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Enhanced dielectric performance of Dy-substituted YMn2O5 for high-frequency applications

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Progress in Natural Science:Materials International 2021年第5期31卷 762-771页

作者： H.Chouaibi K.Khirouni E.Dhahri laboratoire de Physique Appliquée Faculté des Sciences Université de Sfax laboratoire de Physique des Matériaux et des Nanomatériaux Appliquée à l'environnement Faculté des Sciences de Gabès Cité Erriadh Université de Gabès

The dielectric performances as well as the effects of Dy3+ions content at A sites of YMn2O5(YMO) [x=0(YDM0)and x=0.4(YDM0.4)] polycrystalline samples were *** compounds were synthesized via sol-gel method.X-Ray diffraction and Raman measurements proved the high quality of the compounds that crystallized in an orthorhombic structure with the Pbam space ***,impedance spectroscopy and electrical modulus studies revealed that both samples exhibited a non-debye’s type of *** decrease of impedance for YDM0.4compared to the pure YDM0,may be attributed to the decrease in charge transfer *** the fit of impedance spectra,they confirmed that both compounds were simultaneously capacitive and ***,the activation energies obtained from Modulus and complex impedance were proven to be neighboring,suggesting that the relaxation process refers to electron *** each compound,the evolution of ε’and tan & with temperature indicated a clearer relaxor behavior,namely the existence of two *** first one detected at low temperature is related to the charge carriers hopping between Mn3+and Mn4+and the second at high temperature is associated with oxygen *** reduced hopping rate with Dy3+substitution for Y3+ions at A sites is responsible for the decrease in dielectric constant and dielectric *** significant findings demonstrate that these materials can be invested in a fruitful use in UV photo-detector and power applications in high frequency as microwave,millimeter wave signal processing,for civilian,military and space applications.

关键词： Multiferroic Relaxation phenomenon High dielectric constant Relaxor behavior

Mapping global forest biomass and its changes over the first decade of the 21st century

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Science China Earth sciences 2019年第3期62卷 585-594页

作者： Anping CHEN Shushi PENG Songlin FEI department of Forestry and Natural Resources Purdue University The Woods Hole Research Center laboratoire des sciences du Climat et de l'environnement(lSCE) CEA-CNRS-UVSQ

Forests played an important role in carbon sequestration during the past two decades. Using a model tree ensemble method(MTE) to regress the seven reflectance bands of EOS-Terra-MODIS satellite data against country level forest biomass carbon density(BCD) of 2001–2005 provided by United Nations' s Forest Resource Assessment(FRA), we developed a global map of forest BCD at 1 km×1 km resolution for both 2001–2005 and 2006–2010. For 2006–2010, the total global forest biomass carbon stock is estimated as 279.6±7.1 Pg C, and the tropical forest biomass carbon stock is estimated as 174.4±5.4 Pg C. During the first decade of the 21 st century, we estimated an increase of global forest biomass of 0.28±0.75 Pg C yr^(-1). Tropical forest biomass carbon stock slightly decreased(-0.31±0.60 Pg C yr^(-1)); by contrast, temperate and boreal forest biomass increased(0.58±0.28 Pg C yr^(-1)) during the same period. Our estimation of the global forest biomass carbon stock and its changes is subject to uncertainties due to lack of extensive ground measurements in the tropics, spatial heterogeneity in large countries, and different definitions of forest. The continuously monitoring of forest biomass carbon stock with MODIS satellite data will provide useful information for detecting forest changes.

关键词： Forest biomass Carbon stock Model tree ensemble(MTE) MODIS Remote sensing

Sediment fingerprinting in fluvial systems:review of tracers,sediment sources and mixing models

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International Journal of Sediment Research 2013年第4期28卷 560-578页

作者： Arman HADDADCHI Darren S.RYdeR Olivier EVRARD Jon OllEY Australian Rivers Institute Griffith University School of Environmental and Rural sciences University of New England laboratoire des sciences du Climat et de l'environnement(lSCE/IPSl)

Suspended sediments in fluvial systems originate from a myriad of diffuse and point sources,with the relative contribution from each source varying over time and *** process of sediment fingerprinting focuses on developing methods that enable discrete sediment sources to be identified from a composite sample of suspended *** review identifies existing methodological steps for sediment fingerprinting including fluvial and source sampling,and critically compares biogeochcmical and physical tracers used in fingerprinting *** of applying different mixing models to the same source data are explored using data from 41 catchments across Europe,Africa,Australia,Asia,and North and South *** application of seven commonly used mixing models to two case studies from the US(North Fork Broad River watershed) and France(BIcone watershed) with local and global(genetic algorithm) optimization methods identified all outputs remained in the acceptable range of error defined by the original *** propose future sediment fingerprinting studies use models that combine the best explanatory parameters provided by the modified Collins(using correction factors) and Hughes(relying on iterations involving all data,and not only their mean values) models with optimization using genetic algorithms to best predict the relative contribution of sediment sources to fluvial systems.

关键词： watershed fluvial sampling source tracing modeling local optimization genetic algorithm

Numerical Simulation of Turbulent Diffusion Flames of a Biogas Enriched with Hydrogen

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Fluid Dynamics & Materials Processing 2024年第1期20卷 79-96页

作者： Naima Krarraz Amina Sabeur Khadidja Safer Ahmed Ouadha laboratoire des Science et Ingénierie Maritimes Facultéde Génie MécaniqueUniversitédes Sciences et de la Technologie d’Oran Mohamed BoudiafOranAlgérie laboratoire des Carburants Gazeux et de l’environnement Facultéde Génie MécaniqueUniversitédes Sciences et de la Laboratoire des Carburants Gazeux et de l’Environneme

Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly ***,the relatively low calorific value of such gases makes their effective utilization in practical applications relatively *** present study considers the addition of hydrogen as a potential solution to mitigate this *** particular,the properties of turbulent diffusion jet flames and the related pollutant emissions are investigated numerically for different operating *** related numerical simulations are conducted by solving the RANS equations in the frame of the Reynolds Stress Model in combination with the flamelet *** effects are also taken into account and the combustion kinetics are described via the GRI-Mech 3.0 reaction *** considered hydrogen fuel enrichment spans the range from 0%to 50%in terms of *** varies between 1 and 10 *** results show that both hydrogen addition and pressure increase lead to an improvement in terms of mixing quality and have a significant effect on flame temperature and *** also reduce CO_(2) emissions but increase NOx *** NO is shown to be the predominant NO formation mechanism.

关键词： Biogas hydrogen diffusion flame turbulence NO formation route pressure

Characterization of organic matter deposited in the oriental zone from Moknine hypersaline environment, oriental Tunisia

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Chinese Journal Of Geochemistry 2005年第4期24卷 345-351页

作者： Raja CHAIRI Zohra El ASMI DJEllOUlI laboratoire de Ressources Minerales et environnement Faculté des sciences de Tunis 2092 Univ. Tunis El Manar Tunisie Laboratoire de Ressources Minerales et Environnement Faculté des Sciences de Tunis 2092 Univ. Tunis El Manar Tunisie

The geochemistry data show that the total organic carbon (TOC) contents are high in the surface sediments in the eastern part of the Moknine’s Sebkha. low decreasing of organic matter (OM) with increasing depth indicates the good preservation of OM in modern sediments. “lignite levels” inserted in the sand sequence and deposited at the edge and in the intermediate zone are considered as lithologic and organic markers. It is characterized by high TOC and poor hydrogen index (HI), indicating a higher plant origin and good preservation of OM in thin beds under anoxic condition.; In all samples low values of HI are typical for strong terrigenous input in the Sebkha. Gas chromatography (GC) of saturate fraction showed that OM in the border zone is provided from plants but in the central zone OM is a mixture of terrestrial fraction and little fraction from microalgae. The study of free lipids indicated that this environment was influenced by intense bacterial and microbial activities, as evidenced by the abundance of n-alkanes and nC-{18}-nC-{22}.

关键词：突尼斯地球化学有机物质褐煤地质条件

Soil and vegetation water content identify the main terrestrial ecosystem changes

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National Science Review 2023年第5期10卷 167-179页

作者： Diego Bueso Maria Piles Philippe Ciais Jean-Pierre Wigneron álvaro Moreno-Martínez Gustau Camps-Valls Image Processing laboratory Universitat de València laboratoire des sciences du Climat et de l'environnement Université Paris Saclay INRA Centre de Bordeaux Aquitaine Image Processing laboratory Universitat deValència

Environmental change is a consequence of many interrelated *** vegetation responds to natural and human activity still needs to be well establishe d,quantified and *** cent satellite missions providing hydrologic and ecological indicators enable better monitoring of Earth system changes,yet there is no automatic way to address this issue directly from ***,we develop an observation-based methodology to capture evidence of changes in global terrestrial ecosystems and attribute these changes to natural or anthropogenic *** use the longest time record of global microwave l-band soil moisture and vegetation optical depth as satellite data and build spatially explicit maps of change in soil and vegetation water content and biomass reflecting large ecosystem changes during the last decade,*** of prominent trends(from-8% to 9% per year) are observed,especially in humid and semi-arid *** further combine such trends with land cover change maps,vegetation greenness and precipitation variability to assess their relationship with major documented ecosystem *** regions emerge from our *** cluster changes according to human activity drivers,including deforestation(Amazon,Central Africa) and wildfires(East Australia),artificial reforestation(South-East China),abandonment of farm fields(Central Russia) and climate shifts related to changes in precipitation variability(East Africa,North America and Central Argentina).Using the high sensitivity of soil and vegetation water content to ecosystem changes,microwave satellite observations enable us to quantify and attribute global vegetation responses to climate or anthropogenic activities as a direct measure of environmental changes and the mechanisms driving them.

关键词： soil moisture vegetation water content ecosystem trend remote sensing soil moisture and ocean salinity satellite

Numerical Study of Greenhouse Nocturnal Heat losses

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Journal of Thermal Science 2011年第4期20卷 377-384页

作者： F.Berroug E.K.lakhal M.El Omari M.Faraji H.El Qarnia laboratoire d'Automatique de l'environnement et Procédés de Transfert UniversitéCadi AyyadFacultédes Sciences Semlalia-Département de PhysiqueMarrakech-MarocAffiliéau CNRSTURAC 28 laboratoire de Physique des Materiaux MicroelectroniqueAutomatique et TechniqueDepartement de PhysiquesFaculte des Sciences Ain ChockUniversite Hassan IICasablanca-Maroc

In this study we quantify and analyze different components of nocturnal losses from a heated greenhouse with the presence of vegetation for typical winter weather conditions in Marrakesh-Morocco,using a non linear model,based on the greenhouse heat and mass *** was found that 12% of the total input heat was dissipate as a sensible and latent leakage losses,66% was lost by convective exchange through air-inner *** gain of energy at the inner-cover is dissipated at the outer-cover by radiation(66%)and convection(34%).This results point toward some practical measures to reduce heat losses:increasing air tightness,using covering materials with low-emissivity in the long wave band or putting up an external thermal curtain should provide significant energy savings.

关键词： Greenhouse energy balance heat losses numerical analysis.

The B/Ca and Cd/Ca of a subsurface-dwelling foraminifera Pulleniatina obliquiloculata in the tropical Indo-Pacific Ocean: implications for the subsurface carbonate chemistry estimation

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Acta Oceanologica Sinica 2019年第3期38卷 138-150页

作者： Haowen Dang Tingting Wang Peijun Qiao Franck Bassinot Zhimin Jian State Key laboratory of Marine Geology Tongji University laboratoire des sciences du Climat et de l'environnement/IPSl CEA-CNRS-UVSQ Université Paris-Saclay

Pulleniatina obliquiloculata shells from 16 core-top samples from the tropical Indo-Pacific Oceans are analyzed for the ratios of boron and cadmium to calcium(B/Ca and Cd/Ca). The B/Ca ratios show a very weak positive relationship with [B(OH)_4^-] and the dissolved carbonate species at the apparent calcification depth of ***. The boron partition coefficients(K_D) between P. obliquiloculata B/Ca and seawater[B(OH)_4^-]/[HCO_3^-] distribute around 1.1×10^(-3)-1.3×10^(-3) with a mean value of(1.19±0.12)×10^(-3),and are significantly related to the nutrient concentration, especially phosphate. The lack of any clear correlation between the P. obliquiloculata B/Ca and seawater carbonate chemical parameters suggests that the physiochemical controls on boron incorporation are masked by the complexity of natural seawater condition. But the significant dependence of Ku on nutrient may likely be explained by a nutrient related growth-rate effect. Cd/Ca of *** shows significant correlation with seawater phosphate concentration, and its partition coefficients(D_(cd)) are significantly related to temperature. A first-principle methodology of P. obliquiloculata B/Ca is applied;with the aid of Cd/Ca as a phosphate proxy and a constraint on K_D, to estimating sea water carbonate chemistry(e.g., pH). The results are fairly promising and allow us to propose the possibility to apply the combination of B/Ca and Cd/Ca proxies(and also Mg/Ca and δ^(18)O for estimating temperature and salinity) for the paleoreconstruction of seawater carbonate chemistry.

关键词： Pulleniatina obliquiloculata B/Ca Cd/Ca paleo-pH estimation

Effect of Water Quality on Heavy Metal Redistribution and Mobility in Polluted Agricultural Soils in a Semi-Arid Region

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Pedosphere 2019年第6期29卷 730-739页

作者： Rim AZOUZI Abdelkrim CHAREF lamia AYED Samia KHADHAR laboratoire Géoressources Centre des Recherches et Technologies des EauxSoliman 8020(Tunisia) laboratoire d’Analyse Traitement et Valorisation des Polluants de l’Environnement et des ProduitsFacultéde PharmacieRue AvicenneMonastir 5000(Tunisia)

Mornag Plain is a coastal area of the Mediterranean basin, which has undergone an agricultural industrial boom. The aim of this study was to investigate the different water qualities used for irrigation on heavy metal mobility in these polluted agricultural soils. The geo-accumulation indices for heavy metals (Ni, Cr, Pb, Cd, Cu, and Zn) revealed that industrial activities and used treated wastewater (TWW) contributed to soil pollution, and water irrigation always decreased this contamination. After long-term use of different water types, high perturbation of heavy metal redistribution has occurred. Groundwater use altered all heavy metal redistributions in the irrigated soil among various soil-solid and soil-solution fractions, as compared to the unirrigated soil. Slight acid water use transferred some metals from different solid phase components into water-soluble and exchangeable fractions. However, TWW use transformed some Ni, Cr, Cd, Cu, and Zn from water-soluble and exchangeable fractions to less labile fractions, particularly into organically bound fractions. Reuse of conventional water within the same soil decreased the whole soil redistribution index values, indicating tendency to return to the pattern of distribution of groundwater-irrigated soil.

关键词： Exchangeable fraction Geo-accumulation index labile fraction Mobility factor Organically bound fraction Redistribution index Treated wastewater Water-soluble fraction