1,555 research outputs found
Omnidirectional Sensory and Motor Volumes in Electric Fish
Active sensing organisms, such as bats, dolphins, and weakly electric fish, generate a 3-D space for active sensation by emitting self-generated energy into the environment. For a weakly electric fish, we demonstrate that the electrosensory space for prey detection has an unusual, omnidirectional shape. We compare this sensory volume with the animal's motor volume—the volume swept out by the body over selected time intervals and over the time it takes to come to a stop from typical hunting velocities. We find that the motor volume has a similar omnidirectional shape, which can be attributed to the fish's backward-swimming capabilities and body dynamics. We assessed the electrosensory space for prey detection by analyzing simulated changes in spiking activity of primary electrosensory afferents during empirically measured and synthetic prey capture trials. The animal's motor volume was reconstructed from video recordings of body motion during prey capture behavior. Our results suggest that in weakly electric fish, there is a close connection between the shape of the sensory and motor volumes. We consider three general spatial relationships between 3-D sensory and motor volumes in active and passive-sensing animals, and we examine hypotheses about these relationships in the context of the volumes we quantify for weakly electric fish. We propose that the ratio of the sensory volume to the motor volume provides insight into behavioral control strategies across all animals
Massive Neutrinos and (Heterotic) String Theory
String theories in principle address the origin and values of the quark and
lepton masses. Perhaps the small values of neutrino masses could be explained
generically in string theory even if it is more difficult to calculate
individual values, or perhaps some string constructions could be favored by
generating small neutrino masses. We examine this issue in the context of the
well-known three-family standard-like Z_3 heterotic orbifolds, where the theory
is well enough known to construct the corresponding operators allowed by string
selection rules, and analyze the D- and F-flatness conditions. Surprisingly, we
find that a simple see-saw mechanism does not arise. It is not clear whether
this is a property of this construction, or of orbifolds more generally, or of
string theory itself. Extended see-saw mechanisms may be allowed; more analysis
will be needed to settle that issue. We briefly speculate on their form if
allowed and on the possibility of alternatives, such as small Dirac masses and
triplet see-saws. The smallness of neutrino masses may be a powerful probe of
string constructions in general. We also find further evidence that there are
only 20 inequivalent models in this class, which affects the counting of string
vacua.Comment: 18 pages in RevTeX format. Single-column postscript version available
at http://sage.hep.upenn.edu/~bnelson/singpre.p
Mitochondrial DNA suggests at least 11 origins of parasitism in angiosperms and reveals genomic chimerism in parasitic plants
Early JWST imaging reveals strong optical and NIR color gradients in galaxies at driven mostly by dust
Recent studies have shown that galaxies at cosmic noon are redder in the
center and bluer in the outskirts, mirroring results in the local universe.
These color gradients could be caused by either gradients in the stellar age or
dust opacity; however, distinguishing between these two causes is impossible
with rest-frame optical photometry alone. Here we investigate the underlying
causes of the gradients from spatially-resolved rest-frame vs.
color-color diagrams, measured from early observations with the James Webb
Space Telescope. We use NIRCam photometry from the
CEERS survey of a sample of 54 galaxies with at redshifts
selected from the 3D-HST catalog. We model the light profiles in
the F115W, F200W and F356W NIRCam bands using \texttt{imcascade}, a Bayesian
implementation of the Multi-Gaussian expansion (MGE) technique which flexibly
represents galaxy profiles using a series of Gaussians. We construct resolved
rest-frame and color profiles. The majority of star-forming
galaxies have negative gradients (i.e. redder in the center, bluer in the
outskirts) in both and colors consistent with radially decreasing
dust attenuation. A smaller population (roughly 15\%) of star-forming galaxies
have positive but negative gradients implying centrally
concentrated star-formation. For quiescent galaxies we find a diversity of UVJ
color profiles, with roughly one-third showing star-formation in their center.
This study showcases the potential of JWST to study the resolved stellar
populations of galaxies at cosmic noon.Comment: Updated to match published version, new Figure 5 and some text
change
The echo-transponder electrode catheter: A new method for mapping the left ventricle
AbstractThe ability to locate catheter position in the left ventricle with respect to endocardial landmarks might enhance the accuracy of ventricular tachycardia mapping. An echotransponder system (Telectronics, Inc.) was compared with biplane fluoroscopy for left ventricular endocardial mapping. A 6F electrode catheter was modified with the addition of a piezoelectric crystal 5 mm from the tip. This crystal was connected to a transponder that received and transmitted ultrasound, resulting in a discrete artifact on the two-dimensional echocardiographic image corresponding to the position of the catheter tip.Catheters were introduced percutaneously into the left ventricle of nine anesthetized dogs. Two-dimensional echotransponder and biplane fluoroscopic images were recorded on videotape with the catheter at multiple endocardial sites. Catheter location was marked by delivering radiofrequency current to the distal electrode, creating a small endocardial lesion. Catheter location by echo-transponder and by fluoroscopy were compared with lesion location without knowledge of other data. Location by echo-transponder was 8.7 ± 5.1 mm from the center of the radiofrequency lesion versus 14 + 7.8 mm by fluoroscopy (n = 15, p = 0.023). Echo-transponder localization is more precise than is biplane fluoroscopy and may enhance the accuracy of left ventricular eledrophysiologic mapping
Generalised Framework for Controlling and Understanding Ion Dynamics with Passivated Lead Halide Perovskites
Metal halide perovskite solar cells have gained widespread attention due to
their high efficiency and high defect tolerance. The absorbing perovskite layer
is as a mixed electron-ion conductor that supports high rates of ion and charge
transport at room temperature, but the migration of mobile defects can lead to
degradation pathways. We combine experimental observations and drift-diffusion
modelling to demonstrate a new framework to interpret surface photovoltage
(SPV) measurements in perovskite systems and mixed electronic ionic conductors
more generally. We conclude that the SPV in mixed electronic ionic conductors
can be understood in terms of the change in electric potential at the surface
associated with changes in the net charge within the semiconductor system. We
show that by modifying the interfaces of perovskite bilayers, we may control
defect migration behaviour throughout the perovskite bulk. Our new framework
for SPV has broad implications for developing strategies to improve the
stability of perovskite devices by controlling defect accumulation at
interfaces. More generally, in mixed electronic conductors our framework
provides new insights into the behaviour of mobile defects and their
interaction with photoinduced charges, which are foundational to physical
mechanisms in memristivity, logic, impedance, sensors and energy storage
Leveraging 3D-HST Grism Redshifts to Quantify Photometric Redshift Performance
We present a study of photometric redshift accuracy in the 3D-HST photometric catalogs, using 3D-HST grism redshifts to quantify and dissect trends in redshift accuracy for galaxies brighter than JH IR > 24 with an unprecedented and representative high-redshift galaxy sample. We find an average scatter of 0.0197 ± 0.0003(1 + z) in the Skelton et al. photometric redshifts. Photometric redshift accuracy decreases with magnitude and redshift, but does not vary monotonically with color or stellar mass. The 1σ scatter lies between 0.01 and 0.03 (1 + z) for galaxies of all masses and colors below z JH IR 2), dusty star-forming galaxies for which the scatter increases to ~0.1 (1 + z). We find that photometric redshifts depend significantly on galaxy size; the largest galaxies at fixed magnitude have photo-zs with up to ~30% more scatter and ~5 times the outlier rate. Although the overall photometric redshift accuracy for quiescent galaxies is better than that for star-forming galaxies, scatter depends more strongly on magnitude and redshift than on galaxy type. We verify these trends using the redshift distributions of close pairs and extend the analysis to fainter objects, where photometric redshift errors further increase to ~0.046 (1 + z) at HF160W=26. We demonstrate that photometric redshift accuracy is strongly filter dependent and quantify the contribution of multiple filter combinations. We evaluate the widths of redshift probability distribution functions and find that error estimates are underestimated by a factor of ~1.1–1.6, but that uniformly broadening the distribution does not adequately account for fitting outliers. Finally, we suggest possible applications of these data in planning for current and future surveys and simulate photometric redshift performance in the Large Synoptic Survey Telescope, Dark Energy Survey (DES), and combined DES and Vista Hemisphere surveys
REQUIEM-2D: Spatially Resolved Stellar Populations from HST 2D Grism Spectroscopy
We present a novel Bayesian methodology to jointly model photometry and deep
Hubble Space Telescope (HST) 2d grism spectroscopy of high-redshift galaxies.
Our requiem2d code measures both unresolved and resolved stellar populations,
ages, and star-formation histories (SFHs) for the ongoing REQIUEM (REsolving
QUIEscent Magnified) Galaxies Survey, which targets strong gravitationally
lensed quiescent galaxies at z~2. We test the accuracy of \texttt{requiem2d}
using a simulated sample of massive galaxies at z~2 from the Illustris
cosmological simulation and find we recover the general trends in SFH and
median stellar ages. We further present a pilot study for the REQUIEM Galaxies
Survey: MRG-S0851, a quintuply-imaged, massive () red galaxy at . With an estimated gravitational
magnification of , we sample the stellar populations
on 0.6 kpc physical size bins. The global mass-weighted median age is
constrained to be Gyr, and our spatially resolved analysis
reveals that MRG-S0851 has a flat age gradient in the inner 3 kpc core after
taking into account the subtle effects of dust and metallicity on age
measurements, favoring an early formation scenario. The analysis for the full
REQUIEM-2D sample will be presented in a forthcoming paper with a beta-release
of the requiem2d code.Comment: 29 pages, 19 figures, accepted for publication in Ap
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