1,182 research outputs found
Reconstructing Galaxy Spectral Energy Distributions from Broadband Photometry
We present a novel approach to photometric redshifts, one that merges the
advantages of both the template fitting and empirical fitting algorithms,
without any of their disadvantages. This technique derives a set of templates,
describing the spectral energy distributions of galaxies, from a catalog with
both multicolor photometry and spectroscopic redshifts. The algorithm is
essentially using the shapes of the templates as the fitting parameters. From
simulated multicolor data we show that for a small training set of galaxies we
can reconstruct robustly the underlying spectral energy distributions even in
the presence of substantial errors in the photometric observations. We apply
these techniques to the multicolor and spectroscopic observations of the Hubble
Deep Field building a set of template spectra that reproduced the observed
galaxy colors to better than 10%. Finally we demonstrate that these improved
spectral energy distributions lead to a photometric-redshift relation for the
Hubble Deep Field that is more accurate than standard template-based
approaches.Comment: 23 pages, 8 figures, LaTeX AASTeX, accepted for publication in A
Determining the Spectral Signature of Spatial Coherent Structures
We applied to an open flow a proper orthogonal decomposition (pod) technique,
on 2D snapshots of the instantaneous velocity field, to reveal the spatial
coherent structures responsible of the self-sustained oscillations observed in
the spectral distribution of time series. We applied the technique to 2D planes
out of 3D direct numerical simulations on an open cavity flow. The process can
easily be implemented on usual personal computers, and might bring deep
insights on the relation between spatial events and temporal signature in (both
numerical or experimental) open flows.Comment: 4 page
An extension of Wiener integration with the use of operator theory
With the use of tensor product of Hilbert space, and a diagonalization
procedure from operator theory, we derive an approximation formula for a
general class of stochastic integrals. Further we establish a generalized
Fourier expansion for these stochastic integrals. In our extension, we
circumvent some of the limitations of the more widely used stochastic integral
due to Wiener and Ito, i.e., stochastic integration with respect to Brownian
motion. Finally we discuss the connection between the two approaches, as well
as a priori estimates and applications.Comment: 13 page
Bridging Proper Orthogonal Decomposition methods and augmented Newton-Krylov algorithms: an adaptive model order reduction for highly nonlinear mechanical problems
This article describes a bridge between POD-based model order reduction
techniques and the classical Newton/Krylov solvers. This bridge is used to
derive an efficient algorithm to correct, "on-the-fly", the reduced order
modelling of highly nonlinear problems undergoing strong topological changes.
Damage initiation problems are addressed and tackle via a corrected
hyperreduction method. It is shown that the relevancy of reduced order model
can be significantly improved with reasonable additional costs when using this
algorithm, even when strong topological changes are involved
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
Entropy Encoding, Hilbert Space and Karhunen-Loeve Transforms
By introducing Hilbert space and operators, we show how probabilities,
approximations and entropy encoding from signal and image processing allow
precise formulas and quantitative estimates. Our main results yield orthogonal
bases which optimize distinct measures of data encoding.Comment: 25 pages, 1 figur
Coronary revascularisation in stable patients after an acute coronary syndrome: a propensity analysis of early invasive versus conservative management in a register-based cohort study
OBJECTIVES: To compare the effectiveness of in-hospital medical therapy versus coronary revascularisation added to medical therapy in patients who stabilised after an acute coronary syndrome (ACS).
DESIGN: Propensity score-matched cohort study from the database of the Tampere ACS registry.
SETTING: A single academic hospital in Finland.
PARTICIPANTS: 1149 patients with a recent ACS, but no serious coexisting conditions: recurrent ischaemic episodes despite adequate medical therapy, haemodynamic instability, overt congestive heart failure and serious ventricular arrhythmias. PRIMARY AND SECONDARY OUTCOME MEASURES: The composite endpoint of major acute cardiovascular events (MACEs): unstable angina requiring rehospitalisation, stroke, myocardial infarction and all-cause mortality, at 6-month follow-up.
RESULTS: Compared with standard medical treatment, revascularisation was associated with a lower rate of MACEs at 6 months in patients of the first quintile (HR 0.81; 95% CI 0.66 to 0.99), but a higher rate of MACEs in the fifth quintile (HR 4.74, CI 1.36 to 16.49; p=0.014). There were no significant differences in the rates of MACEs in the remaining three quintiles. Patients of the first quintile were the oldest (79.7\ub18.3 years) and had a more significant (p<0.001) history of prior myocardial infarction (37%) and poor renal function (creatine, \ub5mol/l: 114.9\ub170.7). They also showed the highest C reactive protein (7.3\ub19.5 mg/l) levels.
CONCLUSIONS: Our findings suggest that in-hospital coronary revascularisation did not lead to any advantage with signal of possible harm in the great majority of patients who stabilised after an ACS. An early invasive management strategy may be best reserved for elderly patients having high-risk clinical features and biochemical evidence of a strong inflammatory activity
Medico-legal autopsy in postoperative hemodynamic collapse following coronary artery bypass surgery
Sudden unexpected postoperative hemodynamic collapse with a high mortality develops in 1–3% of patients undergoing coronary artery bypass surgery (CABG). The contribution of surgical graft complications to this serious condition is poorly known and their demonstration at autopsy is a challenging task. Isolated CABG was performed in 8,807 patients during 1988–1999. Of the patients, 76 (0.9%) developed sudden postoperative hemodynamic collapse resulting in subsequent emergency reopening of the median sternotomy and open cardiac massage. Further emergency reoperation could be performed in 62 (82%) whereas 14 patients died prior to reoperation and a further 21 did not survive the reoperation or died a few days later. All 35 (46%) patients who did not survive were subjected to medico-legal autopsy combined with postmortem cast angiography. By combining clinical data with autopsy and angiography data, various types of graft complications were observed in 27 (36%, 1.3 per patient) of the 76 patients with hemodynamic collapse. There were no significant differences in the frequency (33 vs. 40%) or number of complicated grafts per patient (1.2 vs. 1.4) between those who survived reoperation and who did not. Autopsy detected 25 major and minor findings not diagnosed clinically. Postmortem cast angiography visualized 2 graft twists not possible to detect by autopsy dissection only. Surgical graft complications were the most frequent single cause for sudden postoperative hemodynamic collapse in CABG patients leading to a fatal outcome in almost half of the cases. Postmortem angiography improved the accuracy of autopsy diagnostics of graft complications
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