Interfaces (and Regional Congruence?) in Spin Glasses

We present a general theorem restricting properties of interfaces between thermodynamic states and apply it to the spin glass excitations observed numerically by Krzakala-Martin and Palassini-Young in spatial dimensions d=3 and 4. We show that such excitations, with interface dimension smaller than d, cannot yield regionally congruent thermodynamic states. More generally, zero density interfaces of translation-covariant excitations cannot be pinned (by the disorder) in any d but rather must deflect to infinity in the thermodynamic limit. Additional consequences concerning regional congruence in spin glasses and other systems are discussed.Comment: 4 pages (ReVTeX); 1 figure; submitted to Physical Review Letter

Realistic spin glasses below eight dimensions: a highly disordered view

By connecting realistic spin glass models at low temperature to the highly disordered model at zero temperature, we argue that ordinary Edwards-Anderson spin glasses below eight dimensions have at most a single pair of physically relevant pure states at nonzero low temperature. Less likely scenarios that evade this conclusion are also discussed.Comment: 18 pages (RevTeX; 1 figure; to appear in Physical Review E

Zero-Temperature Dynamics of Plus/Minus J Spin Glasses and Related Models

We study zero-temperature, stochastic Ising models sigma(t) on a d-dimensional cubic lattice with (disordered) nearest-neighbor couplings independently chosen from a distribution mu on R and an initial spin configuration chosen uniformly at random. Given d, call mu type I (resp., type F) if, for every x in the lattice, sigma(x,t) flips infinitely (resp., only finitely) many times as t goes to infinity (with probability one) --- or else mixed type M. Models of type I and M exhibit a zero-temperature version of ``local non-equilibration''. For d=1, all types occur and the type of any mu is easy to determine. The main result of this paper is a proof that for d=2, plus/minus J models (where each coupling is independently chosen to be +J with probability alpha and -J with probability 1-alpha) are type M, unlike homogeneous models (type I) or continuous (finite mean) mu's (type F). We also prove that all other noncontinuous disordered systems are type M for any d greater than or equal to 2. The plus/minus J proof is noteworthy in that it is much less ``local'' than the other (simpler) proof. Homogeneous and plus/minus J models for d greater than or equal to 3 remain an open problem.Comment: 17 pages (RevTeX; 3 figures; to appear in Commun. Math. Phys.

Hand pollination to increase seed-set of red helleborine Cephalanthera rubra in the Chiltern Hills, Buckinghamshire, England

In 2007 and in previous years, as part of ongoing attempts to improve red helleborine Cephalanthera rubra seed-set, hand pollination of florets has been undertaken at a small colony of this species in Buckinghamshire, southern England. Natural pollination rarely occurs (one mature pod recorded in 10 years) at this site. In 2007, hand pollination resulted in the production of four seed pods, of which one withered and died. Upon ripening, the three remaining pods were removed for attempted micropropagation of the seeds. Ongoing conservation management has probably benefited the solitary bee Chelostoma campanularum which now appears fairly plentiful at the site, but despite the presence of this red helleborine flower visitor, natural pollination remains virtually unrecorded at this locality; field observations suggest that C.campanularum is in fact probably not large enough to act as an effective red helleborine pollinator as it can slip in and out of the flowers without removing the pollinia, unlike it larger relative C.fuliginosum, absent from the UK but which is a known pollinator of red helleborine in continental Europe

Simplicity of State and Overlap Structure in Finite-Volume Realistic Spin Glasses

We present a combination of heuristic and rigorous arguments indicating that both the pure state structure and the overlap structure of realistic spin glasses should be relatively simple: in a large finite volume with coupling-independent boundary conditions, such as periodic, at most a pair of flip-related (or the appropriate number of symmetry-related in the non-Ising case) states appear, and the Parisi overlap distribution correspondingly exhibits at most a pair of delta-functions at plus/minus the self-overlap. This rules out the nonstandard SK picture introduced by us earlier, and when combined with our previous elimination of more standard versions of the mean field picture, argues against the possibility of even limited versions of mean field ordering in realistic spin glasses. If broken spin flip symmetry should occur, this leaves open two main possibilities for ordering in the spin glass phase: the droplet/scaling two-state picture, and the chaotic pairs many-state picture introduced by us earlier. We present scaling arguments which provide a possible physical basis for the latter picture, and discuss possible reasons behind numerical observations of more complicated overlap structures in finite volumes.Comment: 22 pages (LaTeX; needs revtex), 1 figure (PostScript); to appear in Physical Review

Blocking and Persistence in the Zero-Temperature Dynamics of Homogeneous and Disordered Ising Models

A ``persistence'' exponent theta has been extensively used to describe the nonequilibrium dynamics of spin systems following a deep quench: for zero-temperature homogeneous Ising models on the d-dimensional cubic lattice, the fraction p(t) of spins not flipped by time t decays to zero like t^[-theta(d)] for low d; for high d, p(t) may decay to p(infinity)>0, because of ``blocking'' (but perhaps still like a power). What are the effects of disorder or changes of lattice? We show that these can quite generally lead to blocking (and convergence to a metastable configuration) even for low d, and then present two examples --- one disordered and one homogeneous --- where p(t) decays exponentially to p(infinity).Comment: 8 pages (LaTeX); to appear in Physical Review Letter

Analysis of Computer Science Communities Based on DBLP

It is popular nowadays to bring techniques from bibliometrics and scientometrics into the world of digital libraries to analyze the collaboration patterns and explore mechanisms which underlie community development. In this paper we use the DBLP data to investigate the author's scientific career and provide an in-depth exploration of some of the computer science communities. We compare them in terms of productivity, population stability and collaboration trends.Besides we use these features to compare the sets of topranked conferences with their lower ranked counterparts.Comment: 9 pages, 7 figures, 6 table

Finite-element analyses and fracture simulation in thin-sheet aluminum alloy

A two-dimensional, elastic-plastic finite-element analysis was used with a critical crack-tip-opening angle (CTOA) fracture criterion to model stable crack growth in thin-sheet 2024-T3 aluminum alloy under monotonic loading after precracking at different cyclic stress levels. Tests were conducted on three types of specimens: middle-crack, three-hole-crack and blunt-notch tensile specimens. An experiment technique was developed to measure CTOA during crack growth initiation and stable tearing using a high-resolution video camera and recorder. Crack front shapes were also measured during initiation and stable tearing using a fatigue marker-load technique. Three-dimensional elastic-plastic finite-element analyses of these crack shapes for stationary cracks were conducted to study the crack-front opening displacements. Predicted load against crack extension on middle-crack tension specimens agreed well with test results even for large-scale plastic deformations. The analyses were able to predict the effects of specimen size and precracking stress history on stable tearing. Predicted load against load-line displacements agreed well with test results up to maximum load bu the analyses tended to overpredict displacements as crack grew beyond the maximum load under displacement-controlled conditions. During the initiation phase, the measured CTOA values were high but decreased and remained nearly constant after a small amount of stable tearing. The constant value of CTOA agree well with the calculated value from the finite-element analysis. The larger CTOA values measured at the sheet surface during the initiation phase may be associated with the crack tunneling observed in the tests. Three-dimensional analyses for nonstraight crack fronts predicted much higher displacements near the free surface than in the interior

The Effect of Pure State Structure on Nonequilibrium Dynamics

Motivated by short-range Ising spin glasses, we review some rigorous results and their consequences for the relation between the number/nature of equilibrium pure states and nonequilibrium dynamics. Two of the consequences for spin glass dynamics following a deep quench to a temperature with broken spin flip symmetry are: (1) Almost all initial configurations lie on the boundary between the basins of attraction of multiple pure states. (2) Unless there are uncountably many pure states with almost all pairs having zero overlap, there can be no equilibration to a pure state as time goes to infinity. We discuss the relevance of these results to the difficulty of equilibration of spin glasses. We also review some results concerning the ``nature vs. nurture'' problem of whether the large-time behavior of both ferromagnets and spin glasses following a deep quench is determined more by the initial configuration or by the dynamics realization.Comment: 20 page

A title-gap flow model for use in aerodynamic loads assessment of space shuttle thermal protection system: Parallel gap faces

The problem of predicting aerodynamic loads on the insulating tiles of the space shuttle thermal protection system (TPS) is discussed and seen to require a method for predicting pressure and mass flux in the gaps between tiles. A mathematical model of the tile-gap flow is developed, based upon a slow viscous (Stokes) flow analysis, and is verified against experimental data. The tile-gap pressure field is derived from a solution of the two-dimensional Laplace equation; the mass-flux vector is then calculated from the pressure gradient. The means for incorporating this model into a lumped-parameter network analogy for porous-media flow is given. The means for incorporating this model into a lumped-parameter network analogy for porous-media flow is given. The flow model shows tile-gap mass flux to be very sensitive to the gap width indicating a need for coupling the TPS flow and tile displacement calculation. Analytical and experimental work to improve TPS flow predictions and a possible shuttle TPS hardware modification are recommended