1,949 research outputs found
Dynamics of a 1-D model for the emergence of the plasma edge shear flow layer with momentum conserving Reynolds stress
A one-dimensional version of the second-order transition model based on the
sheared flow amplification by Reynolds stress and turbulence supression by
shearing is presented. The model discussed in this paper includes a form of the
Reynolds stress which explicitly conserves momentum. A linear stability
analysis of the critical point is performed. Then, it is shown that the
dynamics of weakly unstable states is determined by a reduced equation for the
shear flow. In the case in which the flow damping term is diffusive, the
stationary solutions are those of the real Ginzburg-Landau equation.Comment: 21 pages, 8 figure
Combination Strategies for Semantic Role Labeling
This paper introduces and analyzes a battery of inference models for the
problem of semantic role labeling: one based on constraint satisfaction, and
several strategies that model the inference as a meta-learning problem using
discriminative classifiers. These classifiers are developed with a rich set of
novel features that encode proposition and sentence-level information. To our
knowledge, this is the first work that: (a) performs a thorough analysis of
learning-based inference models for semantic role labeling, and (b) compares
several inference strategies in this context. We evaluate the proposed
inference strategies in the framework of the CoNLL-2005 shared task using only
automatically-generated syntactic information. The extensive experimental
evaluation and analysis indicates that all the proposed inference strategies
are successful -they all outperform the current best results reported in the
CoNLL-2005 evaluation exercise- but each of the proposed approaches has its
advantages and disadvantages. Several important traits of a state-of-the-art
SRL combination strategy emerge from this analysis: (i) individual models
should be combined at the granularity of candidate arguments rather than at the
granularity of complete solutions; (ii) the best combination strategy uses an
inference model based in learning; and (iii) the learning-based inference
benefits from max-margin classifiers and global feedback
Comparison of Standard and Total Keratometry Astigmatism Measured with three Different Technologies
Purpose: To compare the keratometric and total corneal astigmatism measures provided by three different technologies as well as to assess the level of interchangeability among them. Methods: A Prospective, comparative study enrolling 94 eyes from 53 patients (age, 29-77 years) was carried out. All participants were patients with the diagnosis of cataract or patients with a transparent crystalline lens but seeking surgical presbyopia correction. A complete eye examination was performed in all eyes, including corneal analysis with three different devices: IOL-Master 700 (Carl Zeiss Meditec), Cassini (i-Optics), and Pentacam (Oculus Optikgeräte GmbH). Interchangeability of standard and total keratometric readings (equivalent keratometric readings for Pentacam) and astigmatism measures with these three systems were evaluated with the Bland-Altman analysis. Results: Significantly higher standard and total keratometric readings were obtained with the IOL-Master compared to the other two systems (p<0.001). Likewise, a significantly higher magnitude of standard and total keratometric astigmatism was obtained with the Cassini system (p<0.001). Ranges of the agreement for corneal power measurements between devices varied from 0.58 D to 1.53 D, whereas they ranged from 0.46 D to 1.37 D for standard and total astigmatism measurements. Conclusion: Corneal power and astigmatism measures obtained with IOL-Master 700, Cassini, and Pentacam systems cannot be used interchangeably. The impact of these differences on the refractive predictability achieved with different types of intraocular lenses (IOL) should be evaluated in the future in order to define which is the best corneal evaluation approach for optimizing the IOL power calculations.The author, David P Piñero, has been supported by the Ministry of Economy, Industry, and Competitiveness of Spain within the program Ramón y Cajal, RYC-2016-20471
An Intervention-AUV learns how to perform an underwater valve turning
Intervention autonomous underwater vehicles (I-AUVs) are a promising platform to perform intervention task in underwater environments, replacing current methods like remotely operate underwater vehicles (ROVs) and manned sub-mersibles that are more expensive. This article proposes a complete system including all the necessary elements to perform a valve turning task using an I-AUV. The knowledge of an operator to perform the task is transmitted to an I-AUV by a learning by demonstration (LbD) algorithm. The algorithm learns the trajectory of the vehicle and the end-effector to accomplish the valve turning. The method has shown its feasibility in a controlled environment repeating the learned task with different valves and configurations
First report of an olive ridley (Lepidochelys olivacea) inside the Mediterranean Sea
We report the first confirmed occurrence of a Lepidochelys olivacea in the Mediterranean Sea based on the study of an individual stranded on a beach, located in the town of Oropesa del Mar (40º05ʹ32ʺN, 0º08ʹ02ʺE), Castellón province, East Spain, in May 2014. Morphological and genetic analyses were used to confirm the identification of the species. The individual had a sequence that matched the 470 bp Lepidochelys olivacea haplotype F (Genbank accession number: AF051773), found in several Atlantic populations. This becomes one of the northernmost known occurrences of olive ridleys in the world and is the first reports of this species in the Mediterranean Sea
A sandpile model with tokamak-like enhanced confinement phenomenology
Confinement phenomenology characteristic of magnetically confined plasmas
emerges naturally from a simple sandpile algorithm when the parameter
controlling redistribution scalelength is varied. Close analogues are found for
enhanced confinement, edge pedestals, and edge localised modes (ELMs), and for
the qualitative correlations between them. These results suggest that tokamak
observations of avalanching transport are deeply linked to the existence of
enhanced confinement and ELMs.Comment: Manuscript is revtex (latex) 1 file, 7 postscript figures Revised
version is final version accepted for publication in PRL Revisions are mino
Random walk through fractal environments
We analyze random walk through fractal environments, embedded in
3-dimensional, permeable space. Particles travel freely and are scattered off
into random directions when they hit the fractal. The statistical distribution
of the flight increments (i.e. of the displacements between two consecutive
hittings) is analytically derived from a common, practical definition of
fractal dimension, and it turns out to approximate quite well a power-law in
the case where the dimension D of the fractal is less than 2, there is though
always a finite rate of unaffected escape. Random walks through fractal sets
with D less or equal 2 can thus be considered as defective Levy walks. The
distribution of jump increments for D > 2 is decaying exponentially. The
diffusive behavior of the random walk is analyzed in the frame of continuous
time random walk, which we generalize to include the case of defective
distributions of walk-increments. It is shown that the particles undergo
anomalous, enhanced diffusion for D_F < 2, the diffusion is dominated by the
finite escape rate. Diffusion for D_F > 2 is normal for large times, enhanced
though for small and intermediate times. In particular, it follows that
fractals generated by a particular class of self-organized criticality (SOC)
models give rise to enhanced diffusion. The analytical results are illustrated
by Monte-Carlo simulations.Comment: 22 pages, 16 figures; in press at Phys. Rev. E, 200
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