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排序方式: 共有126条查询结果,搜索用时 15 毫秒
1.
P. Mun F. C. Fonseca R. Muccillo R. F. Jardim 《Physica C: Superconductivity and its Applications》2003,390(4):363-373
A systematic study of the magnetic hysteresis in transport properties of polycrystalline YBa2Cu3O7−δ–Ag compounds has been made based on two kinds of measurements at 77 K and under applied magnetic fields up to 30 mT: critical current density Jc(Ba) and magnetoresistance R(Ba). The R(Ba) curves show a minimum in their decreasing branch occurring at B=Bmin which was found to be both the excitation current Iex and the maximum applied magnetic field Bam dependent. In addition, for a certain value of Bam>5 mT, we have observed that Bmin increases with increasing Iex and reaches a saturation value. The Jc(Ba) curves show a maximum in decreasing applied magnetic fields occurring at B=Bmax. We have also found that Bmax increases with increasing Bam and reaches a saturation value. The minimum in the R(Ba) and the maximum in Jc(Ba) curves were found to be related to the trapped flux within the grains. All the experimental results are discussed within the context of the flux dynamics and transport mechanisms in these high-Tc materials. 相似文献
2.
K. E. Collins M. L. M. M. Granja R. G. Pereira Filho T. A. Anazawa I. C. S. F. Jardim 《Chromatographia》1997,45(1):99-103
Summary Poly(methyloctylsiloxane) (PMOS), sorbed into the pores of HPLC silica particles by solvent evaporation, can function as a
useful stationary phase for reversed-phase chromatography. The present work addresses the question of how the PMOS is distributed
in the pores. Measurements of the surface area (BET, N2) of a series of partially loaded samples (0–40% PMOS, m/m) using a typical batch of HPLC silica (10 μm irregular particles
with 6 nm pores) show that the specific surface area of the samples decreases linearly with the specific loading (mass of
PMOS per gram of silica). This result is not consistent with a “film” model in which the PMOS is deposited uniformly on the
pore walls, but is consistent with a model in which long segmented “plugs” of PMOS are deposited within the pore system.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
3.
4.
A spectrophotometric method for the selective determination of antimony (III) and (V) in antileishmanial drugs is described.
The procedure is based on the reaction of Sb(III) with bromopyrogallol red (BPR) in neutral solution. As a consequence of
the Sb-BPR complex formed, the absorbance of BPR, at 560 nm, decreases proportionally to the amount of Sb(III) in the analyte
solution. The calculated apparent molar absorptivity and determination limits are 3.67 × 104 L · cm–1 · mol–1 and 1.65 × 10–6 mol/L, respectively. Sb(V) is determined after reduction to Sb(III) by iodide. The Sb(V) content determined in ten samples
of Glucantime varied from 75.40 ± 0.97 to 94.47 ± 1.0 mg/mL. Sb(III) was detected in all samples analyzed, and mean values
ranged from 5.19 ± 0.16 to 10.52 ± 0.15 mg/mL. The method is suitable for the routine quality control of pharmaceutical formulations.
Received: 26 July 1996 / Revised: 17 October 1996 / Accepted: 11 December 1996 相似文献
5.
Chromatographic evaluations of a C18 dimethylurea phase in 150 mm x 3.9 mm HPLC columns were performed using the Tanaka and Engelhardt test mixtures. The applicability of the new C18 dimethylurea phase was also evaluated with a mixture of some herbicides and their metabolites. An artificial aging procedure was also performed by passing a potassium phosphate mobile phase buffered at pH 7.0 through C18 50 mm x 3.9 mm dimethylurea columns. The column stability was evaluated by means of the chromatographic parameters obtained for the separation of some compounds from the Neue test mixture, using apolar, polar and highly basic analytes. 相似文献
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Gizelle Cristina Bedendo Isabel Cristina Sales Fontes Jardim Eduardo Carasek 《Journal of chromatography. A》2010,1217(42):6449-6454
A sensitive and precise analysis using hollow fiber renewal liquid membrane (HFRLM) extraction followed by high performance liquid chromatography–tandem mass spectrometry (LC–MS/MS) is described for determination of five sulfonamides in honey samples. In this procedure, the organic solvent introduced directly into the sample matrix extracts the sulfonamides and carries them over the polypropylene porous membrane. An organic solvent is immobilized inside the polypropylene porous membrane, leading to a homogeneous phase. The stripping phase at higher pH in the lumen of the membrane promotes the ionization of the target compounds releasing them to this phase. The most important parameters affecting the extraction efficiency were optimized by multivariable designs (pH and sample mass, pH and buffer for stripping phase, extraction temperature and time, type and volume of extractor solvent and use of salt to saturate the sample). Detection limits in the range of 5.1–27.4 μg kg−1 and linearity coefficient of correlation higher than 0.987 were obtained for the target analytes. The results obtained for the proposed method show that HFRLM–LC–MS/MS can be used for determination of the five sulfonamides studied in honey samples with excellent precision, accuracy, practicality and short analysis time. 相似文献
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9.
Isabel Cristina S. F. Jardim Kenneth E. Collins Carol H. Collins 《Microchemical Journal》2004,77(2):191-198
Polysiloxanes immobilized onto the surfaces of porous silica particles have proven to be good stationary phases for the separation of multiresidues of pesticides and their metabolic/degradation products by reversed-phase high-performance liquid chromatography (RP-HPLC). Similar materials have proven effective for pre-concentration and clean-up procedures using solid phase extraction. The present paper describes the preparation and some applications of several of these packing materials. 相似文献
10.
Takahashi K Kodama R Tanaka KA Hashimoto H Kato Y Mima K Weber FA Barbee TW Da Silva LB 《Physical review letters》2000,84(11):2405-2408
A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front. 相似文献