1. Superfluidity versus Bloch oscillations in confined atomic gases - Büchler, H. P.; Geshkenbein, V. B.; Blatter, G.
We study the superfluid properties of (quasi) one-dimensional bosonic atom gases/liquids in traps with finite geometries in the presence of strong quantum fluctuations. Driving the condensate with a moving defect we find the nucleation rate for phase slips using instanton techniques. While phase slips are quenched in a ring resulting in a superfluid response, they proliferate in a tube geometry where we find Bloch oscillations in the chemical potential. These Bloch oscillations describe the individual tunneling of atoms through the defect and thus are a consequence of particle quantization.
- 23-mar-2007

2. Modellization of hydraulic fracturing of porous materials - Tzschichholz, F.; Wangen, M.
We review microstructural fracture growth models suitable for the study of hydraulic fracture processes in disordered porous materials and present some basic results. It is shown that microstructural models exhibit certain similarities to corresponding theories of continua. These similarities are most easily demonstrated for simple crack geometries, i.e., straight cracks (finite size scalings). However, there exist even scaling relations which are completely independent of the particular employed crack structure. Furthermore it is demonstrated that disorder in cohesional/flow properties can influence the crack growth and the resulting fracture geometry in an essential way.
- 03-mar-2007

3. Droplet shapes on structured substrates and conformal invariance - Parry, A. O.; Macdonald, E. D.; Rascon, C.
We consider the finite-size scaling of equilibrium droplet shapes for fluid adsorption (at bulk two-phase co-existence) on heterogeneous substrates and also in wedge geometries in which only a finite domain $\Lambda_{A}$ of the substrate is completely wet. For three-dimensional systems with short-ranged forces we use renormalization group ideas to establish that both the shape of the droplet height and the height-height correlations can be understood from the conformal invariance of an appropriate operator. This allows us to predict the explicit scaling form of the droplet height for a number of different domain shapes. For systems with long-ranged forces, conformal invariance is not obeyed but the droplet shape is still...
- 23-mar-2007

4. Lattice Resistance and Peierls Stress in Finite-size Atomistic Dislocation Simulations - Olmsted, David L.; Hardikar, Kedar Y.; Phillips, Rob
Atomistic computations of the Peierls stress in fcc metals are relatively scarce. By way of contrast, there are many more atomistic computations for bcc metals, as well as mixed discrete-continuum computations of the Peierls-Nabarro type for fcc metals. One of the reasons for this is the low Peierls stresses in fcc metals. Because atomistic computations of the Peierls stress take place in finite simulation cells, image forces caused by boundaries must either be relaxed or corrected for if system size independent results are to be obtained. One of the approaches that has been developed for treating such boundary forces is by computing them directly and subsequently subtracting their...
- 02-mar-2007

5. Theory of Type-II Superconductors with Finite London Penetration Depth - Brandt, Ernst Helmut
Previous continuum theory of type-II superconductors of various shapes with and without vortex pinning in an applied magnetic field and with transport current, is generalized to account for a finite London penetration depth lambda. This extension is particularly important at low inductions B, where the transition to the Meissner state is now described correctly, and for films with thickness comparable to or smaller than lambda. The finite width of the surface layer with screening currents and the correct dc and ac responses in various geometries follow naturally from an equation of motion for the current density in which the integral kernel now accounts for finite lambda. New geometries considered...
- 23-mar-2007