1,721,007 research outputs found
Self-adjointe extensions for symmetric Laplacians on polygons.
Full text linkBy the results contained in the paper by Birman and Skvortsov “On the square summability of the highest derivatives of the solution to the Dirichlet problem in a region with piecewise smooth boundary" the Laplace operator o on a plane curvilinear polygon with domain the Sobolev space H2() and homogeneous Dirichlet boundary conditions is a closed symmetric operator with deficiency indices (n, n), where n is the number of non-convex corners. Therefore on a non-convex polygon, o has infinite self-adjoint extensions. Such extensions have been recently determined by means of Kreǐn's resolvent formula. The purpose of this thesis is to extend such results to the case of different, more general, boundary conditions. In the first part of the thesis we consider the case of mixed Dirichlet-Neumann conditions, thus allowing each side j of the polygon boundary to support either a Dirichlet or a Neumann homogeneous boundary condition. In this case, building on results by Grisvard, while in the pure Neumann case the dimensions of the defect spaces is the same as in the case of the pure Dirichlet case already studied by Birman and Skvortsov, the mixed case has a different behavior, allowing both convex cases and non-convex cases with double vertex contribution. After explicitly characterizing the defect sub- space we determined the self-adjoint extensions by a Kreǐn's resolvent formula proceeding analogously to the pure Dirichlet case, however taking into account the double contribution due to the vertices with mixed boundary conditions.
In the second part of the thesis we further extend our analysis by allowing some sides j to support Robin boundary conditions. While this is a deformation of the case considered in the first part, some not completely trivial calculations are necessary in order to get results similar to the ones concerning the mixed Dirichlet-Neumann case. By such calculations, one can recover results anologous to the ones in the first part. However also different behaviors are possible:
1. for any > 0, for any 0 < j < , there are parameter values which give dj = 1;
2. for any x < j (3/2) , x 1.43, there are parameter values which give dj = 2.
Moreover, as expected, the dj 's converge to the ones corresponding to the mixed Dirichlet-Neumann case as the j 's converge to either 0 or 1 accordingly to the different possible cases and as in the mixed Dirichlet-Neumann a Kreǐn's formula giving the classification of all the self-adjoint extension is provided in Chapter 4
Valutazione e mitigazione dei rischi geo-idrologici derivanti da eventi catastrofici nell'area del Parco Nazionale delle Cinque Terre
No full textThis research is included in the field of studies for the evaluation and mitigation of geo-hydrological risks deriving from catastrophic rainfall events conducted in the Cinque Terre National Park area (Liguria) by the Department of Earth Sciences of the Environment and Life of University of Genoa (Italy). This activity made it possible to create and test a mathematical simulation model, in a physically based GIS environment, capable of carrying out 3D slope stability analysis (extended to a spatial domain) according to the pluviometric conditions assumed in the calculations.
The experimentation first highlighted the limits of application of the "infinte slope" limit equilibrium method (LEM) used for the spatially 3D slope stability analysis in a GIS computerized geographical environment, also indicating improvement solutions for a more correct use. The input parameters of the soils (geotechnical, hydrogeological and geometric) entering the above mathematical expression were then examined. Their spatial distribution and their relationship with the local geo-morphometric-environmental control factors, on a basin and regional scale, were assessed, as well as their influence on the results was tested by comparing them with real phenomena and geomorphological processes observed in the chosen pilot area (i.e. Vernazza catchment affected on 25/10/2011 by a catastrophic rainfall event). All this experimentation led to the formulation of innovative calculation procedures and methods which were then coded in the Python programming language and developed in the open source QGIS application system in the form of executable "scripts".
The predictive ability of the new model was tested in the aforementioned basin, comparing the spatial output data derived from the mathematical simulation with the real distribution of the surface landslides obtained from the analysis of aerial photos and site surveys. In summary, the system showed excellent potential for the preventive localization of soil mobilization phenomena on the slopes of a territorial domain where, in a neighborhood of 25 m away from the focal landslide areas, it was able to identify the 84% of the phenomena that actually occurred with a probability of 93% of the total of the aforementioned areas (with only 7% of false alarms)
Advanced hybrid laminates: elastomer integration for optimized mechanical properties
Full text linkInterleaving elastomeric flms into polymeric composite materials is a promising technological solution to manufacture components with localized functionalities. To optimize processing time and reduce testing costs, there is an urgent need for modeling strategies to predict the effect of hybridization based on the fundamental properties of singular constituents. In this work, three different laminates with varying numbers and positions of elastomeric layers were manufactured and mechanically tested in fexural configuration. The digital image correlation (DIC) technique is employed to evaluate the displacements and the strain feld on the surface of the sample. A numerical framework for the prediction of the mechanical response, including damage initiation and evolution, was developed and validated against experimental data. The numerical results showed signifcant agreement with the experiments, reporting a maximum mismatch of about 10% in strain distribution and about 2% in the ultimate load. Additionally, degradation trends in the load vs. defection curves were always consistent. Analysis of the fractured surface and predicted failure modes further demonstrated the reliability of the method
To Drag a Long Life Out in a Dark Room: soglie, ragni e ombre nella rappresentazione della donna artista in A.S. Byatt
No full textTo Drag a Long Life Out in a Dark Room: soglie, ragni e ombre nella rappresentazione della donna artista in A.S. Byatt.
No full textInvestigating the strength of adhesively bonded SMC components
Full text linkSheet Molding Compound (SMC) has emerged as a compelling alternative to light metal alloys to produce lightweight structural components in several industries. Despite their advantages, the complexity introduced by random short-fiber reinforcement SMC materials makes their mechanical behavior challenging to predict using Finite Element Analysis (FEA) models. These challenges extend to evaluating and predicting the bonding strength of adhesive joints involving such materials, which is critical in many automotive and aerospace applications. This research proposes a methodology for generating accurate material cards for adhesives/joints. The approach integrates experimental testing, numerical modeling, and optimization. A three-phase process was employed, utilizing software such as Hyper Mesh, Abaqus, and Hyper Study. The optimization phase involved the Design of Experiments (DOE) to explore parameter spaces, fitting to construct response surfaces, and optimization algorithms to refine material properties for curve matching. Despite the challenges posed by the brittle nature of SMC substrates, the approach successfully captured the joint’s mechanical behavior, producing a reliable material card for this specific material combination. This study underscores the potential of the proposed methodology to predict joint strength in large-scale simulations, such as full-vehicle assemblies, with improved accuracy and reliability. By addressing the unique challenges of SMC materials, this work provides a robust framework for adhesive characterization and enhances structural designs in composite bonding applications
Experimental and Numerical Assessment of Sheet Molding Compound Composite Crushing Behavior
No full textThis study investigates the crashworthiness properties of carbon fiber sheet molding compound (CF-SMC) material, highlighting its potential for applications requiring effective energy absorption. While CF-SMC exhibits promising specific energy absorption values, further optimization of both the material and its geometrical design is necessary to enhance performance. Notably, CF-SMC's manufacturing advantages, including faster production and the capability to integrate recycled fibers, make it a cost-effective and sustainable option for industries prioritizing efficiency and environmental responsibility. The short-fiber material model implemented within the ESI-VPS software was calibrated by means of tensile and compressive test simulations, and it was validated through crash simulations. The results indicate a strong correlation between experimental data and numerical predictions, confirming the effectiveness of the modeling approach
Fiber misalignment analysis in PCM-UD composite materials by Full Field Nodal Method
Full text linkIn this work, a new full-field and non-destructive methodology for measuring process-induced fiber waviness in composites are presented, benchmarked, and successfully applied to predict long fiber-reinforced stiffness composite laminates. The proposed method, named the ''Full Field Nodal Method'' (FFNM), computes the misalignment angle by interpolating the displacement measured on a discrete set of sampling points. Sampling points have been traced on the prepreg surface before curing, and bilinear Lagrangian interpolating functions have been adopted and compared. Several samples, made with compression molded prepreg, have been used to test the new method capabilities in this work. A first benchmark was done measuring the fiber waviness on samples through the new method and by another one recently presented in the literature. Average fiber angles predicted by the FFNM, with bilinear interpolating functions, were in high agreement with experimental results. Fiber angle misalignment measured by FFNM was used to orientate the reference system of elements of the FEA model. Numerical results in terms of stiffness and strain field were compared to those detected by the Digital Image Correlation technique (DIC) during the tensile tests. Comparison of numerical and experimental results showed an excellent prediction of material stiffness and the strain field with an error of 15%
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
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