1,530 research outputs found
A Computational Investigation of Cardiac Caveolae as a Source of Persistent Sodium Current
Recent studies of cholesterol-rich membrane microdomains, called caveolae, reveal that caveolae are reservoirs of ârecruitableâ sodium ion channels. Caveolar channels constitute a substantial and previously unrecognized source of sodium current in cardiac cells. In this paper we model for the first time caveolar sodium currents and their contributions to cardiac action potential morphology. We show that the ÎČ-agonist-induced opening of caveolae may have substantial impacts on peak overshoot, maximum upstroke velocity, and ultimately conduction velocity. Additionally, we show that prolonged action potentials and the formation of potentially arrhythmogenic afterdepolarizations, can arise if caveolae open intermittently throughout the action potential. Our simulations suggest that caveolar sodium current may constitute a route, which is independent of channelopathies, to delayed repolarization and the arrhythmias associated with such delays
Multivariate assessments of activity-related skeletal changes: Interpreting Bell Beaker specialized male archery and social organization in Central Europe
Objectives
The Bell Beaker period witnessed the rise of individual inhumations with âwealthyâ burial contexts containing archery-related grave goods, leading archaeologists to label the individuals in these tombs as âarchers.â This study looks to (1) compare the skeletons from male âarcherâ burials with those from male ânon-archerâ burialsâthose not having archery-related grave goodsâin order to assess a possible link between burial context and physical activity, and (2) apply a biomechanics profile to evaluate whether the individuals associated with these âarcherâ burials practiced specialized archer activity.
Materials and Methods
The corpus (males only) included 46 âarchersâ and 40 ânon-archersâ from Bell Beaker individual inhumations. Osteological data included measurements, scores of entheseal changes, and a diagnosis of certain pathologies. Data analyses involved visual observations, hypothesis tests, dimension reduction, and MANOVA, with approaches aimed at exploring the treatment of data missingness.
Results
Measurement data revealed no differences between the two groups. Evaluations of entheseal changes found that ânon-archersâ had consistently more instances of bone surface modifications than âarchers.â Individual assessments of specialized archer occupation identified 11 possible specialized archers.
Discussion
These findings indicate a possible labor differentiation represented through the presence of a probably prestigious âarcherâ burial context. This suggests a link between grave good presence and labor, but not between a Bell Beaker archery occupation and an âarcherâ burial context. Data analyses support the application of biomechanics to osteological analyses in order to assess specialized activity on the skeleton
Scarf osteotomy versus metatarsophalangeal arthrodesis in forefoot first ray disorders: Comparison of functional outcomes
SummaryIntroductionScarf osteotomies of the first metatarsal and metatarsophalangeal arthrodesis are the two most frequent surgical forefoot reconstructive procedures.HypothesisWe compared functional results of isolated arthrodesis of the first metatarsophalangeal joint with an isolated Scarf osteotomy of the first metatarsal.Materials and methodsThis was a retrospective, observational, continuous study of patients operated between 1993 and 2008. After patients who had undergone a procedure on the lateral rays, extremely elderly patients, lost to follow-up patients and those with incomplete questionnaires had been excluded, there remained two comparable groups of 25 patients. Mean age was 60 in the arthrodesis group [41â70] and 59.8 in the Scarf group [47â71]. The Scarf group included 25 hallux valgus (100%) compared to 16 hallux valgus (64%) and nine hallux rigidus (36%) in the arthrodesis group. Complications were recorded. Evaluation of functional results was based on the most recent functional or quality of life scores (AOFAS, FFI, FAAM, SF 36) and a questionnaire on physical and athletic ability.ResultsThere was no significant difference in the rate of complications between the two groups. There was no difference in pain according to the AOFAS score with 35.6/40 (±6.5) in the Scarf group and 34.5 (±5.9) in the arthrodesis group. Global satisfaction was also similar between the Scarf and arthrodesis groups: 91.4% and 90% of very satisfied or satisfied patients, respectively. The FFI score was higher in the Scarf group than in the arthrodesis group: 8.6 (±20.1) and 19.8 (±17.7) respectively. Functional results were better in the Scarf group than in the arthrodesis group with a FAAM Daily Activity score of 80.2 (±12.1) compared to 68 (±7.2), a FAAM Sports Activity score of 29.7 (±6.7) compared to 25.2 (±7.6) and a FAAM Global Function score of 94% (±10.8) compared to 87% (±15.7), respectively. The Global SF36 score was higher in the Scarf group than in the arthrodesis group: 70.9% (±14.1) and 62.3% (±20.6) respectively, which was due to a higher Mental Health score in the Scarf group: 68.7% (±14.2) and 60.4% (±19.3) respectively. In the area of sports activities the Scarf group practiced more hiking than the arthrodesis group (74% versus 42% respectively). There was no difference for other activities.Discussion and conclusionThis study provides detailed information on the level of physical and sports activities that are practiced following these procedures, so that the patient can be better informed.Level of evidenceLevel III. Comparative retrospective
Stability of Horava-Lifshitz Black Holes in the Context of AdS/CFT
The anti--de Sitter/conformal field theory (AdS/CFT) correspondence is a
powerful tool that promises to provide new insights toward a full understanding
of field theories under extreme conditions, including but not limited to
quark-gluon plasma, Fermi liquid and superconductor. In many such applications,
one typically models the field theory with asymptotically AdS black holes.
These black holes are subjected to stringy effects that might render them
unstable. Ho\v{r}ava-Lifshitz gravity, in which space and time undergo
different transformations, has attracted attentions due to its power-counting
renormalizability. In terms of AdS/CFT correspondence, Ho\v{r}ava-Lifshitz
black holes might be useful to model holographic superconductors with Lifshitz
scaling symmetry. It is thus interesting to study the stringy stability of
Ho\v{r}ava-Lifshitz black holes in the context of AdS/CFT. We find that
uncharged topological black holes in Ho\v{r}ava-Lifshitz theory are
nonperturbatively stable, unlike their counterparts in Einstein gravity, with
the possible exceptions of negatively curved black holes with detailed balance
parameter close to unity. Sufficiently charged flat black holes for
close to unity, and sufficiently charged positively curved black
holes with close to zero, are also unstable. The implication to the
Ho\v{r}ava-Lifshitz holographic superconductor is discussed.Comment: 15 pages, 6 figures. Updated version accepted by Phys. Rev. D, with
corrections to various misprints. References update
A teleparallel model for the neutrino
The main result of the paper is a new representation for the Weyl Lagrangian
(massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e.
an orthonormal tetrad of covector fields. We write down a simple Lagrangian -
wedge product of axial torsion with a lightlike element of the coframe - and
show that variation of the resulting action with respect to the coframe
produces the Weyl equation. The advantage of our approach is that it does not
require the use of spinors, Pauli matrices or covariant differentiation. The
only geometric concepts we use are those of a metric, differential form, wedge
product and exterior derivative. Our result assigns a variational meaning to
the tetrad representation of the Weyl equation suggested by J.B.Griffiths and
R.A.Newing.Comment: 4 pages, REVTe
Complete Calabi-Yau metrics from Kahler metrics in D=4
In the present work the local form of certain Calabi-Yau metrics possessing a
local Hamiltonian Killing vector is described in terms of a single non linear
equation. The main assumptions are that the complex -form is of the form
, where is preserved by the Killing
vector, and that the space of the orbits of the Killing vector is, for fixed
value of the momentum map coordinate, a complex 4-manifold, in such a way that
the complex structure of the 4-manifold is part of the complex structure of the
complex 3-fold. The link with the solution generating techniques of [26]-[28]
is made explicit and in particular an example with holonomy exactly SU(3) is
found by use of the linearization of [26], which was found in the context of D6
branes wrapping a holomorphic 1-fold in a hyperkahler manifold. But the main
improvement of the present method, unlike the ones presented in [26]-[28], does
not rely in an initial hyperkahler structure. Additionally the complications
when dealing with non linear operators over the curved hyperkahler space are
avoided by use of this method.Comment: Version accepted for publication in Phys.Rev.
Semi-classical stability of AdS NUT instantons
The semi-classical stability of several AdS NUT instantons is studied.
Throughout, the notion of stability is that of stability at the one-loop level
of Euclidean Quantum Gravity. Instabilities manifest themselves as negative
eigenmodes of a modified Lichnerowicz Laplacian acting on the transverse
traceless perturbations. An instability is found for one branch of the
AdS-Taub-Bolt family of metrics and it is argued that the other branch is
stable. It is also argued that the AdS-Taub-NUT family of metrics are stable. A
component of the continuous spectrum of the modified Lichnerowicz operator on
all three families of metrics is found.Comment: 18 pages, 3 figures; references adde
Remarks on evolution of space-times in 3+1 and 4+1 dimensions
A large class of vacuum space-times is constructed in dimension 4+1 from
hyperboloidal initial data sets which are not small perturbations of empty
space data. These space-times are future geodesically complete, smooth up to
their future null infinity, and extend as vacuum space-times through their
Cauchy horizon. Dimensional reduction gives non-vacuum space-times with the
same properties in 3+1 dimensions.Comment: 10pp, exposition improved; final versio
Near-Constant Mean Curvature Solutions of the Einstein Constraint Equations with Non-Negative Yamabe Metrics
We show that sets of conformal data on closed manifolds with the metric in
the positive or zero Yamabe class, and with the gradient of the mean curvature
function sufficiently small, are mapped to solutions of the Einstein constraint
equations. This result extends previous work which required the conformal
metric to be in the negative Yamabe class, and required the mean curvature
function to be nonzero.Comment: 15 page
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