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  • Morais, Joao  (5)
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  • 1
    Online Resource
    Online Resource
    Hindawi Limited ; 2013
    In:  Abstract and Applied Analysis Vol. 2013 ( 2013), p. 1-14
    In: Abstract and Applied Analysis, Hindawi Limited, Vol. 2013 ( 2013), p. 1-14
    Abstract: We generalize the linear canonical transform (LCT) to quaternion-valued signals, known as the quaternionic linear canonical transform (QLCT). Using the properties of the LCT we establish an uncertainty principle for the QLCT. This uncertainty principle prescribes a lower bound on the product of the effective widths of quaternion-valued signals in the spatial and frequency domains. It is shown that only a 2D Gaussian signal minimizes the uncertainty.
    Type of Medium: Online Resource
    ISSN: 1085-3375 , 1687-0409
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2013
    detail.hit.zdb_id: 2064801-7
    SSG: 17,1
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  • 2
    Online Resource
    Online Resource
    Wiley ; 2016
    In:  Mathematical Methods in the Applied Sciences Vol. 39, No. 10 ( 2016-07), p. 2722-2736
    In: Mathematical Methods in the Applied Sciences, Wiley, Vol. 39, No. 10 ( 2016-07), p. 2722-2736
    Abstract: In the present paper, we generalize the linear canonical transform (LCT) to quaternion‐valued signals, known as the quaternionic LCT (QLCT). Using the properties of the LCT, we establish an uncertainty principle for the two‐sided QLCT. This uncertainty principle prescribes a lower bound on the product of the effective widths of quaternion‐valued signals in the spatial and frequency domains. It is shown that only a Gaussian quaternionic signal minimizes the uncertainty. Copyright © 2016 John Wiley & Sons, Ltd.
    Type of Medium: Online Resource
    ISSN: 0170-4214 , 1099-1476
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 1478610-2
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  • 3
    Online Resource
    Online Resource
    Wiley ; 2018
    In:  Mathematical Methods in the Applied Sciences Vol. 41, No. 11 ( 2018-07-30), p. 4003-4020
    In: Mathematical Methods in the Applied Sciences, Wiley, Vol. 41, No. 11 ( 2018-07-30), p. 4003-4020
    Abstract: One of the fundamental problems in communications is finding the energy distribution of signals in time and frequency domains. It should therefore be of great interest to find the quaternionic signal whose time‐frequency energy distribution is most concentrated in a given time‐frequency domain. The present paper finds a new kind of quaternionic signals whose energy concentration is maximal in both time and frequency under the quaternionic Fourier transform. The new signals are a generalization of the classical prolate spheroidal wave functions to a quaternionic space, which are called the quaternionic prolate spheroidal wave functions. The purpose of this paper is to present the definition and fundamental properties of the quaternionic prolate spheroidal wave functions and to show that they can reach the extreme case within the energy concentration problem both from the theoretical and experimental description. The superiority of the proposed results can be widely applied to the application of 4D valued problems. In particular, these functions are shown as an effective method for bandlimited quaternionic signals relying on the extrapolation problem. Copyright © 2017 John Wiley & Sons, Ltd.
    Type of Medium: Online Resource
    ISSN: 0170-4214 , 1099-1476
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 1478610-2
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  • 4
    Online Resource
    Online Resource
    Informa UK Limited ; 2015
    In:  Journal of Modern Optics Vol. 62, No. 1 ( 2015-01-02), p. 46-55
    In: Journal of Modern Optics, Informa UK Limited, Vol. 62, No. 1 ( 2015-01-02), p. 46-55
    Type of Medium: Online Resource
    ISSN: 0950-0340 , 1362-3044
    Language: English
    Publisher: Informa UK Limited
    Publication Date: 2015
    detail.hit.zdb_id: 2017832-3
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  • 5
    Online Resource
    Online Resource
    Wiley ; 2016
    In:  Mathematical Methods in the Applied Sciences Vol. 39, No. 14 ( 2016-09-30), p. 3961-3978
    In: Mathematical Methods in the Applied Sciences, Wiley, Vol. 39, No. 14 ( 2016-09-30), p. 3961-3978
    Abstract: Over the last years, considerable attention has been paid to the role of the prolate spheroidal wave functions (PSWFs) introduced in the early sixties by D. Slepian and H.O. Pollak to many practical signal and image processing problems. The PSWFs and their applications to wave phenomena modeling, fluid dynamics, and filter design played a key role in this development. In this paper, we introduce the prolate spheroidal quaternion wave functions (PSQWFs), which refine and extend the PSWFs. The PSQWFs are ideally suited to study certain questions regarding the relationship between quaternionic functions and their Fourier transforms. We show that the PSQWFs are orthogonal and complete over two different intervals: the space of square integrable functions over a finite interval and the three‐dimensional Paley–Wiener space of bandlimited functions. No other system of classical generalized orthogonal functions is known to possess this unique property. We illustrate how to apply the PSQWFs for the quaternionic Fourier transform to analyze Slepian's energy concentration problem. We address all of the aforementioned and explore some basic facts of the arising quaternionic function theory. We conclude the paper by computing the PSQWFs restricted in frequency to the unit sphere. The representation of these functions in terms of generalized spherical harmonics is explicitly given, from which several fundamental properties can be derived. As an application, we provide the reader with plot simulations that demonstrate the effectiveness of our approach. Copyright © 2016 John Wiley & Sons, Ltd.
    Type of Medium: Online Resource
    ISSN: 0170-4214 , 1099-1476
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 1478610-2
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