146 research outputs found
The Near Infrared and Multiwavelength Afterglow of GRB 000301c
We present near-infrared observations of the counterpart of GRB 000301c. The
K' filter (2.1 micron) light curve shows a well-sampled break in the decay
slope at t=3.5 days post-burst. The early time slope is very shallow (~ -0.1),
while the late time slope is steep (-2.2). Comparison with the optical (R band)
light curve shows marginally significant differences, especially in the early
time decay slope (which is steeper in the optical) and the break time (which
occurs later in the optical). This is contrary to the general expectation that
light curve breaks should either be achromatic (e.g., for breaks due to
collimation effects) or should occur later at longer wavelengths (for most
other breaks). The observed color variations might be intrinsic to the
afterglow, or might indicate systematic errors of > 0.08 magnitude in all
fluxes. Even if the break is achromatic, we argue that its sharpness poses
difficulties for explanations that depend on collimated ejecta. The R light
curve shows further signs of fairly rapid variability (a bump, steep drop, and
plateau) that are not apparent in the K' light curve. In addition, by combining
the IR-optical-UV data with millimeter and radio fluxes, we are able to
constrain the locations of the self-absorption break and cooling break and to
infer the location of the spectral peak at t=3 days: f_nu = 3.4 mJy at nu=1e12
Hz. Using the multiwavelength spectral energy distribution, we are able to
constrain the blast wave energy, which was E > 3e53 erg if the explosion was
isotropic. This implies a maximum gamma ray production efficiency of ~ 0.15 for
GRB 000301C.Comment: Accepted to The Astrophysical Journal. 24 pages, 4 figures, 3 tables;
uses AASTeX 5 macros. This version includes a new figure (R-K' color vs.
time), a better sampled R band light curve, and more extensive discussion of
the optical data and error analysi
Classifying Data Deposited by Scientists into a Library\u27s Data Repository
In 2014, a team of librarians at Brown University began a concerted effort to ingest, describe, and publish scientific data and digital scholarship into the Brown Library’s data repository, the Brown Digital Repository (BDR). The Library targeted outreach towards student, staff, and faculty researchers in the sciences to encourage them to deposit their digital scholarship, such as digital research products related to grants and data related to their publications, into the BDR. This poster presents a snapshot of the types of scholarship that were deposited by scientists during a 2-year period and classifies the nature of these digital objects. The authors looked at the total number of files deposited by scientists over this period and created a tool to classify and categorize these objects in order to characterize the nature of digital scholarship that scientists were depositing. The instrument classified these objects into several categories and subcategories based on concrete criteria. The first category described digital objects associated with a publication. Data in this category were further classified into the subcategories “underlying data” and “supplementary data”. Underlying data included files that contained the results reported in the publication, files necessary for the peer review of the paper’s reported results and/or necessary for replication or reproduction of research results, such as code that was used to analyze results. The supplementary data were files accompanying a publication, including tables, graphs or visualizations that were not able to be included in the paper or were referenced by authors. The second category was files created by student, staff or faculty researchers not related to a publication but could stand alone as scholarly products equivalent to a publication, such as research posters, animations, visualizations, or software. The last category described digital collections, and included three subcategories: legacy data, digital libraries, and grants. Legacy data were digital products published by retiring faculty or faculty nearing the end of their research careers. Digital libraries included the published collections of scientific data not associated with a single publication. These collections could be published by individual researchers, a collaborative team, labs, and/or departments, and their purpose is to make these items available for other researchers to access and reuse. Lastly, the subcategory grant data contained collections of scientific data and/or other types of digital scholarship associated with a funded-project. These collections could be published by individual researchers, a collaborative team, labs, and/or departments, and the purpose is to disseminate items resulting from sponsored research and/or make these resulting grant-funded digital objects available for other researchers and/or the public
Serendipitously Detected Galaxies in the Hubble Deep Field
We present a catalog of 74 galaxies detected serendipitously during a
campaign of spectroscopic observations of the Hubble Deep Field North (HDF) and
its environs. Among the identified objects are five candidate Ly-alpha emitters
at z > 5, a galaxy cluster at z = 0.85, and a Chandra source with a heretofore
undetermined redshift of z = 2.011. We report redshifts for 25 galaxies in the
central HDF, 13 of which had no prior published spectroscopic redshift. Of the
remaining 49 galaxies, 30 are located in the single-orbit HDF Flanking Fields.
We discuss the redshift distribution of the serendipitous sample, which
contains galaxies in the range 0.10 < z < 5.77 with a median redshift of z =
0.85, and we present strong evidence for redshift clustering. By comparing our
spectroscopic redshifts to optical/IR photometric studies of the HDF, we find
that photometric redshifts are in most cases capable of producing reasonable
predictions of galaxy redshifts. Finally, we estimate the line-of-sight
velocity dispersion and the corresponding mass and expected X-ray luminosity of
the galaxy cluster, we present strong arguments for interpreting the Chandra
source as an obscured AGN, and we discuss in detail the spectrum of one of the
candidate z > 5 Ly-alpha emitters.Comment: 18 pages, 9 figures, accepted for publication in the Astronomical
Journa
Observational implications of gamma-ray burst afterglow jet simulations and numerical light curve calculations
We discuss jet dynamics for narrow and wide gamma-ray burst (GRB) afterglow
jets and the observational implications of numerical simulations of
relativistic jets in two dimensions. We confirm earlier numerical results that
sideways expansion of relativistic jets during the bulk of the afterglow
emission phase is logarithmic in time and find that this also applies to narrow
jets with half opening angle of 0.05 radians. As a result, afterglow jets
remain highly nonspherical until after they have become nonrelativistic.
Although sideways expansion steepens the afterglow light curve after the jet
break, the jet edges becoming visible dominates the jet break, which means that
the jet break is sensitive to the observer angle even for narrow jets. Failure
to take the observer angle into account can lead to an overestimation of the
jet energy by up to a factor 4. This weakens the challenge posed to the
magneter energy limit by extreme events such as GRB090926A. Late time radio
calorimetry based on a spherical nonrelativistic outflow model remains relevant
when the observer is approximately on-axis and where differences of a few in
flux level between the model and the simulation are acceptable. However, this
does not imply sphericity of the outflow and therefore does not translate to
high observer angles relevant to orphan afterglows. For more accurate
calorimetry and in order to model significant late time features such as the
rise of the counterjet, detailed jet simulations remain indispensable.Comment: 7 Figures. Replaced with accepted version. Significantly expanded,
including additional discussion of time scale
Magnetic Shape Memory Micro-Pump for Intra-Cranial Drug Delivery
Magnetic shape-memory alloys exhibit strong magneto-structural coupling enabling large magnetic-field-induced deformation. Local control of twinning via variable inhomogeneous magnetic fields initiates local reversible deformation. Previous work produced a valve-less micropump consisting of a Ni-Mn-Ga single crystal, a casing, and a rod magnet. The micropump successfully pumped fluid in opposite directions when the magnet was turned clockwise and counter clockwise. Our current work modifies this micropump for application in rat a head stage, which would simultaneously monitor electroencephalograph data and deliver 0.5-5.0 μl of a drug solution at 100-500 nl/min directly to the rat’s brain. These improvements and the application of the magnetic-shape-memory-alloy technology will foster further improvements in the technology, as well as stimulate further development of MSMA based actuation and sensor devices
Infrared and Optical Observations of GRB 030115 and its Extremely Red Host Galaxy: Implications for Dark Bursts
We present near-infrared (nIR) and optical observations of the afterglow of
GRB 030115. Discovered in an infrared search at Kitt Peak 5 hours after the
burst trigger, this afterglow is amongst the faintest observed in the R-band at
an early epoch, and exhibits very red colors, with . The
magnitude of the optical afterglow of GRB 030115 is fainter than many upper
limits for other bursts, suggesting that without early nIR observations it
would have been classified as a ``dark'' burst. Both the color and optical
magnitude of the afterglow are likely due to dust extinction and indicate that
at least some optical afterglows are very faint due to dust along the line of
sight. Multicolor {\it Hubble Space Telescope} observations were also taken of
the host galaxy and the surrounding field. Photometric redshifts imply that the
host, and a substantial number of faint galaxies in the field are at . The overdensity of galaxies is sufficiently great that GRB 030115 may
have occurred in a rich high-redshift cluster. The host galaxy shows extremely
red colors (R-K=5) and is the first GRB host to be classified as an Extremely
Red Object (ERO). Some of the galaxies surrounding the host also show very red
colors, while the majority of the cluster are much bluer, indicating ongoing
unobscured star formation. As it is thought that much of high redshift star
formation occurs in highly obscured environments it may be that GRB 030115
represent a transition object, between the relatively unobscured afterglows
seen to date and a population which are very heavily extinguished, even in the
nIR.Comment: 19 Pages. ApJ 2006, 647, 47
The Dynamics and Afterglow Radiation of Gamma-Ray Bursts. I. Constant Density Medium
Direct multi-dimensional numerical simulation is the most reliable approach
for calculating the fluid dynamics and observational signatures of relativistic
jets in gamma-ray bursts (GRBs). We present a two-dimensional relativistic
hydrodynamic simulation of a GRB outflow during the afterglow phase, which uses
the fifth-order weighted essentially non-oscillatory scheme and adaptive mesh
refinement. Initially, the jet has a Lorentz factor of 20. We have followed its
evolution up to 150 years. Using the hydrodynamic data, we calculate
synchrotron radiation based upon standard afterglow models and compare our
results with previous analytic work. We find that the sideways expansion of a
relativistic GRB jet is a very slow process and previous analytic works have
overestimated its rate. In our computed lightcurves, a very sharp jet break is
seen and the post-break lightcurves are steeper than analytic predictions. We
find that the jet break in GRB afterglow lightcurves is mainly caused by the
missing flux when the edge of the jet is observed. The outflow becomes
nonrelativistic at the end of the Blandford-McKee phase. But it is still highly
nonspherical, and it takes a rather long time for it to become a spherical
Sedov-von Neumann-Taylor blast wave. We find that the late-time afterglows
become increasingly flatter over time. But we disagree with the common notion
that there is a sudden flattening in lightcurves due to the transition into the
Sedov-von Neumann-Taylor solution. We have also found that there is a bump in
lightcurves at very late times ( days) due to radiation from the
counter jet. We speculate that such a counter jet bump might have already been
observed in GRB 980703.Comment: Title changed, high-resolution version available at
http://cosmo.nyu.edu/~wqzhang/publications/ag.pdf, movies of the simulation
available at http://cosmo.nyu.edu/~wqzhang/movies
The Hydrodynamics of Gamma-Ray Burst Remnants
This paper reports on the results of a numerical investigation designed to
address how the initially anisotropic appearance of a GRB remnant is modified
by the character of the circumburst medium and by the possible presence of an
accompanying supernova (SN). Axisymmetric hydrodynamical calculations of light,
impulsive jets propagating in both uniform and inhomogeneous external media are
presented, which show that the resulting dynamics of their remnants since the
onset of the non-relativistic phase is different from the standard self-similar
solutions. Because massive star progenitors are expected to have their close-in
surroundings modified by the progenitor winds, we consider both free winds and
shocked winds as possible external media for GRB remnant evolution. Abundant
confirmation is provided here of the important notion that the morphology and
visibility of GRB remnants are determined largely by their circumstellar
environments. For this reason, their detectability is highly biased in favor of
those with massive star progenitors; although, in this class of models, the
beamed component may be difficult to identify because the GRB ejecta is
eventually swept up by the accompanying SN. The number density of asymmetric
GRB remnants in the local Universe could be, however, far larger if they expand
in a tenuous interstellar medium, as expected for some short GRB progenitor
models. In these sources, the late size of the observable, asymmetric remnant
could extend over a wide, possibly resolvable angle and may be easier to
constrain directly.Comment: 10 pages, 12 figures, emulateapj style, submitted to Ap
FIGS -- Faint Infrared Grism Survey: Description and Data Reduction
The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST)
WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four
deep fields. Two fields are located in the Great Observatories Origins Deep
Survey-North (GOODS-N) area and two fields are located in the Great
Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern
fields selected is the Hubble Ultra Deep Field. Each of these four fields were
observed using the WFC3/G102 grism (0.8-1.15 continuous coverage)
with a total exposure time of 40 orbits (~ 100 kilo-seconds) per field. This
reaches a 3 sigma continuum depth of ~26 AB magnitudes and probes emission
lines to . This paper details the four
FIGS fields and the overall observational strategy of the project. A detailed
description of the Simulation Based Extraction (SBE) method used to extract and
combine over 10000 spectra of over 2000 distinct sources brighter than
m_F105W=26.5 mag is provided. High fidelity simulations of the observations is
shown to significantly improve the background subtraction process, the spectral
contamination estimates, and the final flux calibration. This allows for the
combination of multiple spectra to produce a final high quality, deep,
1D-spectra for each object in the survey.Comment: 21 Pages. 17 Figures. To appear in Ap
The intersection of video capsule endoscopy and artificial intelligence: addressing unique challenges using machine learning
Introduction: Technical burdens and time-intensive review processes limit the
practical utility of video capsule endoscopy (VCE). Artificial intelligence
(AI) is poised to address these limitations, but the intersection of AI and VCE
reveals challenges that must first be overcome. We identified five challenges
to address. Challenge #1: VCE data are stochastic and contains significant
artifact. Challenge #2: VCE interpretation is cost-intensive. Challenge #3: VCE
data are inherently imbalanced. Challenge #4: Existing VCE AIMLT are
computationally cumbersome. Challenge #5: Clinicians are hesitant to accept
AIMLT that cannot explain their process.
Methods: An anatomic landmark detection model was used to test the
application of convolutional neural networks (CNNs) to the task of classifying
VCE data. We also created a tool that assists in expert annotation of VCE data.
We then created more elaborate models using different approaches including a
multi-frame approach, a CNN based on graph representation, and a few-shot
approach based on meta-learning.
Results: When used on full-length VCE footage, CNNs accurately identified
anatomic landmarks (99.1%), with gradient weighted-class activation mapping
showing the parts of each frame that the CNN used to make its decision. The
graph CNN with weakly supervised learning (accuracy 89.9%, sensitivity of
91.1%), the few-shot model (accuracy 90.8%, precision 91.4%, sensitivity
90.9%), and the multi-frame model (accuracy 97.5%, precision 91.5%, sensitivity
94.8%) performed well. Discussion: Each of these five challenges is addressed,
in part, by one of our AI-based models. Our goal of producing high performance
using lightweight models that aim to improve clinician confidence was achieved
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