626 research outputs found

    Reflection positive affine actions and stochastic processes

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    In this note we continue our investigations of the representation theoretic aspects of reflection positivity, also called Osterwalder--Schrader positivity. We explain how this concept relates to affine isometric actions on real Hilbert spaces and how this is connected with Gaussian processes with stationary increments

    Reflection negative kernels and fractional Brownian motion

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    In this article we study the connection of fractional Brownian motion, representation theory and reflection positivity in quantum physics. We introduce and study reflection positivity for affine isometric actions of a Lie group on a Hilbert space E and show in particular that fractional Brownian motion for Hurst index 0<H\le 1/2 is reflection positive and leads via reflection positivity to an infinite dimensional Hilbert space if 0<H <1/2. We also study projective invariance of fractional Brownian motion and relate this to the complementary series representations of GL(2,R). We relate this to a measure preserving action on a Gaussian L^2-Hilbert space L^2(E)

    Juice Powder Concentrate and Systemic Blood Pressure, Progression of Coronary Artery Calcium and Antioxidant Status in Hypertensive Subjects: A Pilot Study

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    Because micronutrients from plants may have beneficial cardiovascular effects, the hypothesis that an encapsulated juice powder concentrate might affect several measures of vascular health was tested in free living adults at low cardiovascular risk. Blood pressure, vascular compliance, lipid and antioxidant markers, and serial electron beam tomography (to calculate a coronary artery calcium score as a measure of atherosclerosis burden), were monitored in 51 pre-hypertensive and hypertensive subjects over 2 years. By the end of follow-up, systolic and diastolic blood pressure decreased significantly (−2.4 ± 1.0 mmHg, P < 0.05 and −2.2 ± 0.6 mmHg, P < 0.001), and large artery compliance improved significantly (1.9 ± 0.6 ml mmHg−1 × 100, P < 0.01). The progression of coronary artery calcium score was smaller than expected compared with a historical database (P < 0.001). Laboratory testing showed a significant decrease in homocysteine (P = 0.05), HDL cholesterol (P = 0.025) and Apo A (P = 0.004), as well as a significant increase in β-carotene, folate, Co-Q10 and α-tocopherol (all P < 0.001). The phytonutrient concentrate we utilized induced several favorable modifications of markers of vascular health in the subjects. This study supports the notion that plant nutrients are important components of a heart healthy diet

    Uniqueness of reconstruction and an inversion procedure for thermoacoustic and photoacoustic tomography

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    The paper contains a simple approach to reconstruction in Thermoacoustic and Photoacoustic Tomography. The technique works for any geometry of point detectors placement and for variable sound speed satisfying a non-trapping condition. A uniqueness of reconstruction result is also obtained

    Calibration of input parameters in volcanic areas and an enlarged dataset by stochastic finite-fault simulations

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    The calibration of input parameters is an important task for stochastic finite-fault simulation in volcanic areas, and we manage this in the framework of the European project UPStrat-MaFa. The stochastic simulation method requires the knowledge of fault geometry, source, crust properties of the region, and local site effects. At first, we focused the present study in the pilot test areas: Mt Vesuvius, Campi Flegrei and Mt Etna. Later, we performed two applications for a large magnitude event in the Azores Islands and the South Iceland regions. A general preliminary database of ground-motion records was collected in the test areas, to set up the empirical laws of the ground-motion parameters. The results of the simulations have been compared with observed waveforms and response spectra, to determine the suitability of the parameters used. The results show good agreement between the observed and simulated time histories and response spectra, thus encouraging further efforts towards quantitative high resolution studies on input parameters.Co-financed by the EU - Civil Protection Financial Instrument, in the framework the European project ”Urban disaster Prevention Strategies using MAcroseismic Fields and FAult Sources (Acronym: UPStrat-MAFA, Grant Agreement N. 23031/2011/613486/SUB/A5). http://ec.europa.eu/echo/funding/cp_projects2011_en.htmPublishedLisbon - Portugal4.1. Metodologie sismologiche per l'ingegneria sismicaope

    Calibration of input parameters in volcanic areas and an enlarged dataset by stochastic finite-fault simulations

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    The calibration of input parameters is an important task for stochastic finite-fault simulation in volcanic areas, and we manage this in the framework of the European project UPStrat-MaFa. The stochastic simulation method requires the knowledge of fault geometry, source, crust properties of the region, and local site effects. At first, we focused the present study in the pilot test areas: Mt Vesuvius, Campi Flegrei and Mt Etna. Later, we performed two applications for a large magnitude event in the Azores Islands and the South Iceland regions. A general preliminary database of ground-motion records was collected in the test areas, to set up the empirical laws of the ground-motion parameters. The results of the simulations have been compared with observed waveforms and response spectra, to determine the suitability of the parameters used. The results show good agreement between the observed and simulated time histories and response spectra, thus encouraging further efforts towards quantitative high resolution studies on input parameters

    Small-Size Resonant Photoacoustic Cell of Inclined Geometry for Gas Detection

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    A photoacoustic cell intended for laser detection of trace gases is represented. The cell is adapted so as to enhance the gas-detection performance and, simultaneously, to reduce the cell size. The cell design provides an efficient cancellation of the window background (a parasite response due to absorption of laser beam in the cell windows) and acoustic isolation from the environment for an acoustic resonance of the cell. The useful photoacoustic response from a detected gas, window background and noise are analyzed in demonstration experiments as functions of the modulation frequency for a prototype cell with the internal volume ~ 0.5 cm^3. The minimal detectable absorption for the prototype is estimated to be ~ 1.2 10^{-8} cm^{-1} W Hz^{-1/2}.Comment: 11 pages, 5 figure
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