7,238 research outputs found
Multiplayer Cost Games with Simple Nash Equilibria
Multiplayer games with selfish agents naturally occur in the design of
distributed and embedded systems. As the goals of selfish agents are usually
neither equivalent nor antagonistic to each other, such games are non zero-sum
games. We study such games and show that a large class of these games,
including games where the individual objectives are mean- or discounted-payoff,
or quantitative reachability, and show that they do not only have a solution,
but a simple solution. We establish the existence of Nash equilibria that are
composed of k memoryless strategies for each agent in a setting with k agents,
one main and k-1 minor strategies. The main strategy describes what happens
when all agents comply, whereas the minor strategies ensure that all other
agents immediately start to co-operate against the agent who first deviates
from the plan. This simplicity is important, as rational agents are an
idealisation. Realistically, agents have to decide on their moves with very
limited resources, and complicated strategies that require exponential--or even
non-elementary--implementations cannot realistically be implemented. The
existence of simple strategies that we prove in this paper therefore holds a
promise of implementability.Comment: 23 page
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Current scaling of axially radiated power in dynamic hohlraums and dynamic hohlraum load design for ZR.
We present designs for dynamic hohlraum z-pinch loads on the 28 MA, 140 ns driver ZR. The scaling of axially radiated power with current in dynamic hohlraums is reviewed. With adequate stability on ZR this scaling indicates that 30 TW of axially radiated power should be possible. The performance of the dynamic hohlraum load on the 20 MA, 100 ns driver Z is extensively reviewed. The baseline z-pinch load on Z is a nested tungsten wire array imploding onto on-axis foam. Data from a variety of x-ray diagnostics fielded on Z are presented. These diagnostics include x-ray diodes, bolometers, fast x-ray imaging cameras, and crystal spectrometers. Analysis of these data indicates that the peak dynamic radiation temperature on Z is between 250 and 300 eV from a diameter less than 1 mm. Radiation from the dynamic hohlraum itself or from a radiatively driven pellet within the dynamic hohlraum has been used to probe a variety of matter associated with the dynamic hohlraum: the tungsten z-pinch itself, tungsten sliding across the end-on apertures, a titanium foil over the end aperture, and a silicon aerogel end cap. Data showing the existence of asymmetry in radiation emanating from the two ends of the dynamic hohlraum is presented, along with data showing load configurations that mitigate this asymmetry. 1D simulations of the dynamic hohlraum implosion are presented and compared to experimental data. The simulations provide insight into the dynamic hohlraum behavior but are not necessarily a reliable design tool because of the inherently 3D behavior of the imploding nested tungsten wire arrays
Games on graphs with a public signal monitoring
We study pure Nash equilibria in games on graphs with an imperfect monitoring
based on a public signal. In such games, deviations and players responsible for
those deviations can be hard to detect and track. We propose a generic
epistemic game abstraction, which conveniently allows to represent the
knowledge of the players about these deviations, and give a characterization of
Nash equilibria in terms of winning strategies in the abstraction. We then use
the abstraction to develop algorithms for some payoff functions.Comment: 28 page
Generalized Semilocal Theories and Higher Hopf Maps
\def\mon{S^3\stackrel{S^1}{\rightarrow}S^2}
\def\inst{S^7\stackrel{S^3}{\rightarrow}S^4}
\def\octo{S^{15}\stackrel{S^7}{\rightarrow}S^8} In semilocal theories, the
vacuum manifold is fibered in a non-trivial way by the action of the gauge
group. Here we generalize the original semilocal theory (which was based on the
Hopf bundle \mon) to realize the next Hopf bundle \inst, and its extensions
. The semilocal defects in this class
of theories are classified by , and are interpreted as constrained
instantons or generalized sphaleron configurations. We fail to find a field
theoretic realization of the final Hopf bundle \octo, but are able to
construct other semilocal spaces realizing Stiefel bundles over Grassmanian
spaces.Comment: 15 pages, uses amssymbols.st
Decision Problems for Nash Equilibria in Stochastic Games
We analyse the computational complexity of finding Nash equilibria in
stochastic multiplayer games with -regular objectives. While the
existence of an equilibrium whose payoff falls into a certain interval may be
undecidable, we single out several decidable restrictions of the problem.
First, restricting the search space to stationary, or pure stationary,
equilibria results in problems that are typically contained in PSPACE and NP,
respectively. Second, we show that the existence of an equilibrium with a
binary payoff (i.e. an equilibrium where each player either wins or loses with
probability 1) is decidable. We also establish that the existence of a Nash
equilibrium with a certain binary payoff entails the existence of an
equilibrium with the same payoff in pure, finite-state strategies.Comment: 22 pages, revised versio
Equations of Motion of Spinning Relativistic Particle in Electromagnetic and Gravitational Fields
We consider the motion of a spinning relativistic particle in external
electromagnetic and gravitational fields, to first order in the external field,
but to an arbitrary order in spin. The noncovariant spin formalism is crucial
for the correct description of the influence of the spin on the particle
trajectory. We show that the true coordinate of a relativistic spinning
particle is its naive, common coordinate \r. Concrete calculations are
performed up to second order in spin included. A simple derivation is presented
for the gravitational spin-orbit and spin-spin interactions of a relativistic
particle. We discuss the gravimagnetic moment (GM), a specific spin effect in
general relativity. It is shown that for the Kerr black hole the gravimagnetic
ratio, i.e., the coefficient at the GM, equals unity (just as for the charged
Kerr hole the gyromagnetic ratio equals two). The equations of motion obtained
for relativistic spinning particle in external gravitational field differ
essentially from the Papapetrou equations.Comment: 32 pages, latex, Plenary talk at the Fairbank Meeting on the
Lense--Thirring Effect, Rome-Pescara, 29/6-4/7 199
Equations of Motion of Spinning Relativistic Particle in External Fields
We consider the motion of a spinning relativistic particle in external
electromagnetic and gravitational fields, to first order in the external field,
but to an arbitrary order in spin. The correct account for the spin influence
on the particle trajectory is obtained with the noncovariant description of
spin. Concrete calculations are performed up to second order in spin included.
A simple derivation is presented for the gravitational spin-orbit and spin-spin
interactions of a relativistic particle. We discuss the gravimagnetic moment
(GM), a specific spin effect in general relativity. It is demonstrated that for
the Kerr black hole the gravimagnetic ratio, i.e., the coefficient at the GM,
equals to unity (as well as for the charged Kerr hole the gyromagnetic ratio
equals to two). The equations of motion obtained for relativistic spinning
particle in external gravitational field differ essentially from the Papapetrou
equations.Comment: 22 pages, latex, no figure
The Phase Structure of an SU(N) Gauge Theory with N_f Flavors
We investigate the chiral phase transition in SU(N) gauge theories as the
number of quark flavors, , is varied. We argue that the transition takes
place at a large enough value of so that it is governed by the infrared
fixed point of the function. We study the nature of the phase
transition analytically and numerically, and discuss the spectrum of the theory
as the critical value of is approached in both the symmetric and broken
phases. Since the transition is governed by a conformal fixed point, there are
no light excitations on the symmetric side. We extend previous work to include
higher order effects by developing a renormalization group estimate of the
critical coupling.Comment: 34 pages, 1 figure. More references adde
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God’s gifts: destiny, poverty, and temporality in the mines of Sierra Leone
In Sierra Leone, many artisanal miners share the view that every human act and every event is the realisation of an inscrutable divine plan. Even though notions of fate and destiny are part of the vocabulary of Krio, the country’s lingua franca, miners prefer to use expressions that evoke God and stress His immanent presence and influence in their everyday lives. In order to understand the religious vocabulary of contingency and the cosmology underlying the ways in which miners interpret, reproduce, and imaginatively prepare the conditions to change their lives, this article focuses on the ritual practices connected to artisanal diamond mining. It considers these rituals as attempts to resolve the ever-present temporal and moral tensions between actual conditions of suffering and poverty, and the realisation of the well-being that miners associate with their desired futures
'To live and die [for] Dixie': Irish civilians and the Confederate States of America
Around 20,000 Irishmen served in the Confederate army in the Civil War. As a result, they left behind, in various Southern towns and cities, large numbers of friends, family, and community leaders. As with native-born Confederates, Irish civilian support was crucial to Irish participation in the Confederate military effort. Also, Irish civilians served in various supporting roles: in factories and hospitals, on railroads and diplomatic missions, and as boosters for the cause. They also, however, suffered in bombardments, sieges, and the blockade. Usually poorer than their native neighbours, they could not afford to become 'refugees' and move away from the centres of conflict. This essay, based on research from manuscript collections, contemporary newspapers, British Consular records, and Federal military records, will examine the role of Irish civilians in the Confederacy, and assess the role this activity had on their integration into Southern communities. It will also look at Irish civilians in the defeat of the Confederacy, particularly when they came under Union occupation. Initial research shows that Irish civilians were not as upset as other whites in the South about Union victory. They welcomed a return to normalcy, and often 'collaborated' with Union authorities. Also, Irish desertion rates in the Confederate army were particularly high, and I will attempt to gauge whether Irish civilians played a role in this. All of the research in this paper will thus be put in the context of the Drew Gilpin Faust/Gary Gallagher debate on the influence of the Confederate homefront on military performance. By studying the Irish civilian experience one can assess how strong the Confederate national experiment was. Was it a nation without a nationalism
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