511 research outputs found
On the correct choice of equivalent circuit for fitting bulk impedance data of ionic/electronic conductors
Bulk conductivity data of ionically and electronically conducting solid electrolytes and electronic ceramics invariably show a frequency dependence that cannot be modelled by a single-valued resistor. To model this, common practice is to add a constant phase element (CPE) in parallel with the bulk resistance. To fit experimental data on a wide variety of materials, however, it is also essential to include the limiting, high frequency permittivity of the material in the equivalent circuit. Failure to do so can lead to incorrect values for the sample resistance and CPE parameters and to an inappropriate circuit for materials that are electrically heterogeneous
Polarization inhibits the phase transition of Axelrod''s model
We study the effect of polarization in Axelrod''s model of cultural dissemination. This is done through the introduction of a cultural feature that takes only two values, while the other features can present a larger number of possible traits. Our numerical results and mean-field approximations show that polarization reduces the characteristic phase transition of the original model to a finite-size effect, since at the thermodynamic limit only the ordered phase is present. Furthermore, for finite system sizes, the stationary state depends on the percolation threshold of the network where the model is implemented: a polarized phase is obtained for percolation thresholds below 1/2, and a fragmented multicultural one otherwise. © 2021 American Physical Society
Assessing symmetry of financial returns series
Testing symmetry of a probability distribution is a common question arising
from applications in several fields. Particularly, in the study of observables
used in the analysis of stock market index variations, the question of symmetry
has not been fully investigated by means of statistical procedures. In this
work a distribution-free test statistic Tn for testing symmetry, derived by
Einmahl and McKeague, based on the empirical likelihood approach, is used to
address the study of symmetry of financial returns. The asymptotic points of
the test statistic Tn are also calculated and a procedure for assessing
symmetry for the analysis of the returns of stock market indices is presented.Comment: Econophysics paper. 6 pages 2 figure
Shape matters: Competing mechanisms of particle shape segregation
It is well-known that granular mixtures that differ in size or shape segregate when sheared. In the
past, two mechanisms have been proposed to describe this effect, and it is unclear if both exist. To
settle this question, we consider a bidisperse mixture of spheroids of equal volume in a rotating drum,
where the two mechanisms are predicted to act in opposite directions. We present the first evidence
that there are two distinct segregation mechanisms driven by relative over-stress. Additionally, we
showed that for non-spherical particles, these two mechanisms can act in different directions leading
to a competition between the effects of the two. As a result, the segregation intensity varies nonmonotonically as a function of AR, and at specific points, the segregation direction changes for both
prolate and oblate spheroids, explaining the surprising segregation reversal previously reported.
Consistent with previous results, we found that the kinetic mechanism is dominant for (almost)
spherical particles. Furthermore, for moderate aspect ratios, the kinetic mechanism is responsible
for the spherical particles segregation to the periphery of the drum, and the gravity mechanism
plays only a minor role. Whereas, at the extreme values of AR, the gravity mechanism notably
increases and overtakes its kinetic counterpart
Enhancement of curing properties of cold in-place recycling asphalt mixtures by induction heating
[Abstract:] In this study, samples of cold in-place recycling mix (CIR) with steel fibres were manufactured and heated by electromagnetic induction. Heating was conducted to accelerate the curing process and make the CIR mixtures more competitive against other less-sustainable road materials. Heating can also be applied after years of service life to reduce the viscosity of the binder and make it flow through cracks, healing damage. Cylindrical Marshall samples were heated by induction for different durations immediately after production and their mechanical performance was assessed over different curing periods. In addition, 3-point bending healing tests were carried out on cured semicircular samples. The results showed that the remaining water content in samples heated for 180 s was lower than in control samples (not heated) after 21 days. The Marshall stability and flow after compaction increased by 147% and 144%, respectively, when heating was applied for 240 s. Healing tests produced encouraging results with strength recoveries higher than 50%.Ministerio de Economía y Competitividad; BIA2016-80317-
On fitting the Pareto-Levy distribution to stock market index data: selecting a suitable cutoff value
The so-called Pareto-Levy or power-law distribution has been successfully
used as a model to describe probabilities associated to extreme variations of
worldwide stock markets indexes data and it has the form from
empirical data and consequently, the determination of the exponent alpha, is
often is done by using a simple graphical method based on a log-log scale,
where a power-law probability plot shows a straight line with slope equal to
the exponent of the power-law distribution. This procedure can be considered
subjective, particularly with regard to the choice of the threshold or cutoff
parameter gamma. In this work is presented a more objective procedure, based on
a statistical measure of discrepancy between the empirical and the Pareto-Levy
distribution. The technique is illustrated for data sets from the New York
Stock Exchange Index and the Mexican Stock Market Index (IPC).Comment: Econophysics paper. 5 pages 9 figure
Top quark effects in composite vector pair production at the LHC
In the context of a strongly coupled Electroweak Symmetry Breaking, composite
light scalar singlet and composite triplet of heavy vectors may arise from an
unspecified strong dynamics and the interactions among themselves and with the
Standard Model gauge bosons and fermions can be described by a Effective Chiral Lagrangian. In this framework, the
production of the and final states at the LHC by
gluon fusion mechanism is studied in the region of parameter space consistent
with the unitarity constraints in the elastic channel of longitudinal gauge
boson scattering and in the inelastic scattering of two longitudinal Standard
Model gauge bosons into Standard Model fermions pairs. The expected rates of
same-sign di-lepton and tri-lepton events from the decay of the
final state are computed and their corresponding backgrounds are estimated. It
is of remarkable relevance that the final state can only be
produced at the LHC via gluon fusion mechanism since this state is absent in
the Drell-Yan process. It is also found that the final state
production cross section via gluon fusion mechanism is comparable with the
Drell-Yan production cross section. The comparison of the
and total cross sections will be crucial for
distinguishing the different models since the vector pair production is
sensitive to many couplings. This will also be useful to determine if the heavy
vectors are only composite vectors or are gauge vectors of a spontaneously
broken gauge symmetry.Comment: 18 pages, 5 tables, 6 figures. Missing figures added. Matches
published versio
Palaeoenvironmental analysis of the Aragonian (middle Miocene) mammalian faunas from the Madrid Basin based on body-size structure
As a consequence of the growth of the Antarctic ice-sheet during the middle Miocene, a global decrease of temperatures and an associated increase in aridity provoked several environmental changes all around the world. Such environmental variations can be detected in the continental record of the mammalian prey community structure using a synecological approach. Because of the good quality of its faunas, the rich Aragonian vertebrate fossil record from the Madrid Basin (Spain) appears as a good candidate to explore these environmental changes. In order to analyse the climatic evolution of the Iberian Peninsula associated to the Global Cooling Event, two classic palaeosynecological methodologies (cenograms and body size diversity), based on body-size community structure, were applied to 6 fossil sites from the Madrid Basin, ranging over 2 million years (15.5 – 13.5 Ma). To establish a comparative framework, we used the ecological faunal data from 100 modern localities uniformly distributed all around the world. Our palaeoenvironmental inference is based on multivariate discriminant analysis of the dataset containing both modern and fossil mammals. Finally, we can conclude that the Aragonian mammalian assemblage from the Madrid Basin showed a predominance of semiarid environments with pulses of higher aridity in biozones Dc, E and F associated with the Global Cooling Event of the middle Miocene.Como consecuencia del crecimiento del casquete polar Antártico, durante el Mioceno medio, se produjo un descenso global de la temperatura asociado a un aumento de la aridez. Este tipo de cambios ambientales pueden ser detectados en el registro continental, siguiendo un modelo sinecológico para analizar la estructura de las comunidades de las faunas de mamíferos herbívoros. Debido a la calidad de sus faunas, el registro fósil de las faunas de vertebrados del Aragoniense de la Cuenca de Madrid se antoja como un buen candidato para explorar estos patrones de cambio ambiental. Con el objetivo de analizar la evolución climática de la Península Ibérica asociada al evento de enfriamiento global durante este lapso temporal, dos metodologías paleosinecológicas clásicas (cenogramas y espectros de diversidad de tamaño corporal), basadas en la estructura de tamaños corporales de las comunidades de mamíferos, han sido aplicadas a la fauna de herbívoros fósiles presente en seis yacimientos de la Cuenca de Madrid, abarcando aproximadamente 2 millones de años (15.5 – 13.5 Ma). Se ha establecido un marco comparativo usando los datos ecológicos de la fauna de mamíferos presente en 100 localidades uniformemente distribuidas por todo el planeta. Esta inferencia paleoambiental está basada en la aplicación de análisis discriminante multivariante sobre el conjunto de datos de las faunas actuales y fósiles. Finalmente, las faunas de mamíferos del Aragoniense de la Comunidad de Madrid mostraron una predominancia de ambientes semiáridos con varios pulsos de mayor aridez en las biozonas Dc, E y F asociados al evento de enfriamiento global del Mioceno medio
Statistical auditing and randomness test of lotto k/N-type games
One of the most popular lottery games worldwide is the so-called ``lotto
k/N''. It considers N numbers 1,2,...,N from which k are drawn randomly,
without replacement. A player selects k or more numbers and the first prize is
shared amongst those players whose selected numbers match all of the k randomly
drawn. Exact rules may vary in different countries.
In this paper, mean values and covariances for the random variables
representing the numbers drawn from this kind of game are presented, with the
aim of using them to audit statistically the consistency of a given sample of
historical results with theoretical values coming from a hypergeometric
statistical model. The method can be adapted to test pseudorandom number
generators.Comment: 10 pages, no figure
Harmful and beneficial symbionts of Tenebrio molitor and their implications for disease management
The yellow mealworm, Tenebrio molitor, is currently one of the most important insect species produced for livestock feed and human consumption. High-density rearing conditions make the risk of disease and infections by parasitic symbionts a challenge in the mass production of these insects. However, certain symbionts are beneficial and should be favoured in order to promote healthy insect populations. Knowledge of parasitic symbionts and their management is essential for the insect rearing industry and its associated research. Here we review the documented microbial infectious agents, invertebrate parasites, and beneficial symbionts occurring in T. molitor. Furthermore, we discuss detection, prevention, and treatment methods for disease management in T. molitor production systems to inform future management and decision making in T. molitor rearing
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