933 research outputs found
Thermal state entanglement in harmonic lattices
We investigate the entanglement properties of thermal states of the harmonic
lattice in one, two and three dimensions. We establish the value of the
critical temperature for entanglement between neighbouring sites and give
physical reasons. Further sites are shown to be entangled only due to boundary
effects. Other forms of entanglement are addressed in the second part of the
paper by using the energy as witness of entanglement. We close with a
comprehensive diagram showing the different phases of entanglement versus
complete separability and propose techniques to swap and tune entanglement
experimentally.Comment: 9 pages, 4 figure
Phonon Thermal Transport of URu2Si2: Broken Translational Symmetry and Strong-Coupling of the Hidden Order to the Lattice
A dramatic increase in the total thermal conductivity (k) is observed in the
Hidden Order (HO) state of single crystal URu2Si2. Through measurements of the
thermal Hall conductivity, we explicitly show that the electronic contribution
to k is extremely small, so that this large increase in k is dominated by
phonon conduction. An itinerant BCS/mean-field model describes this behavior
well: the increase in kappa is associated with the opening of a large energy
gap at the Fermi Surface, thereby decreasing electron-phonon scattering. Our
analysis implies that the Hidden Order parameter is strongly coupled to the
lattice, suggestive of a broken symmetry involving charge degrees of freedom.Comment: 17 pages including figures, updated author institutions and
acknowledgement
Echoes in classical dynamical systems
Echoes arise when external manipulations to a system induce a reversal of its
time evolution that leads to a more or less perfect recovery of the initial
state. We discuss the accuracy with which a cloud of trajectories returns to
the initial state in classical dynamical systems that are exposed to additive
noise and small differences in the equations of motion for forward and backward
evolution. The cases of integrable and chaotic motion and small or large noise
are studied in some detail and many different dynamical laws are identified.
Experimental tests in 2-d flows that show chaotic advection are proposed.Comment: to be published in J. Phys.
Ferromagnetic phase transition for the spanning-forest model (q \to 0 limit of the Potts model) in three or more dimensions
We present Monte Carlo simulations of the spanning-forest model (q \to 0
limit of the ferromagnetic Potts model) in spatial dimensions d=3,4,5. We show
that, in contrast to the two-dimensional case, the model has a "ferromagnetic"
second-order phase transition at a finite positive value w_c. We present
numerical estimates of w_c and of the thermal and magnetic critical exponents.
We conjecture that the upper critical dimension is 6.Comment: LaTex2e, 4 pages; includes 6 Postscript figures; Version 2 has
expanded title as published in PR
Exchange Anisotropy in Epitaxial and Polycrystalline NiO/NiFe Bilayers
(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001)
substrates by ion beam sputtering in order to determine the effect that the
crystalline orientation of the NiO antiferromagnetic layer has on the
magnetization curve of the NiFe ferromagnetic layer. Simple models predict no
exchange anisotropy for the (001)-oriented surface, which in its bulk
termination is magnetically compensated. Nonetheless exchange anisotropy is
present in the epitaxial films, although it is approximately half as large as
in polycrystalline films that were grown simultaneously. Experiments show that
differences in exchange field and coercivity between polycrystalline and
epitaxial NiFe/NiO bilayers couples arise due to variations in induced surface
anisotropy and not from differences in the degree of compensation of the
terminating NiO plane. Implications of these observations for models of induced
exchange anisotropy in NiO/NiFe bilayer couples will be discussed.Comment: 23 pages in RevTex format, submitted to Phys Rev B
Membrane geometry with auxiliary variables and quadratic constraints
Consider a surface described by a Hamiltonian which depends only on the
metric and extrinsic curvature induced on the surface. The metric and the
curvature, along with the basis vectors which connect them to the embedding
functions defining the surface, are introduced as auxiliary variables by adding
appropriate constraints, all of them quadratic. The response of the Hamiltonian
to a deformation in each of the variables is examined and the relationship
between the multipliers implementing the constraints and the conserved stress
tensor of the theory established.Comment: 8 page
Anomalous magnetoresistance behavior of CoFe nano-oxide spin valves at low temperatures
We report magnetoresistance curves of CoFe nano-oxide specular spin valves of
MnIr/CoFe/nano-oxidized CoFe/CoFe/Cu/CoFe/nano-oxidized CoFe/Ta at different
temperatures from 300 to 20 K. We extend the Stoner-Wolfarth model of a common
spin valve to a specular spin valve, introducing the separation of the pinned
layer into two sublayers and their magnetic coupling across the nano-oxide. We
study the effect of different coupling/exchange (between the antiferromagnetic
layer and the bottom sublayer) field ratios on the magnetization and
magnetoresistance, corresponding with the experimentally observed anomalous
bumps in low temperature magnetoresistance curves.Comment: 4 pages; 3 figure
Altered Env conformational dynamics as a mechanism of resistance to peptideâtriazole HIVâ1 inactivators.
Background: We previously developed drug-like peptide triazoles (PTs) that target HIV-1 Envelope (Env) gp120,
potently inhibit viral entry, and irreversibly inactivate virions. Here, we investigated potential mechanisms of viral
escape from this promising class of HIV-1 entry inhibitors.
Results: HIV-1 resistance to cyclic (AAR029b) and linear (KR13) PTs was obtained by dose escalation in viral passaging
experiments. High-level resistance for both inhibitors developed slowly (relative to escape from gp41-targeted
C-peptide inhibitor C37) by acquiring mutations in gp120 both within (Val255) and distant to (Ser143) the putative PT
binding site. The similarity in the resistance profiles for AAR029b and KR13 suggests that the shared IXW pharmacophore
provided the primary pressure for HIV-1 escape. In single-round infectivity studies employing recombinant virus,
V255I/S143N double escape mutants reduced PT antiviral potency by 150- to 3900-fold. Curiously, the combined
mutations had a much smaller impact on PT binding affinity for monomeric gp120 (four to ninefold). This binding
disruption was entirely due to the V255I mutation, which generated few steric clashes with PT in molecular docking.
However, this minor effect on PT affinity belied large, offsetting changes to association enthalpy and entropy. The
escape mutations had negligible effect on CD4 binding and utilization during entry, but significantly altered both
binding thermodynamics and inhibitory potency of the conformationally-specific, anti-CD4i antibody 17b. Moreover,
the escape mutations substantially decreased gp120 shedding induced by either soluble CD4 or AAR029b.
Conclusions: Together, the data suggest that the escape mutations significantly modified the energetic landscape of
Envâs prefusogenic state, altering conformational dynamics to hinder PT-induced irreversible inactivation of Env. This
work therein reveals a unique mode of virus escape for HIV-1, namely, resistance by altering the intrinsic conformational
dynamics of the Env trimerpost-print4093 K
Nonequilibrium stationary states and equilibrium models with long range interactions
It was recently suggested by Blythe and Evans that a properly defined steady
state normalisation factor can be seen as a partition function of a fictitious
statistical ensemble in which the transition rates of the stochastic process
play the role of fugacities. In analogy with the Lee-Yang description of phase
transition of equilibrium systems, they studied the zeroes in the complex plane
of the normalisation factor in order to find phase transitions in
nonequilibrium steady states. We show that like for equilibrium systems, the
``densities'' associated to the rates are non-decreasing functions of the rates
and therefore one can obtain the location and nature of phase transitions
directly from the analytical properties of the ``densities''. We illustrate
this phenomenon for the asymmetric exclusion process. We actually show that its
normalisation factor coincides with an equilibrium partition function of a walk
model in which the ``densities'' have a simple physical interpretation.Comment: LaTeX, 23 pages, 3 EPS figure
Indication of Superconductivity at 35 K in Graphite-Sulfur Composites
We report magnetization measurements performed on graphite--sulfur composites
which demonstrate a clear superconducting behavior below the critical
temperature T = 35 K. The Meissner-Ochsenfeld effect, screening
supercurrents, and magnetization hysteresis loops characteristic of type-II
superconductors were measured. The results indicate that the superconductivity
occurs in a small sample fraction, possibly related to the sample surface.Comment: published versio
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