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131.
132.
Peter Bouwknegt Alan L. Carey Varghese Mathai Michael K. Murray Danny Stevenson 《Communications in Mathematical Physics》2002,228(1):17-49
In this note we introduce the notion of bundle gerbe K-theory and investigate the relation to twisted K-theory. We provide some examples. Possible applications of bundle gerbe K-theory to the classification of K-brane charges in nontrivial backgrounds are briefly discussed.
Received: 29 June 2001 / Accepted: 15 October 2001 相似文献
133.
Time-resolved two photon photoemission electron microscopy 总被引:1,自引:0,他引:1
O. Schmidt M. Bauer C. Wiemann R. Porath M. Scharte O. Andreyev G. Schönhense M. Aeschlimann 《Applied physics. B, Lasers and optics》2002,74(3):223-227
Femtosecond, time-resolved two photon photoemission has been used to map the dynamics of photo-excited electrons at a structured
metal/semiconductor surface. A photoemission microscope was employed as a spatially resolving electron detector. This novel
setup has the potential to visualize variations of hot electron lifetimes in the femtosecond regime on heterogeneous sample
surfaces and nanostructures.
Received: 22 October 2001 / Revised version: 10 January 2002 / Published online: 7 February 2002 相似文献
134.
Molecularly Designed Stabilized Asymmetric Hollow Fiber Membranes for Aggressive Natural Gas Separation
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Dr. Gongping Liu Dr. Nanwen Li Dr. Stephen J. Miller Danny Kim Dr. Shouliang Yi Dr. Ying Labreche Prof. Dr. William J. Koros 《Angewandte Chemie (International ed. in English)》2016,55(44):13754-13758
New rigid polyimides with bulky CF3 groups were synthesized and engineered into high‐performance hollow fiber membranes. The enhanced rotational barrier provided by properly positioned CF3 side groups prohibited fiber transition layer collapse during cross‐linking, thereby greatly improving CO2/CH4 separation performance compared to conventional materials for aggressive natural gas feeds. 相似文献
135.
Patel BA Arundell M Quek RG Harvey SL Ellis IR Florence MM Cass AE Schor AM O'Hare D 《Analytical and bioanalytical chemistry》2008,390(5):1379-1387
We have fabricated a six individual addressable gold working electrode microarray. The device is wirebonded to an eight-pin
DIL package that can be easily interconnected to an external multi-channel potentiostat. A polyion complex film coating on
the electrode surface provides a suitable coating for the growth of cells. The responses of oxygen and nitric oxide were assessed
on uncoated and coated devices using electroanalytical methods. The film coating reduced the diffusion current by approximately
20% in both cases. No changes in the electrochemical mechanism were observed. Simultaneous recordings were obtained for 2 h
in the presence of the cells, thus the device is stable for the duration of the bioanalytical measurements. Measurements were
conducted to study the simultaneous changes in oxygen and nitric oxide levels in cultured fibroblast cells in the presence
of growth hormones that cause cell proliferation. Increases in oxygen consumption of the cells were coupled with increases
in nitric oxide levels when in the presence of the growth hormones. Use of a biological detergent to cause an oxidative burst
resulted in a large increase in the current for potentials set to detect nitric oxide and oxygen. 相似文献
136.
137.
The reactions of chiral benzyl carbocations bearing alpha-phenyl substituents with N-sulfonylated indoles afford 1,1,2-triarylalkanes with anti-selectivities. This outcome is a reversal of facial diastereoselectivity relative to Bach's alpha-alkyl-bearing benzyl cations. The reactions are promoted by either a Br?nsted acid (TFA) or Lewis acid (BF3.OEt2), offering differential diastereoselectivities and reactivities. The electronic properties of both reacting partners strongly influence the reaction rates and the product diastereoselectivities and appear to operate under kinetic control. This chemistry provides an efficient access to sterically congested tetrasubstituted ethanes. 相似文献
138.
The packing and covering problems have been considered for several classes of graphs. For instance, Bryant et. al. have investigated the packing problem for paths and cycles, and the packing and covering problems for 3-cubes. The packing and covering problems were settled for stars with up to six edges by Roditty. In this paper, for every possible leave graph (excess graph), we find a corresponding maximum packing (minimum covering) of the complete graph with stars with up to five edges. 相似文献
139.
Danny Ganame 《Tetrahedron letters》2007,48(33):5841-5843
The syntheses of both C9-C29 fragments 3 and 4 of the myxobacteria metabolites ajudazols A (1) and B (2) are described. The key steps were a cyclodehydration to form the oxazole, Sonogashira coupling to form the C18-C19 bond and a P-2 Ni mediated partial alkyne hydrogenation to install the C17-C18 Z-alkene. The C15 alkene in the ajudazol A fragment 3 was introduced in the final steps by elimination of the corresponding primary alcohol. 相似文献
140.
Ramadan D Cline DJ Bai S Thorpe C Schneider JP 《Journal of the American Chemical Society》2007,129(10):2981-2988
While arsenic(III) compounds can exert profound toxicological and pharmacological effects, their modes of action and, in particular, the structural consequences of their binding to cysteinyl side chains in proteins, remain poorly understood. To gain an understanding of how arsenic binding influences beta-structure, pairs of cysteines were introduced into a model monomeric beta-hairpin to yield a family of peptides such that coordination occurs either across the strands or within the same strand of the beta-hairpin. Circular dichroism, NMR, UV-vis spectroscopy, and rapid-reaction studies were used to characterize the binding of monomethylarsonous acid or p-succinylamidephenyl arsenoxide (PSAO) to these peptides. Placement of cysteines at non-hydrogen bond (NHB) positions across the beta-hairpin, such that they occupy the same face of the sheet, was found to enhance the structure as assessed by CD. Cross-strand cysteine residues that project on opposite faces close to the termini of the hairpin can still bind arsenic tightly and show modestly increased beta-sheet content. NMR and modeling studies suggest that arsenic can be accommodated at this locus without disrupting the core interactions stabilizing the turn. However, As(III) binding to nonopposed cysteines, or to cysteines at HB and NHB positions along one strand of the hairpin, caused loss of structure. UV-vis titrations show that all these hairpin peptides bind PSAO stoichiometrically with K(d) values from 13 to 106 nM. Further, binding is moderately rapid, with second-order rate constants for association of 10,000-22,000 M(-1) s(-)1 irrespective of the placement of the cysteines within the hairpin and the consequent extent of structural reorganization required as a result of binding. These studies complement recent work with alpha-helices and further demonstrate that capture of a pair of thiols by As(III) may result in significant changes in local secondary structure in the protein targets of these potent bioactive agents. 相似文献