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171.
Dung T. Tran Ian P. Jones Jon A. Preece Roy L. Johnston Coenraad R. van den Brom 《Journal of nanoparticle research》2011,13(9):4229-4237
Dodecanethiol-capped Cu–Au nanoparticles, synthesized via a successive two-phase (water/toluene) and galvanic-exchange procedure,
were characterized using transmission electron microscopy (TEM). The size range of the particles is around 1–7 nm. Electron-induced
morphological evolution was observed under high resolution (HR) TEM. Cuboctahedral morphology was found to be thermodynamically
stable. Electron-induced aggregation of two particles was also observed. Chemical ordering of cuboctahedral particles was
studied by atomic-resolution high angle annular dark field (HAADF) imaging in scanning TEM (STEM) mode and energy dispersive
X-ray (EDX) element mapping using a silicon drift detector (SDD). The particles were found to be Cu–Au mixed, and to be stable
in air. Surface plasmon resonance (SPR), which is dependent on local structure and morphology, was investigated by electron
energy loss spectroscopy (EELS). 相似文献
172.
While a number of increasingly sophisticated numerical methods have been developed for time-dependent problems in electromagnetics, the Yee scheme is still widely used in the applied fields, mainly due to its simplicity and computational efficiency. A fundamental drawback of the method is the use of staircase boundary approximations, giving inconsistent results. Usually experience of numerical experiments provides guidance of the impact of these errors on the final simulation result. In this paper, we derive exact discrete solutions to the Yee scheme close to the staircase approximated boundary, enabling a detailed theoretical study of the amplitude, phase and frequency errors created. Furthermore, we show how evanescent waves of amplitude \(O(1)\) occur along the boundary. These characterize the inconsistencies observed in electromagnetic simulations and the locality of the waves explain why, in practice, the Yee scheme works as well as it does. The analysis is supported by detailed proofs and numerical examples. 相似文献
173.
174.
Martin Giera Jon S. B. de Vlieger Henk Lingeman Hubertus Irth Wilfried M. A. Niessen 《Rapid communications in mass spectrometry : RCM》2010,24(10):1439-1446
Structural elucidation of six regioisomers of mono‐N‐octyl derivatized neomycin is achieved using MSn (up to n = 4) on an ion trap time‐of‐flight (IT‐TOF) instrument equipped with electrospray ionization. The mixture of six derivatized neomycin analogues was generated by reductive amination in a shotgun synthetic approach. In parallel to the liquid chromatography/mass spectrometry (LC/MS) detection, the antibacterial activity of the neomycin regioisomers was tested by post‐column addition of buffer and bacterial inocula, subsequent microfractionation of the resulting mixture, incubation, and finally a chemiluminescence‐based bioactivity measurement based on the production of bacterial ATP. The MS‐based high‐resolution screening approach described can be applied in medicinal chemistry to help in designing and producing new antibiotic substances, which is particularly challenging due to the high functionality of most antibiotic substances, therefore requiring advanced (hyphenated) separation and detection techniques for compound mixtures. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
175.
176.
Khaled I. Doudin Jon Songstad Karl W. Trnroos 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(4):439-440
In contrast to Se[CH2C(O)OH]2versus S[CH2C(O)OH]2, the title compound, Se[CH2CH2C(O)OH]2 or C6H10O4Se, is structurally quite similar to its sulfur analogue. The molecule has twofold symmetry. The C—Se—C bond angle is 96.48 (8)° and the Se—C bond lengths are 1.9610 (14) Å. The shortest Se?O intermolecular distance is 3.5410 (11) Å. The O?O distances in the carboxylic acid dimers are 2.684 (2) Å. The temperature dependence of the IR spectrum suggests tautomerism in the solid state. 相似文献
177.
We present a spectrally accurate numerical method for finding nontrivial time-periodic solutions of nonlinear partial differential
equations. The method is based on minimizing a functional (of the initial condition and the period) that is positive unless
the solution is periodic, in which case it is zero. We solve an adjoint PDE to compute the gradient of this functional with
respect to the initial condition. We include additional terms in the functional to specify the free parameters, which in the
case of the Benjamin–Ono equation, are the mean, a spatial phase, a temporal phase, and the real part of one of the Fourier
modes at t=0. 相似文献
178.
The lattice Boltzmann method (LBM) is used to simulate the flow through an idealized proton exchange membrane fuel cell (PEMFC) porous transport layer (PTL) geometry generated using a Monte Carlo method. Using the calculated flow field, Darcy's law is applied and the permeability is calculated. This process is applied in both through‐ and in‐plane directions of the paper as both of these permeability values are important in computational fluid dynamics models of PEMFCs. It is shown that the LBM can be used to determine permeability in a random porous media by solving the flow in the microstructure of the material. The permeability in the through‐ and in‐plane directions is shown to be different and the anisotropic nature of the geometry creates anisotropic permeability. It is also found that fiber arrangement plays a large role in the permeability of the PTL. New correlations are presented for in‐ and though‐plane permeabilities of fibrous porous media with (0.6<ε<0.8). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
179.
We present a practical approach to Anstreicher and Lee’s masked spectral bound for maximum-entropy sampling, and we describe
favorable results that we have obtained with a Branch-and-Bound algorithm based on our approach. By representing masks in
factored form, we are able to easily satisfy a semidefiniteness constraint. Moreover, this representation allows us to restrict
the rank of the mask as a means for attempting to practically incorporate second-order information.
Supported in part by NSF Grant CCR-0203426. 相似文献
180.
Research on student achievement within the University of Chicago School Mathematics Project (UCSMP) and Core‐Plus Mathematics Project (CPMP) at the secondary level is beginning to accumulate, however, much less is known about how prepared these students are for post‐secondary education. Therefore this study involving students within one tracked school district used multiple linear regression to examine the role of differential experience within two secondary Standards‐based mathematics programs, gender, and prior mathematics achievement on college algebra and calculus readiness placement test scores. Results show that there are no significant differences between students who had completed three and four years of the CPMP curriculum. UCSMP students with four or five years of experience significantly outperformed CPMP students on both assessments. Prior achievement was a significant predictor of student achievement on both examinations. Male students outperformed female students on the algebra placement exam. Students who had studied from both CPMP and UCSMP significantly outperformed students who had studied from CPMP for four years on the calculus readiness examination. 相似文献