28,555 research outputs found
Recommended from our members
The relationship of drug reimbursement with the price and the quality of pharmaceutical innovations
This paper studies the strategic interaction between pharmaceutical firms' pricing decisions and government agencies' reimbursement decisions which discriminate between patients by giving reimbursement rights to patients for whom the drug is most effective. We show that if the reimbursement decision preceeds the pricing decision, the agency only reimburses some patients if the private and public health benefits from the new drug diverge. That is, when (i) there are large externalities of consuming the drug and (ii) the difference in costs between the new drug and the alternative treatment is large. Alternatively, if the firm can commit to a price in advance of the reimbursement decision, we identify a strategic effect which implies that by committing to a high price ex ante, the firm can force a listing outcome and make the agency more willing to reimburse than in the absence of commitment
Metallicity of high stellar mass galaxies with signs of merger events
We focus on an analysis of galaxies of high stellar mass and low metallicity.
We cross-correlated the Millenium Galaxy Catalogue (MGC) and the Sloan Digital
Sky Survey (SDSS) galaxy catalogue to provide a sample of MGC objects with high
resolution imaging and both spectroscopic and photometric information available
in the SDSS database. For each galaxy in our sample, we conducted a systematic
morphological analysis by visual inspection of MGC images using their
luminosity contours. The galaxies are classified as either disturbed or
undisturbed objects. We divide the sample into three metallicity regions,
within wich we compare the properties of disturbed and undisturbed objects. We
find that the fraction of galaxies that are strongly disturbed, indicative of
being merger remnants, is higher when lower metallicity objects are considered.
The three bins analysed consist of approximatively 15%, 20%, and 50% disturbed
galaxies (for high, medium, and low metallicity, respectively). Moreover, the
ratio of the disturbed to undisturbed relative distributions of the population
age indicator, Dn(4000), in the low metallicity bin, indicates that the
disturbed objects have substantially younger stellar populations than their
undisturbed counterparts. In addition, we find that an analysis of colour
distributions provides similar results, showing that low metallicity galaxies
with a disturbed morphology are bluer than those that are undisturbed. The
bluer colours and younger populations of the low metallicity, morphologically
disturbed objects suggest that they have experienced a recent merger with an
associated enhanced star formation rate. [abridged]Comment: Astronomy & Astrophysics, in pres
On the Potential of Leptonic Minimal Flavour Violation
Minimal Flavour Violation can be realized in several ways in the lepton
sector due to the possibility of Majorana neutrino mass terms. We derive the
scalar potential for the fields whose background values are the Yukawa
couplings, for the simplest See-Saw model with just two right-handed neutrinos,
and explore its minima. The Majorana character plays a distinctive role: the
minimum of the potential allows for large mixing angles -in contrast to the
simplest quark case- and predicts a maximal Majorana phase. This points in turn
to a strong correlation between neutrino mass hierarchy and mixing pattern.Comment: 6 pages; version published on Physics Letters
Hyper-chaotic magnetisation dynamics of two interacting dipoles
The present work is a numerical study of the deterministic spin dynamics of two interacting anisotropic magnetic particles in the presence of a time-dependent external magnetic field using the Landau–Lifshitz equation. Particles are coupled through the dipole–dipole interaction. The applied magnetic field is made of a constant longitudinal amplitude component and a time-dependent transversal amplitude component. Dynamical states obtained are represented by their Lyapunov exponents and bifurcation diagrams. The dependence on the largest and the second largest Lyapunov exponents, as a function of the magnitude and frequency of the applied magnetic field, and the relative distance between particles, is studied. The system presents multiple transitions between regular and chaotic behaviour depending on the control parameters. In particular, the system presents consistent hyper-chaotic states
A photometric study of the hot exoplanet WASP-19b
Context: When the planet transits its host star, it is possible to measure
the planetary radius and (with radial velocity data) the planet mass. For the
study of planetary atmospheres, it is essential to obtain transit and
occultation measurements at multiple wavelengths.
Aims: We aim to characterize the transiting hot Jupiter WASP-19b by deriving
accurate and precise planetary parameters from a dedicated observing campaign
of transits and occultations.
Methods: We have obtained a total of 14 transit lightcurves in the r'-Gunn,
IC, z'-Gunn and I+z' filters and 10 occultation lightcurves in z'-Gunn using
EulerCam on the Euler-Swiss telescope and TRAPPIST. We have also obtained one
lightcurve through the narrow-band NB1190 filter of HAWK-I on the VLT measuring
an occultation at 1.19 micron. We have performed a global MCMC analysis of all
new data together with some archive data in order to refine the planetary
parameters and measure the occultation depths in z'-band and at 1.19 micron.
Results: We measure a planetary radius of R_p = 1.376 (+/-0.046) R_j, a
planetary mass of M_p = 1.165 (+/-0.068) M_j, and find a very low eccentricity
of e = 0.0077 (+/-0.0068), compatible with a circular orbit. We have detected
the z'-band occultation at 3 sigma significance and measure it to be dF_z'= 352
(+/-116) ppm, more than a factor of 2 smaller than previously published. The
occultation at 1.19 micron is only marginally constrained at dF_1190 = 1711
(+/-745) ppm.
Conclusions: We have shown that the detection of occultations in the visible
is within reach even for 1m class telescopes if a considerable number of
individual events are observed. Our results suggest an oxygen-dominated
atmosphere of WASP-19b, making the planet an interesting test case for
oxygen-rich planets without temperature inversion.Comment: Published in Astronomy & Astrophysics. 11 pages, 11 figures, 4 table
Decoherence in a quantum harmonic oscillator monitored by a Bose-Einstein condensate
We investigate the dynamics of a quantum oscillator, whose evolution is
monitored by a Bose-Einstein condensate (BEC) trapped in a symmetric double
well potential. It is demonstrated that the oscillator may experience various
degrees of decoherence depending on the variable being measured and the state
in which the BEC is prepared. These range from a `coherent' regime in which
only the variances of the oscillator position and momentum are affected by
measurement, to a slow (power law) or rapid (Gaussian) decoherence of the mean
values themselves.Comment: 4 pages, 3 figures, lette
Cooler and bigger than thought? Planetary host stellar parameters from the InfraRed Flux Method
Effective temperatures and radii for 92 planet-hosting stars as determined
from the InfraRed Flux Method (IRFM) are presented and compared with those
given by other authors using different approaches. The IRFM temperatures we
have derived are systematically lower than those determined from the
spectroscopic condition of excitation equilibrium, the mean difference being as
large as 110 K. They are, however, consistent with previous IRFM studies and
with the colors derived from Kurucz and MARCS model atmospheres. Comparison
with direct measurements of stellar diameters for 7 dwarf stars, which
approximately cover the range of temperatures of the planet-hosting stars,
suggest that the IRFM radii and temperatures are reliable in an absolute scale.
A better understanding of the fundamental properties of the stars with planets
will be achieved once this discrepancy between the IRFM and the spectroscopic
temperature scales is resolved.Comment: 15 pages, 4 figures. Accepted for publication in Ap
Spatio-temporal dynamics induced by competing instabilities in two asymmetrically coupled nonlinear evolution equations
Pattern formation often occurs in spatially extended physical, biological and
chemical systems due to an instability of the homogeneous steady state. The
type of the instability usually prescribes the resulting spatio-temporal
patterns and their characteristic length scales. However, patterns resulting
from the simultaneous occurrence of instabilities cannot be expected to be
simple superposition of the patterns associated with the considered
instabilities. To address this issue we design two simple models composed by
two asymmetrically coupled equations of non-conserved (Swift-Hohenberg
equations) or conserved (Cahn-Hilliard equations) order parameters with
different characteristic wave lengths. The patterns arising in these systems
range from coexisting static patterns of different wavelengths to traveling
waves. A linear stability analysis allows to derive a two parameter phase
diagram for the studied models, in particular revealing for the Swift-Hohenberg
equations a co-dimension two bifurcation point of Turing and wave instability
and a region of coexistence of stationary and traveling patterns. The nonlinear
dynamics of the coupled evolution equations is investigated by performing
accurate numerical simulations. These reveal more complex patterns, ranging
from traveling waves with embedded Turing patterns domains to spatio-temporal
chaos, and a wide hysteretic region, where waves or Turing patterns coexist.
For the coupled Cahn-Hilliard equations the presence of an weak coupling is
sufficient to arrest the coarsening process and to lead to the emergence of
purely periodic patterns. The final states are characterized by domains with a
characteristic length, which diverges logarithmically with the coupling
amplitude.Comment: 9 pages, 10 figures, submitted to Chao
Importance Sampling: Intrinsic Dimension and Computational Cost
The basic idea of importance sampling is to use independent samples from a
proposal measure in order to approximate expectations with respect to a target
measure. It is key to understand how many samples are required in order to
guarantee accurate approximations. Intuitively, some notion of distance between
the target and the proposal should determine the computational cost of the
method. A major challenge is to quantify this distance in terms of parameters
or statistics that are pertinent for the practitioner. The subject has
attracted substantial interest from within a variety of communities. The
objective of this paper is to overview and unify the resulting literature by
creating an overarching framework. A general theory is presented, with a focus
on the use of importance sampling in Bayesian inverse problems and filtering.Comment: Statistical Scienc
- …