12,712 research outputs found
Strong Correlation to Weak Correlation Phase Transition in Bilayer Quantum Hall Systems
At small layer separations, the ground state of a nu=1 bilayer quantum Hall
system exhibits spontaneous interlayer phase coherence and has a
charged-excitation gap E_g. The evolution of this state with increasing layer
separation d has been a matter of controversy. In this letter we report on
small system exact diagonalization calculations which suggest that a single
phase transition, likely of first order, separates coherent incompressible (E_g
>0) states with strong interlayer correlations from incoherent compressible
states with weak interlayer correlations. We find a dependence of the phase
boundary on d and interlayer tunneling amplitude that is in very good agreement
with recent experiments.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. Let
UMMS: constrained harmonic and anharmonic analyses of macromolecules based on elastic network models
UMass Morph Server (UMMS) has been developed for the broad impact on the study of molecular dynamics (MD). The elastic network model (ENM) of a given macromolecule has been proven as a useful tool for analyzing thermal behaviors locally and predicting folding pathways globally. UMMS utilizes coarse-grained ENMs at various levels. These simplifications remarkably save computation time compared with all-atom MD simulations so that one can bring down massive computational problems from a supercomputer to a PC. To improve computational efficiency and physical reality of ENMs, the symmetry-constrained, rigid-cluster, hybrid and chemical-bond ENMs have been developed and implemented at UMMS. One can request both harmonic normal mode analysis of a single macromolecule and anharmonic pathway generation between two conformations of a same molecule using elastic network interpolation at
Spin mapping, phase diagram, and collective modes in double layer quantum Hall systems at
An exact spin mapping is identified to simplify the recently proposed
hard-core boson description (Demler and Das Sarma, Phys. Rev. Lett., to be
published) of the bilayer quantum Hall system at filling factor 2. The
effective spin model describes an easy-plane ferromagnet subject to an external
Zeeman field. The phase diagram of this effective model is determined exactly
and found to agree with the approximate calculation of Demler and Das Sarma,
while the Goldstone-mode spectrum, order parameter stiffness and
Kosterlitz-Thouless temperature in the canted antiferromagnetic phase are
computed approximately.Comment: 4 pages with 2 figures include
Single-mode approximation and effective Chern-Simons theories for quantum Hall systems
A unified description of elementary and collective excitations in quantum
Hall systems is presented within the single-mode approximation (SMA) framework,
with emphasis on revealing an intimate link with Chern-Simons theories. It is
shown that for a wide class of quantum Hall systems the SMA in general yields,
as an effective theory, a variant of the bosonic Chern-Simons theory. For
single-layer systems the effective theory agrees with the standard Chern-Simons
theory at long wavelengths whereas substantial deviations arise for collective
excitations in bilayer systems. It is suggested, in particular, that Hall-drag
experiments would be a good place to detect out-of-phase collective excitations
inherent to bilayer systems. It is also shown that the intra-Landau-level modes
bear a similarity in structure (though not in scale) to the inter-Landau-level
modes, and its implications on the composite-fermion and composite-boson
theories are discussed.Comment: 9 pages, Revtex
PseudoSkyrmion Effects on Tunneling Conductivity in Coherent Bilayer Quantum Hall States at
We present a mechamism why interlayer tunneling conductivity in coherent
bilayer quantum Hall states at is anomalously large, but finite in the
recent experiment. According to the mechanism, pseudoSkyrmions causes the
finite conductivity, although there exists an expectation that dissipationless
tunneling current arises in the state. PseudoSkyrmions have an intrinsic
polarization field perpendicular to the layers, which causes the dissipation.
Using the mechanism we show that the large peak in the conductivity remains for
weak parallel magnetic field, but decay rapidly after its strength is beyond a
critical one, Tesla.Comment: 6 pages, no figure
Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition
Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure
Simulating Human Tasks Using Simple Natural Language Instructions
We report a simple natural language interface to a human task simulation system that graphically displays the performance of goal-directed tasks by an agent in a workspace. The inputs to the system are simple natural language commands requiring achievement of spatial relationships among objects in the workspace. To animate the behaviors denoted by instructions, a semantics of action verbs and locative expressions is devised in terms of physically based components, in particular geometric or spatial relations among the relevant objects. To generate human body motions to achieve such geometric goals, motion strategies and a planner that used them are devised. The basic idea for the motion strategies is to use commonsensical geometric relationships to determine appropriate body motions. Motion strategies for a given goal specify possibly overlapping subgoals of the relevant body parts in such a way achieving the subgoals makes the goals achieved without collision with objects in the workspace. A motion plan generated using the motion strategies is basically a chart of temporally overlapping goal conditions of the relevant body parts. This motion plan is animated by sending it to a motion human controller, which incrementally finds joint angles of the agent\u27s body that satisfy the goal conditions in the motion plan, and display the body\u27s configurations determined by the joint angles
Persistent Currents and Dissipation in Narrow Bilayer Quantum Hall Bars
Bilayer quantum Hall states support a flow of nearly dissipationless
staggered current which can only decay through collective channels. We study
the dominant finite-temperature dissipation mechanism which in narrow bars is
driven by thermal nucleation of pseudospin solitons. We find the
finite-temperature resistivity, predict the resulting staggered current-voltage
characteristics, and calculate the associated zero-temperature critical
staggered current and gate voltage.Comment: 4 pgs. REVTeX, 3 eps figure
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