16,296 research outputs found
Empirical likelihood confidence intervals for complex sampling designs
We define an empirical likelihood approach which gives consistent design-based confidence intervals which can be calculated without the need of variance estimates, design effects, resampling, joint inclusion probabilities and linearization, even when the point estimator is not linear. It can be used to construct confidence intervals for a large class of sampling designs and estimators which are solutions of estimating equations. It can be used for means, regressions coefficients, quantiles, totals or counts even when the population size is unknown. It can be used with large sampling fractions and naturally includes calibration constraints. It can be viewed as an extension of the empirical likelihood approach to complex survey data. This approach is computationally simpler than the pseudoempirical likelihood and the bootstrap approaches. The simulation study shows that the confidence interval proposed may give better coverages than the confidence intervals based on linearization, bootstrap and pseudoempirical likelihood. Our simulation study shows that, under complex sampling designs, standard confidence intervals based on normality may have poor coverages, because point estimators may not follow a normal sampling distribution and their variance estimators may be biased.<br/
Preserving Value in the Post-BAPCPA Era â An Empirical Study
Through the use of a multivariate regression model, this article studies the effect on debtor reorganization values of the shortened reorganization timeframe imposed by the Bankruptcy Abuse Prevention and Consumer Protection Act (âBAPCPAâ). The study shows that BAPCPA is positively correlated at a statistically significant level with higher reorganization recoveries. This result is attributed to the increased proportion of prepackaged and prenegotiated bankruptcies observed in the post-2005 era, as these âfast-trackâ bankruptcy cases entail lower costs and better preserve the firmâs value
Short Gamma Ray Bursts: a bimodal origin?
Short-hard Gamma Ray Bursts (SGRBs) are currently thought to arise from
gravitational wave driven coalescences of double neutron star systems forming
either in the field or dynamically in globular clusters. For both channels we
fit the peak flux distribution of BATSE SGRBs to derive the local burst
formation rate and luminosity function. We then compare the resulting redshift
distribution with Swift 2-year data, showing that both formation channels are
needed in order to reproduce the observations. Double neutron stars forming in
globular clusters are found to dominate the distribution at z<0.3, whereas the
field population from primordial binaries can account for the high-z SGRBs.
This result is not in contradiction with the observed host galaxy type of
SGRBs.Comment: 5 pages, 2 figures, accepted for publication in MNRA
Optimal Strategies in Infinite-state Stochastic Reachability Games
We consider perfect-information reachability stochastic games for 2 players
on infinite graphs. We identify a subclass of such games, and prove two
interesting properties of it: first, Player Max always has optimal strategies
in games from this subclass, and second, these games are strongly determined.
The subclass is defined by the property that the set of all values can only
have one accumulation point -- 0. Our results nicely mirror recent results for
finitely-branching games, where, on the contrary, Player Min always has optimal
strategies. However, our proof methods are substantially different, because the
roles of the players are not symmetric. We also do not restrict the branching
of the games. Finally, we apply our results in the context of recently studied
One-Counter stochastic games
Tariff-Mediated Network Effects versus Strategic Discounting: Evidence from German Mobile Telecommunications
Mobile telecommunication operators routinely charge subscribers lower prices for calls on their own network than for calls to other networks (on-net discounts). Studies on tariff-mediated network effects suggest this is due to large operators using on-net discounts to damage smaller rivals. Alternatively, research on strategic discounting suggests small operators use on-net discounts to advertise with low on-net prices. We test the relative strength of these effects using data on tariff setting in German mobile telecommunications between 2001 and 2009. We find that large operators are more likely to offer tariffs with on-net discounts but there is no consistently significant difference in the magnitude of discounts. Our results suggest that tariff-mediated network effects are the main cause of on-net discounts
Vortices in simulations of solar surface convection
We report on the occurrence of small-scale vortices in simulations of the
convective solar surface. Using an eigenanalysis of the velocity gradient
tensor, we find the subset of high vorticity regions in which the plasma is
swirling. The swirling regions form an unsteady, tangled network of filaments
in the turbulent downflow lanes. Near-surface vertical vortices are underdense
and cause a local depression of the optical surface. They are potentially
observable as bright points in the dark intergranular lanes. Vortex features
typically exist for a few minutes, during which they are moved and twisted by
the motion of the ambient plasma. The bigger vortices found in the simulations
are possibly, but not necessarily, related to observations of granular-scale
spiraling pathlines in "cork animations" or feature tracking.Comment: 11 pages, 13 figures, accepted for publication in A&A, complementary
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Within You / Without You: Biotechnology, Ontology, and Ethics
As Implantable Cardioverter Defibrillators (ICDs) have become more common, ethical issues have arisen regarding the deactivation of these devices. Goldstein et al., have shown that both patients and cardiologists consider ICD deactivation to be different from the discontinuation of other life-sustaining treatments. It cannot be argued ethically that ICDs raise new questions about the distinction between withholding and withdrawing treatment, and neither the fact that they are used intermittently, nor the duration of therapy, nor the mere fact that they are located inside the body can be considered unique to these devices and morally decisive. However, frequent allusions to the fact that they are located inside the body might provide a clue about what bothers patients and physicians. As technology progresses, some interventions seem to become a part of the patient as a unified whole person, completely replacing body parts and lost physiological functions rather than merely substituting for impaired structure and function. If a life-sustaining intervention can be considered a âreplacementââa part of the patient as a unified whole personâthen it seems that deactivation is better classified as a case of killing rather than a case of forgoing a life-sustaining treatment. ICDs are not a âreplacementâ therapy in this sense. The deactivation of an ICD is best classified, under the proper conditions, as the forgoing of an extraordinary means of care. As technology becomes more sophisticated, however, and new interventions come to be best classified as âreplacementsâ (a heart transplant would be a good example), âdiscontinuingâ these interventions should be much more morally troubling for those clinicians who oppose euthanasia and assisted suicide
Scaling laws for magnetic fields on the quiet Sun
The Sun's magnetic field is structured over a range of scales that span
approximately seven orders of magnitudes, four of which lie beyond the
resolving power of current telescopes. Here we have used a Hinode SOT/SP deep
mode data set for the quiet-sun disk center in combination with constraints
from the Hanle effect to derive scaling laws that describe how the magnetic
structuring varies from the resolved scales down to the magnetic diffusion
limit, where the field ceases to be frozen-in. The focus of the analysis is a
derivation of the magnetic energy spectrum, but we also discuss the scale
dependence of the probability density function (PDF) for the flux densities and
the role of the cancellation function for the average unsigned flux density.
Analysis of the Hinode data set with the line-ratio method reveals a collapsed
flux population in the form of flux tubes with a size distribution that is
peaked in the 10-100 km range. Magnetic energy is injected into this scale
range by the instability mechanism of flux tube collapse, which is driven by
the external gas pressure in the superadiabatic region at the top of the
convection zone. This elevates the magnetic energy spectrum just beyond the
telescope resolution limit. Flux tube decay feeds an inertial range that
cascades down the scale spectrum to the magnetic diffusion limit, and which
contains the tangled, "hidden" flux that is known to exist from observations of
the Hanle effect. The observational constraints demand that the total magnetic
energy in the hidden flux must be of the same order as the total energy in the
kG flux tubes. Both the flux tubes and the hidden flux are found to be
preferentially located in the intergranular lanes, which is to be expected
since they are physically related.Comment: accepted for publication in Astronomy & Astrophysic
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