Cardiovascular fluid-structure interaction: A partitioned approach utilizing the p-FEM

In this paper, we propose a technique for simulating the fluid-structure interaction in blood vessels. A partitioned approach is used, which allows for an independent discretization of the fluid domain and the structural domain. We choose the finite volume method to solve the Navier-Stokes equations and the p-version of the finite element method (p-FEM) to solve the equations of geometrically nonlinear structural dynamics. The solution strategy can be seen as a first approach towards a comprehensive study of the hemodynamics in vascular substitutes with the goal of improving their long term functionality. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

New Poincaré-type inequalities

We present some Poincaré-type inequalities for quadratic matrix fields with applications e.g. in gradient plasticity or fluid dynamics. In particular, applications to the pseudostress–velocity formulation of the stationary Stokes problem and to infinitesimal gradient plasticity are discussed.     

Usage of systematic multi-body equations of motion for the design of a nonlinear vehicle dynamics controller

In this article the authors outline how systematic multi-body equations can efficiently be used to derive a model for the design of a nonlinear vehicle dynamics controller for truck-semitrailer combinations, steering the last trailer axle. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasmon‐enhanced Raman scattering by suspended carbon nanotubes

We report plasmon‐enhanced Raman scattering of the order of 10³ by a metallic carbon nanotube partially suspended inside a near‐field cavity. The tube is part of a small bundle, and is interfaced with an Au nanodisc dimer using a recently developed assembly scheme based on dielectrophoretic deposition. Spatially resolved Raman measurements with two excitation wavelengths and two orthogonal polarizations confirm that the enhancement arises from a 65 nm long suspended tube segment. We show that the orientation of the tube inside the cavity can be as effective for generating enhancement as placing the nanotube precisely in a plasmonic hotspot. Position and shape of the G‐peak show that the suspended part of the tube is free of strain and doped with a Fermi energy shift ≤40 meV. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Optimal single machine scheduling of products with components and changeover cost

We consider the problem of scheduling products with components on a single machine, where changeovers incur fixed costs. The objective is to minimize the weighted sum of total flow time and changeover cost. We provide properties of optimal solutions and develop an explicit characterization of optimal sequences, while showing that this characterization has recurrent properties. Our structural results have interesting implications for practitioners, primarily that the structure of optimal sequences is robust to changes in demand.     

A feasible theory of truth over combinatory algebra

We define an applicative theory of truth _TPT${\mathsf{T}}_{\mathsf{PT}}$ which proves totality exactly for the polynomial time computable functions. _TPT${\mathsf{T}}_{\mathsf{PT}}$ has natural and simple axioms since nearly all its truth axioms are standard for truth theories over an applicative framework. The only exception is the axiom dealing with the word predicate. The truth predicate can only reflect elementhood in the words for terms that have smaller length than a given word. This makes it possible to achieve the very low proof-theoretic strength. Truth induction can be allowed without any constraints. For these reasons the system _TPT${\mathsf{T}}_{\mathsf{PT}}$ has the high expressive power one expects from truth theories. It allows embeddings of feasible systems of explicit mathematics and bounded arithmetic.     

Design and verify: a new scheme for generating cutting-planes

A cutting-plane procedure for integer programming (IP) problems usually involves invoking a black-box procedure (such as the Gomory–Chvátal procedure) to compute a cutting-plane. In this paper, we describe an alternative paradigm of using the same cutting-plane black-box. This involves two steps. In the first step, we design an inequality $cx \le d$ where $c$ and $d$ are integral, independent of the cutting-plane black-box. In the second step, we verify that the designed inequality is a valid inequality by verifying that the set $P \cap \{x\in \mathbb R ^n \mid cx \ge d + 1\} \cap \mathbb Z ^n$ is empty using cutting-planes from the black-box. Here $P$ is the feasible region of the linear-programming relaxation of the IP. We refer to the closure of all cutting-planes that can be verified to be valid using a specific cutting-plane black-box as the verification closure of the considered cutting-plane black-box. This paper undertakes a systematic study of properties of verification closures of various cutting-plane black-box procedures.     

Monte Carlo simulation of osmotic equilibria

We present a Metropolis Monte Carlo simulation algorithm for the Tpπ-ensemble, where T is the temperature, p is the overall external pressure, and π is the osmotic pressure across the membrane. The algorithm, which can be applied to small molecules or sorption of small molecules in polymer networks, is tested for the case of Lennard-Jones interactions.     

Tuning the electronic coupling in a low-bandgap donor-acceptor copolymer via the placement of side-chains

We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor-acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine-alt-5,5'-4',7',-di-2-thienyl-2',1',3'-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor-acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization.     

Ion‐Pairing of Phosphonium Salts in Solution: C?H⋅⋅⋅Halogen and C?H⋅⋅⋅π Hydrogen Bonds

The ¹H NMR chemical shifts of the C(α)? H protons of arylmethyl triphenylphosphonium ions in CD₂Cl₂ solution strongly depend on the counteranions X^?. The values for the benzhydryl derivatives Ph₂CH? PPh₃⁺ X^?, for example, range from δ_H=8.25 (X^?=Cl^?) over 6.23 (X^?=BF₄^?) to 5.72 ppm (X^?=BPh₄^?). Similar, albeit weaker, counterion‐induced shifts are observed for the ortho‐protons of all aryl groups. Concentration‐dependent NMR studies show that the large shifts result from the deshielding of the protons by the anions, which decreases in the order Cl^? > Br^? ? BF₄^? > SbF₆^?. For the less bulky derivatives PhCH₂? PPh₃⁺ X^?, we also find C? H???Ph interactions between C(α)? H and a phenyl group of the BPh₄^? anion, which result in upfield NMR chemical shifts of the C(α)? H protons. These interactions could also be observed in crystals of (p‐CF₃‐C₆H₄)CH₂? PPh₃⁺ BPh₄^?. However, the dominant effects causing the counterion‐induced shifts in the NMR spectra are the C? H???X^? hydrogen bonds between the phosphonium ion and anions, in particular Cl^? or Br^?. This observation contradicts earlier interpretations which assigned these shifts predominantly to the ring current of the BPh₄^? anions. The concentration dependence of the ¹H NMR chemical shifts allowed us to determine the dissociation constants of the phosphonium salts in CD₂Cl₂ solution. The cation–anion interactions increase with the acidity of the C(α)? H protons and the basicity of the anion. The existence of C? H???X^? hydrogen bonds between the cations and anions is confirmed by quantum chemical calculations of the ion pair structures, as well as by X‐ray analyses of the crystals. The IR spectra of the Cl^? and Br^? salts in CD₂Cl₂ solution show strong red‐shifts of the C? H stretch bands. The C? H stretch bands of the tetrafluoroborate salt PhCH₂? PPh₃⁺ BF₄^? in CD₂Cl₂, however, show a blue‐shift compared to the corresponding BPh₄^? salt.