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141.
The rate coefficient, k, of the reaction has been determined in the temperature range 2460–2840 K using a shock tube technique. C2N2? H2O? Ar mixtures were heated behind incident shock waves and the CN and OH concentration time histories were monitored simultaneously using broad-band absorption near 388 nm (CN) and narrow-line laser absorption at 306.67 nm (OH). The rate coefficient expression providing the best fit to the data was with uncertainty limits of about ±45% in the temperature range 2460–2840 K. The rate coefficient of the reverse reaction was calculated using detailed balancing, and its extrapolation to lower temperatures was compared with previously published results. 相似文献
142.
Chromium(II) salts can be used for a variety of reductions in organic chemistry; for example, alkyl halides and suitably substituted olefins may both be reduced to alkanes, and alkynes may be converted into trans-olefins. Several epoxyketones are reduced to α,β-unsaturated ketones or β-hydroxyketones, and a nitro steroid was found to give a hydroxy(hydroxyimino) compound. The reduction of alkyl halides is reported to proceed by a free-radical mechanism; the halogen atom that is set free forms a bridge between two chromium atoms. 相似文献
143.
Wang X Rodriguez JA Hanson JC Gamarra D Martínez-Arias A Fernández-García M 《The journal of physical chemistry. B》2006,110(1):428-434
New information about the active sites for the water gas shift (WGS) reaction over Cu-CeO2 systems was obtained using in-situ, time-resolved X-ray diffraction (TR-XRD), X-ray absorption spectroscopy (TR-XAS, Cu K and Ce L3 edges), and infrared spectroscopy (DRIFTS). Cu-CeO2 nanoparticles prepared by a novel reversed microemulsion method (doped Ce1-xCuxO2 sample) and an impregnation method (impregnated CuOx/CeO2 sample) were studied. The results from all of the samples indicate that both metallic copper and oxygen vacancies in ceria were involved in the generation of active sites for the WGS reaction. Evidence was found for a synergistic Cu-Ovacancy interaction. This interaction enhances the chemical activity of Cu, and the presence of Cu facilitates the formation of O vacancies in ceria under reaction conditions. Water dissociation occurred on the Ovacancy sites or the Cu-Ovacancy interface. No significant amounts of formate were formed on the catalysts during the WGS reaction. The presence of strongly bound carbonates is an important factor for the deactivation of the catalysts at high temperatures. This work identifies for the first time the active sites for the WGS reaction on Cu-CeO2 catalysts and illustrates the importance of in situ structural studies for heterogeneous catalytic reactions. 相似文献
144.
[reaction: see text] Studies probing reactivity and selectivity of cross metathesis (CM) with an exocyclic olefin in a P-chiral bicyclo[4.3.1]phosphate triester are described. Studies have revealed a Type III CM reactivity pattern for the exocyclic olefin within this phosphate triester. This versatile method allows for simple, selective manipulation of a P-chiral building block en route to advanced polyol subunits. 相似文献
145.
The symmetry properties of transport beyond the linear regime in chaotic quantum dots are investigated experimentally. A component of differential conductance that is antisymmetric in both applied source-drain bias V and magnetic field B, absent in linear transport, is found to exhibit mesoscopic fluctuations around a zero average. Typical values of this component allow a measurement of the electron interaction strength. 相似文献
146.
J.R. Petta A.C. Johnson J.M. Taylor E.A. Laird A. Yacoby M.D. Lukin C.M. Marcus M.P. Hanson A.C. Gossard 《Physica E: Low-dimensional Systems and Nanostructures》2006,35(2):251
We use gate voltage control of the exchange interaction to prepare, manipulate, and measure two-electron spin states in a GaAs double quantum dot. By placing two electrons in a single dot at low temperatures we prepare the system in a spin singlet state. The spin singlet is spatially separated by transferring an electron to an adjacent dot. The spatially separated spin singlet state dephases in due to the contact hyperfine interaction with the GaAs host nuclei. To combat the hyperfine dephasing, we develop quantum control techniques based on fast electrical control of the exchange interaction. We demonstrate coherent spin-state rotations in a singlet–triplet qubit and harness the coherent rotations to implement a singlet–triplet spin echo refocusing pulse sequence. The singlet–triplet spin echo extends the spin coherence time to . 相似文献
147.
Jason Hanson 《General Relativity and Gravitation》2013,45(3):599-612
The canonical decomposition of a Lorentz algebra element into a sum of orthogonal simple (decomposable) Lorentz bivectors is defined and discussed. This decomposition on the Lie algebra level leads to a natural decomposition of a proper orthochronous Lorentz transformation into a product of commuting Lorentz transformations, each of which is the exponential of a simple bivector. While this later result is known, we present novel formulas that are independent of the form of the Lorentz metric chosen. As an application of our methods, we obtain an alternative method of deriving the formulas for the exponential and logarithm for Lorentz transformations. 相似文献
148.
Zekai Hong King-Yiu Lam Ritobrata Sur Shengkai Wang David F. Davidson Ronald K. Hanson 《Proceedings of the Combustion Institute》2013,34(1):565-571
Hydrogen peroxide (H2O2) and hydroperoxy (HO2) reactions present in the H2O2 thermal decomposition system are important in combustion kinetics. H2O2 thermal decomposition has been studied behind reflected shock waves using H2O and OH diagnostics in previous studies (Hong et al. (2009) [9] and Hong et al. (2010) [6,8]) to determine the rate constants of two major reactions: H2O2 + M → 2OH + M (k1) and OH + H2O2 → H2O + HO2 (k2). With the addition of a third diagnostic for HO2 at 227 nm, the H2O2 thermal decomposition system can be comprehensively characterized for the first time. Specifically, the rate constants of two remaining major reactions in the system, OH + HO2 → H2O + O2 (k3) and HO2 + HO2 → H2O2 + O2 (k4) can be determined with high-fidelity.No strong temperature dependency was found between 1072 and 1283 K for the rate constant of OH + HO2 → H2O + O2, which can be expressed by the combination of two Arrhenius forms: k3 = 7.0 × 1012 exp(550/T) + 4.5 × 1014 exp(?5500/T) [cm3 mol?1 s?1]. The rate constants of reaction HO2 + HO2 → H2O2 + O2 determined agree very well with those reported by Kappel et al. (2002) [5]; the recommendation therefore remains unchanged: k4 = 1.0 × 1014 exp(?5556/T) + 1.9 × 1011+exp(709/T) [cm3 mol?1 s?1]. All the tests were performed near 1.7 atm. 相似文献
149.
150.
Cynthia Hanson Jacob T. Barney Morgan M. Bishop Elizabeth Vargis 《Electrophoresis》2019,40(10):1446-1456
The traditional bacterial identification method of growing colonies on agar plates can take several days to weeks to complete depending on the growth rate of the bacteria. Successfully decreasing this analysis time requires cell isolation followed by identification. One way to decrease analysis time is by combining dielectrophoresis (DEP), a common technique used for cell sorting and isolation, and Raman spectroscopy for cell identification. DEP‐Raman devices have been used for bacterial analysis, however, these devices have a number of drawbacks including sample heating, cell‐to‐electrode proximity that limits throughput and separation efficiency, electrode fouling, or inability to address sample debris. Presented here is a contactless DEP‐Raman device to simultaneously isolate and identify particles from a mixed sample while avoiding common drawbacks associated with other DEP designs. Using the device, a mixed sample of bacteria and 3 μm polystyrene spheres were isolated from each other and a Raman spectrum of the trapped bacteria was acquired, indicating the potential for cDEP‐Raman devices to decrease the analysis time of bacteria. 相似文献