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排序方式: 共有560条查询结果,搜索用时 593 毫秒
121.
A series of pentacarbonyl complexes of chromium and molybdenum with unicoordinated-diphosphines, M(CO)5(η1-P-P) (P-P = dppe, dppp, dppb) has been prepared by amine oxide-induced phosphine substitution of the binary carbonyls. The basicity of the pendant phosphine groups was demonstrated by their ready conversion to the diphosphine-bridged heterobimetallic complexes (OC)5M(μ-P-P)M′(CO)5 (M, M′= Cr, Mo, W; M ≠ M′) in the presence of MCO)5(CH3CN). The complexes were characterized by IR and NMR (1H and 31P-{1H}) spectroscopy. 相似文献
122.
Elizabeth A. Carter Matthew A. Pasek Tim Smith Terence P. Kee Peter Hines Howell G. M. Edwards 《Analytical and bioanalytical chemistry》2010,397(7):2647-2658
A fulgurite is a naturally occurring glass formed when lightning hits sand, rock, or soil. The formation of fulgurites is
accompanied by mineralogical and sometimes compositional changes, and may record information about the environment in which
they were formed. A previous investigation using Raman point spectroscopy discovered the presence of anatase, a low-temperature
polymorph of TiO2, and polyaromatic hydrocarbons within a fulgurite. These findings indicate that there were regions within the sample that
were not subjected to temperatures of 2,000 K or more that the matrix is reported to attain when struck by lightning. This
paper seeks to expand the previous research by utilizing the capabilities of a new Raman spectroscopic technological development
that enables rapid mapping. The entire surface area of a cross-sectioned fulgurite (∼40 mm × 23 mm) sample was mapped allowing
several regions of polyaromatic hydrocarbons and anatase to be located. Furthermore, shocked quartz was found within the boundary
regions of the fulgurite, and is proposed to have resulted from contact with vaporized material during the lightning strike.
Shocked quartz is typically indicative of extraterrestrial impact, yet its discovery here suggests that its formation is not
exclusive to the impact process. 相似文献
123.
Jimin Yoon Won Gun Kwack Wang-Seob Shim Jun Kyu Lee Dong Kee Jang Namyi Gu Ji-Yoon Cho Kyung-Tae Lee Eun Kyoung Chung 《Biomedical chromatography : BMC》2020,34(12):e4957
Cefpiramide is frequently used to treat biliary infections. However, no bioanalytical method has been validated to quantitate cefpiramide in human samples, particularly in bile. Therefore, this study was conducted to develop a simple, selective and validated high-performance liquid chromatographic method to determine cefpiramide in human plasma and bile. A protein precipitation procedure was used to extract cefpiramide and cefoperazone (internal standard, IS) from 200 μl of plasma and bile. Utilizing a Capcell Pak C18 column (4.6 × 250 mm), cefpiramide and IS were separated using the timed-gradient mobile phase consisting of 0.1 m sodium acetate (pH 5.2) and acetonitrile at a flow rate of 1 ml/min with photodiode array detector (wavelength set at 273 nm). The calibration curves showed linearity at concentrations ranging from 1 to 150 μg/ml in both plasma and bile (r2 > 0.999). The within- and between-run coefficients of variation (CVs) for plasma samples were 0.570–4.43 and 1.10–2.76%, respectively; for bile samples, the within- and between-day precision (CV) was 0.814–6.34 and 2.05–4.00%, respectively. Our newly developed bioanalytical method was successfully employed to quantify cefpiramide concentrations in both plasma and bile at multiple time points in patients with acute cholangitis. 相似文献
124.
Seong-Hoon Kee 《Journal of sound and vibration》2011,330(22):5333-5344
Near-field scattering of surface waves by a single surface-breaking crack in solid medium has been well investigated by prior researchers. However, there have been few studies for more realistic problems involving near scattering of surface waves by distributed surface-breaking cracks. One possible reason is complexity caused by the interaction of surface waves between multiple cracks. In this study, interaction of surface waves between two surface-breaking cracks with various crack spacing was investigated. The experimental study was performed on Plexiglas specimens with non-contact sensors (air-coupled sensors, and a laser vibrometer), and compared with numerical simulation results. The effects of crack depth h, spacing a, and the number of cracks N on surface wave transmission were studied. Analyses show that for the very small crack spacing (a/h<0.2), the distributed cracks can be regarded as a single surface-breaking crack. However, for a/h ranging between approximately 1 and 6, transmission coefficient of surface waves is significantly affected by interaction between cracks. The transmission coefficients have the lowest value when a/h is between 2 and 3. When a/h is large (a/h>6), transmission coefficients obtained from experiments, and numerical simulations agree with the theoretical results based on non-interaction crack assumption. 相似文献
125.
Synthesis of 9‐[2‐(2‐hydroxymethyl‐2‐methyl‐, ‐(2‐acetoxymethyl‐2‐methyl‐, ‐(2,2‐di(hydroxymethyl)‐, and ‐(2,2‐di(acetoxymethyl)‐1,3‐dioxan‐5‐yl)ethyl] derivatives of guanine and 2‐aminopurine, 2–9 , has been accomplished in seven to eight step sequences from readily available 1‐(tert‐butyldiphenylsilyloxy)‐acetone, 1,3‐di(tert‐butyldiphenylsilyloxy)acetone, and the diol 10 . Formation of cyclic ketals 11 and 12 was carried out successfully under an acidic condition using a catalytic amount of methanesulfonic acid along with excess anhydrous copper(II) sulfate in toluene. Subsequent reactions of desilylation, acetylation, hydrogenolysis, and bromination afforded the key intermediates 19 and 20 , which were coupled with 2‐amino‐6‐chloropurine to produce the purine compounds 21 and 22 in good yields. Guanine derivatives 2–5 were obtained from 21 and 22 by hydrolysis and acetylation, while the dechlorination and hydrolysis of 21 and 22 yielded the 2‐aminopurine compounds 6–9 . 相似文献
126.
127.
128.
Le Thi Kim Van Tran Manh Hung Soo Hyun Kim Jin Cheol Kim MinKyun Na Hyun Ju Jung Seung Jun Kwack Kee Tae Kweon Jae Sue Choi Hyeong Kyu Lee KiHwan Bae Byung‐Sun Min 《Helvetica chimica acta》2010,93(9):1803-1807
A new stereoisomer of a tetrahydrofuranoid lignan, acerifuranoid A ( 1 ), and two new oleanane‐type triterpenoids, aceriphyllic acids J and K ( 2 and 3 ), were isolated from the roots of Aceriphyllum rossii. Their structures were elucidated on the basis of spectroscopic analyses and chemical evidence. These isolated compounds exhibited weak cytotoxic activity against various cancer cell lines with IC50>150 μM . 相似文献
129.
Huaning Zhu Nicos S. Martys Chiara Ferraris Daniel De Kee 《ournal of non Newtonian Fluid Mechanics》2010,165(7-8):362-375
In this paper, a Lagrangian formulation of the Navier–Stokes equations, based on the smoothed particle hydrodynamics (SPH) approach, was applied to determine how well rheological parameters such as plastic viscosity can be determined from vane rheometer measurements. First, to validate this approach, a Bingham/Papanastasiou constitutive model was implemented into the SPH model and tests comparing simulation results to well established theoretical predictions were conducted. Numerical simulations for the flow of fluids in vane and coaxial cylinder rheometers were then performed. A comparison to experimental data was also made to verify the application of the SPH method in realistic flow geometries. Finally, results are presented from a parametric study of the flow of Bingham fluids with different yield stresses under various applied angular velocities of the outer cylindrical wall in the vane and coaxial cylinder rheometers. The stress, strain rate and velocity profiles, especially in the vicinity of the vane blades, were computed. By comparing the calculated stress and flow fields between the two rheometers, the validity of the assumption that the vane could be approximated as a cylinder for measuring the rheological properties of Bingham fluids at different shear rates was tested. 相似文献
130.