3,454 research outputs found

    Lema\^{i}tre's Hubble relationship

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    Edwin Hubble is often credited with discovering the expanding Universe based on spectra taken by him. This statement is incorrect and we feel that it is the responsibility of those who are aware of the historical facts to set the record straight.Comment: 3 page letter, more accurately reflects letter published in Physics Today, August 201

    Viewpoints: A high-performance high-dimensional exploratory data analysis tool

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    Scientific data sets continue to increase in both size and complexity. In the past, dedicated graphics systems at supercomputing centers were required to visualize large data sets, but as the price of commodity graphics hardware has dropped and its capability has increased, it is now possible, in principle, to view large complex data sets on a single workstation. To do this in practice, an investigator will need software that is written to take advantage of the relevant graphics hardware. The Viewpoints visualization package described herein is an example of such software. Viewpoints is an interactive tool for exploratory visual analysis of large, high-dimensional (multivariate) data. It leverages the capabilities of modern graphics boards (GPUs) to run on a single workstation or laptop. Viewpoints is minimalist: it attempts to do a small set of useful things very well (or at least very quickly) in comparison with similar packages today. Its basic feature set includes linked scatter plots with brushing, dynamic histograms, normalization and outlier detection/removal. Viewpoints was originally designed for astrophysicists, but it has since been used in a variety of fields that range from astronomy, quantum chemistry, fluid dynamics, machine learning, bioinformatics, and finance to information technology server log mining. In this article, we describe the Viewpoints package and show examples of its usage.Comment: 18 pages, 3 figures, PASP in press, this version corresponds more closely to that to be publishe

    Development and Application of a Thermistor Current Meter

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    This report provides details for the construction of a hot-bead thermistor current meter which is capable of measuring water velocities on a millimeter spatial scale and for the construction of a compact and accurate calibration system. Hot-bead thermistor current meters can be built with response times of 200 ms capable of measuring velocities between 0.1 and 80 cm s-1. The construction of a sturdy probe for application in lotic systems such as high gradient Hawaiian streams was achieved by the use of heavy-duty acrylic tubing, small stainless steel gas-chromatography tubing, and flexible Tygon spaghetti tubing. An acrylic handle anchors the electrical cable at one end and the thermistors at the other. The following criteria were central to the development of the calibration system a accurate calibration b compact unit for storage and use in limited laboratory space c leak-proof system d inexpensive design requirement for readily available materials and e construction requirements for the use of hand tools. The thermistor current meter has been used to measure velocities in the water column and around various substrate features in riverine habitats. More detailed spatial velocity measurements were made in streams by dividing a habitat into small grid cells. With fine spatial scales e.g., grid sizes of 200 to 300 cm 2 or less and repetitive sampling under varying water flow conditions, insights into relationships between various spatial and temporal characteristics of microhabitat velocities were made. The current meter has been used to determine ambient velocity profiles around a variety of benthic stream
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