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排序方式: 共有1442条查询结果,搜索用时 375 毫秒
141.
Luis A. Escudero Luis D. Martinez José A. Salonia José A. Gasquez 《Microchemical Journal》2010,95(2):164-168
An on-line zinc preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The zinc was precipitated and retained on a minicolumn filled with ethyl vinyl acetate (EVA) at pH 9.0, without using any complexing reagent. The zinc ions were eluted from the minicolumn with 10% (v/v) hydrochloric acid. Experimental conditions including pH and sample loading and eluting variables were evaluated and established.An enrichment factor (EF) of 44 was obtained for Zn2+ with a preconcentration time of 120 s. Under the optimal conditions, the value of the limit of detection (3σ) for the preconcentration of 10 mL of sample was 0.08 μg L− 1. The sampling frequency was about 24 h− 1. The precision for six replicate determinations (repeatability conditions) at 50 μg L− 1 Zn level was 3.94% relative deviation standard (RSD), calculated from the peak heights obtained. The methodology was successfully applied to the determination of zinc in tap water samples and in a certified VKI reference material QC Metal LL1 DHI (Water & Environment) Denmark. 相似文献
142.
Cross-coupling reaction of alkyl and aryl magnesium halides with 4-chloro-pyrrolo-[3,2-c]quinoline in the presence of a catalytic amount of iron salt is described. The reactions are completed in 30 min, resulting in moderate to excellent yields of 52–94% in a tetrahydrofuran (THF)–N-methylpyrrolidinone (NMP) solvent mixture. 相似文献
143.
E. R. Dixon M. S. A. Blackwell M. S. Dhanoa Z. Berryman N. de la Fuente Martinez D. Junquera A. Martinez P. J. Murray H. F. Kemp W. Meier‐Augenstein A. Duffy R. Bol 《Rapid communications in mass spectrometry : RCM》2010,24(5):511-518
Variations in natural abundance of carbon (C) and nitrogen (N) stable isotopes are widely used as tools for many aspects of scientific research. By examining variations in the ratios of heavy to light stable isotopes, information can be obtained as to what physical, chemical and biological processes may be occurring. The spatial heterogeneity of soil δ15N‐ and δ13C‐values across a range of scales and under different land use have been described by a number of researchers and the natural abundances of the C and N stable isotopes in soils have been found to be correlated with many factors including hydrology, topography, land use, vegetation cover and climate. In this study the Latin square sampling +1 (LSS+1) sampling method was compared with a simple grid sampling approach for δ13C and δ15N measurement at the field scale. A set of 144 samples was collected and analysed for δ15N and δ13C from a 12 × 12 grid (in a 1 ha improved grassland field in south‐west England). The dimension of each cell of the grid was approximately 11 × 6 m. The 12 × 12 grid was divided into four 6 × 6 grids and the LSS+1 sampling technique was applied to these and the main 12 × 12 grid for a comparison of sample means and variation. The LSS+1 means from the 12 × 12 grid and the four 6 × 6 grids compared well with the overall grid mean because of the low variation within the field. The LSS+1 strategy (13 samples) generated representative samples from the 12 × 12 grid, and hence would be an acceptable method for sampling similar plots for the measurement of mean isotopic composition. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
144.
Ch. Schwan F. Martin G. Jakob J.C. Martinez H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):477-481
We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O and BaTiO3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction.
The ferroelectric behaviour of the BaTiO3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm
and a remanent polarisation of 1.25 μC/cm2. At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indicates
an interaction of domain walls with randomly distributed pinning centres. At a field of 5 MV/m we calculate a 3% contribution
of the irreversible domain wall motion to the total dielectric constant.
Received 24 June 1999 and Received in final form 27 August 1999 相似文献
145.
E. Liarokapis L. T. Wille Th. Leventouri L. Martinez H. Lu
V. Hadjiev
M. Iliev 《Physica C: Superconductivity and its Applications》1990,170(5-6):419-426The effects of Fe-substitution of YBa2Cu3Oy have been investigated by means of Raman scattering, X-ray diffraction, resistivity and susceptibility measurements. A series of samples of YBa2(Cu1 − xFex)3Oy with different dopant concentration (0 x 0.15) has been prepared in two batches, the second set having undergone twice the heat and mechanical treatment used to produce the first batch. Considerable improvement in the superconducting transition temperature, Tc, is obtained upon reprocessing. A phase transformation from orthorhombic to tetragonal symmetry is observed for x=0.05 from the X-ray measurements in agreement with previous work. Using a micro-Raman technique, all five Ag vibrational modes have been measured and their dependence on Fe-concentration is analyzed. There are indications that iron substitutes for copper at both sites and that the structure is a mixture of orthorhombic and tetragonal microdomains for all x. 相似文献
146.
B. J. Garcia J. Martinez J. Piqueras 《Applied Physics A: Materials Science & Processing》1990,51(5):437-445
GaAs melting simulations with a pulsed ruby laser are reported. The presence of a thin metal layer deposited on the GaAs surface gives rise to a reduction in the melting threshold and to an increase of melted depths when compared with nude GaAs surfaces. Melting thresholds around 0.3 J/cm2 for nude GaAs surface and slightly below 0.25 J/cm2 for GaAs covered with a 120 Å tin layer are predicted in reasonable agreement with experimental results. 相似文献
147.
148.
V.B. Timofeev A.V. Larionov J. Zeman G. Martinez V.I. Falko M. Bayer A. Forchel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):39-43
Magnetooptical studies performed on a wide InGaAs/GaAs single quantum well indicate that optically non-active (dark) excitons
with total angular momentum play the role of a reservoir for the creation of free multiparticle excitonic complexes. After analyzing the magnetic field
evolution of the circularly polarized components of the low energy structure appearing in the main excitonic luminescence
line we assign this feature to the excitonic trion formation. The binding energy of the excitonic trions was estimated to
be of the order of 1 meV.
Received: 29 October 1997 / Received in final form: 20 February 1998 / Accepted: 21 February 1998 相似文献
149.