https://revista-em.unex.es/index.php/EM/gateway/plugin/WebFeedGatewayPlugin/atomExtracta Mathematicae2024-06-13T11:43:58+02:00Pedro Martínextracta@unex.esOpen Journal Systems<p style="margin-bottom: 0cm; line-height: 100%;"> </p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">Welcome to the new (as of February 2024) page of Extracta Mathematicae. We have tried our best, but in case any user detects any inaccuracy or malfunction, please contact us <a href="https://revista-em.unex.es/index.php/EM/about/contact">here</a> and we will solve it as soon as possible. <br /></span></span></span></p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">Extracta Mathematicae (E.M.) publishes quality research papers that contain innovative contributions in the <a href="https://revista-em.unex.es/index.php/EM/covered">areas covered</a> by the members of the <a href="https://revista-em.unex.es/index.php/EM/editorial">Editorial Board</a>. E.M. is also open to consider well written survey papers.</span></span></span></p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">Publishing in E.M. is exempt from fees of any kind, and all documents are freely available for reading. 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These are</span></span></span><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;"> the latest volumes of E.M. in <a href="https://www.scopus.com/results/results.uri?sid=ba5d3a69aecc7a73cdde93fb38647c25&src=s&sot=b&sdt=b&origin=searchbasic&rr=&sl=15&s=ISSN(2605-5686)&searchterm1=2605-5686&searchTerms=&connectors=&field1=ISSN&fields=">Scopus.</a> </span></span></span></p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">E.M. is abstracted and indexed in <a href="http://www.ams.org/publications/math-reviews/math-reviews">Mathematical Reviews</a> and <a href="https://zbmath.org/">Zentralblatt MATH</a>. The AMS-Mathematical Citation Quotient (MCQ) average (2000-2017) for E.M. is 0.25 (all publications MCQ average 2000-2017 is 0.22) and the 2022-MCQ is 0.45 (2021-MCQ all journal median is 0.20). The printed version is exchanged with 117 journals in 36 countries all over the world.</span></span></span></p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">E.M. is indexed in <a href="https://www.doaj.org/toc/2605-5686?source=%7B">DOAJ</a>, the Directory of Open Access Journals, as well as in <a href="https://www.latindex.org/latindex/inicio">Latindex 2.0,</a> and is a member of <a href="https://freejournals.org/">Free Journal Network</a>. </span></span></span></p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">E.M. has obtained the <a href="https://evaluacionarce.fecyt.es/Publico/Resolucion/resolucion.aspx">Fecyt Quality seal 2021 </a>and it was renewed in <a href="https://calidadrevistas.fecyt.es/fecyt-publica-el-listado-provisional-de-revistas-que-renuevan-el-sello-de-calidad-en-2022">2022</a> and <a href="https://evaluacionarce.fecyt.es/Publico/Resolucion/__Recursos/2023ListadoProvisionalRenovacion.pdf" target="_blank" rel="noopener">2023</a>.</span></span></span></p> <p><span style="color: #000000;"><span style="font-family: Latin Modern Math;"><span style="font-size: medium;">E.M. uses Open Journal System <a href="https://openjournalsystems.com/">OJS</a>.</span></span></span></p> <p><span style="font-family: Latin Modern Math;"><span style="font-size: medium;"><span style="color: #000000;"><strong>2022 data:</strong><br />From 1st January to 31th December 2022, 71 manuscripts have been received in E.M., and 10 papers have been accepted for publication.<br />Regular number of reviewers for each manuscript: 2.<br />Speed (average):<br />Submission to first decision (all received manuscripts): 48 days<br />Submission to definitive decision (all received manuscripts): 66 days<br />Submission to first decision (accepted manuscripts): 127 days<br />Submission to definitive decision (accepted manuscripts): 134 days<br />Acceptance to online publication: 34 days<br />Acceptance to print publication: 145 days.</span></span></span></p>https://revista-em.unex.es/index.php/EM/article/view/2306Some applications of Q-points and Lebesgue filters to Banach spaces2024-06-13T11:55:22+02:00M. HrušákL. Sáenz
<p>We present a new characterization of Q-point ultrafilters and use it to optimize the result of Avilés, Martı́nez-Cervantes, and Rueda Zoca linking the existence of L-orthogonal sequences and L-orthogonal elements in Banach spaces via ultrafilter limits.</p>
2024-06-13T00:00:00+02:00Copyright (c) 2024 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2304A spectral theorem for a non-Archimedean valued field whose residue field is formally real2024-05-31T17:24:29+02:00K. Ishizuka
<p>In this paper, we will prove a spectral theorem for self-adjoint compactoid operators. Also, we will study the condition on which the coefficient field must be imposed. In order to get the theorems, we will use the Fredholm theory for compactoid operators. Moreover, the property of maximal complete field is important for our study. These facts will allow us to find that the spectral theorem depends only on the residue class field, and is independent of the valuation group of the coefficient field. As a result, we can settle the problem of the spectral theorem in the case where the residue class field is formally real.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.19The Arens-Calderon theorem for commutative topological algebras2024-05-31T17:50:24+02:00M. WeigtI. Zarakas
<p>A theorem of Arens and Calderon states that if A is a commutative Banach algebra with Jacobson radical Rad(A), and if a<sub>0</sub> , . . . , a<sub>n</sub>∈ A with a<sub>0</sub> ∈ Rad(A) and a<sub>1</sub> an invertible element of k A, then there exists y ∈ Rad(A) such that <span style="font-family: Liberation Serif, serif;">Σ</span> a<sub>k</sub> y<sup>k</sup> = 0. In this paper, we give extensions of this result to commutative non-normed topological algebras, as this is vital for extending an embedding theorem of Allan in [2] regarding the embedding of the formal power series algebra C[[X]] into a commutative Banach algebra. </p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.119⊗-Pure model structure on the category of N -complexes2024-05-31T17:50:25+02:00P. BahiraeiJ. Nazaripour
<p>Let G be a closed symmetric monoidal concrete Grothendieck category. In this paper, we introduce a model structure on (C<sub>N </sub>(G), P⊗<sub>dw</sub> ) the exact category of N -complexes with the degree-wise ⊗-pure exact structure. Our result is based on the Gillespie’s Theorem by introducing two compatible cotorsion pairs on this category.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.97On lifts of symplectic vector bundles and connections to Weil bundles2024-05-31T17:50:25+02:00E. Hinamari Mang-massouA. Ntyam
<p>In this paper, we generalize to Frobenius-Weil bundles some lifts of symplectic manifolds and symplectic vector bundles.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.37Unbounded generalized B-Fredholm operators2024-05-31T17:50:26+02:00M. Boudhief
<p>In this paper, we investigate a new class of unbounded linear operators, that is, the unbounded generalized B-Fredholm operators in Banach space. More explicitly, we provide a characterization of this class of operators and some of its basic properties on a Banach space. Moreover, we study the generalized B-Fredholm spectrum and we prove a perturbation result of an unbounded generalized B-Fredholm operator under a commuting power finite-rank operator.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.47A topological characterization of an almost Boolean algebra2024-05-31T17:50:26+02:00K. Ramanuja RaoK. Rama PrasadG. Vara LakshmiCh. Santhi Sundar Raj
<p>For any Boolean space X and a discrete almost distributive lattice D, it is proved that the set C(X, D) of all continuous mappings of X into D, when D is equipped with the discrete topology, is an almost Boolean algebra under pointwise operations. Conversely, it is proved that any almost Boolean algebra is a homomorphic image of C(X,D) for a suitable Boolean space X and a discrete almost distributive lattice D.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.57The current state of play in the Landsberg-Berwald problem of Finsler geometry2024-05-31T17:50:26+02:00M. Crampin
<p>A progress report on the (still unresolved) Landsberg-Berwald problem of Finsler geometry: whether there can be non-Berwaldian regular Landsberg spaces.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.39.1.1On discontinuity of derivations, inducing inequivalent complete metric topologies2024-05-31T17:50:27+02:00S.R. Patel
<p>We give an elementary method for constructing commutative Fréchet algebras with non-unique Fréchet algebra topology. The result is applied to show that the action of any non-algebraic analytic function may fail to be uniquely defined among other useful applications. We give an affirmative answer to a question of Loy (1974) for Fréchet algebras. We also obtain the uniqueness of the Fréchet algebra topology of certain Fréchet algebras with finite dimensional radicals.</p>
2024-05-31T00:00:00+02:00Copyright (c) 2024 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.2.205Continua whose hyperspace of subcontinua is infinite dimensional and a cone2024-01-13T14:30:11+01:00S. Macı́asS.B. Nadler
<p>We determine several classes of continua whose hyperspaces of subcontinua are infinite dimensional and homeomorphic to cones over (usually) other continuum. In particular, we obtain many Peano continua with such a property.</p>
2023-12-01T00:00:00+01:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.2.139Radon-Nikodýmification of arbitrary measure spaces2024-01-13T14:30:12+01:00P. BouafiaT. De Pauw
<p style="margin-bottom: 0cm; line-height: 100%;">We study measurable spaces equipped with a σ-ideal of negligible sets. We find conditions under which they admit a localizable locally determined version – a kind of fiber space that locally describes their directions – defined by a universal property in an appropriate category that we introduce. These methods allow to promote each measure space (X, A , µ) to a strictly localizable version (X̂, Â, µ̂), so that the dual of L<sub>1</sub> (X, A , µ) is L<sub>∞</sub> (X̂, Â, µ̂). Corresponding to this duality is a generalized Radon-Nikodým theorem. We also provide a characterization of the strictly localizable version in special cases that include integral geometric measures, when the negligibles are the purely unrectifiable sets in a given dimension.</p>
2023-12-01T00:00:00+01:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.2.125Results on Lie ideals of prime rings with homoderivations2024-01-13T14:30:12+01:00A. SarikayaÖ. Gölbaşi
<p>Let R be a prime ring of characteristic not 2 and U be a noncentral square closed Lie ideal of R. An additive mapping H on R is called a homoderivation if H(xy) = H(x)H(y)+H (x) y+xH(y) for all x, y ∈ R. In this paper we investigate homoderivations satisfying certain differential identities on square closed Lie ideals of prime rings.</p>
2023-12-01T00:00:00+01:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.2.237Tensorial and Hadamard product inequalities for functions of selfadjoint operators in Hilbert spaces in terms of Kantorovich ratio2024-01-13T14:30:12+01:00S.S. Dragomir
<p style="margin-bottom: 0cm; line-height: 100%;">Let <em>H</em> be a Hilbert space. In this paper we show among others that, if <em>f</em>, <em>g</em> are continuous on the interval <em>I</em> with</p> <p style="margin-bottom: 0cm; font-style: normal; line-height: 100%;"> </p> <p style="margin-bottom: 0cm; line-height: 100%;" align="center"><span style="font-style: normal;">0 <γ ≤ </span><em>f</em><span style="font-style: normal;">(</span><em>t</em><span style="font-style: normal;">)/</span><em>g</em><span style="font-style: normal;">(</span><em>t</em><span style="font-style: normal;">)≤ Γ </span>for t ∈ I</p> <p style="margin-bottom: 0cm; line-height: 100%;"> </p> <p style="margin-bottom: 0cm; line-height: 100%;">and if <em>A</em> and <em>B</em> are selfadjoint operators with Sp (<em>A</em>), Sp (<em>B</em>) ⊂ <em>I</em>, then</p> <p style="margin-bottom: 0cm; line-height: 100%;"> </p> <p style="margin-bottom: 0cm; line-height: 100%;"> </p> <p style="margin-bottom: 0cm; line-height: 100%;"><span style="font-size: large;">[</span>f<sup><span style="font-size: large;">1−ν</span></sup>(A) g<sup><span style="font-size: large;">ν</span></sup> (A)<span style="font-size: large;">]</span> ⊗ <span style="font-size: large;">[</span>f<sup><span style="font-size: large;">ν</span></sup>(B) g<sup><span style="font-size: large;">1−ν</span></sup> (B)<span style="font-size: large;">] </span> ≤ (1 − ν) f (A) ⊗ g (B) + ν g (A) ⊗ f (B)</p> <p style="margin-bottom: 0cm; line-height: 100%;"> ≤ <span style="font-size: large;">[</span>(γ + Γ) <sup><span style="font-size: large;">2</span></sup>/4γΓ<span style="font-size: large;">]</span><sup><span style="font-size: large;">R </span></sup><span style="font-size: large;">[</span><span style="font-size: medium;">f</span><sup><span style="font-size: large;">1−ν</span></sup><span style="font-size: medium;">(A) g</span><sup><span style="font-size: large;">ν</span></sup><span style="font-size: medium;"> (A)</span><span style="font-size: large;">]</span><span style="font-size: medium;"> ⊗ </span><span style="font-size: large;">[</span><span style="font-size: medium;">f</span><sup><span style="font-size: large;">ν</span></sup><span style="font-size: medium;">(</span><span style="font-size: medium;">B</span><span style="font-size: medium;">) g</span><sup><span style="font-size: large;">1−ν</span></sup><span style="font-size: medium;"> (</span><span style="font-size: medium;">B</span><span style="font-size: medium;">)</span><span style="font-size: large;">]. </span></p> <p style="margin-bottom: 0cm; line-height: 100%;"> </p> <p style="margin-bottom: 0cm; line-height: 100%;">The above inequalities also hold for the Hadamard product “ ◦ ” instead of tensorial product “ ⊗ ”.</p>
2023-12-01T00:00:00+01:00Copyright (c) 2023 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2281Estimates of Generalized Nevanlinna Counting Function and Applications to Composition Operators2023-12-21T10:54:47+01:00Z. BendaoudF. KorrichiL. MerghniA. Yagoub
<p>Let φ be a holomorphic self-map of the unit disc. We study the relationship between the generalized Nevanlinna counting function associated with φ and the norms of φn in the Dirichlet spaces. We give examples of Hilbert-Schmidt composition operators on the Dirichlet spaces.</p>
2023-12-21T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2280Virtually (r; r_1, ... , r_n ; s)-nuclear multilinear operators2023-12-21T10:54:47+01:00Dahmane AchourAmar Belacel
<p>In this paper, the space of virtually (r; r_1, ... , r_n; s)-nuclear multilinear operators between Banach spaces is introduced, some of its properties are described and its topological dual is characterized as a Banach space of multiple absolutely (r'; r'_1, ... , r'_n; s')-summing multilinear operators.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2279Powers in Alternating Simple Groups2023-12-21T10:54:47+01:00J. Martínez Carracedo
<p>C. Martínez and E. Zelmanov proved in [12] that for every natural number d and every finite simple group G, there exists a function N = N(d) such that either G^d = 1 or G = {a_1^d, ... , a_N^d : ai \in G}.</p> <p>In a more general context the problem of finding words w such that the word map (g1; ...; gd) --> w(g1; ... ; gd) is surjective for any finite non abelian simple group is a major challenge in Group Theory. In [8] authors give the first example of a word map which is surjective on all finite non-abelian simple groups, the commutator [x; y] (Ore Conjecture).</p> <p>In [11] the conjecture that this is also the case for the word x2y2 is formulated. This conjecture was solved in [9] and, independently, in [6], using deep results of algebraic simple groups and representation theory. An elementary proof of this result for alternating simple groups is presented here.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2278On Additive Preservers of Certain Classes of Algebraic Operators2023-12-21T10:54:48+01:00Khalid Souilah
<p>In this article we provide a complete description of all additive surjective unital maps in the algebra of all bounded linear operators acting on an in nite-dimensional Hilbert space, preserving in both directions the set of non-invertible algebraic operators or the set of invertible algebraic operators.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2277Preservation Results for New Spectral Properties2023-12-21T10:54:48+01:00Hassan Zariouh
<p>A bounded linear operator T is said to satisfy property (SBaw) if </p> <p>s_a(T) \ s_SBF (T) = E_a^0 (T)</p> <p>where s_a(T) is the approximate point spectrum of T; s_SBF (T) is the upper semi-B-Weyl spectrum of T and E_a^0(T) is the set of all eigenvalues of T of finite multiplicity that are isolated in its approximate point spectrum.</p> <p>In this paper we give a characterization of this spectral property for a bounded linear operator having SVEP on the complementary of its upper semi-B-Weyl spectrum, and we study its stability under commuting Riesz-type perturbations. Analogous results are obtained for the properties (SBb); (SBab) and (SBw). The theory is exemplified in the case of some special classes of operators.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2276Jordan Derivations on Triangular Matrix Rings2023-12-21T10:54:49+01:00Bruno Ferreira
<p>Guided by the research line introduced by Martindale III in [5] on the study of the additivity of maps, this article aims establish conditions on triangular matrix rings in order that an map φ satisfying</p> <p>φ(ab + ba) = φ(a)b + aφ(b) + φ(b)a + bφ(a)</p> <p>for all a, b in a triangular matrix ring becomes additive.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2275Banach Lattices with the Positive Dunford-Pettis Relatively Compact Property2023-12-21T10:54:49+01:00Kamal El FahriNabil MachrafiMohammed Moussa
<p>The paper is devoted to such Banach lattices E that every Dunford-Pettis and weakly null sequence (xn) E with disjoint terms is norm null (the positive Dunford-Pettis relatively compact property). It is established that a Banach lattice E has the positive Dunford-Pettis relatively compact property if and only if its almost Dunford-Pettis subsets are L-weakly compact. Consequently, we derive the following result: Banach lattices with the property that their almost Dunford-Pettis subsets are relatively compact, are precisely the discrete KB-spaces.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2274Real Analytic Version of Lévy’s Theorem2023-12-21T10:54:49+01:00A. El KinaniL. Bouchikhi
<p>We obtain real analytic version of the classical theorem of Lévy on absolutely convergent power series. Whence, as a consequence, its harmonic version.</p>
2015-12-01T00:00:00+01:00Copyright (c) 2023 Extracta Mathematicaehttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.2.221The fundamental theorem of affine geometry2024-01-13T14:30:13+01:00J.B. Sancho de Salas
<p>We deal with a natural generalization of the classical Fundamental Theorem of Affine Geometry to the case of non bijective maps. This extension geometrically characterizes semiaffine morphisms. It was obtained by W. Zick in 1981, although it is almost unknown. Our aim is to present and discuss a simplified proof of this result.</p>
2023-12-01T00:00:00+01:00Copyright (c) 2023 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.51On Jordan ideals with left derivations in 3-prime near-rings2023-06-06T10:34:42+02:00A. En-guadyA. Boua
<p>We will extend in this paper some results about commutativity of Jordan ideals proved in [2] and [6]. However, we will consider left derivations instead of derivations, which is enough to get good results in relation to the structure of near-rings. We will also show that the conditions imposed in the paper cannot be removed.</p>
2023-01-23T00:00:00+01:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.1Topologies, posets and finite quandles2023-06-06T10:34:40+02:00M. ElhamdadiH. LahraniT. Gona
<p>An Alexandroff space is a topological space in which every intersection of open sets is open. There is one to one correspondence between Alexandroff T<sub>0</sub> -spaces and partially ordered sets (posets). We investigate Alexandroff T<sub>0</sub> -topologies on finite quandles. We prove that there is a non-trivial topology on a finite quandle making right multiplications continuous functions if and only if the quandle has more than one orbit. Furthermore, we show that right continuous posets on quandles with n orbits are n-partite. We also find, for the even dihedral quandles, the number of all possible topologies making the right multiplications continuous. Some explicit computations for quandles of cardinality up to five are given.</p>
2023-06-01T00:00:00+02:00Copyright (c) 2022 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.27Construction of Hom-pre-Jordan algebras and Hom-J-dendriform algebras2023-06-06T10:34:38+02:00T. ChtiouiS. MabroukA. Makhlouf
<p>The aim of this work is to introduce and study the notions of Hom-pre-Jordan algebra and Hom-J-dendriform algebra which generalize Hom-Jordan algebras. Hom-pre-Jordan algebras are regarded as the underlying algebraic structures of the Hom-Jordan algebras behind the Rota-Baxter operators and O-operators introduced in this paper. Hom-pre-Jordan algebras are also analogues of Hom-pre-Lie algebras for Hom-Jordan algebras. The anti-commutator of a Hom-pre-Jordan algebra is a Hom-Jordan algebra and the left multiplication operator gives a representation of a Hom-Jordan algebra. On the other hand, a Hom-J-dendriform algebra is a Hom-Jordan algebraic analogue of a Hom-dendriform algebra such that the anti-commutator of the sum of the two operations is a Hom-pre-Jordan algebra.</p>
2023-06-01T00:00:00+02:00Copyright (c) 2022 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.17A note on isomorphisms of quantum systems2023-06-06T10:34:36+02:00Martin Weigt
<p>We consider the question as to whether a quantum system is uniquely determined by all values of all its observables. For this, we consider linearly nuclear GB*-algebras over W*-algebras as models of quantum systems.</p>
2023-06-01T00:00:00+02:00Copyright (c) 2022 The authorhttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.67On Lie ideals satisfying certain differential identities in prime rings2023-06-06T10:34:34+02:00B. DharaS. GhoshG.S. Sandhu
<p>Let R be a prime ring of characteristic not 2, L a nonzero square closed Lie ideal of R and let F : R → R, G : R → R be generalized derivations associated with derivations d : R → R, g : R → R respectively. In this paper, we study several conditions that imply that the Lie ideal is central. Moreover, it is shown that the assumption of primeness of R can not be removed.</p>
2023-06-01T00:00:00+02:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.85Estimating the number of limit cycles for one step perturbed homogeneous degenerate centers2023-06-06T10:34:30+02:00M. MolaeiDerakhtenjaniO. RabieiMotlaghH.M. MohammadiNejad
<p>We consider a homogeneous degenerate center of order 2m + 1 and perturb it by a homogeneous polynomial of order 2m. We study the Lyapunov constants around the origin to estimate the number of limit cycles. To do it, we classify the parameters and study their effect on the number of limit cycles. Finally, we find that the perturbed degenerate center without any condition has at least two limit cycles, and the number of the bifurcated limit cycles could reach 2m + 3.</p>
2023-06-01T00:00:00+02:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.38.1.105The character variety of one relator groups2023-06-06T10:34:28+02:00A. CavicchioliF. Spaggiari
<p>We consider some families of one relator groups arising as fundamental groups of 3-dimensional manifolds, and calculate their character varieties in SL(2, <strong>C</strong>). Then we give simple geometrical descriptions of such varieties, and determine the number of their irreducible components. Our paper relates to the work of Baker-Petersen, Qazaqzeh and Morales-Marcén on the character variety of certain classes of one relator groups, but we use different methods based on the concept of palindrome presentations of given groups.</p>
2023-06-01T00:00:00+02:00Copyright (c) 2023 The authorshttps://revista-em.unex.es/index.php/EM/article/view/2605-5686.37.2.243Smooth 2-homogeneous polynomials on the plane with a hexagonal norm2022-11-28T15:55:09+01:00Sung Guen Kim
<p>Motivated by the classifications of extreme and exposed 2-homogeneous polynomials on the plane with the hexagonal norm ||(x, y)|| = max{|y|, |x| + |y|/2} (see [15, 16]), we classify all smooth 2-homogeneous polynomials on R<sup>2</sup> with the hexagonal norm.</p>
2022-12-01T00:00:00+01:00Copyright (c) 2022 The author