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[reaction: see text] Enantiomerically pure 1-(1Z,3E)-sulfinyl iron(0) dienols have been elaborated to bis-olefins capable of undergoing ring-closing metathesis chemistry. Using Grubbs' ruthenium carbene catalyst, a six-membered carbocycle (with one chiral center) and seven-, eight-, and nine-membered carbocycles (with two chiral centers) have been prepared. Novel transformations include the LiClO4-promoted allylation of an alkylidene malonate and a reductive sulfur-carbon bond cleavage to convert a vinyl sulfoxide into an alkene with SmI2. 相似文献
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A method of determining the phase-encode order for MR Fourier-encoded imaging is described, which provides an additional option for optimizing images from samples with signals that change during data acquisition. Examples are in hyperpolarized helium gas imaging of the lungs where polarization is lost with each RF pulse or the signal changes observed in rapid dynamic studies with T1 or T2* contrast agents when mixing is taking place. The method uses a single frequency-encoded projection in the proposed phase-encoding direction. The projection is subsequently sorted into signal-to-noise ratio (SNR) order. The indices of the sorted array are then used to create the phase-encode table to be used for the scan. This phase table is sorted in descending SNR order for signals that decrease during data acquisition and in ascending order for signals that increase during data acquisition. Simulations suggest that this technique can produce higher resolution than centric-ordered phase encoding at the expense of increased modulation (ghosting) artifact for dynamically changing signals. Initial practical implementation of the technique has been carried out on a dedicated 0.2-T Niche MR system, and the test object results agree well with simulations. Hyperpolarized 3-He lung images have also been acquired and postprocessed using the SNR phase order k-space encoding (SPOKE) methodology and show potential for improved imaging with high flip angles where polarization is rapidly lost. Applications may also be found for 3D volumetric acquisitions where two dimensions can be SPOKE encoded. 相似文献
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Fichele S Paley MN Woodhouse N Griffiths PD van Beek EJ Wild JM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(1):1-11
Finite difference simulations have been used to model (3)He gas diffusion in simulated lung tissue. The technique has the advantage that a wide range of structural models and diffusion-sensitizing gradient waveforms can be investigated, for which analytical methods would otherwise be virtually impossible. Results from simulations and in vivo pulsed-gradient-spin-echo (PGSE) experiments show that the apparent diffusion coefficient (ADC) is a function of diffusion time and gradient strength, and suggests diffusion is locally anisotropic. The simulations have been compared to recent work on an analytical model that characterizes lung tissue as a series of independent cylinders. The results presented may have clinical implications for (3)He ADC measurements in assessing lung diseases such as chronic-obstructive-pulmonary-disease. 相似文献
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W. Simarew S. G. Menefee O. R. Overman A. Gorbatschewa H. Chr Jorgensen I. V. Hunt A. Konoplew H. Fincke C. Ehrlich R. Trommsdorff M. Asdrubali S. Hadwen R. Gwatkin F. K. Neave H. D. Kay W. R. Graham R. Aschaffenburg A. Jepsen P. Madelung Ch. Paley H. Kreker A. M. Williams May Davies S. B. Thomas G. M. Phillips W. M. Ashton G. D. Simons J. Davies B. F. Thomas L. Little H. A. Sirks G. Sjöström P. Jaulmes L. Poujol und J. A. B. Smith 《Fresenius' Journal of Analytical Chemistry》1943,126(7):282-286
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Ruoyu Hong * Jianmin Ding Guoliang Zheng College of Chemistry Chemical Engineering Soochow University Suzhou P. R. China Institute of Process Engineering Chinese Academy of Sciences Beijing P. R. China IBM HYDA/- C Highway North Rochester MN USA *Author to whom correspondence should be addressed. E-mail: rhong@suda.edu.cn 《中国颗粒学报》2004,2(5):207-214
1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can … 相似文献
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In this paper, we consider nonlinear Schrödinger (NLS) equations, both in the anomalous and normal dispersive regimes, which govern the propagation of a single field in a fiber medium with phase modulation and fibre gain (or loss). The integrability conditions are arrived from linear eigen value problem. The variable transformations which connect the integrable form of modified NLS equations are presented. We succeed in Hirota bilinearzing the equations and on solving, exact bright and dark soliton solutions are obtained. From the results, we show that the soliton is alive, i.e. pulse area can be conserved by the inclusion of gain (or loss) and phase modulation effects. 相似文献
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Matthew B. Freeman Ozioma D. Edokobi Jonathan H. Gillen Margaret Kocherga Kathleen M. Dipple Prof. Daniel S. Jones Dr. Daniel W. Paley Prof. Le Wang Prof. Christopher M. Bejger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(55):12523-12527
The design of metal–organic frameworks (MOFs) that incorporate more than one metal cluster constituent is a challenging task. Conventional one-pot reaction protocols require judicious selection of ligand and metal ion precursors, yet remain unpredictable. Stable, preformed nanoclusters, with ligand shells that can undergo additional coordination-driven reactions, provide a platform for assembling multi-cluster solids with precision. Herein, a discrete Co6S8(PTA)6 (PTA=1,3,5-triaza-7-phosphaadamantane) superatomic-metalloligand is assembled into a three-dimensional (3D) coordination polymer comprising Cu4I4 secondary building units (SBUs). The resulting heterobimetallic framework ( 1 ) contains two distinct cluster constituents and bifunctional PTA linkers. Solid-state diffuse reflectance studies reveal that 1 is an optical semiconductor with a band-gap of 1.59 eV. Framework-modified electrodes exhibit reversible redox behavior in the solid state arising from the Co6S8 superatoms, which remain intact during framework synthesis. 相似文献
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Kihong Lee Bonnie Choi Dr. Ilan Jen‐La Plante Maria V. Paley Xinjue Zhong Prof. Andrew C. Crowther Prof. Jonathan S. Owen Prof. Xiaoyang Zhu Prof. Xavier Roy 《Angewandte Chemie (International ed. in English)》2018,57(21):6125-6129
Two‐dimensional (2D) materials are commonly prepared by exfoliating bulk layered van der Waals crystals. The creation of synthetic 2D materials from bottom‐up methods is an important challenge as their structural flexibility will enable chemists to tune the materials properties. A 2D material was assembled using C60 as a polymerizable monomer. The C60 building blocks are first assembled into a layered solid using a molecular cluster as structure director. The resulting hierarchical crystal is used as a template to polymerize its C60 monolayers, which can be exfoliated down to 2D crystalline nanosheets. Derived from the parent template, the 2D structure is composed of a layer of inorganic cluster, sandwiched between two monolayers of polymerized C60. The nanosheets can be transferred onto solid substrates and depolymerized by heating. Electronic absorption spectroscopy reveals an optical gap of 0.25 eV, narrower than that of the bulk parent crystalline solid. 相似文献
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The behavior of plutonium ions in a solution of trilon B was investigate At pH 3–5 plutonmin(VI) is reduced to plutonium(V) and a (I I) complex of plutonium(V) and trilon B is formed Withi excess trilon B a plutonium(lV ) -trilon B complex is formed after some time 相似文献