21,466 research outputs found
Transitions in turbulent rotating Rayleigh-B\'enard convection
Numerical simulations of rotating Rayleigh-B\'enard convection are presented
for both no slip and free slip boundaries. The goal is to find a criterion
distinguishing convective flows dominated by the Coriolis force from those
nearly unaffected by rotation. If one uses heat transport as an indicator of
which regime the flow is in, one finds that the transition between the flow
regimes always occurs at the same value of a certain combination of Reynolds,
Prandtl and Ekman numbers for both boundary conditions. If on the other hand
one uses the helicity of the velocity field to identify flows nearly
independent of rotation, one finds the transition at a different location in
parameter space
Recoverable Information and Emergent Conservation Laws in Fracton Stabilizer Codes
We introduce a new quantity, that we term recoverable information, defined
for stabilizer Hamiltonians. For such models, the recoverable information
provides a measure of the topological information, as well as a physical
interpretation, which is complementary to topological entanglement entropy. We
discuss three different ways to calculate the recoverable information, and
prove their equivalence. To demonstrate its utility, we compute recoverable
information for fracton models using all three methods where appropriate. From
the recoverable information, we deduce the existence of emergent
Gauss-law type constraints, which in turn imply emergent conservation
laws for point-like quasiparticle excitations of an underlying topologically
ordered phase.Comment: Added additional cluster model calculation (SPT example) and a new
section discussing the general benefits of recoverable informatio
Topological Entanglement Entropy of Fracton Stabilizer Codes
Entanglement entropy provides a powerful characterization of two-dimensional
gapped topological phases of quantum matter, intimately tied to their
description by topological quantum field theories (TQFTs). Fracton topological
orders are three-dimensional gapped topologically ordered states of matter, but
the existence of a TQFT description for these phases remains an open question.
We show that three-dimensional fracton phases are nevertheless characterized,
at least partially, by universal structure in the entanglement entropy of their
ground state wave functions. We explicitly compute the entanglement entropy for
two archetypal fracton models --- the `X-cube model' and `Haah's code' --- and
demonstrate the existence of a topological contribution that scales linearly in
subsystem size. We show via Schrieffer-Wolff transformations that the
topological entanglement of fracton models is robust against arbitrary local
perturbations of the Hamiltonian. Finally, we argue that these results may be
extended to characterize localization-protected fracton topological order in
excited states of disordered fracton models.Comment: published versio
Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers
We present a comprehensive study of the exchange bias effect in a model
system. Through numerical analysis of the exchange bias and coercive fields as
a function of the antiferromagnetic layer thickness we deduce the absolute
value of the averaged anisotropy constant of the antiferromagnet. We show that
the anisotropy of IrMn exhibits a finite size effect as a function of
thickness. The interfacial spin disorder involved in the data analysis is
further supported by the observation of the dual behavior of the interfacial
uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we
have observed that the antiferromagnetic uncompensated spins are dominantly
frozen with nearly no rotating spins due to the chemical intermixing, which
correlates to the inferred mechanism for the exchange bias.Comment: 4 pages, 3 figure
A Direct Elliptic Solver Based on Hierarchically Low-rank Schur Complements
A parallel fast direct solver for rank-compressible block tridiagonal linear
systems is presented. Algorithmic synergies between Cyclic Reduction and
Hierarchical matrix arithmetic operations result in a solver with arithmetic complexity and memory footprint. We provide a
baseline for performance and applicability by comparing with well known
implementations of the -LU factorization and algebraic multigrid
with a parallel implementation that leverages the concurrency features of the
method. Numerical experiments reveal that this method is comparable with other
fast direct solvers based on Hierarchical Matrices such as -LU and
that it can tackle problems where algebraic multigrid fails to converge
Abundant Methanol Masers but no New Evidence for Star Formation in GCM0.253+0.016
We present new observations of the quiescent giant molecular cloud
GCM0.253+0.016 in the Galactic center, using the upgraded Karl G. Jansky Very
Large Array. Observations were made at wavelengths near 1 cm, at K (24 to 26
GHz) and Ka (27 and 36 GHz) bands, with velocity resolutions of 1-3 km/s and
spatial resolutions of ~0.1 pc, at the assumed 8.4 kpc distance of this cloud.
The continuum observations of this cloud are the most sensitive yet made, and
reveal previously undetected emission which we attribute primarily to free-free
emission from external ionization of the cloud. In addition to the sensitive
continuum map, we produce maps of 12 molecular lines: 8 transitions of NH3 --
(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7) and (9,9), as well as the HC3N (3-2)
and (4-3) lines, and CH3OH 4(-1) - 3(0) the latter of which is known to be a
collisionally-excited maser. We identify 148 CH3OH 4(-1) - 3(0) (36.2 GHz)
sources, of which 68 have brightness temperatures in excess of the highest
temperature measured for this cloud (400 K) and can be confirmed to be masers.
The majority of these masers are concentrated in the southernmost part of the
cloud. We find that neither these masers nor the continuum emission in this
cloud provide strong evidence for ongoing star formation in excess of that
previously inferred by the presence of an H2O maser.Comment: 33 pages, 4 tables, 9 figures; ApJ Accepte
Diabetes distress, depressive, and anxiety symptoms in people with type 2 diabetes: a network analysis approach to understanding comorbidity
Objective
This study aimed to explore interactions between diabetes distress, depressive, and anxiety symptoms in a cohort of adults with type 2 diabetes using network analysis.
Research design and methods
Participants (N = 1,796) were from the Evaluation of Diabetes Insulin Treatment (EDIT) study from Quebec, Canada. A network of diabetes distress symptoms was estimated using the 17 items of the Diabetes Distress Scale (DDS-17). A second network was estimated using the 17 items of the DDS-17, the 9 depressive items of the Patient Health Questionnaire (PHQ-9), and the 7 anxiety items of the Generalized Anxiety Disorder Assessment (GAD-7). Network analysis was used to identify central symptoms, clusters of symptoms, and symptoms that may bridge between diabetes distress, depressive, and anxiety symptoms.
Results
Regimen-related and physician-related diabetes distress symptoms were amongst the most influential (most positive connections to others) in the diabetes distress network. Feeling like a failure (depression) was identified as a potential bridge between depression and diabetes distress, being highly connected to symptoms of diabetes distress. The anxiety symptoms of worrying too much and being unable to stop worrying were found to be bridge symptoms between both anxiety and depression symptoms, and anxiety and diabetes distress symptoms, respectively.
Conclusions
These findings suggest individual symptoms that might be influential to the development and maintenance of diabetes distress and mental health comorbidity in diabetes and warrant further investigation. Study limitations and potential for clinical applicability are discussed
Self-normalizing phase measurement in multimode terahertz spectroscopy based on photomixing of three lasers
Photomixing of two near-infrared lasers is well established for
continuous-wave terahertz spectroscopy. Photomixing of three lasers allows us
to measure at three terahertz frequencies simultaneously. Similar to Fourier
spectroscopy, the spectral information is contained in an nterferogram, which
is equivalent to the waveform in time-domain spectroscopy. We use one fixed
terahertz frequency \nu_ref to monitor temporal drifts of the setup, i.e., of
the optical path-length difference. The other two frequencies are scanned for
broadband high-resolution spectroscopy. The frequency dependence of the phase
is obtained with high accuracy by normalizing it to the data obtained at
\nu_ref, which eliminates drifts of the optical path-length difference. We
achieve an accuracy of about 1-2 microns or 10^{-8} of the optical path length.
This method is particularly suitable for applications in nonideal environmental
conditions outside of an air-conditioned laboratory.Comment: 5 pages, 5 figure
Aldosterone signaling through transient receptor potential melastatin 7 cation channel (TRPM7) and its α-kinase domain
We demonstrated a role for the Mg2 + transporter TRPM7, a bifunctional protein with channel and α-kinase domains, in aldosterone signaling. Molecular mechanisms underlying this are elusive. Here we investigated the function of TRPM7 and its α-kinase domain on Mg2 + and pro-inflammatory signaling by aldosterone. Kidney cells (HEK-293) expressing wild-type human TRPM7 (WThTRPM7) or constructs in which the α-kinase domain was deleted (ΔKinase) or rendered inactive with a point mutation in the ATP binding site of the α-kinase domain (K1648R) were studied. Aldosterone rapidly increased [Mg2 +]i and stimulated NADPH oxidase-derived generation of reactive oxygen species (ROS) in WT hTRPM7 and TRPM7 kinase dead mutant cells. Translocation of annexin-1 and calpain-II and spectrin cleavage (calpain target) were increased by aldosterone in WT hTRPM7 cells but not in α-kinase-deficient cells. Aldosterone stimulated phosphorylation of MAP kinases and increased expression of pro-inflammatory mediators ICAM-1, Cox-2 and PAI-1 in Δkinase and K1648R cells, effects that were inhibited by eplerenone (mineralocorticoid receptor (MR) blocker). 2-APB, a TRPM7 channel inhibitor, abrogated aldosterone-induced Mg2 + responses in WT hTRPM7 and mutant cells. In 2-APB-treated ΔKinase and K1648R cells, aldosterone-stimulated inflammatory responses were unchanged. These data indicate that aldosterone stimulates Mg2 + influx and ROS production in a TRPM7-sensitive, kinase-insensitive manner, whereas activation of annexin-1 requires the TRPM7 kinase domain. Moreover TRPM7 α-kinase modulates inflammatory signaling by aldosterone in a TRPM7 channel/Mg2 +-independent manner. Our findings identify novel mechanisms for non-genomic actions of aldosterone involving differential signaling through MR-activated TRPM7 channel and α-kinase
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