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排序方式: 共有184条查询结果,搜索用时 15 毫秒
21.
The purpose of this study was to characterize, in a period of one year, two glacial lakes, Alice and Meugliano, located in an alpine reservoir on the basis of physical and chemical features. The two lakes show two periods of mixing: one in the spring and one in the autumn, so can be classified as dimictic lakes. They are characterized by pH, alkalinity, low conductivity and and quite dilute ionic concentrations. With regard to nutrients, most nitrogen occurred in the nitric form in the superficial layers. During the period of thermal stratification, in the anoxic layer NO3- decreases and NH4+ increases, confirming the activity of the anaerobic denitrificant bacteria. Total and soluble phosphorus levels show homogeneity during the cold period at different depths, while with stratification concentrations increase in the hypolimnium and metalimnium. In both lakes there is an inverse correlation between transparency and chlorophyll a. To evaluate the trophic state the conventional criteria of Nurnberg 2 and four lake trophic indices (TSIs) are used. Both evaluations suggest that the two lakes are eutrophic, with worse conditions in Alice. Deviations of the trophic states, based on the relation between TSIs, indicate that factors other than phosphorous limit the algal biomass, and that non-algal particles influence light attenuation 相似文献
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23.
Anna Maria Manotti Lanfredi Franco Ugozzoli Annamaria Camus 《Journal of chemical crystallography》1996,26(2):141-145
The title compound was obtained from a CS2 solution of bis(2,2-dipyridylamido)copper(II), by insertion of solvent into this complex. In the structure of the dithiocarbamate the metal atom is approximately square-planar coordinated by four S atoms from two chelating ligands. Considering the long interactions between the metal center and the S(2) atom from a centrosymmetrically related complex [Cu(1)...S(2)=3.230 Å], double bridged dimers are formed with the copper atoms in an elongated square-pyramidal coordination. The crystals are monoclinic, space groupP2
1/n witha=14.549(3),b=11.662(3)c=15.329(4) Å and =114.79(2)°. 相似文献
24.
A synthetic route to enantiopure cis-2,4-disubstituted and 2,4-bridged piperidines is reported, the key step being a stereoselective conjugate addition of an organocuprate to a phenylglycinol-derived unsaturated lactam bearing a substituent at the 8a-position. 相似文献
25.
We present a combined experimental and theoretical investigation into the charge transport and recombination in dye-sensitized mesoporous TiO2. We electronically probe the photoinduced change in conductivity through in-plane devices while simultaneously optically probing signatures of the charge species. Our quasi-continuous wave technique allows us to build data sets of electron mobility and recombination versus charge density over a wide temperature range. We observe that the charge density dependence of mobility in TiO2 is strong at high temperatures and gradually reduces with reducing temperature, to an extent where at temperatures below 260 K the mobility is almost independent of charge density. The mobility first increases and then decreases with reducing temperature at any given charge density. These observed trends are surprising and consistent with the multiple-trapping model for charge transport only if the trap density-of-states (DoS) is allowed to become less deep and narrower as the temperature reduces. Our recombination measurements and simulations over a broad range of charge density and temperature are also consistent with the above-mentioned varying DoS function when the recombination rate constant is allowed to increase with temperature, itself consistent with a thermally activated charge-transfer process. Further to using the Monte Carlo simulations to model the experimental data, we use the simulations to aid our understanding of the limiting factors to charge transport and recombination. According to our model, we find that the charge recombination is mainly governed by the recombination reaction rate constant and the charge density dependence is mainly a result of the bimolecular nature of the recombination process. The implication to future material design is that if the mobility can be enhanced without increasing the charge density in the film, for instance by reducing the average trap depth, then this will not be at the sacrifice of comparably enhanced recombination and it will greatly increase the charge carrier diffusion lengths in dye-sensitized or mesoscopic solar cells. 相似文献
26.
Marilena Muraglia Carlo Franchini Filomena Corbo Antonio Scilimati Vincenzo Tortorella Maria Stefania Sinicropi Annamaria De Luca Michela De Bellis Diana Conte Camerino 《Journal of heterocyclic chemistry》2007,44(5):1099-1103
A simple and convenient procedure for the preparation of beta‐proline like derivatives in their racemic and optically active forms has been reported. The compounds have been screened for their potential activity as sodium channel blockers. 相似文献
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Annamaria Barbagallo Monica-Gabriela Cojocaru 《Mathematical and Computer Modelling》2009,49(5-6):966-976
The aim of this paper is to generalize the oligopolistic market equilibrium problems when the data depend on time. We present results regarding the existence of solutions to such problems. Moreover, we show that continuity regularity results hold, and we use them in order to numerically solve the dynamic equilibrium problem. 相似文献
29.
Bruschi L Fois G Mistura G Tormen M Garbin V di Fabrizio E Gerardino A Natali M 《The Journal of chemical physics》2006,125(14):144709
We have measured the adsorption of argon films on arrays of microscopic nonlinear cusps and of semicircular channels. In the former case, we observe a distinct crossover from a planarlike to a geometry dependent growth behavior near liquid-vapor bulk coexistence, characterized by a growth exponent chi equal to -0.96+/-0.04 in very good agreement with the predictions of a recent scaling theory [C. Rascon and A. O. Parry, J. Chem. Phys. 112, 5175 (2000)]. The crossover location is also consistent with theory. Instead, on the concave channels we find a much steeper growth near saturation that may signal the formation of two menisci at both sides of the channel bottom. 相似文献
30.
A three-core polarization splitter based on a square-lattice photonic-crystal fiber is presented. The component separates the input field into two orthogonally polarized beams that are coupled to the horizontal and vertical output ports. The splitter has been designed through modal and beam propagation analysis by employing high-performance codes based on the finite-element method. Results obtained for a device length of 20 mm show extinction ratios as low as -23 dB with bandwidths as great as 90 nm. 相似文献