13,942 research outputs found

    A new class of two-channel biorthogonal filter banks and wavelet bases

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    We propose a novel framework for a new class of two-channel biorthogonal filter banks. The framework covers two useful subclasses: i) causal stable IIR filter banks. ii) linear phase FIR filter banks. There exists a very efficient structurally perfect reconstruction implementation for such a class. Filter banks of high frequency selectivity can be achieved by using the proposed framework with low complexity. The properties of such a class are discussed in detail. The design of the analysis/synthesis systems reduces to the design of a single transfer function. Very simple design methods are given both for FIR and IIR cases. Zeros of arbitrary multiplicity at aliasing frequency can be easily imposed, for the purpose of generating wavelets with regularity property. In the IIR case, two new classes of IIR maximally flat filters different from Butterworth filters are introduced. The filter coefficients are given in closed form. The wavelet bases corresponding to the biorthogonal systems are generated. the authors also provide a novel mapping of the proposed 1-D framework into 2-D. The mapping preserves the following: i) perfect reconstruction; ii) stability in the IIR case; iii) linear phase in the FIR case; iv) zeros at aliasing frequency; v) frequency characteristic of the filters

    Introgressive Hybridization and the Evolution of Lake-Adapted Catostomid Fishes.

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    Hybridization has been identified as a significant factor in the evolution of plants as groups of interbreeding species retain their phenotypic integrity despite gene exchange among forms. Recent studies have identified similar interactions in animals; however, the role of hybridization in the evolution of animals has been contested. Here we examine patterns of gene flow among four species of catostomid fishes from the Klamath and Rogue rivers using molecular and morphological traits. Catostomus rimiculus from the Rogue and Klamath basins represent a monophyletic group for nuclear and morphological traits; however, the Klamath form shares mtDNA lineages with other Klamath Basin species (C. snyderi, Chasmistes brevirostris, Deltistes luxatus). Within other Klamath Basin taxa, D. luxatus was largely fixed for alternate nuclear alleles relative to C. rimiculus, while Ch. brevirostris and C. snyderi exhibited a mixture of these alleles. Deltistes luxatus was the only Klamath Basin species that exhibited consistent covariation of nuclear and mitochondrial traits and was the primary source of mismatched mtDNA in Ch. brevirostris and C. snyderi, suggesting asymmetrical introgression into the latter species. In Upper Klamath Lake, D. luxatus spawning was more likely to overlap spatially and temporally with C. snyderi and Ch. brevirostris than either of those two with each other. The latter two species could not be distinguished with any molecular markers but were morphologically diagnosable in Upper Klamath Lake, where they were largely spatially and temporally segregated during spawning. We examine parallel evolution and syngameon hypotheses and conclude that observed patterns are most easily explained by introgressive hybridization among Klamath Basin catostomids

    Pulsed laser deposition for growth of high quality epitaxial garnet films for low threshold waveguide lasers

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    Pulsed laser deposition (PLD) is a mature technique capable of producing extremely high quality epitaxial single crystalline films. We have grown Nd:doped garnet films of GGG (Gd The talk will summarise our progress using conventional (single beam) PLD in thin-film and waveguide growth, using both nanosecond and femtosecond lasers, and also introduce our new directions in tri-beam PLD (three targets, three lasers) for growth of some interesting, complex and perhaps impossible structures, such as Gaussian doping, internal voids and even helically doped structures

    Systems, interactions and macrotheory

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    A significant proportion of early HCI research was guided by one very clear vision: that the existing theory base in psychology and cognitive science could be developed to yield engineering tools for use in the interdisciplinary context of HCI design. While interface technologies and heuristic methods for behavioral evaluation have rapidly advanced in both capability and breadth of application, progress toward deeper theory has been modest, and some now believe it to be unnecessary. A case is presented for developing new forms of theory, based around generic “systems of interactors.” An overlapping, layered structure of macro- and microtheories could then serve an explanatory role, and could also bind together contributions from the different disciplines. Novel routes to formalizing and applying such theories provide a host of interesting and tractable problems for future basic research in HCI

    The Adelaide VHF radar: Capabilities and future plans

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    The VHF radar at Buckland Park, South Australia commenced operation in January, 1984. The radar is located adjacent to the 2-MHz ionospheric radar. The routine method for measuring horizontal wind velocity is the space antenna technique (SA) while the Doppler technique is used to measure vertical velocities. It is possible to swing the transmitting beam in the east-west plane, allowing Doppler measurements of the EW wind component

    Species Abundance Patterns in Complex Evolutionary Dynamics

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    An analytic theory of species abundance patterns (SAPs) in biological networks is presented. The theory is based on multispecies replicator dynamics equivalent to the Lotka-Volterra equation, with diverse interspecies interactions. Various SAPs observed in nature are derived from a single parameter. The abundance distribution is formed like a widely observed left-skewed lognormal distribution. As the model has a general form, the result can be applied to similar patterns in other complex biological networks, e.g. gene expression.Comment: 4 pages, 3 figures. Physical Review Letters, in pres

    Rosette‐like structures in the spectrum of spitzoid tumors

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    Background Spitz nevi demonstrate a diverse spectrum of morphologies. Recently, there have been two reported examples of Spitz nevi with rosette‐like structures similar to Homer‐Wright rosettes. Rosettes have also been described in melanomas and in a proliferative nodule arising in a congenital nevus. Methods A retrospective review of 104 cases of Spitz nevi and variants (n = 51), pigmented spindle cell nevi (n = 26), combined melanocytic nevi with features of Spitz (n = 8), atypical Spitz tumor ( AST , n = 9), and spitzoid melanoma (n = 10). Results Rosette‐like structures were present in 3 of the 104 cases (2.9%), including a compound Spitz nevus, a desmoplastic Spitz nevus, and an AST . All three cases demonstrated several foci of small nests of epithelioid cells with peripherally palisaded nuclei arranged around a central area of fibrillar eosinophilic cytoplasm. Immunohistochemical staining of the three spitzoid lesions demonstrated that the rosette‐like structures express S100 protein, Melan‐A, and neuron specific enolase ( NSE ) and lacked expression of neurofilament, glial fibrillary acidic protein and synaptophysin. Conclusions While uncommon, rosette‐like structures can occur as a focal feature in Spitz nevi and AST . Rosette‐like structures may represent a normal morphologic finding in Spitz nevi, and awareness of them may prevent misdiagnosis as a neural tumor or melanoma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99651/1/cup12192.pd
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