10,842 research outputs found
The Desktop Muon Detector: A simple, physics-motivated machine- and electronics-shop project for university students
This paper describes an undergraduate-level physics project that incorporates
various aspects of machine- and electronics-shop technical development. The
desktop muon detector is a self-contained apparatus that employs plastic
scintillator as a detection medium and a silicon photomultiplier for light
collection. These detectors can be used in conjunction with the provided
software to make interesting physics measurements. The total cost of each
counter is approximately $100.Comment: 29 pages, 14 figure
A Measurement of the Absorption of Liquid Argon Scintillation Light by Dissolved Nitrogen at the Part-Per-Million Level
We report on a measurement of the absorption length of scintillation light in
liquid argon due to dissolved nitrogen at the part-per-million (ppm) level. We
inject controlled quantities of nitrogen into a high purity volume of liquid
argon and monitor the light yield from an alpha source. The source is placed at
different distances from a cryogenic photomultiplier tube assembly. By
comparing the light yield from each position we extract the absorption cross
section of nitrogen. We find that nitrogen absorbs argon scintillation light
with strength of ,
corresponding to an absorption cross section of . We obtain the relationship
between absorption length and nitrogen concentration over the 0 to 50 ppm range
and discuss the implications for the design and data analysis of future large
liquid argon time projection chamber (LArTPC) detectors. Our results indicate
that for a current-generation LArTPC, where a concentration of 2 parts per
million of nitrogen is expected, the attenuation length due to nitrogen will be
meters.Comment: v2: Correct mistake in molecular absorption cross section
calculation, and a minor typo in fig
Systematic study of Pt-Ru/C catalysts prepared by chemical deposition for direct methanol fuel cells
In this research, the activity and stability for methanol electro-oxidation on Pt-Ru/C catalysts was increased by optimising the catalyst preparation method. The Pt-Ru/C catalysts were synthesised using Pt(acac)2 and Ru(acac)3 precursors for chemical deposition of the metals. Performance of the catalyst was examined by cyclic voltammetry and chronoamperometry in a methanol-containing electrolyte. TEM, EDS, X-ray photoelectron spectroscopy and XRD were used to physically characterise the catalysts. The parameters investigated were precursor decomposition phase, synthesis temperature and Pt/Ru ratio. Precursor deposition from the liquid phase was more active for methanol electro-oxidation, predominantly due to particle size and degree of alloying achieved during this precursor decomposition phase. Synthesis temperature affected the particle size, active surface area, ruthenium oxidation state and degree of alloying which in turn affected catalyst stability and activity for methanol electro-oxidation. The Pt/Ru ratio greatly affects the performance of the catalyst. The catalyst with the highest activity for methanol electro-oxidation was the catalyst synthesised at 350 °C with a Pt/Ru ratio of 50:50
Mistaking the Map for the Territory: What Society Does With Medicine Comment on "Medicalisation and Overdiagnosis: What Society Does to Medicine"
Bulk de novo mitogenome assembly from pooled total DNA elucidates the phylogeny of weevils (Coleoptera: Curculionoidea)
Complete mitochondrial genomes have been shown to be reliable markers for phylogeny reconstruction among diverse animal groups. However, the relative difficulty and high cost associated with obtaining de novo full mitogenomes have frequently led to conspicuously low taxon sampling in ensuing studies. Here, we report the successful use of an economical and accessible method for assembling complete or near-complete mitogenomes through shot-gun next-generation sequencing of a single library made from pooled total DNA extracts of numerous target species. To avoid the use of separate indexed libraries for each specimen, and an associated increase in cost, we incorporate standard polymerase chain reaction-based “bait” sequences to identify the assembled mitogenomes. The method was applied to study the higher level phylogenetic relationships in the weevils (Coleoptera: Curculionoidea), producing 92 newly assembled mitogenomes obtained in a single Illumina MiSeq run. The analysis supported a separate origin of wood-boring behavior by the subfamilies Scolytinae, Platypodinae, and Cossoninae. This finding contradicts morphological hypotheses proposing a close relationship between the first two of these but is congruent with previous molecular studies, reinforcing the utility of mitogenomes in phylogeny reconstruction. Our methodology provides a technically simple procedure for generating densely sampled trees from whole mitogenomes and is widely applicable to groups of animals for which bait sequences are the only required prior genome knowledge
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