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991.
Ana Gago-Martínez José Manuel Leão Nuria Piñeiro Esther Carballal Estela Vaquero María Nogueiras 《International journal of environmental analytical chemistry》2013,93(6):443-456
In this work capillary electrophoresis (CE) with UV detection has been applied to the analysis of different natural toxins produced in the aquatic environment. This technique is presented as an alternative to other chemical techniques such as HPLC, and the optimisation of analytical methodologies was carried out for diverse marine toxins including Paralytic and Amnesic and some polyether toxins, such as Yessotoxins, as well as for certain microcystin toxins produced by cyanobacteria present in freshwaters. Sample preparation steps were optimised and adequate electrophoretic conditions developed for achieving a complete separation of compounds with similar structures involved in such contamination. The influence of the biological matrices where they are involved has also been studied and the potential use of CE-UV as a tool for monitoring these aquatic toxins is also discussed. 相似文献
992.
Fabiano V. Pereira Redouane Borsali Aloir A. Merlo Nadya P. Da Silveira Corresponding author 《Liquid crystals》2013,40(5):655-661
Small angle X-ray scattering was used to examine the new chiral side chain liquid crystalline polyacrylates (P4M and P11M) and their mixtures (2?wt?%) in the low molar mass nematogenics 4′-n-pentyl-4-cyanobiphenyl (5CB) and 4′-octyl-4-cyanobiphenyl (8CB). Complementary data were obtained by polarizing optical microscopy. In agreement with previous studies, the mesophases of the bulk polymers show a dependence on the aliphatic spacers linking the mesogenic units to the polymer backbone. Chiral nematic and smectic A1 phases were observed for the polyacrylates with four (P4M) and eleven (P11M) methylene units as spacers, respectively. In solution with 5CB and 8CB, P4M exhibits an injected smectic phase, whereas P11M maintains the smectic arrangement already observed in the bulk, with swollen smectic layers. In all the mixtures, layer stability was found to depend on the liquid crystal used as solvent, as well as on the temperature. At temperatures corresponding to the nematic 5CB and 8CB, the coexistence of two mesophases was observed in the mixtures. Moreover, with the liquid crystal solvents in the isotropic phase, microstructures suspended in the solvent matrix containing the liquid crystalline polymer in the smectic arrangement were detected. 相似文献
993.
R. Martins P. Barquinha L. Pereira I. Ferreira E. Fortunato 《Applied Physics A: Materials Science & Processing》2007,89(1):37-42
This paper aims to discuss the effect of order and disorder on the electrical performances of covalent silicon semiconductors
and ZnO based ionic oxide semiconductors used as active channel layers in thin film transistors. The effect of disorder on
covalent semiconductors directly affects their electrical transport properties due to the asymmetric behaviour of sp states,
while in ionic oxide semiconductors it is found that this effect is small due to the fact that angular disorder has no effect
on the spherical symmetry of s states. To this we must add that the mobility of carriers in both systems is quite different,
being also affected by electron–phonon interactions (weak in silicon and strong in ionic oxides leading to formation of polarons).
Besides, the impurity doping effect and the presence of vacancies in disordered silicon and in ionic oxides behave differently,
which will influence the thin film properties and so, the performances of the devices produced.
PACS 81.05.Gc; 81.05.Hd; 85.30.Tv 相似文献
994.
Summary We introduce a simple variation of Doeblin's condition, Condition D*, that assures the uniform ergodicity of a Markov chain.
It is also shown that for non-homogeneous chains our conditions are equivalent to Dobrushin's weak ergodic coefficient. 相似文献
995.
We present a new allocation rule for the class of games with a nonempty core: the core-center. This allocation rule selects a centrally located point within the core of any such game. We provide a deep discussion of
its main properties. 相似文献
996.
A high energy density source based on nuclear isomers may be conceptually attractive; but it is unrealistic if the energy’s price is too excessive. This paper estimates the price of isomeric energy, and shows that isomers can become practical only for low-energy applications. 相似文献
997.
J. Dweck A. L. Cherem da Cunha Carolina Afonso Pinto J. Pereira Gon?alves P. M. Büchler 《Journal of Thermal Analysis and Calorimetry》2009,97(1):85-89
When cement hydrated compositions are analyzed by usual initial mass basis TG curves to calculate mass losses, the higher
is the amount of additive added or is the combined water content, the higher is the cement ‘dilution’ in the initial mass
of the sample. In such cases, smaller mass changes in the different mass loss steps are obtained, due to the actual smaller
content of cement in the initial mass compositions. To have a same mass basis of comparison, and to avoid erroneous results
of initial components content there from, thermal analysis data and curves have to be transformed on cement calcined basis,
i.e. on the basis of cement oxides mass present in the calcined samples or on the sample cement initial mass basis.
The paper shows and discusses the fundamentals of these bases of calculation, with examples on free and combined water analysis,
on calcium sulfate hydration during false cement set and on quantitative evaluation and comparison of pozzolanic materials
activity. 相似文献
998.
P. P. Bakare S. K. Date Y. B. Khollam S. B. Deshpande H. S. Potdar S. Salunke-Gawali F. Varret E. Pereira 《Hyperfine Interactions》2006,168(1-3):1127-1132
Microwave–hydrothermal (MH) route was employed to synthesize various iron oxide phases in ultra-fine crystalline powders by using ferrous sulphate and sodium hydroxide as starting chemicals. All chemical reactions were carried out under identical MH conditions, namely, at 190°C, 154 psi, 30 min, by varying the molar ratio (MR) of FeSO4/NaOH in the aqueous solutions. The variation of MR has a dramatic effect on the crystallization behavior of various phases of iron oxides under MH processing conditions. For example, spherical agglomerates of Fe3O4 powder were obtained if MR equal to 0.133 (pH?>?10 sample A). On the other hand non-stoichiometric Fe3O4 powders (Sample B) were obtained for all higher MR of FeSO4/NaOH between 0.133 and 4.00 (6.6?2O3 powders (sample C) were produced. Fe57 Mössbauer spectra were recorded for all the three sets of samples at room temperature. In the case of sample B, temperature dependent Mössbauer spectra were recorded in the range of 77–300 K to understand the non-stoichiometric nature of Fe3O4 powders. All these results are discussed in the present paper. 相似文献
999.
1000.
J.L. López W.A. Pacheco Serrano S.L. Pereira H.-D. Pfannes 《Hyperfine Interactions》1999,122(1-2):209-215
Mössbauer spectroscopy, magnetization and X-ray diffrraction measurements of the ternary compound Y(Fe0.95Mn0.05)2 prepared by melting were performed in order to investigate the effect of the substitution of Mn on the magnetic properties of YFe2. The experimental results show change of the lattice parameter. The magnetization and the Curie temperature decrease with substitution of Fe by Mn. 相似文献