MR 3219513 Reviewed Venkataramana T. N. Monodromy of cyclic coverings of the projective line. Invent. Math., 197 (2014), 1–-45. (Reviewer Francesca Vetro) 14H30 (14D05 22E40 20F36)

Let $d \geq 2$ and $n \geq 1$ be integers and $P_{n+1}$ be the pure braid group on $n + 1$ strands. In this paper, the author studies the image of $P_{n+1}$ under the monodromy action on the homology of a cyclic covering of degree $d$ of the projective line. More precisely, let $k_{1}, \ldots, k_{n + 1}$ be integers such that $1 \leq k_{i} \leq d - 1$ and gcd$(k_{i}, d) = 1$ for each $i$. Moreover, let $a_{1}, \ldots, a_{n + 1}$ be distinct points of the complex plane and $C$ be the space of points in $\mathbb{C}^{n + 1}$ with all distinct coordinates. Let us denote by $X_{a, k}$ the affine curve defined by the equation $$ y^{d} = (x - a_{1})^{k_{1}} (x - a_{2})^{k_{2}} \cdots (x - a_{n +1}…

Multiple Solutions with Sign Information for a Class of Coercive (p, 2)-Equations

We consider a nonlinear Dirichlet equation driven by the sum of a p-Laplacian and of a Laplacian (a (p, 2)-equation). The hypotheses on the reaction f(z, x) are minimal and make the energy (Euler) functional of the problem coercive. We prove two multiplicity theorems producing three and four nontrivial smooth solutions, respectively, all with sign information. We apply our multiplicity results to the particular case of a class of parametric (p, 2)-equations.

Irreducible components of Hurwitz spaces of coverings with two special fibers

In this paper we prove new results of irreducibility for Hurwitz spaces of coverings whose monodromy group is a Weyl group of type B_d and whose local monodromies are all reflections except two.

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

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.

Fixed Points for Weakα-ψ-Contractions in Partial Metric Spaces

Recently, Samet et al. (2012) introduced the notion ofα-ψ-contractive mappings and established some fixed point results in the setting of complete metric spaces. In this paper, we introduce the notion of weakα-ψ-contractive mappings and give fixed point results for this class of mappings in the setting of partial metric spaces. Also, we deduce fixed point results in ordered partial metric spaces. Our results extend and generalize the results of Samet et al.

MR 2831984 Reviewed Masuda T. Families of finite coverings of the Riemann sphere. Osaka J. Math. 48 (2011), no. 2, 515--540. (Reviewer Francesca Vetro) 14H30 (14H37)

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…

Landesman-Lazer type (p, q)-equations with Neumann condition

We consider a Neumann problem driven by the (p, q)-Laplacian under the Landesman-Lazer type condition. Using the classical saddle point theorem and other classical results of the calculus of variations, we show that the problem has at least one nontrivial weak solution.

F-contractions of Hardy–Rogers-type and application to multistage decision

We prove fixed point theorems for F-contractions of Hardy–Rogers type involving self-mappings defined on metric spaces and ordered metric spaces. An example and an application to multistage decision processes are given to show the usability of the obtained theorems.

Some critical remarks on the paper “A note on the metrizability of tvs-cone metric spaces” / Некоторые критические замечания о работе «Заметки о метризуемости твп-конических пространств» / Neke kritičke napomene o radu “Beleška o metrizabilnosti tvp-konusnih metričkih prostora”

This short and concise note provides a detailed exposition of the approach and results established by (Lin et al, 2015, pp.271-279). We show that the obtained results are not particularly surprising and new. Namely, using an old result due to K. Deimling it is indicated that tvs-cone metric spaces over solid cones are actually cone metric spaces over normal solid cones. Hence, there are only cone metric spaces over normal solid cones or over normal non-solid cones. One question still unanswered is whether an ordered topological vector space with a non-normal non-solid cone exists. / В представленных, в данной статье, заметках приведен подробный обзор методов и полученных результатов исследо…

Remarks on G-Metric Spaces

In 2005, Mustafa and Sims (2006) introduced and studied a new class of generalized metric spaces, which are called G-metric spaces, as a generalization of metric spaces. We establish some useful propositions to show that many fixed point theorems on (nonsymmetric) G-metric spaces given recently by many authors follow directly from well-known theorems on metric spaces. Our technique can be easily extended to other results as shown in application.

Nonlinear Robin problems with unilateral constraints and dependence on the gradient

We consider a nonlinear Robin problem driven by the p-Laplacian, with unilateral constraints and a reaction term depending also on the gradient (convection term). Using a topological approach based on fixed point theory (the Leray-Schauder alternative principle) and approximating the original problem using the Moreau-Yosida approximations of the subdifferential term, we prove the existence of a smooth solution.

Superlinear Robin Problems with Indefinite Linear Part

We consider a semilinear Robin problem with an indefinite linear part and a superlinear reaction term, which does not satisfy the usual in such cases AR condition. Using variational methods, together with truncation–perturbation techniques and Morse theory (critical groups), we establish the existence of three nontrivial solutions. Our result extends in different ways the multiplicity theorem of Wang.

Systems of quasilinear elliptic equations with dependence on the gradient via subsolution-supersolution method

For the homogeneous Dirichlet problem involving a system of equations driven by \begin{document}$(p,q)$\end{document} -Laplacian operators and general gradient dependence we prove the existence of solutions in the ordered rectangle determined by a subsolution-supersolution. This extends the preceding results based on the method of subsolution-supersolution for systems of elliptic equations. Positive and negative solutions are obtained.

Nonlinear concave-convex problems with indefinite weight

We consider a parametric nonlinear Robin problem driven by the p-Laplacian and with a reaction having the competing effects of two terms. One is a parametric (Formula presented.) -sublinear term (concave nonlinearity) and the other is a (Formula presented.) -superlinear term (convex nonlinearity). We assume that the weight of the concave term is indefinite (that is, sign-changing). Using the Nehari method, we show that for all small values of the parameter (Formula presented.), the problem has at least two positive solutions and also we provide information about their regularity.

Approximate fixed points of set-valued mapping in b-metric space

We establish existence results related to approximate fixed point property of special types of set-valued contraction mappings, in the setting of b-metric spaces. As consequences of the main theorem, we give some fixed point results which generalize and extend various fixed point theorems in the existing literature. A simple example illustrates the new theory. Finally, we apply our results to establishing the existence of solution for some differential and integral problems.

A Parametric Dirichlet Problem for Systems of Quasilinear Elliptic Equations With Gradient Dependence

The aim of this article is to study the Dirichlet boundary value problem for systems of equations involving the (pi, qi) -Laplacian operators and parameters μi≥0 (i = 1,2) in the principal part. Another main point is that the nonlinearities in the reaction terms are allowed to depend on both the solution and its gradient. We prove results ensuring existence, uniqueness, and asymptotic behavior with respect to the parameters.

From metric spaces to partial metric spaces

Motivated by experience from computer science, Matthews (1994) introduced a nonzero self-distance called a partial metric. He also extended the Banach contraction principle to the setting of partial metric spaces. In this paper, we show that fixed point theorems on partial metric spaces (including the Matthews fixed point theorem) can be deduced from fixed point theorems on metric spaces. New fixed point theorems on metric spaces are established and analogous results on partial metric spaces are deduced. MSC:47H10, 54H25.

MR 2834249 Reviewed Hoshi Y., Galois-theoretic characterization of isomorphism classes of monodromically full hyperbolic curves of genus zero, Nagoya Math. J. (2011) 203, 47--100 ( Reviewer Francesca Vetro) 14H30 (14H10)

Let K be a finitely generated field of characteristic zero, l be a prime number and S be a scheme. In this paper, the author studies isomorphism classes of hyperbolic curves. The author calls the pair (C, D), where C is a scheme over S and D \subset C is a closed subscheme of C, a hyperbolic curve of type (g, r) over S if C is smooth and proper over S, if any geometric fiber of C \rightarrow S is a connected curve of genus g and if the composite D \rightarrow C \rightarrow S is a finite \'{e}tale covering over S of degree r. The main result of this paper is that the isomorphism class of a hyperbolic curve of genus zero over K that is l-monodromically full is completely determinated by the k…

Solutions with sign information for nonlinear Robin problems with no growth restriction on reaction

We consider a parametric nonlinear Robin problem driven by a nonhomogeneous differential operator. The reaction is a Carathéodory function which is only locally defined (that is, the hypotheses concern only its behaviour near zero). The conditions on the reaction are minimal. Using variational tools together with truncation, perturbation and comparison techniques and critical groups, we show that for all small values of the parameter λ > 0, the problem has at least three nontrivial smooth solutions, two of constant sign and the third nodal.

Multiple solutions with sign information for semilinear Neumann problems with convection

We consider a semilinear Neumann problem with convection. We assume that the drift coefficient is indefinite. Using the theory of nonlinear operators of monotone type, together with truncation and comparison techniques and flow invariance arguments, we prove a multiplicity theorem producing three nontrivial smooth solutions (positive, negative and nodal).

Nonlinear multivalued Duffing systems

We consider a multivalued nonlinear Duffing system driven by a nonlinear nonhomogeneous differential operator. We prove existence theorems for both the convex and nonconvex problems (according to whether the multivalued perturbation is convex valued or not). Also, we show that the solutions of the nonconvex problem are dense in those of the convex (relaxation theorem). Our work extends the recent one by Kalita-Kowalski (JMAA, https://doi.org/10.1016/j.jmaa. 2018.01.067).

On approximating curves associated with nonexpansive mappings

Let X be a Banach space with metric d. Let T, N : X → X be a strict d-contraction and a d-nonexpansive map, respectively. In this paper we investigate the properties of the approximating curve associated with T and N. Moreover, following [3], we consider the approximating curve associated with a holomorphic map f : B → α B and a ρ-nonexpansive map M : B → B, where B is the open unit ball of a complex Hilbert space H, ρ is the hyperbolic metric defined on B and 0 ≤ α < 1. We give conditions on f and M for this curve to be injective, and we show that this curve is continuous.

Three solutions to mixed boundary value problem driven by p(z)-Laplace operator

We prove the existence of at least three weak solutions to a mixed Dirichlet–Neumann boundary value problem for equations driven by the p(z)-Laplace operator in the principal part. Our approach is variational and use three critical points theorems.

Multiple solutions for (p,2)-equations at resonance

We consider a nonlinear nonhomogeneous Dirichlet problem driven by the sum of a p-Laplacian and a Laplacian and a reaction term which is (p− 1)-linear near ±∞ and resonant with respect to any nonprincipal variational eigenvalue of (−∆p, W01,p(Ω)). Using variational tools together with truncation and comparison techniques and Morse Theory (critical groups), we establish the existence of six nontrivial smooth solutions. For five of them we provide sign information and order them.

(p,2)-equations resonant at any variational eigenvalue

We consider nonlinear elliptic Dirichlet problems driven by the sum of a p-Laplacian and a Laplacian (a (p,2) -equation). The reaction term at ±∞ is resonant with respect to any variational eigenvalue of the p-Laplacian. We prove two multiplicity theorems for such equations.

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, 1297 -- 1307. (Reviewer Francesca Vetro) 14H10 (14H30)

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…

Best Proximity Points for Some Classes of Proximal Contractions

Given a self-mapping g: A → A and a non-self-mapping T: A → B, the aim of this work is to provide sufficient conditions for the existence of a unique point x ∈ A, called g-best proximity point, which satisfies d g x, T x = d A, B. In so doing, we provide a useful answer for the resolution of the nonlinear programming problem of globally minimizing the real valued function x → d g x, T x, thereby getting an optimal approximate solution to the equation T x = g x. An iterative algorithm is also presented to compute a solution of such problems. Our results generalize a result due to Rhoades (2001) and hence such results provide an extension of Banach's contraction principle to the case of non-s…

Nonisotrivial families over curves with fixed point free automorphisms

We construct for any smooth projective curve of genus $q\ge 2$ with a fixed point free automorphism a nonisotrivial family of curves. Moreover we study the space of modular curves and that of parameters.

Multiple nodal solutions for semilinear robin problems with indefinite linear part and concave terms

We consider a semilinear Robin problem driven by Laplacian plus an indefinite and unbounded potential. The reaction function contains a concave term and a perturbation of arbitrary growth. Using a variant of the symmetric mountain pass theorem, we show the existence of smooth nodal solutions which converge to zero in $C^1(\overline{\Omega})$. If the coefficient of the concave term is sign changing, then again we produce a sequence of smooth solutions converging to zero in $C^1(\overline{\Omega})$, but we cannot claim that they are nodal.

Positive solutions for singular (p, 2)-equations

We consider a nonlinear nonparametric Dirichlet problem driven by the sum of a p-Laplacian and of a Laplacian (a (p, 2)-equation) and a reaction which involves a singular term and a $$(p-1)$$ -superlinear perturbation. Using variational tools and suitable truncation and comparison techniques, we show that the problem has two positive smooth solutions.

Singular Neumann (p, q)-equations

We consider a nonlinear parametric Neumann problem driven by the sum of a p-Laplacian and of a q-Laplacian and exhibiting in the reaction the competing effects of a singular term and of a resonant term. Using variational methods together with suitable truncation and comparison techniques, we show that for small values of the parameter the problem has at least two positive smooth solutions.

Fixed points for weak alpha-psi-contractions in partial metric spaces

Recently, Samet et al. (2012) introduced the notion of $\alpha $ - $\psi $ -contractive mappings and established some fixed point results in the setting of complete metric spaces. In this paper, we introduce the notion of weak $\alpha $ - $\psi $ -contractive mappings and give fixed point results for this class of mappings in the setting of partial metric spaces. Also, we deduce fixed point results in ordered partial metric spaces. Our results extend and generalize the results of Samet et al.

Pairs of solutions for Robin problems with an indefinite and unbounded potential, resonant at zero and infinity

We consider a semilinear Robin problem driven by the Laplacian plus an indefinite and unbounded potential and a Caratheodory reaction term which is resonant both at zero and $$\pm \infty $$ . Using the Lyapunov–Schmidt reduction method and critical groups (Morse theory), we show that the problem has at least two nontrivial smooth solutions.

Irreducibility of Hurwitz spaces of coverings of an elliptic curve of prime degree with one point of total ramification

Let Y be an elliptic curve, p a prime number and WH_{p,n}(Y) the Hurwitz space that parametrizes equivalence classes of p-sheeted branched coverings of Y , with n branch points, n − 1 of which are points of simple ramification and one of total ramification.In this paper, we prove that WH_{p,n}(Y) is irreducible if n − 1≥ 2 p.

Solutions for parametric double phase Robin problems

We consider a parametric double phase problem with Robin boundary condition. We prove two existence theorems. In the first the reaction is ( p − 1 )-superlinear and the solutions produced are asymptotically big as λ → 0 + . In the second the conditions on the reaction are essentially local at zero and the solutions produced are asymptotically small as λ → 0 + .

Best approximation and variational inequality problems involving a simulation function

We prove the existence of a g-best proximity point for a pair of mappings, by using suitable hypotheses on a metric space. Moreover, we establish some convergence results for a variational inequality problem, by using the variational characterization of metric projections in a real Hilbert space. Our results are applicable to classical problems of optimization theory.

From fuzzy metric spaces to modular metric spaces: a fixed point approach

We propose an intuitive theorem which uses some concepts of auxiliary functions for establishing existence and uniqueness of the fixed point of a self-mapping. First we work in the setting of fuzzy metric spaces in the sense of George and Veeramani, then we deduce some consequences in modular metric spaces. Finally, a sample homotopy result is derived making use of the main theorem.

Multiple solutions for parametric double phase Dirichlet problems

We consider a parametric double phase Dirichlet problem. Using variational tools together with suitable truncation and comparison techniques, we show that for all parametric values [Formula: see text] the problem has at least three nontrivial solutions, two of which have constant sign. Also, we identify the critical parameter [Formula: see text] precisely in terms of the spectrum of the [Formula: see text]-Laplacian.

Fixed point results for nonexpansive mappings on metric spaces

In this paper we obtain some fixed point results for a class of nonexpansive single-valued mappings and a class of nonexpansive multi-valued mappings in the setting of a metric space. The contraction mappings in Banach sense belong to the class of nonexpansive single-valued mappings considered herein. These results are generalizations of the analogous ones in Khojasteh et al. [Abstr. Appl. Anal. 2014 (2014), Article ID 325840].

A coincidence-point problem of Perov type on rectangular cone metric spaces

We consider a coincidence-point problem in the setting of rectangular cone metric spaces. Using alpha-admissible mappings and following Perov's approach, we establish some existence and uniqueness results for two self-mappings. Under a compatibility assumption, we also solve a common fixed-point problem.

The effects of convolution and gradient dependence on a parametric Dirichlet problem

Our objective is to study a new type of Dirichlet boundary value problem consisting of a system of equations with parameters, where the reaction terms depend on both the solution and its gradient (i.e., they are convection terms) and incorporate the effects of convolutions. We present results on existence, uniqueness and dependence of solutions with respect to the parameters involving convolutions.

From Caristi’s Theorem to Ekeland’s Variational Principle in 0σ-Complete Metric-Like Spaces

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

Nonlinear Nonhomogeneous Elliptic Problems

We consider nonlinear elliptic equations driven by a nonhomogeneous differential operator plus an indefinite potential. The boundary condition is either Dirichlet or Robin (including as a special case the Neumann problem). First we present the corresponding regularity theory (up to the boundary). Then we develop the nonlinear maximum principle and present some important nonlinear strong comparison principles. Subsequently we see how these results together with variational methods, truncation and perturbation techniques, and Morse theory (critical groups) can be used to analyze different classes of elliptic equations. Special attention is given to (p, 2)-equations (these are equations driven…

Extremal solutions and strong relaxation for nonlinear multivalued systems with maximal monotone terms

Abstract We consider differential systems in R N driven by a nonlinear nonhomogeneous second order differential operator, a maximal monotone term and a multivalued perturbation F ( t , u , u ′ ) . For periodic systems we prove the existence of extremal trajectories, that is solutions of the system in which F ( t , u , u ′ ) is replaced by ext F ( t , u , u ′ ) (= the extreme points of F ( t , u , u ′ ) ). For Dirichlet systems we show that the extremal trajectories approximate the solutions of the “convex” problem in the C 1 ( T , R N ) -norm (strong relaxation).

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

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.

On Hurwitz spaces of coverings with one special fiber

Let X X' Y be a covering of smooth, projective complex curves such that p is a degree 2 etale covering and f is a degree d covering, with monodromy group Sd, branched in n + 1 points one of which is a special point whose local monodromy has cycle type given by the partition e = (e1,...,er) of d. We study such coverings whose monodromy group is either W(Bd) or wN(W(Bd))(G1)w-1 for some w in W(Bd), where W(Bd) is the Weyl group of type Bd, G1 is the subgroup of W(Bd) generated by reflections with respect to the long roots ei - ej and N(W(Bd))(G1) is the normalizer of G1. We prove that in both cases the corresponding Hurwitz spaces are not connected and hence are not irreducible. In fact, we s…

Robin problems with general potential and double resonance

Abstract We consider a semilinear elliptic problem with Robin boundary condition and an indefinite and unbounded potential. The reaction term is a Caratheodory function exhibiting linear growth near ± ∞ . We assume that double resonance occurs with respect to any positive spectral interval. Using variational tools and critical groups, we show that the problem has a nontrivial smooth solution.

An alternative and easy approach to fixed point results via simulation functions

Abstract We discuss, extend, improve and enrich results on simulation functions established by several authors. Furthermore, by using Lemma 2.1 of Radenovic et al. [Bull. Iran. Math. Soc., 2012, 38, 625],we get much shorter and nicer proofs than the corresponding ones in the existing literature.

Relaxation for a Class of Control Systems with Unilateral Constraints

We consider a nonlinear control system involving a maximal monotone map and with a priori feedback. We assume that the control constraint multifunction $U(t,x)$ is nonconvex valued and only lsc in the $x \in \mathbb{R}^{N}$ variable. Using the Q-regularization (in the sense of Cesari) of $U(t,\cdot )$, we introduce a relaxed system. We show that this relaxation process is admissible.

Irreducibility of Hurwitz spaces of coverings with one special fiber

Abstract Let Y be a smooth, projective complex curve of genus g ⩾ 1. Let d be an integer ⩾ 3, let e = {e1, e2,..., er} be a partition of d and let | e | = Σi=1r(ei − 1). In this paper we study the Hurwitz spaces which parametrize coverings of degree d of Y branched in n points of which n − 1 are points of simple ramification and one is a special point whose local monodromy has cyclic type e and furthermore the coverings have full monodromy group Sd. We prove the irreducibility of these Hurwitz spaces when n − 1 + | e | ⩾ 2d, thus generalizing a result of Graber, Harris and Starr [A note on Hurwitz schemes of covers of a positive genus curve, Preprint, math. AG/0205056].

MR 2827979 Reviewed Lando, S. K. Hurwitz numbers: on the edge between combinatorics and geometry. Proceedings of the International Congress of Mathematicians, volume IV, 2010, 2444--2470. (Reviewer Francesca Vetro) 14N35 (05A15 14H10 14H30 37K20)

Object of study in this paper are the Hurwitz numbers. They were introduced by Hurwitz in the end of nineteenth century and still they are of great interest. The Hurwitz numbers are important in topology because they enumerate ramified coverings of two-dimensional surfaces, but not only. The author observes that their importance in modern research is mainly due to their connections with the geometry of the moduli space of curves. Moreover, they are of interest in mathematical physics and group theory. The purpose of this paper is to describe the progress made in the last couple of decades in understanding Hurwitz numbers.

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

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.

Fixed point for cyclic weak (\psi, C)-contractions in 0-complete partial metric spaces

In this paper, following (W.A. Kirk, P.S. Srinivasan, P. Veeramani, Fixed points for mappings satisfying cyclical contractive conditions, Fixed Point Theory, 4 (2003), 79-89), we give a fixed point result for cyclic weak (ψ,C)-contractions on partial metric space. A Maia type fixed point theorem for cyclic weak (ψ,C)-contractions is also given.

MR 3079286 Reviewed Hoshi Y. On a problem of Matsumoto and Tamagawa concerning monodromic fullness of hyperbolic curves: genus zero case. Tohoku Math. J., 65 (2013), 231–242. (Reviewer Francesca Vetro) 14H30 (14H10)

Let \emph{Primes} be the set of all prime numbers, $k$ be a finite extension of the field of rational numbers and $\bar{k}$ be an algebraic closure of $k$. Let $(g, r)$ be a pair of nonnegative integers such that $2g - 2 + r > 0$ and $X$ be a hyperbolic curve of type $(g, r)$ over $k$. The author observes that, for each $l \in \emph{Primes}$, there are two natural outer representations on $\pi^{\{ l\}}_{1} (X \otimes_{k} \bar{k})$: $$\rho_{X / k} ^{\{ l\}}: G_{k} := Gal(\bar{k} / k) \rightarrow Out (\pi^{\{ l\}}_{1} (X \otimes_{k} \bar{k}))$$ and $$ \rho_{g, [r]} ^{\{ l\}}: \pi_{1}(M_{g, [r]}) \rightarrow Out (\pi^{\{ l\}}_{1} (X \otimes_{k} \bar{k})),$$ where $\pi^{\{ l\}}_{1} (X \otimes_{…

MR 2776821 Reviewed Berger E. Hurwitz equivalence in dihedral groups. The Electronic Journal of Combinatorics 18 (2011), no.1, paper 45, 16 pp. (Reviewer Francesca Vetro) 20F36

In the paper under review, the author studies the orbits of the action of the braid group B_{n} on G^{n} where G denoted a dihedral group. At first, the author considers tuples T consisting only of reflections. In this case, the author proves that the orbits are determinate by three invariants. These invariants are the product of the entries, the subgroup generated by the entries and the number of times each conjugacy class is represented in T. Successively, the author works with tuples whose entries are any elements of dihedral groups. The author shows that, also this time, the above invariants are sufficient in order to determinate the orbits of the action of B_{n} on G^{n}.

An approximate fixed point result for multivalued mappings under two constraint inequalities

We consider an approximate multivalued fixed point problem under two constraint inequalities, for which we provide sufficient conditions for the existence of at least one solution. Then, we present some consequences and related results.

Singular Double Phase Problems with Convection

We consider a nonlinear Dirichlet problem driven by the sum of a $p$ -Laplacian and of a $q$ -Laplacian (double phase equation). In the reaction we have the combined effects of a singular term and of a gradient dependent term (convection) which is locally defined. Using a mixture of variational and topological methods, together with suitable truncation and comparison techniques, we prove the existence of a positive smooth solution.

Metric or partial metric spaces endowed with a finite number of graphs: a tool to obtain fixed point results

Abstract We give some fixed point theorems in the setting of metric spaces or partial metric spaces endowed with a finite number of graphs. The presented results extend and improve several well-known results in the literature. In particular, we discuss a Caristi type fixed point theorem in the setting of partial metric spaces, which has a close relation to Ekelandʼs principle.

Multiple solutions with sign information for a (p,2)-equation with combined nonlinearities

Abstract We consider a parametric nonlinear Dirichlet problem driven by the sum of a p -Laplacian and of a Laplacian (a ( p , 2 ) -equation) and with a reaction which has the competing effects of two distinct nonlinearities. A parametric term which is ( p − 1 ) -superlinear (convex term) and a perturbation which is ( p − 1 ) -sublinear (concave term). First we show that for all small values of the parameter the problem has at least five nontrivial smooth solutions, all with sign information. Then by strengthening the regularity of the two nonlinearities we produce two more nodal solutions, for a total of seven nontrivial smooth solutions all with sign informations. Our proofs use critical p…

Solutions and positive solutions for superlinear Robin problems

We consider nonlinear, nonhomogeneous Robin problems with a (p − 1)-superlinear reaction term, which need not satisfy the Ambrosetti-Rabinowitz condition. We look for positive solutions and prove existence and multiplicity theorems. For the particular case of the p-Laplacian, we prove existence results under a different geometry near the origin.We consider nonlinear, nonhomogeneous Robin problems with a (p − 1)-superlinear reaction term, which need not satisfy the Ambrosetti-Rabinowitz condition. We look for positive solutions and prove existence and multiplicity theorems. For the particular case of the p-Laplacian, we prove existence results under a different geometry near the origin.

The class of F-contraction mappings with a measure of noncompactness

In this chapter we review a class of contraction conditions, which are largely used to obtain interesting generalizations of the Banach fixed-point theorem in various abstract settings. We also present a new fixed-point existence result obtained by considering such a kind of contraction condition and a measure of noncompactness. Moreover, we show the applicability of these results in the theory of functional equations.

Continuous spectrum for a two phase eigenvalue problem with an indefinite and unbounded potential

Abstract We consider a two phase eigenvalue problem driven by the ( p , q ) -Laplacian plus an indefinite and unbounded potential, and Robin boundary condition. Using a modification of the Nehari manifold method, we show that there exists a nontrivial open interval I ⊆ R such that every λ ∈ I is an eigenvalue with positive eigenfunctions. When we impose additional regularity conditions on the potential function and the boundary coefficient, we show that we have smooth eigenfunctions.

Singular (p, q)-equations with superlinear reaction and concave boundary condition

We consider a parametric nonlinear elliptic problem driven by the sum of a p-Laplacian and of a q-Laplacian (a (Formula presented.) -equation) with a singular and (Formula presented.) -superlinear reaction and a Robin boundary condition with (Formula presented.) -sublinear boundary term (Formula presented.). So, the problem has the combined effects of singular, concave and convex terms. We look for positive solutions and prove a bifurcation-type theorem describing the changes in the set of positive solutions as the parameter varies.

Caristi Type Selections of Multivalued Mappings

Multivalued mappings and related selection theorems are fundamental tools in many branches of mathematics and applied sciences. In this paper we continue this theory and prove the existence of Caristi type selections for generalized multivalued contractions on complete metric spaces, by using some classes of functions. Also we prove fixed point and quasi-fixed point theorems.

Common fixed points of mappings satisfying implicit relations in partial metric spaces

Matthews, [S. G. Matthews, Partial metric topology, in: Proc. 8th Summer Conference on General Topology and Applications, in: Ann. New York Acad. Sci., vol. 728, 1994, pp. 183-197], introduced and studied the concept of partial metric space, as a part of the study of denotational semantics of dataflow networks. He also obtained a Banach type fixed point theorem on complete partial metric spaces. Very recently Berinde and Vetro, [V. Berinde, F. Vetro, Common fixed points of mappings satisfying implicit contractive conditions, Fixed Point Theory and Applications 2012, 2012:105], discussed, in the setting of metric and ordered metric spaces, coincidence point and common fixed point theorems fo…

Nonlinear psi-quasi-contractions of Ciric-type in partial metric spaces

In this paper we obtain results of fixed and common fixed points for self-mappings satisfying a nonlinear contractive condition of Ciric-type in the framework of partial metric spaces. We also prove results of fixed point for self-mappings satisfying an ordered nonlinear contractive condition in the setting of ordered partial metric spaces.

On the existence of at least a solution for functional integral equations via measure of noncompactness

In this article, we use fixed-point methods and measure of noncompactness theory to focus on the problem of establishing the existence of at least a solution for the following functional integral equation ¶ \[u(t)=g(t,u(t))+\int_{0}^{t}G(t,s,u(s))\,ds,\quad t\in{[0,+\infty[},\] in the space of all bounded and continuous real functions on $\mathbb{R}_{+}$ , under suitable assumptions on $g$ and $G$ . Also, we establish an extension of Darbo’s fixed-point theorem and discuss some consequences.

A singular (p,q)-equation with convection and a locally defined perturbation

Abstract We consider a parametric Dirichlet problem driven by the ( p , q ) -Laplacian and a reaction which is gradient dependent (convection) and the competing effects of two more terms, one a parametric singular term and a locally defined perturbation. We show that for all small values of the parameter the problem has a positive smooth solution.

MR 2944715 Reviewed Zhu S. On the recursion formula for double Hurwitz numbers. Proceedings of the American Mathematical Society (2012) 140, no. 11, 3749--3760. (Reviewer Francesca Vetro) 14H30 (05E05 14H10)

Let $\mu = (\mu_{1}, \mu_{2}, \ldots, \mu_{m})$ and $\nu = (\nu_{1}, \nu_{2}, \ldots, \nu_{n})$ be two partitions of a positive integer $d$. In this paper, the author considers degree $d$ branched coverings of $\mathbb{P}^{1}$ with at most two special points, $0$ and $\infty$. Specifically, the purpose of the author is to give a recursion formula for double Hurwitz numbers $H^{g}_{\mu, \nu}$ by the cut-join analysis. Here, $H^{g}_{\mu, \nu}$ denotes the number of genus $g$ branched covers of $\mathbb{P}^{1}$ with branching date corresponding to $\mu$ and $\nu$ over $0$ and $\infty$, respectively. Furthemore, as application, the author gets a polynomial identity for linear Goulden-Jackson-Va…

Irreducibility of Hurwitz spaces of coverings with one special fiber and monodromy group a Weyl group of type D d

Let Y be a smooth, connected, projective complex curve. In this paper, we study the Hurwitz spaces which parameterize branched coverings of Y whose monodromy group is a Weyl group of type D d and whose local monodromies are all reflections except one. We prove the irreducibility of these spaces when $$Y \simeq \mathbb {P}^{1}$$ and successively we extend the result to curves of genus g ≥  1.

Constant sign and nodal solutions for nonlinear robin equations with locally defined source term

We consider a parametric Robin problem driven by a nonlinear, nonhomogeneous differential operator which includes as special cases the p-Laplacian and the (p,q)-Laplacian. The source term is parametric and only locally defined (that is, in a neighborhood of zero). Using suitable cut-off techniques together with variational tools and comparison principles, we show that for all big values of the parameter, the problem has at least three nontrivial smooth solutions, all with sign information (positive, negative and nodal).

On the irreducibility of Hurwitz spaces of coverings with an arbitrary number of special points

In this paper we study Hurwitz spaces of coverings of Y with an arbitrary number of special points and with monodromy group a Weyl group of type D_d, where Y is a smooth, complex projective curve. We give conditions for which these spaces are irreducible.

A homotopy fixed point theorem in 0-complete partial metric space

We generalize a result of Feng and Liu, on multi-valued contractive mappings, for studying the relationship between fixed point sets and homotopy fixed point sets. The presented results are discussed in the generalized setting of 0-complete partial metric spaces. An example and a nonlinear alternative of Leray-Schauder type are given to support our theorems.

A generalization of Nadler fixed point theorem

Jleli and Samet gave a new generalization of the Banach contraction principle in the setting of Branciari metric spaces [Jleli, M. and Samet, B., A new generalization of the Banach contraction principle, J. Inequal. Appl., 2014:38 (2014)]. The purpose of this paper is to study the existence of fixed points for multivalued mappings, under a similar contractive condition, in the setting of complete metric spaces. Some examples are provided to illustrate the new theory.

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

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.

Nonlinear vector Duffing inclusions with no growth restriction on the orientor field

We consider nonlinear multivalued Dirichlet Duffing systems. We do not impose any growth condition on the multivalued perturbation. Using tools from the theory of nonlinear operators of monotone type, we prove existence theorems for the convex and the nonconvex problems. Also we show the existence of extremal trajectories and show that such solutions are $C_0^1(T,\mathbb{R}^N)$-dense in the solution set of the convex problem (strong relaxation theorem).

MR 3007673 Reviewed Geiss F. The Unirationality of Hurwitz spaces of 6-gonal curves of small genus. Documenta Mathematica (2012) 17, 627--640. (Reviewer Francesca Vetro) 14H10 (14M20)

Let H (d, w) be the Hurwitz space that parametrizes degree d simple coverings of the projective line with w = 2g + 2d - 2 branch points. A classic result affirms the unirationality of these spaces for d \leq 3. Successively, Arbarello and Cornalba in [E. Arbarello and M. Cornalba, Footnotes to a paper of Beniamino Segre, Math. Ann. 256 (1981), 341--362] prove that the spaces H (d, w) are unirational in the following cases: d \leq 5 and g \geq d - 1, d = 6 and 5 \leq g \leq 10 or g = 12 and d = 7 and g = 7. In this paper, the author studies the problem of unirationality over an algebraically closed field of characteristic zero when d = 6. In particular, the author proves that the spaces H (6…

On a Robin (p,q)-equation with a logistic reaction

We consider a nonlinear nonhomogeneous Robin equation driven by the sum of a \(p\)-Laplacian and of a \(q\)-Laplacian (\((p,q)\)-equation) plus an indefinite potential term and a parametric reaction of logistic type (superdiffusive case). We prove a bifurcation-type result describing the changes in the set of positive solutions as the parameter \(\lambda \gt 0\) varies. Also, we show that for every admissible parameter \(\lambda \gt 0\), the problem admits a smallest positive solution.

Parameter dependence for the positive solutions of nonlinear, nonhomogeneous Robin problems

We consider a parametric nonlinear Robin problem driven by a nonlinear nonhomogeneous differential operator plus an indefinite potential. The reaction term is $$(p-1)$$-superlinear but need not satisfy the usual Ambrosetti–Rabinowitz condition. We look for positive solutions and prove a bifurcation-type result for the set of positive solutions as the parameter $$\lambda >0$$ varies. Also we prove the existence of a minimal positive solution $$u_\lambda ^*$$ and determine the monotonicity and continuity properties of the map $$\lambda \rightarrow u_\lambda ^*$$.

Connected components of Hurwitz spaces of coverings with one special fiber and monodromy groups contained in a Weyl group of type B_d

(p, 2)-Equations with a Crossing Nonlinearity and Concave Terms

We consider a parametric Dirichlet problem driven by the sum of a p-Laplacian ($$p>2$$) and a Laplacian (a (p, 2)-equation). The reaction consists of an asymmetric $$(p-1)$$-linear term which is resonant as $$x \rightarrow - \infty $$, plus a concave term. However, in this case the concave term enters with a negative sign. Using variational tools together with suitable truncation techniques and Morse theory (critical groups), we show that when the parameter is small the problem has at least three nontrivial smooth solutions.

On Noncoercive (p, q)-Equations

We consider a nonlinear Dirichlet problem driven by a (p, q)-Laplace differential operator (1 < q < p). The reaction is (p - 1)-linear near +/-infinity and the problem is noncoercive. Using variational tools and truncation and comparison techniques together with critical groups, we produce five nontrivial smooth solutions all with sign information and ordered. In the particular case when q = 2, we produce a second nodal solution for a total of six nontrivial smooth solutions all with sign information.

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

MR 3215343 Reviewed Pirola G.P., Rizzi C. and Schlesinger E. A new curve algebraically but not rationally uniformized by radicals. Asian J. Math., 18 (2014), 127–142. (Reviewer Francesca Vetro) 14H30 (14H10)

A smooth projective complex curve C is called rationally uniformized by radicals if there exists a covering map C \rightarrow P^1 with solvable Galois group. C is called algebraically uniformized by radicals if there exists a finite covering C^{\prime} \rightarrow C with C^{\prime} rationally uniformized by radicals. Abramovich and Harris posed the following problem in [D. Abramovich and J. Harris, Abelian varieties and curves in $W_{d}(C)$, Compositio Math., 78 (1991), pp. 227–-238]. \vspace{1ex} Statement S(d, h, g): \textit{Suppose C^{\prime} \rightarrow C is a nonconstant map of smooth curves with C of genus g. If C^{\prime} admits a map of degree d or less to a curve of genus h or less…

Irreducibility of Hurwitz spaces of coverings with monodromy groups Weyl groups of type W(B_d)

Let Y be a smooth, connected, projective complex curve of genus ≥0. R. Biggers and M. Fried [J. Reine Angew. Math. 335, 87–121 (1982; Zbl 0484.14002), Trans. Am. Math. Soc. 295, No. 1, 59–70 (1986; Zbl 0601.14022)] proved the irreducibility of the Hurwitz spaces which parametrize coverings of ℙ 1 whose monodromy group is a Weyl of type W(D d ). Here we prove the irreducibility of Hurwitz spaces that parametrize coverings of Y with monodromy group a Weyl group of type W(B d ).

MR 3020148 Reviewed McMullen, C.T. Braid groups and Hodge theory. Mathematische Annalen, vol. 355 (2013), pp.893–-946. (Reviewer Francesca Vetro) 20F36 (14C30)

In this paper, the author studies the unitary representations of the braid group and the geometric structures on moduli space that arise via the Hodge theory of cyclic branched coverings of P^1. In particular, the author is interested in the classification of certain arithmetic subgroups of U(r, s) which envelop the image of the braid group. The author investigates their connections with complex reflection groups, Teichm\"{u}lller curves, ergodic theory and problems in surface topology.

Common fixed points of mappings satisfying implicit contractive conditions

In this article we obtain, in the setting of metric spaces or ordered metric spaces, coincidence point, and common fixed point theorems for self-mappings in a general class of contractions defined by an implicit relation. Our results unify, extend, generalize many related common fixed point theorems from the literature. Mathematics Subject Classification (2000): 47H10, 54H25.

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

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.

Multiple solutions for strongly resonant Robin problems

We consider nonlinear (driven by the p†Laplacian) and semilinear Robin problems with indefinite potential and strong resonance with respect to the principal eigenvalue. Using variational methods and critical groups, we prove four multiplicity theorems producing up to four nontrivial smooth solutions.

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

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 .

Fixed points for multivalued mappings in b-metric spaces

In 2012, Samet et al. introduced the notion ofα-ψ-contractive mapping and gave sufficient conditions for the existence of fixed points for this class of mappings. The purpose of our paper is to study the existence of fixed points for multivalued mappings, under anα-ψ-contractive condition of Ćirić type, in the setting of completeb-metric spaces. An application to integral equation is given.

Existence of positive solutions for nonlinear Dirichlet problems with gradient dependence and arbitrary growth

We consider a nonlinear elliptic problem driven by the Dirichlet $p$-Laplacian and a reaction term which depends also on the gradient (convection). No growth condition is imposed on the reaction term $f(z, \cdot,y)$. Using topological tools and the asymptotic analysis of a family of perturbed problems, we prove the existence of a positive smooth solution.

Applying fuzzy Particle Swarm Optimization to Multi-unit Double Auctions

Abstract In the context of Quadratic Programming Problems, we use a fuzzy Particle Swarm Optimization (PSO) algorithm to analyze a Multi-unit Double Auction (MDA) market. We give also a Linear Programming (LP) based upper bound to help the decision maker in dealing with constraints in the mathematical model. In the computational study, we evaluate our algorithm and show that it is a feasible approach for processing bids and calculating assignments.

Parametric nonlinear singular Dirichlet problems

Abstract We consider a nonlinear parametric Dirichlet problem driven by the p -Laplacian and a reaction which exhibits the competing effects of a singular term and of a resonant perturbation. Using variational methods together with suitable truncation and comparison techniques, we prove a bifurcation-type theorem describing the dependence on the parameter of the set of positive solutions.

MR 3004007 Reviewed Chretien P. and Matignon M. Maximal wild monodromy in unequal characteristic. Journal of Number Theory (2013) 133, 1389--1408. Reviewer Francesca Vetro) 14H30 (11G20)

Let R be a complete discrete valuation ring of mixed characteristic (0, p) with fraction field K. The stable reduction theorem affirms that given a smooth, projective, geometrically connected curve over K, C/K, with genus \geq 2, there exists a unique finite Galois extension M/K minimal for the inclusion relation such that C_{M}:= C x M has stable reduction over M. A such extension is called monodromy extension of C/K and the Galois group Gal(M/K) is called the monodromy group of C/K. In this paper, the authors study stable models of p-cyclic covers of P^1_K. At first, they work with covers of arbitrarily high genus having potential good reduction. In particular, they determine for such cov…

SOLUTION TO RANDOM DIFFERENTIAL EQUATIONS WITH BOUNDARY CONDITIONS

We study a family of random differential equations with boundary conditions. Using a random fixed point theorem, we prove an existence theorem that yields a unique random solution.

MR2388557: Osserman, Brian Linear series and the existence of branched covers. Compos. Math. 144 (2008), no. 1, 89–106.

MR2388557

MR2316356: Romagny, Matthieu; Wewers, Stefan Hurwitz spaces. Groupes de Galois arithmétiques et différentiels, 313–341, Sémin. Congr., 13, Soc. Math. France, Paris, 2006.

MR2316356

MR2464030: Liu, Fu; Osserman, Brian The irreducibility of certain pure-cycle Hurwitz spaces. Amer. J. Math. 130 (2008), no. 6, 1687–1708.

MR2464030

MR2492097: Pjero, N.; Ramasaço, M.; Shaska, T. Degree even coverings of elliptic curves by genus 2 curves. Albanian J. Math. 2 (2008), no. 3, 241–248.

MR2492097