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排序方式: 共有105条查询结果,搜索用时 0 毫秒
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Z. Varga G. Surányi N. Vajda Z. Stefánka 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(1):87-94
A rapid and simple sample preparation method for plutonium determination in environmental samples by inductively coupled plasma
sector field mass spectrometry (ICP-SFMS) and alpha-spectrometry is described. The developed procedure involves a selective
CaF2 co-precipitation for preconcentration followed by extraction chromatographic separation. The proposed method effectively
eliminates the possible interferences in mass spectrometric analysis and also removes interfering radionuclides that may disturb
alpha-spectrometric measurement. For 239Pu, 240Pu and 241Pu limits of detection of 9.0 fg·g−1 (0.021 mBq), 1.7 fg·g−1 (0.014 mBq) and 3.1 fg·g−1 (11.9 mBq) were achieved by ICP-SFMS, respectively, and 0.02 mBq by alpha-spectrometry. Results of certified reference materials
agreed well with the recommended values. 相似文献
5.
The highly hydrophobic neat alkanethiol-coated SAM on evaporated gold shows an unusually low interfacial capacitance in aqueous media. This result cannot be explained by a simple parallel plate model of the double layer with the alkanethiol monolayer as a sole dielectric separator. Interestingly, a hydrophilic SAM prepared from a neat hydroxy thiol does not show any such capacitance lowering in aqueous media. Our results suggest the existence of a "hydrophobic gap" between the alkanethiol SAM-water interface. Such a model is also very much consistent with the predictions of Lum, Chandler, and Weeks theory of length scale dependent hydrophobicity. 相似文献
6.
We describe and interpret computer simulations of the time evolution of a binary alloy on a cubic lattice, with nearest neighbor interactions favoring like pairs of atoms. Initially the atoms are arranged at random; the time evolution proceeds by random interchanges of nearest neighbor pairs, using probabilities compatible with the equilibrium Gibbs distribution at temperatureT. For temperatures 0.59Tc, 0.81 Tc, and 0.89T
c, with density of A atoms equal to that in the B-rich phase at coexistence, the density C1 of clusters ofl A atoms approximately satisfies the following empirical formulas: C1 w(1 –)3 andC
1, (1 –)4Q1w1 (2 l 10). Herew is a parameter and we defineQ
l
=
K
e
–E(K)
, where the sum goes over all translationally nonequivalentl-particle clusters andE(K) is the energy of formation of the clusterK. Forl > 10,Q
1 is not known exactly; so we use an extrapolation formulaQ
l
Aw
s
–l
l
– exp(–bl
), wherew
s is the value ofw at coexistence. The same formula (withw > w
s) also fits the observed values of C, (for small values ofl) at densities greater than the coexistence density (forT=0.59Tc): When the supersaturation is small, the simulations show apparently metastable states, a theoretical estimate of whose lifetime is compatible with the observations. For higher supersaturation the system is observed to undergo a slow process of segregation into two coexisting phases (andw therefore changes slowly with time). These results may be interpreted as a more quantitative formulation (and confirmation) of ideas used in standard nucleation theory. No evidence for a spinodal transition is found.Supported by AFOSR Grant No. 73-2430D and by ERDA Contract No. EY-76-C-02-3077*000. 相似文献
7.
O. Penrose Joel L. Lebowitz J. Marro M. H. Kalos A. Sur 《Journal of statistical physics》1978,19(3):243-267
The results of computer simulations of phase separation kinetics in a binary alloy quenched from a high temperature are analyzed in detail, using the ideas of Lifshitz and Slyozov. The alloy was modeled by a three-dimensional Ising model with Kawasaki dynamics. The temperature after quenching was 0.59T
c, whereT
c
is the critical temperature, and the concentration of minority atoms was=0.075, which is about five times their largest possible single-phase equilibrium concentration at that temperature. The time interval covered by our analysis goes from about 1000 to 6000 attempted interchanges per site. The size distribution of small clusters of minority atoms is fitted approximately byc
1(1-)3
w(t),c
1 (1–)4
Q
l
w(t)l(2l10); wherec
l
is the concentration of clusters of sizel;Q
2,...,Q
10 are known constants, the cluster partition functions;t is the time; andw(t)=0.015(1+7.17t
–1/3). The distribution of large clusters (l20) is fitted approximately by the type of distribution proposed by Lifshitz and Slyozov,c
l
,(t)=–(d/dl)
[lnt+p
(l/t)], where is a function given by those authors and is defined by(x)=C
o
e–x-C
1
e
–4x/3-C
2
e
–5x/3;C
0,C
1,C
2 are constants determined by considering how the total number of particles in large clusters changes with time.Supported by the U.S. Air Force Office of Scientific Research under Grant No. 78-3522 and by the U.S. Department of Energy under Contract No. EY-76-C-02-3077*000. 相似文献
8.
L. H. Klemm Lee Lam Bryon Severns Sandip K. Sur 《Journal of heterocyclic chemistry》1990,27(7):1969-1972
Treatment of phenanthro[4,5-bcd]thiophene ( 2 ) with acetyl chloride and aluminum chloride in nitrobenzene gives acetylation of positions ortho and para to the heteroatomic sulfur atom. In separate experiments, mixtures of 1- and 3-acetyl (50% yield, ratio 1.9:1) or of 1,5-, 1,7-, and 3,5-diacetyl (79% yield, ratio 3:1:1) derivatives were obtained. Isolated as isomerically pure products were the 1-acetyl and the 1,5-diacetyl compounds, as well as the oximes of the 1- and 3-acetyl derivatives. Comparison of these results is made with those reported for nitration of 2 , which also occurs ortho and para to the sulfur atom, and with nitration and acetylation of pyrene (the benzolog of 2 ) which substitutes in the corresponding positions. 相似文献
9.
Analysis of cyanobacterial toxins (anatoxin-a, cylindrospermopsin, microcystin-LR) by capillary electrophoresis 总被引:4,自引:0,他引:4
Capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) were applied to the simultaneous separation of cyanobacterial toxins (anatoxin-a, microcystin-LR, cylindrospermopsin). The analytical performance data of both methods, optimized for the three toxins, were similar with a precision of migration times smaller than 0.8 RSD% and a detection limit in the range of 1-4 microg/mL, using spectrophotometric detection at 230 nm. Both methods were applied to an analysis of cyanotoxins in water bloom samples and crude cyanobacterial extracts. The results obtained indicate that, for complex matrices, the sequential application of CZE and MEKC is necessary. It is recommended to use both CE techniques for the analysis of the same sample in order to confirm the results by an orthogonal approach. 相似文献
10.
Experimental Techniques - Quasi-periodic noise due to various reasons often corrupts strainmaps obtained with full-field measuring systems. The aim of this didactic paper is to show how to remove... 相似文献