11,016 research outputs found
Novel duality in disorder driven local quantum criticality
We find that competition between random Kondo and random magnetic
correlations results in a quantum phase transition from a local Fermi liquid to
a spin liquid. The local charge susceptibility turns out to have exactly the
same critical exponent as the local spin susceptibility, suggesting novel
duality between the Kondo singlet phase and the critical local moment state
beyond the Landau-Ginzburg-Wilson symmetry breaking framework. This leads us to
propose an enhanced symmetry at the local quantum critical point, described by
an O(4) vector for spin and charge. The symmetry enhancement serves mechanism
of electron fractionalization in critical impurity dynamics, where such
fractionalized excitations are identified with topological excitations
ZFOURGE: Extreme 5007 emission may be a common early-lifetime phase for star-forming galaxies at
Using the \prospector\ spectral energy distribution (SED) fitting code, we
analyze the properties of 19 Extreme Emission Line Galaxies (EELGs) identified
in the bluest composite SED in the \zfourge\ survey at .
\prospector\ includes a physical model for nebular emission and returns
probability distributions for stellar mass, stellar metallicity, dust
attenuation, and nonparametric star formation history (SFH). The EELGs show
evidence for a starburst in the most recent 50 Myr, with the median EELG having
a specific star formation rate (sSFR) of 4.6 Gyr and forming 15\% of its
mass in this short time. For a sample of more typical star-forming galaxies
(SFGs) at the same redshifts, the median SFG has a sSFR of 1.1 Gyr and
forms only of its mass in the last 50 Myr. We find that virtually all of
our EELGs have rising SFHs, while most of our SFGs do not. From our analysis,
we hypothesize that many, if not most, star-forming galaxies at
undergo an extreme H+[\hbox{{\rm O}\kern 0.1em{\sc iii}}] emission
line phase early in their lifetimes. In a companion paper, we obtain
spectroscopic confirmation of the EELGs as part of our {\sc MOSEL} survey. In
the future, explorations of uncertainties in modeling the UV slope for galaxies
at are needed to better constrain their properties, e.g. stellar
metallicities.Comment: 11 pages, 5 figures (main figure is fig 5), accepted for publication
in Ap
The Galaxy Populations of X-Ray Detected, Poor Groups
(Abridged) We determine the quantitative morphology and star formation
properties of galaxies in six nearby X-ray detected, poor groups using
multi-object spectroscopy and wide-field R imaging. We measure structural
parameters for each galaxy by fitting a PSF-convolved, two component model to
their surface brightness profiles. To compare directly the samples, we fade,
smooth, and rebin each galaxy image so that we effectively observe each galaxy
at the same redshift (9000 km/s) and physical resolution (0.87h^(-1) kpc). We
compare results for the groups to a sample of field galaxies. We find that: 1)
Galaxies spanning a wide range in morphological type and luminosity are
well-fit by a de Vaucouleurs bulge with exponential disk profile. 2)
Morphologically classifying these nearby group galaxies by their bulge fraction
(B/T) is fairly robust on average, even when their redshift has increased by up
to a factor of four and the effective resolution of the images is degraded by
up to a factor of five. 3) The fraction of bulge-dominated systems in these
groups is higher than in the field (~50% vs. ~20%). 4) The fraction of
bulge-dominated systems in groups decreases with increasing radius, similar to
the morphology-radius (~density) relation observed in galaxy clusters. 5)
Current star formation in group galaxies is correlated with significant
morphological asymmetry for disk-dominated systems (B/T<0.4). 6) The group
galaxies that are most disk-dominated (B/T<0.2) are less star forming and
asymmetric on average than their counterparts in the field.Comment: Accepted for publication in the Astrophysical Journal (26 pages + 12
figures); Figs 1 & 2 also available at
http://www.ucolick.org/~vy/astronomy/groups_figs.tar.g
Near infrared spectroscopy and star-formation histories of 3<z<4 quiescent galaxies
We present Keck-MOSFIRE H and K spectra for a sample of 24 candidate
quiescent galaxies (QGs) at 3<z<4, identified from UVJ colors and photometric
redshifts in the ZFOURGE and 3DHST surveys. We obtain spectroscopic redshifts
for half of the sample, using absorption or emission lines, and confirm the
high accuracy of the photometric redshifts with a median error of 1.2%. Two
galaxies turn out to be dusty objects at lower redshifts (z<2.5), and are the
only two detected in the sub-mm with ALMA. High equivalent-width [OIII] was
observed in two galaxies, contributing up to 30% of the K-band flux and
mimicking the colors of an old stellar population. This implies a failure rate
of only 20% for the UVJ selection at these redshifts. Balmer absorption was
identified in 4 of the brighest galaxies, confirming the absence of OB stars.
Modeling all QGs with a wide range of star-formation histories, we find sSFR a
factor of 10 below the main sequence (MS) for all but one galaxy, and less than
0.01 Gyr for half of the sample. This is consistent with the H
and [OII] luminosities, and the ALMA non-detections. We then find that these
QGs have quenched on average 300 Myr before observation, between z=3.5 and 5,
and that they formed at z~5.5 with a mean SFR~300 Msun/yr. Considering an
alternative selection of QGs based solely on the sSFR from SED modeling, we
find that galaxies a factor 10 below the MS are 40% more numerous than
UVJ-quiescent galaxies, implying that the UVJ selection is pure but incomplete.
Current models fail at reproducing our observations and underestimate either
the number density of QGs by more than an order of magnitude or the duration of
their quiescence by a factor two. Overall, these results confirm the existence
of an unexpected population of QGs at z>3, and offer the first insights on
their formation history. [abridged]Comment: 30 pages (+ appendix), 18 figures, accepted for publication in A&
Fluorescence quenching studies of structure and dynamics in calmodulin-eNOS complexes
This is the peer reviewed version of the following article: Arnett David C.,Persechini Anthony,Tran Quang-Kim,Black D.J. and Johnson Carey K.(2015), Fluorescence quenching studies of structure and dynamics in calmodulinâeNOS complexes, FEBS Letters, 589, doi: 10.1016/j.febslet.2015.03.035, which has been published in final form at http://doi.org/10.1016/j.febslet.2015.03.035. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Activation of endothelial nitric oxide synthase (eNOS) by calmodulin (CaM) facilitates formation of a sequence of conformational states that is not well understood. Fluorescence decays of fluorescently labeled CaM bound to eNOS reveal four distinct conformational states and single-molecule fluorescence trajectories show multiple fluorescence states with transitions between states occurring on time scales of milliseconds to seconds. A model is proposed relating fluorescence quenching states to enzyme conformations. Specifically, we propose that the most highly quenched state corresponds to CaM docked to an oxygenase domain of the enzyme. In single-molecule trajectories, this state occurs with time lags consistent with the oxygenase activity of the enzyme
Fluorescence quenching studies of structure and dynamics in calmodulin-eNOS complexes
This is the peer reviewed version of the following article: Arnett David C.,Persechini Anthony,Tran Quang-Kim,Black D.J. and Johnson Carey K.(2015), Fluorescence quenching studies of structure and dynamics in calmodulinâeNOS complexes, FEBS Letters, 589, doi: 10.1016/j.febslet.2015.03.035, which has been published in final form at http://doi.org/10.1016/j.febslet.2015.03.035. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Activation of endothelial nitric oxide synthase (eNOS) by calmodulin (CaM) facilitates formation of a sequence of conformational states that is not well understood. Fluorescence decays of fluorescently labeled CaM bound to eNOS reveal four distinct conformational states and single-molecule fluorescence trajectories show multiple fluorescence states with transitions between states occurring on time scales of milliseconds to seconds. A model is proposed relating fluorescence quenching states to enzyme conformations. Specifically, we propose that the most highly quenched state corresponds to CaM docked to an oxygenase domain of the enzyme. In single-molecule trajectories, this state occurs with time lags consistent with the oxygenase activity of the enzyme
Consistent dynamical and stellar masses with potential light IMF in massive quiescent galaxies at using velocity dispersions measurements with MOSFIRE
We present the velocity dispersion measurements of four massive
quiescent galaxies at based on deep H and
Kband spectra using the Keck/MOSFIRE near-infrared spectrograph. We find
high velocity dispersions of order km/s based on strong
Balmer absorption lines and combine these with size measurements based on
HST/WFC3 F160W imaging to infer dynamical masses. The velocity dispersion are
broadly consistent with the high stellar masses and small sizes. Together with
evidence for quiescent stellar populations, the spectra confirm the existence
of a population of massive galaxies that formed rapidly and quenched in the
early universe . Investigating the evolution at constant velocity
dispersion between and , we find a large increase in
effective radius dex and in dynamical-to-stellar mass ratio
of 0.33$\pm0.08$ dex, with low expected
contribution from dark matter. The dynamical masses for our $z\sim3.5$ sample
are consistent with the stellar masses for a Chabrier initial mass function
(IMF), with the ratio =
-0.130.10 dex suggesting an IMF lighter than Salpeter may be common for
massive quiescent galaxies at . This is surprising in light of the
Salpeter or heavier IMFs found for high velocity dispersion galaxies at
and cores of present-day ellipticals, which these galaxies are thought
to evolve into. Future imaging and spectroscopic observations with resolved
kinematics using the upcoming James Webb Space Telescope could rule out
potential systematics from rotation, and confirm these results.Comment: 11 pages, 3 figures. Accepted to ApJ Letter
Galaxy Merger Fractions in Two Clusters at Z ⌠2 Using the Hubble Space Telescope
We measure the fraction of galaxy-galaxy mergers in two clusters at z ,F⌠,F2 using imaging and grism observations from the Hubble Space Telescope. The two galaxy cluster candidates were originally identified as overdensities of objects using deep mid-infrared imaging and observations from the Spitzer Space Telescope, and were subsequently followed up with HST/WFC3 imaging and grism observations. We identify galaxy-galaxy merger candidates using high-resolution imaging with the WFC3 in the F105W, F125W, and F160W bands. Coarse redshifts for the same objects are obtained with grism observations in G102 for the z ,F⌠,F1.6 cluster (IRC0222A) and G141 for the z ,F⌠,F2 cluster (IRC0222B). Using visual classifications as well as a variety of selection techniques, we measure merger fractions of in IRC0222A and in IRC0222B. In comparison, we measure a merger fraction of for field galaxies at z ,F⌠,F2. Our study indicates that the galaxy-galaxy merger fraction in clusters at z ,F⌠,F2 is enhanced compared to the field population, but note that more cluster measurements at this epoch are needed to confirm our findings
Crowdsourcing step-by-step information extraction to enhance existing how-to videos
Millions of learners today use how-to videos to master new skills in a variety of domains. But browsing such videos is often tedious and inefficient because video player interfaces are not optimized for the unique step-by-step structure of such videos. This research aims to improve the learning experience of existing how-to videos with step-by-step annotations.
We first performed a formative study to verify that annotations are actually useful to learners. We created ToolScape, an interactive video player that displays step descriptions and intermediate result thumbnails in the video timeline. Learners in our study performed better and gained more self-efficacy using ToolScape versus a traditional video player.
To add the needed step annotations to existing how-to videos at scale, we introduce a novel crowdsourcing workflow. It extracts step-by-step structure from an existing video, including step times, descriptions, and before and after images. We introduce the Find-Verify-Expand design pattern for temporal and visual annotation, which applies clustering, text processing, and visual analysis algorithms to merge crowd output. The workflow does not rely on domain-specific customization, works on top of existing videos, and recruits untrained crowd workers. We evaluated the workflow with Mechanical Turk, using 75 cooking, makeup, and Photoshop videos on YouTube. Results show that our workflow can extract steps with a quality comparable to that of trained annotators across all three domains with 77% precision and 81% recall
Preformed heavy-electrons at the Quantum Critical Point in heavy fermion compounds
The existence of multiple energy scales is regarded as a signature of the
Kondo breakdown mechanism for explaining the quantum critical behavior of
certain heavy fermion compounds, like YbRhSi. The nature of the
intermediate state between the heavy Fermi liquid and the quantum critical
region, however, remains elusive. In this study we suggest an incoherent
heavy-fermion scenario, where inelastic scattering with novel soft modes of the
dynamical exponent gives rise to non-Fermi liquid physics for
thermodynamics and transport despite the formation of the heavy-fermion band.
We discuss a crossover from to for quantum phase fluctuations
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