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Principal components analysis (PCA) factor filtering is implemented for the improvement of background removal in noisy spectra. When PCA is used as a method for filtering before background removal in electron energy loss spectroscopy elemental maps, an improvement in the accuracy of the background fit with very short fitting intervals is achieved, leading to improved quality of elemental maps from noisy spectra. This opens the possibility to use shorter exposure times for elemental mapping, leading to fewer problems with, for example, drift and beam damage. 相似文献
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Sanz-Navarro CF Astrand PO Chen D Rønning M van Duin AC Jacob T Goddard WA 《The journal of physical chemistry. A》2008,112(7):1392-1402
Molecular dynamics simulations have been performed with two reactive force fields to investigate the structure of a Pt100 cluster adsorbed on the three distinct sides of a carbon platelet. A revised Reax force field for the carbon-platinum system is presented. In the simulations, carbon platelet edges both with and without hydrogen termination have been studied. It is found that the initial mismatch between the atomic structure of the platelet egde and the adsorbed face of the Pt100 cluster leads to a desorption of a few platinum atoms from the cluster and the subsequent restructuring of the cluster. Consequently, the average Pt-Pt bond length is enlarged in agreement with experimental results. This change in the bond length is supposed to play an important role in the enhancement of the catalytic activity, which is demonstrated by studying the changes in the bond order of the platinum atoms. We found an overall shift to lower values as well as a loss of the well-defined peak structure in the bond-order distribution. 相似文献
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Kongsted J Osted A Mikkelsen KV Astrand PO Christiansen O 《The Journal of chemical physics》2004,121(17):8435-8445
We present a study of the blueshift of the n-->pi* electronic transition in formaldehyde in aqueous solution using a combined coupled cluster/molecular mechanics model including mutual polarization effects in the Hamiltonian. In addition, we report ground and excited state dipole moments. Configurations are generated from molecular dynamics simulations with two different force fields, one with and one without an explicit polarization contribution. A statistical analysis using 1200 configurations is presented. Effects of explicit polarization contributions are found to be significant. It is found that the main difference in the effects on the excitation energies arises from the fact that the two force fields result in different liquid structures, and thus a different set of configurations is generated for the coupled cluster/molecular mechanics calculations. 相似文献
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Instabilities of a moving nematic-isotropic interface 总被引:1,自引:0,他引:1
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A simple and efficient method has been developed for the synthesis ofα-amino nitriles from aldehydes,amines and trimethylsilyl cyanide(Me3SiCN) in the presence of a catalytic amount of cyanuric acid at room temperature. 相似文献
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Osted A Kongsted J Mikkelsen KV Astrand PO Christiansen O 《The Journal of chemical physics》2006,124(12):124503
Liquid water is investigated theoretically using combined molecular dynamics (MD) simulations and accurate electronic structure methods. The statistical mechanically averaged molecular properties of liquid water are calculated using the combined coupled cluster/molecular mechanics (CC/MM) method for a large number of configurations generated from MD simulations. The method includes electron correlation effects at the coupled cluster singles and doubles level and the use of a large correlation consistent basis set. A polarizable force field has been used for the molecular dynamics part in both the CC/MM method and in the MD simulation. We describe how the methodology can be optimized with respect to computational costs while maintaining the quality of the results. Using the optimized method we study the energetic properties including the heat of vaporization and electronic excitation energies as well as electric dipole and quadrupole moments, the frequency dependent electric (dipole) polarizability, and electric-field-induced second harmonic generation first and second hyperpolarizabilities. Comparisons with experiments are performed where reliable data are available. Furthermore, we discuss the important issue on how to compare the calculated microscopic nonlocal properties to the experimental macroscopic measurements. 相似文献
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Capacity of a Simultaneous Quantum Secure Direct Communication Scheme between the Central Party and Other M Parties 下载免费PDF全文
We analyse the capacity of a simultaneous quantum secure direct communication scheme between the central party and other M parties via M+1-particle GHZ states and swapping quantum entanglement. It is shown that the encoding scheme should be secret if other M parties wants to transmit M + 1 bit classical messages to the centre party secretly. However, when the encoding scheme is announced publicly, we prove that the capacity of the scheme in transmitting the secret messages is 2 bits, no matter how large M is. 相似文献
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An efficient 1-methylimidazole-catalyzed synthesis of dialkyl 2-[(4-methylphenyl)sulfonyl]-1H-pyrrole-3,4-dicarboxylates is described.The reactive 1:1 zwitterionic intermediate formed by the addition of 1-methylimidazole to dialkyl acetylenedicarboxylates is trapped by tosylmethyl isocyanide(TOSMIC) to afford the title compounds in excellent yields. 相似文献