Numerical analysis on auto-ignition of a high pressure hydrogen jet spouting from a tube

In this study, a direct numerical simulation based on compressible flow dynamics has been applied to the autoignition and extinction of a high-pressure hydrogen jet spouting from a tube. The diameter of the tube is 4.8 mm. The length of the tube is 71 mm. At the inlet, pressure is set at 3.6, 5.3 and 21.1 MPa, and temperature is set at 300 K for all cases. To explore the autoignition of hydrogen jet, two-dimensional axisymmetric Navier–Stokes equations with a detailed chemical kinetics and rigorous transport properties have been employed. The hydrogen jet through the tube is choked. The numerical results show that the high-pressure hydrogen jet produces a semi-spherical shock wave in the ambient air at the early time of jetting. The shock wave heats up the air to a high temperature and causes the autoignition of the hydrogen and air mixture in the tube as well as at the tube exit.     

Enhanced gas-sensing behaviour of Ru-doped SnO2 surface: A periodic density functional approach

A theoretical study on Ru-doped rutile SnO₂(1 1 0) surface has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA-RPBE) level with a periodic supercell approach. Electronic structure analysis was performed based on the band structure and partial density of states. The results provide evidence that the electronic structures of SnO₂(1 1 0) surface are modified by the surface Ru dopant, in which Ru 4d orbital are located at the edge of the band gap region. It is demonstrated that molecular oxygen adsorption characteristics on stoichiometric SnO₂(1 1 0) surface are changed from endothermic to exothermic due to the existence of surface Ru dopant. The dissociative adsorption of molecular oxygen on the Ru_5c/SnO₂(1 1 0) surface is exothermic, which indicates that Ru could act as an active site to increase the oxygen atom species on SnO₂(1 1 0) surface. Our present study reveals that the Ru dopant on surface is playing both electronic and chemical role in promoting the SnO₂ gas-sensing property.     

Simultaneous quantitative determination of cyclosporine A and its three main metabolites (AM1, AM4N and AM9) in human blood by liquid chromatography/mass spectrometry using a rapid sample processing method

We have developed a sensitive and specific liquid chromatography/mass spectrometry (LC/MS) method for the simultaneous determination of cyclosporine A (CsA) and its three main metabolites (AM1, AM4N and AM9) in human blood. Following protein precipitation, supernatant was directly injected into the LC/MS system. Chromatographic separation was accomplished on a Symmetry C8 (4.6 x 75 mm, 3.5 microm) column with a linear gradient elution prior to detection by atmospheric pressure chemical ionization (APCI) MS using selected ion monitoring (SIM) in positive mode. This method can be applied to single mass equipment. The analytical range for each analyte was set at 1-2500 ng/mL using 100 microL of blood sample. The analytical method was fully validated according to FDA guidance. Intra-day mean accuracy and precision were 95.2-113.5% and 0.9-8.9%, respectively. Inter-day mean accuracy and precision were 95.8-107.0% and 1.5-10.7%, respectively. In blood all analytes were stable during three freeze/thaw cycles, for 24 h at room temperature and for 12 months at or below -15 degrees C. Stability was also confirmed in processed samples for 24 h at 10 degrees C and for 6 months at 4 degrees C in methanol. In addition, we confirmed the method could avoid matrix effects from transplant subjects' samples. This LC/MS technique provided an excellent method for simultaneous quantitative determination of CsA and its three metabolites for evaluation of their pharmacokinetic profiles.     

Second-harmonic spectroscopy of surface immobilized gold nanospheres above a gold surface supported by self-assembled monolayers

We have investigated linear and nonlinear optical properties of surface immobilized gold nanospheres (SIGNs) above a gold surface with a gap distance of a few nanometers. The nanogap was supported by amine or merocyanine terminated self-assembled monolayers (SAMs) of alkanethiolates. A large second-harmonic generation (SHG) was observed from the SIGN systems at localized surface plasmon resonance condition. The maximum enhancement factor of SHG intensity was found to be 3 x 10(5) for the SIGN system of nanospheres 100 nm in diameter with a gap distance of 0.8 nm. The corresponding susceptibility was estimated to be chi((2))=750 pmV (1.8 x 10(-6) esu). In the SIGN system supported with the merocyanine terminated SAMs, the SHG response was also resonant to the merocyanine in the nanogap. It was found that the SHG response of the SIGN systems is strongly frequency dependent. This leads us to conclude that the large chi((2)) is caused by enhanced electric fields at the localized surface plasmon resonance condition and is not due to an increase of the surface susceptibility following from the presence of the gold nanospheres. The observed SHG was consistent with the theoretical calculations involving Fresnel correction factors, based on the quasistatic approximation.     

The Active Phase of Nickel/Ordered Ce(2) Zr(2) O(x) Catalysts with a Discontinuity (x=7-8) in Methane Steam Reforming

Breaking news: A unique discontinuous property and an active phase of Ni/ordered Ce(2) Zr(2) O(x) (x=7-8) solid-solution catalysts were observed during methane steam reforming. The catalytic performance of Ni/Ce(2) Zr(2) O(x) strongly depended on the phase and oxygen content of the Ce(2) Zr(2) O(x) support.     

Preparation and catalytic performances of a molecularly imprinted Ru-complex catalyst with an NH2 binding site on a SiO2 surface

A catalyst surface with an active metal site, a shape-selective reaction space, and an NH(2) binding site for o-fluorobenzophenone was designed and prepared by the molecular imprinting of a supported metal complex on a SiO(2) surface. A ligand of a SiO(2)-supported Ru complex that has a similar shape to the product of o-fluorobenzophenone hydrogenation was used as a template. An NH(2) binding site for o-fluorobenzophenone was spatially arranged on the wall of a molecularly imprinted cavity with a similar shape to the template. The structures of the SiO(2)-supported and molecularly imprinted Ru catalysts were characterized in a step-by-step manner by means of solid-state magic angle spinning (MAS) NMR, XPS, UV/Vis, N(2) adsorption, XRF, and Ru K-edge EXAFS. The molecularly imprinted Ru catalyst exhibited excellent shape selectivity for the transfer hydrogenation of benzophenone derivatives. It was found that the NH(2) binding site on the wall of the molecularly imprinted cavity enhanced the adsorption of o-fluorobenzophenone, of which the reduction product was imprinted, whereas there was no positive effect in the case of o-methylbenzophenone, which cannot interact with the NH(2) binding site through hydrogen bonding.     

Photoluminescence and magnetic circular dichroism of IrQ(ppy)2-5Cl

Photoluminescence and magnetic circular dichroism of the IrQ(ppy)₂-5Cl compound were investigated between 15 and 295 K. These results have been compared with the output files obtained from Density Functional Theory by using the Gaussian 03W software and some additional packages. The experimental results confirm the first triplet state absorption which arises from d to π_Q transition. The temperature dependence photoluminescence have shown a small interaction with the polystyrene, used for dispersion of IrQ(ppy)₂-5Cl compound. The green and red phosphorescence have the same temperature dependence. The MCD spectra, especially at 15 K, reveals the main transitions involved in the Metal-to-Ligand Charge Transfer processes from the Ir towards the two ligands, phenylpyridine and quinoline, respectively.     

Studies on the mechanism for stereoisomerization of 1-zirconacyclopent-3-yne compounds

The stereoisomerization of 2,5-disubstituted 1-zirconacyclopent-3-yne compounds, stable five-membered cycloalkynes, has been studied with regard to the mechanism. The bimetallic complex of 1,4-bis(trimethylsilyl)butatriene was synthesized and structurally characterized, although it seems unimportant for the stereoisomerization reactions. The isomerization of trans-1,1-bis(η⁵-cyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne 2a into the cis-form in benzene-d₆ solution were observed using ¹H NMR spectroscopy at 50 °C in various concentrations. The reaction was first order with respect to trans-2a. This ruled out the possibility that a bimetallic complex was responsible for the isomerization. A kinetic isotope effect was observed (k_H/k_D = 1.8), suggesting that C–H activation is involved in the rate-determining step. A mechanism via hydrogen elimination from the complex of η⁴-π,π-coordination mode is proposed.     

Three-dimensional numerical simulation of detonations in coaxial tubes

Three-dimensional numerical simulation of detonations in both a circular tube and a coaxial tube are simulated to reveal characteristics of single spinning and two-headed detonations. The numerical results show a feature of a single spinning detonation which was discovered in 1926. Transverse detonations are observed in both tubes, however, the single spinning mode maintains the complex Mach reflection whereas the two-headed mode develops periodically from the single Mach reflection to the complex one. The calculated cell aspect ratio for the two-headed mode changes from 1.09 to 1.34 as the radius of axial insert increases from r ₁/R = 0.1 to 0.9. The calculated cell aspect ratio for r ₁/R = 0.1 is close to the experimental results without an axial insert. The formation of an unreacted gas pocket behind the detonation front was not observed in the single spinning mode; however, the two-headed mode has unreacted gas pocket behind the front near the axial insert.