8,147 research outputs found
The Viability of Cooperation Based on Interpersonal Commitment
A prominent explanation of cooperation in repeated exchange is reciprocity (e.g. Axelrod, 1984). However, empirical studies indicate that exchange partners are often much less intent on keeping the books balanced than Axelrod suggested. In particular, there is evidence for commitment behavior, indicating that people tend to build long-term cooperative relationships characterised by largely unconditional cooperation, and are inclined to hold on to them even when this appears to contradict self-interest. Using an agent-based computational model, we examine whether in a competitive environment commitment can be a more successful strategy than reciprocity. We move beyond previous computational models by proposing a method that allows to systematically explore an infinite space of possible exchange strategies. We use this method to carry out two sets of simulation experiments designed to assess the viability of commitment against a large set of potential competitors. In the first experiment, we find that although unconditional cooperation makes strategies vulnerable to exploitation, a strategy of commitment benefits more from being more unconditionally cooperative. The second experiment shows that tolerance improves the performance of reciprocity strategies but does not make them more successful than commitment. To explicate the underlying mechanism, we also study the spontaneous formation of exchange network structures in the simulated populations. It turns out that commitment strategies benefit from efficient networking: they spontaneously create a structure of exchange relations that ensures efficient division of labor. The problem with stricter reciprocity strategies is that they tend to spread interaction requests randomly across the population, to keep relations in balance. During times of great scarcity of exchange partners this structure is inefficient because it generates overlapping personal networks so that often too many people try to interact with the same partner at the same time.Interpersonal Commitment, Fairness, Reciprocity, Agent-Based Simulation, Help Exchange, Evolution
Liquid Scintillator Time Projection Chamber Concept
Results are presented from a small-scale experiment to investigate the use of
room temperature organic liquid scintillators as the active medium for a time
projection chamber (TPC). The optical properties of liquid scintillators have
long been known, but their ability to transport charge has remained, until now,
largely untested. The idea of using room temperature liquids as an active
medium for an ionisation chamber was first presented in \cite{EnglerTMS}. Since
then the range of liquid scintillators available has been greatly developed. We
present successful transport of ionization charges in a selection of both, pure
organic liquid solvents and liquid scintillator cocktails over 20mm using a
variety of electric drift field strengths. The target of this research is to
offer a cost effective alternative to liquid noble gas detectors in neutrino
physics.Comment: 6 pages, 5 figures, submitted to Proceedings 12th Pisa Meeting on
Advanced Detectors, La Biodola, Isola d'Elba, Ital
Observation of mixed anisotropy in the critical susceptibility of an ultrathin magnetic film
Measurements of the magnetic susceptibility of Fe/W(110) films with thickness
in the range of 1.6 to 2.4 ML Fe, show that in addition to the large response
along the easy axis associated with the Curie transition, there is a much
smaller, paramagnetic hard axis response that is not consistent with the 2D
anisotropic Heisenberg model used to describe homogeneous in-plane ferromagnets
with uniaxial anisotropy. The shape, amplitude, and peak temperature of the
hard axis susceptibility, as well as its dependence upon layer completion close
to 2.0 ML, indicate that inhomogeneities in the films create a system of mixed
anisotropy. A likely candidate for inhomogeneities that are magnetically
relevant in the critical region are the closed lines of step edges associated
with the incomplete layers. According to the Harris criterion, the existence of
magnetically relevant inhomogeneities may alter the critical properties of the
films from those of a 2D Ising model. Experiments in the recent literature are
discussed in this context.Comment: 9 two-column pages, 6 figures. This replacement has a new title and
abstract, and one additional figur
Fusion at deep subbarrier energies: potential inversion revisited
For a single potential barrier, the barrier penetrability can be inverted
based on the WKB approximation to yield the barrier thickness. We apply this
method to heavy-ion fusion reactions at energies well below the Coulomb barrier
and directly determine the inter-nucleus potential between the colliding
nuclei. To this end, we assume that fusion cross sections at deep subbarrier
energies are governed by the lowest barrier in the barrier distribution. The
inverted inter-nucleus potentials for the O +Sm and O
+Pb reactions show that they are much thicker than phenomenological
potentials. We discuss a consequence of such thick potential by fitting the
inverted potentials with the Bass function.Comment: 8 pages, 5 figures. Uses aipxfm.sty. A talk given at the FUSION08:
New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, September
22-26, 2008, Chicago, US
Optimal control of predictive mean-field equations and applications to finance
We study a coupled system of controlled stochastic differential equations
(SDEs) driven by a Brownian motion and a compensated Poisson random measure,
consisting of a forward SDE in the unknown process and a
\emph{predictive mean-field} backward SDE (BSDE) in the unknowns . The driver of the BSDE at time may depend not just upon the
unknown processes , but also on the predicted future
value , defined by the conditional expectation . \\ We give a sufficient and a necessary
maximum principle for the optimal control of such systems, and then we apply
these results to the following two problems:\\ (i) Optimal portfolio in a
financial market with an \emph{insider influenced asset price process.} \\ (ii)
Optimal consumption rate from a cash flow modeled as a geometric It\^ o-L\'
evy SDE, with respect to \emph{predictive recursive utility}
Energy and system dependence of high- triggered two-particle near-side correlations
Previous studies have indicated that the near-side peak of high-
triggered correlations can be decomposed into two parts, the \textit{Jet} and
the \textit{Ridge}. We present data on the yield per trigger of the
\textit{Jet} and the \textit{Ridge} from , and collisions
at = 62.4 GeV and 200 GeV and compare data on the \textit{Jet}
to PYTHIA 8.1 simulations for . PYTHIA describes the \textit{Jet}
component up to a scaling factor, meaning that PYTHIA can provide a better
understanding of the \textit{Ridge} by giving insight into the effects of the
kinematic cuts. We present collision energy and system dependence of the
\textit{Ridge} yield, which should help distinguish models for the production
mechanism of the \textit{Ridge}.Comment: 4 pages, 6 figures, proceedings for Hot Quarks in Estes Park,
Colorad
Possible glueball production in relativistic heavy-ion collisions
Within a thermal model we estimate possible multiplicities of scalar
glueballs in central Au+Au collisions at AGS, SPS, RHIC and LHC energies. For
the glueball mass in the region 1.5-1.7 GeV, the model predicts on average (per
event) 0.5-1.5 glueballs at RHIC and 1.5-4 glueballs at LHC energies. Possible
enhancement mechanisms are discussed.Comment: 8 pages, 2 figure
Studies of multiplicity in relativistic heavy-ion collisions
In this talk I'll review the present status of charged particle multiplicity
measurements from heavy-ion collisions. The characteristic features of
multiplicity distributions obtained in Au+Au collisions will be discussed in
terms of collision centrality and energy and compared to those of p+p
collisions. Multiplicity measurements of d+Au collisions at 200 GeV
nucleon-nucleon center-of-mass energy will also be discussed. The results will
be compared to various theoretical models and simple scaling properties of the
data will be identified.Comment: "Focus on Multiplicity" Internationsl Workshop on Particle
Multiplicity in Relativistic Heavy Ion Collisions, Bari, Italy, June 17-19,
2003, 16 pages, 15 figure
Kaon and production vs Participants in Nuclear Collisions
Data on kaon and production in nuclear collisions as a function of
centrality are analysed both at AGS and SPS energy range. We compare the
results of several experiments, looking for common trend in `participant
scaling' of production yields. We find a smooth description of scaled kaon and
yields as a function of participant density. We also show a participant
density dependence of kaons and produced in the forward hemisphere for
proton-nucleus collisions.Comment: Proceedings of the International Conference on Strangeness in Quark
Matter, 20-25 July 2000, Berkeley, CA. To appear in Journal of Physics G:
Nuclear and Particle Physic
Hints of incomplete thermalization in RHIC data
The large elliptic flow observed in Au-Au collisions at RHIC is often put
forward as a compelling evidence for the formation of a strongly-interacting
quark-gluon plasma. The main argument is that the measured elliptic flow is as
large as the value given by fluid-dynamics models that assume complete
thermalization. It is argued that this claim may not be justified, since a
detailed examination of experimental data rather suggests that the system
created is not fully equilibrated at the time when anisotropic flow develops.Comment: 8 pages, 2 eps-figures, Talk given at the Workshop on QGP
Thermalization (QGPTH05), Vienna, 10-12 Aug 200
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