202 research outputs found
A Uniform Treatment of Architectures in Decentralized Discrete-Event System
Solutions to decentralized discrete-event systems problems are characterized
by the way local decisions are fused to yield a global decision. A fusion rule
is colloquially called an architecture. This paper provides a uniform treatment
of architectures in decentralized discrete-event systems. Current approaches
neither provide a direct way to determine problem solvability conditions under
one architecture, nor a way to compare existing architectures. Determining
whether a new architecture is more general than an existing known architecture
relies on producing examples ad hoc and on individual inspiration that puts the
conditions for solvability in each architecture into some form that admits
comparison. From these research efforts, a method based on morphisms between
graphs has been extracted to yield a uniform approach to decentralized
discrete-event system architectures and their attendant fusion rules. This
treatment provides an easy and direct way to compare the fusion rules -- and
hence to compare the strength or generality of the corresponding architectures
A High Fraction of Ly-alpha-Emitters Among Galaxies with Extreme Emission Line Ratios at z ~ 2
Star-forming galaxies form a sequence in the [OIII]/H-beta vs. [NII]/H-alpha
diagnostic diagram, with low metallicity, highly ionized galaxies falling in
the upper left corner. Drawing from a large sample of UV-selected star-forming
galaxies at z~2 with rest-frame optical nebular emission line measurements from
Keck-MOSFIRE, we select the extreme ~5% of the galaxies lying in this upper
left corner, requiring log([NII]/H-alpha) =
0.75. These cuts identify galaxies with 12 + log(O/H) <~ 8.0, when oxygen
abundances are measured via the O3N2 diagnostic. We study the Ly-alpha
properties of the resulting sample of 14 galaxies. The mean (median) rest-frame
Ly-alpha equivalent width is 39 (36) A, and 11 of the 14 objects (79%) are
Ly-alpha-emitters (LAEs) with W_Lya > 20 A. We compare the equivalent width
distribution of a sample of 522 UV-selected galaxies at 2.0<z<2.6 identified
without regard to their optical line ratios; this sample has mean (median)
Ly-alpha equivalent width -1 (-4) A, and only 9% of these galaxies qualify as
LAEs. The extreme galaxies typically have lower attenuation at Ly-alpha than
those in the comparison sample, and have ~50% lower median oxygen abundances.
Both factors are likely to facilitate the escape of Ly-alpha: in less dusty
galaxies Ly-alpha photons are less likely to be absorbed during multiple
scatterings, while the harder ionizing spectrum and higher ionization parameter
associated with strong, low metallicity star formation may reduce the covering
fraction or column density of neutral hydrogen, further easing Ly-alpha escape.
The use of nebular emission line ratios may prove useful in the identification
of galaxies with low opacity to Ly-alpha photons across a range of redshifts.Comment: 12 pages, 5 figures, 2 tables. Accepted for publication in Ap
Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE
We present initial results of a deep near-IR spectroscopic survey covering
the 15 fields of the Keck Baryonic Structure Survey (KBSS) using MOSFIRE on the
Keck 1 telescope, focusing on a sample of 251 galaxies with redshifts 2.0< z <
2.6, star-formation rates 2 < SFR < 200 M_sun/yr, and stellar masses 8.6 <
log(M*/M_sun) < 11.4, with high-quality spectra in both H- and K-band
atmospheric windows. We show unambiguously that the locus of z~2.3 galaxies in
the "BPT" nebular diagnostic diagram exhibits a disjoint, yet similarly tight,
relationship between the ratios [NII]6585/Halpha and [OIII]/Hbeta as compared
to local galaxies. Using photoionization models, we argue that the offset of
the z~2.3 locus relative to z~ 0 is explained by a combination of harder
ionizing radiation field, higher ionization parameter, and higher N/O at a
given O/H than applies to most local galaxies, and that the position of a
galaxy along the z~2.3 star-forming BPT locus is surprisingly insensitive to
gas-phase oxygen abundance. The observed nebular emission line ratios are most
easily reproduced by models in which the net ionizing radiation field resembles
a blackbody with effective temperature T_eff = 50000-60000 K and N/O close to
the solar value at all O/H. We critically assess the applicability of
commonly-used strong line indices for estimating gas-phase metallicities, and
consider the implications of the small intrinsic scatter in the empirical
relationship between excitation-sensitive line indices and stellar mass (i.e.,
the "mass-metallicity" relation), at z~2.3.Comment: 41 pages, 25 figures, accepted for publication in the Astrophysical
Journal. Version with full-resolution figures available at
http://www.astro.caltech.edu/~ccs/mos_bpt_submit.pd
The Infrared Detection of the Pulsar Wind Nebula in the Galactic Supernova Remnant 3C 58
We present infrared observations of 3C 58 with the Spitzer Space Telescope
and the Canada-France-Hawaii Telescope. Using the IRAC camera, we have imaged
the entire source resulting in clear detections of the nebula at 3.6 and 4.5
microns. The derived flux values are consistent with extrapolation of the X-ray
spectrum to the infrared band, demonstrating that any cooling break in the
synchrotron spectrum must occur near the soft X-ray band. We also detect the
torus surrounding PSR J0205+6449, the 65 ms pulsar that powers 3C 58. The torus
spectrum requires a break between the infrared and X-ray bands, and perhaps
multiple breaks. This complex spectrum, which is an imprint of the particles
injected into the nebula, has considerable consequences for the evolution of
the broadband spectrum of 3C 58. We illustrate these effects and discuss the
impact of these observations on the modeling of broadband spectra of pulsar
wind nebulae.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter
Discovery and Early Evolution of ASASSN-19bt, the First TDE Detected by TESS
We present the discovery and early evolution of ASASSN-19bt, a tidal
disruption event (TDE) discovered by the All-Sky Automated Survey for
Supernovae (ASAS-SN) at a distance of Mpc and the first TDE to be
detected by TESS. As the TDE is located in the TESS Continuous Viewing Zone,
our dataset includes 30-minute cadence observations starting on 2018 July 25,
and we precisely measure that the TDE begins to brighten days before
its discovery. Our dataset also includes 18 epochs of Swift UVOT and XRT
observations, 2 epochs of XMM-Newton observations, 13 spectroscopic
observations, and ground data from the Las Cumbres Observatory telescope
network, spanning from 32 days before peak through 37 days after peak.
ASASSN-19bt thus has the most detailed pre-peak dataset for any TDE. The TESS
light curve indicates that the transient began to brighten on 2019 January 21.6
and that for the first 15 days its rise was consistent with a flux power-law model. The optical/UV emission is well-fit by a blackbody SED,
and ASASSN-19bt exhibits an early spike in its luminosity and temperature
roughly 32 rest-frame days before peak and spanning up to 14 days that has not
been seen in other TDEs, possibly because UV observations were not triggered
early enough to detect it. It peaked on 2019 March 04.9 at a luminosity of
ergs s and radiated
ergs during the 41-day rise to peak. X-ray observations after peak indicate a
softening of the hard X-ray emission prior to peak, reminiscent of the
hard/soft states in X-ray binaries.Comment: 23 pages, 14 figures, 5 tables. A machine-readable table containing
the host-subtracted photometry presented in this manuscript is included as an
ancillary fil
No antidepressant effects of low intensity transcranial pulsed electromagnetic fields for treatment resistant depression
Background: Noninvasive neurostimulation with transcranial Pulsed Electromagnetic Fields (tPEMF) may be a promising method for treatment resistant depression (TRD). Studies shown substantial improvement of depressive symptoms in patients with TRD, but there is no information on long-term antidepressant effects. The aim of this study was to investigate the short- and long-term efficacy of tPEMF in participants with TRD. Methods: Eligible participants with TRD in this sham-controlled double-blind multicenter trial were randomly assigned to five weeks either daily active or sham tPEMF. Severity of depression and anxiety was assessed preand directly post-treatment and five and fifteen weeks post-treatment. Primary outcome was change on the 17item Hamilton depression rating scale directly post-treatment. Secondary outcome was change on the Hamilton17 during follow-up and change on the Inventory of Depressive Symptomatology Self-Report and the Beck Anxiety Index. Results: Of the 55 included participants, 50 completed the treatment protocol. Depressive symptoms improved over time in both groups. The improvement continued until the last follow-up measure. There was no difference in outcome between the active and the sham group on change in depression post-treatment or on any secondary measure. Conclusion: Treatment with this type of active tPEMF was not superior to sham in patients with TRD. This is in contrast to a previous study using a similar design and power calculation, but a higher magnetic field strength, that reported improvement of depression after treatment with tPEMF compared to sham. An important limitation of our study was the fact that no different dosing regimens were tried
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