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301.
[reaction: see text] The ratio of observed rate constants, k/k', for thermal isomerizations of cis-bicyclo[4.2.0]oct-7-ene and its 2,2,5,5-d(4) analogue to cis,cis-1,3-cyclooctadienes at 250 degrees C is 1.17, indicative of a secondary, not a primary, deuterium kinetic isotope effect. The reaction does not occur through a [1,5] hydrogen shift from the transient cis,trans-1,3-cyclooctadiene intermediate to form the observed cis,cis-diene product. 相似文献
302.
Electric field gradient inhcp transition metal scandium has been calculated as the sum of contributions from lattice ions and conduction electrons. For
the lattice contributionq
latt, a point-charge model has been assumed. The contribution from conduction electronsq
el, on the other hand, has been evaluated by carrying out an energy-band calculation using non-local transition-metal model
potential. The results obtained are:q
el=−106.11×1013 esu/cm3 andq
latt=122.17×1013 esu/cm3. The net field gradient (q
el+q
latt) of 16.06×1013 esu/cm3 agrees quite well with the experimental result, |q
expt|=13×1013 esu/cm3. Directions of further improvement in the theory are discussed. 相似文献
303.
In this article we study a linear as well as a quadratic discriminant function for multi-level multivariate repeated measurement data under the assumption of multivariate normality. We assume that the m-variate observations have jointly equicorrelated covariance structure in addition to a Kronecker product structure on the mean vector. The new discriminant functions are very effective in discriminating individuals when the number of observations is very small. The proposed classification rules are demonstrated on a real data set. The error rates of the proposed classification rules are found to be much less than the error rates of the traditional classification rules, when in fact the traditional classification rules fail most of the time owing to the small sample sizes. 相似文献
304.
We study a modified Yakushevich model with different disc diameters representing different bases and find two new in-phase
solitonic solutions. We also discuss here the effect of helical structure which acts as perturbation on soliton centre of
mass. 相似文献
305.
Ahmed F. Ghoniem Anuradha Annaswamy Sungbae Park Ziaieh C. Sobhani 《Proceedings of the Combustion Institute》2005,30(2):1765-1773
We experimentally study lean premixed combustion stabilized behind a backward-facing step. For a propane–air mixture, the lean blowout limit is associated with strong pressure fluctuation arising simultaneously with strong flame–vortex interactions, which have been shown to constitute the mechanism of heat release dynamics in this flow. A high-speed air jet, issuing from a small slot and injected perpendicular to the main flow near the step, is used to disrupt this mechanism. For momentum ratio of jet to main flow below unity, the jet dilutes the mixture, further destabilizing the flame or leading to complete blowout. Above unity, the flame becomes more stable, and the pressure oscillations are suppressed. Flow visualization and OH*/CH* chemiluminescence measurements show that a strong jet produces a more compact flame that is less driven by the wake vortex, anchored closer to the step, and deflected upwards away from the lower wall of the channel. This renders the flame less vulnerable to heat loss and strong strains, which improves its stability and extends the flammability limit. Adding hydrogen to the main fuel improves the flame stability over the entire range of the air jet mass flow, with better results for momentum ratio larger than 1; H2 pulls the flame further upstream, away from the shear zone and the unsteady vortex. NOx emission benefits from the air jet, while, with H2 addition, NOx concentration is higher in the products as the overall burning temperature rises. However, hydrogen addition enables extending the flammability limit further by increasing air supply in the primary stream, hence achieving lower NOx. The study suggests a simpler, almost passive, multi-objective combustion control technique and indicates that hydrogen addition can be a successful in situ approach for NOx reduction. 相似文献
306.
Kiran Prajapati Anuradha Varshney 《Journal of polymer science. Part A, Polymer chemistry》2005,43(24):6524-6533
The free‐radical polymerization of styrene with p‐nitrobenzyl triphenyl phosphonium ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a syndiotactic polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight‐average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the ylide and the free‐radical mode of polymerization. Differential scanning calorimetry studies showed the glass‐transition temperature of the polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005 相似文献
307.
Sarma V. Uma Maheswara Srinivas Pullela V. Anuradha V. Rao J. Madhusudana 《平面色谱法杂志一现代薄层色谱法》2006,19(3):238-240
JPC – Journal of Planar Chromatography – Modern TLC - The dried fruits of Piper longum are extensively used in Ayurvedic medicinal preparations. A simple and convenient HPTLC method has... 相似文献
308.
Dr. Sungho Kim Dr. Gurwinder Singh Dr. CI Sathish Prof. Puspamitra Panigrahi Dr. Rahman Daiyan Dr. Xunyu Lu Prof. Yoshihiro Sugi Prof. In Young Kim Prof. Ajayan Vinu 《化学:亚洲杂志》2021,16(23):3999-4005
We investigated the CO2 adsorption and electrochemical conversion behavior of triazole-based C3N5 nanorods as a single matrix for consecutive CO2 capture and conversion. The pore size, basicity, and binding energy were tailored to identify critical factors for consecutive CO2 capture and conversion over carbon nitrides. Temperature-programmed desorption (TPD) analysis of CO2 demonstrates that triazole-based C3N5 shows higher basicity and stronger CO2 binding energy than g-C3N4. Triazole-based C3N5 nanorods with 6.1 nm mesopore channels exhibit better CO2 adsorption than nanorods with 3.5 and 5.4 nm mesopore channels. C3N5 nanorods with wider mesopore channels are effective in increasing the current density as an electrocatalyst during the CO2 reduction reaction. Triazole-based C3N5 nanorods with tailored pore sizes exhibit CO2 adsorption abilities of 5.6–9.1 mmol/g at 0 °C and 30 bar. Their Faraday efficiencies for reducing CO2 to CO are 14–38% at a potential of −0.8 V vs. RHE. 相似文献
309.
Pyridiniumchlorochromate (PCC) oxidizes aniline and substituted anilines except nitro anilines smoothly in chlorobenzene–nitrobenzene mixtures in the presence of dichloroacetic acid. The reaction has unit dependence on each of the aniline, PCC, and dichloroacetic acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electronwithdrawing groups retard the reaction, and the rate data obey Hammett's relationship. The reaction constant ρ is -3.75. Azobenzene and p-benzoquinone have been obtained as products. The observed experimental data have been rationalized in terms of the formation of an intermediate complex involving PCC–amine undergoing a rapid decomposition to products. 相似文献
310.
Elucidation of functional groups on gram-positive and gram-negative bacterial surfaces using infrared spectroscopy 总被引:1,自引:0,他引:1
Jiang W Saxena A Song B Ward BB Beveridge TJ Myneni SC 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11433-11442
Surface functional group chemistry of intact Gram-positive and Gram-negative bacterial cells and their isolated cell walls was examined as a function of pH, growth phase, and growth media (for intact cells only) using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Infrared spectra of aqueous model organic molecules, representatives of the common functional groups found in bacterial cell walls (i.e., hydroxyl, carboxyl, phosphoryl, and amide groups), were also examined in order to assist the interpretation of the infrared spectra of bacterial samples. The surface sensitivity of the ATR-FTIR spectroscopic technique was evaluated using diatom cells, which possess a several-nanometers-thick layer of glycoprotein on their silica shells. The ATR-FTIR spectra of bacterial surfaces exhibit carboxyl, amide, phosphate, and carbohydrate related features, and these are identical for both Gram-positive and Gram-negative cells. These results provide direct evidence to the previously held conviction that the negative charge of bacterial surfaces is derived from the deprotonation of both carboxylates and phosphates. Variation in solution pH has only a minor effect on the secondary structure of the cell wall proteins. The cell surface functional group chemistry is altered neither by the growth phase nor by the growth medium of bacteria. This study reveals the universality of the functional group chemistry of bacterial cell surfaces. 相似文献