Statistical mechanical approach to secondary processes and structural relaxation in glasses and glass formers

The interrelation of dynamic processes active on separated time-scales in glasses and viscous liquids is investigated using a model displaying two time-scale bifurcations both between fast and secondary relaxation and between secondary and structural relaxation. The study of the dynamics allows for predictions on the system relaxation above the temperature of dynamic arrest in the mean-field approximation, that are compared with the outcomes of the equations of motion directly derived within the Mode Coupling Theory (MCT) for under-cooled viscous liquids. Varying the external thermodynamic parameters a wide range of phenomenology can be represented, from a very clear separation of structural and secondary peak in the susceptibility loss to excess wing structures.Comment: 13 pages, 8 figure

Bilayers connected by threadlike micelles in amphiphilic mixtures:A self-consistent field theory study

Binary mixtures of amphiphiles in solution can self-assemble into a wide range of structures when the two species individually form aggregates of different curvatures. A specific example of this is seen in solutions of lipid mixtures where the two species form lamellar structures and spherical micelles respectively. Here, vesicles connected by thread-like micelles can form in a narrow concentration range of the sphere-forming lipid. We present a self-consistent field theory (SCFT) study of these structures. Firstly, we show that the addition of sphere-forming lipid to a solution of lamella-former can lower the free energy of cylindrical, thread-like micelles and hence encourage their formation. Next, we demonstrate the coupling between composition and curvature; specifically, that increasing the concentration of sphere-former in a system of two bilayers connected by a thread leads to a transfer of amphiphile to the thread. We further show that the two species are segregated within the structure, with the concentration of sphere-former being significantly higher in the thread. Finally, the addition of larger amounts of sphere-former is found to destabilize the junctions linking the bilayers to the cylindrical micelle, leading to a breakdown of the connected structures. The degree of segregation of the amphiphiles and the amount of sphere-former required to destabilize the junctions is shown to be sensitive to the length of the hydrophilic block of the sphere-forming amphiphiles.Comment: 16 pages plus 10 figures; preprint format; submitted to Langmui

Wedge covariance for two-dimensional filling and wetting

A comprehensive theory of interfacial fluctuation effects occurring at two-dimensional wedge (corner) filling transitions in pure (thermal disorder) and impure (random bond disorder) systems is presented. Scaling theory and the explicit results of transfer matrix and replica trick studies of interfacial Hamiltonian models reveal that, for almost all examples of intermolecular forces, the critical behaviour at filling is fluctuation dominated, characterized by universal critical exponents and scaling functions that depend only on the wandering exponent ζ. Within this filling-fluctuation (FFL) regime, the critical behaviour of the midpoint interfacial height, probability distribution function, local compressibility and wedge free energy are identical to corresponding quantities predicted for the strong-fluctuation (SFL) regime for critical wetting transitions at planar walls. In particular the wedge free energy is related to the SFL regime point tension, which is calculated for systems with random bond disorder using the replica trick. The connection with the SFL regime for all these quantities can be expressed precisely in terms of special wedge covariance relations, which complement standard scaling theory and restrict the allowed values of the critical exponents for both FFL filling and SFL critical wetting. The predictions for the values of the exponents in the SFL regime recover earlier results based on random walk arguments. The covariance of the wedge free energy leads to a new, general relation for the SFL regime point tension, which derives the conjectured Indekeu-Robledo critical exponent relation and also explains the origin of the logarithmic singularity for pure systems known from exact Ising studies due to Abraham and co-workers. Wedge covariance is also used to predict the numerical values of critical exponents and position dependence of universal one-point functions for pure systems

Resonant rectification of fluctuations in a Brownian ratchet.

Resonant activation, rectification of fluctuations, and current reversal, are investigated numerically in an asymmetric periodic potential. The results are compared to recent predictions based on the theory of the logarithmic susceptibility. Possible applications are discussed

Recent results from the ATLAS SCT irradiation programme

The irradiation facility at the CERN proton synchrotron, set up to irradiate full-size prototypes of silicon microstrip detectors for the ATLAS semiconductor tracker, is described and measurements of the detector currents during irradiation are reported. The detector dark currents can be described by bulk radiation damage models demonstrating the radiation hardness of the detector design and allowing the current damage factor alpha and the acceptor introduction term p to be determined. Results from testbeam studies of a module with an irradiated detector and binary readout in a magnetic field and with the beam incident over a range of angles are reported. The hit efficiency and spatial resolution satisfy the requirements for the SCT provided the detector is operated at the full charge collection voltage. The Lorentz angle was not found to be affected by the irradiation. (11 refs)