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951.
The effect of replacing the hydrogen atoms in thioformaldehyde by halogen atoms (F, Cl) on the ionisation potential of the
non-bonding electron is analysed by using the Hellman-Feynman theorem, regarding the nuclear charge of the substituent as
a parameter in the many-electron Hamiltonian. The trends predicted by our theory nicely agree with the relevant ionisation
potentials computed either by applying Koopmans’ theorem or by the ΔE
SCF method. For the carbonyls, avaible experimental data indicate the reliability of our prediction. 相似文献
952.
Wen-Chang Chen Samson A. Jenekhe Jeffrey S. Meth Hermann Vanherzeele 《Journal of Polymer Science.Polymer Physics》1994,32(1):195-200
An investigation of the refractive index and third-order nonlinear optical susceptibility χ(3) of two polypernigraniline derivatives, poly (4,4'-diphenylimine methine) (PDPIM) and poly (4,4'-diphenylimine p-heptyloxybenzylidene) (PDPIHB) reveals effects of molecular structure on the linear optical and nonlinear optical properties of conjugated polymers. The χ(3) (?3ωω,ω,ω) of PDPIM was found to decrease relative to polypernigraniline, reflecting the observed decrease of the oscillator strength of the 2.2 eV absorption band when a methine carbon replaces one of the nitrogen atoms of pernigraniline repeat unti. The alkoxyphenylene side group substitution at the methine carbon in PDPIHB, however, significantly enhances the nonlinear optical response of PDPIHB while reducing the refractive index compared to PDPIM and polypernigraniline. The present results suggest that structural changes in conjugated polymers can be made in such a way as to enhance the nonlinear optical properties while modulating the linear optical properties. © 1994 John Wiley & Sons, Inc. 相似文献
953.
Summary Equilibria occurring during the dynamic ion exchange separation of metal ions were examined, and their effect on the chromatography of the metal ions was evaluated. Bonded reversed-phase silica, pure organic reversed phase, and silica columns were used to differentiate between the role of silica and the reverse phase. The results show that system peaks had the most important influence on the applicability of dynamic exchangers to quantitative metal ion determinations. The response of system peaks to sample composition (pH, ionic strength, matrix effects) was complicated and could not be predicted easily. Equilibria effects that can cause analytical errors were identified and recommendations for elimination of such errors are given.Dedicated to Professor S. R. Lipsky on the occasion of his 60th birthday. 相似文献
954.
The elastic differential cross-section forē-Na scattering in the presence of non-resonant laser field is studied for the exchange ofℓ=0, 1, 2 photons. The undressed contribution is evaluated within the framework of the eikonal Born series approximation and
the effect of exchange is taken into account via the Ochkur approximation. The sodium atom has been treated in the frozen
core approximation with special attention to the effect of the dressing of the target by the laser field. The ‘dressing’ of
the target leads to quite an increase in the cross-section over the ‘undressed’ value near the forward direction for the exchange
of one or two photons. 相似文献
955.
Summary The grand potential and energy of a noninteracting uncorrelated two-dimensional electron gas subject to Landau quantization
in a magnetic field are examined here at low temperatures. The DeHaas-Van Alphen oscillatory magnetic susceptibility for the
free 2D gas is calculated and the results presented here incorporate the effects of spin (by allowing that spin splitting
may not, in general, equal Landau level separation) in formulae that have the same analytic structure for both even and odd
numbers of filled Landau levels.
Riassunto Il gran potenziale e l'energia di un gas elettronico bidimensionale non correlato non interagente, soggetto a quantizzazione di Landau in un campo magnetico, sono esaminate qui a basse temperature. La suscettibilità magnetica oscillatoria di De Haas-Van Alphen per il gas libero 2D è calcolata e i risultati presentati qui incorporano gli effetti di spin (tenendo conto che il taglio di spin non può, in generale, eguagliare uguale separazione del livello di Landau) in formule che hanno la stessa struttura analitica per numeri sia pari che dispari dei livelli completi di Landau.
Резюме В зтой работе при низких температурах исследуется потенсиал и знергия невзаимодействующего некоррелированного двумерного злектроннного газа, подчинющегося квантованию Ландау в магнитном поле. Вычисляется осцилляторная магнитная восприимчивость де Гааза-ван Альфена для свободнго двумерного газа. Полученные результаты учитывают спиновые зффекты (допуская, что спиновое расщепление в общем случае может быть не равно интервалу между уровнями Ландау) в формулах, которые имеют ту же аналитическую структуру для четного и нечетного числа заполненных уровней Ландау.相似文献
956.
The electrical resistivity of bulk Ge20Te80 has been measured as a function of pressure and temperature. At 5 GPa, an amorphous semiconductor-to-crystalline metal transition
has been observed. The sample recovered from the high pressure cell, after the application of 7 GPa, has a face-centred cubic
structure with a lattice constant of 6·42 A. In crystalline sample, the semiconductor-to-metal transition occurs at 7 GPa.
The thermoelectric power has also been measured for glassy samples in the temperature range 300–240 K. 相似文献
957.
A very important question in ultrarelativistic heavy ion collisions is that of thermalization of the high energy density quark
gluon plasma forud in the central rapidity region. Different approaches have been adopted by various authors to study this
thermalization problem. These include phenomenological string and capacitor plate models, perturbative QCD based parton cascade
models and the classical non-perturbative approach. In this paper we briefly review the earlier studies and discuss our work
which emphasizes the role of non-perturbative collective effects (classical chaos) in the thermalization of the plasma. In
particular, using classical equations of motion of a coloured parton in self-consistent colour fields, we have carried out
a 1+1 dimensional simulation of coloured partonic matter. We find that in certain parameter domains, the system exhibits chaotic
behaviour in non-abelian plasma oscillations, which then leads to thermalization of the plasma. 相似文献
958.
Aqueous solutions of Nal containing CCl4 and MgCl2 at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I3− was determined. The yield was not affected by MgCl2 at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl2 concentration of 2.5 × 10−3M, the yield decreased to 60% at 1 M MgCl2, the reason being the lower solubility of CCl4 at high MgCl2 concentrations. In the absence of CCl4, another dependence on the MgCl2 concentration was observed: the yield was not affected up to 1 M, and at higher MgCl2 concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles. 相似文献
959.
A technique is presented for the measurement of individual phase flowrates in two-phase flow without separation. The technique is based on signal analysis and pattern recognition methodologies to extract, classify and identify stochastic features from turbulent pressure waveforms. Experiments in a horizontal air-water loop have shown that a set of features is uniquely related to the individual phase flowrates. It is shown that the “flowmeter” can be isolated from installation effects by means of a homogenizer. 相似文献
960.
The influence of concentration, ageing and pH of the gel medium on the periodic precipitation of cobalt oxinate in agar gel
is reported. The results are explained on the basis of Shinohara’s revised flocculation theory. The flocculation value (F) increases with increase in the gel concentration whereas it decreases with increase in ageing and pH of the gel. The raise
in temperature of the gel increases the solubility of the sparingly soluble substance and hence theF value. The effect of additives on the periodic precipitation of cobalt (II) oxinate is reported. 相似文献