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排序方式: 共有86条查询结果,搜索用时 15 毫秒
1.
用自由基溶液降合方法制备一系列苯乙烯-丙烯酸甲酯线型共聚物,用核磁共振测定了苯基在共聚物中的百分比,在该共聚物的四氢呋喃溶液中,用三氟乙酸汞在共聚物的苯环上进行亲电取代反应,得到可溶性汞化共聚物,由于这类泵化共的可溶于四氢呋喃,二氯甲烷等溶剂,用重沉淀法多次提纯,得到了纯度很高,溶解性较好的含重金属二价汞的共聚物,用红外光谱仪测定共聚物上的汞基团,用原子吸收定量测试共聚中的汞的百分聚代率,结果表明 相似文献
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3.
C. Baiocchi D. Giacosa G. Saini P. Cavalli N. Omenetto R. Passarella 《International journal of environmental analytical chemistry》2013,93(1-4):211-218
Abstract Measurements of thallium levels in Antarctic snow samples collected in an area surrounding the Italian Station at Terra Nova Bay in different campaigns have been performed without preconcentration by means of Laser Induced Atomic Fluorescence Spectroscopy (LIAF) as well as by High Resolution Inductively Coupled Plasma Mass Spectrometry (HR ICP-MS). The data obtained by both methods compare favourably and are of the order of tenths of pg/g. The data is discussed taking into account the effect of the marine aerosol and the crustal contribution to the thallium content in samples. 相似文献
4.
We present a practical and accurate technique for retrieving the amplitude and the phase of ultrashort pulses from a nonlinear (second-order) intensity cross correlation and the spectrum that overcomes shortcomings of previous attempts. We apply the algorithm to theoretical and experimental data and compare it with frequency-resolved optical gating. 相似文献
5.
We illustrate observation and characterization of medium- and low-intensity shaped ultrashort pulses at lambda=1.55mum through single-shot geometry (multishot-average) second-harmonic generation-frequency-resolved optical gating. The pulses are shaped by amplitude filters in the Fourier plane of a compact folded shaper. Sensitivity to pulses with energies of less than 20 pJ and high dynamic range is reported for this configuration. Application of this method to the propagation of ~170-fs pulses through a 50-m fiber link is also illustrated. 相似文献
6.
G.D. Boutilier B.D. Pollard J.D. Winefordner T.L. Chester N. Omenetto 《Spectrochimica Acta Part B: Atomic Spectroscopy》1978,33(8):401-416
This part of the review links up with the tutorial discussion in Part I and gives general signal-to-noise expressions for emission and luminescence spectrometric systems. Tabular presentations are used for the expressions and for comparison of noise sources. 相似文献
7.
We describe a new and simple method to aid in the analysis of retrieved pulses from inverted frequency-resolved optical gating (FROG) traces. The analysis can separate noise from distortion and shows that distortion is more deleterious to the retrieved pulse than is pure noise. The analysis relies on the fact that FROG traces can be constructed from a single outer product of two vectors, whereas distortion and noise require the sum of a series of outer products. 相似文献
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G. Cristoforetti A. De Giacomo M. Dell'Aglio S. Legnaioli E. Tognoni V. Palleschi N. Omenetto 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010
In the Laser-Induced Breakdown Spectroscopy (LIBS) technique, the existence of Local Thermodynamic Equilibrium (LTE) is the essential requisite for meaningful application of theoretical Boltzmann–Maxwell and Saha–Eggert expressions that relate fundamental plasma parameters and concentration of analyte species. The most popular criterion reported in the literature dealing with plasma diagnostics, and usually invoked as a proof of the existence of LTE in the plasma, is the McWhirter criterion [R.W.P. McWhirter, in: Eds. R.H. Huddlestone, S.L. Leonard, Plasma Diagnostic Techniques, Academic Press, New York, 1965, pp. 201–264]. However, as pointed out in several papers, this criterion is known to be a necessary but not a sufficient condition to insure LTE. The considerations reported here are meant to briefly review the theoretical analysis underlying the concept of thermodynamic equilibrium and the derivation of the McWhirter criterion, and to critically discuss its application to a transient and non-homogeneous plasma, like that created by a laser pulse on solid targets. Specific examples are given of theoretical expressions involving relaxation times and diffusion coefficients, as well as a discussion of different experimental approaches involving space and time-resolved measurements that could be used to complement a positive result of the calculation of the minimum electron number density required for LTE using the McWhirter formula. It is argued that these approaches will allow a more complete assessment of the existence of LTE and therefore permit a better quantitative result. It is suggested that the mere use of the McWhirter criterion to assess the existence of LTE in laser-induced plasmas should be discontinued. 相似文献
10.
N. Omenetto J.D. Winefordner C.Th.J. Alkemade 《Spectrochimica Acta Part B: Atomic Spectroscopy》1975,30(9):335-341
An expression for the effect of self-absorption on the fluorescence and thermal emission intensities is derived by taking into account stimulated emission. A simple, idealized case is considered, consisting of a two level atomic system, in a flame, homogeneous with respect to temperature and composition, and uniformly illuminated by an external quasi-continuum radiation source. 相似文献