15,987 research outputs found
Effect of Anisotropy on the Localization in a Bifractal System
Bifractal is a highly anisotropic structure where planar fractals are stacked
to form a 3-dimensional lattice. The localization lengths along fractal
structure for the Anderson model defined on a bifractal are calculated. The
critical disorder and the critical exponent of the localization lengths are
obtained from the finite size scaling behavior. The numerical results are in a
good agreement with previous results which have been obtained from the
localization lengths along the perpendicular direction. This suggests that the
anisotropy of the embedding lattice structure is irrelevant to the critical
properties of the localization.Comment: 3 pages, source TeX file and 3 epsi figures. submitted to PR
Contribution of proline to the pre-structuring tendency of transient helical secondary structure elements in intrinsically disordered proteins
Background IDPs function without relying on three-dimensional structures. No clear rationale for such a behavior is available yet. PreSMos are transient secondary structures observed in the target-free IDPs and serve as the target-binding "active" motifs in IDPs. Prolines are frequently found in the flanking regions of PreSMos. Contribution of prolines to the conformational stability of the helical PreSMos in IDPs is investigated. Methods MD simulations are performed for several IDP segments containing a helical PreSMo and the flanking prolines. To measure the influence of flanking-prolines on the structural content of a helical PreSMo calculations were done for wild type as well as for mutant segments with Pro → Asp, His, Lys, or Ala. The change in the helicity due to removal of a proline was measured both for the PreSMo region and for the flanking regions. Results The α-helical content in ~ 70% of the helical PreSMos at the early stage of simulation decreases due to replacement of an N-terminal flanking proline by other residues whereas the helix content in nearly all PreSMos increases when the same replacements occur at the C-terminal flanking region. The helix destabilizing/terminating role of the C-terminal flanking prolines is more pronounced than the helix promoting effect of the N-terminal flanking prolines. General significance This work represents a novel example demonstrating that a proline is encoded in an IDP with a defined purpose. The helical PreSMos presage their target-bound conformations. As they most likely mediate IDP-target binding via conformational selection their helical content can be an important feature for IDP function. © 2013 Elsevier B.V
Hidden Quantum Markov Models and Open Quantum Systems with Instantaneous Feedback
Hidden Markov Models are widely used in classical computer science to model
stochastic processes with a wide range of applications. This paper concerns the
quantum analogues of these machines --- so-called Hidden Quantum Markov Models
(HQMMs). Using the properties of Quantum Physics, HQMMs are able to generate
more complex random output sequences than their classical counterparts, even
when using the same number of internal states. They are therefore expected to
find applications as quantum simulators of stochastic processes. Here, we
emphasise that open quantum systems with instantaneous feedback are examples of
HQMMs, thereby identifying a novel application of quantum feedback control.Comment: 10 Pages, proceedings for the Interdisciplinary Symposium on Complex
Systems in Florence, September 2014, minor correction
Gas of wormholes: a possible ground state of Quantum Gravity
In order to gain insight into the possible Ground State of Quantized
Einstein's Gravity, we have derived a variational calculation of the energy of
the quantum gravitational field in an open space, as measured by an asymptotic
observer living in an asymptotically flat space-time. We find that for Quantum
Gravity (QG) it is energetically favourable to perform its quantum fluctuations
not upon flat space-time but around a ``gas'' of wormholes of mass m_p, the
Planck mass (m_p ~= 10^{19}GeV) and average distance l_p, the Planck length
a_p(a_p ~= 10^{-33}cm). As a result, assuming such configuration to be a good
approximation to the true Ground State of Quantum Gravity, space-time, the
arena of physical reality, turns out to be well described by Wheeler's quantum
foam and adequately modeled by a space-time lattice with lattice constant l_p,
the Planck lattice.Comment: 56 pages, revised version to appear in General Relativity and
Gravitation (2000
The Superconductivity, Intragrain Penetration Depth and Meissner Effect of RuSr2(Gd,Ce)2Cu2O10+delta
The hole concentration (p)(delta), the transition temperature Tc, the
intragrain penetration depth lambda, and the Meissner effect were measured for
annealed RuSr2(Gd,Ce)2Cu2O10+delta samples. The intragrain superconducting
transition temperature Tc} varied from 17 to 40 K while the p changed by only
0.03 holes/CuO2. The intragrain superfluid-density 1/lambda^2 and the
diamagnetic drop of the field-cooled magnetization across Tc (the Meissner
effect), however, increased more than 10 times. All of these findings are in
disagreement with both the Tc vs. p and the Tc vs. 1/lambda^2 correlations
proposed for homogeneous cuprates, but are in line with a possible
phase-separation and the granularity associated with it.Comment: 7 pages, 6 figures, accepted for publication in Phys. Rev. B (May 2,
2002
Unusual Field-Dependence of the Intragrain Superconductive Transition in RuSr2EuCu2O8
A narrow intragrain phase-lock transition was observed in RuSr2EuCu2O8 under
a magnetic field H up to a few Tesla. The corresponding transition temperature,
T2, decreases rapidly (about 100 K/T at low fields) with H indicating that the
grains of RuSr2EuCu2O8 behave like a Josephson-junction-array instead of a
homogeneous bulk superconductor. Our data suggest that the bulk superconducting
transition may occur on a length scale well below the grain size of 2 to 6
micrometer
Extending the first-order post-Newtonian scheme in multiple systems to the second-order contributions to light propagation
In this paper, we extend the first-order post-Newtonian scheme in multiple
systems presented by Damour-Soffel-Xu to the second-order contribution to light
propagation without changing the virtueof the scheme on the linear partial
differential equations of the potential and vector potential. The spatial
components of the metric are extended to second order level both in a global
coordinates () and a local coordinates (). The
equations of (or ) are obtained from the field equations.The
relationship between and are presented in this paper also. In
special case of the solar system (isotropic condition is applied ()), we obtain the solution of . Finally, a further extension
of the second-order contributions in the parametrized post-Newtonian formalism
is discussed.Comment: Latex2e; 6 pages PS fil
X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters II: The Fraction of Galaxies Hosting Active Nuclei
We present a measurement of the fraction of cluster galaxies hosting X-ray
bright Active Galactic Nuclei (AGN) as a function of clustercentric distance
scaled in units of . Our analysis employs high quality Chandra X-ray
and Subaru optical imaging for 42 massive X-ray selected galaxy cluster fields
spanning the redshift range of . In total, our study involves
176 AGN with bright () optical counterparts above a keV flux
limit of . When excluding
central dominant galaxies from the calculation, we measure a cluster-galaxy AGN
fraction in the central regions of the clusters that is times lower
that the field value. This fraction increases with clustercentric distance
before becoming consistent with the field at . Our data
exhibit similar radial trends to those observed for star formation and
optically selected AGN in cluster member galaxies, both of which are also
suppressed near cluster centers to a comparable extent. These results strongly
support the idea that X-ray AGN activity and strong star formation are linked
through their common dependence on available reservoirs of cold gas.Comment: 9 Pages, 4 Figures, accepted for publication in MNRAS, please contact
Steven Ehlert ([email protected]) with any querie
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