91,639 research outputs found
Evidence of instability in previously-mapped landslides as measured using GPS, optical, and SAR data between 2007 and 2017: A case study in the Portuguese Bend Landslide Complex, California
Velocity dictates the destructive potential of a landslide. A combination of synthetic aperture radar (SAR), optical, and GPS data were used to maximize spatial and temporal coverage to monitor continuously-moving portions of the Portuguese Bend landslide complex on the Palos Verdes Peninsula in Southern California. Forty SAR images from the COSMO-SkyMed satellite, acquired between 19 July 2012 and 27 September 2014, were processed using Persistent Scatterer Interferometry (PSI). Eight optical images from the WorldView-2 satellite, acquired between 20 February 2011 and 16 February 2016, were processed using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) technique. Displacement measurements were taken at GPS monuments between September 2007 and May 2017. Incremental and average deformations across the landslide complex were measured using all three techniques. Velocity measured within the landslide complex ranges from slow (\u3e 1.6 m/year) to extremely slow (\u3c 16 mm/year). COSI-Corr and GPS provide detailed coverage of m/year-scale deformation while PSI can measure extremely slow deformation rates (mm/year-scale), which COSI-Corr and GPS cannot do reliably. This case study demonstrates the applicability of SAR, optical, and GPS data synthesis as a complimentary approach to repeat field monitoring and mapping to changes in landslide activity through time
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Risk as reward: Reinforcement sensitivity theory and psychopathic personality perspectives on everyday risk-taking
This study updates and synthesises research on the extent to which impulsive and antisocial disposition predicts everyday pro- and antisocial risk-taking behaviour. We use the Reinforcement Sensitivity Theory (RST) of personality to measure approach, avoidance, and inhibition dispositions, as well as measures of Callous-Unemotional and psychopathic personalities. In an international sample of 454 respondents, results showed that RST, psychopathic personality, and callous-unemotional measures accounted for different aspects of risk-taking behaviour. Specifically, traits associated with ‘fearlessness’ related more to ‘prosocial’ (recreational and social) risk-taking, whilst traits associated with ‘impulsivity’ related more to ‘antisocial’ (ethical and health) risk-taking. Further, we demonstrate that psychopathic personality may be demonstrated by combining the RST and callous-unemotional traits (high impulsivity, callousness, and low fear). Overall this study showed how impulsive, fearless and antisocial traits can be used in combination to identify pro- and anti-social risk-taking behaviours; suggestions for future research are indicated
Sim-to-Real Transfer of Robotic Control with Dynamics Randomization
Simulations are attractive environments for training agents as they provide
an abundant source of data and alleviate certain safety concerns during the
training process. But the behaviours developed by agents in simulation are
often specific to the characteristics of the simulator. Due to modeling error,
strategies that are successful in simulation may not transfer to their real
world counterparts. In this paper, we demonstrate a simple method to bridge
this "reality gap". By randomizing the dynamics of the simulator during
training, we are able to develop policies that are capable of adapting to very
different dynamics, including ones that differ significantly from the dynamics
on which the policies were trained. This adaptivity enables the policies to
generalize to the dynamics of the real world without any training on the
physical system. Our approach is demonstrated on an object pushing task using a
robotic arm. Despite being trained exclusively in simulation, our policies are
able to maintain a similar level of performance when deployed on a real robot,
reliably moving an object to a desired location from random initial
configurations. We explore the impact of various design decisions and show that
the resulting policies are robust to significant calibration error
Contextualized Word Representations for Reading Comprehension
Reading a document and extracting an answer to a question about its content
has attracted substantial attention recently. While most work has focused on
the interaction between the question and the document, in this work we evaluate
the importance of context when the question and document are processed
independently. We take a standard neural architecture for this task, and show
that by providing rich contextualized word representations from a large
pre-trained language model as well as allowing the model to choose between
context-dependent and context-independent word representations, we can obtain
dramatic improvements and reach performance comparable to state-of-the-art on
the competitive SQuAD dataset.Comment: 6 pages, 1 figure, NAACL 201
Variability-selected low-luminosity active galactic nuclei candidates in the 7 Ms Chandra Deep Field-South
In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of
luminosities have been identified. However, cosmologically distant
low-luminosity AGN (LLAGN, erg s)
identification still poses a challenge due to significant contamination from
host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the
longest timescale ( years) deep X-ray survey to date, we utilize an
X-ray variability selection technique to search for LLAGNs that remain
unidentified among the CDF-S X-ray sources. We find 13 variable sources from
110 unclassified CDF-S X-ray sources. Except for one source which could be an
ultraluminous X-ray source, the variability of the remaining 12 sources is most
likely due to accreting supermassive black holes. These 12 AGN candidates have
low intrinsic X-ray luminosities, with a median value of erg
s. They are generally not heavily obscured, with an average effective
power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is
independent of X-ray luminosity and is only restricted by the total number of
observed net counts, confirming previous findings that X-ray variability is a
near-ubiquitous property of AGNs over a wide range of luminosities. There is an
anti-correlation between X-ray luminosity and variability amplitude for
high-luminosity AGNs, but as the luminosity drops to erg
s, the variability amplitude no longer appears dependent on the
luminosity. The entire observed luminosity-variability trend can be roughly
reproduced by an empirical AGN variability model based on a broken power-law
power spectral density function.Comment: 18 pages, 11 figures, accepted for publication in Ap
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