Phase behaviour and dynamics in primitive models of molecular ionic liquids

The phase behaviour and dynamics of molecular ionic liquids are studied using primitive models and extensive computer simulations. The models account for size disparity between cation and anion, charge location on the cation, and cation-shape anisotropy, which are all prominent features of important materials such as room-temperature ionic liquids. The vapour-liquid phase diagrams are determined using high-precision Monte Carlo simulations, setting the scene for in-depth studies of ion dynamics in the liquid state. Molecular dynamics simulations are used to explore the structure, single-particle translational and rotational autocorrelation functions, cation orientational autocorrelations, self diffusion, viscosity, and frequency-dependent conductivity. The results reveal some of the molecular-scale mechanisms for charge transport, involving molecular translation, rotation, and association.Comment: 15 pages, 7 figure

Charge ordering induces a smectic phase in oblate ionic liquid crystals

We report a computer simulation study of an electroneutral mixture of oppositely charged oblate ellipsoids of revolution with aspect ratio A = 1/3. In contrast to hard or soft repulsive ellipsoids, which are purely nematic, this system exhibits a smectic-A phase in which charges of equal sign are counterintuitively packed in layers perpendicular to the nematic director

A convergence analysis of the affine particle-in-cell method and its application in the simulation of extrusion processes

Simulation of extrusion processes represents a large challenge for commonly used numerical methods. In our application for example, a hot melt is extruded whilst being rapidly cooled. Under these conditions of quenching, spinodal phase separation occurs which causes the formation of a characteristic micro-structure of the extrudate, consisting of solid and liquid phases. We model this process using a variant of the Material Point Method (MPM) [4], namely the Affine Particle-In-Cell (APIC) method [13]. Its hybrid particle/grid character is advantageous for simulating both fluid and solid behavior: pure Eulerian particle methods, such as classic SPH, fail for simulating solids, particularly in tension, whereas pure Lagrangian methods generally cannot cope with large deformations caused by material flow. APIC improves upon the original MPM method by using a so-called locally affine velocity representation [13] which allows the conservation of linear and angular momentum without the need of potentially unstable Fluid-Implicit-Particle (FLIP) techniques [3]. We analyze the convergence behavior of APIC and compare its accuracy against a traditional MPM variant, the Generalized Interpolation Material Point Method (GIMP)

Strain measurement by contour analysis

Background: The determination of yield stress curves for ductile metals from uniaxial material tests is complicated by the presence of tri-axial stress states due to necking. A need exists for a straightforward solution to this problem. Objective: This work presents a simple solution for this problem specific to axis-symmetric specimens. Equivalent uniaxial true strain and true stress, corrected for triaxiality effects, are calculated without resorting to inverse analysis methods. Methods: A computer program is presented which takes shadow images from tensile tests, obtained in a backlight configuration. A single camera is sufficient as no stereoscopic effects need to be addressed. The specimen's contours are digitally extracted, and strain is calculated from the contour change. At the same time, stress triaxiality is computed using a novel curvature fitting algorithm. Results: The method is accurate as comparison with manufactured solutions obtained from Finite Element simulations show. Application to 303 stainless steel specimens at different levels of stress triaxiality show that equivalent uniaxial true stress -- true strain relations are accurately recovered. Conclusions: The here presented computer program solves a long-standing challenge in a straightforward manner. It is expected to be a useful tool for experimental strain analysis

Die Anschauungen vom Wesen des Glases vom Mittelalter bis zum Beginn des 19. Jahrhunderts. Teil I.

Die Anschauungen vom Wesen des Glases werden in ihrem Wandel vom Beginn des Mittelalters bis etwa 1830 dargestellt und dabei gezeigt, wie bei Alchemisten und Scholastikern des Mittelalters, bei Humanisten und Naturphilosophen der Renaissance, in der mathematisch-mechanischen Betrachtung der beginnenden Neuzeit, bei den Praktikern des 17. Jahrhunderts und bei den Anhängern der Phlogistontheorie sich die Anschauung vom Wesen des Glases in Übereinstimmung mit den herrschenden naturwissenschaftlichen Lehren gestaltet und in welchem Verhältnis diese Anschauungen zur Praxis der Zeit stehen. Die Arbeit schließt mit einem Blick auf den grundlegenden Wandel, der seit dem Beginn des 19. Jahrhunderts die moderne Chemie hervorgerufen hat

Glastechnisches aus einem „Kunstbuch" des 16. Jahrhunderts.

Die kulturgeschichtliche Bedeutung der sog. Kunstbücher. - Das Kunstbuch des Beringer von Kotzau und Kurfürst Ludwig VI. von der Pfalz. - Medizinisches und Alchemistisches. - Künstliche Edelsteine aus alkalifreiem Bleisilikat und Alkaliglas. - Eine Entlehnung aus dem Opus Minerale des J. I. Hollandus. - Künstliche Kameen. - Reliefs auf Glas