Brownian dynamics simulations of needle chain and nugget chain polymer models--rigid constraint conditions versus infinitely stiff springs

It is well known that orientational correlations appear in polymer chain models when the subunits are linked by ball-socket joints implemented as rigid constraint conditions. These correlations do not appear when the subunits are connected by springlike potential forces, even in the limit of infinitely stiff springs. In a widely used class of algorithms for Brownian dynamics simulations, inertia effects are ignored. However, in the recently introduced needle chain and nugget chain algorithms, the rigid constraint correlations depend on the mass and moment of inertia. This inconsistency does not appear in the bead-rod (Kramers) polymer chain model, which also has orientational correlations introduced by rigid constraint conditions. Explicit expressions for the correlation functions are given for thermodynamic equilibrium states. Analytical expressions for the associated forces ("metric forces") and simulation results showing how the rigid constraint correlations influence dynamical properties, are also presented. Further we discuss the physical relevance of these correlations and show via simulations that their influence on stationary and dynamical properties depend significantly on chain length. We further show that if the metric forces are removed, algorithms designed with rigid constraint conditions describe a chain of segments connected by infinitely stiff springs. Finally we show that the results presented here for needle chains are relevant also for the bead-rod (Kramers) chain model, making it possible to simulate a bead-spring chain with infinitely stiff springs.     

Magnetic and spectroscopic properties of copper(II) complexes with 1-salicoyl-4-phenylthiosemicarbazide

Summary Cu^II complexes of 1-salicoyl-4-phenylthiosemicarbazide (SPT) have been synthesized and characterized by means of elemental analysis, magnetic measurements, and i.r. and e.p.r. spectroscopic methods; ¹H- and ¹³C-n.m.r. and mass spectral data on the thiosemicarbazide are also reported. A paramagnetic complex _eff= 1.298 B.M., is formed with copper(II) sulphate; the low magnetic moment and the e.p.r. spectral data suggest a binuclear species. A diamagnetic complex due to a strong Cu-Cu interaction has been isolated with copper(II) chloride.     

Freezing point and heating curve behavior for an organic reciprocal salt pair system

Binary and quasi-binary freezing point data have been obtained to establish the freezing point diagram for the ternary reciprocal salt pair system involving cyclohexylamine stearate, cyclohexylamine palmitate, 2,2'-dipyridylamine stearate, and 2,2'-dipyridylamine palmitate. The compositions and primary freezing points of the ternary peritectic and eutectic mixtures have been determined Apparent anomalies in the heating curves for selected compositions have been explained on the basis of the existence of metastable equilibria.     

Preparation and polymerization of some vinyl ester amides of pinic acid

The preparation of vinyl 2,2-dimethyl-3-morpholinocarbonylcyclobutaneacetate, vinyl 2,2-dimethyl-3-piperidinocarbonylcyclobutaneacetate, and vinyl 2,2-dimethyl-3-di-n-butylaminocarbonylcyclobutaneacetate has been achieved by selective amination followed by vinyl interchange. Homopolymers and vinyl chloride copolymers containing 25 and 30 wt.-% of the vinyl esteramides were prepared and evaluated as nonrigid plastics. The vinyl esteramides incorporated in vinyl chloride copolymers did impart some plasticization, but their effect was far below the effect of added plasticizer to a vinyl chloride polymer.     

Copolymers of vinyl chloride with the vinyl esters and acrylates of low molecular weight polyesters of hydroxyacids

Vinyl esters and acrylates of polyesters derived from C₁₀?C₁₈ hydroxyacids have been synthesized and copolymerized with vinyl chloride with the hope of achieving an internally plasticized poly(vinyl chloride). Copolymers containing 10–30% polyester are film-forming materials, and the films cast from THF solutions are generally flexible. A number of these vinyl chloride copolymers with polyesters at approximately 15 and 25% level have been tested for various properties. The internal plasticization is not extensive.     

Synthesis of the second generation photoaffinity probes of tautomycin

Five photoaffinity probes of tautomycin, which possess an aromatic azide with linker attached to the 2-position of tautomycin, were prepared in order to study the binding site of tautomycin with protein phosphatase 1γ. The photoaffinity probes were synthesized by selectively introducing the photolabeling units onto the 2-position of tautomycin by using oxime chemistry.     

Determination of Hamaker constants for asphaltenes in a mixture of pentane and benzene

Asphaltene deposition during oil production may lead to expensive and frequent clean-up operations. Knowledge of the interaction between asphaltene particles and deposition is vital in order to predict the magnitude of this problem.Surface energies for asphaltenes precipitated at field conditions are determined from measurements of contact angles of several probe liquids. Using the surface tension component model, the energies are found to be dispersive. Hamaker constants of a simple mixture of pentane and benzene are estimated from the application of Lifshitz theory.The effective Hamaker constants of asphaltenes in a pentane/benzene mixture are calculated. It is shown that increasing amounts of benzene lowers the attractive interaction between asphaltenes. This result is consistent with the definition that asphaltenes are soluble in benzene.     

Determination of copper and lead in schist by anodic stripping voltammetry

Samples were decomposed in HClO₄/HF mixture in a Teflon beaker to avoid electrochemical interference from platinum ions. The residue remaining after evaporation to dryness was taken up in nitric acid and examined by anodic stripping voltammetry. Both the hanging mercury drop electrode and the rotating glassy carbon electrode, mercury-plated in situ, were used with success. Copper at 120 ppm and lead at 40 ppm were determined with a relative standard deviation of 6%. The schist was the Nordic reference sample ASK-2.     

Synergy of electron-cyclotron and lower-hybrid current drive in steady-state plasmas

Improvement (up to a factor of approximately 4) of the electron-cyclotron (EC) current drive efficiency in plasmas sustained by lower-hybrid (LH) current drive has been demonstrated in stationary conditions on the Tore Supra tokamak. This was made possible by feedback controlled discharges at zero loop voltage, constant plasma current, and constant density. This effect, predicted by kinetic theory, results from a favorable interplay of the velocity space diffusions induced by the two waves: the EC wave pulling low-energy electrons out of the Maxwellian bulk, and the LH wave driving them to high parallel velocities.     

A hybrid nonoverlapping domain decomposition scheme for advection dominated advection–diffusion problems

Two nonoverlapping domain decomposition algorithms are proposed for convection dominated convection–diffusion problems. In each subdomain, artificial boundary conditions are used on the inflow and outflow boundaries. If the flow is simple, each subdomain problem only needs to be solved once. If there are closed streamlines, an iterative algorithm is needed and the convergence is proved. Analysis and numerical tests reveal that the methods are advantageous when the diffusion parameter ɛ is small. In such cases, the error introduced by the domain decomposition methods is negligible in comparison with the error in the singular layers, and it allows easy and efficient grid refinement in the singular layers. This revised version was published online in August 2006 with corrections to the Cover Date.