A flow visualization study on self-ignition of high pressure hydrogen gas released into a tube

Hydrogen is known as one of the green energy sources for fuel cells and hydrogen-fueled cars in the next generation. The storage of high-pressure hydrogen gas conditions is preferred to its storage in cryogenic liquid state. However, cases of unidentified self-ignitions were reported, notably when the high-pressure hydrogen gas suddenly leaked out. Only a few of numerical simulations have shown visually the processes of the self-ignition inside a tube. This paper presents a flow visualization study to investigate the self-ignition mechanism in a test tube i.e. how the ignition process is initiated and the flame propagates. In addition to visualization, measurement of a number of pressure and light sensors installed in the tube supported the analysis of the self-ignition and flame propagation. The test result showed that self-ignition takes place at the boundary layer behind the front center of mixing zone at first, and the flame propagates to the front of mixing zone and tail of the mixing zone along the boundary layer. It showed that self-ignition is accompanied with complex mixing induced by shock interaction with the mixing front. It is also suggested that the self-ignition boundary has a certain critical threshold of static pressure at the boundary layer, based on various burst pressures of hydrogen.     

Chemical cleavage reactions of DNA on solid support: application in mutation detection

Background  

The conventional solution-phase Chemical Cleavage of Mismatch (CCM) method is time-consuming, as the protocol requires purification of DNA after each reaction step. This paper describes a new version of CCM to overcome this problem by immobilizing DNA on silica solid supports.     

Theoretical study of the electronic states of calcium and calcium hydride

The lowest states of the calcium atom as a two-electron system have been studied using a non-empirical pseudopotential, valence CI, and perturbative valence—core correlation. The lowest three ²Σ⁺ states and the lowest ²Π state of calcium hydride have also been studied. The precision and the limitations of the perturbative valence—core correlation method based on the valence—core separability are illustrated.     

Ionisation Potential, Electron Affinity and Polar Bond: A First-order Correction Method for Interaction Energy

A new first-order method is proposed to improve the potential energy of the polar molecules. The nature of the polar bonding is illustrated by some examples, LiF, LiO, LiH, ScO, and AlO molecules, covering from strong to weak ionic cases. A simple first-order correction method using the dipole moment or the effective charge, and the experimental and theoretical ionisation potentials and electron affinities is explained. Application of this method to those molecules improves remarkably the spectroscopic constants. This method can be easily extended to polyatomic cases involving a polar bonding between an electropositive moiety (electron donor) and an electronegative functional group (electron acceptor).     

Theoretical study on interaction of hydrogen with single-walled boron nitride nanotubes. II. Collision, storage, and adsorption

Collision and adsorption of hydrogen with high incident kinetic energies on a single-walled boron nitride (BN) nanotube have been investigated. Molecular-dynamics (MD) simulations indicate that at incident energies below 14 eV hydrogen bounces off the BN nanotube wall. On the other hand, at incident energies between 14 and 22 eV each hydrogen molecule is dissociated at the exterior wall to form two hydrogen atoms, but only one of them goes through the wall. However, at the incident energies between 23 and 26 eV all of the hydrogen atoms dissociated at the exterior wall are found to be capable of going inside the nanotube and then to recombine to form hydrogen molecules inside the nanotube. Consequently, it is determined that hydrogen should have the incident energy >22 eV to go inside the nanotube. On the other hand, we find that the collisions using the incident energies >26 eV could result in damaging the nanotube structures. In addition our MD simulations find that hydrogen atoms dissociated at the wall cannot bind to either boron or nitrogen atoms in the interior wall of the nanotube.     

Catalytic asymmetric allylation of ketones and a tandem asymmetric allylation/diastereoselective epoxidation of cyclic enones

A simple procedure is reported for the catalytic asymmetric allylation of ketones, utilizing titanium tetraisopropoxide, BINOL, 2-propanol additive, and tetraallylstannane as allylating agent. A variety of ketone substrates, including acetophenone derivatives and alpha,beta-unsaturated cyclic enones, reacted to form tertiary homoallylic alcohols in good yields (67-99%) and with high levels of enantioselectivity (generally >80%). A novel one-pot enantioselective allylation/diastereoselective epoxidation has also been introduced. Thus, upon completion of the allyl addition to conjugated cyclic enones, 1 equiv of tert-butyl hydroperoxide is added and the directed epoxidation of the allylic double bond ensues to afford the epoxy alcohol with high diastereoselectivity.     

The effect of nonlinearity on unstable zones of Mathieu equation

Mathieu equation is a well-known ordinary differential equation in which the excitation term appears as the non-constant coefficient. The mathematical modelling of many dynamic systems leads to Mathieu equation. The determination of the locus of unstable zone is important for the control of dynamic systems. In this paper, the stable and unstable regions of Mathieu equation are determined for three cases of linear and nonlinear equations using the homotopy perturbation method. The effect of nonlinearity is examined in the unstable zone. The results show that the transition curves of linear Mathieu equation depend on the frequency of the excitation term. However, for nonlinear equations, the curves depend also on initial conditions. In addition, increasing the amplitude of response leads to an increase in the unstable zone.     

The 5Σg and 6Σg Rydberg States of Li2: Observation and Calculation

The ⁷Li₂ 5¹Σ_g⁺ and 6¹Σ_g⁺ states have been studied both experimentally and theoretically. Vibrational levels v=1-26 of the 5¹Σ_g⁺ state and v=2-14 of the 6¹Σ_g⁺ state were observed using pulsed optical-optical double resonance technique. The 5¹Σ_g⁺ state has an unusual potential energy curve with a shelf near v=11. Dunham coefficients for the v=0-9 levels of the 5¹Σ_g⁺ state have been obtained. RKR potential energy curves of these two were generated. Ab initio potentials are in good agreement with the RKR potentials.