744 research outputs found

    Development du systeme racinaire chez le palmier a huile selon l'origine genetique et le regime hydropotassique du sol

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    Rootsystem architecture is important in drought resistance, because of its role in water and nutrient mobilizations. The variability of root system architecture of 3 oil palm crosses B, C and E was studied. The3 crosses were different for their sensitivity to drought. The plants were potted into plastic PVC tubes (95 cm in depth x 10 cm in diameter). Each PVC tube was constructed with 6 small tubes assembled together. Two soil moistures regimes and two levels of potassium (K) were tested. For root length, surface area and dry matter, effects of crosses and "cross x K levels x water regime" interactions were significant. The results suggest that breeders could make more progress in selection of root system adapted to drought, if they consider simultaneously both drought and K deficiency parameters. L'architecture du système racinaire du palmier à huile joue un rôle important dans la résistance à la sécheresse, grâce à la mobilisation de l'eau et des sels minéraux. Le système racinaire des plants issusde 3 croisements de palmier à huile B, C et E a été étudiée. Les plants ont été transférés dans des tubes PVC (95 cm de profondeur x 10 cm de diamètre). Chaque tube PVC a consisté en un assemblage de 6 petitstubes. Deux régimes hydriques et deux niveaux de potassium (K) ont été testés. Les effets des croisements et de l'interaction "croisement x niveau de K x régime hydrique" ont été significatifs pour les paramètres tellesla longueur totale, la surface totale et la matière sèche des racines. Ces résultats montrent que pour plus de progrès dans la sélection du système racinaire adapté à la sécheresse, les sélectionneurs gagneraientà prendre en compte à la fois la sécheresse la déficience potassique

    Physical characteristics of G331.5-0.1: The luminous central region of a Giant Molecular Cloud

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    We report molecular line and dust continuum observations toward the high-mass star forming region G331.5-0.1, one of the most luminous regions of massive star-formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO (J=1-0) and C18O (J=1-0) lines with NANTEN, while its central region was mapped in CS (J=2-1 and J=5-4) with SEST, and in CS (J=7-6) and 13CO (J=3-2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2x10^3 Msun, molecular hydrogen density of 3.7x10^4 cm^{-3}, dust temperature of 32 K, and integrated luminosity of 5.7x10^5 Lsun, consistent with values found toward other massive star forming dust clumps. The CS and 13CO spectra show the presence of two velocity components: a high-velocity component at ~ -89 km s^{-1}, seen toward four of the clumps, and a low-velocity component at ~ -101 km s^{-1} seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8+-0.2 and 1.2+-0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s^{-1} (FWHM) in CS (J=7-6). Observations of SiO (J=7-6 and J=8-7), and SO (J_K=8_8-7_7 and J_K=8_7-7_6) lines provide estimates of the gas rotational temperature toward this outflow >120 K and >75 K, respectively.Comment: 34 pages, 20 figures, 11 tables, Accepted for Publication in The Astrophysical Journa

    3D Radiative Hydrodynamics for Disk Stability Simulations: A Proposed Testing Standard and New Results

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    Recent three-dimensional radiative hydrodynamics simulations of protoplanetary disks report disparate disk behaviors, and these differences involve the importance of convection to disk cooling, the dependence of disk cooling on metallicity, and the stability of disks against fragmentation and clump formation. To guarantee trustworthy results, a radiative physics algorithm must demonstrate the capability to handle both the high and low optical depth regimes. We develop a test suite that can be used to demonstrate an algorithm's ability to relax to known analytic flux and temperature distributions, to follow a contracting slab, and to inhibit or permit convection appropriately. We then show that the radiative algorithm employed by Meji\'a (2004) and Boley et al. (2006) and the algorithm employed by Cai et al. (2006) and Cai et al. (2007, in prep.) pass these tests with reasonable accuracy. In addition, we discuss a new algorithm that couples flux-limited diffusion with vertical rays, we apply the test suite, and we discuss the results of evolving the Boley et al. (2006) disk with this new routine. Although the outcome is significantly different in detail with the new algorithm, we obtain the same qualitative answers. Our disk does not cool fast due to convection, and it is stable to fragmentation. We find an effective α≈10−2\alpha\approx 10^{-2}. In addition, transport is dominated by low-order modes.Comment: Submitted to Ap

    An Ab Initio Approach to the Solar Coronal Heating Problem

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    We present an ab initio approach to the solar coronal heating problem by modelling a small part of the solar corona in a computational box using a 3D MHD code including realistic physics. The observed solar granular velocity pattern and its amplitude and vorticity power spectra, as reproduced by a weighted Voronoi tessellation method, are used as a boundary condition that generates a Poynting flux in the presence of a magnetic field. The initial magnetic field is a potential extrapolation of a SOHO/MDI high resolution magnetogram, and a standard stratified atmosphere is used as a thermal initial condition. Except for the chromospheric temperature structure, which is kept fixed, the initial conditions are quickly forgotten because the included Spitzer conductivity and radiative cooling function have typical timescales much shorter than the time span of the simulation. After a short initial start up period, the magnetic field is able to dissipate 3-4 10^6 ergs cm^{-2} s^{-1} in a highly intermittent corona, maintaining an average temperature of ∼106\sim 10^6 K, at coronal density values for which emulated images of the Transition Region And Coronal Explorer(TRACE) 171 and 195 pass bands reproduce observed photon count rates.Comment: 12 pages, 14 figures. Submitted to Ap

    Synthetic Molecular Clouds from Supersonic MHD and Non-LTE Radiative Transfer Calculations

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    The dynamics of molecular clouds is characterized by supersonic random motions in the presence of a magnetic field. We study this situation using numerical solutions of the three-dimensional compressible magneto-hydrodynamic (MHD) equations in a regime of highly supersonic random motions. The non-LTE radiative transfer calculations are performed through the complex density and velocity fields obtained as solutions of the MHD equations, and more than 5x10^5 synthetic molecular spectra are obtained. We use a numerical flow without gravity or external forcing. The flow is super-Alfvenic and corresponds to model A of Padoan and Nordlund (1997). Synthetic data consist of sets of 90x90 synthetic spectra with 60 velocity channels, in five molecular transitions: J=1-0 and J=2-1 for 12CO and 13CO, and J=1-0 for CS. Though we do not consider the effects of stellar radiation, gravity, or mechanical energy input from discrete sources, our models do contain the basic physics of magneto-fluid dynamics and non-LTE radiation transfer and are therefore more realistic than previous calculations. As a result, these synthetic maps and spectra bear a remarkable resemblance to the corresponding observations of real clouds.Comment: 33 pages, 12 figures included, 5 jpeg figures not included (fig1a, fig1b, fig3, fig4 fig5), submitted to Ap

    Telephone Surveys Underestimate Cigarette Smoking among African-Americans

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    Background: This study tested the hypothesis that data from random digit-dial telephone surveys underestimate the prevalence of cigarette smoking among African-American adults. Method: A novel, community-sampling method was used to obtain a statewide, random sample of N = 2118 California (CA) African-American/Black adults, surveyed door-to-door. This Black community sample was compared to the Blacks in the CA Health Interview Survey (N = 2315), a statewide, random digit-dial telephone survey conducted simultaneously. Results: Smoking prevalence was significantly higher among community (33%) than among telephone survey (19%) Blacks, even after controlling for sample differences in demographics. Conclusion: Telephone surveys underestimate smoking among African-Americans and probably underestimate other health risk behaviors as well. Alternative methods are needed to obtain accurate data on African-American health behaviors and on the magnitude of racial disparities in them

    Usage of FTA (R) Classic Cards for Safe Storage, Shipment, and Detection of Arboviruses

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    Infections caused by arthropod-borne RNA viruses are overrepresented among emerging infectious diseases. Effective methods for collecting, storing, and transporting clinical or biological specimens are needed worldwide for disease surveillance. However, many tropical regions where these diseases are endemic lack analytical facilities and possibility of continuous cold chains, which presents challenges from both a biosafety and material preservation perspective. Whatman (R) FTA (R) Classic Cards may serve as an effective and safe option for transporting hazardous samples at room temperature, particularly for RNA viruses classified as biosafety level (BSL) 2 and 3 pathogens, from sampling sites to laboratories. In this study, we investigated the biosafety and perseverance of representative alpha-and flaviviruses stored on FTA (R) cards. To evaluate the virus inactivation capacity of FTA (R) cards, we used Sindbis virus (SINV), chikungunya virus (CHIKV), and Japanese encephalitis virus (JEV). We inoculated susceptible cells with dilution series of eluates from viral samples stored on the FTA (R) cards and observed for cytopathic effect to evaluate the ability of the cards to inactivate viruses. All tested viruses were inactivated after storage on FTA (R) cards. In addition, we quantified viral RNA of JEV, SINV, and tick-borne encephalitis virus (TBEV) stored on FTA (R) cards at 4 degrees C, 25 degrees C, and 37 degrees C for 30 days using two reverse transcriptase quantitative PCR assays. Viral RNA of SINV stored on FTA (R) cards was not reduced at either 4 degrees C or 25 degrees C over a 30-day period, but degraded rapidly at 37 degrees C. For JEV and TBEV, degradation was observed at all temperatures, with the most rapid degradation occurring at 37 degrees C. Therefore, the use of FTA (R) cards provides a safe and effective workflow for the collection, storage, and analysis of BSL 2- and 3-virus RNA samples, but there is a risk of false negative results if the cards are stored at higher temperatures for long periods of time. Conscious usage of the cards can be useful in disease surveillance and research, especially in tropical areas where transportation and cold chains are problematic

    The Global Mangrove Watch—A New 2010 Global Baseline of Mangrove Extent

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    This study presents a new global baseline of mangrove extent for 2010 and has been released as the first output of the Global Mangrove Watch (GMW) initiative. This is the first study to apply a globally consistent and automated method for mapping mangroves, identifying a global extent of 137,600 km 2 . The overall accuracy for mangrove extent was 94.0% with a 99% likelihood that the true value is between 93.6–94.5%, using 53,878 accuracy points across 20 sites distributed globally. Using the geographic regions of the Ramsar Convention on Wetlands, Asia has the highest proportion of mangroves with 38.7% of the global total, while Latin America and the Caribbean have 20.3%, Africa has 20.0%, Oceania has 11.9%, North America has 8.4% and the European Overseas Territories have 0.7%. The methodology developed is primarily based on the classification of ALOS PALSAR and Landsat sensor data, where a habitat mask was first generated, within which the classification of mangrove was undertaken using the Extremely Randomized Trees classifier. This new globally consistent baseline will also form the basis of a mangrove monitoring system using JAXA JERS-1 SAR, ALOS PALSAR and ALOS-2 PALSAR-2 radar data to assess mangrove change from 1996 to the present. However, when using the product, users should note that a minimum mapping unit of 1 ha is recommended and that the error increases in regions of disturbance and where narrow strips or smaller fragmented areas of mangroves are present. Artefacts due to cloud cover and the Landsat-7 SLC-off error are also present in some areas, particularly regions of West Africa due to the lack of Landsat-5 data and persistence cloud cover. In the future, consideration will be given to the production of a new global baseline based on 10 m Sentinel-2 composites
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