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  • 1. Alexandrova, A. A.
    et al.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Lukashchuk, V. O.
    Group classification and conservation laws of nonlinear filtration equation with a small parameter2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 19, no 2, p. 364-370Article in journal (Refereed)
    Abstract [en]

    Group classification of the perturbed nonlinear filtration equation is performed assuming that the perturbation is an arbitrary function of the dependent variable. The nonlinear self-adjointness of the equation under consideration is investigated. Using these results, the approximate conservation laws are constructed.

  • 2. Avdonina, Elena D.
    et al.
    Ibragimov, Nail H.
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Khamitova, Raisa
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Exact solutions of gasdynamic equations obtained by the method of conservation laws2013In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 18Article in journal (Refereed)
    Abstract [en]

    In the present paper, the recent method of conservation laws for constructing exact solutions for systems of nonlinear partial differential equations is applied to the gasdynamic equations describing one-dimensional and three-dimensional polytropic flows. In the one-dimensional case singular solutions are constructed in closed forms. In the threedimensional case several conservation laws are used simultaneously. It is shown that the method of conservation laws leads to particular solutions different from group invariant solutions.

  • 3. Bahrami, Fariba
    et al.
    Taghvafard, Hadi
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mohammadi, Abbasali
    Stability investigation for steady solutions of the barotropic vorticity equation in R-22013In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 18, no 3, p. 541-546Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the p-norm stability for vortices of geophysical flows over a surface of variable height that are strict maximizers of the kinetic energy relative to all isovortical flows. In this note, stability means nonlinear stability in the p-norm on the space of vorticity.

  • 4. Baikov, V. A.
    et al.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Zheltova, I. S.
    Yakovlev, A. A.
    Conservation laws for two-phase filtration models2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 19, no 2, p. 383-389Article in journal (Refereed)
    Abstract [en]

    The paper is devoted to investigation of group properties of a one-dimensional model of two-phase filtration in porous medium. Along with the general model, some of its particular cases widely used in oil-field development are discussed. The Buckley-Leverett model is considered in detail as a particular case of the one-dimensional filtration model. This model is constructed under the assumption that filtration is one-dimensional and horizontally directed, the porous medium is homogeneous and incompressible, the filtering fluids are also incompressible. The model of "chromatic fluid" filtration is also investigated. New conservation laws and particular solutions are constructed using symmetries and nonlinear self-adjointness of the system of equations.

  • 5. Bozhkov, Y.
    et al.
    Dimas, S.
    Ibragimov, Nail H.
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Conservation laws for a coupled variable-coefficient modified Korteweg–de Vries system in a two-layer fluid model2013In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 18Article in journal (Refereed)
    Abstract [en]

    We find the Lie point symmetries of a coupled variable-coefficient modified Korteweg–de Vries system in a two-layer fluid model. Then we establish its quasi self-adjointness and corresponding conservation laws.

  • 6. Dorodnitsyn, Vladimir
    et al.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    An extension of the Noether theorem: Accompanying equations possessing conservation laws2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 19, no 2, p. 328-336Article in journal (Refereed)
    Abstract [en]

    It is shown that the Noether theorem can be extended for some equations associated (accompanying) with Euler-Lagrange equation. Each symmetry of Lagrangian yields a class of accompanying equations possessing conservation law (first integral). The generalization is done for canonical Hamiltonian equations as well.

  • 7.
    Figueras, Jordi-Lluis
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Haro, Alex
    Universitat de Barcelona, Departament de Matemàtiques i Informàtica.
    Luque, Alejandro
    Consejo Superior de Investigaciones Científicas, CSIC, Instituto de Ciencias Matemáticas.
    On the sharpness of the Rüssmann estimates2017In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 55, p. 42-55Article in journal (Refereed)
    Abstract [en]

    Estimating the norm of the solution of the linear difference equation u (theta) - u (theta + omega) = v (theta) plays a fundamental role in KAM theory. Optimal (in certain sense) estimates for the solution of this equation were provided by Russmann in the mid 70's. The aim of this paper is to compare the sharpness of these classical estimates with more specific estimates obtained with the help of the computer. We perform several experiments to quantify the improvement obtained when using computer assisted estimates. By comparing these estimates with the actual norm of the solution, we can analyze the different sources of overestimation, thus encouraging future improvements.

  • 8.
    Fogelklou, Oswald
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Analysis and Applied Mathematics.
    Tucker, Warwick
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Analysis and Applied Mathematics.
    Kreiss, Gunilla
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Siklosi, Malin
    A computer-assisted proof of the existence of solutions to a boundary value problem with an integral boundary condition2011In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 16, p. 1227-1243Article in journal (Refereed)
  • 9. Gainetdinova, A.
    et al.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Meleshko, Sergey
    Group classification of ODE y‴ = F (x, y, y′)2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 19, no 2, p. 345-349Article in journal (Refereed)
    Abstract [en]

    In his extensive work of 1884 on the group classification of ordinary differential equations Lie performed, inter alia, the group classification of the particular type of the second-order equations y″ = F (x, y). In the present paper we extend Lie's classification to the third-order equations y‴ = F (x, y, y′).

  • 10. Galiakberova, L. R.
    et al.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Nonlinear self-adjointness of the Krichever-Novikov equation2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 19, no 2, p. 361-363Article in journal (Refereed)
    Abstract [en]

    It is known that the classification of third-order evolutionary equations with the constant separant possessing a nontrivial Lie-Bäcklund algebra (in other words, integrable equations) results in the linear equation, the KdV equation and the Krichever-Novikov equation. The first two of these equations are nonlinearly self-adjoint. This property allows to associate conservation laws of the equations in question with their symmetries. The problem on nonlinear self-adjointness of the Krichever-Novikov equation has not been solved yet. In the present paper we solve this problem and find the explicit form of the differential substitution providing the nonlinear self-adjointness.

  • 11. Gandarias, ML
    et al.
    Ibragimov, Nail H.
    Equivalence group of a fourth-order evolution equation unifying various non-linear models2008In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 13, no 2, p. 259-268Article in journal (Refereed)
    Abstract [en]

    A fourth-order non-linear evolutionary partial differential equation containing several arbitrary functions of the dependent variable is considered. This equation arises as a generalization of various non-linear models describing a non-linear heat diffusion, the dynamics of thin liquid films, etc. Equivalence transformations give more flexibility to the unified model. We determine the generators of the equivalence group and use them for specifying certain types of arbitrary functions when the model equation has additional symmetries, and hence admits non-trivial group invariant solutions. (c) 2006 Elsevier B.V. All rights reserved.

  • 12. Gazizov, R. K.
    et al.
    Ibragimov, N. H.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Lukashchuk, S. Yu.
    Nonlinear self-adjointness, conservation laws and exact solutions of time-fractional Kompaneets equations2015In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 23, no 1-3, p. 153-163Article in journal (Refereed)
    Abstract [en]

    Four time-fractional generalizations of the Kompaneets equation are considered. Group analysis is performed for physically relevant approximations. It is shown that all approximations have nontrivial symmetries and conservation laws. The symmetries are used for constructing group invariant solutions, whereas the conservation laws allow to find non-invariant exact solutions. (C) 2014 Elsevier B.V. All rights reserved.

  • 13. Gazizov, Rafail
    et al.
    Ibragimov, Nail
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Rudenko, Oleg
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Effect of resonant absorption in viscous and dry vibrating contact: Mathematical models and theory connected with slow dynamics and friction welding2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 19, no 2, p. 337-344Article in journal (Refereed)
    Abstract [en]

    Process of heating of thin layer located between two vibrating surfaces is studied. Energy loss goes on due to viscous or dry friction. Optimal quantities of shear viscosity and friction corresponding to maximum energy loss are determined. Resonant behavior of loss must be taken into account in the description of "slow dynamics" of rocks and materials exposed to high-intensity seismic or acoustic irradiation as well as in various technologies. Bonding of materials by linear friction welding, widely used in propulsion engineering, can exemplify such a technology.

  • 14. Ibragimov, Nail H.
    Extension of Euler's method to parabolic equations2009In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 14, no 4, p. 1157-1168Article in journal (Refereed)
    Abstract [en]

    Euler generalized d'Alembert's solution to a wide class of linear hyperbolic equations with two independent variables. He introduced in 1769 the quantities that were rediscovered by Laplace in 1773 and became known as the Laplace invariants. The present paper is devoted to an extension of Euler's method to linear parabolic equations with two independent variables. The new method allows one to derive an explicit formula for the general solution of a wide class of parabolic equations. In particular, the general solution of the Black-Scholes equation is obtained. (c) 2008 Elsevier B.V. All rights reserved.

  • 15. Ibragimov, Nail H.
    et al.
    Aitbayev, Rakhim
    Ibragimov, Ranis
    Three-dimensional non-linear rotating surface waves in channels of variable depth in the presence of formation of a small perturbation of atmospheric pressure across the channel2009In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 14, no 11, p. 3811-3820Article in journal (Refereed)
    Abstract [en]

    We consider three-dimensional free-boundary problem on the propagation of incompressible, homogeneous and inviscid fluid with zero surface tension confined in a channel of variable depth. Since for large-scale flows the fluid motion is affected by the rotation of the earth, the model is considered in rotating reference frame. Additionally, small atmospheric pressure variations across the channel are taken into account. It is shown that the non-trivial solution to the problem represents three-dimensional solitary wave which is given by the rotation modified Korteweg-de Vries equation (fKdV): b(1)xi(xxx) + b(2)xi xi(x) + b(3)(f)xi(x) = 0, where x is the down-channel coordinate and the coefficients b(i) (i = 1,2,3) of the resulting fKdV equation depend on the transverse topography of the channel and, additionally, b(3) depends on the Coriolis parameter f. It is also shown that if the vertical profile of the channel is symmetric about the vertical axis, the small atmospheric variations will not appear in the resulting fKdV equation. The effects of channel's cross-sectional geometry on the shape of the resulting three-dimensional wave profile in a longitudinal direction are studied numerically. Additionally, to better understand the effects of the Earth rotation, the above analysis is performed at different latitudes. (C) 2008 Elsevier B.V. All rights reserved.

  • 16.
    Ibragimov, Nail H.
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Mathematics and Natural Sciences.
    Avdonina, Elena D.
    Conservation laws and exact solutions for nonlinear diffusion in anisotropic media2013In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 18, no 10Article in journal (Refereed)
    Abstract [en]

    Conservation laws and exact solutions of nonlinear differential equations describing diffusion phenomena in anisotropic media with external sources are constructed. The construction is based on the method of nonlinear self-adjointness. Numerous exact solutions are obtained by using the recent method of conservation laws. These solutions are different from group invariant solutions and can be useful for investigating diffusion phenomena in complex media, e.g. in oil industry.

  • 17.
    Ibragimov, Nail H.
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Gazizov, Rafail H.
    Approximate symmetries and solutions of the Kompaneets equation2014In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 55, no 2, p. 220-224Article in journal (Refereed)
    Abstract [en]

    Different approximations of the Kompaneets equation are studied using approximate symmetries, which allows consideration of the contributions of all terms of this equation previously neglected in the analysis of the limiting cases.

  • 18. Ibragimov, Nail H.
    et al.
    Ibragimov, Ranis
    Internal gravity wave beams as invariant solutions of Boussinesq equations in geophysical fluid dynamics2010In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 15, no 8, p. 1989-2002Article in journal (Refereed)
    Abstract [en]

    It is shown that Lie group analysis of differential equations provides the exact solutions of two-dimensional stratified rotating Boussinesq equations which are a basic model in geophysical fluid dynamics. The exact solutions are obtained as group invariant solutions corresponding to the translation and dilation generators of the group of transformations admitted by the equations. The comparison with the previous analytic studies and experimental observations confirms that the anisotropic nature of the wave motion allows to associate these invariant solutions with uni-directional internal wave beams propagating through the medium. It is also shown that the direction of internal wave beam propagation is in the transverse direction to one of the invariants which corresponds to a linear combination of the translation symmetries. Furthermore, the amplitudes of a linear superposition of wave-like invariant solutions forming the internal gravity wave beams are arbitrary functions of that invariant. Analytic examples of the latitude-dependent invariant solutions associated with internal gravity wave beams that have different general profiles along the obtained invariant and propagating in the transverse direction are considered. The behavior of the invariant solutions near the critical latitude is illustrated. © 2009 Elsevier B.V. All rights reserved.

  • 19. Ibragimov, Nail H.
    et al.
    Ibragimov, Ranis
    Invariant solutions as internal singularities of nonlinear differential equations and their use for qualitative analysis of implicit and numerical solutions2009In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 14, no 9-10, p. 3537-3547Article in journal (Refereed)
    Abstract [en]

    Lie group analysis of nonlinear differential equations reveals existence of singularities provided by invariant solutions and invisible from the form of the equation in question. We call them internal singularities in contrast with external singularities manifested by the form of the equation. It is illustrated by way of examples that internal singularities are useful for analyzing a behaviour of solutions of nonlinear differential equations near external singularities.

  • 20. Ibragimov, Nail H.
    et al.
    Meleshko, Sergey
    A solution to the problem of invariants for parabolic equations2009In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 14, no 6, p. 2551-2558Article in journal (Refereed)
    Abstract [en]

    The article is devoted to the Solution Of the invariants problem for the one-dimensional parabolic equations written in the two-coefficient canonical form used recently by N.H. Ibragimov: u(t) - u(xx) + a (t, x)u(x) + c(t, x)u = 0. A simple invariant condition is obtained for determining all equations that are reducible to the heat equation by the general group of equivalence transformations. The solution to the problem of invariants is given also in the one-coefficient canonical u(t) - u(xx) + c(t, x)u = 0. One of the main differences between these two canonical forms is that the equivalence group for the two-coefficient form contains the arbitrary linear transformation of the dependent variable whereas this group for the one-coefficient form contains only a special type of the linear transformations of the dependent variable. (C) 2008 Elsevier B.V. All rights reserved.

  • 21. Ibragimov, Nail H.
    et al.
    Meleshko, Sergey
    Invariants and invariant description of second-order ODEs with three infinitesimal symmetries. I2007In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 12, no 8, p. 1370-1378Article in journal (Refereed)
    Abstract [en]

    Lie's group classification of ODEs shows that the second-order equations can possess one, two, three or eight infinitesimal symmetries. The equations with eight symmetries and only these equations can be linearized by a change of variables. Lie showed that the latter equations are at most cubic in the first derivative and gave a convenient invariant description of all linearizable equations. Our aim is to provide a similar description of the equations with three symmetries. There are four different types of such equations. We present here the candidates for all four types. We give an invariant test for existence of three symmetries for one of these candidates.

  • 22. Ibragimov, Nail H.
    et al.
    Meleshko, Sergey
    Invariants and invariant description of second-order ODEs with three infinitesimal symmetries. II.2008In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 13, no 6, p. 1015-1020Article in journal (Refereed)
    Abstract [en]

    The second-order ordinary differential equations can have one, two, three or eight independent symmetries. Sophus Lie showed that the equations with eight symmetries and only these equations can be linearized by a change of variables. Moreover he demonstrated that these equations are at most cubic in the first derivative and gave a convenient invariant description of all linearizable equations. We provide a similar description of the equations with three symmetries. There are four different types of such equations. Classes of equations belonging to one of these types were studied in N.H. Ibragimov and S.V. Meleshko, Invariants and invariant description of second-order ODEs with three infinitesimal symmetries. I, Communications in Nonlinear Science and Numerical Simulation, Vol. 12, No. 8, 2007, pp. 1370--1378. Namely, we presented there the candidates for all four types and studied one of these candidates.The present paper is devoted to other three candidates.

  • 23. Ibragimov, Nail H.
    et al.
    Meleshko, Sergey
    Thailert, E
    Invariants of linear parabolic differential equations2008In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, p. 277-284Article in journal (Refereed)
    Abstract [en]

    The paper is dedicated to construction of invariants for the parabolic equation u(t) + a(t, x)u(xx) + b(t, x)u(x) + c(t, x)u = 0. We consider the equivalence group given by point transformations and find all invariants up to seventh-order, i.e. the invariants involving the derivatives up to seventh-order of the coefficients a, b and c with respect to the independent variables t, x. (c) 2006 Elsevier B.V. All rights reserved.

  • 24. Ibragimov, Nail H.
    et al.
    Sophocleus, C.
    Differential invariants of the one-dimensional quasi-linear second-order evolution equation2007In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 12, no 7, p. 1133-1145Article in journal (Refereed)
    Abstract [en]

    We consider evolution equations of the form ut = f(x, u, ux)uxx + g(x, u, ux) and ut = uxx + g(x, u, ux). In the spirit of the recent work of Ibragimov [Ibragimov NH. Laplace type invariants for parabolic equations. Nonlinear Dynam 2002;28:125-33] who adopted the infinitesimal method for calculating invariants of families of differential equations using the equivalence groups, we apply the method to these equations. We show that the first class admits one differential invariant of order two, while the second class admits three functional independent differential invariants of order three. We use these invariants to determine equations that can be transformed into the linear diffusion equation.

  • 25. Ibragimov, Nail H.
    et al.
    Säfström, Niklas
    The equivalence group and invariant solutions of a tumour growth model2004In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 9, no 1, p. 61-68Article in journal (Refereed)
    Abstract [en]

    Most of mathematical models describing spread of malignant tumours are formulated as systems of nonlinear partial differential equations containing, in general, several unknown functions of dependent variables. Determination of these unknown functions (called in group analysis arbitrary elements) is a complicated problem that challenges researchers. Our aim is to calculate the generators of the equivalence group for one of the known models and, using the equivalence generators, specify arbitrary elements, find additional symmetries and calculate group invariant solutions.

  • 26. Ibragimov, Nail H.
    et al.
    Torrisi, M.
    Valenti, A.
    Differential invariants of nonlinear equations v_{tt} =f(x,v_x) v_{xx} + g(x,v_x)2004In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 9, no 1, p. 69-80Article in journal (Refereed)
    Abstract [en]

    We apply the infinitesimal technique for calculating invariants for the family of nonlinear equations formulated in the title. We show that the infinite-dimensional equivalence Lie algebra has three functionally independent differential invariants of the second order. Knowledge of invariants of families of equations is essential for identifying distinctly different equations and therefore for the problem of group classification.

  • 27.
    Ibragimov, Nail
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Khamitova, Raisa
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mathematics and Natural Sciences.
    Avdonina, E. D.
    Galiakberova, L.R.
    Group analysis of the drift–diffusion model for quantum semiconductors2015In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 20, no 1, p. 74-78Article in journal (Refereed)
    Abstract [en]

    In the present paper a quantum drift–diffusion model describing semi-conductor devices is considered. New conservation laws for the model are computed and used to construct exact solutions.

  • 28. Khamitova, Raisa
    Symmetries and Nonlocal Conservation Laws of the General Magma Equation2009In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 14, no 11, p. 3754-3769Article in journal (Refereed)
    Abstract [en]

    In this paper the general magma equation modelling a melt flow in the Earth's mantle is discussed. Applying the new theorem on nonlocal conservation laws [Ibragimov NH. A new conservation theorem. J Math Anal Appl 2007;333(1):311-28] and using the symmetries of the model equation nonlocal conservation laws are computed. In accordance with Ibragimov [Ibragimov NH. Quasi-self-adjoint differential equations. Preprint in Archives of ALGA, vol. 4, BTH, Karlskrona, Sweden: Alga Publications; 2007. p. 55-60, ISSN: 1652-4934] it is shown that the general magma equation is quasi-self-adjoint for arbitrary m and n and self-adjoint for n = -m. These important properties are used for deriving local conservation laws. © 2008 Elsevier B.V. All rights reserved.

  • 29. Panchuk, A.
    et al.
    Puu, Tönu
    Umeå University, Faculty of Social Sciences, Centre for Regional Science (CERUM).
    Dynamics of a durable commodity market involving trade at disequilibrium2018In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 58, p. 2-14Article in journal (Refereed)
    Abstract [en]

    The present work considers a simple model of a durable commodity market involving two agents who trade stocks of two different types. Stock commodities, in contrast to flow commodities, remain on the market from period to period and, consequently, there is neither unique demand function nor unique supply function exists. We also set up exact conditions for trade at disequilibrium, the issue being usually neglected, though a fact of reality. The induced iterative system has infinite number of fixed points and path dependent dynamics. We show that a typical orbit is either attracted to one of the fixed points or eventually sticks at a no-trade point. For the latter the stock distribution always remains the same while the price displays periodic or chaotic oscillations. (C) 2017 Elsevier B.V. All rights reserved.

  • 30. Suksern, Supaporn
    et al.
    Meleshko, Sergey
    Ibragimov, Nail H.
    Criteria for fourth-order ordinary differential equations to be linearizable by contact transformations2009In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 14, no 6, p. 2619-2628Article in journal (Refereed)
    Abstract [en]

    Solution of linearization problem of fourth-order ordinary differential equations Via contact transformations is presented in the paper. We show that all fourth-order ordinary differential equations that are linearizable by contact transformations are contained in the class of equations which is at most quadratic in the third-order derivative. We provide the linearization test and describe the procedure for obtaining the linearizing transformations as well as the linearized equation. Moreover, we obtain the general form of ordinary differential equations of order greater than four linearizable via contact transformations. (C) 2008 Elsevier B.V. All rights reserved.

  • 31. Zhang, Hong
    et al.
    Georgescu, Paul
    Zhang, Lai
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Periodic patterns and Pareto efficiency of state dependent impulsive controls regulating interactions between wild and transgenic mosquito populations2016In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 31, no 1-3, p. 83-107Article in journal (Refereed)
    Abstract [en]

    It is conceivable that genetically modified mosquitoes could stop the spread of malaria, by outcompeting the wild mosquitoes and interfering with their reproductive processes, and genetically inheriting and further transmitting a diminished potential to carry Plasmodium. To get insight into the possible outcomes, we formulate an ODE model for the interactions between wild and transgenic mosquito populations, which is subject to state-dependent impulsive perturbations. By first investigating the dynamics of the unperturbed system, we determine certain sufficient conditions for the existence and orbital stability of positive order-1 solution of the model system with state-dependent impulsive perturbations. Their feasibility is then illustrated by means of numerical simulations. In addition, to adequately control the wild mosquito population, we use a multi-target approach which, in addition to accounting for the total costs, keeps track of the total size of the wild mosquito population. To trade off these objectives, we consider the concept of Pareto efficiency to determine suitable control strategies which are near-optimal. Finally, we carry out numerical simulations to illustrate the Pareto frontier and then characterize the detailed Pareto efficient control regime. (C) 2015 Elsevier B.V. All rights reserved.

  • 32.
    Zhang, Lai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Liu, Jia
    Banerjee, Malay
    Hopf and steady state bifurcation analysis in a ratio-dependent predator-prey model2017In: Communications in nonlinear science & numerical simulation, ISSN 1007-5704, E-ISSN 1878-7274, Vol. 44, p. 52-73Article in journal (Refereed)
    Abstract [en]

    In this paper, we perform spatiotemporal bifurcation analysis in a ratio-dependent predator prey model and derive explicit conditions for the existence of non-constant steady states that emerge through steady state bifurcation from related constant steady states. These explicit conditions are numerically verified in details and further compared to those conditions ensuring Turing instability. We find that (1) Turing domain is identical to the parametric domain where there exists only steady state bifurcation, which implies that Turing patterns are stable non-constant steady states, but the opposite is not necessarily true; (2) In non-Turing domain, steady state bifurcation and Hopf bifurcation act in concert to determine the emergent spatial patterns, that is, non-constant steady state emerges through steady state bifurcation but it may be unstable if the destabilising effect of Hopf bifurcation counteracts the stabilising effect of diffusion, leading to non-stationary spatial patterns; (3) Coupling diffusion into an ODE model can significantly enrich population dynamics by inducing alternative non-constant steady states (four different states are observed, two stable and two unstable), in particular when diffusion interacts with different types of bifurcation; (4) Diffusion can promote species coexistence by saving species which otherwise goes to extinction in the absence of diffusion.

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