662 research outputs found
Black holes and neutron stars in the generalized tensor-vector-scalar theory
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success
as a relativistic theory of Modified Newtonian Dynamics (MoND). However, recent
work suggests that the dynamics of the theory are fundamentally flawed and
numerous authors have subsequently begun to consider a generalization of TeVeS
where the vector field is given by an Einstein-Aether action. Herein, I develop
strong-field solutions of the generalized TeVeS theory, in particular exploring
neutron stars as well as neutral and charged black holes. I find that the
solutions are identical to the neutron star and black hole solutions of the
original TeVeS theory, given a mapping between the parameters of the two
theories, and hence provide constraints on these values of the coupling
constants. I discuss the consequences of these results in detail including the
stability of such spacetimes as well as generalizations to more complicated
geometries.Comment: Accepted for publication in Physical Review
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Machine learning for automated sonar monitoring of outmigrating American eel behavior
Abundance of American eel (Anguilla rostrata) is low compared to historical levels, which makes it a species of management concern. Adult American eel are vulnerable to hydropower turbine mortality during outmigration from inland waters to their spawning ground in the Sargasso Sea. Morphological and behavioral characteristics of the species make it particularly challenging to provide safe downstream passage at hydropower projects. Furthermore, outmigration of adult eels is episodic and protracted, typically extending over a period of several months or more each year. Consequently, design, optimization, and operation of downstream passage facilities that are economical and biologically effective requires knowledge of eel behavior during their downstream migration. Site-specific information requirements include knowledge of when eels are approaching hydropower facilities; pathways of approach and passage; and near-field behavioral responses to facility structures including intakes, guidance structures, and bypasses.
The EPRI Eel Passage Research Center investigated three sonar technologies for observing the abundance and behavior of outmigrating adult eels. Among the three sonar types tested, ARIS multibeam imaging sonar holds the most promise for correctly identifying eels at up to 16-20 meters range. While multi-beam imaging sonar can provide the needed data, the protracted nature of adult eel outmigration and the rate of sonar data production make automated data analysis essential for cost-effective monitoring.
Our ongoing project has the goal of developing machine-based detection of American eel from ARIS sonar data. The project will: (1) extract training and validation data from ARIS sonar records collected at the Iroquois Water Control Dam on the St. Lawrence River, USA/Canada; (2) utilize two-dimensional wavelet transform analysis to filter noise and increase contrast of the sonar images; (3) apply convolutional neural network analysis to classify the images into three types of objects – background, eel, and moving, non-eel target; (4) quantify the performance of the analysis system
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Eels III: Assessment of Three Sonars to Evaluate the Downstream Migration of American Eels in the St. Lawrence River
Mapping and Assessment of the United States Ocean Wave Energy Resource
This project estimates the naturally available and technically recoverable U.S. wave energy resources, using a 51-month Wavewatch III hindcast database developed especially for this study by National Oceanographic and Atmospheric AdministrationâÃÂÃÂs (NOAAâÃÂÃÂs) National Centers for Environmental Prediction. For total resource estimation, wave power density in terms of kilowatts per meter is aggregated across a unit diameter circle. This approach is fully consistent with accepted global practice and includes the resource made available by the lateral transfer of wave energy along wave crests, which enables wave diffraction to substantially reestablish wave power densities within a few kilometers of a linear array, even for fixed terminator devices. The total available wave energy resource along the U.S. continental shelf edge, based on accumulating unit circle wave power densities, is estimated to be 2,640 TWh/yr, broken down as follows: 590 TWh/yr for the West Coast, 240 TWh/yr for the East Coast, 80 TWh/yr for the Gulf of Mexico, 1570 TWh/yr for Alaska, 130 TWh/yr for Hawaii, and 30 TWh/yr for Puerto Rico. The total recoverable wave energy resource, as constrained by an array capacity packing density of 15 megawatts per kilometer of coastline, with a 100-fold operating range between threshold and maximum operating conditions in terms of input wave power density available to such arrays, yields a total recoverable resource along the U.S. continental shelf edge of 1,170 TWh/yr, broken down as follows: 250 TWh/yr for the West Coast, 160 TWh/yr for the East Coast, 60 TWh/yr for the Gulf of Mexico, 620 TWh/yr for Alaska, 80 TWh/yr for Hawaii, and 20 TWh/yr for Puerto Rico
Methods and systems for advanced spaceport information management
Advanced spaceport information management methods and systems are disclosed. In one embodiment, a method includes coupling a test system to the payload and transmitting one or more test signals that emulate an anticipated condition from the test system to the payload. One or more responsive signals are received from the payload into the test system and are analyzed to determine whether one or more of the responsive signals comprises an anomalous signal. At least one of the steps of transmitting, receiving, analyzing and determining includes transmitting at least one of the test signals and the responsive signals via a communications link from a payload processing facility to a remotely located facility. In one particular embodiment, the communications link is an Internet link from a payload processing facility to a remotely located facility (e.g. a launch facility, university, etc.)
Overcoming data scarcity of Twitter: using tweets as bootstrap with application to autism-related topic content analysis
Notwithstanding recent work which has demonstrated the potential of using
Twitter messages for content-specific data mining and analysis, the depth of
such analysis is inherently limited by the scarcity of data imposed by the 140
character tweet limit. In this paper we describe a novel approach for targeted
knowledge exploration which uses tweet content analysis as a preliminary step.
This step is used to bootstrap more sophisticated data collection from directly
related but much richer content sources. In particular we demonstrate that
valuable information can be collected by following URLs included in tweets. We
automatically extract content from the corresponding web pages and treating
each web page as a document linked to the original tweet show how a temporal
topic model based on a hierarchical Dirichlet process can be used to track the
evolution of a complex topic structure of a Twitter community. Using
autism-related tweets we demonstrate that our method is capable of capturing a
much more meaningful picture of information exchange than user-chosen hashtags.Comment: IEEE/ACM International Conference on Advances in Social Networks
Analysis and Mining, 201
Strong coupling in Horava gravity
By studying perturbations about the vacuum, we show that Horava gravity
suffers from two different strong coupling problems, extending all the way into
the deep infra-red. The first of these is associated with the principle of
detailed balance and explains why solutions to General Relativity are typically
not recovered in models that preserve this structure. The second of these
occurs even without detailed balance and is associated with the breaking of
diffeomorphism invariance, required for anisotropic scaling in the UV. Since
there is a reduced symmetry group there are additional degrees of freedom,
which need not decouple in the infra-red. Indeed, we use the Stuckelberg trick
to show that one of these extra modes become strongly coupled as the parameters
approach their desired infra-red fixed point. Whilst we can evade the first
strong coupling problem by breaking detailed balance, we cannot avoid the
second, whatever the form of the potential. Therefore the original Horava
model, and its "phenomenologically viable" extensions do not have a
perturbative General Relativity limit at any scale. Experiments which confirm
the perturbative gravitational wave prediction of General Relativity, such as
the cumulative shift of the periastron time of binary pulsars, will presumably
rule out the theory.Comment: 11 page
Cosmological equations and Thermodynamics on Apparent Horizon in Thick Braneworld
We derive the generalized Friedmann equation governing the cosmological
evolution inside the thick brane model in the presence of two curvature
correction terms: a four-dimensional scalar curvature from induced gravity on
the brane, and a five-dimensional Gauss-Bonnet curvature term. We find two
effective four-dimensional reductions of the Friedmann equation in some limits
and demonstrate that they can be rewritten as the first law of thermodynamics
on the apparent horizon of thick braneworld.Comment: 25 pages, no figure, a definition corrected, several references
added, more motivation and discussio
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