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831.
Ding Y Haskel D Ovchinnikov SG Tseng YC Orlov YS Lang JC Mao HK 《Physical review letters》2008,100(4):045508
Fe K-edge x-ray magnetic circular dichroism of magnetite (Fe3O4) powders was measured with synchrotron radiation under variable pressure and temperature conditions in diamond anvil cell. The magnetic dichroism was observed to decrease discontinuously by approximately 50% between 12 and 16 GPa, independent of temperature. The magnetic transition is attributed to a high-spin to intermediate-spin transition of Fe2+ ions in the octahedral sites and could account for previously observed structural and electrical anomalies in magnetite at this pressure range. The interpretation of x-ray magnetic circular dichroism data is supported by x-ray emission spectroscopy and theoretical cluster calculations. 相似文献
832.
Saha S Johansson E Flood AH Tseng HR Zink JI Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(23):6846-6858
A tetrathiafulvalene-porphyrin-fullerene (TTF-P-C(60)) molecular triad, which generates electrical current by harnessing light energy when self-assembled onto gold electrodes, has been developed. The triad, composed of three unique electroactive components, namely, 1) an electron-donating TTF unit, 2) a chromophoric porphyrin unit, and 3) an electron-accepting C(60) unit, has been synthesized in a modular fashion. A disulfide-based anchoring group was tagged to the TTF end of the molecule in order to allow its self-assembly on gold surfaces. The surface coverage by the triad in a self-assembled monolayer (SAM) was estimated to be 1.4 nm(2) per molecule, a density which is consistent with hexagonal close-packing of the spherical C(60) component (diameter approximately 1 nm). In a closed electronic circuit, a triad-SAM functionalized working-electrode generates a switchable photocurrent of approximately 1.5 microA cm(-2) when irradiated with a 413 nm Kr-ion laser, a wavelength which is close to the porphyrin chromophore's absorption maximum peak at 420 nm. The electrical energy generated by the triad at the expense of the light energy is ultimately exploited to drive a supramolecular machine in the form of a [2]pseudorotaxane comprised of a pi-electron-deficient tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+)) cyclophane and a pi-electron-rich 1,5-bis[(2-hydroxyethoxy) ethoxy]naphthalene (BHEEN) thread. The redox-induced dethreading of the CBPQT(4+) cyclophane from the BHEEN thread can be monitored by measuring the increase in the fluorescence intensity of the BHEEN unit. A gradual increase in the fluorescence intensity of the BHEEN unit concomitant with the photocurrent generation, even at a potential (0 V) much lower than that required (-300 mV) for the direct reduction of the CBPQT(4+) unit, confirms that the dethreading process is driven by the photocurrent generated by the triad-SAM. 相似文献
833.
834.
Formosadimers A, B, and C, together with one known compound, sugikurojin B, have been isolated from the bark of Calocedrus macrolepis var. formosana. Formosadimers A, B, and C, and sugikurojin B are dimers of the abietane-O-abietane type. Their structures were elucidated principally based on spectroscopic data. 相似文献
835.
Blind source separation of two electromagnetic fields is investigated. The difficulty of this task lies in the fact that only the power, which is the square of the sum of the electromagnetic fields, can be directly measured; the cross term of the electromagnetic fields is inevitable, and a strong correlation occurs in blind deconvolution. However, the relative phase is physically different from the field intensities, and, hence, extracting the phase during separation seems inconceivable. Our results demonstrate that the intensities and the relative phase of two electromagnetic waves can be determined with eigenvalue problem formalism even when the mixing processes are completely unknown. 相似文献
836.
We analyze the convergence rate of an asynchronous space decomposition method for constrained convex minimization in a reflexive Banach space. This method includes as special cases parallel domain decomposition methods and multigrid methods for solving elliptic partial differential equations. In particular, the method generalizes the additive Schwarz domain decomposition methods to allow for asynchronous updates. It also generalizes the BPX multigrid method to allow for use as solvers instead of as preconditioners, possibly with asynchronous updates, and is applicable to nonlinear problems. Applications to an overlapping domain decomposition for obstacle problems are also studied. The method of this work is also closely related to relaxation methods for nonlinear network flow. Accordingly, we specialize our convergence rate results to the above methods. The asynchronous method is implementable in a multiprocessor system, allowing for communication and computation delays among the processors.
837.
Long range 31P? 1H coupling constants of 21 phosphorylated iminothiazolines and two phosphorylated iminooxazolines have been studied. The size of the 31P? 1H coupling in the H? C? N? C?N? P framework is larger than that in the H? C? S? C?N? P framework which is in turn larger than the H? C? O? C?N? P framework. The value of the 31P? 1H coupling through the H? C? N? C?N? P framework decreases in the order of P > PS > PO, whereas a reverse trend is observed for the H? C? S? C?N? P framework. A planar zig-zag configuration has been proposed for the long range 31P? 1H couplings. 相似文献
838.
Capillary electrophoresis using immobilized whole cells with overexpressed endothelin receptor for specific ligand screening 总被引:1,自引:0,他引:1
A new capillary electrophoresis method using immobilized cells as the stationary phase has been developed. The power of this method is demonstrated by the separation and identification of endothelin antagonists on a capillary column coated by the transfected Chinese hamster ovary (CHO) cells with overexpressing endothelin receptors. The screening results are validated by functional assays suppressing the increase of intracellular calcium concentration induced by endothelin-1. Instead of making efforts in isolating protein receptors, the easily prepared whole-cell capillary column provides a superior tool on the basis of ligand/receptor affinity for a rapid screening of potent drug candidates from compound libraries. 相似文献
839.
We demonstrate that the finite pulse RFDR sequence (J. Chem. Phys. 114 (2001) 8473) can be used effectively for 31P double-quantum NMR spectroscopy at a spinning frequency of 10 kHz. The 31P NMR data measured for hydroxyapatite and octacalcium phosphate show that sizable double-quantum excitation efficiency can be obtained with the ratio of the recoupling field to spinning frequency set equal to 1.67. 相似文献
840.