716 research outputs found
Possible field-tuned SIT in high-Tc superconductors: implications for pairing at high magnetic fields
The behavior of some high temperature superconductors (HTSC) such as and , at very high
magnetic field, is similar to that of thin films of amorphous InOx near the
magnetic field-tuned superconductor-insulator transition. Analyzing the InOx
data at high fields in terms of persisting local pairing amplitude, we argue by
analogy that local pairing amplitude also persists well into the dissipative
state of the HTSCs, the regime commonly denoted as the "normal state" in very
high magnetic field experiments.Comment: Revised figures and reference
Erosion waves: transverse instabilities and fingering
Two laboratory scale experiments of dry and under-water avalanches of
non-cohesive granular materials are investigated. We trigger solitary waves and
study the conditions under which the front is transversally stable. We show the
existence of a linear instability followed by a coarsening dynamics and finally
the onset of a fingering pattern. Due to the different operating conditions,
both experiments strongly differ by the spatial and time scales involved.
Nevertheless, the quantitative agreement between the stability diagram, the
wavelengths selected and the avalanche morphology reveals a common scenario for
an erosion/deposition process.Comment: 4 pages, 6 figures, submitted to PR
Order from Disorder in Graphene Quantum Hall Ferromagnet
Valley-polarized quantum Hall states in graphene are described by a
Heisenberg O(3) ferromagnet model, with the ordering type controlled by the
strength and sign of valley anisotropy. A mechanism resulting from electron
coupling to strain-induced gauge field, giving leading contribution to the
anisotropy, is described in terms of an effective random magnetic field aligned
with the ferromagnet z axis. We argue that such random field stabilizes the XY
ferromagnet state, which is a coherent equal-weight mixture of the and
valley states. Other implications such as the Berezinskii-Kosterlitz-Thouless
ordering transition and topological defects with half-integer charge are
discussed.Comment: 4 pages, 2 figure
Stability and instability in parametric resonance and quantum Zeno effect
A quantum mechanical version of a classical inverted pendulum is analyzed.
The stabilization of the classical motion is reflected in the bounded evolution
of the quantum mechanical operators in the Heisenberg picture. Interesting
links with the quantum Zeno effect are discussed.Comment: 6 pages, 3 figure
SecureKeeper: confidential zooKeeper using intel SGX
Cloud computing, while ubiquitous, still suffers from trust issues, especially for applications managing sensitive data. Third-party coordination services such as ZooKeeper and Consul are fundamental building blocks for cloud applications, but are exposed to potentially sensitive application data. Recently, hardware trust mechanisms such as Intel's Software Guard Extensions (SGX) offer trusted execution environments to shield application data from untrusted software, including the privileged Operating System (OS) and hypervisors. Such hardware support suggests new options for securing third-party coordination services. We describe SecureKeeper, an enhanced version of the ZooKeeper coordination service that uses SGX to preserve the confidentiality and basic integrity of ZooKeeper-managed data. SecureKeeper uses multiple small enclaves to ensure that (i) user-provided data in ZooKeeper is always kept encrypted while not residing inside an enclave, and (ii) essential processing steps that demand plaintext access can still be performed securely. SecureKeeper limits the required changes to the ZooKeeper code base and relies on Java's native code support for accessing enclaves. With an overhead of 11%, the performance of SecureKeeper with SGX is comparable to ZooKeeper with secure communication, while providing much stronger security guarantees with a minimal trusted code base of a few thousand lines of code
Particle Motion in Rapidly Oscillating Potentials: The Role of the Potential's Initial Phase
Rapidly oscillating potentials with a vanishing time average have been used
for a long time to trap charged particles in source-free regions. It has been
argued that the motion of a particle in such a potential can be approximately
described by a time independent effective potential, which does not depend upon
the initial phase of the oscillating potential. However, here we show that the
motion of a particle and its trapping condition significantly depend upon this
initial phase for arbitrarily high frequencies of the potential's oscillation.
We explain this novel phenomenon by showing that the motion of a particle is
determined by the effective potential stated in the literature only if its
initial conditions are transformed according to a transformation which we show
to significantly depend on the potential's initial phase for arbitrarily high
frequencies. We confirm our theoretical findings by numerical simulations.
Further, we demonstrate that the found phenomenon offers new ways to manipulate
the dynamics of particles which are trapped by rapidly oscillating potentials.
Finally, we propose a simple experiment to verify the theoretical findings of
this work.Comment: 9 pages, 8 figures, published in PR
Squeezing superfluid from a stone: Coupling superfluidity and elasticity in a supersolid
In this work we start from the assumption that normal solid to supersolid
(NS-SS) phase transition is continuous, and develop a phenomenological Landau
theory of the transition in which superfluidity is coupled to the elasticity of
the crystalline He lattice. We find that the elasticity does not affect the
universal properties of the superfluid transition, so that in an unstressed
crystal the well-known -anomaly in the heat capacity of the superfluid
transition should also appear at the NS-SS transition. We also find that the
onset of supersolidity leads to anomalies in the elastic constants near the
transition; conversely, inhomogeneous strains in the lattice can induce local
variations of the superfluid transition temperature, leading to a broadened
transition.Comment: 4 page
Murine Esophagus Expresses Glial-Derived Central Nervous System Antigens
Multiple sclerosis (MS) has been considered to specifically affect the central nervous system
(CNS) for a long time. As autonomic dysfunction including dysphagia can occur as accompanying
phenomena in patients, the enteric nervous system has been attracting increasing attention over
the past years. The aim of this study was to identify glial and myelin markers as potential target
structures for autoimmune processes in the esophagus. RT-PCR analysis revealed glial fibrillary
acidic protein (GFAP), proteolipid protein (PLP), and myelin basic protein (MBP) expression, but
an absence of myelin oligodendrocyte glycoprotein (MOG) in the murine esophagus. Selected
immunohistochemistry for GFAP, PLP, and MBP including transgenic mice with cell-type specific
expression of PLP and GFAP supported these results by detection of (1) GFAP, PLP, and MBP in
Schwann cells in skeletal muscle and esophagus; (2) GFAP, PLP, but no MBP in perisynaptic Schwann
cells of skeletal and esophageal motor endplates; (3) GFAP and PLP, but no MBP in glial cells
surrounding esophageal myenteric neurons; and (4) PLP, but no GFAP and MBP in enteric glial cells
forming a network in the esophagus. Our results pave the way for further investigations regarding
the involvement of esophageal glial cells in the pathogenesis of dysphagia in MS
Nonlinear waves in counter-current gas–liquid film flow
We investigate the dynamics of a thin laminar liquid film flowing under gravity
down the lower wall of an inclined channel when turbulent gas flows above the
film. The solution of the full system of equations describing the gas–liquid flow faces
serious technical difficulties. However, a number of assumptions allow isolating the
gas problem and solving it independently by treating the interface as a solid wall.
This permits finding the perturbations to pressure and tangential stresses at the
interface imposed by the turbulent gas in closed form. We then analyse the liquid
film flow under the influence of these perturbations and derive a hierarchy of model
equations describing the dynamics of the interface, i.e. boundary-layer equations, a
long-wave model and a weakly nonlinear model, which turns out to be the Kuramoto–
Sivashinsky equation with an additional term due to the presence of the turbulent
gas. This additional term is dispersive and destabilising (for the counter-current case;
stabilizing in the co-current case). We also combine the long-wave approximation with
a weighted-residual technique to obtain an integral-boundary-layer approximation
that is valid for moderately large values of the Reynolds number. This model is
then used for a systematic investigation of the flooding phenomenon observed in
various experiments: as the gas flow rate is increased, the initially downward-falling
film starts to travel upwards while just before the wave reversal the amplitude of the
waves grows rapidly. We confirm the existence of large-amplitude stationary waves by
computing periodic travelling waves for the integral-boundary-layer approximation
and we corroborate our travelling-wave results by time-dependent computations
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