1,408 research outputs found
Columnar defects and vortex fluctuations in layered superconductors
We investigate fluctuations of Josephson-coupled pancake vortices in layered
superconductors in the presence of columnar defects. We study the
thermodynamics of a single pancake stack pinned by columnar defects and obtain
the temperature dependence of localization length, pinning energy and critical
current. We study the creep regime and compute the crossover current between
line-like creep and pancake-like creep motion. We find that columnar defects
effectively increase interlayer Josephson coupling by suppressing thermal
fluctuations of pancakes. This leads to an upward shift in the decoupling line
most pronounced around the matching field.Comment: 5 pages, REVTeX, no figure
Solving Problems of Practice in Education
The authors identify and discuss the many complexities involved in the translation of scientific information in the social sciences into forms usable for solving problems of practice in education. As a means of appropriately handling these complexities and the issues that arise, they prescribe a series of stages to be followed from the advent of a practitioner's situational problem to the design of a response to it. They assert that unless the process of translation is conducted with the prescribed level of understanding, appreciation, and rigor, the application of knowledge will be inaccurate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68934/2/10.1177_107554708400600103.pd
Negotiating the inhuman: Bakhtin, materiality and the instrumentalization of climate change
The article argues that the work of literary theorist Mikhail M. Bakhtin presents a starting point for thinking about the instrumentalization of climate change. Bakhtin’s conceptualization of human–world relationships, encapsulated in the concept of ‘cosmic terror’, places a strong focus on our perception of the ‘inhuman’. Suggesting a link between the perceived alienness and instability of the world and in the exploitation of the resulting fear of change by political and religious forces, Bakhtin asserts that the latter can only be resisted if our desire for a false stability in the world is overcome. The key to this overcoming of fear, for him, lies in recognizing and confronting the worldly relations of the human body. This consciousness represents the beginning of one’s ‘deautomatization’ from following established patterns of reactions to predicted or real changes. In the vein of several theorists and artists of his time who explored similar ‘deautomatization’ strategies – examples include Shklovsky’s ‘ostranenie’, Brecht’s ‘Verfremdung’, Artaud’s emotional ‘cruelty’ and Bataille’s ‘base materialism’ – Bakhtin proposes a more playful and widely accessible experimentation to deconstruct our ‘habitual picture of the world’. Experimentation is envisioned to take place across the material and the textual to increase possibilities for action. Through engaging with Bakhtin’s ideas, this article seeks to draw attention to relations between the imagination of the world and political agency, and the need to include these relations in our own experiments with creating climate change awareness
Brane-skyrmions and wrapped states
In the context of a brane world and including an induced curvature term in
the brane action, we obtain the effective lagrangian for the Goldstone bosons
(branons) associated with the spontaneous breaking of the translational
invariance in the bulk. In addition to the branons, this effective action has
Skyrmion-like solitonic states which can be understood as holes in the brane.
We study their main properties such as mass and size, the Skyrmion-branon
interaction and their possible fermionic quantization. We also consider states
where the brane is wrapped around the extra dimensions and their relation with
the brane-skyrmions. Finally, we extend our results to higher-dimensional
branes, such as those appearing in M-theory, where brane-skyrmions could also
be present.Comment: 35 pages, 7 figures. Revised version. Appendix and new references
included. To appear in Phys. Rev.
A schematic model for QCD I: Low energy meson states
A simple model for QCD is presented, which is able to reproduce the meson
spectrum at low energy. The model is a Lipkin type model for quarks coupled to
gluons. The basic building blocks are pairs of quark-antiquarks coupled to a
definite flavor and spin. These pairs are coupled to pairs of gluons with spin
zero. The multiplicity problem, which dictates that a given experimental state
can be described in various manners, is removed when a particle-mixing
interaction is turned on. In this first paper of a series we concentrates on
the discussion of meson states at low energy, the so-called zero temperature
limit of the theory. The treatment of baryonic states is indicated, also.Comment: 29 pages, 6 figures. submitted to Phys. Rev.
Adsorption-desorption kinetics in nanoscopically confined oligomer films under shear
The method of molecular dynamics computer simulations is employed to study oligomer melts confined in ultra-thin films and subjected to shear. The focus is on the self-diffusion of oligomers near attractive surfaces and on their desorption, together with the effects of increasing energy of adsorption and shear. It is found that the mobility of the oligomers near an attractive surface is strongly decreased. Moreover, although shearing the system forces the chains to stretch parallel to the surfaces and thus increase the energy of adsorption per chain, flow also promotes desorption. The study of chain desorption kinetics reveals the molecular processes responsible for the enhancement of desorption under shear. They involve sequences of conformations starting with a desorbed tail and proceeding in a very fast, correlated, segment-by-segment manner to the desorption of the oligomers from the surfaces.
Scaling Laws and Effective Dimension in Lattice SU(2) Yang-Mills Theory with a Compactified Extra Dimension
Monte Carlo simulations are performed in a five-dimensional lattice SU(2)
Yang-Mills theory with a compactified extra dimension, and scaling laws are
studied. Our simulations indicate that as the compactification radius
decreases, the confining phase spreads more and more to the weak coupling
regime, and the effective dimension of the theory changes gradually from five
to four. Our simulations also indicate that the limit with
kept fixed exists both in the confining and deconfining phases if is
small enough, where is the lattice spacing in the four-dimensional
direction. We argue that the color degrees of freedom in QCD are confined only
for , where a rough estimate shows that lies
in the TeV range. Comments on deconstructing extra dimensions are given.Comment: 15 pages, TeX, 5 figure
Polydisperse star polymer solutions
We analyze the effect of polydispersity in the arm number on the effective
interactions, structural correlations and the phase behavior of star polymers
in a good solvent. The effective interaction potential between two star
polymers with different arm numbers is derived using scaling theory. The
resulting expression is tested against monomer-resolved molecular dynamics
simulations. We find that the theoretical pair potential is in agreement with
the simulation data in a much wider polydispersity range than other proposed
potentials. We then use this pair potential as an input in a many-body theory
to investigate polydispersity effects on the structural correlations and the
phase diagram of dense star polymer solutions. In particular we find that a
polydispersity of 10%, which is typical in experimental samples, does not
significantly alter previous findings for the phase diagram of monodisperse
solutions.Comment: 14 pages, 7 figure
The beam energy measurement system for the Beijing electron-positron collider
The beam energy measurement system (BEMS) for the upgraded Beijing
electron-positron collider BEPC-II is described. The system is based on
measuring the energies of Compton back-scattered photons. The relative
systematic uncertainty of the electron and positron beam energy determination
is estimated as 2 \cdot 10^{-5}. The relative uncertainty of the beam's energy
spread is about 6 %
Spontaneous Coherence and Collective Modes in Double-Layer Quantum Dot Systems
We study the ground state and the collective excitations of
parabolically-confined double-layer quantum dot systems in a strong magnetic
field. We identify parameter regimes where electrons form maximum density
droplet states, quantum-dot analogs of the incompressible states of the bulk
integer quantum Hall effect. In these regimes the Hartree-Fock approximation
and the time-dependent Hartree-Fock approximations can be used to describe the
ground state and collective excitations respectively. We comment on the
relationship between edge excitations of dots and edge magneto-plasmon
excitations of bulk double-layer systems.Comment: 20 pages (figures included) and also available at
http://fangio.magnet.fsu.edu/~jhu/Paper/qdot_cond.ps, replaced to fix figure
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