2,965 research outputs found

    Biogeochemical and microbial community structure differently modulates CO2 and CH4 dynamics in two adjacent volcanic lakes (Monticchio, Italy)

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    By hosting significant amounts of extra-atmospheric dissolved gases, including geogenic CO2 and CH4, volcanic lakes provide relevant ecosystem services through the key role the aquatic microbial community in mediating freshwater carbon fluxes. In view of elucidating the mechanisms governing the microbial spatial distribution and the possible implications for ecosystem functioning, we compared the hydrogeochemical features and the microbial community structure of two adjacent stratified volcanic lakes (Lake Grande - LG and Lake Piccolo - LP). Water chemistry, gases and their isotopic composition were coupled with microbial pigment profiling, cell counting, and phylogenetic analyses. LP showed transparent waters with low concentrations of chlorophyll-a and the occurrence of phycoerytrin-rich cyanobacteria. LG was relatively more eutrophic with a higher occurrence of diatoms and phycocyanine-rich cyanobacteria. Considering the higher concentrations of CO2 and CH4 in bottom waters, the oligotrophic LP was likely a more efficient sink of geogenic CO2 in comparison to the adjacent eutrophic LG. The prokaryotic community was dominated by the mixothrophic hgcI clade (family Sporichthyaceae) in the LG surface waters, while in LP this taxon was dominant down to -15 m. Moreover, in LP, the bottom dark waters harbored a unique strictly anaerobic bacterial assemblage associated with methanogenic Archaea (i.e. Methanomicrobiales), resulting in a high biogenic methane concentration. Water layering and light penetration were confirmed as major factors affecting the microbial distribution patterns. The observed differences in the geochemical and trophic conditions reflected the structure of the aquatic microbial community, with direct consequences on the dynamics of dissolved greenhouse gases

    Strong Interaction Physics at the Luminosity Frontier with 22 GeV Electrons at Jefferson Lab

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    This document presents the initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) to 22 GeV. It is the result of a community effort, incorporating insights from a series of workshops conducted between March 2022 and April 2023. With a track record of over 25 years in delivering the world's most intense and precise multi-GeV electron beams, CEBAF's potential for a higher energy upgrade presents a unique opportunity for an innovative nuclear physics program, which seamlessly integrates a rich historical background with a promising future. The proposed physics program encompass a diverse range of investigations centered around the nonperturbative dynamics inherent in hadron structure and the exploration of strongly interacting systems. It builds upon the exceptional capabilities of CEBAF in high-luminosity operations, the availability of existing or planned Hall equipment, and recent advancements in accelerator technology. The proposed program cover various scientific topics, including Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic highlights the key measurements achievable at a 22 GeV CEBAF accelerator. Furthermore, this document outlines the significant physics outcomes and unique aspects of these programs that distinguish them from other existing or planned facilities. In summary, this document provides an exciting rationale for the energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific potential that lies within reach, and the remarkable opportunities it offers for advancing our understanding of hadron physics and related fundamental phenomena

    Rheological Behaviors of Waste Polyethylene Modified Asphalt Binder: Statistical Analysis of Interlaboratory Testing Results

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    This article investigated the effect of waste polyethylene (PE) on the modified asphalt binders' rheological behavior from a statistical point of view. The interlaboratory testing results from the RILEM Technical Committee 279 Valorization of Waste and Secondary Materials for Roads Task Group 1 were used for this purpose. First, an unaged 70/100 penetration graded neat binder was selected as the reference material. Next, a single 5 % content of waste PE additives (PE-pellets and PE-shreds) was mixed with a 95 % neat binder to prepare two PE modified binders. Then, dynamic shear rheometer-based temperature-frequency sweep tests were performed over a wide range of temperatures and frequencies to evaluate the rheological properties of these three binders. Different rheological behaviors were observed in the isochronal plots at high temperatures. Based on a reproducibility precision requirement proposed for phase angle, 28 degrees C was set as the transition temperature across the rheological behaviors. Next, according to the three rheological behaviors defined in a previous study by the authors, statistical analysis was introduced to identify sensitive rheological parameters and determine the thresholds. Results indicate that the phase angle measured above 28 degrees C and 1.59 Hz can be used as a sensitive parameter to discriminate the three rheological behaviors of PE modified binders. The thresholds among different behaviors were also calculated as an example for phase angle measured at the highest common testing temperature of 70 degrees C. Additional experimental evaluations on more types of PE modified binders, especially at intermediate and high temperatures, are recommended to better understand their influence on the rheological behavior of PE modified binders

    Avaliação econômica de sistemas de produção de bovinos de corte a pasto, incluindo um sistema consorciado com Cajanus cajan.

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    Neste estudo, avaliou-se a viabilidade econômica de três sistemas de produção de bovinos de corte a pasto para entender qual oferece melhor rentabilidade

    Maximizando a produgdo de forragem em sistema silvipastoril por meio do desbaste de árvores.

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    Objetivou-se avaliar o acúmulo de forragem e a porcentagem de folhas do capim Piatd (Urochloa brizantha cv. BRS Piatd) em sistema silvipastoril (SSP) sombreado por eucalipto com baixa densidade populacional-comparado a um sistema a pleno sol (PS) na Embrapa Pecudria Sudeste, São Carlos, SP, Brasil (21°57'S, 47°50'W, 860 m de altitude) de margo-2020 a margo-2023

    Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XIII. Ultraviolet Time Lag of Hβ\beta Emission in Mrk 142

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    We performed a rigorous reverberation-mapping analysis of the broad-line region (BLR) in a highly accreting (L/LEdd=0.74−3.4L/L_{\mathrm{Edd}}=0.74-3.4) active galactic nucleus, Markarian 142 (Mrk 142), for the first time using concurrent observations of the inner accretion disk and the BLR to determine a time lag for the HβH\beta λ\mathrm{\lambda}4861 emission relative to the ultraviolet (UV) continuum variations. We used continuum data taken with the Niel Gehrels Swift Observatory in the UVW2 band, and the Las Cumbres Observatory, Dan Zowada Memorial Observatory, and Liverpool Telescope in the g band, as part of the broader Mrk 142 multi-wavelength monitoring campaign in 2019. We obtained new spectroscopic observations covering the HβH\beta broad emission line in the optical from the Gemini North Telescope and the Lijiang 2.4-meter Telescope for a total of 102 epochs (over a period of eight months) contemporaneous to the continuum data. Our primary result states a UV-to-HβH\beta time lag of 8.68−0.72+0.758.68_{-0.72}^{+0.75} days in Mrk 142 obtained from light-curve analysis with a Python-based Running Optimal Average algorithm. We placed our new measurements for Mrk 142 on the optical and UV radius-luminosity relations for NGC 5548 to understand the nature of the continuum driver. The positions of Mrk 142 on the scaling relations suggest that UV is closer to the "true" driving continuum than the optical. Furthermore, we obtain log⁡(M∙/M⊙)=6.32±0.29\log(M_{\bullet}/M_{\odot}) = 6.32\pm0.29 assuming UV as the primary driving continuum.Comment: 35 pages, 12 figures, 11 tables, accepted for publication in Ap

    Fast-Spiking Interneurons of the Premotor Cortex Contribute to Initiation and Execution of Spontaneous Actions

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    Planning and execution of voluntary movement depend on the contribution of distinct classes of neurons in primary motor and premotor areas. However, timing and pattern of activation of GABAergic cells during specific motor behaviors remain only partly understood. Here, we directly compared the response properties of putative pyramidal neurons (PNs) and GABAergic fast-spiking neurons (FSNs) during spontaneous licking and forelimb movements in male mice. Recordings centered on the face/mouth motor field of the anterolateral motor cortex (ALM) revealed that FSNs fire longer than PNs and earlier for licking, but not for forelimb movements. Computational analysis revealed that FSNs carry vastly more information than PNs about the onset of movement. While PNs differently modulate their discharge during distinct motor acts, most FSNs respond with a stereotyped increase in firing rate. Accordingly, the informational redundancy was greater among FSNs than PNs. Finally, optogenetic silencing of a subset of FSNs reduced spontaneous licking movement. These data suggest that a global rise of inhibition contributes to the initiation and execution of spontaneous motor actions

    Beam Charge Asymmetries for Deeply Virtual Compton Scattering on the Proton at CLAS12

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    International audienceThe parameterization of the nucleon structure through Generalized Parton Distributions (GPDs) shed a new light on the nucleon internal dynamics. For its direct interpretation, Deeply Virtual Compton Scattering (DVCS) is the golden channel for GPDs investigation. The DVCS process interferes with the Bethe-Heitler (BH) mechanism to constitute the leading order amplitude of the eN→eNγeN \to eN\gamma process. The study of the epγep\gamma reaction with polarized positron and electron beams gives a complete set of unique observables to unravel the different contributions to the epγep \gamma cross section. This separates the different reaction amplitudes, providing a direct access to their real and imaginary parts which procures crucial constraints on the model dependences and associated systematic uncertainties on GPDs extraction. The real part of the BH-DVCS interference amplitude is particularly sensitive to the DD-term which parameterizes the Gravitational Form Factors of the nucleon. The separation of the imaginary parts of the interference and DVCS amplitudes provides insights on possible higher-twist effects. We propose to measure the unpolarized and polarized Beam Charge Asymmetries (BCAs) of the e⃗±p→e±pγ\vec{e}^{\pm}p \to e^{\pm}p \gamma process on an unpolarized hydrogen target with {\tt CLAS12}, using polarized positron and electron beams at 10.6~GeV. The azimuthal and tt-dependences of the unpolarized and polarized BCAs will be measured over a large (xB,Q2)(x_B,Q^2) phase space using a 100 day run with a luminosity of 0.66×1035\times 10^{35}cm−2⋅^{-2}\cdots−1^{-1}

    Accurate mass-radius ratios for Hyades white dwarfs

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    We use the ESPRESSO spectrograph at the Very Large Telescope to measure velocity shifts and gravitational redshifts of eight bona fide Hyades white dwarfs, with an accuracy better than 1.5 percent. By comparing the gravitational redshift measurements of the mass-to-radius ratio with the same ratios derived by fitting the \textit{Gaia} photometry with theoretical models, we find an agreement to better than one per cent. It is possible to reproduce the observed white dwarf cooling sequence and the trend of the mass-to-radius ratios as a function of colour using isochrones with ages between 725 and 800 Myr, tuned for the Hyades. One star, EGGR\,29, consistently stands out in all diagrams, indicating that it is possibly the remnant of a blue straggler. We also computed mass-to-radius ratios from published gravities and masses, determined from spectroscopy. The comparison between photometric and spectroscopic stellar parameters reveals that spectroscopic effective temperature and gravity are systematically larger than the photometric values. Spectroscopic mass-to-radius ratios disagree with those measured from gravitational redshift, indicating the presence of systematics affecting the white dwarf parameters derived from the spectroscopic analysis.Comment: MNRAS, accepted for pubblicatio
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