113 research outputs found
Metastability and Transient Effects in Vortex Matter Near a Decoupling Transition
We examine metastable and transient effects both above and below the
first-order decoupling line in a 3D simulation of magnetically interacting
pancake vortices. We observe pronounced transient and history effects as well
as supercooling and superheating between the 3D coupled, ordered and 2D
decoupled, disordered phases. In the disordered supercooled state as a function
of DC driving, reordering occurs through the formation of growing moving
channels of the ordered phase. No channels form in the superheated region;
instead the ordered state is homogeneously destroyed. When a sequence of
current pulses is applied we observe memory effects. We find a ramp rate
dependence of the V(I) curves on both sides of the decoupling transition. The
critical current that we obtain depends on how the system is prepared.Comment: 10 pages, 15 postscript figures, version to appear in PR
Utilizing image texture to detect land-cover change in Mediterranean coastal wetlands
Land-use/cover change dynamics were investigated in a Mediterranean coastal wetland. Change Vector Analysis (CVA) without and with image texture derived from the co-occurrence matrix and variogram were evaluated for detecting land-use/cover change. Three Landsat Thematic Mapper (TM) scenes recorded on July 1985, 1993 and 2005 were used, minimizing change detection error caused by seasonal differences. Images were geometrically, atmospherically and radiometrically corrected. CVA without and with texture measures were implemented and assessed using reference images generated by object-based supervised classification. These outputs were used for cross-classification to determine the ‘from–to’ change used to compare between techniques. The Landsat TM image bands together with the variogram yielded the most accurate change detection results, with Kappa statistics of 0.7619 and 0.7637 for the 1985–1993 and 1993–2005 image pairs, respectively
A Review of Magnetic Phenomena in Probe-Brane Holographic Matter
Gauge/gravity duality is a useful and efficient tool for addressing and
studying questions related to strongly interacting systems described by a gauge
theory. In this manuscript we will review a number of interesting phenomena
that occur in such systems when a background magnetic field is turned on.
Specifically, we will discuss holographic models for systems that include
matter fields in the fundamental representation of the gauge group, which are
incorporated by adding probe branes into the gravitational background dual to
the gauge theory. We include three models in this review: the D3-D7 and D4-D8
models, that describe four-dimensional systems, and the D3-D7' model, that
describes three-dimensional fermions interacting with a four-dimensional gauge
field.Comment: 35 pages, 27 figures, to appear in Lect. Notes Phys. "Strongly
interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K.
Landsteiner, A. Schmitt, H.-U. Yee; references adde
Meson Spectra and Magnetic Fields in the Sakai-Sugimoto Model
We continue our study of the dynamics of the flavour sector of the
Sakai-Sugimoto model in the presence of an external magnetic field, uncovering
several features of the meson spectrum at high and low temperatures. We employ
both analytical and numerical methods to study the coupled non-linear equations
that result from the gravity dual.Comment: 44 pages, multiple figure
Adding Flavor to AdS4/CFT3
Aharony, Bergman, Jafferis, and Maldacena have proposed that the low-energy
description of multiple M2-branes at a C4/Zk singularity is a (2+1)-dimensional
N=6 supersymmetric U(Nc) x U(Nc) Chern-Simons matter theory, the ABJM theory.
In the large-Nc limit, its holographic dual is supergravity in AdS4 x S7/Zk. We
study various ways to add fields that transform in the fundamental
representation of the gauge groups, i.e. flavor fields, to the ABJM theory. We
work in a probe limit and perform analyses in both the supergravity and field
theory descriptions. In the supergravity description we find a large class of
supersymmetric embeddings of probe flavor branes. In the field theory
description, we present a general method to determine the couplings of the
flavor fields to the fields of the ABJM theory. We then study four examples in
detail: codimension-zero N=3 supersymmetric flavor, described in supergravity
by Kaluza-Klein monopoles or D6-branes; codimension-one N=(0,6) supersymmetric
chiral flavor, described by D8-branes; codimension-one N=(3,3) supersymmetric
non-chiral flavor, described by M5/D4-branes; codimension-two N=4
supersymmetric flavor, described by M2/D2-branes. Finally we discuss special
physical equivalences between brane embeddings in M-theory, and their
interpretation in the field theory description.Comment: 60 pages, 1 figure; v2: minor corrections, added two references,
version published in JHE
Phase Behavior of Type-II Superconductors with Quenched Point Pinning Disorder: A Phenomenological Proposal
A general phenomenology for phase behaviour in the mixed phase of type-II
superconductors with weak point pinning disorder is outlined. We propose that
the ``Bragg glass'' phase generically transforms via two separate thermodynamic
phase transitions into a disordered liquid on increasing the temperature. The
first transition is into a glassy phase, topologically disordered at the
largest length scales; current evidence suggests that it lacks the long-ranged
phase correlations expected of a ``vortex glass''. This phase has a significant
degree of short-ranged translational order, unlike the disordered liquid, but
no quasi-long range order, in contrast to the Bragg glass. This glassy phase,
which we call a ``multi-domain glass'', is confined to a narrow sliver at
intermediate fields, but broadens out both for much larger and much smaller
field values. The multi-domain glass may be a ``hexatic glass''; alternatively,
its glassy properties may originate in the replica symmetry breaking envisaged
in recent theories of the structural glass transition. Estimates for
translational correlation lengths in the multi-domain glass indicate that they
can be far larger than the interline spacing for weak disorder, suggesting a
plausible mechanism by which signals of a two-step transition can be obscured.
Calculations of the Bragg glass-multi-domain glass and the multi-domain
glass-disordered liquid phase boundaries are presented and compared to
experimental data. We argue that these proposals provide a unified picture of
the available experimental data on both high-T and low-T materials,
simulations and current theoretical understanding.Comment: 70 pages, 9 postscript figures, modified title and minor changes in
published versio
The L 98-59 System: Three Transiting, Terrestrial-Size Planets Orbiting A Nearby M Dwarf
We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)—a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R⊕ to 1.6 R⊕. All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system
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