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81.
82.
H. Svoboda G. M. Moir C. H. Whitnah S. Dixon J. H. Sugden G. T. Pyne 《Analytical and bioanalytical chemistry》1931,86(11-12):468-471
83.
Parametrical studies of electroosmotic transport characteristics in submicrometer channels 总被引:1,自引:0,他引:1
Postler T Slouka Z Svoboda M Pribyl M Snita D 《Journal of colloid and interface science》2008,320(1):321-332
Spatially two-dimensional nonequilibrium mathematical model describing electroosmotic flow through a submicrometer channel with an electric charge fixed on the channel walls is presented. This system is governed by the hydrodynamic, electrostatic, and mass transport phenomena. The model is based on the coupled mass balances, Poisson, Navier-Stokes, and Nernst-Planck equations. Nonslip boundary conditions are employed. The effect of an imposed electric field on the system behavior is studied by means of a numerical analysis of the model equations. We have obtained the following findings. If the channel width is comparable to the thickness of the electric double layer, the system behaves as an ion-exchange membrane and the dependence of the electric current passing through the channel on the applied voltage is strongly nonlinear. In the case of negatively (positively) charged walls, a narrow region of very low conductivity (so-called ionic gate) is formed in the free electrolyte near the channel entry facing the anode (cathode) side. For a wide channel, the electric current is proportional to the applied voltage and the velocity of electrokinetic flow is linearly proportional to the electric field strength. Complex hydrodynamics (eddy formation and existence of ionic gates) is the most interesting characteristics of the studied system. Hence, current-voltage and velocity-voltage curves and the corresponding spatial distributions of the model variables at selected points are studied and described in detail. 相似文献
84.
Louis R. Pignotti Natcharee Kongprakaiwoot William W. Brennessel Jonas Baltrusaitis Rudy L. Luck Eugenijus Urnezius 《Journal of organometallic chemistry》2008,693(20):3263-3272
Reactions of 1,4-difluoro-2,5-dimethoxybenzene with LDA (1:2) at low temperatures generated organodilithio intermediates; quenching the reaction mixtures with chlorophosphines ClPR2 produced 1,4-bis(phosphino)-2,5-difluoro-3,6-dimethoxybenzenes 1a (R = Ph) and 1b (R = iPr). Demethylation of 1a–b was accomplished by BBr3, yielding bis(phosphino)hydroquinones 2a–b. Treating 2a–b with excess hydrogen peroxide produced bis(phosphinyl)hydroquinones 3a–b. The binucleating properties of 2a were established by the formation of a bimetallic nickel complex upon reaction with Ph2Ni(PMe3)2. Electrochemical activity of hydroquinones 2a–b and 3a–b was examined by cyclic voltammetry. In addition, compounds 2a, 3a and 3b were obtained in crystalline form and characterized by single-crystal X-ray diffraction. The influence of the fluorine substituents on the composition of the frontier orbitals of 2a and 3a was examined by computational methods. 相似文献
85.
Dong Q Todd Monroe W Tiersch TR Svoboda KR 《Journal of photochemistry and photobiology. B, Biology》2008,93(3):162-171
DNA photorepair has been widely studied in simple aquatic organisms that live in the marine environment, but is less understood in more complex species that live in freshwater. In the present study, we evaluated UVA-induced DNA photo recovery in embryonic stages of zebrafish, Danio rerio, a freshwater model species. Evaluation of UVB exposure and UVA photo recovery of zebrafish embryos revealed different UVB tolerances and capacities for UVA photo recovery at different stages of development. Effective UVA photo recovery was observed at 3h post-fertilization (hpf), 6-7 hpf, and 12 hpf, but not in the early cleavage stage (2-32 cells). UVA photo recovery was most effective during the gastrula stage (6-7 hpf) of development, and less effective at earlier stages (e.g., 3 hpf) or later stages (e.g., 12 hpf). Embryos at the cleavage stage of development were found to be tolerant to extreme levels of UVB exposure, and possible mechanisms were discussed. For embryos at 6-7 hpf, examination of time window (or delay of UVA exposure) that would still permit recovery from UVB exposure suggested a short time period of 2h. The transgenic fli-1 zebrafish with fluorescent vascular structure was used to show that embryos with normal morphological appearance could exhibit a disrupted vascular patterning, suggesting that this endpoint could provide a sensitive tool for detection of UV damage. 相似文献
86.
This critical review covers the application of quantum chemistry to the burgeoning area of the heterogeneous oxidation by Au. We focus on the most established reaction, the oxidation of CO at low temperature. The review begins with an overview of the methods available comparing the treatment of the electron-electron interaction and relativistic effects. The structure of Au particles and their interaction with oxide reviews is then discussed in detail. Calculations of the adsorption and reaction of CO and O(2) are then considered and results from isolated and supported Au clusters compared (155 references). 相似文献
87.
The interaction of dissolved organic matter (DOM) with copper and zinc in a concentrated seawater sample was characterised by pseudopolarography. Measurements performed at increased concentrations of copper(II) ions showed successive saturation of active DOM sites which indicate possible partition of copper between (i) free or labile complexes, (ii) reduced and released within the potential window of the method, and (iii) electroinactive copper complexes. Pseudopolarograms measured at pH 4 indicate a release of copper which was bound to the active sites of DOM that formed non-labile complexes. Variation of the peak position and half-peak width along the scanned deposition potentials and with the increasing concentration of copper bear the information about the complex electrochemical processes at the electrode surface and in the bulk of the solution. Pseudopolarograms of zinc showed a strong dependence of the peak current and the peak position along the scanned deposition potentials on pH values, indicating preferentially complexation of zinc with carboxylic-like active sites of DOM in the measured sample. Pseudopolarography is a valuable method in the trace metal complexation and speciation studies, serving as a fingerprint of the analysed sample. 相似文献
88.
Michal Kohout Alexej Bubnov Jiří Šturala Vladimíra Novotná Jiří Svoboda 《Liquid crystals》2016,43(10):1472-1485
Two series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic CA* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour. 相似文献
89.
Photobiological effects of UVA and UVB light in zebrafish embryos: evidence for a competent photorepair system 总被引:2,自引:0,他引:2
Dong Q Svoboda K Tiersch TR Monroe WT 《Journal of photochemistry and photobiology. B, Biology》2007,88(2-3):137-146
The consequences of UVB and UVA irradiation on hatch rate, mortality, and malformation were studied in embryonic zebrafish (Danio rerio). The use of zebrafish embryos has expanded from traditional developmental models to diverse studies, including many techniques utilizing light exposure. To characterize useful indicators of photodamage, the responses and threshold limits of UV radiation as a function of embryonic stage and fish source were evaluated. Significant differences in UVB susceptibility were observed in embryos at 3, 6-7, 12, and 24h post-fertilization (hpf), with the 1000-cell stage (3 hpf) having greatest tolerance to UVB. Embryos derived from zebrafish raised in outdoor ponds were more tolerant to UVB than were embryos from laboratory-raised fish. Combinations of UVB and UVA exposure were used to confirm the presence of a competent photorepair system in zebrafish that could return otherwise malformed embryos to a normal phenotype. Overall, embryonic zebrafish had large tolerances (LD(50) of 850 J/cm(2)) to UVA, confirming their suitability for photoactivation and photorepair studies. 相似文献
90.
Jonathan H. Laurer James F. Mulling Saad A. Khan Richard J. Spontak Rudy Bukovnik 《Journal of Polymer Science.Polymer Physics》1998,36(13):2379-2391
Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated at different oil concentrations to ascertain the effect of composition on TPEG morphology and mechanical properties. The impact of thermal processing is also examined by comparing gels thermally quenched to 0°C or slowly cooled to ambient temperature. Transmission electron micrographs reveal that gels with 70 to 90 wt % oil exhibit styrenic micelles measuring ca. 24 nm in diameter. Variation in composition or cooling rate does not have any perceivable effect on micelle size or shape, whereas the rate at which the gels are cooled influences the extent of microstructural order and the time to rupture (tR) at constant strain. Dynamic rheological testing confirms the presence of a physically crosslinked network at TPEG compositions ranging from 70 to 90 wt % oil, independent of cooling rate. Results presented here suggest that the dynamic elastic shear modulus (G′) scales as tαR where α varies from 0.41 to 0.59, depending on cooling rate. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2379–2391, 1998 相似文献