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1.
Symmetry-induced isotope effects in recombination and collision-induced dissociation reactions are discussed. Progress on understanding the anomalous isotope effects in ozone is reviewed. Then, calculations are performed for the simpler reaction xNe+yNe+H<-->xNeyNe+H, where x and y label either identical or different isotopes. The atomic masses in the model are chosen so that symmetry is the only difference between the systems. Starting from a single potential energy surface, the properties of the bound, quasibound, and continuum states of the neon dimer are calculated. Then, the vibration rotation infinite order sudden approximation is used to calculate cross sections for all possible inelastic and dissociative processes. A rate constant matrix that exactly satisfies detailed balance is constructed. It allows recombination to occur both via direct three-body collisions and via tunneling into the quasibound states of the energy transfer mechanism. The eigenvalue rate coefficients are determined. Significant isotope effects are clearly found, and their behavior depends on the pressure, temperature, and mechanism of the reaction. Both spin statistics and symmetry breaking produce isotope effects. Under most conditions the breaking of symmetry enhances the rates, but a wide spectrum of effects is observed; they range from isotope effects with a normal mass dependence to huge, mass-independent isotope effects to cancellation and even to reversal of the isotope effects. This is the first calculation of symmetry-induced isotope effects in recombination rates from first principles. The relevance of the present effects to ozone recombination is discussed. 相似文献
2.
A diastereoselective, lanthanocene-catalyzed, intramolecular hydroamination reaction was applied to the preparation of 2,6-disubstituted piperidines. Various metal/ligand arrays in the catalysts were examined using a model substrate to allow optimization of the diastereoselectivity. It was determined that the relationship between metal size and ligand bulk plays an integral role in the transformation. The complex Cp2NdCH(TMS)2 converted 2-substituted 8-nonen-4-amines to 2,6-disubsituted piperidines with greater than 100:1 selectivity for the formation of the cis isomer. A short synthesis of pinidinol, an alkaloid isolated from various pine and spruce species, was then carried out to exploit this stereoselective reaction. 相似文献
3.
4.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
5.
An LDV system for making spatial correlation measurements of velocity fluctuations in turbulent nonreacting and reacting flows is presented. The LDV system is the dual beam type and consists of an elongated probe volume and a two-point optical fiber detector. Results are presented of the integral length scale measured in a nonreacting grid generated turbulent flow.A version of this paper was presented at the ASME Winter Annual Meeting of 1984 and printed in AMD, Vol. 66 相似文献
6.
Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film
La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics
are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial
magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears
at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic
conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese
atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance
with the increase in temperature is due to enhanced spin-flip scattering process. 相似文献
7.
Molar extinction coefficients of some carbohydrates viz. l-arabinose (C5H10O5), d-glucose (C6H12O6), d-mannose (C6H12O6), d-galactose (C6H12O6), d(-) fructose (C6H12O6) and maltose (C12H24O12) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a
narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter
polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying
within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well. 相似文献
8.
V. Böhmer J. Engler W. Flauger H. Keim F. Mönnig K. Pack H. Schopper A. Babaev E. Brachmann G. Eliseev A. Ermilov Yu. Galaktionov Yu. Gorodrov Yu. Kamishkov E. Leikin V. Lubimov V. Shevchenko O. Zeldovich 《Nuclear Physics B》1975,91(2):266-278
The neutron-proton elastic differential cross section has been measured for incident momenta between 10 and 70 GeV/c and for values of the momentum transfer squared between 0.1 and 2.8 (GeV/c)2. The forward peak and the break at about ∣t∣ = 1 (GeV/c)2 are very similar to corresponding pp data. 相似文献
9.
Poly(dimethyl dipropargylmalonate) synthesized in scCO2 contained more than 95% five-membered rings, i.e., highly regular polyene was produced, which shows carbon dioxide as a reaction medium plays a significant role in determining a highly selective polymer structure. 相似文献
10.
Kamisetty NK Pack SP Nonogawa M Devarayapalli KC Kodaki T Makino K 《Analytical and bioanalytical chemistry》2006,386(6):1649-1655
Aminosilane-treated molecular layers on glass surfaces are frequently used as functional platforms for biosensor preparation.
All the amino groups present on the surface are not available in reactive forms, because surface amino groups interact with
remaining unreacted surface silanol groups. Such nonspecific interactions might reduce the efficiency of chemical immobilization
of biomolecules such as DNA, enzymes, antibodies, etc., in biosensor fabrication. To improve immobilization efficiency we
have used additional surface silanization with alkylsilane (capping) to convert the remaining silanol groups into Si–O–Si
linkages, thereby liberating the amino groups from nonspecific interaction with the silanol groups. We prepared different
types of capped amine surface and evaluated the effect of capping on immobilization efficiency by investigating the fluorescence
intensity of Cy3-NHS (N-hydroxysuccinimide) dye that reacted with amino groups. The results indicate that most of the capped amine surfaces resulted
in enhanced efficiency of immobilization of Cy3-NHS compared with the untreated control amine surface. We found a trend that
trialkoxysilanes had greater capping effects on immobilization efficiency than monoalkoxysilanes. It was also found that the
aliphatic chain of alkylsilane, which does not participate in the capping of the silanol, had an important function in enhancing
immobilization efficiency. These results would be useful for preparation of an amine-modified surface platform, with enhanced
immobilization efficiency, which is essential for developing many kinds of biosensors on a silica matrix.
Enhancement of amine funtionality by capping with alkylsilane 相似文献