A new sensitive method for the determination of three tetracyclines in surface water samples (tetracycline, chlortetracycline and oxytetracycline) using highly collinear data corresponding to photochemical-induced fluorescence excitation emission matrices, modelled with three-way data arrays chemometric tools has been developed. The method involves irradiation of aqueous basic solution of antibiotics with UV light and fluorescence determination of the generated photoproducts after solid phase preconcentration (SPE) with Oasis hydrophilic lipophilic balance (HLB) cartridges. The chemometric models were built by using an eight samples calibration set and samples corresponding to both a validation set and a test set. The latter set containing unsuspected interferents. Considering this latter samples, recoveries of 101.5, 97.9 and 102.2 were obtained for the three analytes. Evaluation of constant and proportional bias and precision were made by using the elliptical joint confidence region (EJCR) test for the estimated intercept and slope. 相似文献
Electrochemical induced oscillations were studied during ethylene oxidation over Rh films deposited on YSZ. Oscillations period and amplitude were for the first time analyzed depending on the applied potential or current, related with cyclic oxidation and reduction reactions and discussed on the basis of the phenomenon of the electrochemical promotion of catalysis. 相似文献
Zinc oxide nanoparticles were obtained from the hydrolysis of an organometallic precursor in pure hexadecylamine. Interestingly, we demonstrate that the final (anisotropic or isotropic) shape of the nanoparticles is strongly correlated to the existence of a critical temperature. This suggests that the organization of the fatty amines is a paramount parameter in this synthesis. Moreover, the final hybrid ZnO materials systematically exhibit a liquid–crystal smectic phase, whereas no liquid–crystal phase was observed in the pristine reaction media. This simple process is, therefore, a direct and straightforward method to synthesize liquid–crystal hybrid materials. 相似文献
This paper studies the small time behavior of the heat content for rotationally invariant \(\alpha \)-stable processes, \(0<\alpha \le 2\), in domains of \(\mathbb {R}^d\). Unlike the asymptotics for the heat trace, the behavior of the heat content differs depending on the range of \(\alpha \) according to \(0<\alpha <1\), \(\alpha =1\) and \(1<\alpha \le 2\). 相似文献
The SNP haplogroups of the Y‐chromosome are nonrandomly distributed among human populations. They are used for tracing the phylogeographical history of paternal lineages of male individuals and can be a useful tool for approaching the patrilineal bio‐geographic ancestry of unknown forensic evidences. With the aim of facilitating the inference of the principal informative worldwide Y‐SNP haplogroups, we have selected the minimum possible number of key Y‐SNPs to be amplified in a sensitive single multiplex PCR and detected by minisequencing. This assay, that includes 16 Y‐SNPs, was tested for male human specificity, sensitivity, and reproducibility. Its effectiveness was assessed in a set of degraded DNA samples and in a panel of male individuals from different worldwide populations. All these tests demonstrated the convenience of this assay for assigning the major Y haplogroups to forensic evidences by one single PCR‐minisequencing reaction. 相似文献
Many urban settlements result from a spatially distributed, decentralized
building process. Here we analyze the topological patterns of organization
of a large collection of such settlements using the approach of complex
networks. The global efficiency (based on the inverse of shortest-path
lengths), robustness to disconnections and cost (in terms of length) of
these graphs is studied and their possible origins analyzed. A wide range of
patterns is found, from tree-like settlements (highly vulnerable to random
failures) to meshed urban patterns. The latter are shown to be more robust
and efficient. 相似文献
The quality of an antibody is related to its affinity expressed by the equilibrium constant. The biological activity of an antibody can be estimated by the strength of antigen–antibody bridges.
An optical method is proposed to estimate the specific binding energy using the dissociation behavior of suspended RBC agglutinates in a shear flow and measuring laser backscattering. A constant increase of intensity was observed when the shear stress raises, pointing to a progressive dissociation of RBC agglutinates into smaller ones. The final break-up of two-cell rouleaux is produced at critical shear stress (τc), which reflects the mechanical action required to dissociate the molecular bridges between cells. The critical shear stress permitted to define the specific surface adhesive energy (Γ) by using the Derjaguin relation. The determination of τc provides a good way to assess the functional characterization of specific immunoglobulins, which could be very useful for antibody quality control. 相似文献
As cycles are very important in economic models, in this work we analyze what happens for a model given by a piecewise-linear discontinuous map defined on the plane. As the main result, it is proved this model is near to being (locally) topologically equivalent to a rotation. Besides, some counterexamples are provided to demonstrate that the hypotheses assumed are necessary. 相似文献
Aspherical refractive optical elements have been fabricated by an original light-assisted approach for deposition of semiconducting alloys. The fabrication of axicons by this method is reported for the case of an As–S binary glass alloy. The influence of both light intensity and exposure time on the deposit thickness profile is also presented. 相似文献
A detailed, geometrically exact bifurcation analysis is performed for a model of a power-generating tethered device of interest
to the space industries. The structure, a short electrodynamic tether, comprises a thin, long rod that is spun in a horizontal
configuration from a satellite in low Earth orbit, with a massive electrically conducting disk at its free end. The system
is modelled using a Cosserat formulation leading to a system of Kirchhoff equations for the rod's shape as a function of position
and time. Moving to a rotating frame, incorporating the effects of internal damping, intrinsic curvature due to the deployment
method and novel force and moment boundary conditions at the contactor, the problem for steady rotating solutions is formulated
as a two-point boundary value problem. Using numerical continuation methods, a bifurcation analysis is carried out varying
rotation speeds up to many times the critical resonance frequency. Spatial finite differences are used to formulate the stability
problem for each steady state and the corresponding eigenvalues are computed. The results show excellent agreement with earlier
multibody dynamics simulations of the same problem. 相似文献