18,376 research outputs found
The Grism Lens-Amplified Survey from Space (GLASS). XII. Spatially Resolved Galaxy Star Formation Histories and True Evolutionary Paths at z > 1
Modern data empower observers to describe galaxies as the spatially and
biographically complex objects they are. We illustrate this through case
studies of four, systems based on deep, spatially resolved, 17-band
+ G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full
spectrum rest-UV/-optical continuum fitting, we characterize these galaxies'
observed kpc-scale structures and star formation rates (SFRs) and
reconstruct their history over the age of the universe. The sample's
diversity---passive to vigorously starforming; stellar masses to ---enables us to draw spatio-temporal inferences
relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass
progenitors). Specifically, we find signs that bulge mass-fractions () and
SF history shapes/spatial uniformity are linked, such that higher s
correlate with "inside-out growth" and central specific SFRs that peaked above
the global average for all starforming galaxies at that epoch. Conversely, the
system with the lowest had a flat, spatially uniform SFH with normal peak
activity. Both findings are consistent with models positing a feedback-driven
connection between bulge formation and the switch from rising to falling SFRs
("quenching"). While sample size forces this conclusion to remain tentative,
this work provides a proof-of-concept for future efforts to refine or refute
it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data
amenable to this and more sophisticated analyses. These samples---spanning
representative mass, redshift, SFR, and environmental regimes---will be ripe
for converting into thousands of sub-galactic-scale empirical windows on what
individual systems actually looked like in the past, ushering in a new dialog
between observation and theory.Comment: 18 pp, 15 figs, 3 tables (main text); 5 pp, 5 figs, 1 table
(appendix); Submitted to AAS Journals 1 October 201
A Multi-Temporal Object-Based Image Analysis to Detect Long-Lived Shrub Cover Changes in Drylands
Climate change and human actions condition the spatial distribution and structure of vegetation, especially in drylands. In this context, object-based image analysis (OBIA) has been used to monitor changes in vegetation, but only a few studies have related them to anthropic pressure. In this study, we assessed changes in cover, number, and shape of Ziziphus lotus shrub individuals in a coastal groundwater-dependent ecosystem in SE Spain over a period of 60 years and related them to human actions in the area. In particular, we evaluated how sand mining, groundwater extraction, and the protection of the area affect shrubs. To do this, we developed an object-based methodology that allowed us to create accurate maps (overall accuracy up to 98%) of the vegetation patches and compare the cover changes in the individuals identified in them. These changes in shrub size and shape were related to soil loss, seawater intrusion, and legal protection of the area measured by average minimum distance (AMD) and average random distance (ARD) analysis. It was found that both sand mining and seawater intrusion had a negative effect on individuals; on the contrary, the protection of the area had a positive effect on the size of the individualsâ coverage. Our findings support the use of OBIA as a successful methodology for monitoring scattered vegetation patches in drylands, key to any monitoring program aimed at vegetation preservation
Decoding the Encoding of Functional Brain Networks: an fMRI Classification Comparison of Non-negative Matrix Factorization (NMF), Independent Component Analysis (ICA), and Sparse Coding Algorithms
Brain networks in fMRI are typically identified using spatial independent
component analysis (ICA), yet mathematical constraints such as sparse coding
and positivity both provide alternate biologically-plausible frameworks for
generating brain networks. Non-negative Matrix Factorization (NMF) would
suppress negative BOLD signal by enforcing positivity. Spatial sparse coding
algorithms ( Regularized Learning and K-SVD) would impose local
specialization and a discouragement of multitasking, where the total observed
activity in a single voxel originates from a restricted number of possible
brain networks.
The assumptions of independence, positivity, and sparsity to encode
task-related brain networks are compared; the resulting brain networks for
different constraints are used as basis functions to encode the observed
functional activity at a given time point. These encodings are decoded using
machine learning to compare both the algorithms and their assumptions, using
the time series weights to predict whether a subject is viewing a video,
listening to an audio cue, or at rest, in 304 fMRI scans from 51 subjects.
For classifying cognitive activity, the sparse coding algorithm of
Regularized Learning consistently outperformed 4 variations of ICA across
different numbers of networks and noise levels (p0.001). The NMF algorithms,
which suppressed negative BOLD signal, had the poorest accuracy. Within each
algorithm, encodings using sparser spatial networks (containing more
zero-valued voxels) had higher classification accuracy (p0.001). The success
of sparse coding algorithms may suggest that algorithms which enforce sparse
coding, discourage multitasking, and promote local specialization may capture
better the underlying source processes than those which allow inexhaustible
local processes such as ICA
ComQA: A Community-sourced Dataset for Complex Factoid Question Answering with Paraphrase Clusters
To bridge the gap between the capabilities of the state-of-the-art in factoid
question answering (QA) and what users ask, we need large datasets of real user
questions that capture the various question phenomena users are interested in,
and the diverse ways in which these questions are formulated. We introduce
ComQA, a large dataset of real user questions that exhibit different
challenging aspects such as compositionality, temporal reasoning, and
comparisons. ComQA questions come from the WikiAnswers community QA platform,
which typically contains questions that are not satisfactorily answerable by
existing search engine technology. Through a large crowdsourcing effort, we
clean the question dataset, group questions into paraphrase clusters, and
annotate clusters with their answers. ComQA contains 11,214 questions grouped
into 4,834 paraphrase clusters. We detail the process of constructing ComQA,
including the measures taken to ensure its high quality while making effective
use of crowdsourcing. We also present an extensive analysis of the dataset and
the results achieved by state-of-the-art systems on ComQA, demonstrating that
our dataset can be a driver of future research on QA.Comment: 11 pages, NAACL 201
A Water Accounting System for Strategic Water Management
This paper describes a water accounting system (WAS) that has been developed as an innovative new tool for strategic long-term water management. The WAS incorporates both disaggregated water use and availability, provides a comprehensive and consistent historical database, and can integrate climate and hydrological model outputs for the exploration of scenarios. It has been established and tested for the state of Victoria in Australia, and can be extended to cover other or all regions of Australia. The WAS is implemented using stock-and-flow dynamics, currently employing major river basins as the spatial units and a yearly time step. While this system shares features with system dynamics, learning is enhanced and strategic management of water resources is improved by application of a Design Approach and the structure of the WAS. We compare the WAS with other relevant accounting systems and outline its benefits, particularly the potential for resolving tensions between water supply and demand. Integrated management is facilitated by combination with other stocks and flows frameworks that provide data on key drivers such as demography, land-use and electricity production.water accounts, stocks and flows, water budgets, decision support systems, strategic management
Measurement of the Solar Neutrino Capture Rate by the Russian-American Gallium Solar Neutrino Experiment During One Half of the 22-Year Cycle of Solar Activity
We present the results of measurements of the solar neutrino capture rate in
gallium metal by the Russian-American Gallium Experiment SAGE during slightly
more than half of a 22-year cycle of solar activity. Combined analysis of the
data of 92 runs during the 12-year period January 1990 through December 2001
gives a capture rate of solar neutrinos with energy more than 233 keV of 70.8
+5.3/-5.2 (stat.) +3.7/-3.2 (syst.) SNU. This represents only slightly more
than half of the predicted standard solar model rate of 128 SNU. We give the
results of new runs beginning in April 1998 and the results of combined
analysis of all runs since 1990 during yearly, monthly, and bimonthly periods.
Using a simple analysis of the SAGE results combined with those from all other
solar neutrino experiments, we estimate the electron neutrino pp flux that
reaches the Earth to be (4.6 +/- 1.1) E10/(cm^2-s). Assuming that neutrinos
oscillate to active flavors the pp neutrino flux emitted in the solar fusion
reaction is approximately (7.7 +/- 1.8) E10/(cm^2-s), in agreement with the
standard solar model calculation of (5.95 +/- 0.06) E10/(cm^2-s).Comment: English translation of article submitted to Russian journal Zh. Eksp.
Teor. Fiz. (JETP); 12 pages, 5 figures. V2: Added winter-summer difference
and 2 reference
Population Biology and Interactions of Arbuscular Mycorrhizal Fungi and Their Benefits in Strawberry Cultivation
The diversity of arbuscular mycorrhizal fungi (AMF) and relative abundance among species may affect their ecological impact. Species-specific primers for qPCR quantification of Funneliformis geosporus and F.mosseae DNA were developed to quantify their relative abundance for use in studying mixed inocula in roots of strawberry under different conditions of water stress. Co-occupation of the same root by both species was shown to commonly occur but the relative abundance of the two species varied with water stress. Greater root colonisation was observed microscopically under water stress but this increased colonisation was often accompanied with decreased amounts of fungal DNA in the root. Funneliformis mosseae tended to become more abundant under water stress relative to F. geosporus. There was significant correlation in the fungal colonisation measurements from the microscopic and qPCR methods under some conditions, but the nature of this relationship varied greatly with AMF inoculum and abiotic conditions.
Water stress experiments, undertaken with strawberry (Fragaria x ananassa) show a reduction of plant development when subjected to regulated deficit irrigation (RDI) conditions. The effect on growth of AMF colonisation and relative abundance of two co-occurring species of AMF, F. geosporus and F. mosseae, were determined in cultivated strawberry under conditions of water stress. Three AMF inoculation treatments (a single treatment either of F. mosseae BEG25, F. geosporus BEG11 or a 50:50 mixed inoculation treatment of both species) were compared to un-inoculated plants. This study demonstrated that in strawberry plants, under these experimental conditions, single species inoculation treatments gave similar benefits to the host as the mixed inoculation treatment regardless of irrigation regime, suggesting colonisation was of greater importance than mycorrhizal fungal species. The addition of AMF inocula to plants, subjected to reduced irrigation of up to 40%, restored plant growth to the same or higher values as the non-mycorrhizal, fully-watered plants. The water use efficiency of plants was greater under the RDI regime and in AMF-inoculated plants, but there were no significant differences between plants inoculated with the single or combined inoculum.
The occurrence of multiple variant sequences within the rRNA genes of the AMF is now widely accepted; however the mechanisms for this are not currently clear. This work investigated the effect of different culture conditions (in vitro and in planta culture) on sequence diversity and relative abundance of a culture of Rhizophagus clarus. Next generation sequencing, using the Illumina platform, generated three major sequence variants that were the most common sequence variants in all conditions. All other sequences grouped phylogenetically about these three major sequence types along with an outgroup of less common sequence types. This study demonstrated that changes in the frequency of dominant sequence variants had occurred when AMF are maintained for two years under different culture conditions
On Capturing Oil Rents with a National Excise Tax Revisited
In this paper the scope of Bergstromâs (1982) results is studied. Moreover, his analysis is extended assuming that extraction cost is directly related to accumulated extractions. For the case of a competitive market it is found that the optimal policy is a constant tariff if extraction is costless. However, with depletion effects, the optimal tariff must ultimately be decreasing. For the case of a monopolistic market the results depend crucially on the kind of strategies the importing country governments can play and on whether the monopolist chooses the price or extraction rate. For a price-setting monopolist it is shown that the importing countries cannot use a tariff to capture monopoly rents if they are constrained to use open-loop strategies, even if the governments sign a tariff agreement. This result is drastically modified if the importing countries in the tariff agreement use Markov (feedback) strategies. For a quantity-setting monopolist the nature of the game changes and the importing country governments find it advantageous to set a tariff on resource importations. Moreover, in this case the importing countries in a tariff agreement enjoy a strategic advantage which allows them to behave as a leader.Tariffs, Tariff agreements, Non renewable resources, Depletion effects, Price-setting monopolist, Quantity-setting monopolist, Differential games, Open-loop strategies, Linear strategies, Markov-perfect Nash equilibrium, Markov-perfect Stackelberg equilibrium
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