DSpace Collection: Volume 25 Number 1
http://hdl.handle.net/10525/427
Serdica Mathematical Journal Volume 25, Number 1, 1999The Collection's search engineSearch the Channelsearch
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Some Para-Hermitian Related Complex Structures and Non-existence of Semi-Riemannian Metric on Some Spheres
http://hdl.handle.net/10525/438
Title: Some Para-Hermitian Related Complex Structures and Non-existence of Semi-Riemannian Metric on Some Spheres<br/><br/>Authors: Erdem, Sadettin<br/><br/>Abstract: It is shown that the spheres S^(2n) (resp: S^k with k ≡ 1 mod 4)can be given neither an indefinite metric of any signature (resp: of signature(r, k − r) with 2 ≤ r ≤ k − 2) nor an almost paracomplex structure. Furtherfor every given Riemannian metric on an almost para-Hermitian manifoldwith the associated 2-form φ one can construct an almost Hermitian structure(under certain conditions, two different almost Hermitian structures)whose associated 2-form(s) is φ.Nonlinear Wave Equation with Vanishing Potential
http://hdl.handle.net/10525/437
Title: Nonlinear Wave Equation with Vanishing Potential<br/><br/>Authors: Lucente, Sandra<br/><br/>Abstract: We study the Cauchy problem for utt − ∆u + V (x)u^5 = 0 in3–dimensional case. The function V (x) is positive and regular, in particularwe are interested in the case V (x) = 0 in some points. We look for the globalclassical solution of this equation under a suitable hypothesis on the initialenergy.On the Hyperbolicity Domain of the Polynomial x^n + a1x^(n-1) + 1/4+ an
http://hdl.handle.net/10525/436
Title: On the Hyperbolicity Domain of the Polynomial x^n + a1x^(n-1) + 1/4+ an<br/><br/>Authors: Kostov, Vladimir<br/><br/>Abstract: We consider the polynomial Pn = x^n + a1 x^(n−1) + · · · + an ,ai ∈ R. We represent by figures the projections on Oa1 . . . ak , k ≤ 6, of itshyperbolicity domain Π = {a ∈ Rn | all roots of Pn are real}. The set Πand its projections Πk in the spaces Oa1 . . . ak , k ≤ n, have the structure ofstratified manifolds, the strata being defined by the multiplicity vectors. Itis known that for k > 2 every non-empty fibre of the projection Π^k → Π^(k−1)is a segment or a point. We prove that this is also true for the strata of Π ofdimension ≥ k. This implies that for any two adjacent strata there alwaysexist a space Oa1 . . . ak , k ≤ n, such that from the projections of the stratain it one is “above” the other w.r.t. the axis Oak . We show 1) how to find this k and which stratum is “above” just by looking atthe multiplicity vectors of the strata; 2) how to obtain the relative position of a stratum of dimension l and ofall strata of dimension l + 1 and l + 2 to which it is adjacent.<br/><br/>Description: ∗ Partially supported by INTAS grant 97-1644On the sense preserving mappings in the Helm topology in the plane
http://hdl.handle.net/10525/435
Title: On the sense preserving mappings in the Helm topology in the plane<br/><br/>Authors: Pyrih, Pavel<br/><br/>Abstract: We introduce the helm topology in the plane. We show that (assuming the helm local injectivity and the Euclidean continuity) each mapping which is oriented at all points of a helm domain U is oriented at U.<br/><br/>Description: ∗Research supported by the grant No. GAUK 186/96 of Charles University.Limit Theorems for Regenerative Excursion Processes
http://hdl.handle.net/10525/434
Title: Limit Theorems for Regenerative Excursion Processes<br/><br/>Authors: Mitov, Kosto<br/><br/>Abstract: The regenerative excursion process Z(t), t = 0, 1, 2, . . . isconstructed by two independent sequences X = {Xi , i ≥ 1} and Z ={Ti , (Zi (t), 0 ≤ t < Ti ), i ≥ 1}. For the embedded alternating renewal process, with interarrival times Xi– the time for the installation and Ti – the time for the work, are provedsome limit theorems for the spent worktime and the residual worktime, whenat least one of the means of Xi and Ti is infinite. Limit theorems for the process Z(t) are proved, too. Finally, some applications to the branching processes with state-dependentimmigration are given.<br/><br/>Description: This work is supported by Bulgarian NFSI, grant No. MM–704/97Relative Compactness for Hyperspaces
http://hdl.handle.net/10525/433
Title: Relative Compactness for Hyperspaces<br/><br/>Authors: Sianesi, Francesca<br/><br/>Abstract: The present paper contains results characterizing relativelycompact subsets of the space of the closed subsets of a metrizable space,equipped with various hypertopologies.We investigate the hyperspace topologies that admit a representation asweak topologies generated by families of gap functionals defined on closedsets, as well as hit-and-miss topologies and proximal-hit and-miss topologies.On a Conditional Cauchy-type Functional Equation Involving Powers
http://hdl.handle.net/10525/432
Title: On a Conditional Cauchy-type Functional Equation Involving Powers<br/><br/>Authors: Martin-Gutierrez, Emma<br/><br/>Abstract: We solve the functional equation f(x^m + y) = f(x)^m + f(y) in the realm of polynomials with integer coefficients.Some properties of g- and P-spaces
http://hdl.handle.net/10525/431
Title: Some properties of g- and P-spaces<br/><br/>Authors: Kalamidas, N.<br/><br/>Abstract: A γ-space with a strictly positive measure is separable. Anexample of a non-separable γ−space with c.c.c. is given. A P−space withc.c.c. is countable and discrete.