1,214 research outputs found
Optimal generalization of power filters for gravitational wave bursts, from single to multiple detectors
Searches for gravitational wave signals which do not have a precise model
describing the shape of their waveforms are often performed using power
detectors based on a quadratic form of the data. A new, optimal method of
generalizing these power detectors so that they operate coherently over a
network of interferometers is presented. Such a mode of operation is useful in
obtaining better detection efficiencies, and better estimates of the position
of the source of the gravitational wave signal. Numerical simulations based on
a realistic, computationally efficient hierarchical implementation of the
method are used to characterize its efficiency, for detection and for position
estimation. The method is shown to be more efficient at detecting signals than
an incoherent approach based on coincidences between lists of events. It is
also shown to be capable of locating the position of the source.Comment: 16 pages, 5 figure
Chalcogenide-glass polarization-maintaining photonic crystal fiber for mid-infrared supercontinuum generation
In this paper, we report the design and fabrication of a highly birefringent
polarization-maintaining photonic crystal fiber (PM-PCF) made from chalcogenide
glass, and its application to linearly-polarized supercontinuum (SC) generation
in the mid-infrared region. The PM fiber was drawn using the casting method
from As38Se62 glass which features a transmission window from 2 to 10
and a high nonlinear index of 1.13.10mW. It has a
zero-dispersion wavelength around 4.5 and, at this wavelength, a large
birefringence of 6.10 and consequently strong polarization maintaining
properties are expected. Using this fiber, we experimentally demonstrate
supercontinuum generation spanning from 3.1-6.02 and 3.33-5.78
using femtosecond pumping at 4 and 4.53 , respectively. We
further investigate the supercontinuum bandwidth versus the input pump
polarization angle and we show very good agreement with numerical simulations
of the two-polarization model based on two coupled generalized nonlinear
Schr\"odinger equations.Comment: 13 pages, 8 figure
Etude de lâimpact de la dynamique de lâoccupation du sol sur les ressources naturelles dans le sous-bassin de lâOkpara Ă Nano au Nord BĂ©nin
Au BĂ©nin, les pratiques agricoles actuelles caractĂ©risĂ©es par lâagriculture itinĂ©rante sur brĂ»lis, continuent de soumettre lâenvironnement Ă une pression anthropique importante. Lâobjectif de la recherche est dâapporter une contribution Ă la gestion des ressources naturelles et de lâoccupation du sol dans le sous-Bassin versant de lâOkpara Nano. Lâapproche mĂ©thodologique adoptĂ©e a consistĂ© Ă une description, et Ă une Ă©tude analytique des facteurs de la dynamique de lâoccupation du sol et leurs implications sur la gestion des ressources naturelles du sous-Bassin. Lâanalyse des rĂ©sultats a Ă©tĂ© faite Ă lâaide du modĂšle PEIR « Pression-Etat-Impact-RĂ©ponse ». Les rĂ©sultats obtenus ont rĂ©vĂ©lĂ© quâen une vingtaine dâannĂ©es (1992-2012), la population des communes du sous-Bassin de Nano ont connu une augmentation de 74,48 %, passant ainsi de 155 164 habitants en 1992 Ă 608 015 habitants en 2012. Cette situation a conduit Ă une extension des espaces bĂątis au sein du sous-Bassin avec un taux dâaccroissement de lâordre de 3,9 %. Aussi, a-t-il Ă©tĂ© constatĂ© une Ă©volution des unitĂ©s dâoccupation du sol entre les annĂ©es 1985 et 2014 dans le sous-Bassin versant de Nano, une nette rĂ©gression des unitĂ©s de vĂ©gĂ©tation naturelle ou artificielle, exceptĂ© les mosaĂŻques de cultures qui sont en augmentation.
In Benin, current agricultural practices characterized by shifting slash-and-burn agriculture continue to subject the environment to significant human pressure. The objective of the research is to make a contribution to the management of natural resources and land use in the Okpara Nano sub-watershed. The methodological approach adopted consisted of a description and an analytical study of the factors of land use dynamics and their implications on the management of the natural resources of the sub-basin. The results were analyzed using the PEIR "Pressure-State-Impact-Response" model. The results obtained revealed that in about twenty years (1992-2012), the population of the municipalities of the Nano sub-basin experienced an increase of 74.48%, from 155,164 inhabitants in 1992 to 608,015 inhabitants in 2012. This situation has led to an extension of built-up areas within the sub-basin with an increase rate of around 3.9%. Also, it was noted an evolution of the units of land use between the years 1985 and 2014 in the sub-basin of Nano, a clear regression of the units of natural or artificial vegetation, except the mosaics of cultures which are increasing
Primordial and primary prevention of peri-implant diseases: A systematic review and meta-analysis
Aim: This systematic review and meta-analysis aims to assess the efficacy of risk factor control to prevent the occurrence of peri-implant diseases (PIDs) in adult patients awaiting dental implant rehabilitation (primordial prevention) or in patients with dental implants surrounded by healthy peri-implant tissues (primary prevention). Materials and Methods: A literature search was performed without any time limit on different databases up to August 2022. Interventional and observational studies with at least 6 months of follow-up were considered. The occurrence of peri-implant mucositis and/or peri-implantitis was the primary outcome. Pooled data analyses were performed using random effect models according to the type of risk factor and outcome. Results: Overall, 48 studies were selected. None assessed the efficacy of primordial preventive interventions for PIDs. Indirect evidence on the primary prevention of PID indicated that diabetic patients with dental implants and good glycaemic control have a significantly lower risk of peri-implantitis (odds ratio [OR] = 0.16; 95% confidence interval [CI]: 0.03â0.96; I2: 0%), and lower marginal bone level (MBL) changes (OR = â0.36 mm; 95% CI: â0.65 to â0.07; I2: 95%) compared to diabetic patients with poor glycaemic control. Patients attending supportive periodontal/peri-implant care (SPC) regularly have a lower risk of overall PIDs (OR = 0.42; 95% CI: 0.24â0.75; I2: 57%) and peri-implantitis compared to irregular attendees. The risk of dental implant failure (OR = 3.76; 95% CI: 1.50â9.45; I2: 0%) appears to be greater under irregular or no SPC than regular SPC. Implants sites with augmented peri-implant keratinized mucosa (PIKM) show lower peri-implant inflammation (SMD = â1.18; 95% CI: â1.85 to â0.51; I2: 69%) and lower MBL changes (MD = â0.25; 95% CI: â0.45 to â0.05; I2: 62%) compared to dental implants with PIKM deficiency. Studies on smoking cessation and oral hygiene behaviors were inconclusive. Conclusions: Within the limitations of available evidence, the present findings indicate that in patients with diabetes, glycaemic control should be promoted to avoid peri-implantitis development. The primary prevention of peri-implantitis should involve regular SPC. PIKM augmentation procedures, where a PIKM deficiency exists, may favour the control of peri-implant inflammation and the stability of MBL. Further studies are needed to assess the impact of smoking cessation and oral hygiene behaviours, as well as the implementation of standardized primordial and primary prevention protocols for PIDs
The oxygen isotopic composition of phytolith assemblages from tropical rainforest soil tops (Queensland, Australia): validation of a new paleoenvironmental tool
Phytoliths are micrometric particles of amorphous silica that form inside or between the cells of higher plant tissues throughout the life of a plant. With plant decay, phytoliths are either incorporated into soils or exported to sediments via regional watersheds. Phytolith morphological assemblages are increasingly used as proxy of grassland diversity and tree cover density in inter-tropical areas. Here, we investigate whether, along altitudinal gradients in northeast Queensland (Australia), changes in the &delta;<sup>18</sup>O signature of soil top phytolith assemblages reflect changes in mean annual temperature (MAT) and in the oxygen isotopic composition of precipitation (&delta;<sup>18</sup>O<sub>precipitation</sub>), as predicted by equilibrium temperature coefficients previously published for silica. Oxygen isotopic analyses were performed on 16 phytolith samples, after controlled isotopic exchange (CIE), using the IR Laser-Heating Fluorination Technique. Long-term mean annual precipitation (MAP) and MAT values at the sampled sites were calculated by the ANUCLIM software. &delta;<sup>18</sup>O<sub>precipitation</sub> estimates were calculated using the Bowen and Wilkinson (2002) model, slightly modified. An empirical temperature-dependant relationship was obtained: &delta;<sup>18</sup>O<sub>wood phytolith-precipitation</sub> (&permil; vs. VSMOW) = â0.4 (±0.2) <i>t</i> (°C) + 46 (±3) (<i>R</i><sup>2</sup> = 0.4, <i>p</i> < 0.05; <i>n</i> = 12). Despite the various unknowns introduced when estimating &delta;<sup>18</sup>O<sub>precipitation</sub> values and the large uncertainties on &delta;<sup>18</sup>O<sub>wood phytolith</sub> values, the temperature coefficient (â0.4 ± 0.2&permil; °C<sup>â1</sup>) is in the range of values previously obtained for natural quartz, fresh and sedimentary diatoms and harvested grass phytoliths (from â0.2 to â0.5&permil; °C<sup>â1</sup>). The consistency supports the reliability of &delta;<sup>18</sup>O<sub>wood phytolith</sub> signatures for recording relative changes in mean annual &delta;<sup>18</sup>O<sub>soil water</sub> values (which are assumed to be equivalent to the weighted annual &delta;<sup>18</sup>O<sub> precipitation</sub> values in rainforests environments) and MAT, provided these changes were several &permil; and/or several °C in magnitude
Hydrological budget of Lake Chad : assessment of lake-groundwater interaction by coupling Bayesian approach and chemical budget
International audienceEstimation of lake-groundwater interactions is a crucial step to constrain water balance of lacustrine and aquifersystems. Located in the Sahel, the Lake Chad is at the center of an endorheic basin of 2,5.106 km2. One of themost remarkable features of this terminal lake is that, despite the semi-arid context and high evaporation rates of thearea, its waters are fresh. It is proposed in the literature that the solutes are evacuated in the underlying quaternaryaquifer bearing witness to the importance of surface water and groundwater exchanges for the chemical regulationof the lake. The water balance of this system is still not fully understood. The respective roles of evaporation versusinfiltration into the quaternary aquifer are particularly under constrained.To assess lake-groundwater flows, we used the previous conceptual hydrological model of the lake Chad proposedby Bader et al. (Hydrological Sciences Journal, 2011). This model involves six parameters including infiltrationrate. A probabilistic inversion of parameters, based on an exploration of the parameters space through a Metropolisalgorithm (a Monte Carlo Markov Chain method), allows the construction of an a posteriori Probability DensityFunction of each parameter yielding to the best fits between observed lake levels and simulated. Then, a chemicalbudget of a conservative element, such as chloride, is introduced in the water balance model using the optimalparameters resulting from the Bayesian inverse approach.The model simulates lake level and chloride concentration variations of lake Chad from 1956 up to 2008. Simulated lake levels are in overall agreement with the observations, with a Nash-Sutcliffe efficiency coefficient above0.94 for all sets of parameters retained. The infiltration value, obtained by such probabilistic inversion approach,accounts for 120±20 mm/yr, representing 5% of the total outputs of the lake. However, simulated chloride concentrations are overestimated in comparison to the scarce measurements available over that period. As an example,the mean chloride concentration measured in the southern pool on a basis of our synthesis of existing chemicaldata since the 1970âs is approximately three time lower than the computed mean concentration. This may be dueto either the non-representativeness of our chemical dataset or overestimation of the evaporation rate that is fixedto 2000 mm/yr in our model.This study tackles the quantification of the lake water flows to the quaternary aquifer system and the associateduncertainties from a probabilistic point of view. This is an essential step to improve predictions of groundwaterresources in the Lake Chad Basin under climate change
Waterborne virus transport and the associated risks in a large lake
Waterborne enteric viruses in lakes, especially at recreational water sites, may have a negative impact on human health. However, their fate and transport in lakes are poorly understood. In this study, we propose a coupled water quality and quantitative microbial risk assessment (QMRA) model to study the transport, fate and infection risk of four common waterborne viruses (adenovirus, enterovirus, norovirus and rotavirus), using Lake Geneva as a study site. The measured virus load in raw sewage entering the lake was used as the source term in the water quality simulations for a hypothetical scenario of discharging raw wastewater at the lake surface. After discharge into the lake, virus inactivation was modeled as a function of water temperature and solar irradiance that varied both spatially and temporally during transport throughout the lake. Finally, the probability of infection, while swimming at a popular beach, was quantified and compared among the four viruses. Norovirus was found to be the most abundant virus that causes an infection probability that is at least 10 times greater than the other viruses studied. Furthermore, environmental inactivation was found to be an essential determinant in the infection risks posed by viruses to recreational water users. We determined that infection risks by enterovirus and rotavirus could be up to 1000 times lower when virus inactivation by environmental stressors was accounted for compared with the scenarios considering hydrodynamic transport only. Finally, the model highlighted the role of the wind field in conveying the contamination plume and hence in determining infection probability. Our simulations revealed that for beaches located west of the sewage discharge, the infection probability under eastward wind was 43% lower than that under westward wind conditions. This study highlights the potential of combining water quality simulation and virus-specific risk assessment for a safe water resources usage and management
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