Search results for " Geometria"

Euler Characteristics of Moduli Spaces of Curves

2005

Let ${mathcal M}_g^n$ be the moduli space of n-pointed Riemann surfaces of genus g. Denote by ${\bar {\mathcal M}}_g^n$ the Deligne-Mumford compactification of ${mathcal M}_g^n$. In the present paper, we calculate the orbifold and the ordinary Euler characteristic of ${\bar {\mathcal M}}_g^n$ for any g and n such that n>2-2g.

MR 2831984 Reviewed Masuda T. Families of finite coverings of the Riemann sphere. Osaka J. Math. 48 (2011), no. 2, 515--540. (Reviewer Francesca Vetr…

2012

Let $G$ be a finite group and let $H$ be a subgroup of $G$ which does not contain normal subgroups of $G$ except $\{ id \}$. The group $G$ acts on the set of the left coset of $G / H$ as follows: \begin{center} $(g, H a) \rightarrow H a g^{- 1}$. \end{center} The author observes that the action defined above is effective and this gives a permutation representation of $G$, $R: G \rightarrow S_{d}$, where $d =[G : H]$. The condition on $H$ ensures that $R$ is injective. Thus, $G$ can be seen as a transitive subgroup of $S_{d}$. Let $X$ and $ Y$ be connected complex varieties. A finite covering $f: X \rightarrow Y$, which branches at most at $B$, is said a $(G, H)-$coverings if there is a surj…

Restituzioni omografiche di finte cupole: la cupola di Santa Maria dei Rimedi a Palermo

2016

Nel vasto repertorio siciliano delle prospettive solide, un ruolo di spicco è ricoperto da un esempio unico di realizzazione di finta prospettiva di cupola sferica su copertura ad arco ribassato, ricavata sull’incrocio del transetto con la navata centrale nella chiesa di Santa Maria dei Rimedi a Palermo. L’unicità di quest’opera sta nella geometria reale della cupola ribassata. Infatti gli esempi più diffusi di finte cupole in Sicilia sono realizzati su soffitti piani lignei o in calcestruzzo. In Appendice 1 si potrà consultare il repertorio delle finte cupole esistenti in Sicilia per la cui stesura ci si è avvalsi degli studi condotti dall’architetto Giuseppe Ingaglio nell’ambito della sua…

On an idea of Bakhtin and Czerwik for solving a first-order periodic problem

2017

We study the existence of solutions to a first-order periodic problem involving ordinary differential equations, by using the quasimetric structure suggested by Bakhtin and Czerwik. The presented approach involves technical conditions and fixed point iterative schemes to yield new theoretical results guaranteeing the existence of at least one solution.

From Caristi’s Theorem to Ekeland’s Variational Principle in ${0}_{\sigma }$ -Complete Metric-Like Spaces

2014

We discuss the extension of some fundamental results in nonlinear analysis to the setting of ${0}_{\sigma }$ -complete metric-like spaces. Then, we show that these extensions can be obtained via the corresponding results in standard metric spaces.

Fixed point results for α-implicit contractions with application to integral equations

2016

Recently, Aydi et al. [On fixed point results for α-implicit contractions in quasi-metric spaces and consequences, Nonlinear Anal. Model. Control, 21(1):40–56, 2016] proved some fixed point results involving α-implicit contractive conditions in quasi-b-metric spaces. In this paper we extend and improve these results and derive some new fixed point theorems for implicit contractions in ordered quasi-b-metric spaces. Moreover, some examples and an application to integral equations are given here to illustrate the usability of the obtained results.

Sur la fonction croissance des variétés riemanniennes

2012

Nous donnons un aperçu du degré de différentiabilité de la fonction croissance des variétés riemanniennes ainsi que de ses singularités en dimension 2.

A note on some fundamental results in complete gauge spaces and application

2015

We discuss the extension of some fundamental results in nonlinear analysis to the setting of gauge spaces. In particular, we establish Ekeland type and Caristi type results under suitable hypotheses for mappings and cyclic mappings. Our theorems generalize and complement some analogous results in the literature, also in the sense of ordered sets and oriented graphs. We apply our results to establishing the existence of solution to a second order nonlinear initial value problem.

An unbounded family of log Calabi–Yau pairs

2016

We give an explicit example of log Calabi-Yau pairs that are log canonical and have a linearly decreasing Euler characteristic. This is constructed in terms of a degree two covering of a sequence of blow ups of three dimensional projective bundles over the Segre-Hirzebruch surfaces ${\mathbb F}_n$ for every positive integer $n$ big enough.

Some considerations on Hydra groups and a new bound for the length of words

2013