2,740 research outputs found

    Fast Algorithms and Efficient Statistics: N-point Correlation Functions

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    We present here a new algorithm for the fast computation of N-point correlation functions in large astronomical data sets. The algorithm is based on kdtrees which are decorated with cached sufficient statistics thus allowing for orders of magnitude speed-ups over the naive non-tree-based implementation of correlation functions. We further discuss the use of controlled approximations within the computation which allows for further acceleration. In summary, our algorithm now makes it possible to compute exact, all-pairs, measurements of the 2, 3 and 4-point correlation functions for cosmological data sets like the Sloan Digital Sky Survey (SDSS; York et al. 2000) and the next generation of Cosmic Microwave Background experiments (see Szapudi et al. 2000).Comment: To appear in Proceedings of MPA/MPE/ESO Conference "Mining the Sky", July 31 - August 4, 2000, Garching, German

    Modifications to the Aesop's Fable paradigm change New Caledonian crow performances

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    While humans are able to understand much about causality, it is unclear to what extent non-human animals can do the same. The Aesop's Fable paradigm requires an animal to drop stones into a water-filled tube to bring a floating food reward within reach. Rook, Eurasian jay, and New Caledonian crow performances are similar to those of children under seven years of age when solving this task. However, we know very little about the cognition underpinning these birds' performances. Here, we address several limitations of previous Aesop's Fable studies to gain insight into the causal cognition of New Caledonian crows. Our results provide the first evidence that any non-human animal can solve the U-tube task and can discriminate between water-filled tubes of different volumes. However, our results do not provide support for the hypothesis that these crows can infer the presence of a hidden causal mechanism. They also call into question previous object-discrimination performances. The methodologies outlined here should allow for more powerful comparisons between humans and other animal species and thus help us to determine which aspects of causal cognition are distinct to humans.Publisher PDFPeer reviewe

    Microfluidic Chip for High Efficiency Microinjection of Caenorhabditis elegans

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    The terrestrial nematode, Caenorhabditis elegans, is an invaluable model organism for the study of molecular and cellular processes due to their small size, rapid generation time, easy cultivation, and invariant cell number. Additionally, 40% of genes known to be associated with human disease have clear orthologs in the C. elegans genome. In C. elegans genetics research, microinjection of genetic material into the worms is critical. Although an established technique, manual microinjection is tedious, low-throughput, and requires an expert researcher. This thesis details a novel microfluidic device designed to perform high-throughput microinjection. This two-layer, PDMS-based chip integrates microfluidic elements to control worm sorting, reduction of immobilization time and stress, and novel on-chip microinjection using only a positive pressure source. Our project aim is to increase microinjection efficiency, consistency, and accessibility to researchers of all experience levels in order to advance genetics research and genetic engineering technology in C. elegans. Preliminary results are promising, as our on-chip microinjection device has been able to successfully inject dye into C. elegans animals
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