213 research outputs found
Water use of two corn varieties, drought resistant and drought sensitive
In order to understand the mechanism of water use and drought resistance of corn, it is necessary to study effects of these characteristics on water use and drought resistance and to be able to quantify the effects. Two corn hybrids, Pioneer 3343 (P3343) and Pioneer 3379 (P3379) known as drought sensitive and drought resistant, respectively, with a sorghum hybrid, Pioneer 8086 (P8086) as control, were investigated. Our study included measurements of leaf resistance, total plant leaf area, plant height, root weight, and plant water potential and permanent wilting points of soil water content. Experiments were conducted in the greenhouse, growth chamber, and field over a three year period;The field and greenhouse results show that P3379 had greater total plant leaf area, and higher transpiration rates but shorter plant height. The P3379 had the lower permanent wilting point (soil moisture content), and higher water consumption than P3343 in greenhouse experiments. However, there were no differences in soil moisture and grain yield in the field studies. If P3379 is considered to be drought resistant plant, it may be characterized as a water spender that can resist mild drought because it has more available water from its lower permanent wilting point that may result in lower leaf resistance;A computerized model was developed to evaluate plant water use in terms of physiological, morphological and phenological features. The model includes simulation of temperature and vapor profiles in a corn canopy, radiation penetration in the canopy, and development of leaf area index and plant height. The inputs for the model include daily and hourly weather data, maximum plant leaf area, planting date, silking data, maturity date, and planting density. Outputs are daily transpiration, daily plant water use, cumulative water use, total plant leaf area and leaf area index;The validation study indicated that the calculated plant water use and leaf area development agree well with measurements. The sensitivity study showed that plant total leaf area significantly influenced plant water use, especially when leaf area index was low. Increase of leaf area with a fixed planting density would increase plant water use in a growing season. The effect of silking date on plant water use was not as significant as leaf area. However, silking date is an indicator of plant water use. (Abstract shortened by UMI.
Quantifying jet transport properties via large hadron production
Nuclear modification factor for large single hadron is studied
in a next-to-leading order (NLO) perturbative QCD (pQCD) parton model with
medium-modified fragmentation functions (mFFs) due to jet quenching in
high-energy heavy-ion collisions. The energy loss of the hard partons in the
QGP is incorporated in the mFFs which utilize two most important parameters to
characterize the transport properties of the hard parton jets: the jet
transport parameter and the mean free path , both at
the initial time . A phenomenological study of the experimental data
for is performed to constrain the two parameters with
simultaneous fits to RHIC as well as LHC data. We obtain
for energetic quarks GeV/fm and
fm in central collisions at
GeV, while GeV/fm, and
fm in central collisions at
TeV. Numerical analysis shows that the best fit favors a
multiple scattering picture for the energetic jets propagating through the bulk
medium, with a moderate averaged number of gluon emissions. Based on the best
constraints for and , the estimated value for the
mean-squared transverse momentum broadening is moderate which implies that the
hard jets go through the medium with small reflection.Comment: 8 pages, 6 figures, revised versio
Effects of initial state fluctuations on jet energy loss
The effect of initial state fluctuations on jet energy loss in relativistic
heavy-ion collisions is studied in a 2+1 dimension ideal hydrodynamic model.
Within the next-to-leading order perturbative QCD description of hard
scatterings, we find that a jet loses slightly more energy in the expanding
quark-gluon plasma if the latter is described by the hydrodynamic evolution
with fluctuating initial conditions compared to the case with smooth initial
conditions. A detailed analysis indicates that this is mainly due to the
positive correlation between the fluctuation in the production probability of
parton jets from initial nucleon-nucleon hard collisions and the fluctuation in
the medium density along the path traversed by the jet. This effect is larger
in non-central than in central relativistic heavy ion collisions and also for
jet energy loss that has a linear than a quadratic dependence on its path
length in the medium
Lasso adjustments of treatment effect estimates in randomized experiments
We provide a principled way for investigators to analyze randomized
experiments when the number of covariates is large. Investigators often use
linear multivariate regression to analyze randomized experiments instead of
simply reporting the difference of means between treatment and control groups.
Their aim is to reduce the variance of the estimated treatment effect by
adjusting for covariates. If there are a large number of covariates relative to
the number of observations, regression may perform poorly because of
overfitting. In such cases, the Lasso may be helpful. We study the resulting
Lasso-based treatment effect estimator under the Neyman-Rubin model of
randomized experiments. We present theoretical conditions that guarantee that
the estimator is more efficient than the simple difference-of-means estimator,
and we provide a conservative estimator of the asymptotic variance, which can
yield tighter confidence intervals than the difference-of-means estimator.
Simulation and data examples show that Lasso-based adjustment can be
advantageous even when the number of covariates is less than the number of
observations. Specifically, a variant using Lasso for selection and OLS for
estimation performs particularly well, and it chooses a smoothing parameter
based on combined performance of Lasso and OLS
Punch-through jets in collisions at RHIC/LHC
High single and dihadron production is studied within a NLO pQCD parton
model with jet quenching in high energy collisions at the RHIC/LHC
energy. A simultaneous -fit to both single and dihadron spectra can be
achieved within a narrow range of energy loss parameter. Punch-through jets are
found to result in the dihadron suppression factor slightly more sensitive to
medium than the single hadron suppression factor at RHIC. Such jets at LHC are
found to dominate high dihadron production and the resulting dihadron
spectra are more sensitive to the initial parton distribution functions than
the single hadron spectra.Comment: 4 pages, 4 figures, proceedings for the 20th international conference
on ultra-relativistic nucleus-nucleus collisions (QM2008), Jaipur, India,
February 4-10, 200
Suppression of high hadrons in Collisions at LHC
Nuclear modification factor for large transverse momentum
pion spectra in collisions at TeV is predicted within
the NLO perturbative QCD parton model. Effect of jet quenching is incorporated
through medium modified fragmentation functions within the higher-twist
approach. The jet transport parameter that controls medium modification is
proportional to the initial parton density and the coefficient is fixed by the
RHIC data on suppression of large hadron spectra. Data on charged
hadron multiplicity in central collisions
from the ALICE Experiment at the LHC are used to constrain the initial parton
density both for determining the jet transport parameter and the 3+1D ideal
hydrodynamic evolution of the bulk matter that is employed for the calculation
of for neutral pions.Comment: 7 pages in RevTex, 3 figures (some typos corrected
Gamma-Jet Tomography of Quark-Gluon Plasma in High-Energy Nuclear Collisions
Within the next-to-leading order (NLO) perturbative QCD (pQCD) parton model,
suppression of away-side hadron spectra associated with a high photon
due to parton energy loss is shown to provide a complete tomographic picture of
the dense matter formed in high-energy heavy-ion collisions at RHIC. Dictated
by the shape of the -triggered jet spectrum in NLO pQCD, hadron spectra
at large are more susceptible
to parton energy loss and therefore are dominated by surface emission of
-triggered jets, whereas small hadrons mainly come from
fragmentation of jets with reduced energy from volume emission. These lead to
different centrality dependence of the hadron suppression in different regions
of .Comment: 4 pages, 3 figures, proceedings for QM 2009 conferenc
A NLO analysis on fragility of dihadron tomography in high energy collisions
The dihadron spectra in high energy collisions are studied within the
NLO pQCD parton model with jet quenching taken into account. The high
dihadron spectra are found to be contributed not only by jet pairs close and
tangential to the surface of the dense matter but also by punching-through jets
survived at the center while the single hadron high spectra are only
dominated by surface emission. Consequently, the suppression factor of such
high- hadron pairs is found to be more sensitive to the initial gluon
density than the single hadron suppression factor.Comment: 4 pages, 4 figures, proceedings for the 19th international Conference
on ultra-relativistic nucleus-nucleus collisions (QM2006), Shanghai, China,
November 14-20, 200
Regional Variation in Temperature Humidity Index for Poultry Housing
A building thermal model was used to compute hourly values of temperature humidity index (THI) for a broiler house with and without an evaporative misting system. Hourly summer time weather data for 238 U.S.A. locations covering 30 years were used to develop extreme occurrences of THI. Results were incorporated into a Geographical Information System (GIS) database to create isolines of THI and percentage of hours exceeding a heat stress threshold. Regional variations in misting as a suitable cooling technique are presented in terms of hours reduction in annual heat stress. The technique may be used for assisting in management decisions regarding poultry facilities housing design and siting, and with appropriate THI may be extended to other livestock production
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