616 research outputs found
Bayesian Semiparametric Hierarchical Empirical Likelihood Spatial Models
We introduce a general hierarchical Bayesian framework that incorporates a
flexible nonparametric data model specification through the use of empirical
likelihood methodology, which we term semiparametric hierarchical empirical
likelihood (SHEL) models. Although general dependence structures can be readily
accommodated, we focus on spatial modeling, a relatively underdeveloped area in
the empirical likelihood literature. Importantly, the models we develop
naturally accommodate spatial association on irregular lattices and irregularly
spaced point-referenced data. We illustrate our proposed framework by means of
a simulation study and through three real data examples. First, we develop a
spatial Fay-Herriot model in the SHEL framework and apply it to the problem of
small area estimation in the American Community Survey. Next, we illustrate the
SHEL model in the context of areal data (on an irregular lattice) through the
North Carolina sudden infant death syndrome (SIDS) dataset. Finally, we analyze
a point-referenced dataset from the North American Breeding Bird survey that
considers dove counts for the state of Missouri. In all cases, we demonstrate
superior performance of our model, in terms of mean squared prediction error,
over standard parametric analyses.Comment: 29 pages, 3 figue
Eigenvector-Based Centrality Measures for Temporal Networks
Numerous centrality measures have been developed to quantify the importances
of nodes in time-independent networks, and many of them can be expressed as the
leading eigenvector of some matrix. With the increasing availability of network
data that changes in time, it is important to extend such eigenvector-based
centrality measures to time-dependent networks. In this paper, we introduce a
principled generalization of network centrality measures that is valid for any
eigenvector-based centrality. We consider a temporal network with N nodes as a
sequence of T layers that describe the network during different time windows,
and we couple centrality matrices for the layers into a supra-centrality matrix
of size NTxNT whose dominant eigenvector gives the centrality of each node i at
each time t. We refer to this eigenvector and its components as a joint
centrality, as it reflects the importances of both the node i and the time
layer t. We also introduce the concepts of marginal and conditional
centralities, which facilitate the study of centrality trajectories over time.
We find that the strength of coupling between layers is important for
determining multiscale properties of centrality, such as localization phenomena
and the time scale of centrality changes. In the strong-coupling regime, we
derive expressions for time-averaged centralities, which are given by the
zeroth-order terms of a singular perturbation expansion. We also study
first-order terms to obtain first-order-mover scores, which concisely describe
the magnitude of nodes' centrality changes over time. As examples, we apply our
method to three empirical temporal networks: the United States Ph.D. exchange
in mathematics, costarring relationships among top-billed actors during the
Golden Age of Hollywood, and citations of decisions from the United States
Supreme Court.Comment: 38 pages, 7 figures, and 5 table
Prospectus, February 21, 2007
https://spark.parkland.edu/prospectus_2007/1005/thumbnail.jp
Estimating the reproductive number, total outbreak size, and reporting rates for Zika epidemics in South and Central America
As South and Central American countries prepare for increased birth defects
from Zika virus outbreaks and plan for mitigation strategies to minimize
ongoing and future outbreaks, understanding important characteristics of Zika
outbreaks and how they vary across regions is a challenging and important
problem. We developed a mathematical model for the 2015 Zika virus outbreak
dynamics in Colombia, El Salvador, and Suriname. We fit the model to publicly
available data provided by the Pan American Health Organization, using
Approximate Bayesian Computation to estimate parameter distributions and
provide uncertainty quantification. An important model input is the at-risk
susceptible population, which can vary with a number of factors including
climate, elevation, population density, and socio-economic status. We informed
this initial condition using the highest historically reported dengue incidence
modified by the probable dengue reporting rates in the chosen countries. The
model indicated that a country-level analysis was not appropriate for Colombia.
We then estimated the basic reproduction number, or the expected number of new
human infections arising from a single infected human, to range between 4 and 6
for El Salvador and Suriname with a median of 4.3 and 5.3, respectively. We
estimated the reporting rate to be around 16% in El Salvador and 18% in
Suriname with estimated total outbreak sizes of 73,395 and 21,647 people,
respectively. The uncertainty in parameter estimates highlights a need for
research and data collection that will better constrain parameter ranges.Comment: 35 pages, 16 figure
Characterization of a Supersonic Wind Tunnel for the Study of Supersonic Inlet Flow Control
The geometry and the nature of supersonic flow in supersonic mixed compression inlets generate internal shock wave/boundary layer interactions (SWBLIs). Shock waves generated by the inlet cause internal boundary layer disruptions that lead to inlet inefficiencies and possible boundary layer separation. Boundary layer separation is undesirable because it reduces mass flow to the engine and can lead to choking of the inlet or unstart. Current flow control methods are effective in reducing the separation, but are yet to significantly increase the inlet efficiency. Researchers at the Gas Dynamics and Turbulence Laboratory (GDTL) have proposed a new control technique using localized arc-filament plasma actuators (LAFPAs). The LAFPAs are to be tested in a supersonic blow down wind tunnel with a compression ramp shock generator. The characterization of the baseline flow of this facility is vital to researching control of the interaction. Several qualitative and quantitative flow diagnostics were used to characterize this Mach 2.3 flow. The interaction generated in this tunnel was shown to be a separated SWBLI comparable with those studied in literature. It was also found to exhibit the expected low frequency unsteady behavior.Air Force Research Laboratory (Mr. Jon Tinapple and Dr. Jonathan Poggie)Air Force Office of Scientific Research (Dr. John Schmisseur)No embarg
MICROBIAL COMMUNITY FUNCTION IN FRESHWATER WETLAND SOILS: USING EXTRACELLULAR ENZYME ANALYSIS TO STUDY THE EFFECT OF MOISTURE AND VEGETATION
Differences in microbial function via extracellular enzyme activity (EEA) were investigated to determine the potential effects of hydrology and plant-soil-microbe interactions in a young non-tidal freshwater riparian wetland. To study these relationships, three plots were established along a moisture gradient (Wet, Intermediate, Dry) within VCU Rice Center Within each main plot, five subplots were left undisturbed while another five were cleared of all above-ground plant biomass. Homogenized soil cores (top 10 cm) were analyzed for pH, redox, C:N, soil organic matter (SOM) content, saturation, and temperature. Microbial function was assessed using extracellular enzyme analysis. For most enzymes, a site difference was observed due to soil moisture content, which had an effect on soil pH, redox potential, and plant community composition. For most extracellular enzymes the presence of vegetation was associated with higher activity. It is important to note that reestablishing native hydrologic and vegetated conditions are paramount in achieving previous functionality
Equitable allocations in northern fisheries: bridging the divide for Labrador Inuit
© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Kourantidou, M., Hoagland, P., Dale, A., & Bailey, M. Equitable allocations in northern fisheries: bridging the divide for Labrador Inuit. Frontiers in Marine Science, 8, (2021): 590213, https://doi.org/10.3389/fmars.2021.590213.Canada has undertaken commitments to recognize the rights of Indigenous Peoples in fisheries through policies and agreements, including Integrated Fishery Management Plans, the Reconciliation Strategy, and Land Claim Agreements (LCAs). In addition to recognizing rights, these commitments were intended to respect geographic adjacency principles, to enhance the economic viability of Indigenous communities, and to be reflective of community dependence on marine resources. We examined the determinants of quota allocations in commercial fisheries involving Nunatsiavut, Northern Labrador, the first self-governing region for the Inuit peoples in Canada. It has been argued that current fishery allocations for Nunatsiavut Inuit have not satisfied federal commitments to recognize Indigenous rights. Indicators that measure equity in commercial allocations for the turbot or Greenland halibut (Reinhardtius hippoglossoides) and northern shrimp (Pandalus borealis) fisheries were identified and assessed. In these two cases, historical allocations continue to predominate for allocations based upon equity or other social or economic considerations. We illustrate equity-enhancing changes in the quota distribution under scenarios of different levels of inequality aversion, and we make qualitative assessments of the effects of these allocations to Nunatsiavut for socioeconomic welfare. This approach could benefit fisheries governance in Northern Labrador, where federal commitments to equity objectives continue to be endorsed but have not yet been integrated fully into quota allocations.This research was undertaken with funding from the Canada First Research Excellence Fund through the Ocean Frontier Institute (MK and MB) and the Johnson Endowment of the Woods Hole Oceanographic Institution’s (WHOI) Marine Policy Center (PH)
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