Multiple periodic solutions for a nonlinear suspension bridge equation

We investigate nonlinear oscillations in a fourth-order partialdifferential equation which models a suspension bridge. Previouswork establishes multiple periodic solutions when a parameterexceeds a certain eigenvalue. In this paper, we use Leray-Schauderdegree theory to prove that if the parameter is increased further,beyond a second eigenvalue, then additional solutions are created.     

BPA-PC on a Ni111 surface: the interplay between adsorption energy and conformational entropy for different chain-end modifications

We extend a previous dual scale modeling approach for the behavior of polymers near a metal surface to a variety of end groups. Our approach combines a coarse-grained polymer model with ab initio DFT calculations. Such a procedure was applied to a melt of phenolic-like terminated Bisphenol A-polycarbonate (BPA-PC) interacting with a (111) nickel surface (Delle Site, L.; Abrams, C. F.; Alavi, A.; Kremer, K. Phys. Rev. Lett. 2002, 89, 156103. Abrams, C. F.; Delle Site, L.; Kremer, K. Phys. Rev. E 2003, 67, 021807). This work extends this study to different chain-end modifications of BPA-PC, p-tert-butylphenolic, p-tetramethylpropylphenolic, and p-cumylphenolic. We show how the interplay between adsorption energies and conformational entropy selects different morphologies for the various melts at the interface. Implications of these results for realistic technical materials are finally discussed.     

Momentum distribution of the homogeneous electron gas

We calculate the off-diagonal density matrix of the homogeneous electron gas at zero temperature using unbiased reptation Monte Carlo calculations for various densities and extrapolate the momentum distribution and the kinetic and potential energies to the thermodynamic limit. Our results on the renormalization factor allow us to validate approximate G0W0 calculations concerning quasiparticle properties over a broad density region (1≤r(s)?10) and show that, near the Fermi surface, vertex corrections and self-consistency aspects almost cancel each other out.     

Effect of anions on static orientational correlations, hydrogen bonds, and dynamics in ionic liquids: a simulational study

Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and PAdua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM+ is studied in the presence of three different anions, namely, chloride Cl-, tetrafluoroborate BF(4)(-), and bis((trifluoromethyl)sulfonyly)imide TF2N-. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF4] to [EMIM][TF2N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF2N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM][BF4] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.     

Multiscale modelling of mesoscopic phenomena triggered by quantum events: light-driven azo-materials and beyond

The macroscopic functionality of soft (bio-)materials is often triggered by quantum-mechanical events which are highly local in space and time. In order to arrive at the resulting macroscopically observable phenomena, many orders of magnitude need to be bridged on both the time and the length scale. In the present paper, we first introduce a range of simulation methods at different scales as well as theoretical approaches to form bridges between them. We then outline a strategy to develop an adaptive multiscale simulation approach which connects the quantum to the mesoscopic level by bringing together ab initio molecular dynamics (QM), classical (force field) molecular dynamics (MM), and coarse grained (CG) simulation techniques. With a multitude of photoactive materials in mind, we apply our methodology to a prototypical test case-light-induced phase transitions in a liquid crystal containing the azobenzene photoswitch.     

Simulation of Polymer Melts: From Spherical to Ellipsoidal Beads

In a previous work^[1] we presented a coarse‐graining procedure for bonded interactions, while spherical, purely repulsive 6–12 interactions were used to account for the excluded‐volume of the beads of the phantom chains. Here we extend this approach towards ellipsoidal beads whose shapes are extracted from the geometry of the underlying atomistic chains. The influence of the bead shapes on the static and dynamical properties of melts are studied in detail for two modifications of polycarbonates, from 2mers up to 20mers. The results obtained in both cases are discussed in the context of corresponding experiments and atomistic simulations.     

Redox-extraction chromatography. interaction between 2,5-di-tert-pentylhydroquinone and tri-n-octylphosphine oxide in cyclohexane solution,and further analytical applications

Redox-extraction chromatography with 2,5-di-tert-pentylhydroquinone (DPHQ) and tri-n-octylphosphine oxide (TOPO) has been extended to a wider range of hydrochloric acid concentrations for the retention of Th, U, Np and Pu.This system behaves antagonistically with respect to tetra and hexavalent ions at some acidities. When DPHQ is oxidized to the quinone form this effect disappears; the DPQ-TOPO system shows simple redox-extraction features. These results have been used to obtain separations of Pu-Np-U on DPHQ-TOPO and DPQ-TOPO columns.     

Flow boundary conditions for chain-end adsorbing polymer blends

Using the phenol-terminated polycarbonate blend as an example, we demonstrate that the hydrodynamic boundary conditions for a flow of an adsorbing polymer melt are extremely sensitive to the structure of the epitaxial layer. Under shear, the adsorbed parts (chain ends) of the polymer melt move along the equipotential lines of the surface potential whereas the adsorbed additives serve as the surface defects. In response to the increase of the number of the adsorbed additives the surface layer becomes thinner and solidifies. This results in a gradual transition from the slip to the no-slip boundary condition for the melt flow, with a nonmonotonic dependence of the slip length on the surface concentration of the adsorbed ends.     

Radiochemical determination of plutonium in marine samples by extraction chromatography

Very low levels of plutonium (^239,240Pu and ²³⁸Pu) in marine samples (sea water,sediments, marine organisms) are determined by extraction on columns of tri-n-octyl phosphine oxide supported on microporous polyethylene (Micro thene-710), electrode- position, and α-spectrometry. ²³⁶Pu or ²⁴²Pu is added as the yield detector and a high-resolution α-spectrometer is used for counting. The final recoveries are 62.6% ± 9.7(σ)for sea water, 45.4% ± 9.6(0) for sediments and 81.7%± 4.5(σ) for marine organisms. Themethod enables ^239.240pu and ²³⁸Pu to be detected at the femtocurie level.     

Competing adsorption between hydrated peptides and water onto metal surfaces: from electronic to conformational properties

Inorganic-(bio)organic interfaces are of central importance in many fields of current research. Theoretical and computational tools face the difficult problem of the different time and length scales that are involved and linked in a nontrivial way. In this work, a recently proposed hierarchical quantum-classical scale-bridging approach is further developed to study large flexible molecules. The approach is then applied to study the adsorption of oligopeptides on a hydrophilic Pt(111) surface under complete wetting conditions. We examine histidine sequences, which are well known for their binding affinity to metal surfaces. Based on a comparison with phenylalanine, which binds as strong as histidine under high vacuum conditions but, as we show, has no surface affinity under wet conditions, we illustrate the mediating effects of near-surface water molecules. These contribute significantly to the mechanism and strength of peptide binding. In addition to providing physical-chemical insights in the mechanism of surface binding, our computational approach provides future opportunities for surface-specific sequence design.