity values, and demonstration of their use in the programmable one-pot synthesis of various N-acetyllactosamine oligomers. Through a combination of segment condensation, the strategy allows for the preparation of larger oligosaccharides with minimal protecting group manipulation, as illustrated in the synthesis of an octasaccharide in a very short period of time. 相似文献
108.
N-Acyloxy-N-alkoxyamides are anomeric amides that are direct-acting mutagens. They have been shown to damage DNA in the major and the minor grooves in a pH and sequence-selective manner. In acidic media, they damage adenines at N3 in the minor groove but above neutral pH, only guanine is damaged at N7 in the major groove. Both the acyloxy leaving group and the alkoxy group at the amide nitrogen are responsible for their electrophilicity and Salmonella mutagenicities in TA 100 and DNA damage data confirm that the mutagens react with DNA in an intact form, rather than by solvolysis to electrophilic nitrenium ions in the cytosol, or in vitro, prior to reacting with DNA. Hydrophobicity plays a role in both mutagenicity and DNA damage. 相似文献
109.
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
110.
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