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981.
S, S-Dialkylacetals of aldoses, tripodal in structure and recently synthesized in large numbers by three groups, do not exhibit thermotropically a smectic, but a columnar hexagonal mesophase (Hx) as we have proved by X-ray diffraction. The molecular organization in this mesophase is comparable with a similar one known for phasmidic molecules. These various multiols, although different in stereo-chemistry, form only one type of hydrogen-bonded disc-shaped multimer. Its mesophase structure is made up of about five molecules placed in columns with a skeleton of hydrogen-bridged sugar parts surrounded by thioalkyl groups in the periphery. Since three 6-deoxy sugar dithioacetals were shown to be non-thermomesomorphic the terminal hydroxyl function is essential for this molecular arrangement which seems not to be true for missing ones in the inner part of a sugar chain, as we have found in one case. 相似文献
982.
Andreas Richter Ken-ichi Matsuda Tatsushi Akazaki Tadashi Saku Hiroyuki Tamura Yoshiro Hirayama Hideaki Takayanagi 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):472-478
We present studies on the electric transport in a lateral GaAs/AlGaAs quantum dot defined by a patterned single connected metallic front-gate. This gate design allows to easily couple a large number of quantum dots and therefore holds high potential in the design of new materials with tailor-made band structures based on quantum dot superlattices of controlled shape. Clear Coulomb diamond structures and well pronounced tunneling peaks observed in experiment indicate that single-electron control has been achieved. However, the dependence on electron density in the heterostructure embedding the dot, which is controlled by an additional back-gate, reveals that transport characteristics are strongly influenced supposedly by potential fluctuations in the dot and lead regions. 相似文献
983.
984.
Andreas Johann 《Journal of Differential Equations》2002,184(1):224-258
We investigate stationary and travelling wave solutions of a special lattice differential equation in one space dimension. Depending on a parameter λ, results are given on the existence, shape and stability for these kind of solutions. The analysis of travelling wave solutions leads us to a functional differential equation with both forward and backward shifts. The existence of solutions of this equation will be proved by use of the implicit function theorem. In particular, we consider kink solutions and periodic solutions. 相似文献
985.
Andreas Rosenschon 《Topology》2005,44(6):1159-1179
We solve the homotopy limit problem for two-primary algebraic K-theory of fields, that is, the Quillen-Lichtenbaum conjecture at the prime 2. 相似文献
986.
Andreas Blumhofer 《Physics letters. [Part B]》1994,320(3-4):352-358
Quadratic divergencies which lead to the usual fine-tuning or hierarchy problem are discussed in top condensation models. As in the Standard Model a cancellation of quadratic divergencies is not possible without the boson contributions in the radiative corrections which are absent in lowest order of an 1/Nc-expansion. To deal with the cancellation of quadratic divergencies we propose therefore an expansion in the flavor degrees of freedom. In leading order we find the remarkable result that quadratic divergencies automatically disappear. 相似文献
987.
Andreas Fröhlich 《Journal of Evolution Equations》2002,2(4):471-493
We prove estimates in Ls (0, T; Lwq (W)) L^s (0, T; L_w^q (\Omega)) for the solution of the non-stationary Stokes system in an aperture domain, where 1 <s, q< ¥ \infty and the weight function w \omega is in the Muckenhoupt class Aq A_q .¶The result is achieved by combining a characterisation of maximal regularity by R {\mathcal R} -bounded operator families with the fact that R {\mathcal R} -boundedness follows from weighted estimates for Muckenhoupt weights. 相似文献
988.
989.
990.
We show how spectral functions for quantum impurity models can be calculated very accurately using a complete set of discarded numerical renormalization group eigenstates, recently introduced by Anders and Schiller. The only approximation is to judiciously exploit energy scale separation. Our derivation avoids both the overcounting ambiguities and the single-shell approximation for the equilibrium density matrix prevalent in current methods, ensuring that relevant sum rules hold rigorously and spectral features at energies below the temperature can be described accurately. 相似文献