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排序方式: 共有841条查询结果,搜索用时 31 毫秒
811.
We measured thermal conductivity kappa, thermoelectric power S, and electric conductivity sigma of La(5/8-x)Pr(x)Ca(3/8)MnO3, showing an intricate interplay between metallic ferromagnetism (FM) and charge ordering (CO) instability. The change of kappa, S, and sigma with temperature (T) and x agrees well with the effective medium theories for binary metal-insulator mixtures. This agreement clearly demonstrates that with the variation of T as well as x, the relative volumes of FM and CO phases drastically change and percolative metal-insulator transition occurs in the mixture of FM and CO domains. 相似文献
812.
Sijbers J Vanrumste B Van Hoey G Boon P Verhoye M Van der Linden A Van Dyck D 《Magnetic resonance imaging》2000,18(4):485-488
The electrical activity of the brain can be monitored using ElectroEncephaloGraphy (EEG). From the positions of the EEG electrodes, it is possible to localize focal brain activity. Thereby, the accuracy of the localization strongly depends on the accuracy with which the positions of the electrodes can be determined. In this work, we present an automatic, simple, and accurate scheme that detects EEG electrode markers from 3D MR data of the human head. 相似文献
813.
814.
Koster S Duursma MC Boon JJ Nielen MW de Koster CG Heeren RM 《Journal of mass spectrometry : JMS》2000,35(6):750-759
In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (5 Weeks journals - Search completed at 22nd. Mar 2000) 相似文献
815.
We report an inelastic light scattering study of the effects of charge ordering on the spin, charge, and lattice dynamics of Bi1-xCaxMnO3 (x>0.5). We find that charge ordering results in anomalous phonon behavior, such as the appearance of "activated" modes. More significantly, however, the transition to the charge-ordered phase results in the appearance of a quasielastic scattering response with the symmetry of the spin-chirality operator ( T(1g)); this scattering response is thus indicative of magnetic or chiral spin fluctuations in the antiferromagnetic charge-ordered phase. 相似文献
816.
Elizabeth S. Munday Markas A. Grove Taisiia Feoktistova Alexander C. Brueckner Daniel M. Walden Claire M. Young Alexandra M. Z. Slawin Andrew D. Campbell Paul Ha‐Yeon Cheong Andrew D. Smith 《Angewandte Chemie (International ed. in English)》2020,59(20):7897-7905
Axially chiral phenols are attractive targets in organic synthesis. This motif is central to many natural products and widely used as precursors to, or directly, as chiral ligands and catalysts. Despite their utility few simple catalytic methods are available for their synthesis in high enantiopurity. Herein the atropselective acylation of a range of symmetric biaryl diols is investigated using isothiourea catalysis. Studies on a model biaryl diol substrate shows that the high product er observed in the process is a result of two successive enantioselective reactions consisting of an initial enantioselective desymmetrization coupled with a second chiroablative kinetic resolution. Extension of this process to a range of substrates, including a challenging tetraorthosubstituted biaryl diol, led to highly enantioenriched products (14 examples, up to 98:2 er), with either HyperBTM or BTM identified as the optimal catalyst depending upon the substitution pattern within the substrate. Computation has been used to understand the factors that lead to high enantiocontrol in this process, with maintenance of planarity to maximize a 1,5‐S???O interaction within the key acyl ammonium intermediate identified as the major feature that determines atropselective acylation and thus product enantioselectivity. 相似文献
817.
Agus R. Poerwoprajitno Lucy Gloag John Watt Steffen Cychy Soshan Cheong Priyank V. Kumar Tania M. Benedetti Chen Deng Kuang‐Hsu Wu Christopher E. Marjo Dale L. Huber Martin Muhler J. Justin Gooding Wolfgang Schuhmann Da‐Wei Wang Richard D. Tilley 《Angewandte Chemie (International ed. in English)》2020,59(36):15487-15491
Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major challenges in synthesizing nanocatalysts with improved activity and stability. Using a cubic‐core hexagonal‐branch mechanism to form highly monodisperse branched nanoparticles, we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5‐hydroxymethylfurfural (HMF), as an example for biomass conversion. 相似文献
818.
Elizabeth S. Munday Markas A. Grove Taisiia Feoktistova Alexander C. Brueckner Daniel M. Walden Dr. Claire M. Young Prof. Alexandra M. Z. Slawin Dr. Andrew D. Campbell Prof. Paul Ha-Yeon Cheong Prof. Andrew D. Smith 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(20):7971-7979
Axially chiral phenols are attractive targets in organic synthesis. This motif is central to many natural products and widely used as precursors to, or directly, as chiral ligands and catalysts. Despite their utility few simple catalytic methods are available for their synthesis in high enantiopurity. Herein the atropselective acylation of a range of symmetric biaryl diols is investigated using isothiourea catalysis. Studies on a model biaryl diol substrate shows that the high product er observed in the process is a result of two successive enantioselective reactions consisting of an initial enantioselective desymmetrization coupled with a second chiroablative kinetic resolution. Extension of this process to a range of substrates, including a challenging tetraorthosubstituted biaryl diol, led to highly enantioenriched products (14 examples, up to 98:2 er), with either HyperBTM or BTM identified as the optimal catalyst depending upon the substitution pattern within the substrate. Computation has been used to understand the factors that lead to high enantiocontrol in this process, with maintenance of planarity to maximize a 1,5-S⋅⋅⋅O interaction within the key acyl ammonium intermediate identified as the major feature that determines atropselective acylation and thus product enantioselectivity. 相似文献
819.
Michael?Hohensee Shau-Yu?Lan Rachel?Houtz Cheong?Chan Brian?Estey Geena?Kim Pei-Chen?Kuan Holger?MüllerEmail author 《General Relativity and Gravitation》2011,43(7):1905-1930
We study the use of atom interferometers as detectors for gravitational waves in the mHz–Hz frequency band, which is complementary
to planned optical interferometers, such as laser interferometer gravitational wave observatories (LIGOs) and the Laser Interferometer
Space Antenna (LISA). We describe an optimized atomic gravitational wave interferometric sensor (AGIS), whose sensitivity
is proportional to the baseline length to power of 5/2, as opposed to the linear scaling of a more conservative design. Technical
challenges are briefly discussed, as is a table-top demonstrator AGIS that is presently under construction at Berkeley. We
study a range of potential sources of gravitational waves visible to AGIS, including galactic and extra-galactic binaries.
Based on the predicted shot noise limited performance, AGIS should be capable of detecting type Ia supernovae precursors within
500 pc, up to 200 years beforehand. An optimized detector may be capable of detecting waves from RX J0806.3+1527. 相似文献
820.
Wei-Xi Huang Cheong Bong Chang Hyung Jin Sung 《Journal of computational physics》2011,230(12):5061-5079
An improved penalty immersed boundary (pIB) method has been proposed for simulation of fluid–flexible body interaction problems. In the proposed method, the fluid motion is defined on the Eulerian domain, while the solid motion is described by the Lagrangian variables. To account for the interaction, the flexible body is assumed to be composed of two parts: massive material points and massless material points, which are assumed to be linked closely by a stiff spring with damping. The massive material points are subjected to the elastic force of solid deformation but do not interact with the fluid directly, while the massless material points interact with the fluid by moving with the local fluid velocity. The flow solver and the solid solver are coupled in this framework and are developed separately by different methods. The fractional step method is adopted to solve the incompressible fluid motion on a staggered Cartesian grid, while the finite element method is developed to simulate the solid motion using an unstructured triangular mesh. The interaction force is just the restoring force of the stiff spring with damping, and is spread from the Lagrangian coordinates to the Eulerian grids by a smoothed approximation of the Dirac delta function. In the numerical simulations, we first validate the solid solver by using a vibrating circular ring in vacuum, and a second-order spatial accuracy is observed. Then both two- and three-dimensional simulations of fluid–flexible body interaction are carried out, including a circular disk in a linear shear flow, an elastic circular disk moving through a constricted channel, a spherical capsule in a linear shear flow, and a windsock in a uniform flow. The spatial accuracy is shown to be between first-order and second-order for both the fluid velocities and the solid positions. Comparisons between the numerical results and the theoretical solutions are also presented. 相似文献