12,177 research outputs found
Mixing and non-mixing local minima of the entropy contrast for blind source separation
In this paper, both non-mixing and mixing local minima of the entropy are
analyzed from the viewpoint of blind source separation (BSS); they correspond
respectively to acceptable and spurious solutions of the BSS problem. The
contribution of this work is twofold. First, a Taylor development is used to
show that the \textit{exact} output entropy cost function has a non-mixing
minimum when this output is proportional to \textit{any} of the non-Gaussian
sources, and not only when the output is proportional to the lowest entropic
source. Second, in order to prove that mixing entropy minima exist when the
source densities are strongly multimodal, an entropy approximator is proposed.
The latter has the major advantage that an error bound can be provided. Even if
this approximator (and the associated bound) is used here in the BSS context,
it can be applied for estimating the entropy of any random variable with
multimodal density.Comment: 11 pages, 6 figures, To appear in IEEE Transactions on Information
Theor
Antithrombotic strategies in patients undergoing percutaneous coronary intervention for acute coronary syndrome
In patients undergoing percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS), both periprocedural acute myocardial infarction and bleeding complications have been shown to be associated with early and late mortality. Current standard antithrombotic therapy after coronary stent implantation consists of lifelong aspirin and clopidogrel for a variable period depending in part on the stent type. Despite its well-established efficacy in reducing cardiac-related death, myocardial infarction, and stroke, dual antiplatelet therapy with aspirin and clopidogrel is not without shortcomings. While clopidogrel may be of little beneficial effect if administered immediately prior to PCI and may even increase major bleeding risk if coronary artery bypass grafting is anticipated, early discontinuation of the drug may result in insufficient antiplatelet coverage with thrombotic complications. Optimal and rapid inhibition of platelet activity to suppress ischemic and thrombotic events while minimizing bleeding complications is an important therapeutic goal in the management of patients undergoing percutaneous coronary intervention. In this article we present an overview of the literature on clinical trials evaluating the different aspects of antithrombotic therapy in patients undergoing PCI and discuss the emerging role of these agents in the contemporary era of early invasive coronary intervention. Clinical trial acronyms and their full names are provided in Table 1
Hydrogen-oxygen proton-exchange membrane fuel cells and electrolyzers
Hydrogen-oxygen solid polymer electrolyte (SPE) fuel cells and SPE electrolyzers (products of Hamilton Standard) both use a Proton-Exchange Membrane (PEM) as the sole electrolyte. These solid electrolyte devices have been under continuous development for over 30 years. This experience has resulted in a demonstrated ten-year SPE cell life capability under load conditions. Ultimate life of PEM fuel cells and electrolyzers is primarily related to the chemical stability of the membrane. For perfluorocarbon proton exchange membranes an accurate measure of the membrane stability is the fluoride loss rate. Millions of cell hours have contributed to establishing a relationship between fluoride loss rates and average expected ultimate cell life. This relationship is shown. Several features have been introduced into SPE fuel cells and SPE electrolyzers such that applications requiring greater than or equal to 100,000 hours of life can be considered. Equally important as the ultimate life is the voltage stability of hydrogen-oxygen fuel cells and electrolyzers. Here again the features of SPE fuel cells and SPE electrolyzers have shown a cell voltage stability in the order of 1 microvolt per hour. That level of stability has been demonstrated for tens of thousands of hours in SPE fuel cells at up to 500 amps per square foot (ASF) current density
Hydrogen-oxygen proton-exchange membrane fuel cells and electrolyzers
Hydrogen-oxygen SPE fuel cells and SPE electrolyzers (products of Hamilton Standard) both use a Proton-Exchange Membrane (PEM) as the sole electrolyte. The SPE cells have demonstrated a ten year life capability under load conditions. Ultimate life of PEM fuel cells and electrolyzers is primarily related to the chemical stability of the membrane. For perfluorocarbon proton-exchange membranes an accurate measure of the membrane stability is the fluoride loss rate. Millions of cell hours have contributed to establishing a relationship between fluroride loss rates and average expected ultimate cell life. Several features were introduced into SPE fuel cells and SPE electrolyzers such that applications requiring greater than or equal to 100,000 hours of life can be considered. Equally important as the ultimate life is the voltage stability of hydrogen-oxygen fuel cells and electrolyzers. Here again the features of SPE fuel cells and SPE electrolyzers have shown a cell voltage stability in the order of 1 microvolt per hour. That level of stability were demonstrated for tens of thousands of hours in SPE fuel cells at up to 500 amps per square foot (ASF) current density. The SPE electrolyzers have demonstrated the same at 1000 ASF. Many future extraterrestrial applications for fuel cells require that they be self recharged. To translate the proven SPE cell life and stability into a highly reliable extraterrestrial electrical energy storage system, a simplification of supporting equipment is required. Static phase separation, static fluid transport and static thermal control will be most useful in producting required system reliability. Although some 200,000 SPE fuel cell hours were recorded in earth orbit with static fluid phase separation, no SPE electrolyzer has, as yet, operated in space
Optimized FRP Wrapping Schemes for Circular Concrete Columns under Axial Compression
This study investigates the behavior and failure modes of fiber-reinforced polymer (FRP) confined concrete wrapped with different FRP schemes, including fully wrapped, partially wrapped, and nonuniformly-wrapped concrete cylinders. By using the same amount of FRP, this study proposes a new wrapping scheme that provides a higher compressive strength and strain for FRP-confined concrete, in comparison with conventional fully wrapping schemes. A total of 33 specimens were cast and tested, with three of these specimens acting as reference specimens and the remaining specimens wrapped with different types of FRP (CFRP and GFRP) by different wrapping schemes. For specimens that belong to the descending branch type, the partially-wrapped specimens had a lower compressive strength but a higher axial strain as compared to the corresponding fully-wrapped specimens. In addition, the nonuniformly-wrapped specimens achieved both a higher compressive strength and axial strain in comparison with the fully-wrapped specimens. Furthermore, the partially-wrapping scheme changes the failure modes of the specimens and the angle of the failure surface. A new equation that can be used to predict the axial strain of concrete cylinders wrapped partially with FRP is proposed
Neural Relax
We present an algorithm for data preprocessing of an associative memory
inspired to an electrostatic problem that turns out to have intimate relations
with information maximization
Phase diagram analysis of noise-induced transition in an autocatalytic reaction
We present the analysis of the genetic model of autocatalytic chemical reactions proposed by Arnold et al. This model, when subjected to multiplicative white noise modelling environmental fluctuations, can undergo a sudden change from a unimodal state to a bimodal one, while no such transition occurs if the noise is absent. Here, this noise-induced transition is studied analytically by investigating the so-called critical surface in the three-dimensional parameter spac
Maximum usable strain of FRP-confined concrete
This study investigates the progressive failure of FRP-confined concrete. Ten FRP-confined concrete specimens were divided into two groups with different jacket stiffness. One specimen in each group was tested until failure while the others were loaded to target strains and then unloaded in order to monitor the residual strength of the concrete cores. At 1% axial strain of FRP-confined concrete, the residual strength of the concrete cores were reduced more than 56% compared to the reference specimens. Experimental results have shown that the maximum usable strain of 1% is unconservative for FRP-confined concrete. A model is proposed to estimate the residual strength of concrete cores. Predictions from the proposed model fit the experimental results well. In addition, a new procedure is proposed to determine the maximum usable strain of FRP-confined concrete based on the maximum usable strain of unconfined concrete
Spinodal nanodecomposition in magnetically doped semiconductors
This review presents the recent progress in computational materials design,
experimental realization, and control methods of spinodal nanodecomposition
under three- and two-dimensional crystal-growth conditions in spintronic
materials, such as magnetically doped semiconductors. The computational
description of nanodecomposition, performed by combining first-principles
calculations with kinetic Monte Carlo simulations, is discussed together with
extensive electron microscopy, synchrotron radiation, scanning probe, and ion
beam methods that have been employed to visualize binodal and spinodal
nanodecomposition (chemical phase separation) as well as nanoprecipitation
(crystallographic phase separation) in a range of semiconductor compounds with
a concentration of transition metal (TM) impurities beyond the solubility
limit. The role of growth conditions, co-doping by shallow impurities, kinetic
barriers, and surface reactions in controlling the aggregation of magnetic
cations is highlighted. According to theoretical simulations and experimental
results the TM-rich regions appear either in the form of nanodots (the {\em
dairiseki} phase) or nanocolumns (the {\em konbu} phase) buried in the host
semiconductor. Particular attention is paid to Mn-doped group III arsenides and
antimonides, TM-doped group III nitrides, Mn- and Fe-doped Ge, and Cr-doped
group II chalcogenides, in which ferromagnetic features persisting up to above
room temperature correlate with the presence of nanodecomposition and account
for the application-relevant magneto-optical and magnetotransport properties of
these compounds. Finally, it is pointed out that spinodal nanodecomposition can
be viewed as a new class of bottom-up approach to nanofabrication.Comment: 72 pages, 79 figure
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