1,403 research outputs found

    Filling Soil Health Prescriptions with Targeted Cover Crops

    Full text link
    Sustainable farming requires close attention to soil improvement. This project will let vegetable producers use the new Cornell Soil Health Test (CSHT) to identify what needs improvement, and select cover crops that specifically address those needs. Most of the project will be carried out on grower farms, expanding existing relationships that have been developed around soil health, and responding to growers’ desire to act on the new information they get from the CSHT. Most current cover crop recommendations are too general; we will provide locally appropriate targeted guidance for specific soil management goals

    Cooling of 2 kW H subscript 2-O subscript 2 fuel cell

    Get PDF
    An extensive research and development program has been carried out to devise an improved method of removing waste heat of reaction from a developmental 2 kW hydrogen-oxygen fuel cell

    The Dynamical Evolution of Be star disks

    Full text link
    We present a novel theoretical tool to analyze the dynamical behaviour of a Be disk fed by non-constant decretion rates. It is mainly based on the computer code HDUST, a fully three-dimensional radiative transfer code that has been successfully applied to study several Be systems so far, and the SINGLEBE code that solves the 1D viscous diffusion problem. We have computed models of the temporal evolution of different types of Be star disks for different dynamical scenarios. By showing the behaviour of a large number of observables (interferometry, polarization, photometry and spectral line profiles), we show how it is possible to infer from observations some key dynamical parameters of the disk.Comment: IAU 272 symposium proceedings, 3 pages, 1 figur

    Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks

    Full text link
    We discuss the basic hydrodynamics that determines the density structure of the disks around hot stars. Observational evidence supports the idea that these disks are Keplerian (rotationally supported) gaseous disks. A popular scenario in the literature, which naturally leads to the formation of Keplerian disks, is the viscous decretion model. According to this scenario, the disks are hydrostatically supported in the vertical direction, while the radial structure is governed by the viscous transport. This suggests that the temperature is one primary factor that governs the disk density structure. In a previous study we demonstrated, using 3-D NLTE Monte Carlo simulations, that viscous keplerian disks can be highly non-isothermal. In this paper we build upon our previous work and solve the full problem of the steady-state non-isothermal viscous diffusion and vertical hydrostatic equilibrium. We find that the self-consistent solution departs significantly from the analytic isothermal density, with potentially large effects on the emergent spectrum. This implies that non-isothermal disk models must be used for a detailed modeling of Be star disks.Comment: 22 pages, 9 figures, Ap

    On the Modified Random Walk for Monte-Carlo Radiation Transfer

    Full text link
    Min et al. (2009) presented two complementary techniques that use the diffusion approximation to allow efficient Monte-Carlo radiation transfer in very optically thick regions: a modified random walk and a partial diffusion approximation. In this note, I show that the calculations required for the modified random walk method can be significantly simplified. In particular, the diffusion coefficient and the mass absorption coefficients required for the modified random walk are in fact the same as the standard diffusion coefficient and the Planck mean mass absorption coefficient.Comment: Accepted for publication in A&

    Endotoxin: A Twofold Effect on Bone Marrow Ultrastructure

    Get PDF
    Ultrastructural studies of mouse bone marrow reveal that reduction of the marrow-blood barrier precedes the two waves of leukocytosis which follow endotoxin administration. These ultrastructural changes include a decrease in adventitial cover of the marrow sinus wall, an increase in sinus circumference, and a decrease in endothelial cell overlap. The marrow-blood barrier changes which precede the first wave of leukocytosis are transient and are associated with depletion of marrow granulocytes. The changes that precede the second wave of leukocytosis 5 to 6 days later are more sustained and are associated with marked granulocyte hyperplasia. We suggest that endotoxin has two effects on marrow ultrastructure: (1) an early, direct effect on the sinus wall and (2) a later, indirect effect associated with granulocyte proliferation. The late effect may be mediated through endotoxin induced release of colony stimulating factor. Both effects diminish the normal marrow-blood barrier and appear to facilitate cell release from the marrow

    Multitechnique testing of the viscous decretion disk model I. The stable and tenuous disk of the late-type Be star β\beta CMi

    Full text link
    The viscous decretion disk (VDD) model is able to explain most of the currently observable properties of the circumstellar disks of Be stars. However, more stringent tests, focusing on reproducing multitechnique observations of individual targets via physical modeling, are needed to study the predictions of the VDD model under specific circumstances. In the case of nearby, bright Be star β\beta CMi, these circumstances are a very stable low-density disk and a late-type (B8Ve) central star. The aim is to test the VDD model thoroughly, exploiting the full diagnostic potential of individual types of observations, in particular, to constrain the poorly known structure of the outer disk if possible, and to test truncation effects caused by a possible binary companion using radio observations. We use the Monte Carlo radiative transfer code HDUST to produce model observables, which we compare with a very large set of multitechnique and multiwavelength observations that include ultraviolet and optical spectra, photometry covering the interval between optical and radio wavelengths, optical polarimetry, and optical and near-IR (spectro)interferometry. Due to the absence of large scale variability, data from different epochs can be combined into a single dataset. A parametric VDD model with radial density exponent of nn = 3.5, which is the canonical value for isothermal flaring disks, is found to explain observables typically formed in the inner disk, while observables originating in the more extended parts favor a shallower, nn = 3.0, density falloff. Modeling of radio observations allowed for the first determination of the physical extent of a Be disk (355+10^{+10}_{-5} stellar radii), which might be caused by a binary companion. Finally, polarization data allowed for an indirect measurement of the rotation rate of the star, which was found to be W0.98W \gtrsim 0.98, i.e., very close to critical.Comment: 19 pages (35 including online material), 17 figures, 2 online figures, 2 online tables with dat
    corecore