18,430 research outputs found
Prediction of infectious disease epidemics via weighted density ensembles
Accurate and reliable predictions of infectious disease dynamics can be
valuable to public health organizations that plan interventions to decrease or
prevent disease transmission. A great variety of models have been developed for
this task, using different model structures, covariates, and targets for
prediction. Experience has shown that the performance of these models varies;
some tend to do better or worse in different seasons or at different points
within a season. Ensemble methods combine multiple models to obtain a single
prediction that leverages the strengths of each model. We considered a range of
ensemble methods that each form a predictive density for a target of interest
as a weighted sum of the predictive densities from component models. In the
simplest case, equal weight is assigned to each component model; in the most
complex case, the weights vary with the region, prediction target, week of the
season when the predictions are made, a measure of component model uncertainty,
and recent observations of disease incidence. We applied these methods to
predict measures of influenza season timing and severity in the United States,
both at the national and regional levels, using three component models. We
trained the models on retrospective predictions from 14 seasons (1997/1998 -
2010/2011) and evaluated each model's prospective, out-of-sample performance in
the five subsequent influenza seasons. In this test phase, the ensemble methods
showed overall performance that was similar to the best of the component
models, but offered more consistent performance across seasons than the
component models. Ensemble methods offer the potential to deliver more reliable
predictions to public health decision makers.Comment: 20 pages, 6 figure
Complex networks in brain electrical activity
We analyze the complex networks associated with brain electrical activity.
Multichannel EEG measurements are first processed to obtain 3D voxel
activations using the tomographic algorithm LORETA. Then, the correlation of
the current intensity activation between voxel pairs is computed to produce a
voxel cross-correlation coefficient matrix. Using several correlation
thresholds, the cross-correlation matrix is then transformed into a network
connectivity matrix and analyzed. To study a specific example, we selected data
from an earlier experiment focusing on the MMN brain wave. The resulting
analysis highlights significant differences between the spatial activations
associated with Standard and Deviant tones, with interesting physiological
implications. When compared to random data networks, physiological networks are
more connected, with longer links and shorter path lengths. Furthermore, as
compared to the Deviant case, Standard data networks are more connected, with
longer links and shorter path lengths--i.e., with a stronger ``small worlds''
character. The comparison between both networks shows that areas known to be
activated in the MMN wave are connected. In particular, the analysis supports
the idea that supra-temporal and inferior frontal data work together in the
processing of the differences between sounds by highlighting an increased
connectivity in the response to a novel sound.Comment: 22 pages, 5 figures. Starlab preprint. This version is an attempt to
include better figures (no content change
Phase Space Reconstruction and Nonlinear Equilibrium Dynamics in the United States Beef Market
This paper investigates dynamic interactions in the US beef market using phase space reconstruction, which has been developed to analyze nonlinear dynamical systems. This approach provides important and unique empirical insights into consumers behavior in the beef market. Our results from a phase space reconstruction analysis demonstrate distinct differences between intertemporal short run impacts from food safety outbreaks (e.g., E. Coli) and longer run health effects (e.g., cholesterol). Adjustments due to factors such as cholesterol are permanent changes and do not affect the manner by which people consume, while consumers react to food safety scares by adjusting consumption for a short period of time and then returning to their normal steady state cycle of consumption.nonlinear time series, phase space reconstruction, food safety, health effects, Livestock Production/Industries, Marketing,
Investigation of the chemical kinetics of an advanced high energy propellant system Quarterly progress report, 1 Jun. - 1 Sep. 1968
Reaction kinetics of high energy oxygen difluoride diborane propellant syste
Can only flavor-nonsinglet H dibaryons be stable against strong decays?
Using the QCD sum rule approach, we show that the flavor-nonsinglet
dibaryon states with J, J, I=1 (27plet) are nearly
degenerate with the J, I=0 singlet dibaryon, which has been
predicted to be stable against strong decay, but has not been observed. Our
calculation, which does not require an instanton correction, suggests that the
is slightly heavier than these flavor-nonsinglet s over a wide range
of the parameter space. If the singlet mass lies above the threshold (2231~MeV), then the strong interaction breakup to would produce a very broad resonance in the
invariant mass spectrum which would be very difficult to observe. On the other
hand, if these flavor-nonsinglet J=0 and 1 dibaryons are also above the
threshold, but below the breakup threshold (2254
MeV), then because the direct, strong interaction decay to the channel is forbidden, these flavor-nonsinglet states might be more
amenable to experimental observation. The present results allow a possible
reconciliation between the reported observation of
hypernuclei, which argue against a stable , and the possible existence of
dibaryons in general.Comment: 10 pages, 2 figure
Maneuver and buffet characteristics of fighter aircraft
Recent research efforts in the improvement of the maneuverability of fighter aircraft in the high-subsonic and transonic speed range are reviewed with emphasis on the factors affecting aerodynamic boundaries, such as maximum obtainable lift, buffet onset, pitchup, wing rock, and nose slice. The investigations were made using a general research configuration which encompassed a systematic matrix of wing-design parameters. These results illustrated the sensitivity of section and planform geometry to a selected design point. The incorporation of variable-geometry wing devices in the form of flaps or leading-edge slats was shown to provide controlled flow over a wide range of flight conditions and substantial improvements in maneuver capabilities. Additional studies indicated that the blending of a highly swept maneuver strake with an efficient, moderately swept wing offers a promising approach for improving maneuver characteristics at high angles of attack without excessive penalties in structural weight
Evaluating epidemic forecasts in an interval format
For practical reasons, many forecasts of case, hospitalization and death
counts in the context of the current COVID-19 pandemic are issued in the form
of central predictive intervals at various levels. This is also the case for
the forecasts collected in the COVID-19 Forecast Hub
(https://covid19forecasthub.org/). Forecast evaluation metrics like the
logarithmic score, which has been applied in several infectious disease
forecasting challenges, are then not available as they require full predictive
distributions. This article provides an overview of how established methods for
the evaluation of quantile and interval forecasts can be applied to epidemic
forecasts in this format. Specifically, we discuss the computation and
interpretation of the weighted interval score, which is a proper score that
approximates the continuous ranked probability score. It can be interpreted as
a generalization of the absolute error to probabilistic forecasts and allows
for a decomposition into a measure of sharpness and penalties for over- and
underprediction
AN INTRASEASONAL BIOECONOMIC MODEL OF PLRV NET NECROSIS
A bioeconomic model is developed as an IPM planning tool to combat PLRV net necrosis in the PNW potato industry. Environmental/biological and production processes are linked to marketing activities using discrete time control. We find that pesticides can be optimally timed to reduce applications and still protect against net necrosis.Crop Production/Industries, Environmental Economics and Policy,
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