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111.
A critical review of the phonon-assisted hopping theory of the dc conductivity σ is given. It is argued that the current theories either contain uncontrollable approximations, or they yield the result of the same order of magnitude as the approximations used or they may also lead to temperature dependence of σ other than that described by the Mott law. For the simplest usually accepted model of amorphous Ge (a-Ge), the low-temperature asymptote of σ is obtained in the form of a power law. In the experimental part of the work, careful measurements from 300 down to 8 K are reported, both for the pure and the gold-doped a-Ge films. Since the results of such measurements yield a straight line in a wide interval of temperature both in the log σ versus and log σ versus log T scale, the power law appears to be equally well justified as the Mott law, both from the point of view of theory and that of experiment. 相似文献
112.
113.
S. Anić J. Maksimović D. Lončarević N. Pejić Ž. D. Čupić 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(9):1468-1472
The infuence of poly-4-vinylpyridine-co-divinylbenzene-Co2+ catalyst on the Bray-Liebhafsky (BL) oscillator used as the matrix for establishing catalyst’s activity was analyzed. The
addition of the catalyst do not change the dynamics of the reaction in the BL matrix, but the periods of the oscillatory evolution
as well as the preoscillatory period (τ1) and the duration from the beginning of the reaction to the end of the oscillatory state (τend). All experimental results are simulated satisfactory.
The article is published in the original. 相似文献
114.
Nenad Mladenović Milan Dražić Vera Kovačevic-Vujčić Mirjana Čangalović 《European Journal of Operational Research》2008
We suggest a new heuristic for solving unconstrained continuous optimization problems. It is based on a generalized version of the variable neighborhood search metaheuristic. Different neighborhoods and distributions, induced from different metrics are ranked and used to get random points in the shaking step. We also propose VNS for solving constrained optimization problems. The constraints are handled using exterior point penalty functions within an algorithm that combines sequential and exact penalty transformations. The extensive computer analysis that includes the comparison with genetic algorithm and some other approaches on standard test functions are given. With our approach we obtain encouraging results. 相似文献
115.
Sergey Sergeyev Sara Stas Adrienne Remacle Christophe M.L. Vande Velde Bohumil Dolenský Martin Havlík Vladimír Král Jan Čejka 《Tetrahedron: Asymmetry》2009,20(16):1918-1923
The separation of enantiomers of several ‘bis- and tris-Tröger’s bases’ by HPLC on commercially available chiral stationary phase Whelk O1 is described for the first time. The observed structure–enantioselectivity relationships are in agreement with the previously established molecular recognition model. For all ‘bis- and tris-Tröger’s bases’ studied, satisfactory to excellent enantioselectivities were observed. 相似文献
116.
Two-phase additivity rule for radiation yields of p-nitrophenol, m-nitrophenol and p-nitrosophenol has been demonstrated. The data of partial radiation yields indicated that the nitrobenzene phase is by several times more reactive than a water phase /H2O, 3M HNO3 or 1.5M H2SO4/ in respect of nitrophenols formation. 相似文献
117.
118.
A. S. Culf M. Čuperlović‐Culf R. J. Ouellette 《Magnetic resonance in chemistry : MRC》2009,47(2):158-164
Highly coloured Janovsky complexes have been known for over 120 years, being used in many colourimetric analytical procedures. In this present study, two novel and stable nitrocyclohexadienyl spirobicyclic, zwitterionic Janovsky anionic hydantoin σ‐complexes, rac‐1,3‐diisopropyl‐6‐nitro‐2,4‐dioxo‐1,3‐diazaspiro[4.5]deca‐6,9‐dien‐8‐ylideneazinate, ammonium internal salt (1) and 1,3‐diisopropyl‐2,4‐dioxo‐1,3‐diazaspiro[4.5]deca‐6,9‐dien‐8‐ylideneazinate, ammonium internal salt (2) have been prepared and characterised by NMR, electrospray ionization mass spectrometry (ESI‐MS) and UV/visible methods. For the p‐mononitro‐substituted complex (2), we discovered chemical exchange behaviour using 1D saturation transfer and 2D exchange spectroscopy (EXSY) 1H NMR techniques. The coalescence temperature was determined to be 62 °C in d3‐acetonitrile. Analysis of these data provided a Gibbs free energy of activation, ΔG ?, of + 67 kJ mole?1, a rate constant, k, coalescence of 220 Hz and an equilibrium constant, Keqm, of 0.98 as estimates of the exchange process in this solvent. Of the two mechanisms proposed for this fluxional behaviour, ring opening to a substituted benzene or proton exchange, a further theoretical modelling study of 1D 1H NMR spectra was able to confirm that simple proton exchange between the two nitrogen sites of the hydantoin ring provided an accurate simulation of the observed experimental evidence. Interestingly, the o,p‐dinitro‐substituted complex (1) did not show any chemical exchange behaviour up to 150 °C in d3‐acetonitrile (to 75 °C) and d6‐dimethyl sulfoxide (DMSO). Molecular modelling at the MM2 level suggests that steric collisions of an N‐acyl isopropyl substituent of the hydantoin ring with the ortho‐nitro group of the spirofused cyclohexadienyl ring prevents the proposed proton exchange mechanism occurring in this case. Copyright © 2008 Crown in the right of Canada. Published by John Wiley & Sons, Ltd 相似文献
119.
120.
This work presents a comparison of convective interaction media (CIM) and controlled pore glass (CPG) as solid supports for
immunoglobulin antibodies used in bioanalytical detection of allergens in foodstuffs. A flow-injection manifold with highly
sensitive thermal lens spectrometric detection was used for this purpose. Using beta-lactoglobulin, a milk allergen, as a
model analyte, CIM disc supports had a higher linear range (0.2–3.5 μg L−1), better reproducibility (intra-day RSD = 1%, inter-day RSD = 10%), lower consumption of reagents, and better immunocolumn
stability (1 month, over 240 injections of substrate), while providing comparable LODs (0.1 μg L−1). Application of CIM discs as solid supports in immunocolumns for allergen detection enables fast and sensitive screening
of allergens in foodstuffs with sample throughput of up to eight samples per hour. 相似文献