297 research outputs found
Properties of an affine transport equation and its holonomy
An affine transport equation was used recently to study properties of angular
momentum and gravitational-wave memory effects in general relativity. In this
paper, we investigate local properties of this transport equation in greater
detail. Associated with this transport equation is a map between the tangent
spaces at two points on a curve. This map consists of a homogeneous (linear)
part given by the parallel transport map along the curve plus an inhomogeneous
part, which is related to the development of a curve in a manifold into an
affine tangent space. For closed curves, the affine transport equation defines
a "generalized holonomy" that takes the form of an affine map on the tangent
space. We explore the local properties of this generalized holonomy by using
covariant bitensor methods to compute the generalized holonomy around geodesic
polygon loops. We focus on triangles and "parallelogramoids" with sides formed
from geodesic segments. For small loops, we recover the well-known result for
the leading-order linear holonomy ( Riemann area), and we derive
the leading-order inhomogeneous part of the generalized holonomy (
Riemann area). Our bitensor methods let us naturally compute
higher-order corrections to these leading results. These corrections reveal the
form of the finite-size effects that enter into the holonomy for larger loops;
they could also provide quantitative errors on the leading-order results for
finite loops.Comment: 18 pages, 4 figures, new short section (Sec. 5) in v3; updated to
match article published in GR
The Hidden Dichotomy in the Law of Morality
This Comment will begin by exploring the dichotomy itself, and then carefully distinguishing civil and religious morality. The analysis will then examine Lawrence and clarify how the opinion affected the dichotomy. Next, this Comment will apply the post-Lawrence understanding of the rational basis test to several issues of concern raised by opponents of the decision. Finally, this Comment will speculate as to the possible implications of Lawrence for moral issues lying on the horizon
The Hidden Dichotomy in the Law of Morality
This Comment will begin by exploring the dichotomy itself, and then carefully distinguishing civil and religious morality. The analysis will then examine Lawrence and clarify how the opinion affected the dichotomy. Next, this Comment will apply the post-Lawrence understanding of the rational basis test to several issues of concern raised by opponents of the decision. Finally, this Comment will speculate as to the possible implications of Lawrence for moral issues lying on the horizon
ACTH: The Uninhibitable (or is it)?
Adrenal corticotropic hormone, or ACTH, is a peptide hormone secreted by the anterior pituitary gland. The full-length peptide is 39 amino acids long. ACTH signals through a G-protein linked receptor in humans, using the adenylyl cyclase pathway. Potassium and chloride channels have also been implicated in human ACTH signaling.
Tetrahymena thermophila are free-living, ciliated ptotozoans. These organisms exhibit avoidance behavior toward many polycationic peptides, which serve as chemorepellents. The reason for this is unknown; however, it is hypothesized that natural predators of T. thermophila secrete polycationic peptides, and that polycation avoidance allows T. thermophila to escape predation. We obtained a number of peptides derived from ACTH, including ACTH 1-39, ACTH 1-24, ACTH 11-24, ACTH 6-24, and ACTH 1-14. We hypothesized that the more highly charged peptide derivatives would be the most effective chemorepellents. This hypothesis was proven correct, with the most highly charged ACTH derivative, ACTH 6-24, demonstrated as the most effective chemorepellent. The least charged form of ACTH, ACTH 1-39, was least effective at causing avoidance.
We hypothesized that ACTH signaling in T. thermophila would use similar signaling pathways to those previously identified in humans. This, however, has not proven to be the case. We have tested G-protein inhibitors, adenylyl cyclase inhibitors, potassium channel blockers, and chloride channel blockers in T. thermphila. None of these drugs had any measurable effect on ACTH signaling. In addition, we have chelated extracellular calcium (using EGTA) and depleted ER calcium stores (using thapsigargin). Neither of these interventions inhibited ACTH signaling in this organism. Calcium channel blockers also failed to affect avoidance. This is highly unexpected, since all known chemorepellent pathways discovered in Tetrahymena to date are calcium-dependent. It is possible that ACTH is using a novel signaling pathway in T. thermophila. We hope that further testing will enable us to discover more about this signaling mechanism
The Meta-Wisdom of Crowds
It is well-known that people will adjust their first-order beliefs based on observations of others. We explore how such adjustments interact with second-order beliefs regarding universalism and relativism in a population. Across a range of simulations, we show that populations where individuals have a tendency toward universalism converge more quickly in coordination problems, and generate higher total payoffs, than do populations where individuals have a tendency toward relativism. Thus, in contexts where coordination is important, belief in universalism is advantageous. However, we also show, across a range of simulations, that universalism will enshrine inequalities and eliminate diversity, and in these cases it seems that relativism has its own advantages
Alleviating Polarity-Conflict at the Heterointerfaces of KTaO\u3csub\u3e3\u3c/sub\u3e/GdScO\u3csub\u3e3\u3c/sub\u3e Polar Complex-Oxides
We have synthesized and investigated the heterointerfaces of KTaO3 (KTO) and GdScO3 (GSO), which are both polar complex-oxides along the pseudo-cubic [001] direction. Since their layers have the same, conflicting net charges at interfaces, i.e., KO(−1)/ScO2(−1) or TaO2(+1)/GdO(+1), forming the heterointerface of KTO/GSO should be forbidden due to strong Coulomb repulsion, the so-called polarity conflict. However, we have discovered that atomic reconstruction occurs at the heterointerfaces between KTO thin-films and GSO substrates, which effectively alleviates the polarity conflict without destroying the hetero-epitaxy. Our result demonstrates one of the important ways to create artificial heterostructures from polar complex-oxides
Serotonin 5-HT\u3csub\u3e2\u3c/sub\u3e receptor activation prevents allergic asthma in a mouse model
© 2015 the American Physiological Society. Asthma is an inflammatory disease of the lung characterized by airways hyper-responsiveness (AHR), inflammation, and mucus hyperproduction. Current main-stream therapies include bronchodilators that relieve bronchoconstriction and inhaled glucocorticoids to reduce inflammation. The small molecule hormone and neurotransmitter serotonin has long been known to be involved in inflammatory processes; however, its precise role in asthma is unknown. We have previously established that activation of serotonin 5-hydroxytryptamine (5-HT)2A receptors has potent anti-inflammatory activity in primary cultures of vascular tissues and in the whole animal in vasculature and gut tissues. The 5-HT2A receptor agonist, (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] is especially potent. In this work, we have examined the effect of (R)-DOI in an established mouse model of allergic asthma. In the ovalbumin mouse model of allergic inflammation, we demonstrate that inhalation of (R)-DOI prevents the development of many key features of allergic asthma, including AHR, mucus hyperproduction, airways inflammation, and pulmonary eosinophil recruitment. Our results highlight a likely role of the 5-HT2 receptors in allergic airways disease and suggest that 5-HT2 receptor agonists may represent an effective and novel small molecule-based therapy for asthma
The role of orthogonal polynomials in the six-vertex model and its combinatorial applications
The Hankel determinant representations for the partition function and
boundary correlation functions of the six-vertex model with domain wall
boundary conditions are investigated by the methods of orthogonal polynomial
theory. For specific values of the parameters of the model, corresponding to
1-, 2- and 3-enumerations of Alternating Sign Matrices (ASMs), these
polynomials specialize to classical ones (Continuous Hahn, Meixner-Pollaczek,
and Continuous Dual Hahn, respectively). As a consequence, a unified and
simplified treatment of ASMs enumerations turns out to be possible, leading
also to some new results such as the refined 3-enumerations of ASMs.
Furthermore, the use of orthogonal polynomials allows us to express, for
generic values of the parameters of the model, the partition function of the
(partially) inhomogeneous model in terms of the one-point boundary correlation
functions of the homogeneous one.Comment: Talk presented by F.C. at the Short Program of the Centre de
Recherches Mathematiques: Random Matrices, Random Processes and Integrable
Systems, Montreal, June 20 - July 8, 200
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