Mathematics / Matematik

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Now showing 1 - 10 of 26
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Dispersion Estimates for the Boundary Integral Operator Associated With the Fourth Order Schrödinger Equation Posed on the Half Line
    (Element d.o.o., 2022) Özsarı, Türker; Alkan, Kıvılcım; Kalimeris, Konstantinos
    In this paper, we prove dispersion estimates for the boundary integral operator associated with the fourth order Schr¨odinger equation posed on the half line. Proofs of such estimates for domains with boundaries are rare and generally require highly technical approaches, as opposed to our simple treatment which is based on constructing a boundary integral operator of oscillatory nature via the Fokas method. Our method is uniform and can be extended to other higher order partial differential equations where the main equation possibly involves more than one spatial derivatives.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 3
    Integral Characteristics by Keyspace Partitioning
    (Springer, 2022) Demirbaş, Fatih; Kara, Orhun
    In this work, we introduce a new method we call integral by keyspace partitioning to construct integral characteristics for some block ciphers by introducing new integral properties. We introduce the concepts of active with constant difference and identically active integral properties. Then, we divide the key space into equivalence classes and construct integral characteristics for each equivalence class individually by using these integral properties. We exploit the binary diffusion layer and key schedule algorithm of a block cipher to propagate these integral properties through rounds. We apply the new method to the Byte-oriented Substitution-Permutation Network (BSPN) cipher and Midori64 to show its effectiveness. We construct the first iterative integral characteristic for a block cipher to the best of our knowledge. We extend this iterative characteristic for the (M, n)-(BSPN) block cipher where each block of BSPN contains M number of n× n S-Boxes with the block and key sizes M· n. Using at most (M-12)+1 (only 106 when M= 16) chosen plaintexts, we mount key recovery attacks for the first time on BSPN and recover the key for the full round. The time complexity of the key recovery is almost independent of the number of rounds. We also use our method to construct an integral characteristic for Midori64, which can be utilized for a key recovery attack on 11-round Midori64. Our results impose a new security criteria for the design of the key schedule algorithm for some block ciphers.
  • Article
    A Note on Points on Algebraic Sets
    (Hacettepe Üniversitesi, 2021) Çam Çelik, Şermin; Göral, Haydar
    In this short note, we count the points on algebraic sets which lie in a subset of a domain. It is proved that the set of points on algebraic sets coming from certain subsets of a domain has the full asymptotic. This generalizes the first theorem of [E. Alkan and E.S. Yoruk, Statistics and characterization of matrices by determinant and trace, Ramanujan J., 2019] and also anwers some questions from the same article.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Rings With Few Units and the Infinitude of Primes
    (Hacettepe Üniversitesi, 2020) Özcan, Hikmet Burak; Taşkın, Sedef
    In this short note, our aim is to provide novel proofs for the infinitude of primes in an algebraic way. It’s thought that the first proof for the infinitude of primes was given by the Ancient Greek mathematician Euclid. To date, most of the proofs have been based on the fact that every positive integer greater than 1 can be written as a product of prime numbers. However, first we are going to prove a ring theoretic fact that if R is an infinite commutative ring with unity and the cardinality of the set of invertible elements is strictly less than the cardinality of the ring, then there are infinitely many maximal ideals. This fact leads to an elegant proof for the infinitude of primes. In addition, under the same cardinality assumption, we consider the special case in which R is a unique factorization domain (for short UFD) and establish another ring theoretic result. Thanks to it, we give a second proof of the infinitude of primes. © 2020, Hacettepe University. All rights reserved.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 7
    Integrable Systems From Inelastic Curve Flows in 2-And 3-Dimensional Minkowski Space
    (Taylor & Francis, 2016) Alkan, Kıvılcım; Anco, Stephen C.
    Integrable systems are derived from inelastic flows of timelike, spacelike, and null curves in 2-and 3- dimensional Minkowski space. The derivation uses a Lorentzian version of a geometrical moving frame method which is known to yield the modified Korteveg-de Vries (mKdV) equation and the nonlinear Schrodinger (NLS) equation in 2- and 3- dimensional Euclidean space, respectively. In 2-dimensional Minkowski space, time-like/space-like inelastic curve flows are shown to yield the defocusing mKdV equation and its bi-Hamiltonian integrability structure, while inelastic null curve flows are shown to give rise to Burgers' equation and its symmetry integrability structure. In 3-dimensional Minkowski space, the complex defocusing mKdV equation and the NLS equation along with their bi-Hamiltonian integrability structures are obtained from timelike inelastic curve flows, whereas spacelike inelastic curve flows yield an interesting variant of these two integrable equations in which complex numbers are replaced by hyperbolic (split-complex) numbers.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Blow-Up of Solutions of Nonlinear Schrödinger Equations With Oscillating Nonlinearities
    (American Institute of Mathematical Sciences, 2019) Özsarı, Türker
    The finite time blow-up of solutions for 1-D NLS with oscillating nonlinearities is shown in two domains: (1) the whole real line where the nonlinear source is acting in the interior of the domain and (2) the right half-line where the nonlinear source is placed at the boundary point. The distinctive feature of this work is that the initial energy is allowed to be non-negative and the momentum is allowed to be infinite in contrast to the previous literature on the blow-up of solutions with time dependent nonlinearities. The common finite momentum assumption is removed by using a compactly supported or rapidly decaying weight function in virial identities - an idea borrowed from [18]. At the end of the paper, a numerical example satisfying the theory is provided.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    A Perturbative Approach To the Tunneling Phenomena
    (Frontiers Media S.A., 2019) Erman, Fatih; Turgut, Osman Teoman
    The double-well potential is a good example, where we can compute the splitting in the bound state energy of the system due to the tunneling effect with various methods, namely path-integral, WKB, and instanton calculations. All these methods are non-perturbative and there is a common belief that it is dif fi cult to fi nd the splitting in the energy due to the barrier penetration from a perturbative analysis. However, we will illustrate by explicit examples including singular potentials (e.g., Dirac delta potentials supported by points and curves and their relativistic extensions) it is possible to fi nd the splitting in the bound state energies by developing some kind of perturbation method.
  • Article
    Citation - WoS: 40
    Citation - Scopus: 40
    The Initial-Boundary Value Problem for the Biharmonic Schrödinger Equation on the Half-Line
    (American Institute of Mathematical Sciences, 2019) Özsarı, Türker; Yolcu, Nermin
    We study the local and global wellposedness of the initial-boundary value problem for the biharmonic Schrodinger equation on the half-line with inhomogeneous Dirichlet-Neumann boundary data. First, we obtain a representation formula for the solution of the linear nonhomogenenous problem by using the Fokas method (also known as the unified transform method). We use this representation formula to prove space and time estimates on the solutions of the linear model in fractional Sobolev spaces by using Fourier analysis. Secondly, we consider the nonlinear model with a power type nonlinearity and prove the local wellposedness by means of a classical contraction argument. We obtain Strichartz estimates to treat the low regularity case by using the oscillatory integral theory directly on the representation formula provided by the Fokas method. Global wellposedness of the defocusing model is established up to cubic nonlinearities by using the multiplier technique and proving hidden trace regularities.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 5
    The Propagators for Δ and Δ′ Potentials With Time-Dependent Strengths
    (Frontiers Media S.A., 2020) Erman, Fatih; Gadella, Manuel; Uncu, Haydar
    We study the time-dependent Schrodinger equation with finite number of Dirac delta and delta ' potentials with time dependent strengths in one dimension. We obtain the formal solution for generic time dependent strengths and then we study the particular cases for single delta potential and limiting cases for finitely many delta potentials. Finally, we investigate the solution of time dependent Schrodinger equation for delta ' potential with particular forms of the strengths.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    A1-L10 Phase Boundaries and Anisotropy Via Multiple-Order Theory for an Fcc Alloy
    (European Mathematical Society Publishing House, 2003) Tanoğlu, Gamze; Braun, Richard J.; Cahn, John W.; McFadden, Geoffrey B.
    The dependence of thermodynamic properties of planar interphase boundaries (IPBs) and antiphase boundaries (APBs) in a binary alloy on an fcc lattice is studied as a function of their orientation. Using a recently developed diffuse interface model based on three non-conserved order parameters and the concentration, and a free energy density that gives a realistic phase diagram with one disordered phase (A1) and two ordered phases (L12 and L10) such as occur in the Cu-Au system, we are able to find IPBs and APBs between any pair of phases and domains, and for all orientations. The model includes bulk and gradient terms in a free energy functional, and assumes that there is no mismatch in the lattice parameters for the disordered and ordered phases.We catalog the appropriate boundary conditions for all IPBs and APBs. We then focus on the IPB between the disordered A1 phase and the L10 ordered phase. For this IPB we compute the numerical solution of the boundary value problem to find its interfacial energy, γ as a function of orientation, temperature, and chemical potential (or composition). We determine the equilibrium shape for a precipitate of one phase within the other using the Cahn-Hoffman "-vector" formalism. We find that the profile of the interface is determined only by one conserved and one non-conserved order parameter, which leads to a surface energy which, as a function of orientation, is "transversely isotropic" with respect to the tetragonal axis of the L10 phase. We verify the model's consistency with the Gibbs adsorption equation.