610 research outputs found
The Networked Common Goods Game
We introduce a new class of games called the networked common goods game
(NCGG), which generalizes the well-known common goods game. We focus on a
fairly general subclass of the game where each agent's utility functions are
the same across all goods the agent is entitled to and satisfy certain natural
properties (diminishing return and smoothness). We give a comprehensive set of
technical results listed as follows.
* We show the optimization problem faced by a single agent can be solved
efficiently in this subclass. The discrete version of the problem is however
NP-hard but admits an fully polynomial time approximation scheme (FPTAS).
* We show uniqueness results of pure strategy Nash equilibrium of NCGG, and
that the equilibrium is fully characterized by the structure of the network and
independent of the choices and combinations of agent utility functions.
* We show NCGG is a potential game, and give an implementation of best/better
response Nash dynamics that lead to fast convergence to an
-approximate pure strategy Nash equilibrium.
* Lastly, we show the price of anarchy of NCGG can be as large as
(for any ), which means selfish behavior
in NCGG can lead to extremely inefficient social outcomes
Strong duality in conic linear programming: facial reduction and extended duals
The facial reduction algorithm of Borwein and Wolkowicz and the extended dual
of Ramana provide a strong dual for the conic linear program in the absence of any constraint qualification. The facial
reduction algorithm solves a sequence of auxiliary optimization problems to
obtain such a dual. Ramana's dual is applicable when (P) is a semidefinite
program (SDP) and is an explicit SDP itself. Ramana, Tuncel, and Wolkowicz
showed that these approaches are closely related; in particular, they proved
the correctness of Ramana's dual using certificates from a facial reduction
algorithm.
Here we give a clear and self-contained exposition of facial reduction, of
extended duals, and generalize Ramana's dual:
-- we state a simple facial reduction algorithm and prove its correctness;
and
-- building on this algorithm we construct a family of extended duals when
is a {\em nice} cone. This class of cones includes the semidefinite cone
and other important cones.Comment: A previous version of this paper appeared as "A simple derivation of
a facial reduction algorithm and extended dual systems", technical report,
Columbia University, 2000, available from
http://www.unc.edu/~pataki/papers/fr.pdf Jonfest, a conference in honor of
Jonathan Borwein's 60th birthday, 201
Noise reduction in 3D noncollinear parametric amplifier
We analytically find an approximate Bloch-Messiah reduction of a noncollinear
parametric amplifier pumped with a focused monochromatic beam. We consider type
I phase matching. The results are obtained using a perturbative expansion and
scaled to a high gain regime. They allow a straightforward maximization of the
signal gain and minimization of the parametric fluorescence noise. We find the
fundamental mode of the amplifier, which is an elliptic Gaussian defining the
optimal seed beam shape. We conclude that the output of the amplifier should be
stripped of higher order modes, which are approximately Hermite-Gaussian beams.
Alternatively, the pump waist can be adjusted such that the amount of noise
produced in the higher order modes is minimized.Comment: 18 pages, 9 figures, accepted to Applied Physics
1/N_c- expansion of the quark condensate at finite temperature
Previously the quark and meson properties in a many quark system at finite
temperature have been studied within effective QCD approaches in the Hartree
approximation. In the present paper we consider the influence of the mesonic
correlations on the quark self-energy and on the quark propagator within a
systematic - expansion. Using a general separable ansatz for the
nonlocal interaction, we derive a selfconsistent equation for the
correction to the quark propagator. For a separable model with cut-off
formfactor, we obtain a decrease of the condensate of the order of 20\% at zero
temperature. A lowering the critical temperature for the onset of the chiral
restoration transition due to the inclusion of mesonic correlations is obtained
what seems to be closer to the results from lattice calculations.Comment: 19 pages, REVTeX, 5 figure
Participant acceptability of digital footprint data collection strategies:an exemplar approach to participant engagement and involvement in the ALSPAC birth cohort study
INTRODUCTION: Digital footprint records – the tracks and traces amassed by individuals as a result of their interactions with the internet, digital devices and services – can provide ecologically valid data on individual behaviours. These could enhance longitudinal population study databanks; but few UK longitudinal studies are attempting this. When using novel sources of data, study managers must engage with participants in order to develop ethical data processing frameworks that facilitate data sharing whilst safeguarding participant interests. OBJECTIVES: This paper aims to summarise the participant involvement approach used by the ALSPAC birth cohort study to inform the development of a framework for using linked participant digital footprint data, and provide an exemplar for other data linkage infrastructures. METHODS: The paper synthesises five qualitative forms of inquiry. Thematic analysis was used to code transcripts for common themes in relation to conditions associated with the acceptability of sharing digital footprint data for longitudinal research. RESULTS: We identified six themes: participant understanding; sensitivity of location data; concerns for third parties; clarity on data granularity; mechanisms of data sharing and consent; and trustworthiness of the organisation. For cohort members to consider the sharing of digital footprint data acceptable, they require information about the value, validity and risks; control over sharing elements of the data they consider sensitive; appropriate mechanisms to authorise or object to their records being used; and trust in the organisation. CONCLUSION: Realising the potential for using digital footprint records within longitudinal research will be subject to ensuring that this use of personal data is acceptable; and that rigorously controlled population data science benefiting the public good is distinguishable from the misuse and lack of personal control of similar data within other settings. Participant co-development informs the ethical-governance framework for these novel linkages in a manner which is acceptable and does not undermine the role of the trusted data custodian
Implications of the Top Quark Mass Measurement for the CKM Parameters, and CP Asymmetries
Motivated by the recent determination of the top quark mass by the CDF
collaboration, \mt =174 \pm 10 ^{+13}_{-12} GeV, we review and update the
constraints on the parameters of the quark flavour mixing matrix in
the standard model. In performing our fits, we use inputs from the measurements
of the following quantities: (i) \abseps, the CP-violating parameter in
decays, (ii) \delmd, the mass difference due to the \bdbdbar\ mixing, (iii)
the matrix elements \absvcb and \absvub, and (iv) -hadron lifetimes. We
find that the allowed region of the unitarity triangle is very large, mostly
due to theoretical uncertainties. (This emphasizes the importance of
measurements of CP-violating rate asymmetries in the system.) Nevertheless,
the present data do somewhat restrict the allowed values of the coupling
constant product and the renormalization-scale
invariant bag constant . With the updated CKM matrix we present the
currently-allowed range of the ratio , as well as
the standard model predictions for the \bsbsbar\ mixing parameter \xs and the
quantities , and , which characterize
the CP-asymmetries in -decays. The ALEPH collaboration has recently reported
a significant improvement on the lower limit on the \bs-\bsb mass
difference, (95\% C.L.). This has interesting
consequences for the CKM parameters which are also worked out.
NOTE: this is a revised and updated version of our previous paper.Comment: LaTeX, 27 pages, 16 uuencoded figures (enclosed), CERN-TH.7398/94,
UdeM-GPP-TH-94-0
Numerical Portrait of a Relativistic BCS Gapped Superfluid
We present results of numerical simulations of the 3+1 dimensional Nambu -
Jona-Lasinio (NJL) model with a non-zero baryon density enforced via the
introduction of a chemical potential mu not equal to 0. The triviality of the
model with a number of dimensions d>=4 is dealt with by fitting low energy
constants, calculated analytically in the large number of colors (Hartree)
limit, to phenomenological values. Non-perturbative measurements of local order
parameters for superfluidity and their related susceptibilities show that, in
contrast to the 2+1 dimensional model, the ground-state at high chemical
potential and low temperature is that of a traditional BCS superfluid. This
conclusion is supported by the direct observation of a gap in the dispersion
relation for 0.5<=(mu a)<=0.85, which at (mu a)=0.8 is found to be roughly 15%
the size of the vacuum fermion mass. We also present results of an initial
investigation of the stability of the BCS phase against thermal fluctuations.
Finally, we discuss the effect of splitting the Fermi surfaces of the pairing
partners by the introduction of a non-zero isospin chemical potential.Comment: 41 pages, 19 figures, uses axodraw.sty, v2: minor typographical
correction
scattering in the -meson channel at finite temperature
We study scattering in the I=1, channel at finite
temperature in the framework of the extended Nambu-Jona-Lasinio model that
explicitly includes vector and axial-vector degrees of freedom in addition to
the usual scalar and pseudoscalar sector. The S-matrix in the coupled channels
and is constructed via -exchange in the -channel.
The self-energy of the -meson contains both quark and pion loop
contributions. The analytic structure of the S-matrix for is
investigated and the motion of the -pole as a function of coupling
constant and temperature is followed in the complex -plane. For
numerical calculations, parameters are chosen in order that ,
and the experimental phase shifts at zero temperature are
reproduced, and then the behavior of the -pole as well as the
cross section is investigated as a function of the temperature. We find that
the position of the mass stays practically constant for MeV, and then moves down in energy by about 200 MeV for 130 MeV MeV.Comment: 25 pages, 12 figures, to appear in Nucl. Phys.
- …