1,314 research outputs found
Employing combination procedures to short-time EOP prediction
A well known problem with Earth Orientation Parameters (EOP) prediction is
that a prediction strategy proved to be the best for some testing time span and
prediction length may not remain the same for other time intervals. In this
paper, we consider possible strategies to combine EOP predictions computed
using different analysis techniques to obtain a final prediction with the best
accuracy corresponding to the smallest prediction error of input predictions.
It was found that this approach is most efficient for ultra-short-term EOP
forecast.Comment: 7 pages, presented at the IERS Workshop on EOP Combination and
Prediction, Warsaw, Poland, 19-21 Oct 200
Scale space consistency of piecewise constant least squares estimators -- another look at the regressogram
We study the asymptotic behavior of piecewise constant least squares
regression estimates, when the number of partitions of the estimate is
penalized. We show that the estimator is consistent in the relevant metric if
the signal is in , the space of c\`{a}dl\`{a}g functions equipped
with the Skorokhod metric or equipped with the supremum metric.
Moreover, we consider the family of estimates under a varying smoothing
parameter, also called scale space. We prove convergence of the empirical scale
space towards its deterministic target.Comment: Published at http://dx.doi.org/10.1214/074921707000000274 in the IMS
Lecture Notes Monograph Series
(http://www.imstat.org/publications/lecnotes.htm) by the Institute of
Mathematical Statistics (http://www.imstat.org
A gain-loss framework based on ensemble flow forecasts to switch the urban drainage-wastewater system management towards energy optimization during dry periods
Precipitation is the cause of major perturbation to the flow in urban
drainage and wastewater systems. Flow forecasts, generated by coupling
rainfall predictions with a hydrologic runoff model, can potentially be used
to optimize the operation of integrated urban drainage–wastewater systems
(IUDWSs) during both wet and dry weather periods. Numerical weather prediction
(NWP) models have significantly improved in recent years, having increased their
spatial and temporal resolution. Finer resolution NWP are suitable for urban-catchment-scale applications, providing longer lead time than radar
extrapolation. However, forecasts are inevitably uncertain, and fine
resolution is especially challenging for NWP. This uncertainty is commonly
addressed in meteorology with ensemble prediction systems (EPSs). Handling
uncertainty is challenging for decision makers and hence tools are necessary
to provide insight on ensemble forecast usage and to support the rationality
of decisions (i.e. forecasts are uncertain and therefore errors will be made;
decision makers need tools to justify their choices, demonstrating that these
choices are beneficial in the long run).
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This study presents an economic framework to support the decision-making
process by providing information on when acting on the forecast is
beneficial and how to handle the EPS. The relative economic value (REV)
approach associates economic values with the potential outcomes and determines
the preferential use of the EPS forecast. The envelope curve of the REV diagram
combines the results from each probability forecast to provide the highest
relative economic value for a given gain–loss ratio. This approach is
traditionally used at larger scales to assess mitigation measures for
adverse events (i.e. the actions are taken when events are forecast). The
specificity of this study is to optimize the energy consumption in IUDWS
during low-flow periods by exploiting the electrical smart grid market (i.e.
the actions are taken when no events are forecast). Furthermore, the results
demonstrate the benefit of NWP neighbourhood post-processing methods to
enhance the forecast skill and increase the range of beneficial uses
Magnetic dipole moments in single and coupled split-ring resonators
We examine the role of magnetic dipoles in single and coupled pairs of
metallic split-ring resonators by numerically computing their magnitude and
examining their relative contributions to the scattering cross section. We
demonstrate that magnetic dipoles can strongly influence the scattering cross
section along particular directions. It is also found that the magnetic dipole
parallel to the incident magnetic field and/or high-order multipoles may play a
significant role in the linear response of coupled split-ring resonators.Comment: 7 pages, 3 figures, 1 tabl
Kolmogorov Similarity Hypotheses for Scalar Fields: Sampling Intermittent Turbulent Mixing in the Ocean and Galaxy
Kolmogorov's three universal similarity hypotheses are extrapolated to
describe scalar fields like temperature mixed by turbulence. By the analogous
Kolmogorov third hypothesis for scalars, temperature dissipation rates chi
averaged over lengths r > L_K should be lognormally distributed with
intermittency factors I that increase with increasing turbulence energy length
scales L_O as I_chi-r = m_T ln(L_O/r). Tests of Kolmogorovian velocity and
scalar universal similarity hypotheses for very large ranges of turbulence
length and time scales are provided by data from the ocean and the Galactic
interstellar medium. The universal constant for turbulent mixing intermittency
m_T is estimated from oceanic data to be 0.44+-0.01, which is remarkably close
to estimates for Kolmogorov's turbulence intermittency constant m_u of
0.45+-0.05 from Galactic as well as atmospheric data. Extreme intermittency
complicates the oceanic sampling problem, and may lead to quantitative and
qualitative undersampling errors in estimates of mean oceanic dissipation rates
and fluxes. Intermittency of turbulence and mixing in the interstellar medium
may be a factor in the formation of stars.Comment: 23 pages original of Proc. Roy. Soc. article, 8 figures; in
"Turbulence and Stochastic Processes: Kolmogorov's ideas 50 years on", London
The Royal Society, 1991, J.C.R. Hunt, O.M. Phillips, D. Williams Eds., pages
1-240, vol. 434 (no. 1890) Proc. Roy. Soc. Lond. A, PDF fil
Prescription patterns of benzodiazepine and benzodiazepine-related drugs in the peripartum period: A population-based study
Using prescription drugs during pregnancy is challenging and approached with caution. In this study, we present population-based information on prescription patterns of benzodiazepines and benzodiazepine-related drugs in the peripartum period. A population-based study of 1,154,817 pregnancies between 1997 and 2015 in Denmark, of which 205,406 (17.8%) pregnancies in women with a psychiatric history. Prescription drugs starting with Anatomical Therapeutic Chemical codes N05BA, N05CD, and N05CF from 12 months before pregnancy to 12 months following pregnancy were identified. We used generalised estimating equations to estimate the adjusted 5 year risk difference in the proportion of women redeeming benzodiazepines from 1 year to 5 years after. Logistic regression was used to analyze the association between characteristics and discontinuation of benzodiazepines during pregnancy. The prevalence of benzodiazepine prescriptions was 1.9% before pregnancy, 0.6% during pregnancy, and 1.3% after pregnancy. In women with a psychiatric history, the prevalence was 5–6 times higher. A significant decrease in prescriptions to women with a psychiatric history was observed, which was less profound among women with no psychiatric history. Approximately 90% of women discontinue benzodiazepines during pregnancy, with a higher percentage of women discontinuing from 1997 to 2015. The observed decrease is likely explained by changing treatment guidelines
Influence of bottom topography on integral constraints in zonal flows with parameterized potential vorticity fluxes
An integral constraint for eddy fluxes of potential vorticity (PV), corresponding to global momentum conservation, is applied to two-layer zonal quasi-geostrophic channel flow. This constraint must be satisfied for any type of parameterization of eddy PV fluxes. Bottom topography strongly influence the integral constraint compared to a flat bottom channel. An analytical solution for the mean flow solution has been found by using asymptotic expansion in a small parameter which is the ratio of the Rossby radius to the meridional extent of the channel. Applying the integral constraint to this solution, one can find restrictions for eddy PV transfer coefficients which relate the eddy fluxes of PV to the mean flow. These restrictions strongly deviate from restrictions for the channel with flat bottom topography
The generalized non-conservative model of a 1-planet system - revisited
We study the long-term dynamics of a planetary system composed of a star and
a planet. Both bodies are considered as extended, non-spherical, rotating
objects. There are no assumptions made on the relative angles between the
orbital angular momentum and the spin vectors of the bodies. Thus, we analyze
full, spatial model of the planetary system. Both objects are assumed to be
deformed due to their own rotations, as well as due to the mutual tidal
interactions. The general relativity corrections are considered in terms of the
post-Newtonian approximation. Besides the conservative contributions to the
perturbing forces, there are also taken into account non-conservative effects,
i.e., the dissipation of the mechanical energy. This dissipation is a result of
the tidal perturbation on the velocity field in the internal zones with
non-zero turbulent viscosity (convective zones). Our main goal is to derive the
equations of the orbital motion as well as the equations governing
time-evolution of the spin vectors (angular velocities). We derive the
Lagrangian equations of the second kind for systems which do not conserve the
mechanical energy. Next, the equations of motion are averaged out over all fast
angles with respect to time-scales characteristic for conservative
perturbations. The final equations of motion are then used to study the
dynamics of the non-conservative model over time scales of the order of the age
of the star. We analyze the final state of the system as a function of the
initial conditions. Equilibria states of the averaged system are finally
discussed.Comment: 37 pages, 13 figures, accepted to Celestial Mechanics and Dynamical
Astronom
ESA CryoVEx 2011:Airborne field campaign with ASIRAS radar, EM induction sounder and laser scanner
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