630 research outputs found
Automated Quantitative Description of Spiral Galaxy Arm-Segment Structure
We describe a system for the automatic quantification of structure in spiral
galaxies. This enables translation of sky survey images into data needed to
help address fundamental astrophysical questions such as the origin of spiral
structure---a phenomenon that has eluded theoretical description despite 150
years of study (Sellwood 2010). The difficulty of automated measurement is
underscored by the fact that, to date, only manual efforts (such as the citizen
science project Galaxy Zoo) have been able to extract information about large
samples of spiral galaxies. An automated approach will be needed to eliminate
measurement subjectivity and handle the otherwise-overwhelming image quantities
(up to billions of images) from near-future surveys. Our approach automatically
describes spiral galaxy structure as a set of arcs, precisely describing spiral
arm segment arrangement while retaining the flexibility needed to accommodate
the observed wide variety of spiral galaxy structure. The largest existing
quantitative measurements were manually-guided and encompassed fewer than 100
galaxies, while we have already applied our method to more than 29,000
galaxies. Our output matches previous information, both quantitatively over
small existing samples, and qualitatively against human classifications from
Galaxy Zoo.Comment: 9 pages;4 figures; 2 tables; accepted to CVPR (Computer Vision and
Pattern Recognition), June 2012, Providence, Rhode Island, June 16-21, 201
Scalable Automated Detection of Spiral Galaxy Arm Segments
Given an approximately centered image of a spiral galaxy, we describe an
entirely automated method that finds, centers, and sizes the galaxy and then
automatically extracts structural information about the spiral arms. For each
arm segment found, we list the pixels in that segment and perform a
least-squares fit of a logarithmic spiral arc to the pixels in the segment. The
algorithm takes about 1 minute per galaxy, and can easily be scaled using
parallelism. We have run it on all ~644,000 Sloan objects classified as
"galaxy" and large enough to observe some structure. Our algorithm is stable in
the sense that the statistics across a large sample of galaxies vary smoothly
based on algorithmic parameters, although results for individual galaxies can
sometimes vary in a non-smooth but easily understood manner. We find a very
good correlation between our quantitative description of spiral structure and
the qualitative description provided by humans via Galaxy Zoo. In addition, we
find that pitch angle often varies significantly segment-to-segment in a single
spiral galaxy, making it difficult to define "the" pitch angle for a single
galaxy. Finally, we point out how complex arm structure (even of long arms) can
lead to ambiguity in defining what an "arm" is, leading us to prefer the term
"arm segments".Comment: 4 pages (twocolumn),5 figures, 2 tables. Submitted to ApJ. Letter
Design and Pilot Biomechanical Evaluation of a New Device for the Surgical Treatment of Atlanto-Axial Instability
The purpose of this paper was a biomechanical review of a new device, BTS (Bilateral Transarticular Spacer), to stabilize atlanto-axial motion. The biomechanical performance of the BTS and Harms techniques were compared using 6 cadaveric spines. The BTS was also designed to lessen the risks of damaging life sustaining nerves and arteries during placement at the atlanto-axial joint. Two hypotheses were postulated: 1.) The BTS will be able to stabilize the atlanto-axial joint after a type 2 odontoid fracture; and 2.) BTS will function biomechanically similar to the traditional Harms stabilization technique. In conclusion, the testing performed provided initial feasibility evidence that the new BTS device reduced atlanto-axial motion (P \u3c 0.01) and provided stabilization similar to the Harms technique (p\u3c0.01) with loads of 1.5 Nm in flexion-extension, axial rotation, and lateral bending
Using Power Diagrams to Build Optimal Unstructured Meshes for C-Grid Models
The Model for Prediction Across Scales (MPAS) for Ocean (-O), Sea-Ice (-SI) and Land-Ice (-LI), in addition to the Coastal Ocean Marine Prediction Across Scales (COMPAS) are two novel general circulation models designed to resolve coupled ocean-ice dynamics over variable spatial scales using non-uniform unstructured grids. Both models are based on a conservative mimetic finite-difference/volume formulation (TRiSK), in which staggered momentum, vorticity and mass-based degrees- of-freedom are distributed over an orthogonal 'primal-dual' mesh
Behavioral Evidence for Chemosensory and Thermosensory Pathway Convergence in the Caenorhabditis Elegans Nervous System
The nematode, Caenorhabditis elegans, is an established model system to explore the ways simple nervous systems detect and direct organismal responses to environmental changes. C. elegans possesses specialized receptor cells for the detection of a variety of environmental stimuli. Separate cell types respond to volatile chemical and thermal stimuli and the neural pathways for these show anatomical evidence of convergence. This work reports findings from behavioral assays during simultaneous exposure of nematodes to both thermal differences and attractant volatile chemicals. Combined exposure to benzaldehyde and cold neutralized the behavioral responses to both stimuli in 24°C acclimated worms. Diacetyl and mild thermal stimulation produced the same effect with 16°C acclimated worms. Benzaldehyde appears to interfere with thermophilic circuitry while diacetyl acts similarly with cryophilic circuitry
Measuring Galaxy Environments with Deep Redshift Surveys
We study the applicability of several galaxy environment measures
(n^th-nearest-neighbor distance, counts in an aperture, and Voronoi volume)
within deep redshift surveys. Mock galaxy catalogs are employed to mimic
representative photometric and spectroscopic surveys at high redshift (z ~ 1).
We investigate the effects of survey edges, redshift precision, redshift-space
distortions, and target selection upon each environment measure. We find that
even optimistic photometric redshift errors (\sigma_z = 0.02) smear out the
line-of-sight galaxy distribution irretrievably on small scales; this
significantly limits the application of photometric redshift surveys to
environment studies. Edges and holes in a survey field dramatically affect the
estimation of environment, with the impact of edge effects depending upon the
adopted environment measure. These edge effects considerably limit the
usefulness of smaller survey fields (e.g. the GOODS fields) for studies of
galaxy environment. In even the poorest groups and clusters, redshift-space
distortions limit the effectiveness of each environment statistic; measuring
density in projection (e.g. using counts in a cylindrical aperture or a
projected n^th-nearest-neighbor distance measure) significantly improves the
accuracy of measures in such over-dense environments. For the DEEP2 Galaxy
Redshift Survey, we conclude that among the environment estimators tested the
projected n^th-nearest-neighbor distance measure provides the most accurate
estimate of local galaxy density over a continuous and broad range of scales.Comment: 17 pages including 16 figures, accepted to Ap
Compact Modeling for a Double Gate MOSFET
MOSFETs (metal-oxide-silicon field-effect transistors) are an integral part of modern electronics. Improved designs are currently under investigation, and one that is promising is the double gate MOSFET.
Understanding device characteristics is critical for the design of MOSFETs as part of design tools for integrated circuits such as SPICE. Current methods involve the numerical solution of PDEs governing electron transport. Numerical solutions are accurate, but do not provide an appropriate way to optimize the design of the device, nor are they suitable for use in chip simulation software such as SPICE. As chips contain more and more transistors, this problem will get more and more acute.
There is hence a need for analytic solutions of the equations governing the performance of MOSFETs, even if these are approximate. Almost all solutions in the literature treat the long-channel case (thin devices) for which the PDEs reduce to ODEs. The goal of this problem is to produce analytical solutions based on the underlying PDEs that are rapid to compute (e.g. require solving only a small number of algebraic equations rather than systems of PDEs).
Guided by asymptotic analysis, a fast numerical procedure has been developed to obtain approximate solutions of the governing PDEs governing MOSFET properties, namely electron density, Fermi potential and electrostatic potential. The approach depends on the channel’s being long enough, and appears accurate in this limit
A New Utah Forest Insect Pest: Balsam Woolly Adelgid
This fact sheet introduces an invasive forest pest, the balsam woolly adelgid and discusses its impacts on Utah forests, life cycle traits, identifying characteristics, control methods, and steps that Utah partners are taking to combat this pest
Pressure profiles of plasmas confined in the field of a magnetic dipole
Equilibrium pressure profiles of plasmas confined in the field of a dipole magnet are reconstructed using magnetic and x-ray measurements on the levitated dipole experiment (LDX). LDX operates in two distinct modes: with the dipole mechanically supported and with the dipole magnetically levitated. When the dipole is mechanically supported, thermal particles are lost along the field to the supports, and the plasma pressure is highly peaked and consists of energetic, mirror-trapped electrons that are created by electron cyclotron resonance heating. By contrast, when the dipole is magnetically levitated losses to the supports are eliminated and particles are lost via slower cross-field transport that results in broader, but still peaked, plasma pressure profiles.United States. Dept. of Energy (National Science Foundation (U.S.). Partnership in Plasma Science. Grant DE-FG02-00ER54585)United States. Dept. of Energy (National Science Foundation (U.S.). Partnership in Plasma Science. Award PHY-1201896
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