2,666 research outputs found
A closer look at arrested spinodal decomposition in protein solutions
Concentrated aqueous solutions of the protein lysozyme undergo a liquid solid
transition upon a temperature quench into the unstable spinodal region below a
characteristic arrest temperature of Tf=15C. We use video microscopy and
ultra-small angle light scattering in order to investigate the arrested
structures as a function of initial concentration, quench temperature and rate
of the temperature quench. We find that the solid-like samples show all the
features of a bicontinuous network that is formed through an arrested spinodal
decomposition process. We determine the correlation length Xi and demonstrate
that Xi exhibits a temperature dependence that closely follows the critical
scaling expected for density fluctuations during the early stages of spinodal
decomposition. These findings are in agreement with an arrest scenario based on
a state diagram where the arrest or gel line extends far into the unstable
region below the spinodal line. Arrest then occurs when during the early stage
of spinodal decomposition the volume fraction phi2 of the dense phase
intersects the dynamical arrest threshold phi2Glass, upon which phase
separation gets pinned into a space-spanning gel network with a characteristic
length Xi
Quantum Hall Spherical Systems: the Filling Fraction
Within the newly formulated composite fermion hierarchy the filling fraction
of a spherical quantum Hall system is obtained when it can be expressed as an
odd or even denominator fraction. A plot of as a function
of for a constant number of particles (up to N=10001) exhibits structure
of the fractional quantum Hall effect. It is confirmed that
for all particle-hole conjugate systems, except systems with , and
.Comment: 3 pages, Revtex, 7 PostScript figures, submitted to Phys. Rev. B
Rapid Communicatio
Theory of Anomalous Quantum Hall Effects in Graphene
Recent successes in manufacturing of atomically thin graphite samples
(graphene) have stimulated intense experimental and theoretical activity. The
key feature of graphene is the massless Dirac type of low-energy electron
excitations. This gives rise to a number of unusual physical properties of this
system distinguishing it from conventional two-dimensional metals. One of the
most remarkable properties of graphene is the anomalous quantum Hall effect. It
is extremely sensitive to the structure of the system; in particular, it
clearly distinguishes single- and double-layer samples. In spite of the
impressive experimental progress, the theory of quantum Hall effect in graphene
has not been established. This theory is a subject of the present paper. We
demonstrate that the Landau level structure by itself is not sufficient to
determine the form of the quantum Hall effect. The Hall quantization is due to
Anderson localization which, in graphene, is very peculiar and depends strongly
on the character of disorder. It is only a special symmetry of disorder that
may give rise to anomalous quantum Hall effects in graphene. We analyze the
symmetries of disordered single- and double-layer graphene in magnetic field
and identify the conditions for anomalous Hall quantization.Comment: 13 pages (article + supplementary material), 5 figure
A new Proposal for a Quasielectron Trial Wavefunction for the FQHE on a Disk
In this letter, we propose a new quasielectron trial wavefunction for
interacting electrons in two dimensions moving in a strong magnetic field in a
disk geometry. Requiring that the trial wavefunction exhibits the correct
filling factor of a quasielectron wavefunction, we obtain angular
momentum eigenfunctions. The expectation values of the energy are calculated
and compared with the data of an exact numerical diagonalization.Comment: 8 page
Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope
Doppler and transit surveys are finding extrasolar planets of ever smaller
mass and radius, and are now sampling the domain of superEarths (1-3 Earth
radii). Recent results from the Doppler surveys suggest that discovery of a
transiting superEarth in the habitable zone of a lower main sequence star may
be possible. We evaluate the prospects for an all-sky transit survey targeted
to the brightest stars, that would find the most favorable cases for
photometric and spectroscopic characterization using the James Webb Space
Telescope (JWST). We use the proposed Transiting Exoplanet Survey Satellite
(TESS) as representative of an all-sky survey. We couple the simulated TESS
yield to a sensitivity model for the MIRI and NIRSpec instruments on JWST. We
focus on the TESS planets with radii between Earth and Neptune. Our simulations
consider secondary eclipse filter photometry using JWST/MIRI, comparing the 11-
and 15-micron bands to measure CO2 absorption in superEarths, as well as
JWST/NIRSpec spectroscopy of water absorption from 1.7-3.0 microns, and CO2
absorption at 4.3-microns. We project that TESS will discover about eight
nearby habitable transiting superEarths. The principal sources of uncertainty
in the prospects for JWST characterization of habitable superEarths are
superEarth frequency and the nature of superEarth atmospheres. Based on our
estimates of these uncertainties, we project that JWST will be able to measure
the temperature, and identify molecular absorptions (water, CO2) in one to four
nearby habitable TESS superEarths.Comment: accepted for PASP; added discussion and figure for habitable planets;
abridged Abstrac
Fractional Statistics in terms of the r-Generalized Fibonacci Sequences
We develop the basis of the two dimensional generalized quantum statistical
systems by using results on -generalized Fibonacci sequences. According to
the spin value of the 2d-quasiparticles, we distinguish four classes of
quantum statistical systems indexed by , ,
and . For quantum gases of quasiparticles
with , , we show that the statistical weights densities
are given by the integer hierarchies of Fibonacci sequences. This is a
remarkable result which envelopes naturally the Fermi and Bose statistics and
may be thought of as an alternative way to the Haldane interpolating
statistical method.Comment: Late
Fundamental constants in effective theory
There is a discussion between L. B. Okun, G. Veneziano and M. J. Duff,
concerning the number of fundamental dimensionful constants in physics
(physics/0110060). They advocated correspondingly 3, 2 and 0 fundamental
constants. Here we consider this problem on example of the effective
relativistic quantum field theory, which emerges in the low energy corner of
quantum liquids and which reproduces many features of our physics including
chiral fermions, gauge fields and dynamical gravity.Comment: LaTeX file, 9 pages, version submitted to JETP Letter
Topological Quantum Phase Transitions in Topological Superconductors
In this paper we show that BF topological superconductors (insulators) exibit
phase transitions between different topologically ordered phases characterized
by different ground state degeneracy on manifold with non-trivial topology.
These phase transitions are induced by the condensation (or lack of) of
topological defects. We concentrate on the (2+1)-dimensional case where the BF
model reduce to a mixed Chern-Simons term and we show that the superconducting
phase has a ground state degeneracy and not . When the symmetry is
, namely when both gauge fields are compact, this model is
not equivalent to the sum of two Chern-Simons term with opposite chirality,
even if naively diagonalizable. This is due to the fact that U(1) symmetry
requires an ultraviolet regularization that make the diagonalization
impossible. This can be clearly seen using a lattice regularization, where the
gauge fields become angular variables. Moreover we will show that the phase in
which both gauge fields are compact is not allowed dynamically.Comment: 5 pages, no figure
Recommended from our members
The Role of Microstructural Phenomena in Magnetic Thin Films
We have pursued two lines of research during the first year and a half of this work. In the main portion of the project we have performed fundamental investigations of the microstructure and crystallographic texture of Co based alloys deposited on Cr underlayers. This has included atomic resolution electron microscopy of the cross-sections of CoNiCr on Cr thin films, as well as studies of the microstructures and properties of magnetic thin films produced with interlayers of Cr. The other portion of our work has centered on understanding the crystallography and crystal structure of CoSm/Cr thin films. These CoSm films have the potential of being utilized as high density media, but their structure is not yet understood
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