Damage identification on spatial Timoshenko arches by means of genetic algorithms

In this paper a procedure for the dynamic identification of damage in spatial Timoshenko arches is presented. The proposed approach is based on the calculation of an arbitrary number of exact eigen-properties of a damaged spatial arch by means of the Wittrick and Williams algorithm. The proposed damage model considers a reduction of the volume in a part of the arch, and is therefore suitable, differently than what is commonly proposed in the main part of the dedicated literature, not only for concentrated cracks but also for diffused damaged zones which may involve a loss of mass. Different damage scenarios can be taken into account with variable location, intensity and extension of the damage as well as number of damaged segments. An optimization procedure, aiming at identifying which damage configuration minimizes the difference between its eigen-properties and a set of measured modal quantities for the structure, is implemented making use of genetic algorithms. In this context, an initial random population of chromosomes, representing different damage distributions along the arch, is forced to evolve towards the fittest solution. Several applications with different, single or multiple, damaged zones and boundary conditions confirm the validity and the applicability of the proposed procedure even in presence of instrumental errors on the measured data.Comment: 34 pages, 19 figure

Measurement of spontaneous emission from a two-dimensional photonic band gap defined microcavity at near-infrared wavelengths

An active, photonic band gap-based microcavity emitter in the near infrared is demonstrated. We present direct measurement of the spontaneous emission power and spectrum from a microcavity formed using a two-dimensional photonic band gap structure in a half wavelength thick slab waveguide. The appearance of cavity resonance peaks in the spectrum correspond to the photonic band gap energy. For detuned band gaps, no resonances are observed. For devices with correctly tuned band gaps, a two-time enhancement of the extraction efficiency was demonstrated compared to detuned band gaps and unpatterned material

A new multiparametric topological method for determining the primary cosmic ray mass composition in the knee energy region

The determination of the primary cosmic ray mass composition from the characteristics of extensive air showers (EAS), obtained at an observation level in the lower half of the atmosphere, is still an open problem. In this work we propose a new method of the Multiparametric Topological Analysis and show its applicability for the determination of the mass composition of the primary cosmic rays at the PeV energy region.Comment: 8 pages, 4 figures, talk given at Vulcano 2004 Workshop 'Frontier Objects in Physics and Astrophysics', Vulcano, Italy, 24-29.05.04, to be published in the Proceedings of the Worksho

Precise determination of muon and electromagnetic shower contents from shower universality property

We consider two new aspects of Extensive Air Shower development universality allowing to make accurate estimation of muon and electromagnetic (EM) shower contents in two independent ways. In the first case, to get muon (or EM) signal in water Cherenkov tanks or in scintillator detectors it is enough to know the vertical depth of shower maximum and the total signal in the ground detector. In the second case, the EM signal can be calculated from the primary particle energy and the zenith angle. In both cases the parametrizations of muon and EM signals are almost independent on primary particle nature, energy and zenith angle. Implications of the considered properties for mass composition and hadronic interaction studies are briefly discussed. The present study is performed on 28000 of proton, oxygen and iron showers, generated with CORSIKA 6.735 for $E^{-1}$ spectrum in the energy range log(E/eV)=18.5-20.0 and uniformly distributed in cos^2(theta) in zenith angle interval theta=0-65 degrees for QGSJET II/Fluka interaction models.Comment: Submitted to Phys. Rev.

Optical Relative Calibration and Stability Monitoring for the Auger Fluorescence Detector

The stability of the fluorescence telescopes of the Pierre Auger Observatory is monitored with the optical relative calibration setup. Optical fibers distribute light pulses to three different diffuser groups within the optical system. The total charge per pulse is measured for each pixel and compared with reference calibration measurements. This allows monitoring the short and long term stability with respect of the relative timing between pixels and the relative gain for each pixel. The designs of the LED calibration unit (LCU) and of the Xenon flash lamp used for relative calibration, are described and their capabilities to monitor the stability of the telescope performances are studied. We report the analysis of relative calibration data recorded during 2004. Fluctuations in the relative calibration constants provide a measure of the stability of the FD.Comment: 4 pp. To appear in the proceedings of 29th International Cosmic Ray Conference (ICRC 2005), Pune, India, 3-11 Aug 200

Fluorescence and Hybrid Detection Aperture of the Pierre Auger Observatory

The aperture of the Fluorescence Detector (FD) of the Pierre Auger Observatory is evaluated from simulated events using different detector configurations: mono, stereo, 3-FD and 4-FD. The trigger efficiency has been modeled using shower profiles with ground impacts in the field of view of a single telescope and studying the trigger response (at the different levels) by that telescope and by its neighbours. In addition, analysis cuts imposed by event reconstruction have been applied. The hybrid aperture is then derived for the Auger final extension. Taking into account the actual Surface Detector (SD) array configuration and its trigger response, the aperture is also calculated for a typical configuration of the present phase.Comment: contribution to the 29th International Cosmic Ray Conference, Pune, India, 3-10 August 200

Solitary pulmonary nodules: Morphological and metabolic characterisation by FDG-PET-MDCT [Nodulo polmonare solitario: Caratterizzazione morfologico-metabolica mediante imaging integrato TCms/FDG-PET]

Purpose. This study was done to analyse the additional morphological and functional information provided by the integration of [18F]-2-fluoro- 2-deoxy-D-glucose positron emission tomography ([18F]-FDG-PET) with contrast-enhanced multidetector computed tomography (MDCT) in the characterisation of indeterminate solitary pulmonary nodules (SPNs). Materials and methods. Fifty-six SPNs, previously classified as indeterminate, were evaluated using a Discovery ST16 PET/CT system (GE Medical Systems) with nonionic iodinated contrast material and [18F]-FDG as a positron emitter. Images were evaluated on a dedicated workstation. Semiquantitative parameters of [18F]-FDG uptake and morphological, volumetric and densitometric parameters before and after contrast administration were analysed. Results were correlated with the histological and follow-up findings. Results. Twenty-six SPNs were malignant and 30 were benign. Malignant lesions at both PET/CT and histology had a mean diameter of 1.8±1.2 cm, a volume doubling time (DT) of 222 days, a mean standardized uptake value (SUV) of 4.7 versus 1.08 in benign lesions and a mean postcontrast enhancement of 44.8 HU as opposed to 4.8 HU in benign nodules. Malignant lesions had a significantly shorter doubling time and significantly greater postcontrast enhancement compared with benign nodules. Based on the SUV and using a cut-off value of >2.5, PET/CT had a sensitivity of 76.9%, specificity of 100%, diagnostic accuracy of 89.2%, positive predictive value (PPV) of 100% and negative predictive value (NPV) of 83.3%. Based on doubling time (cut off <400 days), it had a sensitivity of 76.9%, specificity of 93.3%, accuracy of 85.7%, PPV of 90.9% and NPV of 82.3%. Based on postcontrast enhancement (cut off >15 HU), it had a sensitivity of 92.3%, specificity of 100%, accuracy of 96.4%, PPV of 100% and NPV of 93.7%. Conclusion. PET/CT allows accurate analysis of anatomical/morphological and metabolic/functional correlations of SPN, providing useful data for identifying and locating the disease, for differentiating between malignant and benign nodules and for establishing the aggressiveness and degree of vascularity of pulmonary lesions. Therefore, partly in view of the considerable reduction in time and cost of the single examinations, we believe that PET/CT will gain an increasingly dominant role in the diagnostic and therapeutic approach to lung cancer, especially in the preclinical phase. © 2007 Springer-Verlag

Parametric Inversion of Brillouin spectra using L-curve criterion to enhance the accuracy of distributed strain measurement

International audienceTo ensure stability and durability of engineering structure in natural soil, optical fiber sensors have gained interest over last decade. In addition to conventional geophysical sensors, Brillouin spectra based sensor enables to perform distributed strain measurement. Its algorithm performs a strain measurement with a 40cm spatial sampling over several kilometers. The monitoring of engineering installations needs a centimeter spatial sampling and a better strain accuracy. Previous works highlighted that the industrialized algorithm has great limitation for the exploitation of the local information contained into Brillouin spectra. Indeed, based on its asymmetry and broadening, it is possible to estimate local Brillouin frequencies with a better strain accuracy. We propose here to apply a parametric inverse method using L-curve criterion to estimate the strain with a 5cm spatial sampling. To validate this method, a one-to-one scale experiment has been implemented by optical fiber cable at several depths. Comparing the distributed strain provided by the Brillouin based sensor and our algorithm with a reference strain sensor, the proposed algorithm successfully fulfills the combination of a 5cm spatial sampling over kilometers and a high strain accuracy