University of Guelph

About: University of Guelph is a education organization based out in Guelph, Ontario, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 26542 authors who have published 50553 publications receiving 1715255 citations. The organization is also known as: U of G & Guelph University.

Phase retrieval, error reduction algorithm, and Fienup variants: a view from convex optimization.

Abstract: The phase retrieval problem is of paramount importance in various areas of applied physics and engineering. The state of the art for solving this problem in two dimensions relies heavily on the pioneering work of Gerchberg, Saxton, and Fienup. Despite the widespread use of the algorithms proposed by these three researchers, current mathematical theory cannot explain their remarkable success. Nevertheless, great insight can be gained into the behavior, the shortcomings, and the performance of these algorithms from their possible counterparts in convex optimization theory. An important step in this direction was made two decades ago when the error reduction algorithm was identified as a nonconvex alternating projection algorithm. Our purpose is to formulate the phase retrieval problem with mathematical care and to establish new connections between well-established numerical phase retrieval schemes and classical convex optimization methods. Specifically, it is shown that Fienup’s basic input–output algorithm corresponds to Dykstra’s algorithm and that Fienup’s hybrid input–output algorithm can be viewed as an instance of the Douglas–Rachford algorithm. We provide a theoretical framework to better understand and, potentially, to improve existing phase recovery algorithms.

Canal preparation using only one Ni-Ti rotary instrument: preliminary observations

Abstract: Yared G. Canal preparation using only one Ni-Ti rotary instrument: preliminary observations. International Endodontic Journal. Aim To describe a novel canal preparation technique using only one Ni-Ti rotary instrument. Summary In this novel technique, the canal is negotiated to the working length with a size 08 hand file. Then, the canal preparation is completed with an F2 ProTaper instrument used in a reciprocating movement. In larger canals, the use of additional hand files may be required to complete the apical enlargement. Key learning points • A novel canal preparation technique is introduced using only one Ni-Ti rotary instrument in a reciprocating movement. • The advantages of the technique include a reduced number of instruments, lower cost, a reduced instrument fatigue and the elimination of possible prion cross-contamination associated with the single use of endodontic instruments.

A minimalist barcode can identify a specimen whose DNA is degraded

Abstract: A DNA barcode based on 650 bp of mitochondrial gene cytochrome c oxidase I is proving to be highly functional in species identification for various animal groups. However, DNA degradation complicates the recovery of a full-length barcode from many museum specimens. Here we explore the use of shorter barcode sequences for identification of such specimens. We recovered short sequences — i.e. ∼ 100 bp — with a single PCR pass from more than 90% of the specimens in assemblages of moth and wasp museum specimens from which full barcode recovery was only 50%, and the latter were usually less than 8 years old. Short barcodes were effective in identifying specimens, confirming their utility in circumstances where full barcodes are too expensive to obtain and the identification comparisons are within a confined taxonomic group.

Productivity Is a Poor Predictor of Plant Species Richness

Abstract: For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters−2) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.