2,955 research outputs found
Bidding process in online auctions and winning strategy:rate equation approach
Online auctions have expanded rapidly over the last decade and have become a
fascinating new type of business or commercial transaction in this digital era.
Here we introduce a master equation for the bidding process that takes place in
online auctions. We find that the number of distinct bidders who bid times,
called the -frequent bidder, up to the -th bidding progresses as
. The successfully transmitted bidding rate by the
-frequent bidder is obtained as , independent of
for large . This theoretical prediction is in agreement with empirical data.
These results imply that bidding at the last moment is a rational and effective
strategy to win in an eBay auction.Comment: 4 pages, 6 figure
From time series to superstatistics
Complex nonequilibrium systems are often effectively described by a
`statistics of a statistics', in short, a `superstatistics'. We describe how to
proceed from a given experimental time series to a superstatistical
description. We argue that many experimental data fall into three different
universality classes: chi^2-superstatistics (Tsallis statistics), inverse
chi^2-superstatistics, and log-normal superstatistics. We discuss how to
extract the two relevant well separated superstatistical time scales tau and T,
the probability density of the superstatistical parameter beta, and the
correlation function for beta from the experimental data. We illustrate our
approach by applying it to velocity time series measured in turbulent
Taylor-Couette flow, which is well described by log-normal superstatistics and
exhibits clear time scale separation.Comment: 7 pages, 9 figure
Spin constrained orbital angular momentum control in high-harmonic generation
The interplay between spin and orbital angular momentum in the up-conversion
process allows us to control the macroscopic wave front of high harmonics by
manipulating the microscopic polarizations of the driving field. We demonstrate
control of orbital angular momentum in high harmonic generation from both solid
and gas phase targets using the selection rules of spin angular momentum. The
gas phase harmonics extend the control of angular momentum to
extreme-ultraviolet wavelength. We also propose a bi-color scheme to produce
spectrally separated extreme-ultraviolet radiation carrying orbital angular
momentum
Ancient stars beyond the Local Group: RR Lyrae variables and Blue Horizontal Branch stars in Sculptor Group Dwarf Galaxies
We have used Hubble Space Telescope ACS images to generate color-magnitude
diagrams that reach below the magnitude of the horizontal branch in the
Sculptor Group dwarf galaxies ESO294-010 and ESO410-005. In both diagrams blue
horizontal branch stars are unambiguously present, a signature of the existence
of an ancient stellar population whose age is comparable to that of the
Galactic halo globular clusters. The result is reinforced by the discovery of
numerous RR Lyrae variables in both galaxies. The occurrence of these stars in
the first direct confirmation of the existence of ancient stellar populations
beyond the Local Group and indicates that star formation can occur at the
earliest epochs even in low density environments.Comment: 11 pages, 2 figures, accepted for publication in Astrophysical
Journal Letter
Fluence correction factor for graphite calorimetry in a clinical high-energy carbon-ion beam
The aim of this work is to develop and adapt a formalism to determine absorbed dose to water from graphite calorimetry measurements in carbon-ion beams. Fluence correction factors, kfl, needed when using a graphite calorimeter to derive dose to water, were determined in a clinical high-energy carbon-ion beam. Measurements were performed in a 290 MeV/n carbon-ion beam with a field size of 11 x 11 cm2, without modulation. In order to sample the beam, a plane-parallel Roos ionization chamber was chosen for its small collecting volume in comparison with the field size. Experimental information on fluence corrections was obtained from depth-dose measurements in water. This procedure was repeated with graphite plates in front of the water phantom. Fluence corrections were also obtained with Monte Carlo simulations through the implementation of three methods based on (i) the fluence distributions differential in energy, (ii) a ratio of calculated doses in water and graphite at equivalent depths and (iii) simulations of the experimental setup. The kfl term increased in depth from 1.00 at the entrance toward 1.02 at a depth near the Bragg peak, and the average difference between experimental and numerical simulations was about 0.13%. Compared to proton beams, there was no reduction of the kfl due to alpha particles because the secondary particle spectrum is dominated by projectile fragmentation. By developing a practical dose conversion technique, this work contributes to improving the determination of absolute dose to water from graphite calorimetry in carbon-ion beams
Time Periodic Behavior of Multiband Superlattices in Static Electric Fields
We use an analytic perturbation expansion for the two-band system of tight
binding electrons to discuss Bloch oscillations and Zener tunneling within this
model. We make comparison with recent numerical results and predict
analytically the frequency of radiation expected from Zener tunneling,
including its disappearance, as a function of the system parameters.Comment: 12 pages, no figure include
Taming open/closed string duality with a Losev trick
A target space string field theory formulation for open and closed B-model is
provided by giving a Batalin-Vilkovisky quantization of the holomorphic
Chern-Simons theory with off-shell gravity background. The target space
expression for the coefficients of the holomorphic anomaly equation for open
strings are obtained. Furthermore, open/closed string duality is proved from a
judicious integration over the open string fields. In particular, by
restriction to the case of independence on continuous open moduli, the shift
formulas of [7] are reproduced and shown therefore to encode the data of a
closed string dual.Comment: 22 pages, no figures; v.2 Refs. and a comment added
Fitness benefits of prolonged post-reproductive lifespan in women
Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. In theory, a prolonged post-reproductive lifespan will evolve when females can gain greater fitness by increasing the success of their offspring than by continuing to breed themselves. Although reproductive success is known to decline in old age, it is unknown whether women gain fitness by prolonging lifespan post-reproduction. Using complete multi-generational demographic records, we show that women with a prolonged post-reproductive lifespan have more grandchildren, and hence greater fitness, in pre-modern populations of both Finns and Canadians. This fitness benefit arises because post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently and more successfully. Finally, the fitness benefits of prolonged lifespan diminish as the reproductive output of offspring declines. This suggests that in female humans, selection for deferred ageing should wane when one's own offspring become post-reproductive and, correspondingly, we show that rates of female mortality accelerate as their offspring terminate reproduction
Superstatistics, thermodynamics, and fluctuations
A thermodynamic-like formalism is developed for superstatistical systems
based on conditional entropies. This theory takes into account large-scale
variations of intensive variables of systems in nonequilibrium stationary
states. Ordinary thermodynamics is recovered as a special case of the present
theory, and corrections to it can be systematically evaluated. A generalization
of Einstein's relation for fluctuations is presented using a maximum entropy
condition.Comment: 16 pages, no figures. The title changed, some explanations and
references added. Accepted for publication in Phys. Rev.
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