890 research outputs found
Tidal Disruption Event Host Galaxies in the Context of the Local Galaxy Population
We study the properties of tidal disruption event (TDE) host galaxies in the
context of a catalog of ~500,000 galaxies from the Sloan Digital Sky Survey. We
explore whether selection effects can account for the overrepresentation of
TDEs in E+A/post-starburst galaxies by creating matched galaxy samples.
Accounting for possible selection effects due to black hole (BH) mass, redshift
completeness, strong AGN presence, bulge colors, and surface brightness can
reduce the apparent overrepresentation of TDEs in E+A host galaxies by a factor
of ~4 (from ~100-190 to ~25-48), but cannot fully explain the
preference. We find that TDE host galaxies have atypical photometric properties
compared to similar, "typical" galaxies. In particular, TDE host galaxies tend
to live in or near the "green valley" between star-forming and passive
galaxies, and have bluer bulge colors ( mag), lower
half-light surface brightnesses (by ~1 mag/arcsec), higher Sersic indices
(), and higher bulge-to-total-light ratios () than galaxies with matched BH masses. We find that TDE host
galaxies appear more centrally concentrated and that all have high galaxy
Sersic indices and fractions---on average in the top 10% of galaxies of
the same BH mass---suggesting a higher nuclear stellar density. We identify a
region in Sersic index and BH mass parameter space that contains ~2% of our
reference catalog galaxies but of TDE host galaxies. The unique
photometric properties of TDE host galaxies may be useful for selecting
candidate TDEs for spectroscopic follow-up observations in large transient
surveys.Comment: 26 pages, 11 figures, 5 tables. Published in Ap
Climatic versus biotic constraints on carbon and water fluxes in seasonally drought-affected ponderosa pine ecosystems
We investigated the relative importance of climatic versus biotic controls on gross primary production (GPP) and water vapor fluxes in seasonally drought-affected ponderosa pine forests. The study was conducted in young (YS), mature (MS), and old stands (OS) over 4 years at the AmeriFlux Metolius sites. Model simulations showed that interannual variation of GPP did not follow the same trends as precipitation, and effects of climatic variation were smallest at the OS (50%), and intermediate at the YS (<20%). In the young, developing stand, interannual variation in leaf area has larger effects on fluxes than climate, although leaf area is a function of climate in that climate can interact with age-related shifts in carbon allocation and affect whole-tree hydraulic conductance. Older forests, with well-established root systems, appear to be better buffered from effects of seasonal drought and interannual climatic variation. Interannual variation of net ecosystem exchange (NEE) was also lowest at the OS, where NEE is controlled more by interannual variation of ecosystem respiration, 70% of which is from soil, than by the variation of GPP, whereas variation in GPP is the primary reason for interannual changes in NEE at the YS and MS. Across spatially heterogeneous landscapes with high frequency of younger stands resulting from natural and anthropogenic disturbances, interannual climatic variation and change in leaf area are likely to result in large interannual variation in GPP and NEE
A Bayesian analysis of classical shadows
The method of classical shadows heralds unprecedented opportunities for
quantum estimation with limited measurements [H.-Y. Huang, R. Kueng, and J.
Preskill, Nat. Phys. 16, 1050 (2020)]. Yet its relationship to established
quantum tomographic approaches, particularly those based on likelihood models,
remains unclear. In this article, we investigate classical shadows through the
lens of Bayesian mean estimation (BME). In direct tests on numerical data, BME
is found to attain significantly lower error on average, but classical shadows
prove remarkably more accurate in specific situations -- such as high-fidelity
ground truth states -- which are improbable in a fully uniform Hilbert space.
We then introduce an observable-oriented pseudo-likelihood that successfully
emulates the dimension-independence and state-specific optimality of classical
shadows, but within a Bayesian framework that ensures only physical states. Our
research reveals how classical shadows effect important departures from
conventional thinking in quantum state estimation, as well as the utility of
Bayesian methods for uncovering and formalizing statistical assumptions.Comment: 8 pages, 5 figure
Estimation and uncertainty quantification for the output from quantum simulators
The problem of estimating certain distributions over is
considered here. The distribution represents a quantum system of qubits,
where there are non-trivial dependencies between the qubits. A maximum entropy
approach is adopted to reconstruct the distribution from exact moments or
observed empirical moments. The Robbins Monro algorithm is used to solve the
intractable maximum entropy problem, by constructing an unbiased estimator of
the un-normalized target with a sequential Monte Carlo sampler at each
iteration. In the case of empirical moments, this coincides with a maximum
likelihood estimator. A Bayesian formulation is also considered in order to
quantify posterior uncertainty. Several approaches are proposed in order to
tackle this challenging problem, based on recently developed methodologies. In
particular, unbiased estimators of the gradient of the log posterior are
constructed and used within a provably convergent Langevin-based Markov chain
Monte Carlo method. The methods are illustrated on classically simulated output
from quantum simulators
Logistic regression for simulating damage occurrence on a fruit grading line
Many factors influence the incidence of mechanical damage in fruit handled on a grading line. This makes it difficult to address damage estimation from an analytical point of view. During fruit transfer from one element of a grading line to another, damage occurs as a combined effect of machinery roughness and the intrinsic susceptibility of fruit. This paper describes a method to estimate bruise probability by means of logistic regression, using data yielded by specific laboratory tests. Model accuracy was measured via the statistical significance of its parameters and its classification ability. The prediction model was then linked to a simulation model through which impacts and load levels, similar to those of real grading lines, could be generated. The simulation output sample size was determined to yield reliable estimations. The process makes it possible to derive a suitable line design and the type of fruit that should be handled to maintain bruise levels within European Union (EU) Standards. A real example with peaches was carried out with the aid of the software implementation SIMLIN®, developed by the authors and registered by Madrid Technical University. This kind of tool has been demanded by inter-professional associations and grading lines designers in recent year
The Landscape of Galaxies Harboring Changing-Look Active Galactic Nuclei in the Local Universe
We study the properties of the host galaxies of Changing-Look Active Galactic
Nuclei (CL AGNs) with the aim of understanding the conditions responsible for
triggering CL activity. We find that CL AGN hosts primarily reside in the
so-called green valley that is located between spiral-like star-forming
galaxies and dead ellipticals, implying that CL AGNs are activated during
distinct periods of quenching and galaxy transformation processes. CL AGN hosts
have low galaxy asymmetry indicators, suggesting that secular evolutionary
processes (the influence of bars and spirals, and possibly minor mergers) might
be the primary mechanism for transporting gas to the vicinity of the
supermassive black hole (SMBH) rather than major mergers. Similar to tidal
disruption events (TDEs) and highly variable AGNs, we find that CL AGN hosts
are associated with SMBHs residing in high density pseudo-bulges and appear to
overlap most significantly with the population of low-ionization nuclear
emission-line region (LINER) galaxies. As such, CL AGN are likely fueled by
strong episodic bursts of accretion activity, which appear to take place
preferentially as the amount of material accessible for star formation and
accretion dwindles. We also identify that CL AGN hosts are characterized by
either large S\'ersic indices or high bulge fractions, which suggests a simple
metric for identifying candidates for spectroscopic follow-up observations in
forthcoming synoptic surveys.Comment: 17 pages, 9 figures. Accepted to ApJ Letters. Revised version
includes an expanded discussion on asymmetry measurements and galaxy
disturbance
Multi-site Integrated Optical Addressing of Trapped Ions
One of the most effective ways to advance the performance of quantum
computers and quantum sensors is to increase the number of qubits or quantum
resources used by the system. A major technical challenge that must be solved
to realize this goal for trapped-ion systems is scaling the delivery of optical
signals to many individual ions. In this paper we demonstrate an approach
employing waveguides and multi-mode interferometer splitters to optically
address multiple ions in a surface trap by delivering all
wavelengths required for full qubit control. Measurements of hyperfine
spectroscopy and Rabi flopping were performed on the E2 clock transition, using
integrated waveguides for delivering the light needed for Doppler cooling,
state preparation, coherent operations, and detection. We describe the use of
splitters to address multiple ions using a single optical input per wavelength
and use them to demonstrate simultaneous Rabi flopping on two different
transitions occurring at distinct trap sites. This work represents an important
step towards the realization of scalable integrated photonics for atomic clocks
and trapped-ion quantum information systems.Comment: 7 pages, 4 figures (+2 supplementary figures
No Radio Bursts Detected from FIRST J141918.9+394036 in Green Bank Telescope Observations
Precise localization of the first-known repeating fast radio burst source, FRB 121102 (Spitler et al. 2016; Chatterjee et al. 2017), led to its association with a star-forming region inside a low-metallicity dwarf host galaxy (Tendulkar et al. 2017). This host environment is similar to that typically associated with long gamma-ray bursts (GRB) and superluminous supernovae, potentially linking these astrophysical phenomena (Metzger et al. 2017). In addition, the bursting source is found to be spatially coincident with a compact (< 0.7 pc; Marcote et al. 2017), persistent radio source (Chatterjee et al. 2017). Ofek (2017) identified similar radio sources in the Very Large Array FIRST survey (Becker et al. 1995). One of these sources, FIRST J141918.9+394036 (hereafter FIRST J1419+3940), was identified as a radio transient decaying in brightness by a factor of ~50 over several decades (Law et al. 2018). Very-long-baseline radio interferometric observations support the theory that FIRST J1419+3940 is the afterglow of a long GRB, based on the inferred physical size of the emission region (1.6 ± 0.3 pc; Marcote et al. 2019)
No Radio Bursts Detected from FIRST J141918.9+394036 in Green Bank Telescope Observations
Precise localization of the first-known repeating fast radio burst source, FRB 121102 (Spitler et al. 2016; Chatterjee et al. 2017), led to its association with a star-forming region inside a low-metallicity dwarf host galaxy (Tendulkar et al. 2017). This host environment is similar to that typically associated with long gamma-ray bursts (GRB) and superluminous supernovae, potentially linking these astrophysical phenomena (Metzger et al. 2017). In addition, the bursting source is found to be spatially coincident with a compact (< 0.7 pc; Marcote et al. 2017), persistent radio source (Chatterjee et al. 2017). Ofek (2017) identified similar radio sources in the Very Large Array FIRST survey (Becker et al. 1995). One of these sources, FIRST J141918.9+394036 (hereafter FIRST J1419+3940), was identified as a radio transient decaying in brightness by a factor of ~50 over several decades (Law et al. 2018). Very-long-baseline radio interferometric observations support the theory that FIRST J1419+3940 is the afterglow of a long GRB, based on the inferred physical size of the emission region (1.6 ± 0.3 pc; Marcote et al. 2019)
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