8,706 research outputs found
Periodic Strategies: A New Solution Concept and an Algorithm for NonTrivial Strategic Form Games
We introduce a new solution concept, called periodicity, for selecting
optimal strategies in strategic form games. This periodicity solution concept
yields new insight into non-trivial games. In mixed strategy strategic form
games, periodic solutions yield values for the utility function of each player
that are equal to the Nash equilibrium ones. In contrast to the Nash
strategies, here the payoffs of each player are robust against what the
opponent plays. Sometimes, periodicity strategies yield higher utilities, and
sometimes the Nash strategies do, but often the utilities of these two
strategies coincide. We formally define and study periodic strategies in two
player perfect information strategic form games with pure strategies and we
prove that every non-trivial finite game has at least one periodic strategy,
with non-trivial meaning non-degenerate payoffs. In some classes of games where
mixed strategies are used, we identify quantitative features. Particularly
interesting are the implications for collective action games, since there the
collective action strategy can be incorporated in a purely non-cooperative
context. Moreover, we address the periodicity issue when the players have a
continuum set of strategies available.Comment: Revised version, similar to the one published in Advances in Complex
System
Heat transfer and Fourier's law in off-equilibrium systems
We study the most suitable procedure to measure the effective temperature in
off-equilibrium systems. We analyze the stationary current established between
an off-equilibrium system and a thermometer and the necessary conditions for
that current to vanish. We find that the thermometer must have a short
characteristic time-scale compared to the typical decorrelation time of the
glassy system to correctly measure the effective temperature. This general
conclusion is confirmed analyzing an ensemble of harmonic oscillators with
Monte Carlo dynamics as an illustrative example of a solvable model of a glass.
We also find that the current defined allows to extend Fourier's law to the
off-equilibrium regime by consistently defining effective transport
coefficients. Our results for the oscillator model explain why thermal
conductivities between thermalized and frozen degrees of freedom in structural
glasses are extremely small.Comment: 7 pages, REVTeX, 4 eps figure
Optimal Topological Test for Degeneracies of Real Hamiltonians
We consider adiabatic transport of eigenstates of real Hamiltonians around
loops in parameter space. It is demonstrated that loops that map to nontrivial
loops in the space of eigenbases must encircle degeneracies. Examples from
Jahn-Teller theory are presented to illustrate the test. We show furthermore
that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let
Representation Class and Geometrical Invariants of Quantum States under Local Unitary Transformations
We investigate the equivalence of bipartite quantum mixed states under local
unitary transformations by introducing representation classes from a
geometrical approach. It is shown that two bipartite mixed states are
equivalent under local unitary transformations if and only if they have the
same representation class. Detailed examples are given on calculating
representation classes.Comment: 11 page
Transport and thermoelectric properties of the LaAlO/SrTiO interface
The transport and thermoelectric properties of the interface between
SrTiO and a 26-monolayer thick LaAlO-layer grown at high
oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and
in magnetic fields up to 18 T. For 4.2 K, two different electron-like
charge carriers originating from two electron channels which contribute to
transport are observed. We probe the contributions of a degenerate and a
non-degenerate band to the thermoelectric power and develop a consistent model
to describe the temperature dependence of the thermoelectric tensor. Anomalies
in the data point to an additional magnetic field dependent scattering.Comment: 7 pages, 4 figure
Participatory investigation of important animal health problems amongst the Turkana pastoralists: Relative incidence, impact on livelihoods and suggested interventions
This report describes a study of the principal animal health problems in central and southern parts of Turkana South District, with particular emphasis on their relative importance, factors that promote their occurrence and persistence, and the perceived impact of intervention measures applied previously by the Turkana Livestock Development Program (TLDP). The study was conceived and supported by VSF Belgium, a non-governmental organization (NGO) which is implementing the TLDP. The first phase of the program was implemented between 2000 and 2005, and the second phase was initiated in 2006. The overall objective of the first phase, which occurred largely in Turkana Central (Turkwell, Loima and Kerio Divisions), was to improve the livelihoods of vulnerable pastoral communities through enhanced livestock production, increased access to water, improved marketing opportunities and peace building initiatives. The second phase of the program builds on the achievements of the TLDP I and seeks to expand the target area to include Turkana South (Kainuk, Katilu, Lokichar and Lokori Divisions). The study utilized participatory epidemiological techniques to capture and prioritize animal health problems observed in the target area. Topics of discussion include livestock species and benefits received from them; livestock diseases and interventions; effect of nomadic pastoralism on disease persistence and transmission; impacts of conflicts on livestock husbandry and disease occurrence and persistence; livestock species and disease priorities; disease control; access and utilization of veterinary inputs; community animal health workers; pastoralism and transboundary disease; and conflict and animal health care
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