1,721,019 research outputs found
Interaction of neutral polysaccharides with phosphatidylcholine multilamellar liposomes. Phase transitions studied by the binding of fluorescein-conjugated dextrans
No full textA theory for the estimation of SNR degradation caused by clock litter in MRI systems
No full textRecent advances in high-speed acquisition of MR signals demand higher levels of performance from RF receiver chain. High-performance ADCs require a highly stable clock in terms of short-term changes defined by the jitter specification. In this note, we propose a theory for the estimation of clock jitter influence on the final image SNR. In particular, starting from a typical RF receiver chain design specification, which is required to obtain the desired SNR, we analyze the influence of clock noise on the MR signal dynamic. The entire offset frequency range (0-10 MHz OFR) is split into two intervals according to different estimation methods. The obtained results show that, in our specific application, the jitter influence does not affect the final image SNR value. The presented methodology can be easily extended to every MR application thanks to its high flexibility; in fact, the implemented concepts allow choosing, in each case, the optimal oscillator with the desired clock jitter, or quantifying the system performance degradation
Aerodynamic and Aeroelastic Tool for Wind Turbine Applications
Full text linkThe work focuses on the unsteady aerodynamics and aeroelastic properties of a small-medium sized wind-turbine blade operating under ideal conditions. A tapered/twisted blade representative of commercial blades used in an experiment setup at the National Renewable Energy Laboratory is considered. The aerodynamic loads are computed using Computational Fluid Dynamics (CFD) techniques. For this purpose, FLUENT®, a commercial finite-volume code that solves the Navier-Stokes and the Reynolds-Averaged Navier-Stokes (RANS) equations, is used. Turbulence effects in the 2-D simulations are modeled using Wilcox k-ω model for validation of the CFD approach. For the 3-D aerodynamic simulations, the unsteady laminar Navier-Stokes equations were used to determine the unsteady loads acting on the blades. Five different blade pitch angles were considered and their aerodynamic performance compared. The structural dynamics of the flexible wind-turbine blade undergoing significant elastic displacements has been described by a nonlinear flap-lag-torsion slender-beam differential model. The aerodynamic quasi-steady forcing terms needed for the aeroelastic governing equations have been predicted through a strip-theory based on a simple 2-D model, and the pertinent aerodynamic coefficients and the distribution over the blade span of the induced velocity derived using CFD. The resulting unsteady hub loads are achieved by a first space integration of the aeroelastic equations by applying the Galerkin’s approach and by a time integration using a harmonic balance scheme. Comparison among two- and three- dimensional computations for the unsteady aerodynamic load, the flap, lag and torsional deflections, forces and moments are presented in the paper. Results, discussions and pertinent conclusions are outlined
A Novel Magnetic Resonance Phased-Array Coil Designed with FDTD Algorithm
No full textRadio-frequency receiver phased-array coils in magnetic resonance imaging systems are used to pick up the signals emitted by the nuclei with high signal-to-noise ratio and a large region of sensitivity. Since the quality of obtained images strongly depends upon the correct choice of the coil geometry and position, array coils have to be designed by minimizing the mutual interaction among nearby coil elements and this is generally achieved by overlapping such adjacent elements. In this paper, we describe the use of a numerical solver based on finite-difference time-domain method to determine the optimal overlap distance, which guarantees the maximum decoupling level between the coil loops, for array coils constituted by various geometry elements. A novel array coil was designed, constituted by a couple of elliptical geometry elements in "folding" version around the animals' spine curvature, for small animals' imaging applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Manufatti dipinti su supporto tessile; la reintegrazione delle lacune: proposta di materiali alternativi
No full textIl contributo descrive alcuni stucchi messi a paragone fra di loro dal punto di visto delle carattersitiche chimiche, fisiche e del comportamento meccanico: gesso e colla, balsite, Aquazol. ecc.
Durante l’intervento di presentazione estetica di un manufatto tessile, le operazioni di stuccatura delle lacune
reintegrabili vengono di norma effettuate sempre con gli stessi materiali, ovvero con gesso biidrato e colla
animale e più raramente con prodotti surrogati più o meno validi già confezionati. Nonostante il binomio gesso e
colla animale sia del tutto compatibile con i materiali costitutivi delle opere, si deve rilevare il forte ritiro che
subisce in fase di asciugatura, la scarsa resistenza meccanica e soprattutto la possibilità che funga da substrato per
agenti biodeteriogeni in particolari condizioni termoigrometriche. Allo stesso modo, i prodotti pronti all’uso quali
il Modostuc e la Polyfilla sono caratterizzati da un forte ritiro ma anche da una scarsa resistenza meccanica.
Al fine di fornire una valida alternativa a questi prodotti sono stati analizzati alcuni materiali quali la Balsite®,
l’Aquazol e il BEVA® Gesso, verificandone l’aspetto estetico, la lavorabilità, la resistenza meccanica, il ritiro
dimensionale, la reversibilità ed infine la resistenza agli attacchi biologici. Le indagini eseguite hanno fornito
risultati molto positivi, tali da suggerire l’impiego di questi prodotti in sostituzione degli impasti di uso comune
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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