839 research outputs found
CVcat: an interactive database on cataclysmic variables
CVcat is a database that contains published data on cataclysmic variables and
related objects. Unlike in the existing online sources, the users are allowed
to add data to the catalogue. The concept of an ``open catalogue'' approach is
reviewed together with the experience from one year of public usage of CVcat.
New concepts to be included in the upcoming AstroCat framework and the next
CVcat implementation are presented. CVcat can be found at http://www.cvcat.org.Comment: 5 pages A&A Latex, 4 figures, accepted for publication in A&
Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas
Plasma fluctuations in the scrape-off layer of the Alcator C-Mod tokamak in
ohmic and high confinement modes have been analyzed using gas puff imaging
data. In all cases investigated, the time series of emission from a single
spatially-resolved view into the gas puff are dominated by large-amplitude
bursts, attributed to blob-like filament structures moving radially outwards
and poloidally. There is a remarkable similarity of the fluctuation statistics
in ohmic plasmas and in edge localized mode-free and enhanced D-alpha high
confinement mode plasmas. Conditionally averaged wave forms have a two-sided
exponential shape with comparable temporal scales and asymmetry, while the
burst amplitudes and the waiting times between them are exponentially
distributed. The probability density functions and the frequency power spectral
densities are self-similar for all these confinement modes. These results are
strong evidence in support of a stochastic model describing the plasma
fluctuations in the scrape-off layer as a super-position of uncorrelated
exponential pulses. Predictions of this model are in excellent agreement with
experimental measurements in both ohmic and high confinement mode plasmas. The
stochastic model thus provides a valuable tool for predicting
fluctuation-induced plasma-wall interactions in magnetically confined fusion
plasmas.Comment: 17 pages, 10 figure
Comparison between mirror Langmuir probe and gas puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer
Statistical properties of the scrape-off layer (SOL) plasma fluctuations are
studied in ohmically heated plasmas in the Alcator C-Mod tokamak. For the first
time, plasma fluctuations as well as parameters that describe the fluctuations
are compared across measurements from a mirror Langmuir probe (MLP) and from
gas-puff imaging (GPI) that sample the same plasma discharge. This comparison
is complemented by an analysis of line emission time-series data, synthesized
from the MLP electron density and temperature measurements. The fluctuations
observed by the MLP and GPI typically display relative fluctuation amplitudes
of order unity together with positively skewed and flattened probability
density functions. Such data time series are well described by an established
stochastic framework which model the data as a superposition of uncorrelated,
two-sided exponential pulses. The most important parameter of the process is
the intermittency parameter, {\gamma} = {\tau}d / {\tau}w where {\tau}d denotes
the duration time of a single pulse and {\tau}w gives the average waiting time
between consecutive pulses. Here we show, using a new deconvolution method,
that these parameters can be consistently estimated from different statistics
of the data. We also show that the statistical properties of the data sampled
by the MLP and GPI diagnostic are very similar. Finally, a comparison of the
GPI signal to the synthetic line-emission time series suggests that the
measured emission intensity can not be explained solely by a simplified model
which neglects neutral particle dynamics
IMPLEMENTATION OF THE SINGLE FUEL CONCEPT FOR THE NAVY'S SURFACE FLEET: AN ANALYSIS OF LONG-TERM SOLUTIONS
The U.S. Navy’s surface fleet has been operating on two primary types of fuel for several decades, F-76 for ships and JP-5 for maritime aircraft. Since the implementation of these two fuels, multiple research projects have been conducted to recommend a Single Fuel Concept (SFC), but the Navy has not changed its fuel concept. In today's environment, the Navy needs solutions to cut costs and simplify the supply chain in an effort to focus on the Great Power Competition (GPC) while being mindful of defense budget constraints. Over the past several years, the JP-5 and F-76 price differential has decreased significantly, which provides an opportunity to implement an SFC based on cost benefits. This paper conducts regression analyses on both types of fuel and predicts consumption trends for the future based on the large fleet expansion set forth by the 30-Year Shipbuilding Plan. Cost and standard pricing metrics are used to show the possible cost savings by using JP-5 as a single fuel across the fleet. Implementation of an SFC will take time, especially with a growing fleet, so a phased rollout plan was developed to recommend timeframes for introduction of the SFC while mitigating risk to the fleet. This thesis recommends immediate implementation of the SFC in a phased rollout in order to cut costs, simplify the supply chain, and provide a long-term solution to a growing logistics problem.Monterey, CA, 93943Lieutenant, United States NavyLieutenant, United States NavyApproved for public release. Distribution is unlimited
Eclipse Mapping of the Accretion Stream in UZ Fornacis
We present a new method to map the surface brightness of the accretionstreams in AM Herculis systems from observed light curves. Extensive tests ofthe algorithm show that it reliably reproduces the intensity distribution ofthe stream for data with a signal-to-noise ratio >5. As a first application, wemap the accretion stream emission of Civ lambda 1550 in the polar UZ Fornacisusing HST FOS high state spectra. We find three main emission regions along theaccretion stream: (1) On the ballistic part of the accretion stream, (2) on themagnetically funneled stream near the primary accretion spot, and (3) on themagnetically funneled stream at a position above the stagnation region
Are depressive symptoms linked to a reduced pupillary response to novel positive information?:An eye tracking proof-of-concept study
Introduction:Depressive symptoms have been linked to difficulties in revising established negative beliefs in response to novel positive information. Recent predictive processing accounts have suggested that this bias in belief updating may be related to a blunted processing of positive prediction errors at the neural level. In this proof-of-concept study, pupil dilation in response to unexpected positive emotional information was examined as a psychophysiological marker of an attenuated processing of positive prediction errors associated with depressive symptoms.Methods: Participants (N = 34) completed a modified version of the emotional Bias Against Disconfirmatory Evidence (BADE) task in which scenarios initially suggest negative interpretations that are later either confirmed or disconfirmed by additional information. Pupil dilation in response to the confirmatory and disconfirmatory information was recorded. Results: Behavioral results showed that depressive symptoms were related to difficulties in revising negative interpretations despite disconfirmatory positive information. The eye tracking results pointed to a reduced pupil response to unexpected positive information among people with elevated depressive symptoms. Discussion: Altogether, the present study demonstrates that the adapted emotional BADE task can be appropriate for examining psychophysiological aspects such as changes in pupil size along with behavioral responses. Furthermore, the results suggest that depression may be characterized by deviations in both behavioral (i.e., reduced updating of negative beliefs) and psychophysiological (i.e., decreased pupil dilation) responses to unexpected positive information. Future work should focus on a larger sample including clinically depressed patients to further explore these findings.</p
Local Communication Protocols for Learning Complex Swarm Behaviors with Deep Reinforcement Learning
Swarm systems constitute a challenging problem for reinforcement learning
(RL) as the algorithm needs to learn decentralized control policies that can
cope with limited local sensing and communication abilities of the agents.
While it is often difficult to directly define the behavior of the agents,
simple communication protocols can be defined more easily using prior knowledge
about the given task. In this paper, we propose a number of simple
communication protocols that can be exploited by deep reinforcement learning to
find decentralized control policies in a multi-robot swarm environment. The
protocols are based on histograms that encode the local neighborhood relations
of the agents and can also transmit task-specific information, such as the
shortest distance and direction to a desired target. In our framework, we use
an adaptation of Trust Region Policy Optimization to learn complex
collaborative tasks, such as formation building and building a communication
link. We evaluate our findings in a simulated 2D-physics environment, and
compare the implications of different communication protocols.Comment: 13 pages, 4 figures, version 2, accepted at ANTS 201
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