Influence of Water Uptake on Dynamic Fracture Behavior of Poly(Methyl Methacrylate)

A study was completed to assess the effects of various humidity levels and amount of sorbed water on the fracture behavior of notched poly(methyl methacrylate) (PMMA) samples subjected to stress pulses generated by the impact of a projectile launched from an air gun. Impact experiments were performed on six sets of samples conditioned in different environments: dry samples; samples exposed to three different relative humidity environments (11 %, 60 %, and 98 %) using saturated salt solutions (Lithium Chloride, Sodium Bromide, and Potassium Sulfate, respectively); and distilled water- and seawater-exposed samples. Experiments varied by immersion time and water content, while loading conditions were kept constant. The main goal of this study was to understand the effects of sorbed water on the fracture behavior of PMMA when subjected to high strain rate impacts. It was observed that when PMMA is subjected to strain rates of 10² s ^?1, the effect of water content is not a dominant mechanism on the crack initiation and crack-tip speed of PMMA.     

Parameter investigation with line-implicit lower–upper symmetric Gauss–Seidel on 3D stretched grids

An implicit lower–upper symmetric Gauss–Seidel (LU-SGS) solver has been implemented as a multigrid smoother combined with a line-implicit method as an acceleration technique for Reynolds-averaged Navier–Stokes (RANS) simulation on stretched meshes. The computational fluid dynamics code concerned is Edge, an edge-based finite volume Navier–Stokes flow solver for structured and unstructured grids. The paper focuses on the investigation of the parameters related to our novel line-implicit LU-SGS solver for convergence acceleration on 3D RANS meshes. The LU-SGS parameters are defined as the Courant–Friedrichs–Lewy number, the left-hand side dissipation, and the convergence of iterative solution of the linear problem arising from the linearisation of the implicit scheme. The influence of these parameters on the overall convergence is presented and default values are defined for maximum convergence acceleration. The optimised settings are applied to 3D RANS computations for comparison with explicit and line-implicit Runge–Kutta smoothing. For most of the cases, a computing time acceleration of the order of 2 is found depending on the mesh type, namely the boundary layer and the magnitude of residual reduction.     

Cationic polyfluorene: Conformation and aggregation in a “good” solvent

The conjugated polyelectrolyte (CPE) poly{9,9′-bis[6″-(N,N,N-trimethylammonium)-hexylfluorene-alt-co-phenylene] dibromide} (PFPN⁺Br⁻) demonstrates a high solubility in methanol in comparison to other more hydrophilic or hydrophobic solvents. We have employed a combination of pulsed-field-gradient-NMR, photoluminescence (PL), and Raman spectroscopy to establish the conformation and aggregation behavior of PFPN⁺Br⁻ in methanol, with the aim to attain information on how to design CPEs with a high solubility in a preferred solvent. We find that the diffusion coefficient and PL spectrum of PFPN⁺Br⁻, as well as the Raman-active methyl rocking mode of methanol, all exhibit a strong dependence on PFPN⁺Br⁻ concentration. We rationalize our findings with a model in which PFPN⁺Br⁻ forms aggregates via π–π interactions between main-chain segments, while the ionic side chains are surrounded and electrostatically screened by the methanol solvent. Accordingly, the notably high solubility of PFPN⁺Br⁻ in methanol is rationalized by favorable interactions between the ionic side chains and the methanol molecules. We propose that an appropriate design of a high-solubility CPE should consider a matching of the mixed hydrophobic/hydrophilic character of the ionic side chain with that of the preferred solvent.     

Starch-lipid interactions studied by differential scanning calorimetry

The amylose-lipid complex shows an endothermic transition around 100 °C in excess water. Complexes were prepared by adding lipids to an amylose-solution, and the precipitated complex was studied in the DSC during a heating and cooling sequence. The thermal stability of the complex depends on the lipid part, and the reversibility during cooling depends on presence of excess lipids.The influence of lipids on the gelatinization of starch was studied by adding lipids to wheat and potato starch, respectively, before the DSC-analysis. Depending on the lipid, an earlier as well as a delayed gelatinisation could be obtained.     

Connecting shock velocities to electron-injection mechanisms

Electrons can be accelerated by their interaction with nonlinearly saturated electrostatic waves up to speeds with which they can undergo diffusive acceleration across supernova remnant shocks. Here, we model this wave-electron interaction by particle-in-cell and Vlasov simulations. We find that the lifetime of the saturated wave is considerably longer in the Vlasov simulation, due to differences in how these simulation methods approximate the plasma. Electron surfing acceleration which requires a stable saturated wave may thus be more important for electron acceleration at shocks than previously thought. For beam speeds above a critical value, which we estimate here, both simulation codes exclude surfing acceleration due to a rapid wave collapse.     

Accuracy of heterodyne holographic strain and stress determination

The basic equations for the evaluation of surface displacement, strain and stress from holographic interferograms are derived. The object shape and the geometry of the optical setup are taken in to account. A corresponding computer program is described. Heterodyne holographic interferometry is used for fringe interpolation (better than 1/1000 of a fringe) to get sufficient accuracy and spatial resolution. Errors and accuracy of holographic strain and stress determination are discussed with the aid of the computer program. A cylindrical tube under pressure load is presented as a numerical example.     

Controlling the form of strong converging shocks by means of disturbances

The influence of artificial disturbances on the behavior of strong converging cylindrical shocks is investigated experimentally and numerically. Ring-shaped shocks, generated in an annular cross sectional shock tube are transformed to converging cylindrical shocks in a thin cylindrical test section, mounted at the rear end of the shock tube. The converging cylindrical shocks are perturbed by small cylinders placed at different locations and in various patterns in the test section. Their influence on the shock convergence and reflection process is investigated. It is found that disturbances arranged in a symmetrical pattern will produce a symmetrical deformation of the converging shockfront. For example, a square formation produces a square-like shock and an octagon formation a shock with an octagonal front. This introduces an alternative way of tailoring the form of a converging shock, instead of using a specific form of a reflector boundary. The influence of disturbances arranged in non-symmetric patterns on the shape of the shockfront is also investigated.      

Nonlinear interactions between electromagnetic waves and electron plasma oscillations in quantum plasmas

We consider nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in a dense quantum plasma, taking into account the electron density response in the presence of the relativistic ponderomotive force and mass increase in the CPEM wave fields. The dynamics of the CPEM waves and EPOs is governed by the two coupled nonlinear Schr?dinger equations and Poisson's equation. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave pipes in the electron density hole that is associated with a positive potential distribution in our dense plasma. The relevance of our investigation to the next generation intense laser-solid density plasma interaction experiments is discussed.