3,100 research outputs found
Planetary Collisions outside the Solar System: Time Domain Characterization of Extreme Debris Disks
Luminous debris disks of warm dust in the terrestrial planet zones around
solar-like stars are recently found to vary, indicative of ongoing large-scale
collisions of rocky objects. We use Spitzer 3.6 and 4.5 {\mu}m time-series
observations in 2012 and 2013 (extended to 2014 in one case) to monitor 5 more
debris disks with unusually high fractional luminosities ("extreme debris
disk"), including P1121 in the open cluster M47 (80 Myr), HD 15407A in the AB
Dor moving group (80 Myr), HD 23514 in the Pleiades (120 Myr), HD 145263 in the
Upper Sco Association (10 Myr), and the field star BD+20 307 (>1 Gyr). Together
with the published results for ID8 in NGC 2547 (35 Myr), this makes the first
systematic time-domain investigation of planetary impacts outside the solar
system. Significant variations with timescales shorter than a year are detected
in five out of the six extreme debris disks we have monitored. However,
different systems show diverse sets of characteristics in the time domain,
including long-term decay or growth, disk temperature variations, and possible
periodicity.Comment: 50 pages, 14 figures, 9 tables; Accepted for publication in the
Astrophysical Journa
Deep Learning with Photonic Neural Cellular Automata
Rapid advancements in deep learning over the past decade have fueled an
insatiable demand for efficient and scalable hardware. Photonics offers a
promising solution by leveraging the unique properties of light. However,
conventional neural network architectures, which typically require dense
programmable connections, pose several practical challenges for photonic
realizations. To overcome these limitations, we propose and experimentally
demonstrate Photonic Neural Cellular Automata (PNCA) for photonic deep learning
with sparse connectivity. PNCA harnesses the speed and interconnectivity of
photonics, as well as the self-organizing nature of cellular automata through
local interactions to achieve robust, reliable, and efficient processing. We
utilize linear light interference and parametric nonlinear optics for
all-optical computations in a time-multiplexed photonic network to
experimentally perform self-organized image classification. We demonstrate
binary classification of images in the fashion-MNIST dataset using as few as 3
programmable photonic parameters, achieving an experimental accuracy of 98.0%
with the ability to also recognize out-of-distribution data. The proposed PNCA
approach can be adapted to a wide range of existing photonic hardware and
provides a compelling alternative to conventional photonic neural networks by
maximizing the advantages of light-based computing whilst mitigating their
practical challenges. Our results showcase the potential of PNCA in advancing
photonic deep learning and highlights a path for next-generation photonic
computers
Performance of cages as large animal-exclusion devices in the deep sea
Sedimentary, deep-sea communities include megafaunal animals (e.g., sea cucumbers, brittle stars, crabs) and demersal fishes, collectively termed the large, motile epifauna (LME). Individuals of the LME are common, and their biomass approximates that of the macrofauna. Based on analogies with shallow-water animals, they are likely to be sources of mortality for the infauna and to create spatial and temporal heterogeneity in the community. Given present theories of deep-sea community organization, such effects could be important. Unfortunately, this hypothesis has not been tested because of the difficulty of conducting experiments in the deep sea and because tools for manipulating the LME have not been developed. We studied the suitability of exclusion cages for this purpose at 780 m depth in San Diego Trough. We placed 16 cages of two mesh sizes for 4.5 months over regions of the seafloor that appeared free of LME. Time-lapse photographs of a cage and a control plot coupled with observations of all cages at the end of the experiment indicated that small (1.27-cm Ă 1.27-cm square)-mesh cages were effective at excluding LME. Further, the cages were essentially free of cage artifacts that have been reported in shallow-water studies. Large, mobile and disruptive animals (e.g., fishes, crabs) did not establish long-term residence adjacent to or on the cages. Bio-fouling slightly reduced the open surface area of the cage mesh, potentially reducing flow through the cage, but the composition of surface sediments in terms of organic C and N, phytoplankton-derived pigments, and grain size was indistinguishable between cages and control areas. Activities of excess 234Th were significantly higher (average = 37%) inside of small-mesh cages, which might suggest enhanced particulate deposition inside cages. However, this measurement was an artifact of experimental manipulation. Particles that accumulated on the cage during the experiment were dislodged and settled to the seafloor when the cage was opened just prior to sampling. These particles would have been highly enriched in 234Th, and their inclusion in core samples artificially inflated the calculated sediment accumulation rates inside cages. Therefore, the cages performed well; they excluded the targeted LME without causing artifacts and thus should be useful for experimental study of a group of animals that may have substantial impact on the structure and organization of deep-sea communities
Configurational Entropy of Folded Proteins and its Importance for Intrinsically Disordered Proteins
Many pairwise additive force fields are in active use for intrinsically
disordered proteins (IDPs) and regions (IDRs), some of which modify energetic
terms to improve description of IDPs/IDRs, but are largely in disagreement with
solution experiments for the disordered states. We have evaluated
representative pairwise and many-body protein and water force fields against
experimental data on representative IDPs and IDRs, a peptide that undergoes a
disorder-to-order transition, and for seven globular proteins ranging in size
from 130-266 amino acids. We find that force fields with the largest
statistical fluctuations consistent with the radius of gyration and universal
Lindemann values for folded states simultaneously better describe IDPs and IDRs
and disorder to order transitions. Hence the crux of what a force field should
exhibit to well describe IDRs/IDPs is not just the balance between protein and
water energetics, but the balance between energetic effects and configurational
entropy of folded states of globular proteins
ALTERATION OF THE EPHA2/EPHRIN-A SIGNALING AXIS IN PSORIATIC EPIDERMIS
EphA2 is a receptor tyrosine kinase (RTK) that triggers keratinocyte differentiation upon activation and subsequently down-regulation by ephrin-A1 ligand. The objective for this study was to determine if the EphA2/ephrin-A1 signaling axis was altered in psoriasis, an inflammatory skin condition where keratinocyte differentiation is abnormal. Microarray analysis of skin biopsies from psoriasis patients revealed increased mRNA transcripts for several members of this RTK family in plaques, including the EphA1, EphA2 and EphA4 subtypes prominently expressed by keratinocytes. Of these, EphA2 showed the greatest up-regulation, a finding that was confirmed by quantitative RT-PCR, IHC analysis and ELISA. In contrast, psoriatic lesions exhibited reduced ephrin-A ligand immunoreactivity. Exposure of primary keratinocytes induced to differentiated in high calcium or a 3-dimensiosnal raft culture of human epidermis to a combination of growth factors and cytokines elevated in psoriasis increased EphA2 mRNA and protein expression while inducing S100A7 and disrupting differentiation. Pharmacological delivery of a soluble ephrin-A1 peptidomimetic ligand led to a reduction in EphA2 expression and ameliorated proliferation and differentiation in raft cultures exposed to EGF and IL-1α. These findings suggest that ephrin-A1-mediated down-regulation of EphA2 supports keratinocyte differentiation in the context of cytokine perturbation
First Science Observations with SOFIA/FORCAST: Properties of Intermediate-Luminosity Protostars and Circumstellar Disks in OMC-2
We examine eight young stellar objects in the OMC-2 star forming region based
on observations from the SOFIA/FORCAST early science phase, the Spitzer Space
Telescope, the Herschel Space Observatory, 2MASS, APEX, and other results in
the literature. We show the spectral energy distributions of these objects from
near-infrared to millimeter wavelengths, and compare the SEDs with those of
sheet collapse models of protostars and circumstellar disks. Four of the
objects can be modelled as protostars with infalling envelopes, two as young
stars surrounded by disks, and the remaining two objects have double-peaked
SEDs. We model the double-peaked sources as binaries containing a young star
with a disk and a protostar. The six most luminous sources are found in a dense
group within a 0.15 x 0.25 pc region; these sources have luminosities ranging
from 300 L_sun to 20 L_sun. The most embedded source (OMC-2 FIR 4) can be fit
by a class 0 protostar model having a luminosity of ~50 L_sun and mass infall
rate of ~10^-4 solar masses per year.Comment: Accepted by ApJ Letter
A general algorithm for manipulating non-linear and linear entanglement witnesses by using exact convex optimization
A generic algorithm is developed to reduce the problem of obtaining linear
and nonlinear entanglement witnesses of a given quantum system, to convex
optimization problem. This approach is completely general and can be applied
for the entanglement detection of any N-partite quantum system. For this
purpose, a map from convex space of separable density matrices to a convex
region called feasible region is defined, where by using exact convex
optimization method, the linear entanglement witnesses can be obtained from
polygonal shape feasible regions, while for curved shape feasible regions,
envelope of the family of linear entanglement witnesses can be considered as
nonlinear entanglement witnesses. This method proposes a new methodological
framework within which most of previous EWs can be studied. To conclude and in
order to demonstrate the capability of the proposed approach, besides providing
some nonlinear witnesses for entanglement detection of density matrices in
unextendible product bases, W-states, and GHZ with W-states, some further
examples of three qubits systems and their classification and entanglement
detection are included. Also it is explained how one can manipulate most of the
non-decomposable linear and nonlinear three qubits entanglement witnesses
appearing in some of the papers published by us and other authors, by the
method proposed in this paper. Keywords: non-linear and linear entanglement
witnesses, convex optimization. PACS number(s): 03.67.Mn, 03.65.UdComment: 37 page
Formation and Evolution of Planetary Systems: Cold Outer Disks Associated with Sun-like stars
We present the discovery of debris systems around three solar mass stars
based upon observations performed with the Spitzer Space Telescope as part of a
Legacy Science Program, ``the Formation and Evolution of Planetary Systems''
(FEPS). We also confirm the presence of debris around two other stars. All the
stars exhibit infrared emission in excess of the expected photospheres in the
70 micron band, but are consistent with photospheric emission at <= 33 micron.
This restricts the maximum temperature of debris in equilibrium with the
stellar radiation to T < 70 K. We find that these sources are relatively old in
the FEPS sample, in the age range 0.7 - 3 Gyr. Based on models of the spectral
energy distributions, we suggest that these debris systems represent materials
generated by collisions of planetesimal belts. We speculate on the nature of
these systems through comparisons to our own Kuiper Belt, and on the likely
planet(s) responsible for stirring the system and ultimately releasing dust
through collisions. We further report observations of a nearby star HD 13974 (d
=11 pc) that is indistinguishable from a bare photosphere at both 24 micron and
70 micron. The observations place strong upper limits on the presence of any
cold dust in this nearby system (L_IR/L_* < 10^{-5.2}).Comment: 31 pages, 9 figures, accepted for publication in Ap
Factors Associated with Suicide Ideation in Severely Obese Bariatric SurgeryâSeeking Individuals
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93709/1/j.1943-278X.2012.00110.x.pd
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