A Vectorized Algorithm for Molecular Dynamics of Short Range Interacting Particles

We report on a lattice based algorithm, completely vectorized for molecular dynamics simulations. Its algorithmic complexity is of the order O(N), where $N$ is the number of particles. The algorithm works very effectively when the particles have short range interaction, but it is applicable to each kind of interaction. The code was tested on a Cray ymp el in a simulation of flowing granular material.Comment: 9 pages, 6 figures, Late

Avalanche statistics of sand heaps

Large scale computer simulations are presented to investigate the avalanche statistics of sand piles using molecular dynamics. We could show that different methods of measurement lead to contradicting conclusions, presumably due to avalanches not reaching the end of the experimental table.Comment: 6 pages, 4 figure

The Effect of Surfaces on the Tunneling Density of States of an Anisotropically Paired Superconductor

We present calculations of the tunneling density of states in an anisotropically paired superconductor for two different sample geometries: a semi-infinite system with a single specular wall, and a slab of finite thickness and infinite lateral extent. In both cases we are interested in the effects of surface pair breaking on the tunneling spectrum. We take the stable bulk phase to be of $d_{x^2-y^2}$ symmetry. Our calculations are performed within two different band structure environments: an isotropic cylindrical Fermi surface with a bulk order parameter of the form $\Delta\sim k_x^2-k_y^2$, and a nontrivial tight-binding Fermi surface with the order parameter structure coming from an anti-ferromagnetic spin-fluctuation model. In each case we find additional structures in the energy spectrum coming from the surface layer. These structures are sensitive to the orientation of the surface with respect to the crystal lattice, and have their origins in the detailed form of the momentum and spatial dependence of the order parameter. By means of tunneling spectroscopy, one can obtain information on both the anisotropy of the energy gap, |\Delta(\p)|, as well as on the phase of the order parameter, \Delta(\p) = |\Delta(\p)|e^{i\varphi(\p)}.Comment: 14 pages of revtex text with 11 compressed and encoded figures. To appear in J. Low Temp. Phys., December, 199

Thermodynamic properties of thin films of superfluid 3He-A

The pairing correlations in superfluid He-3 are strongly modified by quasiparticle scattering off a surface or an interface. We present theoretical results and predictions for the order parameter, the quasiparticle excitation spectrum and the free energy for thin films of superfluid He-3. Both specular and diffuse scattering by a substrate are considered, while the free surface is assumed to be a perfectly reflecting specular boundary. The results are based on self-consistent calculations of the order parameter and quasiparticle excitation spectrum at zero pressure. We obtain new results for the phase diagram, free energy, entropy and specific heat of thin films of superfluid He-3.Comment: Replaced with an updated versio

Odd-frequency pairing in normal metal/superconductor junctions

We study the induced odd-frequency pairing states in ballistic normal metal/superconductor (N/S) junctions where a superconductor has even-frequency symmetry in the bulk and a normal metal layer has an arbitrary length. Using the quasiclassical Green's function formalism, we demonstrate that, quite generally, the pair amplitude in the junction has an admixture of an odd-frequency component due to the breakdown of translational invariance near the N/S interface where the pair potential acquires spatial dependence. If a superconductor has even-parity pair potential (spin-singlet s-wave state), the odd-frequency pairing component with odd-parity is induced near the N/S interface, while in the case of odd-parity pair potential (spin-triplet $p_{x}$-wave or spin-singlet $d_{xy}$-wave) the odd-frequency component with even-parity is generated. We show that in conventional s-wave junctions, the amplitude of the odd-frequency pairing state is enhanced at energies corresponding to the peaks in the local density of states (LDOS). In $p_x$- and $d_{xy}$-wave junctions, the amplitude of the odd-frequency component on the S side of the N/S interface is enhanced at zero energy where the midgap Andreev resonant state (MARS) appears due to the sign change of the pair potential. The odd-frequency component extends into the N region and exceeds the even-frequency component at energies corresponding to the LDOS peak positions, including the MARS.Comment: 27 pages, 12 figure

The effect of the contract-relax-antagonist-contract (CRAC) stretch of hamstrings on range of motion, sprint and agility performance in moderately active males: A randomised control trial

Background: Although stretching is done routinely to prevent injury during explosive sport activities, there is some concern that effective stretching might negatively impact on performance. Objectives: This study’s main objective was to investigate the impact of a specific stretch (CRAC), in which the muscle to be stretched, hamstrings, is actively contracted then relaxed. This is then followed by the antagonist muscle (quadriceps) contracting. Secondly, the impact of the stretch on performance was examined. Methods: A randomised control trial was used. Forty healthy active males between 21 and 35 years of age were assigned to either receive three repetitions of CRAC or rest. Hamstring flexibility and the Illinois Agility Test were the primary outcome measures. Results: The intervention was effective in improving hamstring flexibility by 37% immediately post-application and this was maintained for eight minutes thereafter. It had no significant effect on agility or sprint times. Conclusions: CRAC applied to stretch the hamstring muscles of active males resulted in a large increase of active knee extension range of motion, without decreasing performance. CRAC appears to be a safe and effective method of increasing the length of the hamstrings pre-sport activity and should be utilised by sports physiotherapists if deemed necessary and beneficial following initial assessment

The influence of chiral surface states on the London penetration depth in Sr2_2RuO4_4

The London penetration depth for the unconventional superconductor Sr$_2$RuO$_4$ is analyzed assuming an order parameter which breaks time reversal symmetry and parity simultaneously. Such a superconducting state possesses chiral quasiparticle states with subgap energies at the surface. We show that these subgap states can give a significant contribution to the low-temperature behavior of the London penetration depth yielding a $T^2$ power-law even though bulk quasiparticle spectrum is gapped. The presence of several electron bands gives rise to interband transition among the subgap surface states and influences the properties of the surface impedance. Furthermore, the surface states lead also to a non-linear Meissner effect.Comment: 4 pages, 1 figure, the definition of the Nambu field operator introduced, and some typos correcte

D-Wave Superconductors near Surfaces and Interfaces: A Scattering Matrix Approach within the Quasiclassical Technique

A recently developed method [A. Shelankov and M. Ozana, Phys. Rev. B 61, 7077 (2000)] is applied to investigate d-wave superconductors in the vicinity of (rough) surfaces. While this method allows the incorporation of arbitrary interfaces into the quasiclassical technique, we discuss, as examples, diffusive surfaces and boundaries with small tilted mirrors (facets). The properties of the surface enter via the scattering matrix in the boundary condition for the quasiclassical Green's function. The diffusive surface is described by an ensemble of random scattering matrices. We find that the fluctuations of the density of states around the average are small; the zero bias conductance peak broadens with increasing disorder. The faceted surface is described in the model where the scattering matrix couples m in- and m out-trajectories (m>=2). No zero bias conductance peak is found for [100] surfaces; the relation to the model of Fogelstrom et al. [Phys. Rev. Lett. 79, 281 (1997)] is discussed.Comment: RevTeX, 19 pages, 18 figure

Parity-sensitive measurements based on ferromagnet/superconductor tunneling junctions

A method to identify the parity of unconventional superconductors is proposed based on tunneling spectroscopy. For a model of calculation, we adopt a ferromagnet/superconductor (F/S) junction of which tunneling current is spin polarized. The tunneling conductance spectra are shown to be quite sensitive to the direction of the magnetization axis in the ferromagnet only when the superconductor has odd parity. Therefore, it is possible to distinguish the parity of the superconductor by measuring the tunneling spectroscopy in F/S junctions.Comment: 4 pages, 5 figure. To appear in J. Phys. Soc. Jp