Search results for " coverings"

Infinitesimal deformations of double covers of smooth algebraic varieties

2003

The goal of this paper is to give a method to compute the space of infinitesimal deformations of a double cover of a smooth algebraic variety. The space of all infinitesimal deformations has a representation as a direct sum of two subspaces. One is isomorphic to the space of simultaneous deformations of the branch locus and the base of the double covering. The second summand is the subspace of deformations of the double covering which induce trivial deformations of the branch divisor. The main result of the paper is a description of the effect of imposing singularities in the branch locus. As a special case we study deformations of Calabi--Yau threefolds which are non--singular models of do…

Prime evidenze degli effetti delle nuove coperture sul microclima della Villa romana del Casale

2012

In September 2011 has started a new in situ microclimatic monitoring to detect the environmental conditions created by the new covering system of the Villa del Casale di Piazza Armerina (Sicily). The investigation regards sample room, on which the new covering system has been completed, and rooms that still are covered by the methacrylate old system, realized in the 60s, and so many times modified in the following decades. The comparison between the environmental parameters related to the existing covering system that, such as is demonstrated by the previous survey, causes undesired effect both for fruition and for conservation, and the data related to the new covering system, allow to veri…

Hurwitz spaces of coverings with two special fibers and monodromy group a Weyl group of typeBd

2012

f! Y; where is a degree-two coverings with n1 branch points and branch locus D and f is a degree-d coverings with n2 points of simple branching and two special points whose local monodromy is given by e and q, respectively. Furthermore the covering f has monodromy group Sd and f. D /\ D fD? where D f denotes the branch locus of f . We prove that the corresponding Hurwitz spaces are irreducible under the hypothesis n2 s r dC 1.

A note on coverings with special fibres and monodromy group $ S_{d}$

2012

We consider branched coverings of degree over with monodromy group , points of simple branching, special points and fixed branching data at the special points, where is a smooth connected complex projective curve of genus , and , are integers with . We prove that the corresponding Hurwitz spaces are irreducible if .

Verbal sets and cyclic coverings

2010

Abstract We consider groups G such that the set of all values of a fixed word w in G is covered by a finite set of cyclic subgroups. Fernandez-Alcober and Shumyatsky studied such groups in the case when w is the word [ x 1 , x 2 ] , and proved that in this case the corresponding verbal subgroup G ′ is either cyclic or finite. Answering a question asked by them, we show that this is far from being the general rule. However, we prove a weaker form of their result in the case when w is either a lower commutator word or a non-commutator word, showing that in the given hypothesis the verbal subgroup w ( G ) must be finite-by-cyclic. Even this weaker conclusion is not universally valid: it fails …

The miniaturised emission chamber system and home-made passive flux sampler studies of monoaromatic hydrocarbons emissions from selected commercially…

2017

Abstract The estimation of the emission rate of organic compounds released from various types of indoor materials can be performed using stationary environmental test chambers (ETC) classified as ex-situ methods or small-scale portable analytical devices based on the use of passive technique at the stage of analytes sampling from the gaseous phase (in-situ methods). The paper presents results of emissions of selected organic compounds from the monoaromatic hydrocarbons group (benzene, toluene, ethylbenzene, p,m-xylene and styrene) emitted from the surfaces of various types of commercially-available floor coverings and the underlay made of polyurethane foam which might be installed indoors u…

MR 2918162 Reviewed Van der Geer G. and Kouvidakis A. The Hodge bundle on Hurwitz spaces. Pure and Applied Mathematics Quarterly (2011) 7, no. 4, 129…

2012

In this paper the authors consider the Hurwitz space $H_{g, \, d}$ that parametrizes degree $d$ simple coverings of $\mathbb{P}^{1}$ with $b = 2 g - 2 + 2d$ branch points. The compactification $\bar{H}_{g, \, d}$ of this Hurwitz space is the space of admissible covers of genus $g$ and degree $d$, $f: C \rightarrow P$, where $C$ is a nodal curve and $P$ is a stable $b$-pointed curve of genus $0$. Assigning to $f: C \rightarrow P$ the stabilized model of $C$, one defines a natural map $\phi: \bar{H}_{g, \, d} \rightarrow \bar{M}_{g}$ where $\bar{M}_{g}$ denotes the moduli space of stable curves of genus $g$. The Hurwitz space $\bar{H}_{g, \, d}$ carries a natural $\mathbb{Q}$-divisor class, t…

Modular Calabi-Yau threefolds of level eight

2005

In the studies on the modularity conjecture for rigid Calabi-Yau threefolds several examples with the unique level 8 cusp form were constructed. According to the Tate Conjecture correspondences inducing isomorphisms on the middle cohomologies should exist between these varieties. In the paper we construct several examples of such correspondences. In the constructions elliptic fibrations play a crucial role. In fact we show that all but three examples are in some sense built upon two modular curves from the Beauville list.

Corrigendum: Unirationality of Hurwitz Spaces of Coverings of Degree ≤5

2017

We correct Proposition 3.12 and Lemma 3.13 of the paper published in Vol. 2013, No.13, pp.3006-3052. The corrections do not affect the other statements of the paper. In this note, we correct a flow in the statement of Proposition 3.12 of [1] which also leads to a modification in the statement of Lemma 3.13 of [1]. We recall that in this proposition one considers morphisms of schemes X ?→π Y ?→q S, where q is proper, flat, with equidimensional fibers of dimension n and π is finite, flat and surjective. Imposing certain conditions on the fibers it is claimed that the loci of s € S fulfilling these conditions are open subsets of S. A missing condition should be added and the correct version of…

On the irreducibility of Hurwitz spaces of coverings with two special fibers

2012