Search results for " Compression"
showing 10 items of 400 documents
Octave-spanning coherent supercontinuum generation in a step-index tellurite fiber and towards few-cycle pulse compression at 2 μ m
2021
Abstract We experimentally demonstrate 140-THz bandwidth (at −20 dB) supercontinuum generation in a 10 cm-long all-normal dispersion step-index tellurite fiber pumped by a turn-key femtosecond fiber laser emitting at 2 . 11 μ m at a repetition rate of 19 MHz. The soliton self-frequency shifted thulium-doped fiber mode-locked laser emits initial transform-limited pulses, with 85-fs pulse duration, that are subsequently quasi-linearly chirped (over more than 50 THz) during the above nJ-level nonlinear propagation. Moreover, we numerically demonstrate the possible pulse compression down to 12 fs by means of additional linear propagation in a standard step-index fluoride fiber with anomalous di…
General stress-strain model for concrete or masonry response under uniaxial cyclic compression
2002
The paper proposes analytical forms able to represent with very good approximation the constitutive law experimentally deducible by means of uniaxial cyclic compressive tests on material having softening post-peak behaviour in compression and negligible tensile strength. The envelope, unloading and reloading curves characterizing the proposed model adequately approach structural responses corresponding to different levels of nonlinearity and ductility, requiring a not very high number of parameters to be calibrated experimentally. The reliability of the model is shown by comparing the results that it is able to provide with the ones analytically deduced from two reference models (one for co…
A Standardised Approach to the Biomechanical Evaluation of Tracheal Grafts
2021
[EN] The ideal tracheal substitute must have biomechanical properties comparable to the native trachea, but currently there is no standardised approach to evaluating these properties. Here we propose a novel method for evaluating and comparing the properties of tracheal substitutes, thus systematising both measurement and data curation. This system was tested by comparing native rabbit tracheas to frozen and decellularised specimens and determining the histological characteristics of those specimens. We performed radial compression tests on the anteroposterior tracheal axis and longitudinal axial tensile tests with the specimens anastomosed to the jaw connected to a measuring system. All ca…
Phase-matching measurements and Sellmeier equations over the complete transparency range of KTiOAsO_4, RbTiOAsO_4, and CsTiOAsO_4
2000
The sphere method is used for the direct measurement of sum- and difference-frequency generation phase matched in the principal planes of KTiOAsO4, RbTiOAsO4, and CsTiOAsO4, including the tuning curves of 1.064-µm-pumped OPO’s emitting between 3 and 5 µm. The nonlinear least-squares fitting of our experimental data leads to refined dispersion equations of the principal refractive indices; the resulting dual-oscillator form equations are valid over the complete transparency range of the three studied materials.
Behaviour in compression of lightweight fiber reinforced concrete confined with transverse steel reinforcement
2004
Abstract The compressive behavior of lightweight fiber reinforced concrete confined with transverse reinforcement consisting of steel stirrups or spirals was analyzed. Pumice stone and expanded clay aggregates were utilized to decrease the weight of the composite; hooked steel fibers were also added. The investigation was carried out by testing cylindrical and prismatic specimens of different sizes in compression using an open-loop displacement control machine, recording the full load–deformation curves. The influence of the dimensions and shape on the bearing capacity and on the ductility of the specimens confined with transverse steel reinforcements was analyzed. The results show the poss…
The Reconstruction of Polyominoes from Approximately Orthogonal Projections
2001
The reconstruction of discrete two-dimensional pictures from their projection is one of the central problems in the areas of medical diagnostics, computer-aided tomography, pattern recognition, image processing, and data compression. In this note, we determine the computational complexity of the problem of reconstruction of polyominoes from their approximately orthogonal projections. We will prove that it is NP-complete if we reconstruct polyominoes, horizontal convex polyominoes and vertical convex polyominoes. Moreover we will give the polynomial algorithm for the reconstruction of hv-convex polyominoes that has time complexity O(m3n3).
Adaptive surface compression with geometric wavelets.
2008
The recent advances in computer graphics and digitization allow access to an ever finer three-dimensional modelling of the world. The critical challenges with 3D models lie in their transmission and rendering, which must fit the heterogeneity of the end resources (network bandwidth, display terminals . . . ). In this context, this thesis investigates the progressive compression and transmission of 3D models, based on multiresolution analysis, to provide a scalable representation of these geometric models. This work is part of "CoSurf", a collaborative research project involving LIRIS laboratory and France Télécom R&D in Rennes. The proposed hierarchical compression method is based on a wave…
Statistical atmospheric parameter retrieval largely benefits from spatial-spectral image compression
2021
The infrared atmospheric sounding interferometer (IASI) is flying on board of the Metop satellite series, which is part of the EUMETSAT Polar System. Products obtained from IASI data represent a significant improvement in the accuracy and quality of the measurements used for meteorological models. Notably, the IASI collects rich spectral information to derive temperature and moisture profiles, among other relevant trace gases, essential for atmospheric forecasts and for the understanding of weather. Here, we investigate the impact of near-lossless and lossy compression on IASI L1C data when statistical retrieval algorithms are later applied. We search for those compression ratios that yield…
Landmarks for vertebral artery repositioning in bulbar compression syndrome: anatomic and microsurgical nuances
2004
Abstract OBJECTIVE: The purpose of this study was to better elucidate the anatomic relationship between the vertebral artery (VA) along with its perforating vessels and the brainstem to develop anatomic guidelines that would be helpful when decompressing medulla oblongata compressed by the VA. METHODS: Microanatomy dissection was performed in six formalin-fixed cadaveric heads. The VA, posteroinferior cerebellar artery (PICA), anteroinferior cerebellar artery (AICA), and lower brainstem perforators were examined under magnification using a surgical microscope. The outer diameters of the VA, PICA, and AICA were measured. The distance between the VA, lying within the lateral cerebellomedullar…
Ultimate Shear of RC Beams with Corroded Stirrups and Strengthened with FRP
2019
Transverse reinforcement plays a key role in the response behavior of reinforced concrete beams. Therefore, corrosion of steel stirrups may change the failure mode of elements from bending to shear, leading to a brittle and catastrophic crisis. It is important to strengthen reinforced concrete beams with corroded stirrups to enhance the shear resistance. This paper presents a formulation, based on the modified compression field theory, to estimate the ultimate shear of reinforced concrete beams strengthened with FRP, because of stirrup corrosion. The detrimental effect of corrosion on steel stirrup yield strength was taken into account by introducing an empirical decay law. The effective st…