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131.
The concept of local concurrence is used to quantify the entanglement between a single qubit and the remainder of a multiqubit system. For the ground state of the BCS model in the thermodynamic limit the set of local concurrences completely describes the entanglement. As a measure for the entanglement of the full system we investigate the average local concurrence (ALC). We find that the ALC satisfies a simple relation with the order parameter. We then show that for finite systems with a fixed particle number, a relation between the ALC and the condensation energy exposes a threshold coupling. Below the threshold, entanglement measures besides the ALC are significant. 相似文献
132.
In this Letter, we investigate a class of Hamiltonians which, in addition to the usual center-of-mass momentum conservation, also have center-of-mass position conservation. We find that, regardless of the particle statistics, the energy spectrum is at least q-fold degenerate when the filling factor is p/q, where and are coprime integers. Interestingly, the simplest Hamiltonian respecting this type of symmetry encapsulates two prominent examples of novel states of matter, namely, the fractional quantum Hall liquid and the quantum dimer liquid. We discuss the relevance of this class of Hamiltonian to the search for featureless Mott insulators. 相似文献
133.
We give explicit formulae for the Euler characteristic and 2-cohomology of the group of motions of the trivial link, or isomorphically the group of free group automorphisms that send each standard generator to a conjugate of itself. The method is primarily combinatorial and ultimately relies on a computation of the Möbius function for the poset of labelled hypertrees.Partially supported by NSF grant no. DMS-0101506Partially supported by an AMS Centennial Research Fellowship 相似文献
134.
Ene-chlorination of olefins by N-chlorosuccinimide is catalyzed by phenylselenenyl chloride. This reaction demonstrates the catalytic conversion of C-H bonds into more reactive C-Cl bonds. [reaction: see text] 相似文献
135.
[structure: see text] Two novel hybrid polyketide-terpenoid metabolites were isolated from a Penicillium sp. growing in the Berkeley Pit Lake of Butte, Montana. Their structures were deduced by spectroscopic analysis and confirmed by single-crystal X-ray analysis on berkeleydione (1). Both compounds inhibited matrix metalloproteinase-3 and caspase-1, and berkeleydione showed activity toward non-small-cell lung cancer in NCI's human cell line antitumor screen. 相似文献
136.
Busacca CA Grossbach D Campbell SJ Dong Y Eriksson MC Harris RE Jones PJ Kim JY Lorenz JC McKellop KB O'Brien EM Qiu F Simpson RD Smith L So RC Spinelli EM Vitous J Zavattaro C 《The Journal of organic chemistry》2004,69(16):5187-5195
The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems. 相似文献
137.
The mechanism of decomposition of dialkylamino diazeniumdiolate salts, R(2)N[NONO](-)M(+), to form nitric oxide, NO, was explored using theoretical methods. B3LYP/6-311+G(d) density functional theory calculations gave the optimized geometries, and energetics were further evaluated with the high accuracy CBS-QB3 method, when feasible. Relative pK(a) values were estimated using the PCM model for aqueous solvation. The terminal oxygen is the most basic site, followed closely by the internal oxygen. Protonation of these sites does not lead to decomposition. However, protonation of the weakly basic amino nitrogen leads to very rapid decomposition and NO generation. 相似文献
138.
Selenium-catalyzed halolactonization: nucleophilic activation of electrophilic halogenating reagents
Diphenyl diselenide catalyzes the halolactonization of unsaturated acids with N-halosuccinimides under mild conditions. The diselenide not only accelerates the reactions, but in some cases affords regiocontrol in favor of gamma-lactone products. Experiments show that the regioselectivity in favor of gamma-lactones is a result of kinetic rather than thermodynamic control. 相似文献
139.
140.
Nagarajan K Joshi HK Chaudhury PK Pal K Cooney JJ Enemark JH Sarkar S 《Inorganic chemistry》2004,43(15):4532-4533
Synthesis of [PPh4]2[Mo(SPh)2(S2C2(CN)2)2] (2) from [PPh4]2[MoO(S2C2(CN)2)2] (1) has been achieved to mimic the postulated [Mo(S)6] core of polysulfide reductase with two thiolates and two bis(ene-dithiolate) ligands. Compound 2 reacts with polysulfide to yield H2S, modeling the function of polysulfide reductase. The facile conversion of 2 back to 1 in moist solvent suggests that the interconversion of the [MoIV = O] and [MoIV - X] (X = O-Ser, S-Cys, Se-Cys) moieties might occur in the DMSO reductase class of enzymes under appropriate hydrophobic/hydrophilic conditions. 相似文献