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• 1.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Department of Mathematics, University of Bristol, Bristol, United Kingdom. Department of Mathematics, Uppsala Universitet, Uppsala, Sweden. Mathematics Institute, University of Warwick, Coventry, United Kingdom.
Multifractal analysis of non-uniformly hyperbolic systems2010Ingår i: Israel Journal of Mathematics, ISSN 0021-2172, E-ISSN 1565-8511, Vol. 177, nr 1, s. 125-144Artikel i tidskrift (Refereegranskat)

We prove a multifractal formalism for Birkhoff averages of continuous functions in the case of some non-uniformly hyperbolic maps, which includes interval examples such as the Manneville-Pomeau map.

• 2.
Högskolan i Gävle, Institutionen för matematik, natur- och datavetenskap, Ämnesavdelningen för matematik och statistik.
Square summability of variations of g-functions and uniqueness of g-measures2003Ingår i: Mathematical Research Letters, ISSN 1073-2780, E-ISSN 1945-001X, Vol. 10, nr 5, s. 587-601Artikel i tidskrift (Refereegranskat)

We prove uniqueness of $g$-measures for $g$-functions satisfying quadratic summability of variations. Our result is in contrast to the situation of, \eg, the one-dimensional Ising model with long-range interactions, since $\ell_1$-summability of variations is required for general potentials. We illustrate this difference with some examples. To prove our main result we use a product martingale argument. We also give conditions for uniqueness of general $G$-measures, \ie, the case for general potentials, based on our investigation of the probabilistic case involving $g$-functions.

• 3.
Högskolan i Gävle, Institutionen för matematik, natur- och datavetenskap, Ämnesavdelningen för matematik och statistik.
Department of Mathematics, Uppsala University, Uppsala, Sweden. Mathematics Institute, University of Warwick, Coventry, United Kingdom.
Countable state shifts and uniqueness of g-measures2007Ingår i: American Journal of Mathematics, ISSN 0002-9327, E-ISSN 1080-6377, Vol. 129, nr 6, s. 1501-1511Artikel i tidskrift (Refereegranskat)

In this paper we present a new approach to studying $g$-measures which is based upon local absolute continuity. We extend an earlier result that square summability of variations of $g$ ensures uniqueness of $g$-measures. The first extension is to the case of countably many symbols. The second extension is to some cases where $g \geq 0$, relaxing the earlier requirement that $\inf g>0$.

• 4.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Uppsala University. University of Warwick, Coventry, UK.
Phase transitions in long-range Ising models and an optimal condition for factors of g-measures2019Ingår i: Ergodic Theory and Dynamical Systems, ISSN 0143-3857, E-ISSN 1469-4417, Vol. 39, nr 5, s. 1317-1330Artikel i tidskrift (Refereegranskat)

We weaken the assumption of summable variations in a paper by Verbitskiy [On factors of g-measures. Indag. Math. (N.S.) 22 (2011), 315-329] to a weaker condition, Berbee's condition, in order for a one-block factor (a single-site renormalization) of the full shift space on finitely many symbols to have a g-measure with a continuous g-function. But we also prove by means of a counterexample that this condition is (within constants) optimal. The counterexample is based on the second of our main results, where we prove that there is a critical inverse temperature in a one-sided long-range Ising model which is at most eight times the critical inverse temperature for the (two-sided) Ising model with long-range interactions.

• 5.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik. Uppsala University, Department of Mathematics.
Uppsala University, Department of Mathematics. University of Warwick, Mathematics Institute.
Unique Bernoulli g-measures2012Ingår i: Journal of the European Mathematical Society (Print), ISSN 1435-9855, E-ISSN 1435-9863, Vol. 14, nr 5, s. 1599-1615Artikel i tidskrift (Refereegranskat)

We improve and subsume the conditions of Johansson and Öberg and Berbee for uniqueness of a g-measure, i.e., a stationary distribution for chains with complete connections. In addition, we prove that these unique g-measures have Bernoulli natural extensions. We also conclude that we have convergence in the Wasserstein metric of the iterates of the adjoint transfer operator to the g-measure.

• 6.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, Industriell ekonomi.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, Industriell ekonomi.
Faktorer kring äldres måltidssituation och deras påverkan på lönsamhet: Innovativa lösningar genom offentlig upphandling2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)

• 7.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap.
The Dirichlet Series To The Riemann Hypothesis2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)

This paper examines the Riemann zeta-function and its relation to the prime distribution. In this work, I present the journey from the Dirichlet series to the Riemann hypothesis. Furthermore, I discuss the prime counting function, the Riemann prime counting function and the Riemann explicit function for distribution of primes. This paper explains that the non-trivial zeros of the zeta-function are the key to understand the prime distribution.

• 8.
T. Shevchenko Kyiv National University, Kyiv, Ukraine.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Mixed variational approach to finding guaranteed estimates from solutions and right-hand sides of the second-order linear elliptic equations under incomplete data2016Ingår i: Minimax Theory and its Applications, ISSN 2199-1413, Vol. 1, nr 2, s. 197-244Artikel i tidskrift (Refereegranskat)

We investigate the problem of guaranteed estimation of values of linear continuous functionals defined on solutions to mixed variational equations generated by linear elliptic problems from indirect noisy observations of these solutions. We assume that right-hand sides of the equations, as well as the second moments of noises in observations are not known; the only available information is that they belong to given bounded sets in the appropriate functional spaces. We are looking for linear with respect to observations optimal estimates of solutions of aforementioned equations called minimax or guaranteed estimates. We develop constructive methods for finding these estimates and estimation errors which are expressed in terms ofsolutions to special mixed variational equations and prove that Galerkin approximations of the obtained variational equations converge to their exact solutions. We study also the problem of guaranteed estimation of right-hand sides of mixed variational equations.

• 9.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
On a spectrum of complex waves in open metal-dielectric waveguides [О спектре комплексных волн в открытых металлических диэлектрических волноводах]2018Ingår i: Современные методы теории краевых задач: материалы международной конференции, посвящённой 90-летию Владимира Александровича Ильина (2-6 мая 2018 г., Москва): Понтрягинские чтения - XXIX / [ed] Budak Alexander Borisovich [Будак Александр Борисович], Moscow: Moscow State University Press , 2018, s. 243-244Konferensbidrag (Refereegranskat)
• 10.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Resonant states in forward and inverse waveguide scattering problems2015Ingår i: Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications: ICEAA 2015, IEEE Press, 2015, s. 31-34Konferensbidrag (Refereegranskat)

It is shown that the transmission coefficient of parallel-plane multi-sectional dielectric diaphragms in a waveguide of rectangular cross section has singularities in the complex plane of the longitudinal wavenumber of each section and the singularities are associated with resonant states of the transmission problem.

• 11.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Penza State University, Penza, Ryssland.
Advanced mathematical techniques  for the analysis of inverse scattering  in waveguides2014Ingår i: Proceedings of the 7th International Conference Inverse Problems: Modeling and Simulation (IPMS 2014): Ölüdeniz, Fethiye, Turkey, May 22–30,2014 / [ed] A. Hasanov, 2014, s. 32-Konferensbidrag (Refereegranskat)
• 12.
Penza State University, Penza, Ryssland.
Eigenwaves in Waveguides with Dielectric Inclusions : Spectrum2014Ingår i: Applicable Analysis, ISSN 0003-6811, E-ISSN 1563-504X, Vol. 93, nr 2, s. 408-427Artikel i tidskrift (Refereegranskat)

We consider fundamental issues of the mathematical theory of the wave propagation in waveguides with inclusions. Analysis is performed in terms of a boundary eigenvalue problem for the Maxwell equations which is reduced to an eigenvalue problem for an operator pencil. We formulate the definition of eigenwaves and associated waves using the system of eigenvectors and associated vectors of the pencil and prove that the spectrum of normal waves forms a non-empty set of isolated points localized in a strip with at most finitely many real points.

• 13.
Penza State University, Penza, Ryssland.
Eigenwaves in waveguides with dielectric inclusions: completeness2014Ingår i: Applicable Analysis, ISSN 0003-6811, E-ISSN 1563-504X, Vol. 93, nr 9, s. 1824-1845Artikel i tidskrift (Refereegranskat)

We formulate the definition of eigenwaves and associated waves in a nonhomogeneously filled waveguide using the system of eigenvectors and associated vectors of a pencil and prove its double completeness with a finite defect or without a defect. Then, we prove the completeness of the system of transversal components of eigenwaves and associated waves as well as the ‘mnimality’ of this system and show that this system is generally not a Schauder basis. This work is a continuation of the paper Eigenwaves in waveguides with dielectric inclusions: spectrum. Appl. Anal. 2013. doi:10.1080/00036811.2013.778980 by Y. Smirnov and Y. Shestopalov. Therefore, we omit the problem statements and all necessary basic definitions given in the previous paper.

• 14.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Macquarie University, Sydney, Australia. Macquarie University, Sydney, Australia.
The effect of inserts upon propagation modes in a waveguide2018Ingår i: Proceedings of 2018 International Conference on Electromagnetics in Advanced Application (ICEAA), Piscataway, New Jersey, USA: IEEE, 2018, s. 315-318, artikel-id 8520404Konferensbidrag (Refereegranskat)

When a perfectly electrically conducting (PEC) waveguide is perturbed by the insertion of a PEC structure aligned with its axis, its propagation constants are perturbed. The underlying boundary value problem may be converted to a homogeneous Fredholm matrix equation in which the propagation constants are found from the roots of the determinant of the matrix; stable and numerically efficient processes may be employed to find the propagation constants. There is no constraint on the size or shape of the inserts. As well as determining the empty waveguide parameters, this approach provides an estimate of the perturbation to the propagation constants of the empty waveguide.

• 15.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Resonant states in waveguide transmission problems2015Ingår i: Progress in Electromagnetics Research B, ISSN 1937-6472, E-ISSN 1937-6472, Vol. 64, nr 1, s. 119-143Artikel i tidskrift (Refereegranskat)

We prove the existence of complex eigenfrequencies of open waveguide resonators in the form of parallel-plate waveguides and waveguides of rectangular crosssection containing layered dielectric inclusions. It is shown that complex eigenfrequencies are finite-multiplicity poles of the analytical continuation of the operator of the initial diffraction problem and its Green's function to a multi-sheet Riemann surface, and also of the transmission coefficient extended to the complex plane of some of the problem parameters. The eigenfrequencies are associated with resonant states (RSs) and eigenvalues of distinct families of Sturm-Liouville problems on the line; they form countable sets of points in the complex plane with the only accumulation point at infinity and depend continuously on the problem parameters. The set of complex eigenfrequencies is similar in its structure to the set of eigenvalues of a Laplacian in a rectangle. The presence of a resonance domain in the form of a parallel-plane layered dielectric insert removes the continuous frequency spectrum and gives rise to a discrete set of points shifted to (upper half of) the complex plane.

• 16.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Resonant states in waveguide transmission problems2015Ingår i: 2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC), New York: Institute of Electrical and Electronics Engineers (IEEE), 2015Konferensbidrag (Refereegranskat)

We prove the existence of complex eigenfrequencies of open waveguide resonators in the form of parallel-plate waveguides and waveguides of rectangular crosssection containing layered dielectric inclusions. It is shown that complex eigenfrequencies are finite-multiplicity poles of the analytical continuation of the operator of the initial diffraction problem and its Green's function to a multi-sheet Riemann surface, and also of the transmission coefficient extended to the complex plane of some of the problem parameters. The eigenfrequencies are associated with resonant states (RSs) and eigenvalues of distinct families of Sturm-Liouville problems on the line; they form countable sets of points in the complex plane with the only accumulation point at infinity and depend continuously on the problem parameters. The set of complex eigenfrequencies is similar in its structure to the set of eigenvalues of a Laplacian in a rectangle. The presence of a resonance domain in the form of a parallel-plane layered dielectric insert removes the continuous frequency spectrum and gives rise to a discrete set of points shifted to (upper half of) the complex plane.

• 17.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
T. Shevchenko Kyiv National University, Kyiv, Ukraine. T. Shevchenko Kyiv National University, Kyiv, Ukraine.
Estimation of Parameters of Boundary Value Problems for Linear Ordinary Differential Equations with Uncertain Data2014Ingår i: Advances in Pure Mathematics, ISSN 2160-0368, E-ISSN 2160-0384, Vol. 4, nr 4, s. 118-146Artikel i tidskrift (Refereegranskat)

In this paper we construct optimal, in certain sense, estimates of values of linear functionals on solutions to two-point boundary value problems (BVPs) for systems of linear first-order ordinary differential equations from observations which are linear transformations of the same solutions perturbed by additive random noises. It is assumed here that right-hand sides of equations and boundary data as well as statistical characteristics of random noises in observations are not known and belong to certain given sets in corresponding functional spaces. This leads to the necessity of introducing minimax statement of an estimation problem when optimal estimates are defined as linear, with respect to observations, estimates for which the maximum of mean square error of estimation taken over the above-mentioned sets attains minimal value. Such estimates are called minimax mean square or guaranteed estimates. We establish that the minimax mean square estimates are expressed via solutions of some systems of differential equations of special type and determine estimation errors.

• 18.
Lomonosov Moscow State University, Russia.
Lomonosov Moscow State University, Russia. Lomonosov Moscow State University, Russia. Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik.
Absorbing boundary conditions for FDTD analysis of rectangular waveguide with non-uniform dielectric inclusions2015Ingår i: 2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC), New York: Institute of Electrical and Electronics Engineers (IEEE), 2015Konferensbidrag (Refereegranskat)

When the finite-difference time-domain method is used for analysis of waveguide structures, incident waves are needed for calculating electromagnetic parameters and effective absorbing boundary conditions are required for terminating open waveguide structures.

• 19.
Lomonosov Moscow State University, Russian Federation .
Lomonosov Moscow State University, Russian Federation . Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik. Lomonosov Moscow State University, Russian Federation .
Numerical simulation of a nonuniform dielectric inclusion in a waveguide aimed at reconstructing its permittivity2015Ingår i: Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications: ICEAA 2015, IEEE Press, 2015, s. 419-421Konferensbidrag (Refereegranskat)

We consider numerical determination of the dielectric media parameters of inclusions in a waveguide of rectangular cross-section from the transmission coefficient. We develop and apply computer codes implementing the FDTD algorithm for nonstationary Maxwell’s equations with perfectly matched layer (PML) absorbing boundary conditions using the Berenger layout and estimate parameter ranges providing the prescribed accuracy for solving forward and inverse scattering problems for waveguides with inclusions.

• 20.
Penza State University, Penza, Ryssland.
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik. Penza State University, Penza, Russia.
Solution to the Inverse Problem of Reconstructing Permittivity of an n-Sectional Diaphragm in a Rectangular Waveguide2014Ingår i: Algebra, Geometry and Mathematical Physics: AGMP, Mulhouse, France, October 2011, Springer Berlin/Heidelberg, 2014, Vol 85, s. 555-566Konferensbidrag (Refereegranskat)

We have developed a numerical-analytical method of solution to the inverse problem of reconstructing permittivities ofn-sectional diaphragms in a waveguide of rectangular cross section. For a one-sectional diaphragm, a solution in the closed form is obtained and the uniqueness is proved.

• 21.
Tomas Bata University in Zlin, Zlin, Czech Republic .
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik. Tomas Bata University in Zlin, Zlin, Czech Republic .
Comparison of selected evolutionary techniques used in reconstruction of permittivity2015Ingår i: Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications: ICEAA 2015, IEEE conference proceedings, 2015, s. 614-617, artikel-id 7297189Konferensbidrag (Refereegranskat)

This work aims at comparison of some traditional evolutionary algorithms (GA, DE, PSO) used in the computation and optimization of transmission coefficients of waveguide filters and in the estimation of the permittivity formed by multi-sectional diaphragms in a waveguide of rectangular cross-section.

• 22.
Tomas Bata University in Zlin, Zlin, Czech Republic .
Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för elektronik, matematik och naturvetenskap, Matematik. Tomas Bata University in Zlin, Zlin, Czech Republic .
Reconstruction of permittivity of multiple layers in free space2015Ingår i: Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications: ICEAA 2015, IEEE conference proceedings, 2015, s. 610-613Konferensbidrag (Refereegranskat)

The goal of this theoretical study is the improvement of the techniques of determining electromagnetic permittivity. However, it may be developed and applied for the reconstruction of other parameters. The work is aimed at the preliminary design and implementation of a system solving inverse problem of reconstruction permittivities of materials consisting of several dielectric layers based on real measurements of the transmission and reflection coefficients in free space.

1 - 22 av 22
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