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591.
Dr. Dymytrii Listunov Prof. Ole Hammerich Irving Caballero-Quintana Dr. Albert Poater Cécile Barthes Dr. Carine Duhayon Dr. Mie Højer Larsen Dr. José-Luis Maldonado Dr. Gabriel Ramos-Ortiz Prof. Mogens Brøndsted Nielsen Dr. Valérie Maraval Prof. Remi Chauvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10707-10711
carbo-Benzene is an aromatic molecule devised by inserting C2 units within each C−C bond of the benzene molecule. By integrating the corresponding carbo-quinoid core as bridging unit in a π-extended tetrathiafulvalene (exTTF), it is shown that a carbo-benzene ring can be reversibly formed by electrochemical reduction or oxidation. The so-called carbo-exTTF molecule was thus experimentally prepared and studied by UV–visible absorption spectroscopy and cyclic voltammetry, as well as by X-ray crystallography and by scanning tunneling microscopy (STM) on a surface of highly oriented pyrolytic graphite (HOPG). The molecule and its oxidized and reduced forms were subjected to a computational study at the density functional theory (DFT) level, supporting carbo-aromaticity as a driving force for the formation of the dication, radical cation, and radical anion. By allowing co-planarity of the dithiolylidene rings and carbo-quinoidal core, carbo-exTTFs present a promising new class of redox-active systems. 相似文献
592.
Dr. Ting Wu Dr. Isabelle Leray Dr. Valérie Génot Jean Pierre Lefèvre Alexandre Korovitch Dr. Nguyêt‐Thanh Ha‐Duong Dr. Jean‐Michel El Hage Chahine Prof. Jacques Alexis Delaire 《Chemphyschem》2010,11(15):3355-3362
The thermodynamics and kinetics of the complexation reaction between lead ions and the fluorescent sensor Calix‐DANS4 are determined to optimize the geometry of the microreactor used for the flow‐injection analysis of lead and to tune the working conditions of this microdevice. Under our experimental conditions (pH 3.2, low concentration of Calix‐DANS4) the 1:1 Pb2+‐Calix‐DANS4 complex is predominantly formed with a high stability constant (log K1:1=6.82) and a slow second‐order rate constant (k=9.4×104 L mol?1 s?1). Due to this sluggish complexation reaction, the microchannel length must be longer than 130 mm and the flow rate lower than 0.25 mL h?1 to have an almost complete reaction at the output of the microchannel and a high sensitivity for the heavy metal detection. After determination of the values of the reaction times in our different microdevices, it is possible to simulate the calibration curves for the fluorimetric detection of lead under different conditions. An original method is also presented to determine mixing times in microreactors. 相似文献
593.
Fanny Claverie Christophe Pcheyran Sandra Mounicou Guillaume Ballihaut Beatriz Fernandez Joël Alexis Ryszard Lobinski Olivier F.X. Donard 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009,64(7):649-658
A 2D high repetition rate femtosecond laser ablation strategy (2-mm wide lane) previously developed for the detection of selenoproteins in gel electrophoresis by inductively coupled plasma mass spectrometry was found to increase signal sensitivity by a factor of 40 compared to conventional nanosecond ablation (0.12-mm wide lane) [G. Ballihaut, F. Claverie, C. Pécheyran, S. Mounicou, R. Grimaud and R. Lobinski, Sensitive Detection of Selenoproteins in Gel Electrophoresis by High Repetition Rate Femtosecond Laser Ablation-Inductively Coupled Plasma Mass Spectrometry, Anal. Chem. 79 (2007) 6874–6880]. Such improvement couldn't be explained solely by the difference of amount of material ablated, and then, was attributed to the aerosol properties. In order to validate this hypothesis, the characterization of the aerosol produced by nanosecond and high repetition rate femtosecond laser ablation of polyacrylamide gels was investigated. Our 2D high repetition rate femtosecond laser ablation strategy of 2-mm wide lane was found to produce aerosols of similar particle size distribution compared to nanosecond laser ablation of 0.12-mm wide lane, with 38% mass of particles < 1 µm. However, at high repetition rate, when the ablated surface was reduced, the particle size distribution was shifted toward thinner particle diameter (up to 77% for a 0.12-mm wide lane at 285 µm depth). Meanwhile, scanning electron microscopy was employed to visualize the morphology of the aerosol. In the case of larger ablation, the fine particles ejected from the sample were found to form agglomerates due to higher ablation rate and then higher collision probability. Additionally, investigations of the plasma temperature changes during the ablation demonstrated that the introduction of such amount of polyacrylamide gel particles had very limited impact on the ICP source (ΔT~ 25 ± 5 K). This suggests that the cohesion forces between the thin particles composing these large aggregates were weak enough to have negligible impact on the ICPMS detection. 相似文献
594.
María Maldonado Santoyo 《Talanta》2009,79(3):706-18
In this work, the quantification of two mercury species (Hg2+ and CH3Hg+) in fish tissues has been revisited. The originality of our approach relies on the use of Bi3+ as internal standard (IS) and on the modification of typical extraction conditions. The IS (125 μl, 1000 μg l−1 Bi3+) was added to the aliquot of fresh fish tissue (400-500 mg). A high-speed blender and ultrasound-assisted homogenization/extraction was carried out in the presence of perchloric acid (1.5 ml, 0.6 mol l−1), l-cysteine (500 μl, 0.75 mol l−1) and 500 μl toluene:methanol (1:1). Perchloric acid was used for protein denaturation and precipitation, toluene helped to destroy lipid structures potentially sequestering CH3Hg+, l-cysteine was used to form water-soluble complexes with Bi3+, Hg2+ and CH3Hg+. The excess of perchloric acid was eliminated by addition of potassium hydroxide (pH 5 with acetic acid). The obtained extract, was diluted with the mobile phase (1:1) and introduced (20 μl) to the reversed phase HPLC-ICP-MS system. The separation was achieved by isocratic elution (2.5 mmol l−1 cysteine, 12.5 mmol l−1 (NH4)2HPO4, 0.05% triethylamine, pH 7.0:methanol (96:4)) at a flow rate 0.6 ml min−1. Column effluent was on-line introduced to ICP-MS for specific detection of 202Hg, 200Hg and 209Bi. Analytical signal was defined as the ratio between 202Hg/209Bi peak areas. The detection limits evaluated for Hg2+ and CH3Hg+ were 0.8 and 0.7 μg l−1. Recovery of the procedure, calculated as the sum of species concentrations found in the sample with respect to total ICP-MS-determined Hg was 91.9% for king mackerel muscle and 89.5% for red snapper liver. In the standard addition experiments, the recovery results were 98.9% for Hg2+ and 100.6% for CH3Hg+. It should be stressed that the use of Bi3+ as IS enabled to improve analytical performance by compensating for incomplete extraction and for imprecision of sample handling during relatively non-rigorous protocol. 相似文献
595.
This work presents a Bayesian semiparametric approach for dealing with regression models where the covariate is measured with error. Given that (1) the error normality assumption is very restrictive, and (2) assuming a specific elliptical distribution for errors (Student-t for example), may be somewhat presumptuous; there is need for more flexible methods, in terms of assuming only symmetry of errors (admitting unknown kurtosis). In this sense, the main advantage of this extended Bayesian approach is the possibility of considering generalizations of the elliptical family of models by using Dirichlet process priors in dependent and independent situations. Conditional posterior distributions are implemented, allowing the use of Markov Chain Monte Carlo (MCMC), to generate the posterior distributions. An interesting result shown is that the Dirichlet process prior is not updated in the case of the dependent elliptical model. Furthermore, an analysis of a real data set is reported to illustrate the usefulness of our approach, in dealing with outliers. Finally, semiparametric proposed models and parametric normal model are compared, graphically with the posterior distribution density of the coefficients. 相似文献
596.
In this article, a nonlinear family of spaces, based on the energy dissipation, is introduced. This family bridges an energy space (containing weak solutions to Navier–Stokes equation) to a critical space (invariant through the canonical scaling of the Navier–Stokes equation). This family is used to get uniform estimates on higher derivatives to solutions to the 3D Navier–Stokes equations. Those estimates are uniform, up to the possible blowing-up time. The proof uses blow-up techniques. Estimates can be obtained by this means thanks to the galilean invariance of the transport part of the equation. 相似文献
597.
Alexis Tchoudjem 《Transformation Groups》2010,15(3):655-700
Let X be a complete symmetric variety, i.e., the wonderful compactification of a symmetric G-homogeneous space (where G is a simply connected semi-simple linear algebraic group). If L is a line bundle over X and if C is a Bialynicki-Birula cell of codimension c in X, then the Lie algebra $ \mathfrak{g} $ of G operates naturally on the cohomology group with support H C c (L). A necessary condition on C for the existence of a finite-dimensional simple subquotient of this $ \mathfrak{g} $ -module is given. As applications one calculates the Euler–Poincaré characteristic of L over X, estimates the higher cohomology group H d (X, L), d ≥ 0, and obtains the exact formulas in some cases including that of the complete conic variety. 相似文献
598.
Alexis Kaporis Christos Makris George Mavritsakis Spyros Sioutas Athanasios Tsakalidis Kostas Tsichlas Christos Zaroliagis 《Journal of Discrete Algorithms》2010,8(4):373-387
We present the interpolation search B-tree (ISB-tree), a new cache-aware indexing scheme that supports update operations (insertions and deletions) in worst-case block transfers and search operations in expected block transfers, where B represents the disk block size and n denotes the number of stored elements. The expected search bound holds with high probability for a large class of (unknown) input distributions. The worst-case search bound of our indexing scheme is block transfers. Our update and expected search bounds constitute a considerable improvement over the worst-case block transfer bounds for search and update operations achieved by the B-tree and its numerous variants. This is also verified by an accompanying experimental study. 相似文献
599.
Florent Berthelin Athanasios E. Tzavaras Alexis Vasseur 《Journal of statistical physics》2009,135(1):153-173
This article is devoted to the proof of the hydrodynamic limit for a discrete velocity Boltzmann equation before appearance
of shocks in the limit system.
Partially supported by the National Science Foundation Grants DMS-0607053, DMS-0555272 and DMS-0757227, and by the program
“Pythagoras” of the Greek Secretariat of Research. 相似文献
600.
Shaama Mallikarjun Sharada David Stück Eric J. Sundstrom Alexis T. Bell 《Molecular physics》2015,113(13-14):1802-1808
Wavefunction stability analysis is commonly applied to converged self-consistent field (SCF) solutions to verify whether the electronic energy is a local minimum with respect to second-order variations in the orbitals. By iterative diagonalisation, the procedure calculates the lowest eigenvalue of the stability matrix or electronic Hessian. However, analytical expressions for the electronic Hessian are unavailable for most advanced post-Hartree–Fock (HF) wave function methods and even some Kohn–Sham (KS) density functionals. To address such cases, we formulate the Hessian-vector product within the iterative diagonalisation procedure as a finite difference of the electronic gradient with respect to orbital perturbations in the direction of the vector. As a model application, following the lowest eigenvalue of the orbital-optimised second-order Møller–Plesset perturbation theory (OOMP2) Hessian during H2 dissociation reveals the surprising stability of the spin-restricted solution at all separations, with a second independent unrestricted solution. We show that a single stable solution can be recovered by using the regularised OOMP2 method (δ-OOMP2), which contains a level shift. Internal and external stability analyses are also performed for SCF solutions of a recently developed range-separated hybrid density functional, ωB97X-V, for which the analytical Hessian is not yet available due to the complexity of its long-range non-local VV10 correlation functional. 相似文献