21,606 research outputs found
Novel characterization method of impedance cardiography signals using time-frequency distributions
The purpose of this document is to describe a methodology to select the most adequate time-frequency distribution (TFD) kernel for the characterization of impedance cardiography signals (ICG). The predominant ICG beat was extracted from a patient and was synthetized using time-frequency variant Fourier approximations. These synthetized signals were used to optimize several TFD kernels according to a performance maximization. The optimized kernels were tested for noise resistance on a clinical database. The resulting optimized TFD kernels are presented with their performance calculated using newly proposed methods. The procedure explained in this work showcases a new method to select an appropriate kernel for ICG signals and compares the performance of different time-frequency kernels found in the literature for the case of ICG signals. We conclude that, for ICG signals, the performance (P) of the spectrogram with either Hanning or Hamming windows (PÂż=Âż0.780) and the extended modified beta distribution (PÂż=Âż0.765) provided similar results, higher than the rest of analyzed kernels.Peer ReviewedPostprint (published version
Detection of Coherent Vorticity Structures using Time-Scale Resolved Acoustic Spectroscopy
We describe here an experimental technique based on the acoustic scattering
phenomenon allowing the direct probing of the vorticity field in a turbulent
flow. Using time-frequency distributions, recently introduced in signal
analysis theory, for the analysis of the scattered acoustic signals, we show
how the legibility of these signals is significantly improved (time resolved
spectroscopy). The method is illustrated on data extracted from a highly
turbulent jet flow : discrete vorticity events are clearly evidenced. We claim
that the recourse to time-frequency distributions lead to an operational
definition of coherent structures associated with phase stationarity in the
time-frequency plane.Comment: 26 pages, 6 figures. Latex2e format Revised version : Added
references, figures and Changed conten
Double hard scattering without double counting
Double parton scattering in proton-proton collisions includes kinematic
regions in which two partons inside a proton originate from the perturbative
splitting of a single parton. This leads to a double counting problem between
single and double hard scattering. We present a solution to this problem, which
allows for the definition of double parton distributions as operator matrix
elements in a proton, and which can be used at higher orders in perturbation
theory. We show how the evaluation of double hard scattering in this framework
can provide a rough estimate for the size of the higher-order contributions to
single hard scattering that are affected by double counting. In a numeric
study, we identify situations in which these higher-order contributions must be
explicitly calculated and included if one wants to attain an accuracy at which
double hard scattering becomes relevant, and other situations where such
contributions may be neglected.Comment: 80 pages, 20 figures. v2: clarifications in section 4, extended
section 8, small changes elsewher
PHOTOS Monte Carlo: a precision tool for QED corrections in Z and W decays
We present a discussion of the precision for the PHOTOS Monte Carlo
algorithm, with improved implementation of QED interference and multiple-photon
radiation. The main application of PHOTOS is the generation of QED radiative
corrections in decays of any resonances, simulated by a "host" Monte Carlo
generator. By careful comparisons automated with the help of the MC-TESTER tool
specially tailored for that purpose, we found that the precision of the current
version of PHOTOS is of 0.1% in the case of Z and W decays. In the general
case, the precision of PHOTOS was also improved, but this will not be
quantified here.Comment: Version 2: -Figure 8a replaced by link to hep-ph/040600
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Study on Actuator Line Modeling of Two NREL 5-MW Wind Turbine Wakes
The wind turbine wakes impact the efficiency and lifespan of the wind farm. Therefore, to improve the wind plant performance, research on wind plant control is essential. The actuator line model (ALM) is proposed to simulate the wind turbine efficiently. This research investigates the National Renewable Energy Laboratory 5 Million Watts (NREL 5-MW) wind turbine wakes with Open Field Operation and Manipulation (OpenFOAM) using ALM. Firstly, a single NREL 5-MW turbine is simulated. The comparison of the power and thrust with Fatigue, Aerodynamics, Structures, and Turbulence (FAST) shows a good agreement below the rated wind speed. The information relating to wind turbine wakes is given in detail. The top working status is proved at the wind speed of 8 m/s and the downstream distance of more than 5 rotor diameters (5D). Secondly, another case with two NREL 5-MW wind turbines aligned is also carried out, in which 7D is validated as the optimum distance between the two turbines. The result also shows that the upstream wind turbine has an obvious influence on the downstream one
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