234 research outputs found
Region-of-influence approach to a frequency analysis of heavy precipitation in Slovakia
International audienceThe L-moment-based regionalization approach developed by Hosking and Wallis (1997) is a frequently used tool in regional frequency modeling of heavy precipitation events. The method consists of the delineation of homogeneous pooling groups with a fixed structure, which may, however, lead to undesirable step-like changes in growth curves and design value estimates in the case of a transition from one pooling group to another. Unlike the standard methodology, the region-of-influence (ROI) approach does not make use of groups of sites (regions) with a fixed structure; instead, each site has its own "region", i.e. a group of sites that are sufficiently similar to the site of interest. The aim of the study is to develop a version of the ROI approach, which was originally proposed in order to overcome inconsistencies involved in flood frequency analysis, for the modeling of probabilities of heavy precipitation amounts. Various settings of the distance metric and pooled weighting factors are evaluated, and a comparison with the standard regional frequency analysis over the area of Slovakia is performed. The advantages of the ROI approach are assessed by means of simulation studies. It is demonstrated that almost any setting of parameters of the ROI method yields estimates of growth curves and design values at individual sites that are superior to the standard regional and at-site estimates
Selection of intense rainfall events based on intensity thresholds and lightning data in Switzerland
This paper presents a method to identify intense warm season storms with
convective character based on intensity thresholds and the presence of
lightning, and analyzes their statistical properties. Long records of
precipitation and lightning data at 4 stations and 10 min resolution in
different climatological regions in Switzerland are used. Our premise is that
thunderstorms associated with lightning generate bursts of high rainfall
intensity. We divided all recorded storms into those accompanied by lightning
and those without lightning and found the threshold <i>I</i><sup>*</sup> that separates
intense events based on peak 10 min intensity <i>I</i><sub>p</sub> ≥ <i>I</i><sup>*</sup> for a
chosen misclassification rate α. The performance and robustness of the
selection method was tested by investigating the inter-annual variability of
<i>I</i><sup>*</sup> and its relation to the frequency of lightning strikes. The probability
distributions of the main storm properties (rainfall depth <i>R</i>, event
duration <i>D</i>, average storm intensity <i>I</i><sub>a</sub> and peak 10 min
intensity <i>I</i><sub>p</sub>) for the intense storm subsets show that the event
average and peak intensities are significantly different between the
stations. Non-parametric correlations between the main storm properties were
estimated for intense storms and all storms including stratiform rain. The
differences in the correlations between storm subsets are greater than those
between stations, which indicates that care must be exercised not to mix
events of different origin when they are sampled for multivariate analysis,
for example, copula fitting to rainfall data
Magnetotransport studies of Superconducting PrFeAsTeO
We report a detailed study of the electrical transport properties of single
crystals of PrFeAsTeO, a recently discovered iron-based
superconductor. Resistivity, Hall effect and magnetoresistance are measured in
a broad temperature range revealing the role of electrons as dominant charge
carriers. The significant temperature dependence of the Hall coefficient and
the violation of Kohler's law indicate multiband effects in this compound. The
upper critical field and the magnetic anisotropy are investigated in fields up
to 16 T, applied parallel and perpendicular to the crystallographic c-axis.
Hydrostatic pressure up to 2 GPa linearly increases the critical temperature
and the resistivity residual ratio. A simple two-band model is used to describe
the transport and magnetic properties of PrFeAsTeO. The
model can successfully explain the strongly temperature dependent negative Hall
coefficient and the high magnetic anisotropy assuming that the mobility of
electrons is higher than that of holes
Calculating all elements of minimal index in the infinite parametric family of simplest quartic fields
summary:It is a classical problem in algebraic number theory to decide if a number field is monogeneous, that is if it admits power integral bases. It is especially interesting to consider this question in an infinite parametric family of number fields. In this paper we consider the infinite parametric family of simplest quartic fields generated by a root of the polynomial , assuming that , and has no odd square factors. In addition to generators of power integral bases we also calculate the minimal index and all elements of minimal index in all fields in this family
Ab-initio calculations of the optical properties of the Si(113)3x2ADI surface
We investigated the stable silicon (113) surface with a 3x2ADI reconstruction
by ab-initio methods. The ground state properties have been obtained using the
density-functional theory. We present the dispersion of the electronic band
structure, where the surface bands have been distinguished from the projected
bulk bands by calculating their localization in the slab. The optical spectra,
here the reflectance anisotropy (RAS), have been obtained within the
independent particle random phase approximation. We identified surface features
in the spectra tracing them back to the responsible electronic states and,
studied their localization in the slab. A comparison with available
experimental data for the band structure and the RAS shows a good agreement.Comment: 10 pages, 10 figure
Pressure effects on the transport coefficients of Ba(Fe1-xCox)2As2
We report the temperature dependence of the resistivity and thermoelectric
power under hydrostatic pressure of the itinerant antiferromagnet BaFe2As2 and
the electron-doped superconductor Ba(Fe0.9Co0.1)2As2. We observe a hole-like
contribution to the thermopower below the structural-magnetic transition in the
parent compound that is suppressed in magnitude and temperature with pressure.
Pressure increases the contribution of electrons to transport in both the doped
and undoped compound. In the 10% Co-doped sample, we used a two-band model for
thermopower to estimate the carrier concentrations and determine the effect of
pressure on the band structure
Preferences of Hungarian consumers for quality, access and price attributes of health care services — result of a discrete choice experiment
In 2010, a household survey was carried out in Hungary among 1037 respondents to study consumer preferences and willingness to pay for health care services. In this paper, we use the data from the discrete choice experiments included in the survey, to elicit the preferences of health care consumers about the choice of health care providers. Regression analysis is used to estimate the effect of the improvement of service attributes (quality, access, and price) on patients’ choice, as well as the differences among the socio-demographic groups. We also estimate the marginal willingness to pay for the improvement in attribute levels by calculating marginal rates of substitution. The results show that respondents from a village or the capital, with low education and bad health status are more driven by the changes in the price attribute when choosing between health care providers. Respondents value the good skills and reputation of the physician and the attitude of the personnel most, followed by modern equipment and maintenance of the office/hospital. Access attributes (travelling and waiting time) are less important. The method of discrete choice experiment is useful to reveal patients’ preferences, and might support the development of an evidence-based and sustainable health policy on patient payments
Upper critical field, pressure-dependent superconductivity and electronic anisotropy of SmFeAsTeOF
We present a detailed study of the electrical transport properties of a
recently discovered iron-based superconductor:
SmFeAsTeOF. We followed the temperature
dependence of the upper critical field by resistivity measurement of single
crystals in magnetic fields up to 16 T, oriented along the two main
crystallographic directions. This material exhibits a zero-temperature upper
critical field of 90 T and 65 T parallel and perpendicular to the FeAs
planes, respectively. An unprecedented superconducting magnetic anisotropy
is observed near Tc, and it decreases
at lower temperatures as expected in multiband superconductors. Direct
measurement of the electronic anisotropy was performed on microfabricated
samples, showing a value of that raises up to
19 near Tc. Finally, we have studied the pressure and temperature dependence of
the in-plane resistivity. The critical temperature decreases linearly upon
application of hydrostatic pressure (up to 2 GPa) similarly to overdoped
cuprate superconductors. The resistivity shows saturation at high temperatures,
suggesting that the material approaches the Mott-Ioffe-Regel limit for metallic
conduction. Indeed, we have successfully modelled the resistivity in the normal
state with a parallel resistor model that is widely accepted for this state.
All the measured quantities suggest strong pressure dependence of the density
of states
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