740,532 research outputs found

    Neutrino-Induced Giant Air Showers in Large Extra Dimension Models

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    In models based on large extra dimensions where massive spin 2 exchange can dominate at high energies, the neutrino-proton cross section can rise to typical hadronic values at energies above 10^20 eV. The neutrino then becomes a candidate for the primary that initiates the highest energy cosmic ray showers. We investigate characteristics of neutrino-induced showers compared to proton-induced showers. The comparison includes study of starting depth, profile with depth, lateral particle distribution at ground and muon lateral distribution at ground level. We find that for cross sections above 20 mb there are regions of parameter space where the two types of showers are essentially indistinguishable. We conclude that the neutrino candidate hypothesis cannot be ruled out on the basis of shower characteristics.Comment: 24 pages, latex, 19 figures; text discussion and references added, typos corrected; figures and conclusions unchange

    Depth of sojourn and niche differentiation of benthic blennies (Pisces, Blenniidae) in the Mediterranean sea (Catalonia, NE Spain and Italian coast of the Tyrrhenian sea)

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    The vertical distribution of nine species of combtooth blennies between the surface and 1,5 m depth was studied at selected rocky shore sections of the Mediterranean Sea in NE Spain and the W coast of Italy. Significant differences in mean depths of sojourn and the degree of depth overlap allow the distinction of species subgroups: species preferring the uppermost shore (Coryphoblennius galerita, Aidablennius sphynx and Lipophrys trigloides), those mostly found in a middle stratum (Lipophrys canevai, Scartella cristata, Parablennius incognitus, Parablennius gattorugine) and two species with the lowest depth of sojourn (Parablennius pilicornis, Parablennius zvonimir). The relative depth position showed little seasonal variation and was similar at both Spanish and ltalian sites. The species of each subgroup which shows a high degree of spatial overlap is distinguished in other dimensions of its ecological niches, in particular by different feeding habits and differences in shelter characteristics. On the basis of exact depth distribution data the present study indicates that depth differences of Mediterranean blennies are very finely tuned and species-specific, even on a broad geographical and seasonal scale. Key words: Vertical zonation, Rocky shore, Ecological niches, Overlap, Microhabitat, Fish assemblageThe vertical distribution of nine species of combtooth blennies between the surface and 1,5 m depth was studied at selected rocky shore sections of the Mediterranean Sea in NE Spain and the W coast of Italy. Significant differences in mean depths of sojourn and the degree of depth overlap allow the distinction of species subgroups: species preferring the uppermost shore (Coryphoblennius galerita, Aidablennius sphynx and Lipophrys trigloides), those mostly found in a middle stratum (Lipophrys canevai, Scartella cristata, Parablennius incognitus, Parablennius gattorugine) and two species with the lowest depth of sojourn (Parablennius pilicornis, Parablennius zvonimir). The relative depth position showed little seasonal variation and was similar at both Spanish and ltalian sites. The species of each subgroup which shows a high degree of spatial overlap is distinguished in other dimensions of its ecological niches, in particular by different feeding habits and differences in shelter characteristics. On the basis of exact depth distribution data the present study indicates that depth differences of Mediterranean blennies are very finely tuned and species-specific, even on a broad geographical and seasonal scale. Key words: Vertical zonation, Rocky shore, Ecological niches, Overlap, Microhabitat, Fish assemblageThe vertical distribution of nine species of combtooth blennies between the surface and 1,5 m depth was studied at selected rocky shore sections of the Mediterranean Sea in NE Spain and the W coast of Italy. Significant differences in mean depths of sojourn and the degree of depth overlap allow the distinction of species subgroups: species preferring the uppermost shore (Coryphoblennius galerita, Aidablennius sphynx and Lipophrys trigloides), those mostly found in a middle stratum (Lipophrys canevai, Scartella cristata, Parablennius incognitus, Parablennius gattorugine) and two species with the lowest depth of sojourn (Parablennius pilicornis, Parablennius zvonimir). The relative depth position showed little seasonal variation and was similar at both Spanish and ltalian sites. The species of each subgroup which shows a high degree of spatial overlap is distinguished in other dimensions of its ecological niches, in particular by different feeding habits and differences in shelter characteristics. On the basis of exact depth distribution data the present study indicates that depth differences of Mediterranean blennies are very finely tuned and species-specific, even on a broad geographical and seasonal scale. Key words: Vertical zonation, Rocky shore, Ecological niches, Overlap, Microhabitat, Fish assemblag

    On the quality of randomized approximations of Tukey's depth

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    Tukey's depth (or halfspace depth) is a widely used measure of centrality for multivariate data. However, exact computation of Tukey's depth is known to be a hard problem in high dimensions. As a remedy, randomized approximations of Tukey's depth have been proposed. In this paper we explore when such randomized algorithms return a good approximation of Tukey's depth. We study the case when the data are sampled from a log-concave isotropic distribution. We prove that, if one requires that the algorithm runs in polynomial time in the dimension, the randomized algorithm correctly approximates the maximal depth 1/21/2 and depths close to zero. On the other hand, for any point of intermediate depth, any good approximation requires exponential complexity

    Effect of crowning radius on rolling contact fatigue strength for traction drive elements

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    A simulation of the rolling contact fatigue strength of a traction drive element was developed. This simulation accounts for both the distribution of sizes of inclusions in the element material and the influence of traction forces at the element surface. The shear strength of the matrix structure surrounding an inclusion was estimated with an equation. The hardness distribution and the Weibull distribution of inclusion dimensions, which are necessary parameters to calculate the rolling contact fatigue strength, were determined by observation of an actual test specimen. The purpose of this report is simulations to evaluate the effect of the crowning radius on the rolling contact fatigue strength and the torque capacity. The simulations were carried out by varying the crowning radius of the virtual roller. To consider the effect of the crowning radius, a simulated two-dimensional virtual roller, which has actual material properties, was modified to a roller multilayered toward the axial direction. The simulation assuming the actual roller led to a difference of 1.0% from the experimental rolling contact fatigue strength. This difference was 2.4 points smaller than the result for the two-dimensional virtual roller. The rolling contact fatigue strength decreased with increasing crowning radius for two reasons. One was the increase in the number of inclusions under the high stress due to the increasing crowning radius. The other was the expansion of the portion of the roller subject to high stresses down to a depth having small hardness. However, the torque capacity calculated from the contact force resulting in failure increased with the increasing crowning radius

    Depairing currents in superconducting films of Nb and amorphous MoGe

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    We report on measuring the depairing current J_{dp} in thin superconducting films as a function of temperature. The main difficulties in such measurements are that heating has to be avoided, either due to contacts, or to vortex flow. The latter is almost unavoidable since the sample cross-section is usually larger than the superconducting coherence length \xi_s and the magnetic field penetration depth \lambda_s. On the other hand, vortex flow is helpful since it homogenizes the distribution of the current across the sample. We used a pulsed current method, which allows to overcome the difficulties caused by dissipation and measured the depairing current in films of thin polycrystalline Nb (low \lambda_s, low specific resistance \rho) and amorphous Mo_{0.7}Ge_{0.3} (high \lambda_s, high \rho), structured in the shape of bridges of various width. The experimental values of J_{dp} for different bridge dimensions are compared with theoretical predictions by Kupriyanov and Lukichev for dirty limit superconductors. For the smallest samples we find a very good agreement with theory, over essentially the whole temperature interval below the superconducting critical temperature.Comment: 5 pages, 6 figure

    Fine‐scale measurement of diffusivity in a microbial mat with nuclear magnetic resonance imaging

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    Noninvasive 1H‐nuclear magnetic resonance (NMR) imaging was used to investigate the diffusive properties of microbial mats in two dimensions. Pulsed field gradient NMR was used to acquire images of the H2O diffusion coefficient, Ds, and multiecho imaging NMR was used to obtain images of the water density in two structurally different microbial mats sampled from Solar Lake (Egypt). We found a pronounced lateral and vertical variability of both water density and water diffusion coefficient, correlated with the laminated and heterogeneous distribution of microbial cells and exopolymers within the mats. The average water density varied from 0.5 to 0.9, whereas the average water diffusion coefficient ranged from 0.4 to 0.9 relative to the values obtained in the stagnant water above the mat samples. The apparent water diffusivities estimated from NMR imaging compared well to apparent O2 diffusivities measured with a diffusivity microsensor. Analysis of measured O2 concentration profiles with a diffusion‐reaction model showed that both the magnitude of calculated rates and the depth distribution of calculated O2 consumption/production zones changed when the observed variations of diffusivity were taken into account. With NMR imaging, diffusivity can be determined at high spatial resolution, which can resolve inherent lateral and vertical heterogeneities found in most natural benthic systems

    3_D modeling using TLS and GPR techniques to characterize above and below-ground wood distribution in pyroclastic deposits along the Blanco River (Chilean Patagonia)

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    To date, the study of in-stream wood in rivers has been focused mainly on quantifying wood pieces deposited above the ground. However, in some particular river systems, the presence of buried dead wood can also represent an important component of wood recruitment and budgeting dynamics. This is the case of the Blanco River (Southern Chile) severely affected by the eruption of Chait\ue9n Volcano occurred between 2008 and 2009. The high pyroclastic sediment deposition and transport affected the channel and the adjacent forest, burying wood logs and standing trees. The aim of this contribution is to assess the presence and distribution of wood in two study areas (483 m2 and 1989 m2, respectively) located along the lower streambank of the Blanco River, and covered by thick pyroclastic deposition up to 5 m. The study areas were surveyed using two different devices, a Terrestrial Laser Scanner (TLS) and a Ground Penetrating Radar (GPR). The first was used to scan the above surface achieving a high point cloud density ( 48 2000 points m-2) which allowed us to identify and measure the wood volume. The second, was used to characterize the internal morphology of the volcanic deposits and to detect the presence and spatial distribution of buried wood up to a depth of 4 m. Preliminary results have demonstrated differences in the numerousness and volume of above wood between the two study areas. In the first one, there were 43 wood elements, 33 standing trees and 10 logs, with a total volume of 2.96 m3 (109.47 m3 km-1), whereas the second one was characterized by the presence of just 7 standing trees and 11 wood pieces, for a total amount of 0.77 m3 (7.73 m3 km-1). The dimensions of the wood elements vary greatly according to the typology, standing trees show the higher median values in diameter and length (0.15 m and 2.91 m, respectively), whereas the wood logs were smaller (0.06 m and 1.12 m, respectively). The low dimensions of deposited wood can be probably connected to their origin, suggesting that these elements were generated by toppling and breaking of surrounding dead trees. Results obtained with the GPR confirm the ability of this instrument to localize the presence and distribution of buried wood. From the 3- D analysis it was possible to assess the spatial distribution and to estimate, as first approach, the volume of the buried wood which represents approximately 0.04% of the entire volcanic deposit. Further analysis will focus on additional GPR calibration with different wood sizes for a more accurate estimation of the volume. The knowledge of the overall wood amount stored in a fluvial system that can be remobilized over time, represent an essential factor to ensure better forest and river management actions

    Microscopy techniques for dye distribution in DSCs nanocrystalline TiO2 films 

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    Capture of sunlight has attracted an increasing interest in the scientific community and triggered the development of efficient and cheap photovoltaic devices. Amongst recent generation technologies for solar energy conversion, dye-sensitized solar cells (DSCs) show an optimal trade-off between high-conversion efficiency and low-cost manufacturing. For the last two decades, significant progress has been made and best energy conversion efficiency of the DSC at the laboratory scale has surpassed 12% [1]. A lot of work has focused on the enlargement of surface areas to enhance the amount of adsorbed dyes by reduction of nanoparticle sizes or utilization of novel structures. Nevertheless there remain some crucial details of DSC operation for which limited information is available, namely dye diffusion and adsorption, surface coverage and dye distribution throughout the nc-TiO2 film. Microprobe techniques can be powerful tools to evaluate the dye load, the dye distribution and dye depth profile in sensitized films. Electron Probe Microanalysis (EPMA) and Ion Beam Analytical (IBA) techniques using a micro-ion beam, namely micro-Particle Induced X-ray Emission ( PIXE) and Rutherford Backscattering Spectrometry (RBS), were used to quantify and to study the distribution of the ruthenium organometallic (N719) dye in TiO2 films, profiting from the different penetration depth and beam sizes of each technique. Two different types of films were prepared and sensitized, mesoporous nanoparticles and 1D nanostructured TiO2 films (figure 1). Despite the low concentration of Ru, the high sensitive analytical techniques used allowed to assess the Ru surface distribution and depth profile. Fig. 2 shows the PIXE maps of Ru and Ti indicating an homogeneous surface distribution. The same figure presents the RBS spectra obtained with a 2 MeV proton beam of the same sample showing that a good spectra fit is obtained considering only two sample layers: the first one with a 1.7 ìm thickness; the second one being the SiO2 substrate. The Ru RBS signal also shows that the dye has an homogeneous depth distribution. Due to the fine spatial resolution of the EPMA/WDS (Wavelength Dispersive Spectroscopy) technique it was possible to visualise the dye distribution in sample cross-section (with micrometer or submicrometer dimensions) as presented in Fig. 3 for the elemental mapping of a mesoporous nanoparticle TiO2 film. Dye load evaluation by two different techniques (ìPIXE and EPMA/WDS) provided similar results (Ru/Ti values around 0.5 %). The distribution analysis of the organometallic dye (N719) was done through ruthenium distribution via X-ray mapping. RBS was used to assess the ruthenium depth profile. This assessment can lead to a better understanding of the device performance

    Allocation of Time within Italian Couples: Exploring the Role of Institutional Factors and their Effects on Household's Wellbeing

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    Italy is characterized by a very uneven distribution of paid and unpaid work in gender terms. Italy has the lowest female employment rate apart from Malta in the European region, with a tangibly wide gender gap in employment and participation rates to the disadvantage of women. Furthermore, the female labour supply is very unevenly distributed across the Italian regions, and both institutional and labour market factors may be considered as lying at the basis of the high regional heterogeneity. This paper aims at understanding more in depth the uneven allocation of time by gender in Italian households. For this purpose we propose a model on the partners' allocation of time, that takes into account the simultaneity of partners' allocation of time decisions, as well as the issue of censored observations in some partenrs' uses of time. In order to estimate this model, we use IT SILC 2007 data that provides us with information on income and hours of work as well as on other relevant sociodemographic variables, maintaining the significance at regional level. This also allows us to analyze the contribution of institutional factors (like the heterogeneous distribution of childcare services in Italy and labour market differences) and interaction with various dimensions of wellbeing. Our findings suggest that an increase in women's wages affects women's working time, both by directly increasing womens paid hours of work, and decreasing the time devoted to household activities and indirectly via a more equal distribution of unpaid work within the couple. The presence of children in the household tends to reduce women's paid work, while having a positive effect on the time spent by the husband in paid work and on both partners supply of unpaid work. We also note that the availability of childcare services represents the most relevant factor affecting women's participatory decisions as well as their hours of paid work.
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