http://acutm.math.ut.ee/index.php/acutm/issue/feedActa et Commentationes Universitatis Tartuensis de Mathematica2019-01-22T07:41:44+00:00Enno Kolkenno.kolk@ut.eeOpen Journal Systems<p><em>Acta et Commentationes Universitatis Tartuensis de Mathematica </em>(ACUTM) is an international journal of pure and applied mathematics.</p>http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.14On a class of N(k)-mixed generalized quasi-Einstein manifolds2019-01-22T07:41:44+00:00Arindam Bhattacharyyabhattachar1968@yahoo.co.inSampa Pahansampapahan25@gmail.com<p>The objective of the present paper is to study N(<em>k</em>)-mixed generalized quasi-Einstein manifolds. We prove the existence of these manifolds. Later we establish some curvature properties of N(<em>k</em>)-mixed generalized quasi-Einstein manifolds under certain conditions. In the last section, we give two examples of N(<em>k</em>)-mixed generalized quasi-Einstein manifolds.</p>2019-01-02T10:32:22+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.15Inequalities of Hermite–Hadamard type for HH-convex functions2019-01-22T07:41:44+00:00Sever Silvestru Dragomirsever.dragomir@vu.edu.au<p>Some inequalities of Hermite–Hadamard type for <em>HH</em>-convex functions defined on positive intervals are given. Applications for special means are also provided.</p>2019-01-02T10:39:06+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.16Matrix transformations related to I-convergent sequences2019-01-22T07:41:43+00:00Enno Kolkenno.kolk@ut.ee<p>Characterized are matrix transformations related to certain subsets of the space of ideal convergent sequences. Obtained here results are connected with the previous investigations of the author on some transformations defined by infinite matrices of bounded linear operators.</p>2019-01-02T13:55:52+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.17On new extensions of the generalized Hermite matrix polynomials2019-01-22T07:41:43+00:00Ayman Shehatadrshehata2006@yahoo.com<p>Various families of generating matrix functions have been established in diverse ways. The objective of the present paper is to investigate these generalized Hermite matrix polynomials, and derive some important results for them, such as, the generating matrix functions, matrix recurrence relations, an expansion of <em>x<sup>n</sup>I</em>, finite summation formulas, addition theorems, integral representations, fractional calculus operators, and certain other implicit summation formulae.</p>2019-01-02T14:02:13+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.18Boundedness of the L-index in a direction of entire solutions of second order partial differential equation2019-01-22T07:41:42+00:00Andriy Banduraandriykopanytsia@gmail.comOleh Skaskivolskask@gmail.com<p>See PDF</p>2019-01-02T14:08:27+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.19Asymptotics of approximation of conjugate functions by Poisson integrals2019-01-22T07:41:41+00:00Yu. I. Kharkevychkharkevich.juriy@gmail.comK. V. Pozharskakate.shvai@gmail.com<p>We obtain a decomposition of the upper bound for the deviation of Poisson integrals of conjugate periodic functions. The decomposition enables one to provide the Kolmogorov–Nikol'skii constants of an arbitrary order.</p>2019-01-02T14:14:07+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.20Second approximation of local functions in ideal topological spaces2019-01-22T07:41:41+00:00Md. Monirul Islammoni.math007@gmail.comShyamapada Modakspmodak2000@yahoo.co.in<p>This paper gives a new dimension to discuss the local function in ideal topological spaces. We calculate error operators for various type of local functions and introduce more perfect approximation of the local functions for discussing their properties. We have also reached a topological space with the help of semi-closure.</p>2019-01-02T14:21:12+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.21On two integrability methods2019-01-22T07:41:40+00:00H. N. Özgennogduk@gmail.com<p>See PDF</p>2019-01-02T14:26:05+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.22Extremal tricyclic, tetracyclic, and pentacyclic graphs with respect to the Narumi–Katayama index2019-01-22T07:41:40+00:00Ali Reza Ashrafiashrafi@kashanu.ac.irMehdi EliasiEliasi@math.iut.ac.irAli Ghalavandalighalavand@grad.kashanu.ac.irOttorino Oriottorino.ori@gmail.com<p>See PDF</p>2019-01-02T14:33:01+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.23On concircular curvature tensor in a Lorentzian α-Sasakian manifold with respect to the quarter-symmetric non-metric connection2019-01-22T07:41:39+00:00Abdul Haseebmalikhaseeb80@gmail.comRajendra Prasadrp.manpur@rediffmail.com<p>In the present paper, some properties of concircular curvature tensor in a Lorentzian <em>α</em>-Sasakian manifold with respect to the quarter-symmetric non-metric connection have been studied.</p>2019-01-02T14:38:36+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.24Simplifying coefficients in a family of nonlinear ordinary differential equations2019-01-22T07:41:39+00:00Feng Qiqifeng618@gmail.com<p>By virtue of the Faá di Bruno formula, properties of the Stirling numbers and the Bell polynomials of the second kind, the binomial inversion formula, and other techniques in combinatorial analysis, the author finds a simple, meaningful, and signicant expression for coefficients in a family of nonlinear ordinary differential equations.</p>2019-01-02T14:45:09+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.25Behaviour of multivariate tail dependence coefficients2019-01-22T07:41:38+00:00Gaida Petteregaida@latnet.lvIrina Voronovairina.voronova@rtu.lvIlze Zariņailzezarina@inbox.lv<p>In applications tail dependence is an important property of a copula. Bivariate tail dependence is investigated in many papers, but multivariate tail dependence has not been studied widely. We define multivariate upper and lower tail dependence coefficients as limits of the probability that values of one marginal will be large if at least one of other marginals will be as large also. Further we derive some relations between introduced tail dependence and bivariate tail dependence coefficients. Applications have shown that the multivariate <em>t</em>-copula has been successfully used in practice because of its tail dependence property. Therefore, <em>t</em>-copula can be used as an alternative method for risk assessment under Solvency II for insurance models. We have paid attention to the properties of the introduced multivariate tail dependence coefficient for <em>t</em>-copula and examine it in the simulation experiment.</p>2019-01-02T14:52:16+00:00##submission.copyrightStatement##http://acutm.math.ut.ee/index.php/acutm/article/view/ACUTM.2018.22.26Empirical cumulant function based parameter estimation in stable laws2019-01-22T07:41:37+00:00Annika Kruttokrutto@ut.ee<p>Stable distributions are a subclass of infinitely divisible distributions that form the only family of possible limiting distributions for sums of independent identically distributed random variables. A challenging problem is estimating their parameters because many have densities with no explicit form and infinite moments. To address this problem, a class of closed-form estimators, called cumulant estimators, has been introduced. Cumulant estimators are derived from the logarithm of empirical characteristic function at two arbitrary distinct positive real arguments. This paper extends cumulant estimators in two directions: (i) it is proved that they are asymptotically normal and (ii) a sample based rule for selecting the two arguments is proposed. Extensive simulations show that under the provided selection rule, the closed-form cumulant estimators generally outperform the well-known algorithmic methods.</p>2019-01-02T14:57:36+00:00##submission.copyrightStatement##