523 research outputs found
Context Modeling for Ranking and Tagging Bursty Features in Text Streams
Bursty features in text streams are very useful in many text mining applications. Most existing studies detect bursty features based purely on term frequency changes without taking into account the semantic contexts of terms, and as a result the detected bursty features may not always be interesting or easy to interpret. In this paper we propose to model the contexts of bursty features using a language modeling approach. We then propose a novel topic diversity-based metric using the context models to find newsworthy bursty features. We also propose to use the context models to automatically assign meaningful tags to bursty features. Using a large corpus of a stream of news articles, we quantitatively show that the proposed context language models for bursty features can effectively help rank bursty features based on their newsworthiness and to assign meaningful tags to annotate bursty features. ? 2010 ACM.EI
The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b
The absorption signals of metastable He in HD 209458b and several other
exoplanets can be explained via escaping atmosphere model with a subsolar He/H
ratio. The low abundance of helium can be a result of planet formation if there
is a small amount of helium in their primordial atmosphere. However, another
possibility is that the low He/H ratio is caused by the process of mass
fractionation of helium in the atmosphere. In order to investigate the effect
of the fractionation in the hydrogen-helium atmosphere, we developed a
self-consistent multi-fluid 1D hydrodynamic model based on the well-known
open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be
produced spontaneously in the multi-fluid model. We further modeled the
transmission spectra of He 10830 lines for HD 209458b in a broad parameter
space. The transmission spectrum of the observation can be fitted in the
condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet
Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen,
, is 0.039. Our results indicate that the mass fractionation of
helium to hydrogen can naturally interpret the low He/H ratio required by the
observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the
abundance of helium in the atmosphere is not needed even if its He abundance is
similar to that of the Sun. The simulation presented in this work hints that in
the escaping atmosphere, mass fractionation can also occur on other exoplanets,
which needs to be explored further.Comment: Accepted by Ap
Monitoring the Characteristics of the Bohai Sea Ice Using High-Resolution Geostationary Ocean Color Imager (GOCI) Data
Satellite remote sensing data, such as moderate resolution imaging spectroradiometers (MODIS) and advanced very high-resolution radiometers (AVHRR), are being widely used to monitor sea ice conditions and their variability in the Bohai Sea, the southernmost frozen sea in the Northern Hemisphere. Monitoring the characteristics of the Bohai Sea ice can provide crucial information for ice disaster prevention for marine transportation, oil field operation, and regional climate change studies. Although these satellite data cover the study area with fairly high spatial resolution, their typically limited cloudless images pose serious restrictions for continuous observation of short-term dynamics, such as sub-seasonal changes. In this study, high spatiotemporal resolution (500 m and eight images per day) geostationary ocean color imager (GOCI) data with a high proportion of cloud-free images were used to monitor the characteristics of the Bohai Sea ice, including area and thickness. An object-based feature extraction method and an albedo-based thickness inversion model were used for estimating sea ice area and thickness, respectively. To demonstrate the efficacy of the new dataset, a total of 68 GOCI images were selected to analyze the evolution of sea ice area and thickness during the winter of 2012–2013 with severe sea ice conditions. The extracted sea ice area was validated using Landsat Thematic Mapper (TM) data with higher spatial resolution, and the estimated sea ice thickness was found to be consistent with in situ observation results. The entire sea ice freezing–melting processes, including the key events such as the day with the maximum ice area and the first and last days of the frozen season, were better resolved by the high temporal-resolution GOCI data compared with MODIS or AVHRR data. Both characteristics were found to be closely correlated with cumulative freezing/melting degree days. Our study demonstrates the applicability of the GOCI data as an improved dataset for studying the Bohai Sea ice, particularly for purposes that require high temporal resolution data, such as sea ice disaster monitoring
1,1′-Bicyclohexyl-1,1′-diyl 1,1′-biphenyl-2,2′-dicarboxylate
The title compound, C26H28O4, lies about a crystallographic twofold rotation axis. The cyclohexane rings adopt a chair conformation. The two benzene rings form a dihedral angle of 40.82 (3)°. No significant intra- or intermolecular interactions are observed in the crystal structure
Modeling H and He 10830 transmission spectrum of WASP-52b
Escaping atmosphere has been detected by the excess absorption of Ly,
H and He triplet (10830) lines. Simultaneously modeling the
absorption of the H and He 10830 lines can provide useful constraints
about the exoplanetary atmosphere. In this paper, we use a hydrodynamic model
combined with a non-local thermodynamic model and a new Monte Carlo simulation
model to obtain the H(2) and He(2S) populations. The Monte Carlo
simulations of Ly radiative transfer are performed with assumptions of
a spherical stellar Ly radiation and a spherical planetary atmosphere,
for the first time, to calculate the Ly mean intensity distribution
inside the planetary atmosphere, necessary in estimating the H(2) population.
We model the transmission spectra of the H and He 10830 lines
simultaneously in hot Jupiter WASP-52b. We find that models with many different
H/He ratios can reproduce the H observations well if the host star has
(1) a high X-ray/extreme ultraviolet (XUV) flux () and a
relatively low X-ray fraction in XUV radiation (), or (2) a low
and a high . The simulations of He 10830
triplet suggest that a high H/He ratio ( 98/2) is required to fit the
observation. The models that fit both lines well confine to be
about 0.5 times the fiducial value and to have a value around 0.3.
The models also suggest that hydrogen and helium originate from the escaping
atmosphere, and the mass-loss rate is about 2.8 g s.Comment: Accepted for publication in ApJ, 48 page
The Causal Learning of Retail Delinquency
This paper focuses on the expected difference in borrower's repayment when
there is a change in the lender's credit decisions. Classical estimators
overlook the confounding effects and hence the estimation error can be
magnificent. As such, we propose another approach to construct the estimators
such that the error can be greatly reduced. The proposed estimators are shown
to be unbiased, consistent, and robust through a combination of theoretical
analysis and numerical testing. Moreover, we compare the power of estimating
the causal quantities between the classical estimators and the proposed
estimators. The comparison is tested across a wide range of models, including
linear regression models, tree-based models, and neural network-based models,
under different simulated datasets that exhibit different levels of causality,
different degrees of nonlinearity, and different distributional properties.
Most importantly, we apply our approaches to a large observational dataset
provided by a global technology firm that operates in both the e-commerce and
the lending business. We find that the relative reduction of estimation error
is strikingly substantial if the causal effects are accounted for correctly.Comment: This paper was accepted and will be published in the Thirty-Fifth
AAAI Conference on Artificial Intelligence (AAAI-21
Degenerate-Generalized Likelihood Ratio Test for One-Sided Composite Hypotheses
We propose the degenerate-generalized likelihood ratio test (DGLRT) for one-sided composite hypotheses in cases of independent and dependent observations. The theoretical results show that the DGLRT has controlled error probabilities and stops sampling with probability 1 under some regularity conditions. Moreover, its stopping boundaries are constants and can be easily determined using the provided searching algorithm. According to the simulation studies, the DGLRT has less overall expected sample sizes and less relative mean index (RMI) values in comparison with the sequential probability ratio test (SPRT) and double sequential probability ratio test (2-SPRT). To illustrate the application of it, a real manufacturing data are analyzed
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