Boundary selectivity of crack paths in corrosion fatigue of stainless steel

Stress corrosion and corrosion fatigue cracks are frequently very branched and there have been extensive attempts to define the characteristics of crack-stopping features. EBSD has been used to examine the full length (~8mm) of a corrosion fatigue crack in stainless steel. The grain boundary character distribution of the cracked boundaries is compared to that of the rest of the material and observations presented on the effect of grain boundary character on the choice of crack path at grain boundary junctions of different configurations and orientations with restect to the principle stres

Tube dimpling tool Patent

Hand tool for forming dimples and nipples on end portion of tube

Modeling a falling slinky

A slinky is an example of a tension spring: in an unstretched state a slinky is collapsed, with turns touching, and a finite tension is required to separate the turns from this state. If a slinky is suspended from its top and stretched under gravity and then released, the bottom of the slinky does not begin to fall until the top section of the slinky, which collapses turn by turn from the top, collides with the bottom. The total collapse time t_c (typically ~0.3 s for real slinkies) corresponds to the time required for a wave front to propagate down the slinky to communicate the release of the top end. We present a modification to an existing model for a falling tension spring (Calkin 1993) and apply it to data from filmed drops of two real slinkies. The modification of the model is the inclusion of a finite time for collapse of the turns of the slinky behind the collapse front propagating down the slinky during the fall. The new finite-collapse time model achieves a good qualitative fit to the observed positions of the top of the real slinkies during the measured drops. The spring constant k for each slinky is taken to be a free parameter in the model. The best-fit model values for k for each slinky are approximately consistent with values obtained from measured periods of oscillation of the slinkies.Comment: 30 pages, 11 figure

Hole-pair hopping in arrangements of hole-rich/hole-poor domains in a quantum antiferromagnet

We study the motion of holes in a doped quantum antiferromagnet in the presence of arrangements of hole-rich and hole-poor domains such as the stripe-phase in high-$T_C$ cuprates. When these structures form, it becomes energetically favorable for single holes, pairs of holes or small bound-hole clusters to hop from one hole-rich domain to another due to quantum fluctuations. However, we find that at temperature of approximately 100 K, the probability for bound hole-pair exchange between neighboring hole-rich regions in the stripe phase, is one or two orders of magnitude larger than single-hole or multi-hole droplet exchange. As a result holes in a given hole-rich domain penetrate further into the antiferromagnetically aligned domains when they do it in pairs. At temperature of about 100 K and below bound pairs of holes hop from one hole-rich domain to another with high probability. Therefore our main finding is that the presence of the antiferromagnetic hole-poor domains act as a filter which selects, from the hole-rich domains (where holes form a self-bound liquid), hole pairs which can be exchanged throughout the system. This fluid of bound hole pairs can undergo a superfluid phase ordering at the above mentioned temperature scale.Comment: Revtex, 6 two-column pages, 4 figure

Finite volume effects in a quenched lattice-QCD quark propagator

We investigate finite volume effects in the pattern of chiral symmetry breaking. To this end we employ a formulation of the Schwinger-Dyson equations on a torus which reproduces results from the corresponding lattice simulations of staggered quarks and from the overlap action. Studying the volume dependence of the quark propagator we find quantitative differences with the infinite volume result at small momenta and small quark masses. We estimate the minimal box length L below which chiral perturbation theory cannot be applied to be L \simeq 1.6 fm. In the infinite volume limit we find a chiral condensate of ||_{\bar{MS}}^{2 GeV} = (253 \pm 5.0 MeV)^3, an up/down quark mass of m_{\bar{MS}}^{2 GeV} = 4.1 \pm 0.3 MeV and a pion decay constant which is only ten percent smaller than the experimental value.Comment: 19 pages, 8 figures. v2: minor clarifications added, version published in PR

Quark Condensates: Flavour Dependence

We determine the q-bar q condensate for quark masses from zero up to that of the strange quark within a phenomenologically successful modelling of continuum QCD by solving the quark Schwinger-Dyson equation. The existence of multiple solutions to this equation is the key to an accurate and reliable extraction of this condensate using the operator product expansion. We explain why alternative definitions fail to give the physical condensate.Comment: 9 pages, 7 figures, uses appolb.cls, LaTeX. Talk presented by R. Williams at the EURIDICE Final Meeting, August 24-27th, 2006, Kazimierz, Polan