Numerical Results for the Ground-State Interface in a Random Medium

The problem of determining the ground state of a $d$-dimensional interface embedded in a $(d+1)$-dimensional random medium is treated numerically. Using a minimum-cut algorithm, the exact ground states can be found for a number of problems for which other numerical methods are inexact and slow. In particular, results are presented for the roughness exponents and ground-state energy fluctuations in a random bond Ising model. It is found that the roughness exponent $\zeta = 0.41 \pm 0.01, 0.22 \pm 0.01$, with the related energy exponent being $\theta = 0.84 \pm 0.03, 1.45 \pm 0.04$, in $d = 2, 3$, respectively. These results are compared with previous analytical and numerical estimates.Comment: 10 pages, REVTEX3.0; 3 ps files (separate:tar/gzip/uuencoded) for figure

Stability of Elastic Glass Phases in Random Field XY Magnets and Vortex Lattices in Type II Superconductors

A description of a dislocation-free elastic glass phase in terms of domain walls is developed and used as the basis of a renormalization group analysis of the energetics of dislocation loops added to the system. It is found that even after optimizing over possible paths of large dislocation loops, their energy is still very likely to be positive when the dislocation core energy is large. This implies the existence of an equilibrium elastic glass phase in three dimensional random field X-Y magnets, and a dislocation free, bond-orientationally ordered ``Bragg glass'' phase of vortices in dirty Type II superconductors.Comment: 12 pages, Revtex, no figures, submitted to Phys Rev Letter

C-shaped specimen plane strain fracture toughness tests

Test equipment, procedures, and data obtained in the evaluation of C-shaped specimens are presented. Observations reported on include: specimen preparation and dimensional measurement; modifications to the standard ASTM E 399 displacement gage, which permit punch mark gage point engagement; and a measurement device for determining the interior and exterior radii of ring segments. Load displacement ratios were determined experimentally which agreed with analytically determined coefficients for three different gage lengths on the inner surfaces of radially-cracked ring segments

A Comprehensive Method of Estimating Electric Fields from Vector Magnetic Field and Doppler Measurements

Photospheric electric fields, estimated from sequences of vector magnetic field and Doppler measurements, can be used to estimate the flux of magnetic energy (the Poynting flux) into the corona and as time-dependent boundary conditions for dynamic models of the coronal magnetic field. We have modified and extended an existing method to estimate photospheric electric fields that combines a poloidal-toroidal (PTD) decomposition of the evolving magnetic field vector with Doppler and horizontal plasma velocities. Our current, more comprehensive method, which we dub the "{\bf P}TD-{\bf D}oppler-{\bf F}LCT {\bf I}deal" (PDFI) technique, can now incorporate Doppler velocities from non-normal viewing angles. It uses the \texttt{FISHPACK} software package to solve several two-dimensional Poisson equations, a faster and more robust approach than our previous implementations. Here, we describe systematic, quantitative tests of the accuracy and robustness of the PDFI technique using synthetic data from anelastic MHD (\texttt{ANMHD}) simulations, which have been used in similar tests in the past. We find that the PDFI method has less than $1$ error in the total Poynting flux and a $10$ error in the helicity flux rate at a normal viewing angle $(\theta=0$) and less than $25$ and $10$ errors respectively at large viewing angles ($\theta<60^\circ$). We compare our results with other inversion methods at zero viewing angle, and find that our method's estimates of the fluxes of magnetic energy and helicity are comparable to or more accurate than other methods. We also discuss the limitations of the PDFI method and its uncertainties.Comment: 56 pages, 10 figures, ApJ (in press

Fluctuating loops and glassy dynamics of a pinned line in two dimensions

We represent the slow, glassy equilibrium dynamics of a line in a two-dimensional random potential landscape as driven by an array of asymptotically independent two-state systems, or loops, fluctuating on all length scales. The assumption of independence enables a fairly complete analytic description. We obtain good agreement with Monte Carlo simulations when the free energy barriers separating the two sides of a loop of size L are drawn from a distribution whose width and mean scale as L^(1/3), in agreement with recent results for scaling of such barriers.Comment: 11 pages, 4 Postscript figure

Phase diagram of vortex matter in layered superconductors with random point pinning

We study the phase diagram of the superconducting vortex system in layered high-temperature superconductors in the presence of a magnetic field perpendicular to the layers and of random atomic scale point pinning centers. We consider the highly anisotropic limit where the pancake vortices on different layer are coupled only by their electromagnetic interaction. The free energy of the vortex system is then represented as a Ramakrishnan-Yussouff free energy functional of the time averaged vortex density. We numerically minimize this functional and examine the properties of the resulting phases. We find that, in the temperature ($T$) -- pinning strength ($s$) plane at constant magnetic induction, the equilibrium phase at low $T$ and $s$ is a Bragg glass. As one increases $s$ or $T$ a first order phase transition occurs to another phase that we characterize as a pinned vortex liquid. The weakly pinned vortex liquid obtained for high $T$ and small $s$ smoothly crosses over to the strongly pinned vortex liquid as $T$ is decreased or $s$ increased -- we do not find evidence for the existence, in thermodynamic equilibrium, of a distinct vortex glass phase in the range of pinning parameters considered here. %cdr We present results for the density correlation functions, the density and defect distributions, and the local field distribution accessible via $\mu$SR experiments. These results are compared with those of existing theoretical, numerical and experimental studies.Comment: 15 pages, including figures. Higher resolution files for Figs 3a and 11 available from author

Natural materials – nature of materials

The material world is recently and very rapidly changing; altering the relationships between materials – the substance of everyday life – and designers – the professionals who are responsible for transforming materials into daily life objects. This vibrant context prompts us to explore and attempt to conceptualise these fluid relationships and review conceptual tools that will help to open up the scope of materials based research in design. To address the multiple and multi-faceted relationships designers are situated in, we borrow concepts from social sciences that explore materiality within its multiple environments. We draw on conceptualisations of materials as active and as having capacities to bring about change and proliferate relations, and responding to new developments of biotic materials. By considering historic materials, particularly milk-based plastics, we propose a new category of autonomous materials. We discuss the emerging designer-material relationships with the hope of directing future enquiry into materials and discuss the implications of a new class of materials – the ‘autonomoids’ – for design research