1,512 research outputs found
Organizational Issues in the Agrifood Sector: Toward a Comparative Approach
This paper outlines a research program comparing the economic organization of agriculture in the United States and European Union. Both have highly developed agricultural sectors but their organizational arrangements vary widely. Comparative analysis not only provides a broad set of firms and industries to compare, but also highlights the interaction between the institutional environment and the arrangements established to govern agricultural transactions. We first assess the common trend toward consolidation and vertical integration, turning next to the economic organization of formal and informal networks. While history and path dependence explain some of the variety among U.S. and European practices, other local conditions are important as well. We conclude by assessing the policy implications of recent changes in economic organization.
The accumulation and trapping of grains at planet gaps: effects of grain growth and fragmentation
We model the dust evolution in protoplanetary disks with full 3D, Smoothed
Particle Hydrodynamics (SPH), two-phase (gas+dust) hydrodynamical simulations.
The gas+dust dynamics, where aerodynamic drag leads to the vertical settling
and radial migration of grains, is consistently treated. In a previous work, we
characterized the spatial distribution of non-growing dust grains of different
sizes in a disk containing a gap-opening planet and investigated the gap's
detectability with the Atacama Large Millimeter/submillimeter Array (ALMA).
Here we take into account the effects of grain growth and fragmentation and
study their impact on the distribution of solids in the disk. We show that
rapid grain growth in the two accumulation zones around planet gaps is strongly
affected by fragmentation. We discuss the consequences for ALMA observations.Comment: Accepted for publication in Planetary and Space Science. 13 pages, 4
figure
Galaxy Morphology - Halo Gas Connections
We studied a sample of 38 intermediate redshift MgII absorption-selected
galaxies using (1) Keck/HIRES and VLT/UVES quasar spectra to measure the halo
gas kinematics from MgII absorption profiles and (2) HST/WFPC-2 images to study
the absorbing galaxy morphologies. We have searched for correlations between
quantified gas absorption properties, and host galaxy impact parameters,
inclinations, position angles, and quantified morphological parameters. We
report a 3.2-sigma correlation between asymmetric perturbations in the host
galaxy morphology and the MgII absorption equivalent width. We suggest that
this correlation may indicate a connection between past merging and/or
interaction events in MgII absorption-selected galaxies and the velocity
dispersion and quantity of gas surrounding these galaxies.Comment: 6 pages; 3 figures; contributed talk for IAU 199: Probing Galaxies
through Quasar Absorption Line
Immunogenicity and Immunosensitivity of Urethane-induced Murine Lung Adenomata, in Relation to the Immunological Impairment of the Primary Tumour Host
The depression of the immunological status of BALB/c mice treated during infancy with two different doses of urethane, alone or combined with cortisone, was evaluated by counting the number of plaque forming cells at 30 or 50 days of age. The incidence of lung adenomatous nodules was directly related to the degree of immunological impairment at 50 days of age. Twenty-seven lung adenomata were tested in an in vitro system involving spleen cells immune against the same single tumour used as target cell. Eighty-six per cent of tumours in the most immunodepressed group of mice were positive compared with 20-40% in the less immunodepressed groups. Syngeneic cross-reaction tests showed that non-immunogenic tumours were immunosensitive since 66% positive tests were obtained when target cells belonging to the less immunodepressed groups were tested with spleen cells of mice immunized with immunogenic adenomata
Embryonic Antigens and Growth of Murine Fibrosarcomata
The amount of embryonic antigens (EA) was estimated in 13 BALB/c fibrosarcomata by in vitro cell mediated cytotoxicity of anti-embryo spleen cells and by quantitative absorption of an anti-embryo antiserum. A direct relationship between amount of EA and tumour growing capacity was found. EA were detected also on fast dividing testicular cells. It is suggested that EA expression on tumour cells is related to a cell membrane function controlling mitosis rather than to a function specifically related to the neoplastic status. Tumour take of low doses of 2 EA-bearing sarcomata was found to be enhanced in anti-embryo immune BALB/c mice in comparison with that in normal and anti-fibroblast immune mice
Dust in the Circumgalactic Medium of Low-Redshift Galaxies
Using spectroscopically selected galaxies from the Sloan Digital Sky Survey
we present a detection of reddening due to dust in the circumgalactic medium of
galaxies. We detect the mean change in the colors of "standard crayons"
correlated with the presence of foreground galaxies at z ~0.05 as a function of
angular separation. Following Peek & Graves (2010), we create standard crayons
using passively evolving galaxies corrected for Milky Way reddening and
color-redshift trends, leading to a sample with as little as 2% scatter in
color. We devise methods to ameliorate possible systematic effects related to
the estimation of colors, and we find an excess reddening induced by foreground
galaxies at a level ranging from 10 to 0.5 millimagnitudes on scales ranging
from 30 kpc to 1 Mpc. We attribute this effect to a large-scale distribution of
dust around galaxies similar to the findings of Menard et al. 2010. We find
that circumgalactic reddening is a weak function of stellar mass over the range
-- and note that this
behavior appears to be consistent with recent results on the distribution of
metals in the gas phase.Comment: Submitted to Ap
Herschel PACS Observations and Modeling of Debris Disks in the Tucana-Horologium Association
We present Herschel PACS photometry of seventeen B- to M-type stars in the 30
Myr-old Tucana-Horologium Association. This work is part of the Herschel Open
Time Key Programme "Gas in Protoplanetary Systems" (GASPS). Six of the
seventeen targets were found to have infrared excesses significantly greater
than the expected stellar IR fluxes, including a previously unknown disk around
HD30051. These six debris disks were fitted with single-temperature blackbody
models to estimate the temperatures and abundances of the dust in the systems.
For the five stars that show excess emission in the Herschel PACS photometry
and also have Spitzer IRS spectra, we fit the data with models of optically
thin debris disks with realistic grain properties in order to better estimate
the disk parameters. The model is determined by a set of six parameters:
surface density index, grain size distribution index, minimum and maximum grain
sizes, and the inner and outer radii of the disk. The best fitting parameters
give us constraints on the geometry of the dust in these systems, as well as
lower limits to the total dust masses. The HD105 disk was further constrained
by fitting marginally resolved PACS 70 micron imaging.Comment: 15 pages, 7 figures, Accepted to Ap
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