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201.
Ho-Chul Shin Richard Prager James Ng Henry Gomersall Nick Kingsbury Graham Treece Andrew Gee 《Ultrasonics》2009,49(3):344-357
Clinical ultrasound images are often perceived as difficult to interpret due to image blurring and speckle inherent in the ultrasound imaging. But the image quality can be improved by deconvolution using an estimate of the point-spread function. However, it is difficult to obtain a sufficiently accurate estimate of the point-spread function in vivo because of the unknown properties of the soft tissue in clinical applications. Local variations in the speed of sound and attenuation change the pulse and beam shape. These in turn affect the point-spread function. The purpose and novelty of this paper is therefore to explore the sensitivity of a state-of-the-art deconvolution algorithm to uncertainty in the point-spread function. The point-spread function in our restoration algorithm is made shift invariant in the lateral dimension but shift dependent in the axial direction, and is modelled to match a 128-element 1D linear array often found in clinical use. We present simulated and in vitro sensitivity analyses of two-dimensional deconvolution while varying six parameters on which the point-spread function depends. Uncertainty in the ultrasound machine is analysed by varying the axial depths of lateral and elevational foci alongside height and width of transducer elements. Sensitivity to tissue influence is investigated by varying the speed of sound and frequency-dependent attenuation of the electro-mechanical impulse response. The results are analysed both quantitatively and in terms of the perceived image quality. First, the assessment of deconvolution using the logarithmic image amplitude is found to be a better indicator of the perceived improvement in the restoration. Secondly, the two most critical parameters for two-dimensional deconvolution are discovered to be the lateral focus and the speed of sound, because the success of deconvolution is perceived primarily in terms of deblurring. We also observed similar patterns for the simulation and in vitro experiment. Finally, we show that it is possible to restore in vivo ultrasound images using an assumed point-spread function and hence conclude that an exact point-spread function is not necessary for enhancing ultrasound image quality by deconvolution. 相似文献
202.
A synthesis of 2-epi-fagomine via a highly stereoselective gold(I)-catalysed allene cyclisation is described. The stereochemical outcome of the cyclisation is opposite to that observed in previous studies. In contrast, gold(III)-catalysed cyclisation is inefficient and gives rise to double cyclisation by-products. 相似文献
203.
A perturbation analysis is carried out to the second order to give effective equations for Darcy–Brinkman flow through a porous channel with slightly corrugated walls. The flow is either parallel or normal to the corrugations, and the corrugations of the two walls are either in phase or half-period out of phase. The present study is based on the assumptions that the corrugations are periodic sinusoidal waves of small amplitude, and the channel is filled with a sparse porous medium so that the flow can be described by the Darcy–Brinkman model, which approaches the Darcian or Stokes flow limits for small or large permeability of the medium. The Reynolds number is also assumed to be so low that the nonlinear inertia can be ignored. The effects of the corrugations on the flow are examined, quantitatively and qualitatively, as functions of the flow direction, the phase difference, and the wavelength of the corrugations, as well as the permeability of the channel. It is found that the corrugations will have greater effects when it is nearer the Stokes’ flow limit than the Darcian flow limit, and when the wavelength is shorter. For the same wavelength and phase difference, cross flow is more affected than longitudinal flow by the corrugations. Opposite effects can result from 180° out-of-phase corrugations, depending on the flow direction, the wavelength, as well as the permeability. 相似文献
204.
A mixture of food additives is separated using ion-pairing electrokinetic chromatography with on-column ultraviolet detection at 190 nm. Tetrabutyl ammonium hydrogen sulfate (TBA) is used as modifier. The effect of the concentration of TBA on the migration behavior of the solutes is investigated. This method is used for the determination of the amount of additives in food samples. The percent relative standard deviation (%RSD) for the migration time is found to be less than 0.9% and that of the peak area is less than 2.5%. 相似文献
205.
The structure of {[Zn2(1,2,4,5‐btc)(pz)(H2O)4]·2(H2O)}n (1,2,4,5‐btc = 1, 2, 4, 5‐benzenetetracarboxylate, pz = pyrazine) is a two‐dimensional coordination network. The zinc(II) center is in a distorted octahedral NO5 coordination environment that is defined by one nitrogen atom of pyrazine, three oxygen atoms of carboxyl groups from 1,2,4,5‐benzenetetracarboxylate tetraanions and two water molecules. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
206.
Ng Seik Weng 《结构化学》2009,28(12):1657-1660
The procedure for collecting diffraction data at –173 °C on a twinned specimen of methyl 2-aminopyrazine-3-carboxylate by using the APEX-II software followed by de-twinning the non-merohedrally-twinned reflection data with PLATON is described. De-twinning significantly lowers the R index from 0.141 to 0.038 owing to 49% twinning. Crystal data: C6H7N3O2,monoclinic,P21/c (a = 6.3149(1),b = 16.5274(2),c = 6.4544(1) A,β = 95.759(1)°,V = 670.24(2) A^3). 相似文献
207.
Yaoyu Feng Say‐Leong Ong Jiangyong Hu Wun‐Jern Ng 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m34-m35
Reaction of 1,10‐phenanthroline (phen) with iron trichloride in the presence of sodium nitrilotriacetate (NTA) resulted in the formation of red crystals of the title complex, [Fe(C6H6NO6)(C12H8N2)(H2O)]·H2O. The Fe atom has a distorted capped trigonal prismatic coordination comprised of one tetradentate NTA, one bidentate phen molecule and a water molecule. Intermolecular O—H?O hydrogen bonds link the molecules into infinite chains. The chains are crosslinked by hydrogen bonds involving the solvent water molecule, leading to an infinite ladder packing mode. 相似文献
208.
209.
The adsorption and thermal decomposition of perfluorodimethyl ether, (CF3)2O, on a high-surface-area Al2O3 surface was investigated by FTIR under both vacuum and pressure conditions. IR spectra in the 4000-1050 cm−1 range were collected and the spectral assignments were assisted by quantum chemical ab initio calculations. The spectral evidence indicated that (CF3)2O decomposed to form adsorbed fluoroformate, FCOO (ads). Increases of temperature (up to 525 K) caused the FCOO (ads) to convert to hydrogen formate, HCOO (ads). Surface hydroxyl groups participated in the decomposition of (CF3)2O and the conversion of FCOO (ads) to HCOO (ads). A decomposition mechanism is proposed. 相似文献
210.