排序方式: 共有58条查询结果,搜索用时 15 毫秒
41.
Davis JJ Bruce D Canters GW Crozier J Hill HA 《Chemical communications (Cambridge, England)》2003,(5):576-577
Engineered metalloproteins and enzymes can be self assembled on pristine gold electrodes in robust, electrochemically-addressable, arrays. 相似文献
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In the 32S(t,p)34S reaction at 10 MeV, qualitative differences appear in the 0+ → 0+ angular distributions even at forward angles. Qualitatively similar differences result from simple distorted-wave calculations, using pure microscopic configurations. 相似文献
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In order to study the effect of substitution of Fe3+ by Al3+ and Cr3+ in Li0.5Fe2.5O4 on its structural and magnetic properties, the spinel system Li0.5Al x Cr x Fe2.5?2x O4 (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and 57Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al3+ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5). 相似文献
44.
Wei Q Liu F Xia L Crozier S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,172(2):222-230
This paper presents a finite-difference time-domain (FDTD) simulator for electromagnetic analysis and design applications in MRI. It is intended to be a complete FDTD model of an MRI system including all RF and low-frequency field generating units and electrical models of the patient. The program has been constructed in an object-oriented framework. The design procedure is detailed and the numerical solver has been verified against analytical solutions for simple cases and also applied to various field calculation problems. In particular, the simulator is demonstrated for inverse RF coil design, optimized source profile generation, and parallel imaging in high-frequency situations. The examples show new developments enabled by the simulator and demonstrate that the proposed FDTD framework can be used to analyze large-scale computational electromagnetic problems in modern MRI engineering. 相似文献
45.
Zhao H Crozier S Doddrell DM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,140(2):340-346
Two-dimensional 1H/13C polarization inversion spin exchange at the magic angle experiments were applied to single crystal samples of amino acids to demonstrate their potential utility on oriented samples of peptides and proteins. High resolution is achieved and structural information obtained on backbone and side chain sites from these spectra. A triple-resonance experiment that correlates the 1H-13Calpha dipolar coupling frequency with the chemical shift frequencies of the alpha-carbon, as well as the directly bonded amide 15N site, is also demonstrated. In this experiment the large 1H-13Calpha heteronuclear dipolar interaction provides an independent frequency dimension that significantly improves the resolution among overlapping 13C resonances of oriented polypeptides, while simultaneously providing measurements of the 13Calpha chemical shift, 1H-13C dipolar coupling, and 15N chemical shift frequencies and angular restraints for backbone structure determination. 相似文献
46.
Determination of diquat and paraquat in water by liquid chromatography-(electrospray ionization) mass spectrometry 总被引:1,自引:0,他引:1
Vince Y. Taguchi Steve W. D. Jenkins Patrick W. Crozier David T. Wang 《Journal of the American Society for Mass Spectrometry》1998,9(8):830-839
A method for the determination of the herbicides diquat and paraquat in water was developed using liquid chromatography-(electrospray ionization) mass spectrometry [LC-(ESI)MS]. The analytes were isolated on an ENVI-8 DSK solid phase extraction (SPE) disk and eluted with 5-M trifluoroacetic acid (TFA). The eluate was evaporated to dryness and the analytes were redissolved in the mobile phase (7% methanol/93% water/25-mM TFA). The extract was analyzed by liquid chromatography (C1 column) with postcolumn addition of propionic acid/methanol followed by (ESI)MS. Diquat was detected using the [M2+ ? H+] ion (M2+ = dication) at m/z 183, whereas paraquat was detected using the mono-trifluoroacetate ion pair [M2+/?OOCCF3] at m/z 299. Quantitation was done by isotope dilution mass spectrometry using d 4-diquat and d 8-paraquat and the corresponding ions [M2+ ? D+] and [M2+/?OOCCF3] at m/z 186 and m/z 307, respectively. Detection limits of 0. 1 and 0. 2 µg/L, respectively (based on the dications), were adequate to meet the Ontario Drinking Water Objectives of 70 and 10 µg/L, respectively, and the Ontario Provincial Water Quality Objective for diquat of 0. 5 µg/L. Precision and accuracy were 14% and 6% for diquat and 12% and 3% for paraquat. 相似文献
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48.
Huawei Zhao Stuart Crozier David M. Doddrell 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,141(2):340
This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. A new type of asymmetric magnet is proposed in this work. The asymmetric MRI magnet allows the diameter spherical imaging volume to be positioned close to one end of the magnet. The main advantages of making the magnet asymmetric include the potential to reduce the perception of claustrophobia for the patient, better access to the patient by attending physicians, and the potential for reduced peripheral nerve stimulation due to the gradient coil configuration. The results highlight that the method can be used to obtain an asymmetric MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1.2 m in length. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries. 相似文献
49.
Massimo Catalano Antonietta Taurino Jiangtao Zhu Peter A. Crozier Simone Dal Zilio Matteo Amati Luca Gregoratti Benedetto Bozzini Claudio Mele 《Journal of Solid State Electrochemistry》2018,22(12):3761-3773
Dy- and Tb-doped CeO2-Ni cermets for highly active solid-oxide fuel-cell (SOFC) anodes were fabricated by a one-pot electrodeposition process. Undoped, singly-doped, and co-doped powders were synthesized in an X-ray amorphous state, heat treated in air, and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) at different crystallization stages. In particular, in situ TEM analyses were carried out during heating in an oxygen atmosphere, in order to follow the evolution of structure and morphology and to understand the role of the dopants. The key structural effect of dopants was the inhibition of grain coarsening during heat treatment. Functional tests were carried out with micro-single chamber SOFCs, fed with a CH4/O2 mixture, the anodes of which were prepared with the CeO2-Ni powders synthesized in this study. A correlation was established between the electrocatalytic performance and the morphology of the anodic material, pinpointing that the finer and more homogeneous nanocrystalline structure of the doped powders results in better-defined and more active catalytic sites, thus improving the performance of the cell. 相似文献
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