1,734 research outputs found
Disorder effect on the localization/delocalization in incommensurate potential
The interplay between incommensurate (IC) and random potentials is studied in
a two-dimensional symplectic model with the focus on
localization/delocalization problem. With the IC potential only, there appear
wavefunctions localized along the IC wavevector while extended perpendicular to
it. Once the disorder potential is introduced, these turn into two-dimensional
anisotropic metallic states beyond the scale of the elastic mean free path, and
eventually becomes localized in both directions at a critical strength of the
disorder. Implications of these results to the experimental observation of the
IC-induced localization is discussed.Comment: 4 pages, 3 figures (7 files), RevTe
Nonaxisymmetric instability of rapidly rotating black hole in five dimensions
We present results from numerical solution of Einstein's equation in five
dimensions describing evolution of rapidly rotating black holes. We show, for
the first time, that the rapidly rotating black holes in higher dimensions are
unstable against nonaxisymmetric deformation; for the five-dimensional case,
the critical value of spin parameter for onset of the instability is .Comment: 4 pages, 3 figures, accepted for publication in PRD(R
Lyman Emitters beyond Redshift 5:The Dawn of Galaxy Formation
The 8m class telescopes in the ground-based optical astronomy together with
help from the ultra-sharp eye of the Hubble Space Telescope have enabled us to
observe forming galaxies beyond redshift . In particular, more than twenty
Ly-emitting galaxies have already been found at . These findings
provide us with useful hints to investigate how galaxies formed and then
evolved in the early universe. Further, detailed analysis of Ly
emission line profiles are useful in exploring the nature of the intergalactic
medium because the trailing edge of cosmic reionization could be close to -- 7, at which forming galaxies have been found recently. We also
discuss the importance of superwinds from forming galaxies at high redshift,
which has an intimate relationship between galaxies and the intergalactic
medium. We then give a review of early cosmic star formation history based on
recent progress in searching for Ly-emitting young galaxies beyond
redshift 5.Comment: 23 pages, 12 figures, jkas35.sty. To appear in the proceedings of the
APCTP WoFormation and Interaction of Galaxies, edited by Hyung Mok Leerkshop
o
Entropy and Barrier-Hopping Determine Conformational Viscoelasticity in Single Biomolecules
Biological macromolecules have complex and non-trivial energy landscapes,
endowing them a unique conformational adaptability and diversity in function.
Hence, understanding the processes of elasticity and dissipation at the
nanoscale is important to molecular biology and also emerging fields such as
nanotechnology. Here we analyse single molecule fluctuations in an atomic force
microscope (AFM) experiment using a generic model of biopolymer viscoelasticity
that importantly includes sources of local `internal' conformational
dissipation. Comparing two biopolymers, dextran and cellulose, polysaccharides
with and without the well-known `chair-to-boat' transition, reveals a signature
of this simple conformational change as minima in both the elasticity and
internal friction around a characteristic force. A calculation of two-state
populations dynamics offers a simple explanation in terms of an elasticity
driven by the entropy, and friction by barrier-controlled hopping, of
populations on a landscape. The microscopic model, allows quantitative mapping
of features of the energy landscape, revealing unexpectedly slow dynamics,
suggestive of an underlying roughness to the free energy.Comment: 25 pages, 7 figures, naturemag.bst, modified nature.cls
(naturemodified.cls
Inverse scattering method for square matrix nonlinear Schr\"odinger equation under nonvanishing boundary conditions
Matrix generalization of the inverse scattering method is developed to solve
the multicomponent nonlinear Schr\"odinger equation with nonvanishing boundary
conditions. It is shown that the initial value problem can be solved exactly.
The multi-soliton solution is obtained from the Gel'fand--Levitan--Marchenko
equation.Comment: 25 pages, 2 figures; (v2) title changed, typos in equations
corrected, sec.3.1 modified and extende
Gravitational waves from black hole-neutron star binaries I: Classification of waveforms
Using our new numerical-relativity code SACRA, long-term simulations for
inspiral and merger of black hole (BH)-neutron star (NS) binaries are
performed, focusing particularly on gravitational waveforms. As the initial
conditions, BH-NS binaries in a quasiequilibrium state are prepared in a
modified version of the moving-puncture approach. The BH is modeled by a
nonspinning moving puncture and for the NS, a polytropic equation of state with
and the irrotational velocity field are employed. The mass ratio of
the BH to the NS, , is chosen in the range between 1.5
and 5. The compactness of the NS, defined by , is chosen to be between 0.145 and 0.178. For a large value of for
which the NS is not tidally disrupted and is simply swallowed by the BH,
gravitational waves are characterized by inspiral, merger, and ringdown
waveforms. In this case, the waveforms are qualitatively the same as that from
BH-BH binaries. For a sufficiently small value of Q \alt 2, the NS may be
tidally disrupted before it is swallowed by the BH. In this case, the amplitude
of the merger and ringdown waveforms is very low, and thus, gravitational waves
are characterized by the inspiral waveform and subsequent quick damping. The
difference in the merger and ringdown waveforms is clearly reflected in the
spectrum shape and in the "cut-off" frequency above which the spectrum
amplitude steeply decreases. When an NS is not tidally disrupted (e.g., for
Q=5), kick velocity, induced by asymmetric gravitational wave emission, agrees
approximately with that derived for the merger of BH-BH binaries, whereas for
the case that the tidal disruption occurs, the kick velocity is significantly
suppressed.Comment: 25 pages, 3 jpg figures, accepted for publication in PRD; erratum is
added on Jul 23. 201
Inferring the neutron star equation of state from binary inspiral waveforms
The properties of neutron star matter above nuclear density are not precisely
known. Gravitational waves emitted from binary neutron stars during their late
stages of inspiral and merger contain imprints of the neutron-star equation of
state. Measuring departures from the point-particle limit of the late inspiral
waveform allows one to measure properties of the equation of state via
gravitational wave observations. This and a companion talk by J. S. Read
reports a comparison of numerical waveforms from simulations of inspiraling
neutron-star binaries, computed for equations of state with varying stiffness.
We calculate the signal strength of the difference between waveforms for
various commissioned and proposed interferometric gravitational wave detectors
and show that observations at frequencies around 1 kHz will be able to measure
a compactness parameter and constrain the possible neutron-star equations of
state.Comment: Talk given at the 12th Marcel Grossman Meeting, Paris, France, 12-18
Jul 200
Gravitational waves and neutrino emission from the merger of binary neutron stars
Numerical simulations for the merger of binary neutron stars are performed in
full general relativity incorporating a finite-temperature (Shen's) equation of
state (EOS) and neutrino cooling for the first time. It is found that for this
stiff EOS, a hypermassive neutron star (HMNS) with a long lifetime (
ms) is the outcome for the total mass \alt 3.0M_{\odot}. It is shown that the
typical total neutrino luminosity of the HMNS is --
ergs/s and the effective amplitude of gravitational waves from the HMNS is
4-- at --2.5 kHz for a source distance of 100 Mpc. We
also present the neutrino luminosity curve when a black hole is formed for the
first time.Comment: 4 pages, 4 figures (Fig.2 is in low resolution), Accepted for
publication in PR
Influence of self-gravity on the runaway instability of black hole-torus systems
Results from the first fully general relativistic numerical simulations in
axisymmetry of a system formed by a black hole surrounded by a self-gravitating
torus in equilibrium are presented, aiming to assess the influence of the torus
self-gravity on the onset of the runaway instability. We consider several
models with varying torus-to-black hole mass ratio and angular momentum
distribution orbiting in equilibrium around a non-rotating black hole. The tori
are perturbed to induce the mass transfer towards the black hole. Our numerical
simulations show that all models exhibit a persistent phase of axisymmetric
oscillations around their equilibria for several dynamical timescales without
the appearance of the runaway instability, indicating that the self-gravity of
the torus does not play a critical role favoring the onset of the instability,
at least during the first few dynamical timescales.Comment: To appear on Phys.Rev.Let
Design of Practical Superconducting DC Power Cable With REBCO Coated Conductors
critical current density of a superconductor in a parallel magnetic field. It was expected that a cable with a high current-carrying capacity could be realized with REBa2Cu3O7-σ (REBCO) coated conductors. However, the critical current density in most commercial coated conductors does not increase but slightly decreases with increasing parallel magnetic field. Nevertheless, the critical current density in the parallel magnetic field is remarkably higher than that in a normal in-plane magnetic field, and it is possible to construct a dc cable with a higher current-carrying capacity using this characteristic in comparison with conventional superconducting cables. In this paper, we propose a new design of dc power cable suitable for present commercial coated conductors. The optimal condition of the cable is discussed
- …