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AMS Acta (11.050 recursos)

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  1. Approximating the 2-dimensional matching distance

    Biasotti, Silvia; Cerri, Andrea; Frosini, Patrizio; Giorgi, Daniela
    Some new approximation results about the 2-dimensional matching distance are presented, leading to the formulation of an algorithm for its computation (up to an arbitrary input error).

  2. Higher secant varieties of $\mathbb{P}^n \times \mathbb{P}^m$ embedded in bi-degree $(1,d)$

    Bernardi, Alessandra; Carlini, Enrico; Catalisano, Maria Virginia
    Let $X^{(n,m)}_{(1,d)}$ denote the Segre-Veronese embedding of $\mathbb{P}^n \times \mathbb{P}^m$ via the sections of the sheaf $\mathcal{O}(1,d)$. We study the dimensions of higher secant varieties of $X^{(n,m)}_{(1,d)}$ and we prove that there is no defective $s^{th}$ secant variety, except possibly for $n$ values of $s$. Moreover when ${m+d \choose d}$ is multiple of $(m+n+1)$, the $s^{th}$ secant variety of $X^{(n,m)}_{(1,d)}$ has the expected dimension for every $s$.

  3. Decomposition of homogeneous polynomials over an algebraically closed field.

    Ballico, Edoardo; Bernardi, Alessandra
    Let $F$ be a homogeneous polynomial of degree $d$ in $m+1$ variables defined over an algebraically closed field of characteristic zero and suppose that $F$ belongs to the $s$-th secant varieties of the standard Veronese variety $X_{m,d}\subset \mathbb{P}^{{m+d\choose d}-1}$ but that its minimal decomposition as sum of $d$-th powers of linear forms $M_1, \ldots , M_r$ is $F=M_1^d+\cdots + M_r^d$ with $r>s$. We show that if $s+r\leq 2d+1$ then such a decomposition of $F$ can be split in two parts: one of them is uniquely determined by linear forms that can be written using only two variables, the other part...

  4. La "malizia" della "universita' dei tiranni": chiamare "ribellione" il "resistere". Argomenti della comunicazione politica nel Seicento

    De Benedictis, Angela
    Relazione presentata alla IX Giornata Luigi Firpo, Tirannide e dispotismo nel dibattito politico tra Cinque e Seicento, Torino 27-28 settembre 2002. Gli Atti della Giornata, a cura di Artemisio Enzo Baldini, risultano in corso di preparazione nel catalogo dell’editore Olschki: http://www.olschki.it/cgi-bin/olscq2.pl?num=3794&lang=it, ISBN: 978 88 222 5739 0, Fondazione Luigi Firpo. Centro di studi sul pensiero politico - Studi e testi, vol. 28. Consegnato al curatore nell’agosto 2003, dall’aprile 2006 il presente saggio si trova nello stato di I bozza per la stampa. Il saggio analizza linguaggio politico e discorso politico di un pamphlet che fu parte della rivolta catalana del...

  5. Polynomial-based non-uniform interpolatory subdivision with features control

    Beccari, Carolina; Casciola, Giulio; Romani, Lucia
    Starting from a well-known construction of polynomial-based interpolatory 4-point schemes, in this paper we present an original affine combination of quadratic polynomial samples that leads to a non-uniform 4-point scheme with edge parameters. This blending-type formulation is then further generalized to provide a powerful subdivision algorithm that combines the fairing curve of a non-uniform refinement with the advantages of a shape-controlled interpolation method and an arbitrary point insertion rule. The result is a non-uniform interpolatory 4-point scheme that is unique in combining a number of distinctive properties. In fact it generates visually-pleasing limit curves where special features ranging from cusps and flat edges to point/edge tension...

  6. Non-uniform interpolatory curve subdivision with edge parameters built-upon compactly supported cardinal splines

    Beccari, Carolina; Casciola, Giulio; Romani, Lucia
    In this paper we present a family of Non-Uniform Local Interpolatory (NULI) subdivision schemes, derived from compactly supported cardinal splines with non-uniform knots (NULICS). For this spline family, the knot partition is defined by a sequence of break points and by one additional knot, arbitrarily placed along each knot-interval. The resulting refinement algorithms are linear and turn out to contain a set of edge parameters that, when fixed to a value in the range [0,1], allow us to move each auxiliary knot to any position between the break points to simulate the behavior of the NULICS interpolants. Among all the members of this...

  7. «Militari apparenti». La Guardia Civica di Bologna per lo statuto fondamentale fra monarchia pontificia e cittadinanza

    De Benedictis, Angela
    Il contributo consta della relazione presentata al Convegno internazionale "Fra Cadice e Palermo. Nazione, Rivoluzione, Costituzione: rappresentanza politica, forme di governo, libertà garantite", svoltosi tra Palermo e Messina nei giorni 5-10 dicembre 2005. Gli Atti sono in corso di preparazione a cura di Andrea Romano (Università di Messina, Facoltà di Scienze Politiche, Dipartimento di Storia e Comparazione degli Ordinamenti Giuridici e Politici). Il contributo è stato consegnato per gli Atti nel maggio 2006 ed è stato accettato. Il Convegno era stato organizzato dal DiSCOGiPo, Dipartimento di Storia e Comparazione degli Ordinamenti Giuridici e Politici dell’Università degli Studi di Messina; dal FSE, Fondo...

  8. On the X-rank with respect to linearly normal curves.

    Ballico, Edoardo; Bernardi, Alessandra
    In this paper we study the X-rank of points with respect to smooth linearly normal curves X contained in P^n of genus g and degree n+g. We prove that, for such a curve X, under certain circumstances, the X-rank of a general point of X-border rank equal to s is less or equal than n+1-s. In the particular case of g=2 we give a complete description of the X-rank if n=3,4; while if n is greter or equal than 5 we study the X-rank of points belonging to the tangential variety of X.

  9. Longevity pattern in Emilia Romagna (Italy) in a dynamic perspective

    Roli, Giulia; Miglio, Rossella; Rettaroli, Rosella; Samoggia, Alessandra
    In this paper, we investigate the pattern of longevity during the last 15 years in Emilia Romagna, a North-Eastern region of Italy, at a municipality level. We consider a specific index of extreme longevity based on people aged 95 and over in two different periods (1995-1999 and 2005-2009). Spatio-temporal modeling is used to tackle at both periods the random variations in the occurrence of people 95+, due to the increasingly rareness of such events, especially in small areas. This method exploits the spatial proximity and the consequent interaction of the geographical areas to smooth the observations, as well as to...

  10. Estimation of multiple correlated effects on a disease outcome when the data are nested: a hierarchical Bayesian approach

    Roli, Giulia
    The paper deals with the analysis of multiple exposures on the occurrence of a disease. We consider observational case-control data in a multilevel setting, with subjects nested in clusters. A hierarchical Bayesian model is proposed to tackle the within-cluster dependence and the correlation among the exposures, simultaneously. To do that, we assign prior distributions on the crucial parameters by exploiting additional information at different levels, as well as reasonable assumptions and previous knowledge. The model is applied to a multi-centric study aiming to investigate the association of dietary exposures with the colon-rectum cancer. Compared with results obtained with conventional regressions,...

  11. Metodi statistici a variabili latenti per lo studio di fenomeni finanziari

    De Angelis, Luca
    Negli ultimi decenni il concetto di variabile latente ha riscosso un enorme successo nelle discipline statistiche come attestano i numerosi lavori scientifici presenti in letteratura. In particolare, nelle scienze sociali e in psicometria, l’uso del concetto di variabile latente è stato largamente adottato per far fronte al problema di misurare quantità che, in natura, non possono essere direttamente osservate. La vasta letteratura riguardante questa metodologia si espande, in maniera più limitata, anche al campo della ricerca economica ed econometrica. Nonostante esistano studi di modelli a struttura latente applicati a variabili di tipo economico, molto pochi sono i lavori che considerano...

  12. Valuing patents for accounting purposes

    Morricone, S

  13. Patent Commercialization Strategy and IPO Underpricing: Evidence from the US Semiconductor Industry

    Morricone, S; Munari, F; Oriani, R
    R&D and innovation are critical factors to succeed. Nevertheless, they generate information asymmetries between corporate insiders and external investors. Within the context of an IPO, information asymmetries increase the risk of underpricing. In this paper, we claim that the patent commercialization strategy of the firm going public affects information asymmetries and IPO underpricing. In particular, underpricing will be higher when a firm’s patent commercialization strategy is more based on licenses. A firm’s stock of patent attenuates this effect. Our results on a sample of 130 IPOs in the US semiconductor industry confirm these predictions.

  14. Studiare, documentare, incontrarsi: indagine sull'utenza delle Biblioteche Universitarie nei Poli della Romagna - Questionario

    Citti, Alessandra; Politi, Angela Maria; Sabattini, Fulvia; Semenzato, Chiara; Sangiorgi, Sergio

  15. On the X-rank with respect to linear projections of projective varieties

    Ballico, Edoardo; Bernardi, Alessandra
    In this paper we improve the known bound for the $X$-rank $R_{X}(P)$ of an element $P\in {\mathbb{P}}^N$ in the case in which $X\subset {\mathbb P}^n$ is a projective variety obtained as a linear projection from a general $v$-dimensional subspace $V\subset {\mathbb P}^{n+v}$. Then, if $X\subset {\mathbb P}^n$ is a curve obtained from a projection of a rational normal curve $C\subset {\mathbb P}^{n+1}$ from a point $O\subset {\mathbb P}^{n+1}$, we are able to describe the precise value of the $X$-rank for those points $P\in {\mathbb P}^n$ such that $R_{X}(P)\leq R_{C}(O)-1$ and to improve the general result. Moreover we give a stratification,...

  16. Viaggiatori e viaggiatrici. Letture storico-geografiche

    Marchi, Marzia
    Il viaggio- una pratica sociale profondamente mutata in Europa dai pellegrinaggi medievali fino ai turismi contemporanei- è qui indagato attraverso letture sul ruolo di alcuni fra i molti protagonisti, che hanno innovato le modalità di viaggiare e proposto diverse visioni sul mondo esterno. In particolare si dà conto del contributo di alcune figure femminili alla difficile conquista della libertà di viaggiare da parte delle donne europee, ed inoltre della più recente valorizzazione di altri viaggiatori non europei, che si sono cimentati, nei secoli scorsi, in lunghi itinerari attorno al mondo.

  17. Computing symmetric rank for symmetric tensors.

    Bernardi, Alessandra; Gimigliano, Alessandro; Idà, Monica
    We consider the problem of determining the symmetric tensor rank for symmetric tensors with an algebraic geometry approach. We give algorithms for computing the symmetric rank for $2\times \cdots \times 2$ tensors and for tensors of small border rank. From a geometric point of view, we describe the symmetric rank strata for some secant varieties of Veronese varieties.

  18. Dealing with multiple criteria in test assembly

    Veldkamp, Bernard P.; Matteucci, Mariagiulia
    It is quite common that tests or exams are being used for more then one purpose. First of all, they are used to measure the ability of the students in a reliable manner. Besides, they can be used for pass/fail decisions or to predict future behavior of the candidate, like future job behavior or academic performance. The question remains how to assemble a test that can be used for all these different purposes, that is, how to assemble a multi-objective test. Besides, multiple objectives can result from different purposes, but also from the way test specifications have been implemented. For...

  19. Misspecification Resistant Model Selection Using Information Complexity With Applications

    Bozdogan, Hamparsum; Howe, Andrew; Katragadda, Suman; Liberati, Caterina

  20. Computer adaptive testing with empirical prior information: a Gibbs sampler approach for ability estimation

    Matteucci, Mariagiulia; Veldkamp, Bernard P.
    In this paper, empirical prior information is introduced in computer adaptive testing. Despite its increasing use, the method suffers from a weak measurement precision, especially under particular conditions. Therefore, it is shown how the inclusion of background variables both in the initialization and the ability estimation is able to improve the accuracy of ability estimates. In particular, a Gibbs sampler scheme is proposed in the phases of interim and final ability estimation. By using simulated data, it is demonstrated that the method produces more accurate ability estimates, especially for short tests and when reproducing boundary abilities.

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