3,388 research outputs found
Outperforming Game Theoretic Play with Opponent Modeling in Two Player Dominoes
Dominoes is a partially observable extensive form game with probability. The rules are simple; however, complexity and uncertainty of this game make it difficult to apply standard game theoretic methods to solve. This thesis applies strategy prediction opponent modeling to work with game theoretic search algorithms in the game of two player dominoes. This research also applies methods to compute the upper bound potential that predicting a strategy can provide towards specific strategy types. Furthermore, the actual values are computed according to the accuracy of a trained classifier. Empirical results show that there is a potential value gain over a Nash equilibrium player in score for fully and partially observable environments for specific strategy types. The actual value gained is positive for a fully observable environment for score and total wins and ties. Actual value gained over the Nash equilibrium player from the opponent model only exist for score, while the opponent modeler demonstrates a higher potential to win and/or tie in comparison to a pure game theoretic agent
New Phases of SU(3) and SU(4) at Finite Temperature
The addition of an adjoint Polyakov loop term to the action of a pure gauge
theory at finite temperature leads to new phases of SU(N) gauge theories. For
SU(3), a new phase is found which breaks Z(3) symmetry in a novel way; for
SU(4), the new phase exhibits spontaneous symmetry breaking of Z(4) to Z(2),
representing a partially confined phase in which quarks are confined, but
diquarks are not. The overall phase structure and thermodynamics is consistent
with a theoretical model of the effective potential for the Polyakov loop based
on perturbation theory.Comment: 18 pages, 17 figures, RevTeX
MPD thruster technology
MPD (MagnetoPlasmaDynamic) thrusters demonstrated between 2000 and 7000 seconds specific impulse at efficiencies approaching 40 percent, and were operated continuously at power levels over 500 kW. These demonstrated capabilities, combined with the simplicity and robustness of the thruster, make them attractive candidates for application to both unmanned and manned orbit raising, lunar, and planetary missions. To date, however, only a limited number of thruster configurations, propellants, and operating conditions were studied. The present status of MPD research is reviewed, including developments in the measured performance levels and electrode erosion rates. Theoretical studies of the thruster dynamics are also described. Significant progress was made in establishing empirical scaling laws, performance and lifetime limitations and in the development of numerical codes to simulate the flow field and electrode processes
The Spitzer c2d Survey of Nearby Dense Cores. IX. Discovery of a Very Low Luminosity Object Driving a Molecular Outflow in the Dense Core L673-7
We present new infrared, submillimeter, and millimeter observations of the
dense core L673-7 and report the discovery of a low-luminosity, embedded Class
0 protostar driving a molecular outflow. L673-7 is seen in absorption against
the mid-infrared background in 5.8, 8, and 24 micron Spitzer images, allowing
for a derivation of the column density profile and total enclosed mass of
L673-7, independent of dust temperature assumptions. Estimates of the core mass
from these absorption profiles range from 0.2-4.5 solar masses. Millimeter
continuum emission indicates a mass of about 2 solar masses, both from a direct
calculation assuming isothermal dust and from dust radiative transfer models
constrained by the millimeter observations. We use dust radiative transfer
models to constrain the internal luminosity of L673-7, defined to be the
luminosity of the central source and excluding the luminosity from external
heating, to be 0.01-0.045 solar luminosities, with 0.04 solar luminosities the
most likely value. L673-7 is thus classified as a very low luminosity object
(VeLLO), and is among the lowest luminosity VeLLOs yet studied. We calculate
the kinematic and dynamic properties of the molecular outflow in the standard
manner, and we show that the expected accretion luminosity based on these
outflow properties is greater than or equal to 0.36 solar luminosities. The
discrepancy between this expected accretion luminosity and the internal
luminosity derived from dust radiative transfer models indicates that the
current accretion rate is much lower than the average rate over the lifetime of
the outflow. Although the protostar embedded within L673-7 is consistent with
currently being substellar, it is unlikely to remain as such given the
substantial mass reservoir remaining in the core.Comment: 19 pages, 14 figures. Accepted by Ap
How to Host a Data Competition: Statistical Advice for Design and Analysis of a Data Competition
Data competitions rely on real-time leaderboards to rank competitor entries
and stimulate algorithm improvement. While such competitions have become quite
popular and prevalent, particularly in supervised learning formats, their
implementations by the host are highly variable. Without careful planning, a
supervised learning competition is vulnerable to overfitting, where the winning
solutions are so closely tuned to the particular set of provided data that they
cannot generalize to the underlying problem of interest to the host. This paper
outlines some important considerations for strategically designing relevant and
informative data sets to maximize the learning outcome from hosting a
competition based on our experience. It also describes a post-competition
analysis that enables robust and efficient assessment of the strengths and
weaknesses of solutions from different competitors, as well as greater
understanding of the regions of the input space that are well-solved. The
post-competition analysis, which complements the leaderboard, uses exploratory
data analysis and generalized linear models (GLMs). The GLMs not only expand
the range of results we can explore, they also provide more detailed analysis
of individual sub-questions including similarities and differences between
algorithms across different types of scenarios, universally easy or hard
regions of the input space, and different learning objectives. When coupled
with a strategically planned data generation approach, the methods provide
richer and more informative summaries to enhance the interpretation of results
beyond just the rankings on the leaderboard. The methods are illustrated with a
recently completed competition to evaluate algorithms capable of detecting,
identifying, and locating radioactive materials in an urban environment.Comment: 36 page
Recommended from our members
Dendrimer-Encapsulated Nanoparticles: New Synthetic and Characterization Methods and Catalytic Applications
In this article we describe the synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles (DENs). These materials are synthesized using a template approach in which metal ions are extracted into the interior of dendrimers and then subsequently reduced chemically to yield nearly size-monodisperse particles having diameters in the 1-2 nm range. Monometallic, bimetallic (alloy and core@shell), and semiconductor nanoparticles have been prepared by this route. The dendrimer component of these composites serves not only as a template for preparing the nanoparticle replica, but also as a stabilizer for the nanoparticle. In this perspective, we report on progress in the synthesis, characterization, and applications of these materials since our last review in 2005. Significant advances in the synthesis of core@shell DENs, characterization, and applications to homogeneous and heterogeneous catalysis (including electrocatalysis) are emphasized.U.S. Department of Energy, Office of Basic Energy Sciences DE-FG02-09ER16090U.S. National Science Foundation 0847957Robert A. Welch Foundation F-0032Chemistr
The evolutionary development of high specific impulse electric thruster technology
Electric propulsion flight and technology demonstrations conducted primarily by Europe, Japan, China, the U.S., and the USSR are reviewed. Evolutionary mission applications for high specific impulse electric thruster systems are discussed, and the status of arcjet, ion, and magnetoplasmadynamic thrusters and associated power processor technologies are summarized
Three-Dimensional Magnetohydrodynamics Simulations Of Counter-Helicity Spheromak Merging In The Swarthmore Spheromak Experiment
Recent counter-helicity spheromak merging experiments in the Swarthmore Spheromak Experiment (SSX) have produced a novel compact torus (CT) with unusual features. These include a persistent antisymmetric toroidal magnetic field profile and a slow, nonlinear emergence of the n = 1 tilt mode. Experimental measurements are inconclusive as to whether this unique CT is a fully merged field-reversed configuration (FRC) with strong toroidal field or a partially merged doublet CT configuration with both spheromak- and FRC-like characteristics. In this paper, the SSX merging process is studied in detail using three-dimensional resistive MHD simulations from the Hybrid Magnetohydrodynamics (HYM) code. These simulations show that merging plasmas in the SSX parameter regime only partially reconnect, leaving behind a doublet CT rather than an FRC. Through direct comparisons, we show that the magnetic structure in the simulations is highly consistent with the SSX experimental observations. We also find that the n = 1 tilt mode begins as a fast growing linear mode that evolves into a slower-growing nonlinear mode before being detected experimentally. A simulation parameter scan over resistivity, viscosity, and line-tying shows that these parameters can strongly affect the behavior of both the merging process and the tilt mode. In fact, merging in certain parameter regimes is found to produce a toroidal-field-free FRC rather than a doublet CT. (C) 2011 American Institute of Physics. [doi:10.1063/1.3660533
Can Protostellar Outflows Set Stellar Masses?
The opening angles of some protostellar outflows appear too narrow to match
the expected core-star mass efficiency SFE = 0.3-0.5 if outflow cavity volume
traces outflow mass, with a conical shape and a maximum opening angle near 90
deg. However, outflow cavities with paraboloidal shape and wider angles are
more consistent with observed estimates of the SFE. This paper presents a model
of infall and outflow evolution based on these properties. The initial state is
a truncated singular isothermal sphere which has mass 1 ,
free fall time 80 kyr, and small fractions of magnetic, rotational,
and turbulent energy. The core collapses pressure-free as its protostar and
disk launch a paraboloidal wide-angle wind. The cavity walls expand radially
and entrain envelope gas into the outflow. The model matches SFE values when
the outflow mass increases faster than the protostar mass by a factor 1 - 2,
yielding protostar masses typical of the IMF. It matches observed outflow
angles if the outflow mass increases at nearly the same rate as the cavity
volume. The predicted outflow angles are then typically 50 deg as they
increase rapidly through the stage 0 duration of 40 kyr. They increase
more slowly up to 110 deg during their stage I duration of 70 kyr.
With these outflow rates and shapes, model predictions appear consistent with
observational estimates of typical stellar masses, SFEs, stage durations, and
outflow angles, with no need for external mechanisms of core dispersal.Comment: Accepted for publication by The Astrophysical Journal; 47 pages, 10
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