557 research outputs found
The Allen-Cahn equation with dynamic boundary conditions and mass constraints
The Allen-Cahn equation, coupled with dynamic boundary conditions, has
recently received a good deal of attention. The new issue of this paper is the
setting of a rather general mass constraint which may involve either the
solution inside the domain or its trace on the boundary. The system of
nonlinear partial differential equations can be formulated as variational
inequality. The presence of the constraint in the evolution process leads to
additional terms in the equation and the boundary condition containing a
suitable Lagrange multiplier. A well-posedness result is proved for the related
initial value problem.Comment: Key words: Allen-Cahn equation, dynamic boundary condition, mass
constraint, variational inequality, Lagrange multiplie
Topology of supersymmetric N=1, D=4 supergravity horizons
All supersymmetric N=1, D=4 supergravity horizons have toroidal or spherical
topology, irrespective of whether the black hole preserves any supersymmetry.Comment: 17 pages, latex. Alterations to introduction and section 3.
Probing sporadic and familial Alzheimer's disease using induced pluripotent stem cells.
Our understanding of Alzheimer's disease pathogenesis is currently limited by difficulties in obtaining live neurons from patients and the inability to model the sporadic form of the disease. It may be possible to overcome these challenges by reprogramming primary cells from patients into induced pluripotent stem cells (iPSCs). Here we reprogrammed primary fibroblasts from two patients with familial Alzheimer's disease, both caused by a duplication of the amyloid-β precursor protein gene (APP; termed APP(Dp)), two with sporadic Alzheimer's disease (termed sAD1, sAD2) and two non-demented control individuals into iPSC lines. Neurons from differentiated cultures were purified with fluorescence-activated cell sorting and characterized. Purified cultures contained more than 90% neurons, clustered with fetal brain messenger RNA samples by microarray criteria, and could form functional synaptic contacts. Virtually all cells exhibited normal electrophysiological activity. Relative to controls, iPSC-derived, purified neurons from the two APP(Dp) patients and patient sAD2 exhibited significantly higher levels of the pathological markers amyloid-β(1-40), phospho-tau(Thr 231) and active glycogen synthase kinase-3β (aGSK-3β). Neurons from APP(Dp) and sAD2 patients also accumulated large RAB5-positive early endosomes compared to controls. Treatment of purified neurons with β-secretase inhibitors, but not γ-secretase inhibitors, caused significant reductions in phospho-Tau(Thr 231) and aGSK-3β levels. These results suggest a direct relationship between APP proteolytic processing, but not amyloid-β, in GSK-3β activation and tau phosphorylation in human neurons. Additionally, we observed that neurons with the genome of one sAD patient exhibited the phenotypes seen in familial Alzheimer's disease samples. More generally, we demonstrate that iPSC technology can be used to observe phenotypes relevant to Alzheimer's disease, even though it can take decades for overt disease to manifest in patients
Nernst branes from special geometry
We construct new black brane solutions in gauged
supergravity with a general cubic prepotential, which have entropy density
as and thus satisfy the Nernst Law. By using
the real formulation of special geometry, we are able to obtain analytical
solutions in closed form as functions of two parameters, the temperature
and the chemical potential . Our solutions interpolate between
hyperscaling violating Lifshitz geometries with at the
horizon and at infinity. In the zero temperature limit,
where the entropy density goes to zero, we recover the extremal Nernst branes
of Barisch et al, and the parameters of the near horizon geometry change to
.Comment: 37 pages. v2: numerical pre-factors of scalar fields q_A corrected in
Section 3. No changes to conclusions. References adde
A Black Ring with two Angular Momenta in Taub-NUT
We use the recently-constructed explicit duality transformation that relates
a rotating anti-D6-D4-D2-D0 black hole solution to a rotating M5-M2-P black
string to construct a non-supersymmetric black ring in Taub-NUT that has two
angular momenta, as well as M2 charges and M5 dipole moments. This is the first
black ring solution that has both dipole charges and rotation along the S^2 of
the horizon, and hence can be thought of as the "Pomeransky-Senkov" version of
the M5-M2 black ring in Taub-NUT. Its physics should provide a testing ground
for the applicability of the blackfold approach to charged rotating black
branes, and should elucidate the phase space of charged dipole rings in various
backgrounds.Comment: 20 pages, LaTe
The Socio-Cultural Benefits of Urban Agriculture: A Review of the Literature
© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Despite extensive literature on the socio-cultural services of urban open spaces, the role of food-producing spaces has not received sufficient attention. This hampers advocacy for preserving and growing urban agricultural activities, often dismissed on justifications that their contributions to overall food supply are negligible. To understand how the social benefits of urban agriculture have been measured, we conducted a systematic review of 272 peer-reviewed publications, which drew on insights from urban agriculture sites in 57 different countries. Through content analysis, we investigated socio-cultural benefits in four spheres: engaged and cohesive communities, health and well-being, economic opportunities, and education. The analysis revealed growth in research on the social impacts of gardens and farms, with most studies measuring the effects on community cohesion and engagement, followed by increased availability and consumption of fruits and vegetables associated with reduced food insecurity and better health. Fewer studies assessed the impact of urban farming on educational and economic outcomes. Quantifying the multiple ways in which urban agriculture provides benefits to people will empower planners and the private sector to justify future investments. These findings are also informative for research theorizing cities as socio-ecological systems and broader efforts to measure the benefits of urban agriculture, in its many forms.Peer reviewedFinal Published versio
Status of ANITA and ANITA-lite
We describe a new experiment to search for neutrinos with energies above 3 x
10^18 eV based on the observation of short duration radio pulses that are
emitted from neutrino-initiated cascades. The primary objective of the
ANtarctic Impulse Transient Antenna (ANITA) mission is to measure the flux of
Greisen-Zatsepin-Kuzmin (GZK) neutrinos and search for neutrinos from Active
Galactic Nuclei (AGN). We present first results obtained from the successful
launch of a 2-antenna prototype instrument (called ANITA-lite) that circled
Antarctica for 18 days during the 03/04 Antarctic campaign and show preliminary
results from attenuation length studies of electromagnetic waves at radio
frequencies in Antarctic ice. The ANITA detector is funded by NASA, and the
first flight is scheduled for December 2006.Comment: 9 pages, 8 figures, to be published in Proceedings of International
School of Cosmic Ray Astrophysics, 14th Course: "Neutrinos and Explosive
Events in the Universe", Erice, Italy, 2-13 July 200
Observations of the Askaryan Effect in Ice
We report on the first observations of the Askaryan effect in ice: coherent impulsive radio Cherenkov radiation from the charge asymmetry in an electromagnetic (EM) shower. Such radiation has been observed in silica sand and rock salt, but this is the first direct observation from an EM shower in ice. These measurements are important since the majority of experiments to date that rely on the effect for ultra-high energy neutrino detection are being performed using ice as the target medium. As part of the complete validation process for the Antarctic Impulsive Transient Antenna (ANITA) experiment, we performed an experiment at the Stanford Linear Accelerator Center (SLAC) in June 2006 using a 7.5 metric ton ice target, yielding results fully consistent with theoretical expectations
Absolute Objects and Counterexamples: Jones-Geroch Dust, Torretti Constant Curvature, Tetrad-Spinor, and Scalar Density
James L. Anderson analyzed the novelty of Einstein's theory of gravity as its
lack of "absolute objects." Michael Friedman's related work has been criticized
by Roger Jones and Robert Geroch for implausibly admitting as absolute the
timelike 4-velocity field of dust in cosmological models in Einstein's theory.
Using the Rosen-Sorkin Lagrange multiplier trick, I complete Anna Maidens's
argument that the problem is not solved by prohibiting variation of absolute
objects in an action principle. Recalling Anderson's proscription of
"irrelevant" variables, I generalize that proscription to locally irrelevant
variables that do no work in some places in some models. This move vindicates
Friedman's intuitions and removes the Jones-Geroch counterexample: some regions
of some models of gravity with dust are dust-free and so naturally lack a
timelike 4-velocity, so diffeomorphic equivalence to (1,0,0,0) is spoiled.
Torretti's example involving constant curvature spaces is shown to have an
absolute object on Anderson's analysis, viz., the conformal spatial metric
density. The previously neglected threat of an absolute object from an
orthonormal tetrad used for coupling spinors to gravity appears resolvable by
eliminating irrelevant fields. However, given Anderson's definition, GTR itself
has an absolute object (as Robert Geroch has observed recently): a change of
variables to a conformal metric density and a scalar density shows that the
latter is absolute.Comment: Minor editing, small content additions, added references. Forthcoming
in_Studies in History and Philosophy of Modern Physics_, June 200
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