178,104 research outputs found
Analysis of a Multiscale Discontinuous Galerkin Method for Convection-Diffusion Problems
No full textWe study a multiscale discontinuous Galerkin method introduced in [T. J. R. Hughes, G. Scovazzi, P. Bochev, and A. Buffa, Comput. Meth. Appl. Mech. Engrg., 195 (2006), pp. 2761–2787] that reduces the computational complexity of the discontinuous Galerkin method, seemingly without adversely affecting the quality of results. For a stabilized variant we are able to obtain the same error estimates for the convection-diffusion equation as for the usual discontinuous Galerkin method. We assess the stability of the unstabilized case numerically and find that the inf-sup constant is positive, bounded uniformly away from zero, and very similar to that for the usual discontinuous Galerkin method
Isogeometric Discrete Differential Forms in Three Dimensions
No full textThe concept of isogeometric analysis (IGA) was first applied to the approximation of Maxwell equations in [A. Buffa, G. Sangalli, and R. Vázquez, Comput. Methods Appl. Mech. Engrg., 199 (2010), pp. 1143–1152]. The method is based on the construction of suitable B-spline spaces such that they verify a De Rham diagram. Its main advantages are that the geometry is described exactly with few elements, and the computed solutions are smoother than those provided by finite elements. In this paper we develop the theoretical background to the approximation of vector fields in IGA. The key point of our analysis is the definition of suitable projectors that render the diagram commutative. The theory is then applied to the numerical approximation of Maxwell source problems and eigenproblems, and numerical results showing the good behavior of the scheme are also presented
On the Choice of Tool Material in Friction Stir Welding of Titanium Alloys
No full textFriction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, is now being successfully used also for magnesium alloys, copper and steels. The wide diffusion the process is having is due to the possibility to weld both materials traditionally considered difficult to be welded or "unweldable" by traditional fusion welding processes due to peculiar thermal and chemical material properties, and complex geometries as sandwich structures and straightening panels. Recently, research is focusing on titanium alloys thanks to the high interest that such materials are getting from the industry due to the extremely high strength-weight ratio together with good corrosion resistance properties. At the moment, the main limit to the industrial applicability of FSW to titanium alloys is the tool life, as ultra wear and deformation resistant materials must be used. In this paper a, experimental study of the tool life in FSW of titanium alloys sheets at the varying of the main process parameters is performed. Numerical simulation provided important information for the fixture design and analysis of results. Tungsten and Rhenium alloy W25Re tools are found to be the most reliable among the ones considered
Don Procopio // opera buffa // in // Due atti (manuscrit autographe)
No full textTitre uniforme : Bizet, Georges (1838-1875). Compositeur. [Don Procopio. GB 3]Autre mention au titre, au crayon : "Rome 1858-1859". - Au fol. 2 r°, distribution et table des matières. - Livret de Carlo Cambiaggio. - Manuscrit autographe à l'encre. - Foliotation continue ajoutée au crayon ; le manuscrit comporte aussi deux paginations autographes, l'une par numéros, l'autre continue (de 1 à 236), ne prenant pas en compte les fol. 1, 2 (feuillets liminaires) et 66 (inutilisé). - Manuscrit retrouvé dans les papiers d'Auber selon le catalogue sur fiches du fonds du Conservatoire ; à mettre en relation avec le livret TH B-2876 (1-3), dont s'est servi Bizet, également retrouvé dans les papiers d'AuberPrésentation musicale : [Partition]Opéras buffa -- +* 1800......- 1899......+:19e siècle
Corrigendum to "Lower lean mass and higher percent fat mass in patients with Alzheimer's disease" [Exp. Gerontol. 58 (2014) 30-33]
No full textThe authors regret to report a miscalculation of three bioelectrical variables, namely specific resistance, specific reactance and specific impedance, in the sample of patients with Alzheimer's disease. The correct values are: Rsp (men: 410.4 ± 49.3; women: 441.1 ± 66.2); Xcsp (men: 38.1 ± 5.6; women: 38.3 ± 7.4); Zsp (men: 412.1 ± 49.3; women: 442.9 ± 66.4). Phase angle values have been unaffected by the error. As in the original paper, patients have a significantly lower specific reactance and phase angle than the reference population (p = 0.000). Also the internal comparisons of bioelectrical variables are unchanged: female patients with worse cognitive and functional impairment show a lower phase angle and a longer vector, respectively. In contrast to the original results, Rsp and Zsp values are not yet significantly higher in patients than in the reference population. However, a new research (Mereu et al., Exp Gerontol, 102:145–148, 2018, https://doi.org/10.1016/j.exger.2017.11.011) performed in a larger sample of patients with Alzheimer's disease and using a control of healthy elders better matched for age and population confirms and strengthens the conclusions obtained in the paper by Buffa et al. (2014): a lower phase and a longer vector in patients with Alzheimer's disease, i.e., lower lean mass and higher percent fat mass. The authors apologise for any inconvenience caused
Maximal coherence in a three-level autoionising atom for the generation of subpicosecond pulses in the extreme ultraviolet
No full textWe discuss the possibility of using a three-level ladder atomic system, with a final autoionizing state, for the efficient generation of short radiation pulses in the extreme ultraviolet through a process of sum-frequency mixing in the presence of maximal coherence. The results of numerical calculations are presented, investigating the effects of photoionization, dynamic Stark shift and electron impact dephasing on the conversion efficiency in a single atom model.
The results of this investigation can be useful in identifying a real candidate for a possible experiment
Design of the friction stir welding tool using the continuum based FEM model
No full textIn friction stir welding (FSW), the welding tool geometry plays a fundamental role in obtaining desirable microstructures in the weld and
the heat-affected zones, and consequently improving strength and fatigue resistance of the joint. In this paper, a FSW process with varying pin geometries (cylindrical and conical) and advancing speeds is numerically modeled, and a thermo-mechanically coupled, rigid-viscoplastic, fully 3D FEM analysis able to predict the process variables as well as the material flow pattern and the grain size in the welded joints is performed. The obtained results allow finding optimal tool geometry and advancing speed for improving nugget integrity of aluminum alloys
Mechanical and metallurgical effects of in process cooling during friction stir welding of AA7075-T6 butt joints
No full textThis paper presents the results of a combined experimental and numerical investigation focused on the effects of an in process water cooling treatment aimed at improving the final quality of friction stir welded butt joints in terms of mechanical resistance and metallurgy of the processed material. Micro and macro observations, together with the evolution of an already developed finite element tool, have
been used to analyze specimens obtained under different process conditions. Water cooling was found to enhance joint strength, reducing the material softening usually observed in the thermo-mechanically affected zone area, with no detrimental effect on nugget integrity
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