7,834 research outputs found
Planning Against Fictitious Players in Repeated Normal Form Games
Planning how to interact against bounded memory and unbounded memory learning opponents needs different treatment. Thus far, however, work in this area has shown how to design plans against bounded memory learning opponents, but no work has dealt with the unbounded memory case. This paper tackles this gap. In particular, we frame this as a planning problem using the framework of repeated matrix games, where the planner's objective is to compute the best exploiting sequence of actions against a learning opponent. The particular class of opponent we study uses a fictitious play process to update her beliefs, but the analysis generalizes to many forms of Bayesian learning agents. Our analysis is inspired by Banerjee and Peng's AIM framework, which works for planning and learning against bounded memory opponents (e.g an adaptive player). Building on this, we show how an unbounded memory opponent (specifically a fictitious player) can also be modelled as a finite MDP and present a new efficient algorithm that can find a way to exploit the opponent by computing in polynomial time a sequence of play that can obtain a higher average reward than those obtained by playing a game theoretic (Nash or correlated) equilibrium
The Semantic Grid: A future e-Science infrastructure
e-Science offers a promising vision of how computer and communication technology can support and enhance the scientific process. It does this by enabling scientists to generate, analyse, share and discuss their insights, experiments and results in an effective manner. The underlying computer infrastructure that provides these facilities is commonly referred to as the Grid. At this time, there are a number of grid applications being developed and there is a whole raft of computer technologies that provide fragments of the necessary functionality. However there is currently a major gap between these endeavours and the vision of e-Science in which there is a high degree of easy-to-use and seamless automation and in which there are flexible collaborations and computations on a global scale. To bridge this practiceâaspiration divide, this paper presents a research agenda whose aim is to move from the current state of the art in e-Science infrastructure, to the future infrastructure that is needed to support the full richness of the e-Science vision. Here the future e-Science research infrastructure is termed the Semantic Grid (Semantic Grid to Grid is meant to connote a similar relationship to the one that exists between the Semantic Web and the Web). In particular, we present a conceptual architecture for the Semantic Grid. This architecture adopts a service-oriented perspective in which distinct stakeholders in the scientific process, represented as software agents, provide services to one another, under various service level agreements, in various forms of marketplace. We then focus predominantly on the issues concerned with the way that knowledge is acquired and used in such environments since we believe this is the key differentiator between current grid endeavours and those envisioned for the Semantic Grid
An improved model for the nonlinear velocity power spectrum
The velocity divergence power spectrum is a key ingredient in modelling
redshift space distortion effects on quasi-linear and nonlinear scales. We
present an improved model for the z=0 velocity divergence auto and cross power
spectrum which was originally suggested by Jennings et al. 2011. Using
numerical simulations we measure the velocity fields using a Delaunay
tesselation and obtain an accurate prediction of the velocity divergence power
spectrum on scales k < 1 hMpc^{-1}. We use this to update the model which is
now accurate to 2% for both P_{\theta \theta} and P_{\theta \delta} at z=0 on
scales k <0.7 hMpc^{-1} and k <0.5 hMpc^{-1} respectively. We find that the
formula for the redshift dependence of the velocity divergence power spectra
proposed by Jennings et al. 2011 recovers the measured z>0 P(k) to markedly
greater accuracy with the new model. The nonlinear P_{\theta \theta} and
P_{\theta \delta} at z =1 are recovered accurately to better than 2% on scales
k<0.2 hMpc^{-1}. Recently it was shown that the velocity field shows larger
differences between modified gravity cosmologies and \Lambda CDM compared to
the matter field. An accurate model for the velocity divergence power spectrum,
such as the one presented here, is a valuable tool for analysing redshift space
distortion effects in future galaxy surveys and for constraining deviations
from general relativity.Comment: 5 pages, 2 figures, Accepted for publication in MNRA
Single particle strength restoration and nuclear transparency in high Q^2 exclusive (e,e'p) reactions
Quenching of the single particle strength which previously precluded
unambiguous measurement of nuclear transparency in quasifree (e,e'p) reactions
at high momentum transfer is evaluated from the cross sections of measured
processes. We have demonstrated evidence of the single particle strength
restoration with increase of the momentum transfer in exclusive (e,e'p)
reactions and argue that in practically interesting cases of study the nuclear
transparency in these processes quenching is weakly depends on the probability
of short range nucleon correlations. It is shown that use of Glauber
approximation well describes NE18 and E94-139 (e,e'p) data at the momentum
transfers 1 GeV^2 < Q^2 < 3 GeV^2. This gives a further support to our
observation that the quenching of nuclear levels strongly depends on the
resolution (Q^2)and practically disappears at Q^2>1GeV^2.Comment: 15 pages, 5 figures; references added, discussion extende
On Resilient Behaviors in Computational Systems and Environments
The present article introduces a reference framework for discussing
resilience of computational systems. Rather than a property that may or may not
be exhibited by a system, resilience is interpreted here as the emerging result
of a dynamic process. Said process represents the dynamic interplay between the
behaviors exercised by a system and those of the environment it is set to
operate in. As a result of this interpretation, coherent definitions of several
aspects of resilience can be derived and proposed, including elasticity, change
tolerance, and antifragility. Definitions are also provided for measures of the
risk of unresilience as well as for the optimal match of a given resilient
design with respect to the current environmental conditions. Finally, a
resilience strategy based on our model is exemplified through a simple
scenario.Comment: The final publication is available at Springer via
http://dx.doi.org/10.1007/s40860-015-0002-6 The paper considerably extends
the results of two conference papers that are available at http://ow.ly/KWfkj
and http://ow.ly/KWfgO. Text and formalism in those papers has been used or
adapted in the herewith submitted pape
Mapping the co-benefits of climate change action to issues of public concern in the UK: a narrative review
To avoid a 1·5°C rise in global temperatures above preindustrial levels, the next phase of reductions in greenhouse gas emissions will need to be comparatively rapid. Linking the co-benefits of climate action to wider issues that the public are concerned about can help decision makers to prioritise decarbonisation options that increase the chance of public support for such changes, while ensuring that a just transition is delivered. We identified key issues of concern to the UK public by use of Ipsos MORI public opinion data from 2007 to 2020 and used these data to guide a narrative review of academic and grey literature on the co-benefits of climate change action for the UK. Correspondence with civil servants, third sector organisations, and relevant academics allowed us to identify omissions and to ensure policy relevance of the recommendations. This evidence-based Review of the various co-benefits of climate change action for the UK identifies four main areas: health and the National Health Service; security; economy and unemployment; and poverty, housing, and inequality. Associated trade-offs are also discussed. City-level and regional-level governments are particularly well placed to incorporate co-benefits into their decision making because it is at this scale that co-benefits most clearly manifest, and where interventions can have the most immediate effects
The Onset of Color Transparency in Reactions on Nuclei
Quantum filtering of the ejectile wave packet from hard scattering on
bound nucleons puts stringent constraints on the onset of color transparency in
reactions in nuclei at moderate energies. Based on
multiple-scattering theory, we derive a novel formula for nuclear transparency
and discuss its energy dependence in terms of a color transparency sum rule.Comment: 14 pages (LATEX), 3 figures (not included, available from the
authors), KFA-IKP(TH)-1992-1
Diquarks and antiquarks in exotics: a menage a trois and a menage a quatre
A menage a trois is very different from an ordinary family. Similarly, exotic
hadrons with both qq and qbar q pairs have important color-space correlations
that are completely absent in ordinary mesons and baryons. The presence of both
types of pairs requires attention to the basic QCD physics that the q qbar
interaction is much stronger than the qq interaction. This new physics in
multiquark systems produces color structures totally different from those of
normal hadrons, for example the ud system is utterly unlike the ud diquark in
the uds Lambda baryon. The color-space correlations produce unusual
experimental properties in tetraquarks with heavy quark pairs which may be
relevant for newly discovered mesons like the X(3872) resonance. Tetraquark
masses can be below the two-meson threshold for sufficiently high quark masses.
A simple model calculation shows the b q bbar ubar and b q cbar qbar
tetraquarks below the B Bbar and B Dbar thresholds. Some of these states have
exotic electric charge and their decays might have striking signatures
involving monoenergetic photons and/or pions.Comment: Journal version (PLB
Lie Algebras and Growth in Branch Groups
We compute the structure of the Lie algebras associated to two examples of
branch groups, and show that one has finite width while the other, the
``Gupta-Sidki group'', has unbounded width. This answers a question by Sidki.
More precisely, the Lie algebra of the Gupta-Sidki group has Gelfand-Kirillov
dimension .
We then draw a general result relating the growth of a branch group, of its
Lie algebra, of its graded group ring, and of a natural homogeneous space we
call "parabolic space", namely the quotient of the group by the stabilizer of
an infinite ray. The growth of the group is bounded from below by the growth of
its graded group ring, which connects to the growth of the Lie algebra by a
product-sum formula, and the growth of the parabolic space is bounded from
below by the growth of the Lie algebra.
Finally we use this information to explicitly describe the normal subgroups
of the "Grigorchuk group". All normal subgroups are characteristic, and the
number of normal subgroups of index is odd and is asymptotically
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