Reaction between triphenylphosphine and aromatic amines in the presence of diethyl azodicarboxylate: an efficient synthesis of aryliminophosphoranes under neutral and mild conditions

An efficient synthesis of aryliminophosphoranes is described. A mixture of an aromatic amine, diethyl azodicarboxylate and triphenylphosphine undergo a Mitsonobu type reaction at ambient temperature in dry dichloromethane to afford aryliminophosphoranes in excellent yields.     

Integrated photonic crystal spectrometers for sensing applications

A combination of negative refraction and diffraction compensation in a superprism-based photonic crystal structure is used to demonstrate a compact on-chip photonic crystal spectrometer. This structure provides strong dispersion and signal isolation, which are essential for forming an efficient and compact spectrometer. Performance of these spectrometers as spectral pattern detectors is discussed. The experimental results show that a PC structure with 80 μm × 220 μm dimension can locate a single spectral feature with better than 10 pm accuracy over a bandwidth of 50 nm around 1550 nm center wavelength at an output signal-to-noise ratio of 13 dB.     

FDTD Simulation of Electromagnetic Pulse Interaction with a Switched Plasma Slab

This paper deals with the Finite Difference Time Domain (FDTD) simulation of interaction of an electromagnetic wave with a switched plasma slab. In formulating the simulation the well-known concepts of (a) total-field/scattered-field formulation (b) and PML lattice truncation are adapted to suit the simulation under consideration.FDTD is particularly well suited to handle the switched (time-varying) medium (including sudden switching) since the time varying parameters of the medium can be easily interpreted in the algorithm. The technique is applied to the difficult problem of interaction of an electromagnetic pulse source wave of frequency ₀ and a gaussian envelope with a newly created plasma slab of time-varying and space varying electron density profile. The creation of a pulse of Wiggler magnetic field in the slab is illustrated.     

Conceptual linearization of Euler governing equations to solve high speed compressible flow using a pressure‐based method

The main objective of the current work is to introduce a new conceptual linearization strategy to improve the performance of a primitive shock‐capturing pressure‐based finite‐volume method. To avoid a spurious oscillatory solution in the chosen collocated grids, both the primitive and extended methods utilize two convecting and convected momentum expressions at each cell face. The expressions are obtained via a physical‐based discretization of two inclusive statements, which are constructed via a novel incorporation of the continuity and momentum governing equations. These two expressions in turn provide a strong coupling among the Euler conservative statements. Contrary to the primitive work, the linearization in the current work respects the definitions and essence of physics behind deriving the Euler governing equations. The accuracy and efficiency of the new formulation are then investigated by solving the shock tube as a problem with moving normal and expansion waves and the converging‐diverging nozzle as a problem with strong stationary normal shock. The results show that there is good improvement in performance of the primitive pressure‐based shock‐capturing method while its superior accuracy is not deteriorated at all. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008     

On hydraulic permeability of random packs of monodisperse spheres: Direct flow simulations versus correlations

Hydraulic permeability is studied in porous media consisting of randomly distributed monodisperse spheres by means of computational fluid dynamics (CFD) simulations. The packing of spheres is generated by inserting a certain number of nonoverlapping spherical particles inside a cubic box at both low and high packing fractions using proper algorithms. Fluid flow simulations are performed within the interparticulate porous space by solving Navier-Stokes equations in a low-Reynolds laminar flow regime. The hydraulic permeability is calculated from the Darcy equation once the mean values of velocity and pressure gradient are calculated across the particle packing. The simulation results for the pressure drop across the packing are verified by the Ergun equation for the lower range of porosities (<0.75), and the Stokes equation for higher porosities (∼1). Using the results of simulations, the effects of porosity and particle diameters on the hydraulic permeability are investigated. Simulations precisely specified the range of applicability of empirical or semi-empirical correlations for hydraulic permeability, namely the Carman-Kozeny, Rumpf-Gupte, and Howells-Hinch formulas. The number of spheres in the model is gradually decreased from 2000 to 20 to discover the finite-size effect of pores on the hydraulic permeability of spherical packing, which has not been clearly addressed in the literature. In addition, the scale dependence of hydraulic permeability is studied via simulations of the packing of spheres shrunk to lower scales. The results of this work not only reveal the validity range of the aforementioned correlations, but also show the finite-size effect of pores and the scale-independence of direct CFD simulations for hydraulic permeability.     

Design and synthesis of a new series of amphiphilic peptide-β-cyclodextrins as phase transfer carriers for glucosamine

A new series of amphiphilic β-cyclodextrins were designed and synthesized by grafting peptide chains on to all primary hydroxyl groups via ester bond formation. The desired amphiphilic structures have been produced from ester connection between the C-6 of β-cyclodextrin and the carboxyl group of N-acetylated resides: H₂N-Leu-COOH, H₂N-Leu-Gly-COOH, H₂N-Leu-Gly-Leu-COOH, and H₂N-Leu-Gly-Leu-Gly-COOH (3a-d). The synthetic pathway involves selective bromination of all primary hydroxyls of β-cyclodextrins and then substitution with the carboxylate moiety of the mentioned N-acetyl residues in the presence of DBU (1,8-diazabicyclo[5,4,0]undec-7-ene). The ability of the synthetic compounds for extraction and phase transfer of glucosamine, as a hydrophilic organic compound, was then studied. The results showed a considerable ability of these amphiphilic compounds for extraction and a selective tendency of 3c for phase transfer of glucosamine.     

Poly[dimethyldiphenylphosphonium [di‐μ4‐iodido‐tetra‐μ3‐iodido‐pentacopper(I)]]

The title compound, {(C₁₄H₁₆P)[Cu₅I₆]}_n, prepared from the reaction between copper powder, iodine and dimethyldiphenylphosphonium iodide in hydroxyacetone, features an anion that consists of a continuous two‐dimensional Cu–I sheet [Cu—I = 2.5960 (14)–2.6994 (13) Å and Cu—I—Cu = 63.28 (5)–114.25 (5)°]. The cation, which lies on a mirror plane, is a typical dimethyldiphenylphosphonium ion. The structure shows a strong tendency towards segregation of the inorganic and organic parts of the structure into separate subspaces. The two‐dimensional Cu–I sheet displays a pronounced subcell with pseudo‐tetragonal symmetry that is broken by ordered vacancies on the Cu position. The symmetry is further reduced by the orientation of the interleaved organic counter‐ion that is inclined with respect to the pseudo‐mirror planes defined by the Cu–I sheet normal, perpendicular to the b axis.     

Generalized framework for robust design of tuned mass damper systems

The primary purpose of this contribution is to develop a novel framework for generalized robust design of tuned mass damper (TMD) systems as passive vibration controllers for uncertain structures. This versatile strategy is intended to be free of any restriction on the structure-TMD system configuration, the performance criterion, and the number of uncertain parameters. The main idea pursued is to adopt methods and concepts from the robust control literature, including: (1) the linear fractional transformation (LFT) formulation pertaining to the structured singular value (μ) framework; (2) the concept of weighted multi-input multi-output (MIMO) norms for characterizing performance; and (3) a worst-case performance assessment method to avoid the unacceptable computation burden involved with exhaustive search or Monte Carlo methods in the presence of multiple uncertainties. Based on these, the robust design framework is organized into four steps: (1) modeling and casting the overall dynamics into the proposed LFT framework that isolates the TMD system as the controller, and the uncertainties as a structured perturbation to the nominal dynamics; (2) setting up the optimization problem based on generalized indices of nominal performance, robustness, and worst-case performance; (3) implementing a genetic algorithm (GA) for solution of the optimization problem; and (4) post-processing the results for systematic visualization, validation, and selection of preferred designs. This strategy has been implemented on several illustrative design examples involving a seismically excited multi-story building with different combinations of assumptions on the uncertainty, TMD configuration, excitation scenarios, and performance criteria. The resulting solution sets have been studied through various post-processing methods, including visualization of Pareto fronts, uncertain frequency response plots, time-domain simulations, and random vibration analysis.     

The comparative study in transport properties of furan, thiophene and selenophene dithiols in nano electronic

The electron transport properties of furan, thiophene and selenophene dithiols based molecular wires through two electrodic systems using non-equilibrium Green’s functions technique (NEGF) are investigated. The electron transport of the above systems is systematically studied by analysis of transmission function, density of states, current–voltage characteristics, and conductance of the systems. The maximum current is occurred at the vicinity of 2.0 V and the values are 90.37, 98.82 and 100.31 μA for furan, thiophene and selenophene dithiols, respectively. These results can be attributed to the molecular projected self consistent Hamiltonian (MPSH) of two electrodic systems with different molecules at different bias voltage and also to quality of resonance of π electrons of heterocyclic ring. We can foresee that the furan, thiophene, and selenophene dithiols can be applied at electronic devices because of switching the high and low current.     

Ammonia adsorption on the C30B15N15 heterofullerene: DFT study of nuclear magnetic shielding and electric field gradient tensors of N and B nuclei

Ammonia adsorption on the external surface of C₃₀B₁₅N₁₅ heterofullerene was studied using density functional calculations. Three models of the ammonia-attached C₃₀B₁₅N₁₅ together with the perfect model were optimized at the B3LYP/6-31G^? level. The optimization process reveals that dramatic influences occurred for the geometrical structure of C₃₀B₁₅N₁₅ after ammonia adsorption; the B atom relaxes outwardly and consequently the heterofullerene distorts from the spherical form in the adsorption sites. The chemical shielding (CS) tensors and nuclear quadrupole coupling constants of B and N nuclei were calculated at the B3LYP/6-311G^** level. Our calculations reveal that the B atom is chemically bonded to NH₃ molecule. The B atom in the NH₃-attached form has the largest chemical shielding isotropic (CSI) value among the other boron nuclei. The C_Q parameters of B nuclei at the interaction sites are significantly decreased after ammonia adsorption.