| 1. |
- Laksman, Efraim, et al.
(author)
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Generalized upper bounds on the minimum distance of PSK block codes
- 2015
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In: IMA Journal of Mathematical Control and Information. - : Oxford Journals. - 0265-0754 .- 1471-6887. ; 32:2, s. 305-327
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Research review (peer-reviewed)abstract
- This paper generalizes previous optimal upper bounds on the minimum Euclidean distance for phase shift keying (PSK) block codes, that are explicit in three parameters: alphabet size, block length and code size. The bounds are primarily generalized from codes over symmetric PSK to codes over asymmetric PSK and also to general alphabet size. Furthermore, block codes are optimized in the presence of other types of noise than Gaussian, which induces also non-Euclidean distance measures. In some instances, codes over asymmetric PSK prove to give higher Euclidean distance than any code over symmetric PSK with the same parameters. We also provide certain classes of codes that are optimal among codes over symmetric PSK.
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| 2. |
- Lamers, Jules, 1986
(author)
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The Functional Method for the Domain-Wall Partition Function
- 2018
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In: Symmetry, Integrability and Geometry - Methods and Applications. - 1815-0659. ; 14
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Research review (peer-reviewed)abstract
- We review the (algebraic-)functional method devised by Galleas and further developed by Galleas and the author. We first explain the method using the simplest example: the computation of the partition function for the six-vertex model with domain-wall boundary conditions. At the heart of the method lies a linear functional equation for the partition function. After deriving this equation we outline its analysis. The result is a closed expression in the form of a symmetrized sum - or, equivalently, multiple-integral formula - that can be rewritten to recover Izergin's determinant. Special attention is paid to the relation with other approaches. In particular we show that the Korepin-Izergin approach can be recovered within the functional method. We comment on the functional method's range of applicability, and review how it is adapted to the technically more involved example of the elliptic solid-on-solid model with domain walls and a reflecting end. We present a new formula for the partition function of the latter, which was expressed as a determinant by Tsuchiya-Filali-Kitanine. Our result takes the form of a 'crossing-symmetrized' sum with 2(L) terms featuring the elliptic domain-wall partition function, which appears to be new also in the limiting case of the six-vertex model. Further taking the rational limit we recover the expression obtained by Frassek using the boundary perimeter Bethe ansatz.
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| 3. |
- Gustafsson, Björn, 1947-
(author)
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Quadrature for quadrics
- 2023
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In: European Journal of Mathematics. - : Springer Science and Business Media Deutschland GmbH. - 2199-675X .- 2199-6768. ; 9:4
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Research review (peer-reviewed)abstract
- We make a systematic investigation of quadrature properties for quadrics, namely integration of holomorphic functions over planar domains bounded by second degree curves. A full understanding requires extending traditional settings by allowing domains which are multi-sheeted, in other words domains which really are branched covering surfaces of the Riemann sphere, and in addition usage of the spherical area measure instead of the Euclidean. The first part of the paper discusses two different points of view of real algebraic curves: traditionally they live in the real projective plane, which is non-orientable, but for their role for quadrature they have to be pushed to the Riemann sphere. The main results include clarifying a previous theorem (joint work with V. Tkachev), which says that a branched covering map produces a domain with the required quadrature properties if and only it extends to be meromorphic on the double of the parametrizing Riemann surface. In the second half of the paper domains bounded by ellipses, hyperbolas, parabolas and their inverses are studied in detail, with emphasis on the hyperbola case, for which some of the results appear to be new.
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| 4. |
- Lenells, Jonatan, 1981-, et al.
(author)
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Linearizable boundary value problems for the elliptic sine-Gordon and the elliptic Ernst equations
- 2020
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In: Journal of Nonlinear Mathematical Physics. - : TAYLOR & FRANCIS LTD. - 1402-9251 .- 1776-0852. ; 27:2, s. 337-356
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Research review (peer-reviewed)abstract
- By employing a novel generalization of the inverse scattering transform method known as the unified transform or Fokas method, it can be shown that the solution of certain physically significant boundary value problems for the elliptic sine-Gordon equation, as well as for the elliptic version of the Ernst equation, can be expressed in terms of the solution of appropriate 2x2-matrix Riemann-Hilbert (RH) problems. These RH problems are defined in terms of certain functions, called spectral functions, which involve the given boundary conditions, but also unknown boundary values. For arbitrary boundary conditions, the determination of these unknown boundary values requires the analysis of a nonlinear Fredholm integral equation. However, there exist particular boundary conditions, called linearizable, for which it is possible to bypass this nonlinear step and to characterize the spectral functions directly in terms of the given boundary conditions. Here, we review the implementation of this effective procedure for the following linearizable boundary value problems: (a) the elliptic sine-Gordon equation in a semi-strip with zero Dirichlet boundary values on the unbounded sides and with constant Dirichlet boundary value on the bounded side; (b) the elliptic Ernst equation with boundary conditions corresponding to a uniformly rotating disk of dust; (c) the elliptic Ernst equation with boundary conditions corresponding to a disk rotating uniformly around a central black hole; (d) the elliptic Ernst equation with vanishing Neumann boundary values on a rotating disk.
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| 5. |
- Manzetti, Sergio
(author)
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Mathematical Modeling of Rogue Waves : A Survey of Recent and Emerging Mathematical Methods and Solutions
- 2018
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In: Axioms. - : MDPI AG. - 2075-1680. ; 7:2
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Research review (peer-reviewed)abstract
- Anomalous waves and rogue events are closely associated with irregularities and unexpected events occurring at various levels of physics, such as in optics, in oceans and in the atmosphere. Mathematical modeling of rogue waves is a highly active field of research, which has evolved over the last few decades into a specialized part of mathematical physics. The applications of the mathematical models for rogue events is directly relevant to technology development for the prediction of rogue ocean waves and for signal processing in quantum units. In this survey, a comprehensive perspective of the most recent developments of methods for representing rogue waves is given, along with discussion of the devised forms and solutions. The standard nonlinear Schrödinger equation, the Hirota equation, the MMT equation and other models are discussed and their properties highlighted. This survey shows that the most recent advancement in modeling rogue waves give models that can be used to establish methods for the prediction of rogue waves in open seas, which is important for the safety and activity of marine vessels and installations. The study further puts emphasis on the difference between the methods and how the resulting models form the basis for representing rogue waves in various forms, solitary or with a wave background. This review has also a pedagogic component directed towards students and interested non-experts and forms a complete survey of the most conventional and emerging methods published until recently.
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| 6. |
- McCall, Martin, et al.
(author)
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Roadmap on transformation optics
- 2018
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In: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:6
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Research review (peer-reviewed)abstract
- Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.
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| 7. |
- Schippers, Eric, et al.
(author)
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A Survey of Scattering Theory on Riemann Surfaces with Applications in Global Analysis and Geometry
- 2023
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In: Vietnam Journal of Mathematics. - : Springer. - 2305-221X .- 2305-2228. ; 51:4, s. 911-934
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Research review (peer-reviewed)abstract
- This paper gives an overview of our work on a scattering theory of one-forms and functions in a system of quasicircles on Riemann surfaces. It is rooted in an "overfare" process which takes a harmonic function on one side of the system of quasicircles to a harmonic function on the other side, with the same boundary values in a certain intrinsic non-tangential sense. This is bounded with respect to Dirichlet energy. If extra cohomological data is specified, one can apply this process to harmonic one-forms, and the resulting "scattering matrix" in terms of the holomorphic and anti-holomorphic components of the one-form is unitary. We describe applications to approximation theory, global analysis of singular integral operators on Riemann surfaces, and a new extension of the classical period map to surfaces of genus g with n boundary curves.
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| 8. |
- Singh, Harpal, et al.
(author)
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Recent trends in operation modal analysis techniques and its application on a steel truss bridge
- 2019
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In: Nonlinear Studies. - : Cambridge Scientific Publishers. - 1359-8678. ; 26:4, s. 911-927
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Research review (peer-reviewed)abstract
- Aging of infrastructure causes many problems with great consequences, essentially economical. Operation modal analysis (OMA) is one of the most crucial techniques used for dynamic analysis of civil engineering structures (e.g. bridges, dams or tunnels). OMA uses various time and frequency domain methods to obtain the modal parameters. The analysis of OMA techniques can be used to detect, locate and quantify the damage in a structure. The major challenge for damage detection using OMA is the analysis of a large amount of noisy data collected from sensors. New signal processing techniques and artificial intelligence can play an important role in future research in the area. In this article, we present and discuss recent developments in OMA techniques and also give a concrete example on a steel truss bridge, where the most popular OMA techniques have been implemented and applied.
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| 9. |
- Skagerstam, Bo-Sture K., et al.
(author)
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Causality in quantum field theory with classical sources
- 2019
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In: Journal of Physics Communications. - : IOP Publishing. - 2399-6528. ; 3:8
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Research review (peer-reviewed)abstract
- In an exact quantum-mechanical framework we show that space-time expectation values of the second-quantized electromagnetic fields in the Coulomb gauge in the presence of a classical conserved source automatically lead to causal and properly retarded h-independent electromagnetic field strengths. The classical h-independent and gauge invariant Maxwell's equations naturally emerge in terms of quantum-mechanical expectation values and are therefore also consistent with the classical special theory of relativity. The fundamental difference between interference phenomena due to the linear nature of the classical Maxwell theory as considered in, e.g., classical optics, and interference effects of quantum states is clarified. In addition to these issues, the framework outlined also provides for a simple approach to invariance under time-reversal, some spontaneous photon emission and/or absorption processes as well as an approach to Vavilov-Cherenkov radiation. The inherent and necessary quantum uncertainty, limiting a precise space-time knowledge of expectation values of the quantum fields considered, is, finally, recalled.
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