3,661 research outputs found
Service training in the agriculture equipment industry
Plan B Paper. 2012. Master of Science in Agricultural Education--University of Wisconsin-River Falls. Agricultural Education Department. 33 leaves. Includes bibliographical references (leaf 33).The demand for service training continues to increase in the agriculture equipment industry as technology is adopted and advancements continue to be made on equipment. Service technicians need to be prepared when servicing customer's equipment. In this study I investigated the structure of service training and components of service training. The survey provided feedback on service training from service managers at dealerships. This information will allow service training to be effective and efficient. The population surveyed consisted of service managers from AGCO, Case IH, John Deere and New Holland dealerships. For the first part of the study I sent out a survey to the service managers that asked questions related to the structure, location, and cost of service training. Then I conducted phone interviews with service managers about the structure and components of service training, while receiving feedback on instructor and web based training. This study showed that there is a similar structure in service training among the four major North American equipment manufacturers surveyed. There were similarities in materials used during instructor based courses, along with advantages and disadvantages of web based learning courses among the manufactures. I believe there will continue to be a mixture of instructor and web based service training courses because the research showed that hands on activities are an important part of learning
Wide field imaging of distant clusters
Wide field imaging is key to understanding the build-up of distant clusters
and their galaxy population. By focusing on the so far unexplored outskirts of
clusters, where infalling galaxies first hit the cluster potential and the hot
intracluster medium, we can help separate cosmological field galaxy evolution
from that driven by environment. I present a selection of recent advancements
in this area, with particular emphasis on Hubble Space Telescope wide field
imaging, for its superior capability to deliver galaxy morphologies and precise
shear maps of distant clusters.Comment: Invited contribution. To appear in "Outskirts of galaxy clusters:
intense life in the suburbs", A. Diaferio et al. eds. 7 pages, 5 figures.
Refereed versio
On the average density profile of dark-matter halos in the inner regions of massive early-type galaxies
We study a sample of 39 massive early-type lens galaxies at redshift z < 0.3
to determine the slope of the average dark-matter density profile in the
innermost regions. We keep the strong lensing and stellar population synthesis
modeling as simple as possible to measure the galaxy total and luminous masses.
By rescaling the values of the Einstein radius and dark-matter projected mass
with the values of the luminous effective radius and mass, we combine all the
data of the galaxies in the sample. We find that between 0.3 and 0.9 times the
value of the effective radius the average logarithmic slope of the dark-matter
projected density profile is -1.0 +/- 0.2 (i.e., approximately isothermal) or
-0.7 +/- 0.5 (i.e., shallower than isothermal), if, respectively, a constant
Chabrier or heavier, Salpeter-like stellar IMF is adopted. These results
provide positive evidence of the influence of the baryonic component on the
contraction of the galaxy dark-matter halos, compared to the predictions of
dark matter-only cosmological simulations, and open a new way to test models of
structure formation and evolution within the standard LCDM cosmological
scenario.Comment: 5 pages, 2 figures, published in Astrophysical Journal Letters 747,
L1
The Galaxy UV Luminosity Function Before the Epoch of Reionization
We present a model for the evolution of the galaxy ultraviolet (UV)
luminosity function (LF) across cosmic time where star formation is linked to
the assembly of dark matter halos under the assumption of a mass dependent, but
redshift independent, efficiency. We introduce a new self-consistent treatment
of the halo star formation history, which allows us to make predictions at
(lookback time Myr), when growth is rapid. With a
calibration at a single redshift to set the stellar-to-halo mass ratio, and no
further degrees of freedom, our model captures the evolution of the UV LF over
all available observations (). The significant drop in
luminosity density of currently detectable galaxies beyond is
explained by a shift of star formation toward less massive, fainter galaxies.
Assuming that star formation proceeds down to atomic cooling halos, we derive a
reionization optical depth , fully consistent
with the latest Planck measurement, implying that the universe is fully
reionized at . In addition, our model naturally
produces smoothly rising star formation histories for galaxies with in agreement with observations and hydrodynamical simulations. Before the
epoch of reionization at we predict the LF to remain well-described by a
Schechter function, but with an increasingly steep faint-end slope
( at ). Finally, we construct forecasts for surveys
with \JWST~and \WFIRST and predict that galaxies out to will be
observed. Galaxies at will likely be accessible to JWST and WFIRST only
through the assistance of strong lensing magnification.Comment: Accepted for publication in ApJ. 11 pages, 13 figures. Corrected
mislabelled redshifts in Figure
Dark Matter Contraction and the Stellar Content of Massive Early-type Galaxies: Disfavoring "Light" Initial Mass Functions
We use stellar dynamics, strong lensing, stellar population synthesis models,
and weak lensing shear measurements to constrain the dark matter (DM) profile
and stellar mass in a sample of 53 massive early-type galaxies. We explore
three DM halo models (unperturbed Navarro Frenk & White [NFW] halos and the
adiabatic contraction models of Blumenthal and Gnedin) and impose a model for
the relationship between the stellar and virial mass (i.e., a relationship for
the star-formation efficiency as a function of halo mass). We show that, given
our model assumptions, the data clearly prefer a Salpeter-like initial mass
function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of
the choice of DM halo. In addition, we find that the data prefer at most a
moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is
strongly disfavored) and are only consistent with no adiabatic contraction
(i.e., a NFW halo) if a mass-dependent IMF is assumed, in the sense of a more
massive normalization of the IMF for more massive halos.Comment: 6 pages, 3 figures; submitted to ApJL, including revisions based upon
the referee repor
Spheroids scaling relations over cosmic time
I report on recent measurements of two scaling relations of spheroids in the
distant universe: the Fundamental Plane, and the relation between lensing
velocity dispersion and stellar velocity dispersion. The joint analysis of the
two scaling relations indicates that the most massive (above 10^11.5 solar
masses) spheroids are consistent with no evolution since z~1 both in terms of
star formation and internal structure. Furthermore their total mass density
profile is on average well described by an isothermal sphere with no evidence
for redshift evolution. At smaller masses the picture appears to be
substantially different, as indicated by evidence for substantial recent star
formation (as much as 20-40% of stellar mass formed since z~1), and by hints of
a reduced dark matter content at smaller masses. A larger sample of lenses
extending to velocity dispersions below 200 km/s, and to redshifts above >0.5
is needed to verify these trends.Comment: invited paper at the 235th IAU symposium Galaxy evolution across the
Hubble Tim
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