1,720,986 research outputs found
On the Gorenstein locus of some punctual Hilbert schemes
No full textLet be an algebraically closed field and let \Hilb_{d}^{G}(\p{N}) be the open locus of the Hilbert scheme \Hilb_{d}(\p{N}) corresponding to Gorenstein subschemes. We prove that \Hilb_{d}^{G}(\p{N}) is irreducible for . Moreover we also give a complete picture of its singular locus in the same range . Such a description of the singularities gives some evidence to a conjecture on the nature of the singular points in \Hilb_{d}^{G}(\p{N}) that we state at the end of the pape
On the description and identifiability analysis of mixture designs
No full textIn a mixture experiment the collinearity problems, implied by the sum to one functional relationship among the factors, have strong consequences for the identification and analysis of regression models for such designs. Here, to address these problems, mixture designs are represented as sets of homogeneous polynomials. Techniques from computational commutative algebra are employed to deduce generalized confounding relationships on power products and to determine families of identifiable models
Novel centrality measures and applications to underground networks
Full text linkTwo novel centrality indices, PathRank and Icentr, are defined. PathRank is a generalization of the PageRank algorithm, suitable to rank nodes of undirected graphs according to number and weight of paths in the graph. Icentr ranks the nodes of the graph by means of a combination of the weights of nodes and edges, scaled according to the distance from each node, one at a time. We apply the two novel indices to underground transportation networks, since these networks represent an infrastructural backbone for the transportation system of most big cities over the world. The characterization of the most important components of those networks and the simulation of their responses when they stop working properly, are vital for maintaining the mobility service at a desirable level. Since there are different ways to associate a graph to an underground network according to the degree of detail and aims of the study, we describe the methodology we adopted to associate a graph to such a network. The methodology was applied to 34 underground networks of worldwide cities, and the resulting graphs constitute the reference dataset. A detailed study of both Boston network and the dataset is proposed as prototypal for either a graph alone or all graphs in a dataset. Results show how different features of graphs are revealed by the two novel indices
Remarks on degree 4 projective curves
No full textIn this paper we characterize the degree 4 multiple lines with generic embedding dimension 3 and among them the ones with very degenerate hyperplanc section, and the ones which contain a degree 3 planar subcurve. Using that characterization, we prove that the degree 4 curves containing a planar subcurve of degree 3 are the general element of all irreducible component of the Hilbert scheme. Moreover, we show that all the multiple lines we consider belong to the same connected component of the corresponding Hilbert scheme
Vector bundles and low codimensional subvarieties: state of the art and recent developments
No full textInvestigation on AC Losses in the End Conductors of Additively Manufactured Hairpin Windings
No full textHairpin windings (HWs) have recently been one of the most adopted solutions to enhance torque and power density of electrical machines (EMs) in automotive applications. However, they are typically characterized by high AC losses at high-frequency operation. While several research works have focused on how to model and reduce these losses within the active parts of HWs, only a few studies on their impact in the end winding (EW) regions are available, and mainly for classical HWs featuring constant cross section. This work investigates the AC losses occurring in the EWs of a traction motor with an asymmetrical HW printed with additive manufacturing (AM). The analyses are carried out through 3D finite element (FE) simulations over a wide frequency range. The losses in the EWs are determined for both copper and AlSi10Mg conductors. Comparative considerations are finally drawn, with the aim to providing general guidelines on how to model and print the EWs of asymmetrical HWs
AC Losses Analysis and Design Guidelines for Hairpin Windings With Segmented Conductors
No full textIn the last years, hairpin windings (HWs) are amongst the most studied and implemented winding topologies to increase torque and power densities of electrical machines, especially in the traction field. However, their main drawback remains the elevated ohmic losses generated at high-frequency operations. Recently, HWs with segmented conductors have been proposed to overcome this challenge, but an analytical model to predict the losses in such unconventional winding is missing, as well as a critical analysis of the extra manufacturing complexities needed. In this article, first, a simple analytical formulation for the estimation of ac losses in segmented hairpin conductors is proposed, developed, and validated at various operating frequencies, both through finite element (FE) analyses and experimental measurements. Then, an in-depth analysis of the main advantages and disadvantages of this winding topology is proposed with the aim of providing guidelines and recommendations for their practical realization, adopting standard methodologies for their connection and transposition
An Asymmetrical Additively Manufactured Hairpin Winding for increased efficiency and sustainability
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