15,611 research outputs found
On Colorful Bin Packing Games
We consider colorful bin packing games in which selfish players control a set
of items which are to be packed into a minimum number of unit capacity bins.
Each item has one of colors and cannot be packed next to an item of
the same color. All bins have the same unitary cost which is shared among the
items it contains, so that players are interested in selecting a bin of minimum
shared cost. We adopt two standard cost sharing functions: the egalitarian cost
function which equally shares the cost of a bin among the items it contains,
and the proportional cost function which shares the cost of a bin among the
items it contains proportionally to their sizes. Although, under both cost
functions, colorful bin packing games do not converge in general to a (pure)
Nash equilibrium, we show that Nash equilibria are guaranteed to exist and we
design an algorithm for computing a Nash equilibrium whose running time is
polynomial under the egalitarian cost function and pseudo-polynomial for a
constant number of colors under the proportional one. We also provide a
complete characterization of the efficiency of Nash equilibria under both cost
functions for general games, by showing that the prices of anarchy and
stability are unbounded when while they are equal to 3 for black and
white games, where . We finally focus on games with uniform sizes (i.e.,
all items have the same size) for which the two cost functions coincide. We
show again a tight characterization of the efficiency of Nash equilibria and
design an algorithm which returns Nash equilibria with best achievable
performance
Polarization and readout of coupled single spins in diamond
We study the coupling of a single nitrogen-vacancy center in diamond to a
nearby single nitrogen defect at room temperature. The magnetic dipolar
coupling leads to a splitting in the electron spin resonance frequency of the
nitrogen-vacancy center, allowing readout of the state of a single nitrogen
electron spin. At magnetic fields where the spin splitting of the two centers
is the same we observe a strong polarization of the nitrogen electron spin. The
amount of polarization can be controlled by the optical excitation power. We
combine the polarization and the readout in time-resolved pump-probe
measurements to determine the spin relaxation time of a single nitrogen
electron spin. Finally, we discuss indications for hyperfine-induced
polarization of the nitrogen nuclear spin
Chemical equilibrium and stable stratification of a multi-component fluid: thermodynamics and application to neutron stars
A general thermodynamic argument shows that multi-component matter in full
chemical equilibrium, with uniform entropy per baryon, is generally stably
stratified. This is particularly relevant for neutron stars, in which the
effects of entropy are negligible compared to those of the equilibrium
composition gradient established by weak interactions. It can therefore be
asserted that, regardless of the uncertainties in the equation of state of
dense matter, neutron stars are stably stratified. This has important,
previously discussed consequences for their oscillation modes, magnetic field
evolution, and internal angular momentum transport.Comment: AASTeX, 8 pages, including 1 PS figure. Accepted for publication in
The Astrophysical Journa
Causal perturbation theory in terms of retarded products, and a proof of the Action Ward Identity
In the framework of perturbative algebraic quantum field theory a local
construction of interacting fields in terms of retarded products is performed,
based on earlier work of Steinmann. In our formalism the entries of the
retarded products are local functionals of the off shell classical fields, and
we prove that the interacting fields depend only on the action and not on terms
in the Lagrangian which are total derivatives, thus providing a proof of
Stora's 'Action Ward Identity'. The theory depends on free parameters which
flow under the renormalization group. This flow can be derived in our local
framework independently of the infrared behavior, as was first established by
Hollands and Wald. We explicitly compute non-trivial examples for the
renormalization of the interaction and the field.Comment: 76 pages, to appear in Rev. Math. Phy
Electron-Temperature Measurement In Laser-Produced Plasmas By The Ratio Of Isoelectronic Line-Intensities
A class of spectroscopic line ratios has been adapted as a diagnostic of electron temperature from \u3c 100 eV to \u3e 1 keV. The diagnostic makes use of the ratio of line intensities from isoelectronic states of different elements in specially prepared targets. The diagnostic is simple to interpret, shows weak dependence on plasma density, requires only low to moderate spectral resolution, uses a single charge state, and can be adapted to minimize line reabsorption and wavelength coincidences with other spectral lines. We present theoretical and experimental results
Co-evolutionnary network approach to cultural dynamics controlled by intolerance
Starting from Axelrod's model of cultural dissemination, we introduce a
rewiring probability, enabling agents to cut the links with their unfriendly
neighbors if their cultural similarity is below a tolerance parameter. For low
values of tolerance, rewiring promotes the convergence to a frozen monocultural
state. However, intermediate tolerance values prevent rewiring once the network
is fragmented, resulting in a multicultural society even for values of initial
cultural diversity in which the original Axelrod model reaches globalization
Investment under ambiguity with the best and worst in mind
Recent literature on optimal investment has stressed the difference between the impact of risk and the impact of ambiguity - also called Knightian uncertainty - on investors' decisions. In this paper, we show that a decision maker's attitude towards ambiguity is similarly crucial for investment decisions. We capture the investor's individual ambiguity attitude by applying alpha-MEU preferences to a standard investment problem. We show that the presence of ambiguity often leads to an increase in the subjective project value, and entrepreneurs are more eager to invest. Thereby, our investment model helps to explain differences in investment behavior in situations which are objectively identical
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