1,721,191 research outputs found
Attualità e future prospettive terapeutiche
Full text linkLa ricerca di base e clinica sul glaucoma costituisce
oggi uno dei principali campi di impegno scientifico
del mondo oftalmologico. E questo dipende da svariati
fattori, quali la cronicità di una patologia seconda
causa di cecità nel mondo, con il conseguente
onere sociale che ne deriva; il progressivo invecchiamento
anagrafico delle aree occidentali con incremento
di prevalenza del glaucoma primario ad angolo
aperto (POAG) o chiuso (PACG); i recenti successi
terapeutici in campo chirurgico e soprattutto
medico, che negli ultimi 25 anni hanno creato un circolo
virtuoso in termini di impiego di uomini e di
risorse. C’è da aggiungere che man mano che la
generazione del “baby boom” post-bellico invecchia,
si incrementerà la richiesta di un trattamento che
preservi la visione, senza intaccare il godimento di
attività sociali e ricreative che è oggi tipico anche
dell’età avanzata.
I tentativi di ridurre in modo sostanziale il deficit
visivo e la cecità da glaucoma necessiteranno di una
diagnostica sempre più aggressiva, in modo da rendere
coscienti della propria condizione un maggior
numero di pazienti. Inoltre è necessario un più
attento trattamento di POAG e PACG che possa
includere le acquisizioni derivanti dalla ricerca corrente.
A causa delle conseguenze della cecità sulla
salute e sull’economia, il fardello di POAG e POCG
ricade non solo sui pazienti e i loro medici ma anche,
come detto, sulla società. Pertanto le strategie di
controllo della malattia devono andare oltre il semplice
input al medico di base per uno screening sistematico,
avvalendosi di più ampie campagne di informazione
pubblica che possano sottolineare la necessità
di un periodico esame dell’occhio, specialmente
tra coloro con storia familiare o altri fattori di rischio
per il glaucoma.
Le metodiche per la diagnosi precoce e per il followup
della malattia sono sempre più raffinate e promettenti
per il futuro, come le sezioni precedenti di
questo volume hanno evidenziato. Una loro trattazione
prospettica renderebbe troppo ampio questo
capitolo, che pertanto si incentrerà sulle problematiche
future terapeutiche, mediche e chirurgiche
Quanto può essere distorsivo il premio di maggioranza? Considerazioni costituzionalistico-matematiche a partire dalla sent. n. 1 del 2014
No full textLarge-Eddy Simulation of Bypass Transition on a Zero-Pressure-Gradient Flat Plate Using the Spectral-Element Dynamic Model
No full textThe present paper deals with the large-eddy simulation (LES) of a zero-pressure-gradient smooth flat-plate boundary layer undergoing bypass transition due to the presence of freestream turbulence of intensity around 3.0 %. Transition has been achieved by the introduction of synthetic turbulence into the freestream in a manner designed to invoke a behaviour closely resembling that of the ERCOFTAC T3A experiment. We make use of the spectral-element dynamic model (SEDM), implemented within the framework of a high-order spectral-difference solver, to carry out LES upon several sets of computational grids. Furthermore, comparisons against several other well known models such as the WALE and SIGMA model, are performed and presented in addition to implicit-LES (ILES). Our results show that the SEDM inputs relatively minor levels of dissipation into the pre-transitional region. This allows the fluctuating stresses to grow unhindered, until the critical amplitude, required for transition to occur, is reached. Furthermore, within the transitional region, the eddy-viscosity is dominant near the wall and not at the interface between the freestream and boundary layer where the breakdown mechanism predominates. The rapid grid convergence properties of the SEDM, demonstrated in this work, make them well-suited for use in conjunction with other high-order schemes
A Comparative Study from Spectral Analyses of High-Order Methods with Non-Constant Advection Velocities
No full textThe response of numerical methods to flow properties dynamic changes is a key ingredient of numerical modeling calibration. In this context, a range of spectral analyses and canonical fluid mechanics problems are explored to compare the responses of the high-order spectral difference scheme and of the flux reconstruction methods. Spatial eigen-analysis (Hu et al. in J Comput Phys 151(2):921–946, 1999; Hu and Atkins in J Comput Phys 182(2):516–545, 2002), based on spatially evolving oscillations, is used to get useful insights for problems with inflow/outflow boundary conditions (i.e., non-periodic), while non-modal analysis (Fernandez et al. in Comput Methods Appl Mech Eng 346:43–62, 2019. https://doi.org/10.1016/j.cma.2018.11.027) focusses on the short-term dynamics of the discretised system. These two approaches are also extended to the general scalar conservation law with non-constant advection velocity. All these tools are used to obtain more insight about the expected behavior of the mentioned numerical methods for typical engineering applications. On this regard, despite the lack of a mathematical proof of stability in the non-linear case, the selected numerical schemes, for which an extensive literature is available for applications to Euler and Navier–Stokes equations, will be assumed to be stable. Findings are then verified considering one-dimensional linear advection, and two- and three-dimensional flows modeled with the compressible Euler equations. Implications in the accurate control of numerical dissipation for turbulent flows is also addressed. Within the context of high-order methods, this work complement the former temporal spectral analyses of the discontinuous Galerkin approach discretising the linear advection equation
Resolved images of self-gravitating circumstellar discs with ALMA
No full textIn this paper, we present simulated observations of massive self-gravitating circumstellar discs using the Atacama Large Millimetre/sub-millimetre Array (ALMA). Using a smoothed particle hydrodynamics model of a 0.2-Msolar disc orbiting a 1-Msolar protostar, with a cooling model appropriate for discs at temperatures below ~160K and representative dust opacities, we have constructed maps of the expected emission at sub-mm wavelengths. We have then used the Common Astronomy Software Applications ALMA simulator to generate simulated images and visibilities with various array configurations and observation frequencies, taking into account the expected thermal noise and atmospheric opacities. We find that at 345GHz (870μm) spiral structures at a resolution of a few au should be readily detectable in approximately face-on discs out to distances of the Taurus-Auriga star-forming complex
Entropy preserving low dissipative shock capturing with wave-characteristic based sensor for high-order methods
No full textShock capturing procedures are required to stabilise numerical simulations of gas dynamics problems featuring non-isentropic discontinuities. In the present work, particular attention is focused on the expected non-monotonicity of the entropy profile across shock waves. A peculiar physical property which was not considered so far in the evaluation of shock capturing techniques. In the context of high-order spectral difference methods and using most recent discontinuity sensors based on the decay rate of the modes of the amplitude of characteristic waves, results show how the choice of a physical-based procedure (additional viscosity) returns a better description of shocks compared to approaches relying on the direct addition of a Laplacian term in the solved equations. Various canonical compressible flows are simulated, in one-, two-, and three-dimensional setups, to illustrate the performance and flexibility of the proposed approach. It is shown that the addition of a well-calibrated bulk viscosity is capable of smoothing out discontinuities without an excessive damping of vortical structures, preserving also specific compressible flow physics, as the non-monotonic entropy profiles through the shocks
Analysis of High-order Explicit LES Dynamic Modeling Applied to Airfoil Flows
No full textA high-order low dissipative numerical framework is discussed to tackle simultaneously the modeling of unresolved sub-grid scale flow turbulence and the capturing of shock waves. The flows around two different airfoil profiles are simulated using a Spectral Difference discretisation scheme. First, a transitional, almost incompressible, low Reynolds number flow over a Selig-Donovan 7003 airfoil. Second, a high Reynolds number flow over a RAE2822 airfoil under transonic conditions. These flows feature both laminar and turbulent flow physics and are thus particularly challenging for turbulence sub-grid scale modeling. The accuracy of the recently developed Spectral Element Dynamic Model, specifically capable of detecting spatial under-resolution in high-order flow simulations, is evaluated. Concerning the test in transonic conditions, the additional complexity due to the presence of shock waves has been handled using an artificial viscosity shock-capturing technique based on bulk viscosity. To mitigate the impact of the shock-capturing on turbulence dissipation, it was necessary to combine the high-order modal-type shock detection with a usual sensor measuring the local flow compressibility
Turbulence kinetic energy transfers in direct numerical simulation of shock-wave–turbulence interaction in a compression/expansion ramp
No full textA direct numerical simulation is performed for a supersonic turbulent boundary layer interacting with a compression/expansion ramp at an angle alpha = 24 degrees, matching the same operating conditions of the direct numerical simulation by Priebe & Martin (J. Fluid Mech., vol. 699, 2012, pp. 1-49). The adopted numerical method relies on the high-order spectral difference scheme coupled with a bulk-based, low-dissipative, artificial viscosity for shock-capturing purposes (Tonicello et al., Comput. Fluids, vol. 197, 2020, 104357). Filtered and averaged fields are evaluated to study total kinetic energy transfers in the presence of non-negligible compressibility effects. The compression motions are shown to promote forward transfer of kinetic energy down the energy cascade, whereas expansion regions are more likely to experience backscatter of kinetic energy. A standard decomposition of the subgrid scale tensor in deviatoric and spherical parts is proposed to study the compressible and incompressible contributions in the total kinetic energy transfers across scales. On average, the correlation between subgrid scale dissipation and large-scale dilatation is shown to be caused entirely by the spherical part of the Reynolds stresses (i.e. the turbulent kinetic energy). On the other hand, subtracting the spherical contribution, a mild correlation is still noticeable in the filtered fields. For compressible flows, it seems reasonable to assume that the eddy-viscosity approximation can be a suitable model for the deviatoric part of the subgrid scale tensor, which is exclusively causing forward kinetic energy cascade on average. Instead, more complex models are likely to be needed for the spherical part, which, even in statistical average, provides an important mechanism for backscatter
Multifocal choroiditis: Indocyanine green angiographic features
No full textThe aim of this study is to retrospectively evaluate the indocyanine green (ICG) angiographic features in 13 patients affected by multifocal choroiditis. We identified two clinical and angiographic patterns. The 'active' pattern showed hypofluorescence up to the late phases and more extensive choroidal involvement than presumed by ophthalmoscopy and fluorescein angiography. In the 'inactive' pattern, ICG angiography showed hypofluorescence during all the phases: no increase in lesion number was observed between early and late phases. Choroidal neovascularization was present in 10 patients, and it was bilateral in 2 of these: it occurred only in the inactive stage. The appearance of choroidal lesions in IGC angiography supports the hypothesis of inflammatory involvement of the choriocapillaris as the pathophysiological mechanism of the disease
Dust trapping by spiral arms in gravitationally unstable protostellar discs
No full textIn this paper, we discuss the influence of gravitational instabilities in massive protostellar discs on the dynamics of dust grains. Starting from a smoothed particle hydrodynamics simulation, we have computed the evolution of the dust in a quasi-static gas density structure typical of self-gravitating disc. For different grain size distributions, we have investigated the capability of spiral arms to trap particles. We have run 3D radiative transfer simulations in order to construct maps of the expected emission at (sub-)millimetre and near-infrared wavelengths. Finally, we have simulated realistic observations of our disc models at (sub-)millimetre and near-infrared wavelengths as they may appear with the Atacama Large Millimetre/submillimetre Array (ALMA) and the High-Contrast Coronographic Imager for Adaptive Optics (HiCIAO) in order to investigate whether there are observational signatures of the spiral structure. We find that the pressure inhomogeneities induced by gravitational instabilities produce a non-negligible dynamical effect on centimetre-sized particles leading to significant overdensities in spiral arms. We also find that the spiral structure is readily detectable by ALMA over a wide range of (sub-)millimetre wavelengths and by HiCIAO in near-infrared scattered light for non-face-on discs located in the Ophiuchus star-forming region. In addition, we find clear spatial spectral index variations across the disc, revealing that the dust trapping produces a migration of large grains that can be potentially investigated through multiwavelength observations in the (sub-)millimetric. Therefore, the spiral arms observed to date in protoplanetary disc might be interpreted as density waves induced by the development of gravitational instabilities
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