Mechanism and kinetics of the reaction of the 2-propargyl radical with ammonia

Gas-phase mechanism and kinetics of the reactions of the 2-propargyl radical (H₂CCCH), an important intermediate in combustion processes, with ammonia were investigated using ab initio molecular orbital theory at the coupled-cluster CCSD(T)//B3LYP/6-311++G(3df,2p) method in conjunction with transition state theory (TST), variational transition state theory (VTST), and Rice–Ramsperger–Kassel–Macus (RRKM) calculations for rate constants. The potential energy surface (PES) constructed shows that the C₃H₃ + NH₃ reaction has four main entrances, including two H-abstraction and two addition channels in which the former are energetically more favorable. The H-abstraction channels occur via energy barriers of 24 (T0/P2) and 26 kcal/mol (T0/P3) forming loose van de Waals complexes, COM_1 (12 kcal/mol) and COM_2 (14 kcal/mol), respectively. These complexes can easily be decomposed via barrier-less processes resulting HCCCH₃ + NH₂ (P2, 14 kcal/mol) and HCCCH₃ + NH₂ (P3, 15 kcal/mol), respectively. The additional channels occur initially by formation of two intermediate states, H₂CCCHNH₃ (35 kcal/mol) and H₂CC(NH₃)CH (37 kcal/mol) via energy barriers of 37 and 40 kcal/mol at T0/1 and T0/5, respectively, followed by isomerization and decomposition yielding 21 different products. These processes are fully depicted in an as-complete-as-possible PES. The rate constants and product branching ratios for the low-energy channels calculated show that the C₃H₃ + NH₃ reaction is almost pressure-independent. For the temperature range of 300–2000 K, the HCCCH₃ + NH₂ is the major product, whereas the minor one, HCCCH₃ + NH₂, has more contribution when temperature increases. Theoretical results on the mechanism and kinetics of the reaction considered may be helpful for future experiments as well as for understanding the role of the propargyl radical in combustion chemistry.     

Design and identification of high performance steel alloys for structures subjected to underwater impulsive loading

Martensitic and austenitic steel alloys were designed to optimize the performance of structures subjected to impulsive loads. The deformation and fracture characteristics of the designed steel alloys were investigated experimentally and computationally. The experiments were based on an instrumented fluid–structure interaction apparatus, in which deflection profiles are recorded using a shadow Moiré technique combined with high speed imaging. Fractographic analysis and post-mortem thickness reduction measurements were also conducted in order to identify deformation and fracture modes. The computational study was based on a modified Gurson damage model able to accurately describe ductile failure under various loading paths. The model was calibrated for two high performance martensitic steels (HSLA-100 and BA-160) and an austenitic steel (TRIP-120). The martensitic steel (BA-160) was designed to maximize strength and fracture toughness while the austenitic steel (TRIP-120) was designed to maximize uniform ductility, in other words, to delay necking instability. The combined experimental–computational approach provided insight into the relationships between material properties (strength, uniform ductility, and post-necking ductility) and blast resistance of structures. In particular, the approach allowed identification of material/structure performances by identifying impulse-center deflection behavior and the impulse leading to panel fracture.     

Synthesis and molecular structure of bis(areno)piperidinoaza-14(17)-crowns-4(5)

The condensation of dialkyl ketones with α,ω-bis(2-formylphenoxy)- or α,ω-bis(1-formylnaphthalen-2-yloxy)-3-oxapentane and-3,6-dioxaoctane in the presence of ammonium acetate according to Petrenko-Kritchenko gave 14–41% of new bis(areno) aza crowns, bis(areno)piperidinoaza-14-crown-4 and bis(benzo)-piperidinoaza-17-crown-5, having functional substituents in the piperidine fragment. The yield of the aza crown ether appreciably decreases upon extension of the polyether chain in the aldehyde component. The molecular structure of two of the obtained macrocyclic compounds and the relative configuration of asymmetric carbon atoms in the piperidine ring were determined by X-ray analysis, and the size of their internal cavities was estimated.     

Optimality conditions in terms of contingent epiderivatives for strict local Pareto minima in vector optimization problems with constraints

Positivity - In this paper, primal and dual necessary/sufficient optimality conditions are investigated for vector optimization problem with set, cone and equality constraints. We establish some...     

Local moving least square‐one‐dimensional integrated radial basis function networks technique for incompressible viscous flows

This paper presents a local moving least square‐one‐dimensional integrated radial basis function networks method for solving incompressible viscous flow problems using stream function‐vorticity formulation. In this method, the partition of unity method is employed as a framework to incorporate the moving least square and one‐dimensional integrated radial basis function networks techniques. The major advantages of the proposed method include the following: (i) a banded sparse system matrix which helps reduce the computational cost; (ii) the Kronecker‐ δ property of the constructed shape function which helps impose the essential boundary condition in an exact manner; and (iii) high accuracy and fast convergence rate owing to the use of integration instead of conventional differentiation to construct the local radial basis function approximations. Several examples including two‐dimensional (2D) Poisson problems, lid‐driven cavity flow and flow past a circular cylinder are considered, and the present results are compared with the exact solutions and numerical results from other methods in the literature to demonstrate the attractiveness of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.     

The isomeric ratios in photonuclear reactions of natural barium induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We have determined the isomeric ratios in ¹³⁰Ba(γ, n)^129m,gBa, ¹³²Ba(γ, n)^131m,gBa and ¹³⁴Ba(γ, n)^133m,gBa photonuclear reactions of natural barium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region. The investigated samples were irradiated at electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The gamma spectra of the samples irradiated were measured with spectroscopic system consisting of 8192 channel analyzer and high-energy resolution (180 keV at gamma ray 1332 keV of ⁶⁰Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors.     

A filter method with a priori and a posteriori parameter choice for the regularization of Cauchy problems for biharmonic equations

Numerical Algorithms - In the present paper, we devote our effort to Cauchy boundary value problems for biharmonic equations. In general, the investigated problem is ill-posed. Therefore, we...     

Conjugate duality for vector-maximization problems

In this article we present a conjugate duality for a problem of maximizing a polyhedral concave nondecreasing homogeneous function over a convex feasible set in the nonnegative n-dimensional orthant. Using this duality we obtain a zero-gap duality for a vector-maximization problem.     

Correction to "combinatiorial properties of some classes of matrices over GF(2)"

Due to my oversight in checking the galley proofs, an error has occured in Tran [1]. The wording of proposition 4.2 on page 162 should read.