1,403 research outputs found
Filling Soil Health Prescriptions with Targeted Cover Crops
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
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
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
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
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
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 CMi
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 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 = 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, = 3.0, density falloff. Modeling of radio
observations allowed for the first determination of the physical extent of a Be
disk (35 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 , i.e.,
very close to critical.Comment: 19 pages (35 including online material), 17 figures, 2 online
figures, 2 online tables with dat
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