Search results for "J28"
showing 10 items of 12 documents
Projective models of K3 surfaces with an even set
2006
The aim of this paper is to describe algebraic K3 surfaces with an even set of rational curves or of nodes. Their minimal possible Picard number is nine. We completely classify these K3 surfaces and after a carefull analysis of the divisors contained in the Picard lattice we study their projective models, giving necessary and sufficient conditions to have an even set. Moreover we investigate their relation with K3 surfaces with a Nikulin involution.
Bhabha Scattering and a special pencil of K3 surfaces
2018
We study a pencil of K3 surfaces that appeared in the $2$-loop diagrams in Bhabha scattering. By analysing in detail the Picard lattice of the general and special members of the pencil, we identify the pencil with the celebrated Ap\'ery--Fermi pencil, that was related to Ap\'ery's proof of the irrationality of $\zeta(3)$ through the work of F. Beukers, C. Peters and J. Stienstra. The same pencil appears miraculously in different and seemingly unrelated physical contexts.
Symplectic automorphisms of prime order on K3 surfaces
2006
The aim of this paper is to study algebraic K3 surfaces (defined over the complex number field) with a symplectic automorphism of prime order. In particular we consider the action of the automorphism on the second cohomology with integer coefficients. We determine the invariant sublattice and its perpendicular complement, and show that the latter coincides with the Coxeter-Todd lattice in the case of automorphism of order three. We also compute many explicit examples, with particular attention to elliptic fibrations.
Symmetries and equations of smooth quartic surfaces with many lines
2017
We provide explicit equations of some smooth complex quartic surfaces with many lines, including all 10 quartics with more than 52 lines. We study the relation between linear automorphisms and some configurations of lines such as twin lines and special lines. We answer a question by Oguiso on a determinantal presentation of the Fermat quartic surface.
Lines on K3 quartic surfaces in characteristic 2
2016
We prove that a K3 quartic surface defined over a field of characteristic 2 can contain at most 68 lines. If it contains 68 lines, then it is projectively equivalent to a member of a 1-dimensional family found by Rams and Sch\"utt.
Arithmetic and geometry of a K3 surface emerging from virtual corrections to Drell--Yan scattering
2019
We study a K3 surface, which appears in the two-loop mixed electroweak-quantum chromodynamic virtual corrections to Drell--Yan scattering. A detailed analysis of the geometric Picard lattice is presented, computing its rank and discriminant in two independent ways: first using explicit divisors on the surface and then using an explicit elliptic fibration. We also study in detail the elliptic fibrations of the surface and use them to provide an explicit Shioda--Inose structure. Moreover, we point out the physical relevance of our results.
Some families of big and stable bundles on $K3$ surfaces and on their Hilbert schemes of points
2021
Here we investigate meaningful families of vector bundles on a very general polarized $K3$ surface $(X,H)$ and on the corresponding Hyper--Kaehler variety given by the Hilbert scheme of points $X^{[k]}:= {\rm Hilb}^k(X)$, for any integer $k \geqslant 2$. In particular, we prove results concerning bigness and stability of such bundles. First, we give conditions on integers $n$ such that the twist of the tangent bundle of $X$ by the line bundle $nH$ is big and stable on~$X$; we then prove a similar result for a natural twist of the tangent bundle of $X^{[k]}$. Next, we prove global generation, bigness and stability results for tautological bundles on $X^{[k]}$ arising either from line bundles…
Satisfacción laboral de los asalariados en España
2012
El objetivo de este trabajo es identificar los factores determinantes del nivel de satisfacción laboral de los asalariados en España, haciendo especial hincapié en las diferencias de género y de nacionalidad. Para ello, se estima un modelo de respuesta múltiple ordenada, utilizando los datos de la Encuesta de Calidad de Vida en el Trabajo, para el período que abarca desde 2006 a 2010. Los resultados obtenidos muestran que, después de controlar por las características personales y laborales de los asalariados, se obtiene un diferencial positivo en la satisfacción laboral en favor de las mujeres, mientras que no se evidencia la existencia de un efecto diferencial entre los asalariados nativos…
ESCOLARIZACIÓN, TRABAJO INFANTIL Y SATISFACCIÓN LABORAL: EVIDENCIA PARA ETIOPÍA
2012
En ligne sur http://www.staragon.com/revecap/revista/numeros/58/pdf/gamero_lassibille.pdf; International audience; Tomando como referencia Etiopía, este artículo investiga, en el marco de un modelo probit bivariante, cuáles son los factores que influyen en las probabilidades de que un niño trabaje o siga escolarizado. Los resultados muestran que el trabajo infantil desplaza efectivamente a la demanda de educación y sugieren que prohibir el trabajo infantil, para romper la competencia que se ejerce entre la educación y el empleo, podría perpetuar el nivel de pobreza de las generaciones futuras. Por otro lado, se analizan los factores de los que depende su satisfacción laboral, poniendo espec…
Job Satisfaction among Primary School Personnel
2016
International audience; This article analyzes the job satisfaction of primary school teachers inMadagascar. Based on the estimation of multilevel models, low wages and problems getting paid, job insecurity, lack of in-service training, high pupil-teacher ratios, and lack of basic infrastructure and teaching materials are identified as the main reasons for dissatisfaction. Principals' control of teachers' activities also adversely affects satisfaction, suggesting that, in Malagasy schools, neither school directors nor teachers have succeeded in adopting organizational cultures based on cooperation among their members. These results are likely to stimulate debates on educational policy, both …