Synthesis, Characterization and Crystal Structure of [Na2(APZC)2(μ-H2O)2(μ3-H2O)]n

The synthesis and spectroscopic properties of a Na^＋ complex with ligand 3-aminopyrazine-2-carboxylic acid were described. The resulting complex was characterized by elemental analysis, IR, UV-Vis, NMR spectroscopy and single crystal X-ray diffraction method. The title compound crystallizes in the triclinic system with space group . The crystalline structure of this compound consists of supramolecular architectures involving strong intramolecular N—H…O in pyrazine molecules and intermolecular O—H…N, O—H…O, and N—H…N hydrogen bonds between substituted pyrazine and water molecules.     

Implementation of high‐order compact finite‐difference method to parabolized Navier–Stokes schemes

The numerical solution to the parabolized Navier–Stokes (PNS) and globally iterated PNS (IPNS) equations for accurate computation of hypersonic axisymmetric flowfields is obtained by using the fourth‐order compact finite‐difference method. The PNS and IPNS equations in the general curvilinear coordinates are solved by using the implicit finite‐difference algorithm of Beam and Warming type with a high‐order compact accuracy. A shock‐fitting procedure is utilized in both compact PNS and IPNS schemes to obtain accurate solutions in the vicinity of the shock. The main advantage of the present formulation is that the basic flow variables and their first and second derivatives are simultaneously computed with the fourth‐order accuracy. The computations are carried out for a benchmark case: hypersonic axisymmetric flow over a blunt cone at Mach 8. A sensitivity study is performed for the basic flowfield, including profiles and their derivatives obtained from the fourth‐order compact PNS and IPNS solutions, and the effects of grid size and numerical dissipation term used are discussed. The present results for the flowfield variables and also their derivatives are compared with those of other basic flow models to demonstrate the accuracy and efficiency of the proposed method. The present work represents the first known application of a high‐order compact finite‐difference method to the PNS schemes, which are computationally more efficient than Navier–Stokes solutions. Copyright © 2008 John Wiley & Sons, Ltd.     

Highly nonlinear chalcogenide fibres for all-optical signal processing

Chalcogenide glasses offer many attractive properties for all-optical signal processing including large Kerr nonlinearity (up to 500 × silica glass), an intrinsic ultrafast response time and low to moderate two-photon absorption (TPA). These properties together with the convenience of a fibre format allow us to achieve all-optical signal processing at low peak power and in a very compact form. In this paper, several nonlinear processing functions will be demonstrated including: femto-second pedestal free, pulse compression; all-optic wavelength conversion; and all-optical regenerator. In addition, we show enhanced nonlinearity for more efficient signal processing by tapering the As₂Se₃ fibre. These applications show chalcogenide glass fibres are very promising candidate materials for nonlinear all-optic signal processing.     

Synthesis and characterization of a novel polyurethane/polypyrrole‐p‐toluenesulfonate (PU/PPy‐pTS) electroactive nanofibrous bending actuator

Electroactive actuators based on conductive polymers currently have attracted a great deal of attention. In this study, a nanofibrous structure of polypyrrole (PPy) was used to fabricate an electroactive bending actuator. For this purpose, polyurethane/PPy (PU/PPy) nanofibrous bending actuator was fabricated through the combined use of electrospinning and in‐situ chemical polymerization. The response surface methodology (RSM) was considered to find the optimal electrospinning conditions for producing PU nanofibers with the minimum diameter. The in‐situ chemical polymerization method was then used to prepare a conductive layer of PPy on the surface of optimum electrospun nanofibers with p‐toluenesulfonate (pTS) as the dopant. The coated nanofibers were used in the fabrication of PU/PPy‐pTS nanofibrous bending actuator. The morphology and electrical, thermal, electrochemical, and electrochemomechanical properties of the fabricated actuator were investigated. By using optimum conditions of electrospinning, PU nanofibers were obtained with a diameter of 221 nm. The results showed that the produced PU/PPy‐pTS nanofibers enjoy good thermal stability and have an electrical conductivity of about 276.34 S/cm. The obtained cyclic voltammetric and dynamo‐voltammetric responses showed that the dominant mechanism of actuation in the fabricated PU/PPy‐pTS nanofibrous actuator is the exchange of perchlorate anions with a partial exchange of lithium cations in 1M lithium perchlorate electrolyte solution. The fabricated actuator was capable of undergoing 141° reversible angular displacement during a potential cycle. The results demonstrated that, given high porosity, large specific surface area, flexibility, and desirable electrical properties, PU/PPy nanofibrous electroactive actuator provides a lot of potential for developing artificial muscle applications.     

A Simple Method for Reliable Estimation of the Bubble Energy in the Underwater Explosion

The bubble energy is the main part of the chemical energy of the explosive that is formed upon the propagation of a shock wave through the water for the underwater explosion. A simple method is introduced for reliable prediction of the bubble energy of composite explosives containing aluminum (Al) and/or ammonium perchlorate (AP). It is shown that the bubble energy of composite Al/AP explosives depends on the number of moles of chlorine, carbon, and Al atoms. Experimental data of 56 composite Al/AP explosives are used to construct and test the novel model of the bubble energy. Statistical parameters of the new model, in external validation containing 35 composite Al/AP explosives as the training set, have the values 0.43 and 1.15 MJ · kg^–1 for the root mean squared error (RMSE) and maximum of errors (Max Error) of the new model, respectively. The values of RMSE and Max Error for 21 composite Al/AP explosives as test set are also 0.60 and 2.22 MJ · kg^–1, respectively. Cross validations of the new method corresponding to the coefficients of determination for leave‐one‐out (Q²_LOO) and the fivefold cross validation (Q²_5CV) are 0.8573 and 0.8403, respectively, which confirms goodness‐of‐fit, goodness‐of‐prediction, accuracy and precision of the novel model. It is shown that the novel correlation can be applied for pure and composite explosives, which do not contain Al/AP.     

Finite-Difference Approximation for Fluid-Flow Simulation and Calculation of Permeability in Porous Media

We introduce a finite-difference method to simulate pore scale steady-state creeping fluid flow in porous media. First, a geometrical approximation is invoked to describe the interstitial space of grid-based images of porous media. Subsequently, a generalized Laplace equation is derived and solved to calculate fluid pressure and velocity distributions in the interstitial space domain. We use a previously validated lattice-Boltzmann method (LBM) as ground truth for modeling comparison purposes. Our method requires on average 17 % of the CPU time used by LBM to calculate permeability in the same pore-scale distributions. After grid refinement, calculations of permeability performed from velocity distributions converge with both methods, and our modeling results differ within 6 % from those yielded by LBM. However, without grid refinement, permeability calculations differ within 20 % from those yielded by LBM for the case of high-porosity rocks and by as much as 100 % in low-porosity and highly tortuous porous media. We confirm that grid refinement is essential to secure reliable results when modeling fluid flow in porous media. Without grid refinement, permeability results obtained with our modeling method are closer to converged results than those yielded by LBM in low-porosity and highly tortuous media. However, the accuracy of the presented model decreases in pores with elongated cross sections.     

Crystal structure and molecular stereochemistry of polymeric Cu2(DMP)4(DMSO) as a platform for phosphate diester binding

Treatment of a solution of CuCl₂ in dimethyl phosphate (DMP) in an inert solvent under nitrogen atmosphere resulted in a light blue fluorescence powder. Slow evaporation of H₂O‐DMSO solution of this powder led to the formation of blue‐sky crystals of a new polymeric Cu(II) complex, with a unit cell composed of Cu₂(DMP)₄(DMSO), (1). The crystal and molecular structure of the complex was established crystallographically. Compound (1) crystallizes in the monoclinic space group P2₁/n with a = 12.8920(11)Å, b = 13.1966(11)Å, c = 14.7926(13)Å, α = 90°, β = 98.943(2)°, γ = 90° and Z = 4. A square pyramidal environment for the metal center is established by coordination of oxygen atoms of four bridging DMP ligands in the basal positions and a tri‐centered oxygen atom of DMSO in the apical disposition. The sixth position is also affected by a weak interaction with the sulfur atom of DMSO. The phosphorous atom in the bridging DMP is arranged in a deformed tetrahedron with gg conformation for methyl esters with C_2v symmetry. Accordingly, the angles of methoxy substituents are unexpectedly smaller than the bridging oxygens, and synchronous z‐in and z‐out distortions are suggested for DMP anion. The oxygen atom of SOCuCu’ fragment derived from DMSO, functions as a tri‐centered nuclei lie almost in a trigonal triangle environment. This study helps provide further insights into the binding nature of phosphate esters to the active sites of enzymes, which catalyze phosphoryl transfer reactions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comprehensive Study of Free Radical Copolymerization Using a Monte Carlo Simulation Method, 1

Summary: In order to investigate the influence of reactivity ratios and initial feed composition on the microstructure of macromolecules in free radical copolymerization, a comprehensive study was carried out using a Monte Carlo simulation method. As a result, a new procedure was introduced to modify the works of others on the initiation step. The variation of the copolymer composition and the fashion of the arrangement of monomers in simulated chains were evaluated as a function of copolymerization parameters. The model was capable of monitoring any change in azeotropy as well as the magnitude and direction of composition drift from the azeotrope point. The maximum reachable conversion (MRC) was predicted for different combinations of initial feed compositions and reactivity ratios. According to the simulation results, a critical conversion where the macromolecules produced inherited the maximum allowed alternation was obtained for the reactivity ratios given.

Change of sequence distribution of simulated copolymer chains with conversion for various initial feed compositions on a triangular graph (r_A = 0.5, r_B = 0.9).     

K-theory tools for local and asymptotic cyclic cohomology

A generalization of the Connes-Thom isomorphism is given for stable, homotopy invariant, and split exact functors on separable -algebras. As examples of these functors, we concentrate on asymptotic and local cyclic cohomology, and the result is applied to improve some formulas in asymptotic and local cyclic cohomology of -algebras. As another application, it is shown that these cyclic theories are rigid under Rieffel's deformation quantizations.