184 research outputs found
XOR style tasks for testing visual object processing in monkeys
AbstractUsing visually complex stimuli, three monkeys learned visual exclusive-or (XOR) tasks that required detecting two way visual feature conjunctions. Monkeys with passive exposure to the test images, or prior experience, were quicker to acquire an XOR style task. Training on each pairwise comparison of the stimuli to be used in an XOR task provided nearly complete transfer when stimuli became intermingled in the full XOR task. Task mastery took longer, accuracy was lower, and response times were slower for conjunction stimuli. Rotating features of the XOR stimuli did not adversely effect recognition speed or accuracy
Gemini Imaging of the Host Galaxies of Changing-Look Quasars
Changing-look quasars are a newly-discovered class of luminous active
galactic nuclei that undergo rapid (10 year) transitions between Type
1 and Type 1.9/2, with an associated change in their continuum emission. We
characterize the host galaxies of four faded changing-look quasars using
broadband optical imaging. We use \textit{gri} images obtained with the Gemini
Multi Object Spectrograph (GMOS) on Gemini North to characterize the surface
brightness profiles of the quasar hosts and search for [O III]
emission from spatially extended regions, or
voorwerpjes, with the goal of using them to examine past luminosity history.
Although we do not detect, voorwerpjes surrounding the four quasar host
galaxies, we take advantage of the dim nuclear emission to characterize the
colors and morphologies of the host galaxies. Three of the four galaxies show
morphological evidence of merger activity or tidal features in their residuals.
The three galaxies which are not highly distorted are fit with a single
S\'ersic profile to characterize their overall surface brightness profiles. The
single-S\'ersic fits give intermediate S\'ersic indices between the of
disk galaxies and the of ellipticals. On a color-magnitude diagram, our
changing-look quasar host galaxies reside in the blue cloud, with other AGN
host galaxies and star-forming galaxies. On a color-S\'ersic index diagram the
changing-look quasar hosts reside with other AGN hosts in the "green valley".
Our analysis suggests that the hosts of changing-look quasars are predominantly
disrupted or merging galaxies that resemble AGN hosts, rather than inactive
galaxies.Comment: 20 pages, 5 figure
Towards an Understanding of Changing-Look Quasars: An Archival Spectroscopic Search in SDSS
The uncertain origin of the recently-discovered `changing-looking' quasar
phenomenon -- in which a luminous quasar dims significantly to a quiescent
state in repeat spectroscopy over ~10 year timescales -- may present unexpected
challenges to our understanding of quasar accretion. To better understand this
phenomenon, we take a first step to building a sample of changing-look quasars
with a systematic but simple archival search for these objects in the Sloan
Digital Sky Survey Data Release 12. By leveraging the >10 year baselines for
objects with repeat spectroscopy, we uncover two new changing-look quasars, and
a third discovered previously. Decomposition of the multi-epoch spectra and
analysis of the broad emission lines suggest that the quasar accretion disk
emission dims due to rapidly decreasing accretion rates (by factors of >2.5),
while disfavoring changes in intrinsic dust extinction for the two objects
where these analyses are possible. Broad emission line energetics also support
intrinsic dimming of quasar emission as the origin for this phenomenon rather
than transient tidal disruption events or supernovae. Although our search
criteria included quasars at all redshifts and transitions from either
quasar-like to galaxy-like states or the reverse, all of the clear cases of
changing-look quasars discovered were at relatively low-redshift (z ~ 0.2 -
0.3) and only exhibit quasar-like to galaxy-like transitions.Comment: 15 pages, 8 figures. Updated to accepted versio
Mechanistic Insight into the Regulation of Lipoxygenase-Driven Lipid Peroxidation Events in Human Spermatozoa and Their Impact on Male Fertility
Probing the Origin of Changing-look Quasar Transitions with Chandra
Extremely variable quasars can also show strong changes in broad-line
emission strength and are known as changing-look quasars (CLQs). To study the
CLQ transition mechanism, we present a pilot sample of CLQs with X-ray
observations in both the bright and faint states. From a sample of quasars with
bright-state archival SDSS spectra and (Chandra or XMM-Newton) X-ray data, we
identified five new CLQs via optical spectroscopic follow-up, and then obtained
new target-of-opportunity X-ray observations with Chandra. No strong absorption
is detected in either the bright- or the faint-state X-ray spectra. The
intrinsic X-ray flux generally changes along with the optical variability, and
the X-ray power-law slope becomes harder in the faint state. Large amplitude
mid-infrared variability is detected in all five CLQs, and the MIR variability
echoes the variability in the optical with a time lag expected from the
light-crossing time of the dusty torus for CLQs with robust lag measurements.
The changing-obscuration model is not consistent with the observed X-ray
spectra and spectral energy distribution changes seen in these CLQs. It is
highly likely that the observed changes are due to the changing accretion rate
of the supermassive black hole, so the multiwavelength emission varies
accordingly, with promising analogies to the accretion states of X-ray
binaries.Comment: Accepted for publication in ApJ; 30 pages, 12 figure
The Time-Domain Spectroscopic Survey: Understanding the Optically Variable Sky with SEQUELS in SDSS-III
The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject
primarily aimed at obtaining identification spectra of ~220,000
optically-variable objects systematically selected from SDSS/Pan-STARRS1
multi-epoch imaging. We present a preview of the science enabled by TDSS, based
on TDSS spectra taken over ~320 deg^2 of sky as part of the SEQUELS survey in
SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the
15,746 TDSS-selected single-epoch spectra of photometrically variable objects
in SEQUELS, we determine the demographics of our variability-selected sample,
and investigate the unique spectral characteristics inherent in samples
selected by variability. We show that variability-based selection of quasars
complements color-based selection by selecting additional redder quasars, and
mitigates redshift biases to produce a smooth quasar redshift distribution over
a wide range of redshifts. The resulting quasar sample contains systematically
higher fractions of blazars and broad absorption line quasars than from
color-selected samples. Similarly, we show that M-dwarfs in the TDSS-selected
stellar sample have systematically higher chromospheric active fractions than
the underlying M-dwarf population, based on their H-alpha emission. TDSS also
contains a large number of RR Lyrae and eclipsing binary stars with
main-sequence colors, including a few composite-spectrum binaries. Finally, our
visual inspection of TDSS spectra uncovers a significant number of peculiar
spectra, and we highlight a few cases of these interesting objects. With a
factor of ~15 more spectra, the main TDSS survey in SDSS-IV will leverage the
lessons learned from these early results for a variety of time-domain science
applications.Comment: 17 pages, 14 figures, submitted to Ap
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Spring 1959
Seed testing - A Service for You by Miss Jessie L. Anderson (page 1) Increased Interest in Two-Year Turf Course by Fred P. Jeffrey - Director of Stockbridge (4) From the Editor (4) Message From Winter School President of 1959 (5) Turf club News (6) Number One Graduate (8) Liquid Fertilization by A.B. Longo (9) Public School Grounds by James Woodhouse (12) Comments on the 1959 Winter School (14) Picture - Stockbridge Turf Majors (16) Picture - Honorary Members of Turf Management Club (17) Letter on Chemical Compatibility (18) The Most Outstanding Turf Senior for 1958 (19) What it Means to be a Turf Manager by R. Russell (20) 10 Steps to a Better Lawn by P. Pedrazzi (24) A Scene to Remember (25) I switched from Hots to Cools by J. Spodnik (26) Why Attend Turfgrass Conferences (27) Picture - Winter School for Turf Managers - 1959 (29) Picture - University of Masssachusetts Annual Turfgrass Conference (30) Organic Fertilizers by O.J. Noer (A-1) Inorganic Fertilizers by Charles Winchell (A-1) Urea Formaldehyde by G.F. Stewart (A-2) Phosphorus and Potash Fertilization by Raph Donaldson (A-3) Questions on Fertilization to the Panel (A-4) Cemetery Maintenance by S.E. Robbins (A-6) Lime by Anson Brewer (A-6) Limited Budgets by R.W. Sharkey (A-7) Fertilization of Park Turf by E.J. Pyle (A-7) Disease and Insect Control by Orlando Capizzi (A-8) Cost of Establishing Turf by Victor Taricano (A-9) Question and Answers (A-10) Control of Pests of Ornamentals and Turf Occuring on Golf Courses by John C. Schread (A-12) Behind the Scenes in Soil Testing and What it Means to You Bertram Gersten and Wm. G. Colby (A-19) Lessons Learned from the 1958 Season as Applied to Golf Course Maintenance by A.M. Radko (A-21) The Outlook in Chemical Weed Control on Fine Turf by John Gallagher (A-24) New Developments in Turfgrass Disease Diagnosis and Control by Frank Howard (A-26
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