2,791 research outputs found
Improving Wildflower Longevity in Roadside Seeding Areas
Re-vegetation efforts on bare roadsides of newly-constructed highways are primarily focused on the stabilization of soil to reduce rates of erosion. The Nebraska Department of Transportation (NDOT) seeds roadsides with a diverse mixture of grasses and wildflowers for site stabilization as well as to enhance the visual quality of roadsides. Although grasses dominate roadside plantings in terms of cover and density, wildflowers are largely responsible for the visual enhancement of recently-seeded roadsides. In addition to the visual component, wildflowers provide essential ecological functions on roadsides. Wildflowers improve water and nutrient cycling in the compacted roadside soils by increasing water infiltration and nutrient availability. Leguminous wildflower species increase nitrogen content of soil. The variability of wildflower leaf size, shape and orientation provides a more continuous soil cover than grass alone. The diversity of wildflower growth habits and life cycles also allows for a greater range of stand establishment and persistence when compared to sites seeded to grasses alone. This article presents strategies for increasing wildflower success in roadside plantings
Next-to-leading order QCD calculations with parton showers II: soft singularities
Programs that calculate observables in quantum chromodynamics at
next-to-leading order typically generate events that consist of partons rather
than hadrons -- and just a few partons at that. These programs would be much
more useful if the few partons were turned into parton showers, which could be
given to one of the Monte Carlo event generators to produce hadron showers. In
a previous paper, we have seen how to generate parton showers related to the
final state collinear singularities of the perturbative calculation for the
example of e+ + e- --> 3 jets. This paper discusses the treatment of the soft
singularities.Comment: 26 pages with 5 figures. This version is close to the version to be
publishe
Estimates of T-odd distribution and fragmentation functions
Estimates of the T-odd fragmentation and distribution functions,
and , are presented. Our evaluations are based on a fit on
experimental data of polarized proton-proton scattering. We use our estimates
to make predictions for electron polarized-proton azimuthal asymmetries.Comment: Contribution to the Proceedings of the 7th International Workshop on
Deep Inelastic Scattering and QCD, DIS99, DESY-Zeuthen, April 1999; Nucl.
Phys. B (Proc. Suppl.
PLANT COMMUNITY COMPOSITION, FLORISTIC QUALITY, AND ESTABLISHMENT OF ROADSIDE REVEGETATION IN NEBRASKA, USA.
Roadside revegetation poses a challenge and opportunity for biodiversity conservation, as the land area occupied by roadsides is not expected to decline in the future. In the context of roadside revegetation activities in rural regions dominated by agricultural land uses, revegetation efforts can establish plant communities that offer unique species that would otherwise be absent on the landscape. To determine the efficacy of roadside revegetation efforts in 1) providing plant communities of high biodiversity value and 2) meeting the expectations of roadside revegetation managers for establishment, we quantified botanical composition, floristic quality, and success in seeding efforts to meet manager expectations. We evaluate the outcome of roadside revegetation conducted by Nebraska Department of Transportation for five regions across Nebraska, USA: Loess hills and Glacial drift sites within the tallgrass prairie region, central Loess plains region, Sandhills region, and High Plains Panhandle region. Hereafter, we refer to these geographical areas as Northeast, Southeast, Central, Sandhills, and Panhandle regions, respectively. We found species richness and biodiversity of roadsides was greatest in the western regions of Nebraska. Biomass production on roadsides declined on an east to west gradient, but the component species responsible for this gradient were unique to each region. Manager expectations for established plant communities along roadsides were met at five of our 10 study sites, where significant correlations between managers’ expected communities and actual plant communities were observed. Our assessment occurred on average 13.2 years (range: 10-17) post-revegetation, thus, providing insight into what established roadside vegetation communities can be expected after a decade or more.
Advisor: Walter H. Schach
Vibrational Features of Water at the Low-Density/High-Density Liquid Structural Transformations
A structural transformation in water upon compression was recently observed
at the temperature ~K in the vicinity of the pressure ~Atm [R.M. Khusnutdinoff, A.V. Mokshin, J. Non-Cryst. Solids
\textbf{357}, 1677 (2011)]. It was found that the transformations are related
with the principal structural changes within the first two coordination shells
as well as the deformation of the hydrogen-bond network. In this work we study
in details the influence of these structural transformations on the vibrational
molecular dynamics of water by means of molecular dynamics simulations on the
basis of the model Amoeba potential (~K, ~Atm). The
equation of state and the isothermal compressibility are found for the
considered (,)-range. The vibrational density of states extracted for
-frequency range manifests the two distinct modes, where the
high-frequency mode is independent on pressure whereas the low-frequency one
has the strong, non-monotonic pressure-dependence and exhibits a step-like
behavior at the pressure ~Atm. The extended analysis of the
local structural and vibrational properties discovers that there is a strong
correlation between the primary structural and vibrational aspects of the
liquid-liquid structural transformation related with the molecular
rearrangement within the range of the second coordination shell.Comment: Accepted to Physica A: Statistical Mechanics and its Application
Modeling the Dynamics of Compromised Networks
Accurate predictive models of compromised networks would contribute greatly to improving the effectiveness and efficiency of the detection and control of network attacks. Compartmental epidemiological models have been applied to modeling attack vectors such as viruses and worms. We extend the application of these models to capture a wider class of dynamics applicable to cyber security. By making basic assumptions regarding network topology we use multi-group epidemiological models and reaction rate kinetics to model the stochastic evolution of a compromised network. The Gillespie Algorithm is used to run simulations under a worst case scenario in which the intruder follows the basic connection rates of network traffic as a method of obfuscation
X-ray Diffraction and Molecular Dynamics Study of Medium-range Order in Ambient and Hot Water
We have developed x-ray diffraction measurements with high energy-resolution
and accuracy to study water structure at three different temperatures (7, 25
and 66 C) under normal pressure. Using a spherically curved Ge crystal an
energy resolution better than 15 eV has been achieved which eliminates
influence from Compton scattering. The high quality of the data allows a
precise oxygen-oxygen pair correlation function (PCF) to be directly derived
from the Fourier transform of the experimental data resolving shell structure
out to ~12 {\AA}, i.e. 5 hydration shells. Large-scale molecular dynamics (MD)
simulations using the TIP4P/2005 force-field reproduce excellently the
experimental shell-structure in the range 4-12 {\AA} although less agreement is
seen for the first peak in the PCF. The Local Structure Index [J. Chem. Phys.
104, 7671 (1996)] identifies a tetrahedral minority giving the
intermediate-range oscillations in the PCF and a disordered majority providing
a more featureless background in this range. The current study supports the
proposal that the structure of liquid water, even at high temperatures, can be
described in terms of a two-state fluctuation model involving local structures
related to the high-density and low-density forms of liquid water postulated in
the liquid-liquid phase transition hypothesis.Comment: Submitted to Phys. Chem. Chem. Phy
Diversity of Diet Composition Decreases with Conjoint Grazing of Cattle with Sheep and Goats
Conjoint or mixed grazing can affect the diet selected by each species (Nicol & Collins, 1990). Diet similarity coefficients are often used to compare pairs of diets (Krebs, 1999). However this approach is awkward when a number of contrasts are required in a multifactorial comparison. Species diversity is a descriptor of a particular environment. Many models provide an estimate of species diversity, the most common of these being a log-normal distribution (Tokeshi, 1996). We tested whether this model could be applied to dietary components selected from a pasture, and thus provide a coefficient of dietary diversity for the individual diets of cattle, sheep and goats when grazed alone or in mixtures, which could then be statistically compared
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