1,140 research outputs found
Survival of technologies: an evolutionary game approach
This paper models technology adoption as an evolutionary and asymmetric game based on a pairwise contest involving two populations, firms and consumers. First, externalities are considered only on the supply side, leading to the usual results found in the recent economic literature on the subject: path dependence, lock-in, and the possibility ofselecting inferior technology. Next externalities are introduced on the demand side, which in Leibenstein's classic paper leads to bandwagon and snob effects, and interactions between supply and demand are examined
Parameterizing the Power Spectrum: Beyond the Truncated Taylor Expansion
The power spectrum is traditionally parameterized by a truncated Taylor
series: . It is
reasonable to truncate the Taylor series if , but
it is not if . We argue that there is no good
theoretical reason to prefer , and show that current
observations are consistent with even for
. Thus, there are regions of parameter space, which are both
theoretically and observationally relevant, for which the traditional truncated
Taylor series parameterization is inconsistent, and hence it can lead to
incorrect parameter estimations. Motivated by this, we propose a simple
extension of the traditional parameterization, which uses no extra parameters,
but that, unlike the traditional approach, covers well motivated inflationary
spectra with . Our parameterization therefore covers not only
standard-slow-roll inflation models but also a much wider class of inflation
models. We use this parameterization to perform a likelihood analysis for the
cosmological parameters.Comment: References added. Typo correcte
Orbital-dependent modifications of electronic structure across magneto-structural transition in BaFe2As2
Laser angle-resolved photoemission spectroscopy (ARPES) is employed to
investigate the temperature (T) dependence of the electronic structure in
BaFe2As2 across the magneto-structural transition at TN ~ 140 K. A drastic
transformation in Fermi surface (FS) shape across TN is observed, as expected
by first-principles band calculations. Polarization-dependent ARPES and band
calculations consistently indicate that the observed FSs at kz ~ pi in the
low-T antiferromagnetic (AF) state are dominated by the Fe3dzx orbital, leading
to the two-fold electronic structure. These results indicate that
magneto-structural transition in BaFe2As2 accompanies orbital-dependent
modifications in the electronic structure.Comment: 13 pages, 4 figures. accepted by Physical Review Letter
Evaluating methods for ranking differentially expressed genes applied to microArray quality control data
<p>Abstract</p> <p>Background</p> <p>Statistical methods for ranking differentially expressed genes (DEGs) from gene expression data should be evaluated with regard to high sensitivity, specificity, and reproducibility. In our previous studies, we evaluated eight gene ranking methods applied to only Affymetrix GeneChip data. A more general evaluation that also includes other microarray platforms, such as the Agilent or Illumina systems, is desirable for determining which methods are suitable for each platform and which method has better inter-platform reproducibility.</p> <p>Results</p> <p>We compared the eight gene ranking methods using the MicroArray Quality Control (MAQC) datasets produced by five manufacturers: Affymetrix, Applied Biosystems, Agilent, GE Healthcare, and Illumina. The area under the curve (AUC) was used as a measure for both sensitivity and specificity. Although the highest AUC values can vary with the definition of "true" DEGs, the best methods were, in most cases, either the weighted average difference (WAD), rank products (RP), or intensity-based moderated <it>t </it>statistic (ibmT). The percentages of overlapping genes (POGs) across different test sites were mainly evaluated as a measure for both intra- and inter-platform reproducibility. The POG values for WAD were the highest overall, irrespective of the choice of microarray platform. The high intra- and inter-platform reproducibility of WAD was also observed at a higher biological function level.</p> <p>Conclusion</p> <p>These results for the five microarray platforms were consistent with our previous ones based on 36 real experimental datasets measured using the Affymetrix platform. Thus, recommendations made using the MAQC benchmark data might be universally applicable.</p
Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights
The temperature dependence and anisotropy of optical spectral weights
associated with different multiplet transitions is determined by the spin and
orbital correlations. To provide a systematic basis to exploit this close
relationship between magnetism and optical spectra, we present and analyze the
spin-orbital superexchange models for a series of representative
orbital-degenerate transition metal oxides with different multiplet structure.
For each case we derive the magnetic exchange constants, which determine the
spin wave dispersions, as well as the partial optical sum rules. The magnetic
and optical properties of early transition metal oxides with degenerate
orbitals (titanates and vanadates with perovskite structure) are shown
to depend only on two parameters, viz. the superexchange energy and the
ratio of Hund's exchange to the intraorbital Coulomb interaction, and on
the actual orbital state. In systems important corrections follow from
charge transfer excitations, and we show that KCuF can be classified as a
charge transfer insulator, while LaMnO is a Mott insulator with moderate
charge transfer contributions. In some cases orbital fluctuations are quenched
and decoupling of spin and orbital degrees of freedom with static orbital order
gives satisfactory results for the optical weights. On the example of cubic
vanadates we describe a case where the full quantum spin-orbital physics must
be considered. Thus information on optical excitations, their energies,
temperature dependence and anisotropy, combined with the results of magnetic
neutron scattering experiments, provides an important consistency test of the
spin-orbital models, and indicates whether orbital and/or spin fluctuations are
important in a given compound.Comment: 34 pages, 16 figure
Constraining Scale-Dependent Non-Gaussianity with Future Large-Scale Structure and the CMB
We forecast combined future constraints from the cosmic microwave background
and large-scale structure on the models of primordial non-Gaussianity. We study
the generalized local model of non-Gaussianity, where the parameter f_NL is
promoted to a function of scale, and present the principal component analysis
applicable to an arbitrary form of f_NL(k). We emphasize the complementarity
between the CMB and LSS by using Planck, DES and BigBOSS surveys as examples,
forecast constraints on the power-law f_NL(k) model, and introduce the figure
of merit for measurements of scale-dependent non-Gaussianity.Comment: 28 pages, 8 figures, 2 tables; v2: references update
Optimizing Information Freshness in Wireless Networks under General Interference Constraints
Age of information (AoI) is a recently proposed metric for measuring
information freshness. AoI measures the time that elapsed since the last
received update was generated. We consider the problem of minimizing average
and peak AoI in a wireless networks, consisting of a set of source-destination
links, under general interference constraints. When fresh information is always
available for transmission, we show that a stationary scheduling policy is peak
age optimal. We also prove that this policy achieves average age that is within
a factor of two of the optimal average age. In the case where fresh information
is not always available, and packet/information generation rate has to be
controlled along with scheduling links for transmission, we prove an important
separation principle: the optimal scheduling policy can be designed assuming
fresh information, and independently, the packet generation rate control can be
done by ignoring interference. Peak and average AoI for discrete time G/Ber/1
queue is analyzed for the first time, which may be of independent interest
Higher order terms in the inflaton potential and the lower bound on the tensor to scalar ratio r
The MCMC analysis of the CMB+LSS data in the context of the Ginsburg-Landau
approach to inflation indicated that the fourth degree double--well inflaton
potential best fits the present CMB and LSS data. This provided a lower bound
for the ratio r of the tensor to scalar fluctuations and as most probable value
r = 0.05, within reach of the forthcoming CMB observations. We systematically
analyze here the effects of arbitrary higher order terms in the inflaton
potential on the CMB observables: spectral index ns and ratio r. Furthermore,
we compute in close form the inflaton potential dynamically generated when the
inflaton field is a fermion condensate in the inflationary universe. This
inflaton potential turns to belong to the Ginsburg-Landau class too. The
theoretical values in the (ns,r) plane for all double well inflaton potentials
in the Ginsburg-Landau approach (including the potential generated by fermions)
turn to be inside a universal banana-shaped region B. The upper border of the
banana-shaped region B is given by the fourth order double--well potential and
provides an upper bound for the ratio r.The lower border of B is defined by the
quadratic plus an infinite barrier inflaton potential and provides a lower
bound for the ratio r. For example, the current best value of the spectral
index ns = 0.964, implies r is in the interval: 0.021 < r < 0.053.
Interestingly enough, this range is within reach of forthcoming CMB
observations.Comment: 24 pages, 10 figures. Presentation improved. To appear in Annals of
Physic
From the Spectrum to Inflation : An Inverse Formula for the General Slow-Roll Spectrum
We propose a general inverse formula for extracting inflationary parameters
from the observed power spectrum of cosmological perturbations. Under the
general slow-roll scheme, which helps to probe the properties of inflation in a
model independent way, we invert the leading order, single field, power
spectrum formula. We also give some physically interesting examples to
demonstrate its wide applicability and illuminate its properties.Comment: 8 pages, no figure ; References expande
Flavour constraints on scenarios with two or three heavy squark generations
We re-assess constraints from flavour-changing neutral currents in the kaon
system on supersymmetric scenarios with a light gluino, two heavy generations
of squarks and a lighter third generation. We compute for the first time limits
in scenarios with three heavy squark families, taking into account QCD
corrections at the next-to-leading order. We compare our limits with those in
the case of two heavy families. We use the mass insertion approximation and
consider contributions from gluino exchange to constrain the mixing between the
first and second squark generation. While it is not possible to perform a
general analysis, we assess the relevance of each kind of flavour- and
CP-violating parameters. We also provide ready to use magic numbers for the
computation of the Wilson coefficients at 2 GeV for these scenarios.Comment: 23 pages, 14 figures; v3: matches published version (contains
improvements in the presentation and clarifications
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