214 research outputs found
Water scarcity and managing seasonal water crisis: lessons from the Kirindi Oya Project in Sri Lanka
Irrigation management / Water management / Irrigation programs / Irrigated farming / Rain / Crop production / Crop yield / Rice / Case studies / River basins / Catchment areas / Irrigation scheduling / Water allocation / Water use efficiency / Water scarcity / Water shortage / Water demand / Reservoirs / Flow / Farmer participation / Farmer-agency interactions / Farmers' associations / Seasonal variation / Water distribution / Sri Lanka / Kirindi Oya / Ellegala / Lunugamwehera Reservoir
Water productivity in Zhanghe Irrigation System: issues of scale
Irrigation systemsWater productivityReservoirsWater useWater stressWater conservationRicePaddy fieldsCrop yield
Karhunen-Loeve representation of stochastic ocean waves
A new stochastic representation of a seastate is developed based on the Karhunen–Loeve spectral decomposition of stochastic signals and the use of Slepian prolate spheroidal wave functions with a tunable bandwidth parameter. The new representation allows the description of stochastic ocean waves in terms of a few independent sources of uncertainty when the traditional representation of a seastate in terms of Fourier series requires an order of magnitude more independent components. The new representation leads to parsimonious stochastic models of the ambient wave kinematics and of the nonlinear loads and responses of ships and offshore platforms. The use of the new representation is discussed for the derivation of critical wave episodes, the derivation of up-crossing rates of nonlinear loads and responses and the joint stochastic representation of correlated wave and wind profiles for use in the design of fixed or floating offshore wind turbines. The forecasting is also discussed of wave elevation records and vessel responses for use in energy yield enhancement of compliant floating wind turbines.ALSTOM (Firm)Ente nazionale per l'energia elettricab_TE
Spectral Analysis of Multi-dimensional Self-similar Markov Processes
In this paper we consider a discrete scale invariant (DSI) process with scale . We consider to have some fix number of
observations in every scale, say , and to get our samples at discrete points
where is obtained by the equality
and . So we provide a discrete time scale
invariant (DT-SI) process with parameter space . We find the spectral representation of the covariance function of
such DT-SI process. By providing harmonic like representation of
multi-dimensional self-similar processes, spectral density function of them are
presented. We assume that the process is also Markov
in the wide sense and provide a discrete time scale invariant Markov (DT-SIM)
process with the above scheme of sampling. We present an example of DT-SIM
process, simple Brownian motion, by the above sampling scheme and verify our
results. Finally we find the spectral density matrix of such DT-SIM process and
show that its associated -dimensional self-similar Markov process is fully
specified by where is
the covariance function of th and th observations of the process.Comment: 16 page
Endoscopic colorectal cancer screening: a cost-saving analysis
BACKGROUND: Comprehensive analyses have shown that screening for cancer
usually induces net costs. In this study, the possible costs and savings
of endoscopic colorectal cancer screening are explored to investigate
whether the induced savings may compensate for the costs of screening.
METHODS: A simulation model for evaluation of colorectal cancer screening,
MISCAN-COLON, is used to predict costs and savings for the U.S.
population, assuming that screening is performed during a period of 30
years. Plausible baseline parameter values of epidemiology, natural
history, screening test characteristics, and unit costs are based on
available data and expert opinion. Important parameters are varied to
extreme but plausible values. RESULTS: Given the expert opinion-based
assumptions, a program based on every 5-year sigmoidoscopy screenings
could result in a net savings of direct health care costs due to
prevention of cancer treatment costs that compensate for the costs of
screening, diagnostic follow-up, and surveillance. This result persists
when costs and health effects are discounted at 3%. The "break-even"
point, the time required before savings exceed costs, is 35 years for a
screening program that terminates after 30 years and 44 years for a
screening program that continues on indefinitely. However, net savings
increase or turn into net costs when alternative assumptions about natural
history of colorectal cancer, costs of screening, surveillance, and
diagnostics are considered. CONCLUSIONS: Given the present, limited
knowledge of the disease process of colorectal cancer, test
characteristics, and costs, it may well be that the induced savings by
endoscopic colorectal cancer screening completely compensate for the
costs
Model Reduction in Flexible-Aircraft Dynamics with Large Rigid-Body Motion
This paper investigates the model reduction, using balanced realizations, of the unsteady aerodynamics of maneuvering flexible aircraft. The aeroelastic response of the vehicle, which may be subject to large wing deformations at trimmed flight, is captured by coupling a displacement-based, flexible-body dynamics formulation with an aerodynamic model based on the unsteady vortex lattice method. Consistent linearization of the aeroelastic problem allows the projection of the structural degrees of freedom on a few vibration modes of the unconstrained vehicle, but preserves all couplings between the rigid and elastic motions and permits the vehicle fiight dynamics to have arbitrarily-large angular velocities. The high-order aerodynamic system, which defines the mapping between the small number of generalized coordinates and unsteady aerodynamic loads, is then reduced using the balanced truncation method. Numerical studies on a representative high-altitude, long-endurance aircraft show a very substantial reduction in model size, by up to three orders of magnitude, that leads to model orders (and computational cost) similar to those in conventional frequency-based methods but with higher modeling fidelity to compute maneuver loads. Closed-loop results for the Goland wing finally demonstrate the application of this approach in the synthesis of a robust flutter suppression controller. © 2013 by Henrik Hesse and Rafael Palacios
PCA-based lung motion model
Organ motion induced by respiration may cause clinically significant
targeting errors and greatly degrade the effectiveness of conformal
radiotherapy. It is therefore crucial to be able to model respiratory motion
accurately. A recently proposed lung motion model based on principal component
analysis (PCA) has been shown to be promising on a few patients. However, there
is still a need to understand the underlying reason why it works. In this
paper, we present a much deeper and detailed analysis of the PCA-based lung
motion model. We provide the theoretical justification of the effectiveness of
PCA in modeling lung motion. We also prove that under certain conditions, the
PCA motion model is equivalent to 5D motion model, which is based on physiology
and anatomy of the lung. The modeling power of PCA model was tested on clinical
data and the average 3D error was found to be below 1 mm.Comment: 4 pages, 1 figure. submitted to International Conference on the use
of Computers in Radiation Therapy 201
Precision measurements of the top quark mass from the Tevatron in the pre-LHC era
The top quark is the heaviest of the six quarks of the Standard Model.
Precise knowledge of its mass is important for imposing constraints on a number
of physics processes, including interactions of the as yet unobserved Higgs
boson. The Higgs boson is the only missing particle of the Standard Model,
central to the electroweak symmetry breaking mechanism and generation of
particle masses. In this Review, experimental measurements of the top quark
mass accomplished at the Tevatron, a proton-antiproton collider located at the
Fermi National Accelerator Laboratory, are described. Topologies of top quark
events and methods used to separate signal events from background sources are
discussed. Data analysis techniques used to extract information about the top
mass value are reviewed. The combination of several most precise measurements
performed with the two Tevatron particle detectors, CDF and \D0, yields a value
of \Mt = 173.2 \pm 0.9 GeV/.Comment: This version contains the most up-to-date top quark mass averag
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