14,897 research outputs found
Parallel and Distributed Statistical-based Extraction of Relevant Multiwords from Large Corpora
The amount of information available through the Internet has been showing a significant
growth in the last decade. The information can result from various sources such as
scientific experiments resulting from particle acceleration, recording the flight data of a
commercial aircraft, or sets of documents from a given domain such as medical articles,
news headlines from a newspaper, or social networks contents.
Due to the volume of data that must be analyzed, it is necessary to endow the search
engines with new tools that allow the user to obtain the desired information in a timely
and accurate manner. One approach is the annotation of documents with their relevant
expressions. The extraction of relevant expressions from natural language text documents can be accomplished by the use of semantic, syntactic, or statistical techniques. Although the latter tend to be not so accurate, they have the advantage of being independent of the language. This investigation was performed in the context of LocalMaxs, which is a statistical method, thus language-independent, capable of extracting relevant expressions from natural language corpora.
However, due to the large volume of data involved, the sequential implementations of
the above techniques have severe limitations both in terms of execution time and memory space. In this thesis we propose a distributed architecture and strategies for parallel implementations of statistical-based extraction of relevant expressions from large corpora.
A methodology was developed for modeling and evaluating those strategies based on
empirical and theoretical approaches to estimate the statistical distribution of n-grams in natural language corpora. These approaches were applied to guide the design and evaluation of the behavior of LocalMaxs parallel and distributed implementations on cluster and cloud computing platforms. The implementation alternatives were compared regarding their precision and recall, and their performance metrics, namely, execution time, parallel speedup and sizeup. The performance results indicate almost linear speedup and sizeup for the range of large corpora sizes
Multicolour Optical Imaging of IR-Warm Seyfert Galaxies. V. Morphologies and Interactions. Challenging the Orientation Model
This paper is the last in a series, investigating the optical properties of a
sample of mid-IR Warm Seyfert galaxies and of a control sample of mid-IR cold
galaxies. In the present paper we parametrize the morphologies and interaction
properties of the host galaxies and combine these with the major conclusions in
our previous papers. Our results confirm that nuclear activity is linked to
galactic interactions. We suggest an alternative view for the simple
orientation-obscuration model postulated for Seyfert types 1 and 2, that takes
into account the time evolution of their environmental and morphological
properties. Within this view, an evolutionary link between starburst-dominated
and AGN-dominated IR emission is also suggested, to account for the
observational discriminator (mid-IR excess) between our Warm and Cold samples.Comment: 24 pages, including 6 figures and 3 tables (figure 5 included as
independent file), Submitted to Ap
Characterizing 51 Eri b from 1-5 m: a partly-cloudy exoplanet
We present spectro-photometry spanning 1-5 m of 51 Eridani b, a 2-10
M planet discovered by the Gemini Planet Imager Exoplanet Survey.
In this study, we present new (1.90-2.19 m) and (2.10-2.40
m) spectra taken with the Gemini Planet Imager as well as an updated
(3.76 m) and new (4.67 m) photometry from the NIRC2 Narrow
camera. The new data were combined with (1.13-1.35 m) and
(1.50-1.80 m) spectra from the discovery epoch with the goal of better
characterizing the planet properties. 51 Eri b photometry is redder than field
brown dwarfs as well as known young T-dwarfs with similar spectral type
(between T4-T8) and we propose that 51 Eri b might be in the process of
undergoing the transition from L-type to T-type. We used two complementary
atmosphere model grids including either deep iron/silicate clouds or
sulfide/salt clouds in the photosphere, spanning a range of cloud properties,
including fully cloudy, cloud free and patchy/intermediate opacity clouds.
Model fits suggest that 51 Eri b has an effective temperature ranging between
605-737 K, a solar metallicity, a surface gravity of (g) = 3.5-4.0 dex,
and the atmosphere requires a patchy cloud atmosphere to model the SED. From
the model atmospheres, we infer a luminosity for the planet of -5.83 to -5.93
(), leaving 51 Eri b in the unique position as being one of
the only directly imaged planet consistent with having formed via cold-start
scenario. Comparisons of the planet SED against warm-start models indicates
that the planet luminosity is best reproduced by a planet formed via core
accretion with a core mass between 15 and 127 M.Comment: 27 pages, 19 figures, Accepted for publication in The Astronomical
Journa
GOODS-Herschel: Separating High Redshift active galactic Nuclei and star forming galaxies Using Infrared Color Diagnostics
We have compiled a large sample of 151 high redshift (z=0.5-4) galaxies
selected at 24 microns (S24>100 uJy) in the GOODS-N and ECDFS fields for which
we have deep Spitzer IRS spectroscopy, allowing us to decompose the
mid-infrared spectrum into contributions from star formation and activity in
the galactic nuclei. In addition, we have a wealth of photometric data from
Spitzer IRAC/MIPS and Herschel PACS/SPIRE. We explore how effective different
infrared color combinations are at separating our mid-IR spectroscopically
determined active galactic nuclei from our star forming galaxies. We look in
depth at existing IRAC color diagnostics, and we explore new color-color
diagnostics combining mid-IR, far-IR, and near-IR photometry, since these
combinations provide the most detail about the shape of a source's IR spectrum.
An added benefit of using a color that combines far-IR and mid-IR photometry is
that it is indicative of the power source driving the IR luminosity. For our
data set, the optimal color selections are S250/S24 vs. S8.0/S3.6 and S100/S24
vs. S8.0/S3.6; both diagnostics have ~10% contamination rate in the regions
occupied primarily by star forming galaxies and active galactic nuclei,
respectively. Based on the low contamination rate, these two new IR color-color
diagnostics are ideal for estimating both the mid-IR power source of a galaxy
when spectroscopy is unavailable and the dominant power source contributing to
the IR luminosity. In the absence of far-IR data, we present color diagnostics
using the WISE mid-IR bands which can efficiently select out high z (z~2) star
forming galaxies.Comment: Accepted for publication in ApJ. 13 pages, 8 figure
Climatological Assessment of Urban Effects on Precipitation: Final Report Part I
published or submitted for publicationis peer reviewedOpe
Graph-based prediction of missing KPIs through optimization and random forests for KPI systems
Key performance indicators (KPIs) are widely used to monitor and control the production in industry. On an aggregated level, often represented as graphs or interrelated KPI systems, a comprehensive overview is given. However, missing or inaccurate sensor data and KPIs, as well inconsistencies in KPI based management are a major hurdle disturbing operations. To counter the impact of such missing KPIs, we propose a value optimization based approach to reconstruct the values of missing KPIs within a KPI system. While the approach shows successful reconstruction in the case study, the value optimization can be sped up through a random forest prediction of the initial optimization set. Thus, the inclusion of previous knowledge about the system behavior proves beneficial and superior to the pure optimization based approach, as validated by both randomized and simulation-based measurement data
On the absence of appreciable half-life changes in alpha emitters cooled in metals to 1 Kelvin and below
The recent suggestion that dramatic changes may occur in the lifetime of
alpha and beta decay when the activity, in a pure metal host, is cooled to a
few Kelvin, is examined in the light of published low temperature nuclear
orientation (LTNO) experiments, with emphasis here on alpha decay. In LTNO
observations are made of the anisotropy of radioactive emissions with respect
to an axis of orientation. Correction of data for decay of metallic samples
held at temperatures at and below 1 Kelvin for periods of days and longer has
been a routine element of LTNO experiments for many years. No evidence for any
change of half life on cooling, with an upper level of less than 1%, has been
found, in striking contrast to the predicted changes, for alpha decay, of
several orders of magnitude. The proposal that such dramatic changes might
alleviate problems of disposal of long-lived radioactive waste is shown to be
unrealistic.Comment: 27 pages, 12 figures, accepted for publication in Nucl.Phys.A.
Revised version, including quantitative analysis of the sensitivity of
nuclear orientation experiments, discussed in this work, to changes of
alpha-decay lifetimes in metals at low temperatures. Conclusions remain
unchange
The Distribution and Condition of the Warm Molecular Gas in Abell 2597 and Sersic 159-03
We have used the SINFONI integral field spectrograph to map the near-infrared
K-band emission lines of molecular and ionised hydrogen in the central regions
of two cool core galaxy clusters, Abell 2597 and Sersic 159-03. Gas is detected
out to 20 kpc from the nuclei of the brightest cluster galaxies and found to be
distributed in clumps and filaments around it. The ionised and molecular gas
phases trace each other closely in extent and dynamical state. Both gas phases
show signs of interaction with the active nucleus. Within the nuclear regions
the kinetic luminosity of this gas is found to be somewhat smaller than the
current radio luminosity. Outside the nuclear region the gas has a low velocity
dispersion and shows smooth velocity gradients. There is no strong correlation
between the intensity of the molecular and ionised gas emission and either the
radio or X-ray emission. The molecular gas in Abell 2597 and Sersic 159-03 is
well described by a gas in local thermal equilibrium (LTE) with a single
excitation temperature T_exc ~ 2300 K. The emission line ratios do not vary
strongly as function of position, with the exception of the nuclear regions
where the ionised to molecular gas ratio is found decrease. These constant line
ratios imply a single source of heating and excitation for both gas phases.Comment: 44 pages, 32 figures, accepted for publication in MNRA
Evaluation of exercises designed to increase children's use of descriptive words.
Thesis (Ed.M.)--Boston Universit
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