14,541 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
Comparison of two cardiac output monitors, qCO and LiDCO, during general anesthesia
Background: Optimization of cardiac output (CO) has been evidenced to reduce postoperative complications and to expedite the recovery. Likewise, CO and other dynamic cardiac parameters can describe the systemic blood flow and tissue oxygenation state and can be useful in different clinical fields. This study aimed to validate the qCO monitor (Quantium Medical, Barcelona, Spain), a new device to estimate CO and other related parameters in a continuous, fully non-invasive way using advanced digital signal processing of impedance cardiography.
Methods: The LiDCOrapidv2 (LiDCO Ltd, London, UK) was used to compare the performance of the qCO in 15 patients during major surgery under general anesthesia. Full surgeries were recorded and cardiac output obtained by both devices was compared by using correlation and Bland-Altman analysis.
Results: The Bland-Altman analysis showed sufficient agreement with a mean bias of -0.03 ± 0.71 L/min.
Conclusions: The findings showed that both systems offered comparable values and thus the non-invasive measurement of CO with qCO is a promising, feasible method. Further investigation will be required to validate this new device against calibrated devices and outcome studies would also be highly recommended.Postprint (author's final draft
Zipf's Law and Avoidance of Excessive Synonymy
Zipf's law states that if words of language are ranked in the order of
decreasing frequency in texts, the frequency of a word is inversely
proportional to its rank. It is very robust as an experimental observation, but
to date it escaped satisfactory theoretical explanation. We suggest that Zipf's
law may arise from the evolution of word semantics dominated by expansion of
meanings and competition of synonyms.Comment: 47 pages; fixed reference list missing in v.
Boundary Effects in 2+1 Dimensional Maxwell-Chern-Simons Theory
The boundary effects in the screening of an applied magnetic field in a
finite temperature 2+1 dimensional model of charged fermions minimally coupled
to Maxwell and Chern-Simons fields are investigated. It is found that in a
sample with only one boundary -a half-plane- a total Meissner effect takes
place, while in a sample with two boundaries -an infinite strip- the external
magnetic field partially penetrates the material.Comment: revte
Fuel Modelling Characterisation Using Low-Density LiDAR in the Mediterranean: An Application to a Natural Protected Area
Fuel structure and characteristics are important to better understand and predict wildfire behaviour. The aim of the present study was to develop a methodology for characterising fuel models using low-density and free LiDAR data that facilitate the work of managers of protected territories. Field inventories were carried out in order to understand the characteristics of the stand and the variables that fuel models must include. This information, together with the use of the intensity and structure provided by LiDAR, was used to perform statistical analyses. The linear regressions obtained to characterise the stand of the mixed Quercus spp.âPinus ssp.-dominated stand had an R2 value ranging from 0.4393 to 0.66. While working with low-density LiDAR data (which has more difficulties crossing the canopy), in addition to the obtained results, we performed the statistical analysis of the dominant stand to obtain models with R2 values ranging from 0.8201 to 0.8677. The results of this research show that low-density LiDAR data are significant; however, in mixed stands, it is necessary to only use the dominant stratum because other components generate noise, which reduces the predictive capacity of the models. Additionally, by using the decision tree developed in combination, it is possible to update the mapping of fuel models in inaccessible areas, thereby significantly reducing costs
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
We study the metal-insulator transition in individual self-assembled quantum
wires and report optical evidences of metallic liquid condensation at low
temperatures. Firstly, we observe that the temperature and power dependence of
the single nanowire photoluminescence follow the evolution expected for an
electron-hole liquid in one dimension. Secondly, we find novel spectral
features that suggest that in this situation the expanding liquid condensate
compresses the exciton gas in real space. Finally, we estimate the critical
density and critical temperature of the phase transition diagram at
cm and K, respectively.Comment: 4 pages, 5 figure
Beyond-Constant-Mass-Approximation Magnetic Catalysis in the Gauge Higgs-Yukawa Model
Beyond-constant-mass approximation solutions for magnetically catalyzed
fermion and scalar masses are found in a gauge Higgs-Yukawa theory in the
presence of a constant magnetic field. The obtained fermion masses are several
orders of magnitude larger than those found in the absence of Yukawa
interactions. The masses obtained within the beyond-constant-mass approximation
exactly reduce to the results within the constant-mass approach when the
condition is satisfied. Possible
applications to early universe physics and condensed matter are discussed.Comment: Revised numerical results. New figures. Several sections rewritte
Performance of the Micromegas detector in the CAST experiment
The gaseous Micromegas detector designed for the CERN Axion search experiment
CAST, operated smoothly during Phase-I, which included the 2003 and 2004
running periods. It exhibited linear response in the energy range of interest
(1-10keV), good spatial sensitivity and energy resolution (15-19% FWHM at
5.9keV)as well as remarkable stability. The detector's upgrade for the 2004
run, supported by the development of advanced offline analysis tools, improved
the background rejection capability, leading to an average rate 5x10^-5
counts/sec/cm^2/keV with 94% cut efficiency. Also, the origin of the detected
background was studied with a Monte Carlo simulation, using the GEANT4 package.Comment: Prepared for PSD7: The Seventh International Conference on Position
Sensitive Detectors, Liverpool, United Kingdom, 12-16 Sep. 200
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