• A note on a conjecture of Xiao 

    Barja Yáñez, Miguel Ángel; Zucconi, Franco (1998)
    Artículo
    Acceso abierto
  • A note on a question of Fujita and a conjecture of Xiao 

    Barja Yáñez, Miguel Ángel (1998)
    Artículo
    Acceso abierto
  • Experiència pràctica de comunicació de Matemàtiques a la ciutadania i a secundària – 2a fase 

    Alberich Carramiñana, Maria; Barja Yáñez, Miguel Ángel; Borràs Sol, Júlia; Plans Berenguer, Bernat; Quer Bosor, Jordi; Thomas, Federico; Torras, Carme; Xambó Descamps, Sebastián (Universitat Politècnica de Catalunya. Institut de Ciències de l'Educació, 2013-02-08)
    Texto en actas de congreso / Comunicación de congreso
    Acceso restringido por decisión del autor
    El projecte implementa experiències pràctiques dels estudis universitaris de matemàtiques (grau, llicenciatura i màsters) en l'àmbit de la docència i la divulgació científica. La finalitat divulgativa pretén fomentar ...
  • Extension of maps defined on many fibres 

    Barja Yáñez, Miguel Ángel; Naranjo, J. C. (1997)
    Artículo
    Acceso abierto
    Let S be a fibred surface. We prove that the existence of morphisms from non countably many fibres to curves implies, up to base change, the existence of a rational map from S to another surface fibred over the same base ...
  • Generalized Clifford-Severi inequality and the volume of irregular varieties 

    Barja Yáñez, Miguel Ángel (2013-03-02)
    Report de recerca
    Acceso restringido por decisión del autor
    We give a sharp lower bound for the selfintersection of a nef li ne bundle L on an irregular variety X in terms of its continuous global sections and the Albanese dim ension of X, which we call the Generalized Clifford-Severi ...
  • Generalized Clifford-Severi inequality and the volume of irregular varieties 

    Barja Yáñez, Miguel Ángel (2015-02-15)
    Artículo
    Acceso abierto
    We give a sharp lower bound for the self-intersection of a nef line bundle L on an irregular variety X in terms of its continuous global sections and the Albanese dimension of X, which we call the generalized Clifford-Severi ...
  • Numerical Bounds of Canonical Varieties 

    Barja Yáñez, Miguel Ángel (1998)
    Artículo
    Acceso abierto
    We study surfaces and threefolds whose canonical maps are birational (canonical surfaces and threefolds). In the case of canonical surfaces we prove that the known inequlity for its invariants is not sharp if the surface ...
  • On a conjecture of Fujita 

    Barja Yáñez, Miguel Ángel (2000)
    Artículo
    Acceso abierto
  • On the bicanonical map of irregular varieties 

    Barja Yáñez, Miguel Ángel; Lahoz Vilalta, Martí; Naranjo del Val, Joan Carles; Pareschi, Giusseppe (2010-02)
    Report de recerca
    Acceso abierto
    From the point of view of uniform bounds for the birationality of pluricanonical maps, irregular varieties of general type and maximal Albanese dimension behave similarly to curves. In fact Chen-Hacon showed that, at least ...
  • On the slope of bielliptic fibrations 

    Barja Yáñez, Miguel Ángel (1997)
    Artículo
    Acceso abierto
    Let $\pi :S\longrightarrow B$ be a bielliptic fibration. We prove $S$ is, up to base change, a rational double cover of an elliptic fibration and that $\pi $ is isotrivial provided it is smooth. Finally, we prove that the ...
  • On the slope of fibred surfaces 

    Barja Yáñez, Miguel Ángel; Zucconi, Franco (1998)
    Artículo
    Acceso abierto
  • On the slope of fibred surfaces 

    Barja Yáñez, Miguel Ángel; Zucconi, Franco (2000)
    Artículo
    Acceso abierto
    We give an asymptotically sharp lower bound for the slope $\lambda (f)$ of a fibration $f:S\longrightarrow B$, where $S$ is a surface and $B$ is a curve, if there exists an involution on the general fibre $F$ of $f$. ...
  • On the slope of fibred threefolds 

    Barja Yáñez, Miguel Ángel (1998)
    Artículo
    Acceso abierto
    We study from a geographical point of wiew fibrations of threefolds over smooth curves $f: T \longrightarrow B$ such that the general fibre is of general type. We prove the non-negativity of certain relative invariants under ...
  • On the topological index of irregular surfaces 

    Barja Yáñez, Miguel Ángel; Naranjo, J. C.; Pirola, Gian Pietro (2005)
    Artículo
    Acceso abierto
    We study the topological index of some irregular surfaces that we call generalized Lagrangian. We show that under certain hypotheses on the base locus of the Lagrangian system the topological index is non-negative. For ...
  • Positivity properties of relative complete intersections 

    Barja Yáñez, Miguel Ángel; Stoppino, Lidia (2014-10)
    Report de recerca
    Acceso abierto
    We give conditions for f-positivity of relative complete intersections in projective bundles. We also derive an instability result for the fibres.
  • Stability and singularities of relative hypersurfaces 

    Barja Yáñez, Miguel Ángel; Stoppino, Lidia (2014-07-30)
    Report de recerca
    Acceso abierto
    We study relative hypersurfaces, and prove an instability condition for the fibres. This is the starting point for an investigation of the geometry of effective divisors on relative projective bundles.
  • Surfaces on the Severi line 

    Barja Yáñez, Miguel Ángel; Pardini, Rita; Stoppino, Lidia (2016-05-01)
    Artículo
    Acceso abierto
    Let S be a minimal complex surface of general type and of maximal Albanese dimension; by the Severi inequality one has K-S(2) >= 4 chi(O-S). We prove that the equality K-S(2) = 4 chi(O-S) holds if and only if q(S) := ...
  • The representation problem of pairs of symmetric second order tensors in the context of solid mechanics 

    Barja Yáñez, Miguel Ángel; Carol, Ignacio; Planas Vilanova, Francesc d'Assís; Rizzi, Egidio (2003)
    Report de recerca
    Acceso restringido por decisión del autor
  • The structure and slope of bielliptic fibrations 

    Barja Yáñez, Miguel Ángel (1997)
    Artículo
    Acceso abierto
  • Xiao's conjuecture for general fibred surfaces 

    Barja Yáñez, Miguel Ángel; González Alonso, Víctor; Naranjo del Val, Joan Carles (2014-01-10)
    Report de recerca
    Acceso abierto
    We prove that the genus g, the relative irregularity q_f and the Clifford index c_f of a non-isotrivial fibration f satisfy the inequality q_f=g-c_f. This gives in particular a proof of Xiao’s conjecture for fibrations ...