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排序方式: 共有394条查询结果,搜索用时 15 毫秒
51.
Romanov AN Gularyan SK Polyak BM Sakovich RA Dobretsov GE Sarkisov OM 《Physical chemistry chemical physics : PCCP》2011,13(20):9518-9524
Quantum-chemical calculations of ground and excited states for membrane fluorescent probe 4-dimethylaminochalcone (DMAC) in vacuum were performed. Optimized geometries and dipole moments for lowest-lying singlet and triplet states were obtained. The nature of these electronic transitions and the relaxation path in the excited states were determined; changes in geometry and charge distribution were assessed. It was shown that in vacuum the lowest existed level is of (n, π*) nature, and the closest to it is the level of (π, π*) nature; the energy gap between them is narrow. This led to an effective (1)(π, π*) →(1)(n, π*) relaxation. After photoexcitation the molecule undergoes significant transformations, including changes in bond orders, pyramidalization angle of the dimethylamino group, and planarity of the molecule. Its dipole moment rises from 5.5 Debye in the ground state to 17.1 Debye in the (1)(π, π*) state, and then falls to 2 Debye in the (1)(n, π*) state. The excited (1)(n, π*) state is a short living state; it has a high probability of intersystem crossing into the (3)(π, π*) triplet state. This relaxation path explains the low quantum yield of DMAC fluorescence in non-polar media. It is possible that (3)(π, π*) is responsible for observed DMAC phosphorescence. 相似文献
52.
Cholinesterase sensors based on screen-printed electrodes for detection of organophosphorus and carbamic pesticides 总被引:4,自引:0,他引:4
Ivanov A Evtugyn G Budnikov H Ricci F Moscone D Palleschi G 《Analytical and bioanalytical chemistry》2003,377(4):624-631
Cholinesterase sensors based on screen-printed electrodes modified with polyaniline, 7,7,8,8-tetracyanoquinodimethane (TCNQ), and Prussian blue have been developed and tested for detection of anticholinesterase pesticides in aqueous solution and in spiked grape juice. The influence of enzyme source and detection mode on biosensor performance was explored. It was shown that modification of the electrodes results in significant improvement of their analytical characteristics for pesticide determination. Thus, the slopes of the calibration curves obtained with modified electrodes were increased twofold and the detection limits of the pesticides were reduced by factors of 1.6 to 1.8 in comparison with the use of unmodified transducers. The biosensors developed make it possible to detect down to 2×10–8 mol L–1 chloropyrifos-methyl, 5×10–8 mol L–1 coumaphos, and 8×10–9 mol L–1 carbofuran in aqueous solution and grape juice. The optimal conditions for grape juice pretreatment were determined to diminish interference from the sample matrix.Abbreviations ChE Cholinesterase - TCNQ 7,7,8,8-Tetracyanoquinodimethane - ChO Choline oxidase - AChE Acetylcholinesterase - BChE Butyrylcholinesterase - BSA Bovine serum albumin - 2-PAM 2-Pyridine aldoxime methiodide 相似文献
53.
Makoto Maejima Gennady Samorodnitsky 《Annals of the Institute of Statistical Mathematics》1999,51(3):449-462
We study the extent to which the property of semistability of a random vector in
d
is determined by semistability of its marginals, and the place of semistable laws within the family of type G and sub-stable laws. Similarities and differences between stable and semistable laws are discussed. 相似文献
54.
An Asymptotic Model of Seismic Reflection from a Permeable Layer 总被引:1,自引:0,他引:1
Analysis of compression wave propagation in a poroelastic medium predicts a peak of reflection from a high-permeability layer
in the low-frequency end of the spectrum. An explicit formula expresses the resonant frequency through the elastic moduli
of the solid skeleton, the permeability of the reservoir rock, the fluid viscosity and compressibility, and the reservoir
thickness. This result is obtained through a low-frequency asymptotic analysis of Biot’s model of poroelasticity. A review
of the derivation of the main equations from the Hooke’s law, momentum and mass balance equations, and Darcy’s law suggests
an alternative new physical interpretation of some coefficients of the classical poroelasticity. The velocity of wave propagation,
the attenuation factor, and the wave number are expressed in the form of power series with respect to a small dimensionless
parameter. The absolute value of this parameter is equal to the product of the kinematic reservoir fluid mobility and the
wave frequency. Retaining only the leading terms of the series leads to explicit and relatively simple expressions for the
reflection and transmission coefficients for a planar wave crossing an interface between two permeable media, as well as wave
reflection from a thin highly permeable layer (a lens). Practical applications of the obtained asymptotic formulae are seismic
modeling, inversion, and attribute analysis. 相似文献
55.
Alexander V. Butin Vladimir V. Mel'chin Wolfgang Bender Gennady D. Krapivin 《Tetrahedron》2006,62(34):8045-8053
The synthesis of a number of naphtho[2,3-b]furan derivatives, containing a furyl substituent in position 9 by intramolecular cyclization of 2-carboxy and 2-formylbis(5-alkylfur-2-yl)methanes is described. The reactivity of the title compounds in formylation, acetylation, nitration, and oxidation reactions has been investigated. It was shown that nitration of 2-methyl-9-(5-methyl-2-furyl)naphtho[2,3-b]furan-4-yl acetate leads to oxidative furan ring opening rather than to electrophilic substitution. 相似文献
56.
57.
Valery A. Loiko Gennady I. Ruban Alexey D. Gruzdev Natalia V. Goncharova 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(1):73-84
The peripheral blood lymphocytes of normal individuals are investigated by methods of specialized light microscopy. Lymphocytes as a whole and T-cell subpopulation are considered. Lymphocyte structure is characterized with reference to polarizing scanning flow cytometry. The lymphocyte and lymphocyte nucleus shapes are analyzed. Linear correlation dependence between sizes of lymphocyte and its nucleus is indicated. A morphometric model of a lymphocyte is constructed using the obtained data. The findings can be used, for instance, as input parameters to solve the direct and inverse light-scattering problems of turbidimetry, nephelometry, and flow cytometry. 相似文献
58.
We provide analogues of Carathéodory's theorem for integer cones and apply our bounds to integer programming and to the cutting stock problem. In particular, we provide an NP certificate for the latter, whose existence has not been known so far. 相似文献
59.
The amperometric and EQCM aptasensors based on DNA aptamers immobilized by avidin‐biotin method or by electrostatic adsorption onto multiwalled carbon nanotube layer contained methylene blue (MB) have been developed and examined for thrombin detection in buffer and in spiked blood serum. The presence of MB increases the binding capacity of the surface layer and enhances the range of thrombin concentrations to be determined. This results in significant improvement of analytical characteristics of thrombin detection. The EQCM aptasensors allowed us to detect 0.3–100 nM and amperometric aptasensors 10–1000 nM of thrombin. 相似文献
60.