293 research outputs found
New inscriptions from Asido Caeserina
Los autores presentan tres nuevos epígrafes de la colonia Asido Caesarina, de difícil interpretación, aunque de notable singularidad, que vienen a enriquecer el ya amplio corpus epigráfico de la colonia.The authors present three new inscriptions from the colony Asido Caesarina, which are difficult to interpret, though of notable singularity. These inscriptions broaden the already wide epigraphic corpus of the colony
Household water consumption in Spain: disparities between region
This paper studies the regional consumption of household water in Spain in the period 2000–2018. The use of the methodology proposed by Phillips and Sul allows us to conclude that there is no single pattern of behavior across the Spanish regions. By contrast, we can determine the existence of three convergence clubs, confirming serious regional disparities in water consumption. Navarra, País Vasco, La Rioja, and Cataluña are included in the convergence club that shows the lowest levels of household water consumption, while the Islas Canarias, Comunidad Valenciana, Castilla y León and Cantabria belong to that with the highest consumption. The determinants of the forces that drive these convergence clubs are difficult to identify because the demographic, economic and structural variables of the network interact in different ways. Nevertheless, we can select a group of explanatory variables that help to explain the formation of the convergence clubs. These are regional household income, the birth rate in the regions, and the regional spending on environmental protection. Increments in the levels of these variables are helpful for reducing household water consumption. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
Are prices converging in the global sawnwood market?
This paper aims at addressing if the increasing globalization in the international sawnwood markets has caused export prices to converge to a single reference price or, alternatively, certain restrictions remain to generate a segmented market where different reference prices for each market segment co-exist. Annual price series for the top-10 exporting countries are considered for that purpose. Results show that the data cannot support the null hypothesis of convergence. Instead, the global sawnwood market appears to be segmented into two convergence clubs (Chile-USA-Latvia-New Zealand and Canada-Germany-Austria-Finland-Sweden), while the Russian Federation exhibits an independent pathway. Causality tests are conducted to analyze the price dynamics in the global sawnwood products indicating that international price relationships are demand-driven. Finally, results suggest that the inclusion of a country in a particular convergence club is mainly determined by the price differential between countries (competition factors), and to a lesser extent, by the countries' combined market share in the global market (catching-up factors)
Local and global gating of synaptic plasticity
Mechanisms influencing learning in neural networks are usually investigated
on either a local or a global scale. The former relates to synaptic
processes, the latter to unspecific modulatory systems. Here we study the
interaction of a local learning rule that evaluates coincidences of pre- and
postsynaptic action potentials and a global modulatory mechanism, such
as the action of the basal forebrain onto cortical neurons. The simulations
demonstrate that the interaction of these mechanisms leads to a learning
rule supporting fast learning rates, stability, and flexibility. Furthermore,
the simulations generate two experimentally testable predictions on the
dependence of backpropagating action potential on basal forebrain activity
and the relative timing of the activity of inhibitory and excitatory
neurons in the neocortex.We are grateful to Konrad Körding and Mike Merzenich for valuable discussions
of the previous work on the learning rule and the experimental data
and Daniel Kiper for comments on a previous version of the manuscript.
We are happy to acknowledge the support of SPP Neuroinformatics (grants
5002–44888/2&3 to P. F. M. J. V.), SNF (grant 31-51059.97, awarded to P. K.),
and an FPU grant from MEC (M. A. S.-M., Spain)
Confirmation of an exoplanet using the transit color signature: Kepler-418b, a blended giant planet in a multiplanet system
We announce confirmation of Kepler-418b, one of two proposed planets in this
system. This is the first confirmation of an exoplanet based primarily on the
transit color signature technique. We used the Kepler public data archive
combined with multicolor photometry from the Gran Telescopio de Canarias and
radial velocity follow-up using FIES at the Nordic Optical Telescope for
confirmation. We report a confident detection of a transit color signature that
can only be explained by a compact occulting body, entirely ruling out a
contaminating eclipsing binary, a hierarchical triple, or a grazing eclipsing
binary. Those findings are corroborated by our radial velocity measurements,
which put an upper limit of ~1 Mjup on the mass of Kepler-418b. We also report
that the host star is significantly blended, confirming the ~10% light
contamination suspected from the crowding metric in the Kepler light curve
measured by the Kepler team. We report detection of an unresolved light source
that contributes an additional ~40% to the target star, which would not have
been detected without multicolor photometric analysis. The resulting
planet-star radius ratio is 0.110 +/- 0.0025, more than 25% more than the 0.087
measured by Kepler, leading to a radius of 1.20 +/- 0.16 Rjup instead of the
0.94 Rjup measured by the Kepler team. This is the first confirmation of an
exoplanet candidate based primarily on the transit color signature,
demonstrating that this technique is viable from ground for giant planets. It
is particularly useful for planets with long periods such as Kepler-418b, which
tend to have long transit durations. Additionally, multicolor photometric
analysis of transits can reveal unknown stellar neighbors and binary companions
that do not affect the classification of the transiting object but can have a
very significant effect on the perceived planetary radius.Comment: accepted by Astronomy & Astrophysic
Sub-Nanosecond Switching of HV SiC MOS Transistors for Impact Ionisation Triggering
Pulse generators with multi kV/kA pulses are necessary for the particle accelerator environment for beam transfer magnets. Traditionally these generators are using thyratrons - until recently the only switches capable of switching such pulses within tens of ns. There is a strong demand to replace thyratrons with semiconductor switches to avoid their future obsolescence. Very promising candidates are components from the family of fast ionization dynistors triggered by impact ionization. Their sub-nanosecond switching time and extreme current densities can provide performances superior to that of thyratrons. Recent investigations showed that impact ionization triggering is feasible also in cheap industrial thyristors. The main issue is the generation of triggering pulses with slew rates in the multi kV/ns region and with the required output current for charging the parasitic capacitance of the thyristor. We present an approach of generating > 1 kV/ns pulses by ultra-boosted gate driving of HV SiC MOS transistors. We found that the MOS lifetime under these extreme triggering conditions can still reach more than 10⁸ pulses, enough for kicker generator applications
Evaluation of negentropy-based cluster validation techniques in problems with increasing dimensionality
The aim of a crisp cluster validity index is to quantify the quality of a given data partition. It allows to select the best partition out of a set of potential ones, and to determine the number of clusters. Recently, negentropy-based cluster validation has been introduced. This new approach seems to perform better than other state of the art techniques, and its computation is quite simple. However, like many other cluster validation approaches, it presents problems when some partition regions have a small number of points. Different heuristics have been proposed to cope with this problem. In this article we systematically analyze the performance of different negentropy-based validation approaches, including a new heuristic, in clustering problems of increasing dimensionality, and compare them to reference criteria such as AIC and BIC. Our results on synthetic data suggest that the newly proposed negentropy-based validation strategy can outperform AIC and BIC when
the ratio of the number of points to the dimension is not high, which is a very common situation in most real applications.The authors thank the financial support from DGUI-CAM/UAM (Project CCG10-UAM/TIC-5864
Ultra-Fast Generator for Impact Ionization Triggering
Impact ionization triggering can be successfully applied to standard thyristors, thus boosting their dI/dt capability by up to 1000x. This groundbreaking triggering requires applying significant overvoltage on the anode-cathode of thyristor with a slew rate > 1kV/ns. Compact pulse generators based on commercial off-the-shelf (COTS) components would allow the spread of this technology into numerous applications, including fast kicker generators for particle accelerators. In our approach, the beginning of the triggering chain is a HV SiC MOS with an ultra-fast super-boosting gate driver. The super boosting of a 1.7kV rated SiC MOS allows to reduce the MOS rise time by a factor of > 25 (datasheet tr = §I{20}{ns} vs. measured tr 1kV/ns and an amplitude > 1kV. Additional boosting is obtained by a Marx generator with GaAs diodes, reaching an output voltage slew rate > 11kV/ns. The final stage will be a Marx generator with medium size thyristors triggered in impact ionization mode with sufficient voltage and current rating necessary for the triggering of a big thyristor. This paper presents the impact ionization triggering of a small size thyristor
- …