7,217 research outputs found
High Pressure X-Ray Diffraction Study of UMn2Ge2
Uranium manganese germanide, UMn2Ge2, crystallizes in body-centered
tetragonal ThCr2Si2 structure with space group I4/mmm, a = 3.993A and c =
10.809A under ambient conditions. Energy dispersive X-ray diffraction was used
to study the compression behaviour of UMn2Ge2 in a diamond anvil cell. The
sample was studied up to static pressure of 26 GPa and a reversible structural
phase transition was observed at a pressure of ~ 16.1 GPa. Unit cell parameters
were determined up to 12.4 GPa and the calculated cell volumes were found to be
well reproduced by a Murnaghan equation of state with K0 = 73.5 GPa and K' =
11.4. The structure of the high pressure phase above 16.0 GPa is quite
complicated with very broad lines and could not be unambiguously determined
with the available instrument resolution
Instantaneous frequency and amplitude of complex signals based on quaternion Fourier transform
The ideas of instantaneous amplitude and phase are well understood for
signals with real-valued samples, based on the analytic signal which is a
complex signal with one-sided Fourier transform. We extend these ideas to
signals with complex-valued samples, using a quaternion-valued equivalent of
the analytic signal obtained from a one-sided quaternion Fourier transform
which we refer to as the hypercomplex representation of the complex signal. We
present the necessary properties of the quaternion Fourier transform,
particularly its symmetries in the frequency domain and formulae for
convolution and the quaternion Fourier transform of the Hilbert transform. The
hypercomplex representation may be interpreted as an ordered pair of complex
signals or as a quaternion signal. We discuss its derivation and properties and
show that its quaternion Fourier transform is one-sided. It is shown how to
derive from the hypercomplex representation a complex envelope and a phase.
A classical result in the case of real signals is that an amplitude modulated
signal may be analysed into its envelope and carrier using the analytic signal
provided that the modulating signal has frequency content not overlapping with
that of the carrier. We show that this idea extends to the complex case,
provided that the complex signal modulates an orthonormal complex exponential.
Orthonormal complex modulation can be represented mathematically by a polar
representation of quaternions previously derived by the authors. As in the
classical case, there is a restriction of non-overlapping frequency content
between the modulating complex signal and the orthonormal complex exponential.
We show that, under these conditions, modulation in the time domain is
equivalent to a frequency shift in the quaternion Fourier domain. Examples are
presented to demonstrate these concepts
Analytic Metaphysics versus Naturalized Metaphysics: The Relevance of Applied Ontology
The relevance of analytic metaphysics has come under criticism: Ladyman & Ross, for instance, have suggested do discontinue the field. French & McKenzie have argued in defense of analytic metaphysics that it develops tools that could turn out to be useful for philosophy of physics. In this article, we show first that this heuristic defense of metaphysics can be extended to the scientific field of applied ontology, which uses constructs from analytic metaphysics. Second, we elaborate on a parallel by French & McKenzie between mathematics and metaphysics to show that the whole field of analytic metaphysics, being useful not only for philosophy but also for science, should continue to exist as a largely autonomous field
Size distribution of fine particles in stack emissions of a 600-MWe coal-fired power plant
International audienceMonitoring emissions of particles with a diameter smaller than 10 µm (PM10) has become of growing interest. However, measuring such particles is rather difficult. It appears as a result necessary to develop and assess measurement methods for the monitoring of PM10 from stack and fugitive emissions. The aim of the GAEC program [Granulométrie des Aérosols dans les Emissions Canalisées: Aerosol size distribution from stack emissions] is double: to develop monitoring methods and improve knowledge on fine particulate stack emissions. Three institutes were involved in the program: Séchaud Environnement (formerly LECES), INERIS and CERTAM. This paper presents the mains results of the evaluation of a cascade impactor (Johnas), aerosol size distribution measurement techniques (ELPI Dekati, FPS, SMPS TSI) applied on size characterization of fine particulate matter in stack emissions of a 600-MWe coal-fired power plant
Estimation of Fiber Orientations Using Neighborhood Information
Data from diffusion magnetic resonance imaging (dMRI) can be used to
reconstruct fiber tracts, for example, in muscle and white matter. Estimation
of fiber orientations (FOs) is a crucial step in the reconstruction process and
these estimates can be corrupted by noise. In this paper, a new method called
Fiber Orientation Reconstruction using Neighborhood Information (FORNI) is
described and shown to reduce the effects of noise and improve FO estimation
performance by incorporating spatial consistency. FORNI uses a fixed tensor
basis to model the diffusion weighted signals, which has the advantage of
providing an explicit relationship between the basis vectors and the FOs. FO
spatial coherence is encouraged using weighted l1-norm regularization terms,
which contain the interaction of directional information between neighbor
voxels. Data fidelity is encouraged using a squared error between the observed
and reconstructed diffusion weighted signals. After appropriate weighting of
these competing objectives, the resulting objective function is minimized using
a block coordinate descent algorithm, and a straightforward parallelization
strategy is used to speed up processing. Experiments were performed on a
digital crossing phantom, ex vivo tongue dMRI data, and in vivo brain dMRI data
for both qualitative and quantitative evaluation. The results demonstrate that
FORNI improves the quality of FO estimation over other state of the art
algorithms.Comment: Journal paper accepted in Medical Image Analysis. 35 pages and 16
figure
Prostate Diffusion Weighted-Magnetic Resonance Image analysis using Multivariate Curve Resolution methods
[EN] Multivariate Curve Resolution (MCR) has been applied on prostate Diffusion Weighted-Magnetic Resonance Images (DW-MRI). Different physiological-based modeling approaches of the diffusion process have been submitted to validation by sequentially incorporating prior knowledge on the MCR constraints. Results validate the biexponential diffusion modeling approach and show the capability of the MCR models to find, characterize and locate the behaviors related to the presence of an early prostate tumor.The authors want to thank prof. Anna de Juan for her comments and help in using the software for this study. This research work was partially supported by the Spanish Ministry of Economy and Competitiveness under the project DPI 2011-28112-004-02.Aguado Sarrió, E.; Prats-Montalbán, JM.; Sanz Requena, R.; Marti Bonmati, L.; Alberich Bayarri, Á.; Ferrer Riquelme, AJ. (2015). Prostate Diffusion Weighted-Magnetic Resonance Image analysis using Multivariate Curve Resolution methods. Chemometrics and Intelligent Laboratory Systems. 140:43-48. https://doi.org/10.1016/j.chemolab.2014.11.002S434814
UWB Vivaldi Antenna Array Lower Band Improvement for Ground Penetrating Radar Applications
This paper concerns a ground penetrating radar system (GPR) presenting beam forming ability. This ability is due to a great flexibility in the emission of wavefronts. The innovative concept is to use an array of antennas which can reconfigure itself dynamically, in order to focus on a desired target. This antennas system can act as a new microwave sensor to detect and characterize buried targets in an inhomogeneous medium which is the case study in various application fields such as geophysics, medical, planetology… Its electronics are in development with the DORT (Time reversal technique) method integration for optimizing the localization of buried target. This paper aims are to present the antenna optimization used in the GPR applications. Typical antennas used in GPR are generally Vivaldi ones directly on the ground. Especially, in the context of the space mission ExoMars 2020, the radar antenna is set on a mobile station at a distance of about 30 cm from the ground to avoid any contact. However, they are limited by their important size, due to the lowest frequency of their bandwidth. Results of this work concern an increase of the antenna bandwidth by shifting the lower-band limit, making it a UWB type [500 MHz - 4 GHz] without changing its size. As low frequency waves can spread deeper into probed medium, this optimization can improve the radar data inversion performances
Preoperative left ventricular ejection fraction and left atrium reverse remodeling after mitral regurgitation surgery
Background: Left atrium enlargement has been associated with cardiac events in patients with mitral regurgitation (MR). Left atrium reverse remodeling (LARR) occur after surgical correction of MR, but the preoperative predictors of this phenomenon are not well known. It is therefore important to identify preoperative predictors for postoperative LARR.Methods: We enrolled 62 patients with chronic severe MR (prolapse or flail leaflet) who underwent successful mitral valve surgery (repair or replacement); all with pre-and postoperative echocardiography. LARR was defined as a reduction in left atrium volume index (LAVI) of >= 25%. Stepwise multiple regression analysis was used to identify independent predictors of LARR.Results: LARR occurred in 46 patients (74.2%), with the mean LAVI decreasing from 85.5 mL/m(2) to 49.7 mL/m(2) (p = 25% with a sensitivity of 71.7% and a specificity of 56.3%.Conclusions: LARR occurs frequently after mitral valve surgery and is associated with preoperative LVEF higher than 63.5%.Inst Dante Pazzanese Cardiol, São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, São Paulo, BrazilDisciplina Cardiol, BR-04024002 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, São Paulo, BrazilWeb of Scienc
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