1,721,188 research outputs found
Stable and Robust Sampling Strategies for Compressive Imaging
No full textIn many signal processing applications, one wishes to acquire images that are sparse in transform domains such as spatial finite differences or wavelets using frequency domain samples. For such applications, overwhelming empirical evidence suggests that superior image reconstruction can be obtained through variable density sampling strategies that concentrate on lower frequencies. The wavelet and Fourier transform domains are not incoherent because low-order wavelets and low-order frequencies are correlated, so compressive sensing theory does not immediately imply sampling strategies and reconstruction guarantees. In this paper, we turn to a more refined notion of coherence-the so-called local coherence-measuring for each sensing vector separately how correlated it is to the sparsity basis. For Fourier measurements and Haar wavelet sparsity, the local coherence can be controlled and bounded explicitly, so for matrices comprised of frequencies sampled from a suitable inverse square power-law density, we can prove the restricted isometry property with near-optimal embedding dimensions. Consequently, the variable-density sampling strategy we provide allows for image reconstructions that are stable to sparsity defects and robust to measurement noise. Our results cover both reconstruction by l(1)-minimization and total variation minimization. The local coherence framework developed in this paper should be of independent interest, as it implies that for optimal sparse recovery results, it suffices to have bounded average coherence from sensing basis to sparsity basis-as opposed to bounded maximal coherence-as long as the sampling strategy is adapted accordingly
The use of denaturing gradient gel electrophoresis in examining the species-specific influence of ectomycorrhizal fungi on selective bacteria enrichment in the mycorrhizosphere of Pinius rigida grown in a natural pine barrens habitat
No full textThe study presented here describes the results of denaturing gradient gel electrophoresis (DGGE) used to detect bacterial diversity and selection in the ectomycorrhizasphere of Pinius rigida growing in a natural pine barrens habitat This study was the first to explore such a relationship in an environmental setting. Two study sites were chosen from the pine barrens in southern New Jersey, one from Rutgers Pinelands Field Station and one from Double Trouble State Park. Soils were from similar habitats and were similar in total phosphorous. The two sites were selected based on preliminary information that mercury content was high in the Double Trouble. However, upon further analysis, results showed that mercury was at a non-contaminant level in both sites. DGGE analysis of ectomycorrhiza fungi present on a root tip revealed that there were multiple species occurring where one morphotype was apparent from inspection through a dissecting microscope. DGGE analysis of ectomycorrhiza associated bacteria revealed a highly diverse community with little enrichment. While there was some enrichment noted on the bacterial DGGE profiles, this did not correspond to a species-specific link between ectomycorrhiza fungi and their associated bacteria. It is the conclusion of this study that the natural ectomycorrhizasphere is a highly complex environment, and that this complexity diffuses the influence of any one ectomycorrhizal species on the enrichement on bacteria present in the ectomycorrhizasphere.M.S.Includes bibliographical references (p. 64-66)
Lower bounds for the error decay incurred by coarse quantization schemes
No full textAbstractSeveral analog-to-digital conversion methods for bandlimited signals used in applications, such as ΣΔ quantization schemes, employ coarse quantization coupled with oversampling. The standard mathematical model for the error accrued from such methods measures the performance of a given scheme by the rate at which the associated reconstruction error decays as a function of the oversampling ratio λ. It was recently shown that exponential accuracy of the form O(2−αλ) can be achieved by appropriate one-bit Sigma–Delta modulation schemes. However, the best known achievable rate constants α in this setting differ significantly from the general information theoretic lower bound. In this paper, we provide the first lower bound specific to coarse quantization, thus narrowing the gap between existing upper and lower bounds. In particular, our results imply a quantitative correspondence between the maximal signal amplitude and the best possible error decay rate. Our method draws from the theory of large deviations
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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