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71.
Schulz M Fritze H Tuller HL Seh H 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2004,51(11):1381-1387
Oxygen and gallium diffusivities in langasite were experimentally determined by analysis of diffusion profiles of 18O and 71Ga tracers by SIMS analysis as functions of temperature and doping. Strontium-enhanced diffusivities and activation energies of approximately 1.2+/-0.2 eV confirm the predominant role of oxygen vacancies in controlling the electrical conductivity of langasite at elevated temperature and oxygen partial pressure. The potential impact of high levels of porosity and the use of an oxygen primary ion beam on the accuracy of some of the data is discussed. The gallium diffusivity, with activation energy of 3.13 eV, was found to be more than two orders of magnitude lower than that of oxygen. Surface exchange measurements enabled estimation of gallium loss at elevated temperatures and oxygen partial pressure; the level is not believed to be of major concern for resonator performance. 相似文献
72.
Toxicity increases in ice containing monochlorophenols upon photolysis: environmental consequences 总被引:4,自引:0,他引:4
Bláha L Klánová J Klán P Janosek J Skarek M Růzicka R 《Environmental science & technology》2004,38(10):2873-2878
The toxic effects of photoproducts formed upon the photolysis of 2- and 4-chlorophenol (CP) frozen solutions in polycrystalline ice phase were determined with a bacterial luminescence test (Vibrio fisheri), and in vitro biomarker assay for dioxin-like effects (inductions of AhR-dependent luciferase in H4IIE-luc cells) and compared to the toxic effects of products of the same photoreaction in aquatic phase. Coupling photoproducts formed in ice samples (3'-chlorobiphenyl-2,4'-diol and 3-chlorobiphenyl-2,2'-diol from 2-CP photolysis and 5-chlorobiphenyl-2,4'-diol from 4-CP photolysis) were found to be more toxic to V. fisheri than parent CPs and elicited significant inductions of dioxin-like effects (the effective concentrations EC50 approximately 3 x 10(-5) mol L(-1) corresponded to known weaker ligands of AhR, such as nonplanar polychlorinated biphenyls or polycyclic aromatic hydrocarbons). To complete the picture, a photoproduct formed from 4-CP (5-chlorobiphenyl-2,4'-diol) was synthesized, and a detailed toxicity assessment with purified compound confirmed the results obtained with irradiated samples. Our findings support a recently proposed model according to which solar radiation can trigger the formation of new types of organic pollutants in polar ice or tropospheric ice cloud particles, presenting possibly greater risk to the environment than the parent compounds. 相似文献
73.
Palecek E Masarík M Kizek R Kuhlmeier D Hassmann J Schülein J 《Analytical chemistry》2004,76(19):5930-5936
MutS protein plays an important role in the DNA repair system in prokaryotic and eukaryotic cells; it recognizes unpaired and mispaired bases in duplex DNA and can be used for detection of point mutations in vitro. We have shown that small amounts of this protein can be detected electrochemically at mercury and carbon electrodes without any labeling. Using constant current stripping analysis (CPSA) and mercury electrodes, tens of attomoles of this protein can be detected. The sensitivity of the determination at carbon electrodes is by more than 3 orders of magnitude lower. Using biotinylated DNA duplexes attached to magnetic beads, single-base mismatches and insertion/deletions were recognized by MutS. Picogram amounts of this protein were detected by CPSA after MutS releasing from the beads. 相似文献
74.
75.
Masarik M Kizek R Kramer KJ Billova S Brazdova M Vacek J Bailey M Jelen F Howard JA 《Analytical chemistry》2003,75(11):2663-2669
The proteins streptavidin and avidin were electrochemically detected in solution by adsorptive transfer stripping square wave voltammetry (AdTS SWV) at a carbon paste electrode (CPE). AdTS SWV was used to quantify biotinylated oligonucleotides, DNA hybridizations, and avidin in extracts of transgenic avidin maize. The detection limits of denatured and native streptavidin were 6 pM and 120 nM, respectively. The results demonstrated that streptavidin/avidin AdTS SWV is a sensitive and specific method for quantifying DNA and proteins in biological samples such as foods and tissue extracts, including genetically modified crops (avidin maize) and other plants in neighboring fields. 相似文献
76.
Reclaimed wastewater and, particularly, secondary effluent used for irrigation, may contain considerable amounts of mineral and organic N. The knowledge regarding N-transformations of effluent-originated organic N in soil is not well established. A method based on ion-exchangers (IE) was developed to remove the mineral N and other ionic species from the effluents, enabling a better follow-up of the reactions of effluent-originated organic N. Modifications of two incubation methods were used to evaluate net mineralization rates and the contributions of ammonification and nitrification of the effluent-originated organic N. A mixture of the ion-exchangers, IRN-77 (H+) and IRN-78 (OH–), was found effective in removing mineral N and other ions from effluents without significantly affecting the content of organic N. In suspension-based experiments performed with a microbially active calcareous clay soil, the nitrification started after about a 1 to 4 d lag (higher lag associated with higher BOD), and the total mineral N reached plateau values after about 9 to 14 d. The time estimated for completion of ammonification of the organic N in the well-mixed and aerated suspensions was 3 to 6 d. Soil incubations were performed after adding the IE-treated effluents to small soil columns. Ammonification of both soil and effluent-originated organic N occurred concomitantly with the nitrification, making the evaluation of rates more complicated. Tracing the time differences in total mineral N between the soils irrigated with the IE-treated effluent and the blank (no added N) enabled the estimation of first order rate constants for the net mineralization of the effluent-originated organic N in: a sandy loam (0.3 wk–1), a loess (0.4 wk–1), and in the calcareous clay (1.1 wk–1). About two thirds of the organic N added to the soils in the columns during the pre-incubation stage were not retained in the soils, whereas ammonium was practically not leached out. The relatively fast movement of the effluent-originated organic N in soil and its mineralization characteristics indicate that this fraction significantly affects the short (days) and middle (weeks) range transformations of N in effluent-irrigated soils. 相似文献
77.
Michal Kunc 《Theory of Computing Systems》2007,40(4):521-551
We construct a finite language L such that the largest language commuting with L is not recursively enumerable. This gives
a negative answer to the question raised by Conway in 1971 and also strongly disproves Conway's conjecture on context-freeness
of maximal solutions of systems of semi-linear inequalities. 相似文献
78.
79.
The analysis addresses a typical failure development pattern in thin films consisting of a system of multiple surface cracks leading to and branching along or near the interface between the film and the base material. The process is driven by thermal residual stresses and/or mechanical loading. Due to the high temperature gradients during the fabrication process, usually a net of surface cracks develops, which gives the appearance of a granular structure of the surface. A periodic array of parallel surface cracks is assumed. A “unit cell” or single cracked segment attached to the substrate is analyzed instead by assuming the channel cracks are spaced more or less uniformly and perfectly aligned in parallel in the transverse direction of the coating. The analysis is specialized to orthotropic and transversally isotropic materials. The problem is solved using FEM combined with the reciprocal theorem. Matched asymptotic procedure [Leguillon D, Sanchez-Palencia E. Computation of singular solutions in elliptic problems and elasticity. Paris: Masson; 1987; Vu-Quoc L, Tran VX. Singularity analysis and fracture energy-release rate for composites: piecewise homogenous-anisotropic materials. Comput Methods Appl Mech Engng 2006;195:5162-97] is used to derive the change of potential energy. Higher-order terms in the asymptotics are considered. The competition between penetration and debond for periodically distributed edge cracks especially near the critical value of the ratio of fracture spacing to the layer thickness is examined. 相似文献
80.
Michal Soreni‐Harari David Mocatta Marina Zimin Yair Gannot Uri Banin Nir Tessler 《Advanced functional materials》2010,20(6):1005-1010
InAs nanocrystals field‐effect transistors with an ON/OFF ratio of 105 are reported. By tailoring the interface regions in the active layer step‐by‐step, the evolution of the ON/OFF ratio can be followed from approximately 5 all the way to around 105. The formation of a semiconducting solid from colloidal nanocrystals is achieved through targeted design of the nanocrystal–nanocrystal interaction. The manipulation characteristics of the nanocrystal interfaces include the matrix surrounding the inorganic core, the interparticle distance, and the order of nanocrystals in the 3D array. Through careful analysis of device characteristics following each treatment, the effect of each on the physical properties of the films are able to be verified. The enhanced performance is related to interparticle spacing, reduction in sub‐gap states, and better electronic order (lower σ parameter). Films with enhanced charge transport qualities retain their quantum‐confined characteristics throughout the procedure, thus making them useful for optoelectronic applications. 相似文献