Discontinuous Galerkin spatial discretisation of the neutron transport equation with pyramid finite elements and a discrete ordinate (SN) angular approximation

In finite element analysis it is well known that hexahedral elements are the preferred type of three dimensional element because of their accuracy and convergence properties. However, in general it is not possible to mesh complex geometry problems using purely hexahedral meshes. Indeed for highly complex geometries a mixture of hexahedra and tetrahedra is often required. However, in order to geometrically link hexahedra and tetrahedra, in a conforming finite element mesh, pyramid elements will be required. Until recently the basis functions of pyramid elements were not fully understood from a mathematical or computational perspective. Indeed only first-order pyramid basis functions were rigorously derived and used within the field of finite elements. This paper makes use of a method developed by Bergot that enables the generation of second and higher-order basis functions, applying them to finite element discretisations of the neutron transport equation in order to solve nuclear reactor physics, radiation shielding and nuclear criticality problems. The results demonstrate that the pyramid elements perform well in almost all cases in terms of both solution accuracy and convergence properties

Influence of variability of material mechanical properties on seismic performance of steel and steel-concrete composite structures

Modern standards for constructions in seismic zones allow the construction of buildings able to dissipate the energy of the seismic input through an appropriate location of cyclic plastic deformations involving the largest possible number of structural elements, forming thus a global collapse mechanisms without failure and instability phenomena both at local and global level. The key instrument for this purpose is the capacity design approach, which requires an appropriate selection of the design forces and an accurate definition of structural details within the plastic hinges zones, prescribing at the same time the oversizing of non-dissipative elements that shall remain in the elastic field during the earthquake. However, the localization of plastic hinges and the development of the global collapse mechanism is strongly influenced by the mechanical properties of materials, which are characterized by an inherent randomness. This variability can alter the final structural behaviour not matching the expected performance. In the present paper, the influence of the variability of material mechanical properties on the structural behaviour of steel and steel/concrete composite buildings is analyzed, evaluating the efficiency of the capacity design approach as proposed by Eurocode 8 and the possibility of introducing an upper limitation to the nominal yielding strength adopted in the design

Computational Fluid Dynamic Simulation of Single Bubble Growth under High-Pressure Pool Boiling Conditions

Component-scale modeling of boiling is predominantly based on the Eulerian–Eulerian two-fluid approach. Within this framework, wall boiling is accounted for via the Rensselaer Polytechnic Institute (RPI) model and, within this model, the bubble is characterized using three main parameters: departure diameter (D), nucleation site density (N), and departure frequency (f). Typically, the magnitudes of these three parameters are obtained from empirical correlations. However, in recent years, efforts have been directed toward mechanistic modeling of the boiling process. Of the three parameters mentioned above, the departure diameter (D) is least affected by the intrinsic uncertainties of the nucleate boiling process. This feature, along with its prominence within the RPI boiling model, has made it the primary candidate for mechanistic modeling ventures. Mechanistic modeling of D is mostly carried out through solving of force balance equations on the bubble. Forces incorporated in these equations are formulated as functions of the radius of the bubble and have been developed for, and applied to, low-pressure conditions only. Conversely, for high-pressure conditions, no mechanistic information is available regarding the growth rates of bubbles and the forces acting on them. In this study, we use direct numerical simulation coupled with an interface tracking method to simulate bubble growth under high (up to 45 bar) pressure, to obtain the kind of mechanistic information required for an RPI-type approach. In this study, we compare the resulting bubble growth rate curves with predictions made with existing experimental data

ISG Indice di Sensibilità di Genere su base Regionale. Struttura e metodologia

L’ISG – Indice di sensibilità di genere - ideato dall’Isfol - in collaborazione con esperti del settore, consente di mettere insieme i fattori rilevanti per definire un territorio “sensibile al genere” (mercato del lavoro, servizi, governance istituzionale e scelte politiche), stabilirne il grado di rilevanza e quindi misurarne la combinazione in ogni regione. Costruito sulla base del modello del Global gender gap index dell’OCSE, si compone di due macroindicatori aggregati e correlati: IREG- Indice Regionale di equità di genere (che misura gli aspetti strutturali del mercato del lavoro e dei servizi dei territori di riferimento); ISGP- Indice di sensibilità di genere delle politiche (che misura gli assetti e le scelte politiche). Operativamente, il risultato dell’ISG, ottenuto attraverso apposita metodologia qui descritta, si concretizza in un numero, che varia da 0 a 1, sulla base del quale è possibile stilare una graduatoria delle regioni italiane in termini di “sensibilità di genere”, monitorabile periodicamente. L’indice non risponde solo a finalità di ricerca e monitoraggio dei fenomeni, ma rappresenta anche uno strumento a sostegno delle Amministrazioni regionali che, attraverso il monitoraggio delle singole componenti, possono essere supportate nella migliore implementazione delle proprie politiche

Stereo- and regioselectivity of cyclization reactions in conformationally restricted epoxy ketones: evaluation of C-versus O-alkylation process

The intramolecular addition reaction of metal enolates of ketones to oxiranes has been applied to a series of epoxy ketones derived from cyclohexene oxide. γ-Hydroxy ketones (γ-HKs, C-alkylation products) or hydroxy enol ethers (HEEs, O-alkylation products) are obtained, depending on the nature of the cyclic transition state in each case involved and the application of the Fürst-Plattner rule. The formation of HEEs by reaction of the same epoxy ketones under acid conditions is also described. In some cases, regioconvergent or chemoselective processes are conveniently obtained. © 2001 Elsevier Science Ltd. All rights reserved

Vulnerability to child maltreatment and neglect in Italy: A proposal of an indicator

Background: Child maltreatment and neglect is a significant social problem. Present work addresses the important issue of quantifying the vulnerability to child maltreatment and neglect, proposing the application in the Italian context of a new General Index on Vulnerability to Maltreatment and Neglect to achieve a more comprehensive understanding of this phenomenon. Methods: The paper presents the first findings of the vulnerability among Italian minors, obtained through the new General Index, based on a set of 65 indicators that already existed at the regional and national levels. Results: The General Index summarizes both the weaknesses of territory in terms of risk factors and its ability to react according to the policies and public services. A global index could be useful for allocating resources and monitoring progress. To understand and ensure the effectiveness of preventive interventions, it is essential to build both an overall picture at the national and regional levels. Conclusion: This new index could give policymakers information on where to direct their efforts to prevent child maltreatment

Pyramid finite elements for discontinuous and continuous discretizations of the neutron diffusion equation with applications to reactor physics

When using unstructured mesh finite element methods for neutron diffusion problems, hexahedral elements are in most cases the most computationally efficient and accurate for a prescribed number of degrees of freedom. However, it is not always practical to create a finite element mesh consisting entirely of hexahedral elements, particularly when modelling complex geometries, making it necessary to use tetrahedral elements to mesh more geometrically complex regions. In order to avoid hanging nodes, wedge or pyramid elements can be used in order to connect hexahedral and tetrahedral elements, but it was not until 2010 that a study by Bergot established a method of developing correct higher order basis functions for pyramid elements. This paper analyses the performance of first and second-order pyramid elements created using the Bergot method within continuous and discontinuous finite element discretisations of the neutron diffusion equation. These elements are then analysed for their performance using a number of reactor physics benchmarks. The accuracy of solutions using pyramid elements both alone and in a mixed element mesh is shown to be similar to that of meshes using the more standard element types. In addition, convergence rate analysis shows that, while problems discretized with pyramids do not converge as well as those with hexahedra, the pyramids display better convergence properties than tetrahedra