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81.
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
82.
83.
84.
85.
Evans DA Seidel D Rueping M Lam HW Shaw JT Downey CW 《Journal of the American Chemical Society》2003,125(42):12692-12693
A highly enantioselective, nitroaldol reaction catalyzed by a chiral Cu(II) bis(oxazoline) complex has been developed. The reaction scope includes both aromatic and aliphatic aldehydes (15 examples) affording products in good yields and enantioselectivities (87-94% ee). An X-ray structure of the catalyst has been provided along with a rationalization of the sense of asymmetric induction. 相似文献
86.
Schweiger M Seidel SR Arif AM Stang PJ 《Angewandte Chemie (International ed. in English)》2001,40(18):3467-3469
87.
We investigate polyelectrolyte brushes in the osmotic regime using both theoretical analysis and molecular dynamics simulation techniques. In the simulations at moderate Bjerrum length, we observe that the brush height varies weakly with grafting density, in contrast to the accepted scaling law, which predicts a brush thickness independent of the grafting density. We show that such behavior can be explained by considering lateral electrostatic effects (within the non-linear Poisson-Boltzmann theory) combined with the coupling between lateral and longitudinal degrees of freedom due to the conserved polymer volume (which are neglected in scaling arguments). We also take the non-linear elasticity of polyelectrolyte chains into consideration, which makes significant effects as chains are almost fully stretched in the osmotic regime. It is shown that all these factors lead to a non-monotonic behavior for the brush height as a function of the grafting density. At large grafting densities, the brush height increases with increasing the grafting density due to the volume constraint. At small grafting densities, we obtain a re-stretching of the chains for decreasing grafting density, which is caused by lateral electrostatic contributions and is controlled by the counterion-condensation process around polyelectrolyte chains. These results are obtained assuming all counterions to be trapped within the brush, which is valid for sufficiently long chains of large charge fraction.Received: 14 May 2003, Published online: 11 November 2003PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 36.20.-r Macromolecules and polymer molecules - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc. 相似文献
88.
Katja Heinig Thomas Wirz Moucun Yuan Michael Tingler William Mylott 《Biomedical chromatography : BMC》2011,25(11):1215-1221
89.
Gerald Steiner Valdas Sablinskas Wolfgang Seidel Reiner Salzer 《Analytical and bioanalytical chemistry》2009,395(6):1641-1650
Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is a very sensitive technique to characterize
the degree of molecular ordering in thin films on metallic surfaces. This is the first report of the coupling of a PM-IRRAS
microscope to a free electron laser (FEL), a light source of highest brilliance. Some FELs emit in the infrared region and
permit the mapping of molecular properties at high lateral resolution. We studied the molecular orientation of octadecanephosphonic
acid (OPA) attached to a gold surface with microstructured aluminum oxide islands on the gold. The spatial resolution achieved
is 12 μm which corresponds to the diffraction limit of the infrared light used in this study. This is a substantial improvement
compared to previous studies using a PM-IRRA accessory together with a commercial Fourier transform infrared spectrometer,
where the lateral resolution is noise-limited rather than diffraction-limited. The spectral maps reveal that OPA is preferably
attached to the aluminum oxide islands via the bidentate binding mode whereas the tridentate mode is dominating in case of
OPA attached to the gold areas. 相似文献
90.
Tobias Krüger Katja Vorndran Dr. Torsten Linker Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(44):12082-12091
Arenes with various alkyl side‐chains were synthesized in high yields and excellent regioselectivities. Starting from toluic and naphthoic acids, the carboxylate group was conveniently substituted by alkyl halides by Birch reduction and subsequent decarbonylation. The method is characterized by inexpensive starting materials and reagents, and methylation of arenes was realized. Besides simple alkyl substituents, the scope of arene functionalization was extended by benzyl, fluoro, amino, and ester groups. We were able to control the alkylation of 1‐naphthoic acid during Birch reduction by the addition of tert‐butanol. This allowed the regioselective synthesis of mono and bis‐substituted naphthalenes from the same starting material. 相似文献