Double noding technique for mixed mode crack propagation studies

A simple dynamic finite element algorithm for analyzing a propagating mixed mode crack tip is presented. A double noding technique, which can be easily incorporated into existing dynamic finite element codes, is used together with a corrected J integral to extract modes I and II dynamic stress intensity factors of a propagating crack. The utility of the procedure is demonstrated by analyzing test problems involving a mode I central crack propagating in a plate subjected to uniaxial tension, a mixed mode I and II stationary, slanted central crack in a plate subjected to uniaxial impact loading, and a mixed mode I and II extending, slanted single edge crack in a plate subjected to uniaxial tension

Stripes, Non-Fermi-Liquid Behavior, and High-Tc Superconductivity

The electronic structure of the high-Tc cuprates is studied in terms of "large-U" and "small-U" orbitals. A striped structure and three types of quasiparticles are obtained, polaron-like "stripons" carrying charge, "svivons" carrying spin, and "quasielectrons" carrying both. The anomalous properties are explained, and specifically the behavior of the resistivity, Hall constant, and thermoelectric power. High-temperature superconductivity results from transitions between pair states of quasielectrons and stripons.Comment: 4 page

Stripe-Like Inhomogeneities, Spectroscopies, Pairing, and Coherence in the High-Tc Cuprates

It is found that the carriers of the high-T_c cuprates are polaron-like "stripons" carrying charge and located in stripe-like inhomogeneities, "quasi-electrons" carrying charge and spin, and "svivons" carrying spin and lattice distortion. This is shown to result in the observed anomalous spectroscopic properties of the cuprates. The AF/stripe-like inhomogeneities result from the Bose condensation of the svivon field, and the speed of their dynamics is determined by the width of the double-svivon neutron-resonance peak. Pairing results from transitions between pair states of stripons and quasi-electrons through the exchange of svivons. The obtained pairing symmetry is of the d_{x^2-y^2} type; however, sign reversal through the charged stripes results in features not characteristic of this symmetry. The phase diagram is determined by a pairing and a coherence line, associated with a Mott transition, and the pseudogap state corresponds to incoherent pairing.Comment: 13 pages, 8 figures; version including recent references, to be published in J. Phys. Chem. Solid

Imitation, mirror neurons and autism

Various deficits in the cognitive functioning of people with autism have been documented in recent years but these provide only partial explanations for the condition. We focus instead on an imitative disturbance involving difficulties both in copying actions and in inhibiting more stereotyped mimicking, such as echolalia. A candidate for the neural basis of this disturbance may be found in a recently discovered class of neurons in frontal cortex, 'mirror neurons' (MNs). These neurons show activity in relation both to specific actions performed by self and matching actions performed by others, providing a potential bridge between minds. MN systems exist in primates without imitative and ‘theory of mind’ abilities and we suggest that in order for them to have become utilized to perform social cognitive functions, sophisticated cortical neuronal systems have evolved in which MNs function as key elements. Early developmental failures of MN systems are likely to result in a consequent cascade of developmental impairments characterised by the clinical syndrome of autism

Specification of the power supply for a 6-pole combined horizontal and vertical corrector magnet

Light Source Note LS-176 lists four types of corrector magnets and their power supply specifications. In order to simplify the AC operation of corrector magnets for closed orbit correction feedback, adopting a single type of corrector magnet for the whole ring is currently considered. This corrector magnet has six poles (an adaption from the ring sextupole magnet) and has coil windings producing independent horizontal and vertical bending fields. As in the other correctors, the vacuum chamber eddy current dominates the AC operation of the magnet which affects the voltage specification of the power supplies. In this note, the physical requirements of the magnets will be reviewed, and the relevant magnet and power supply parameters will be reported. A few assumptions on the local bump geometries have changed since the publication of LS-176. The inner correctors of the straight section bump have been moved about 0.15 m inwards to conform with current vacuum chamber design. This decreases the required magnet strengths by 15% relative to those in LS-176. As of the publication date of this report, the locations of the two outboard correctors of the straight section bump are set midway between the quadrupoles Ql and Q2. Moving these correctors closer to the Q2`s will further reduce the corrector strength required. Therefore, two results are presented: one with the two outward correctors remaining at their current design locations, and one with the outward correctors moved right up against quadrupole Q2. Also, the parameters for the bending magnet beamline bump are recalculated for a photon source placed 1/8th downstream of the entrance of the magnet

Mathematical model and the dynamic simulation of an electromechanical rotary device. [SLENOID]

A mathematical model of an electro-mechanical rotary device is presented. This device contains a rotor, stator, and two spring-loaded arms which restrict the rotor motion. The desired action is the alignment of the rotor and the consequent movement of the arms. The SLENOID computer program for calculating the magnetic torque, air gap permeance, spring torque, damping effects, and motion of the rotor and arms is described. (LCL