1,972 research outputs found
Geant4 Applications for Modeling Molecular Transport in Complex Vacuum Geometries
We discuss a novel use of the Geant4 simulation toolkit to model molecular
transport in a vacuum environment, in the molecular flow regime. The Geant4
toolkit was originally developed by the high energy physics community to
simulate the interactions of elementary particles within complex detector
systems. Here its capabilities are utilized to model molecular vacuum transport
in geometries where other techniques are impractical. The techniques are
verified with an application representing a simple vacuum geometry that has
been studied previously both analytically and by basic Monte Carlo simulation.
We discuss the use of an application with a very complicated geometry, that of
the Large Synoptic Survey Telescope camera cryostat, to determine probabilities
of transport of contaminant molecules to optical surfaces where control of
contamination is crucial.Comment: 7 pages, 4 figures, 2 tables, to appear in IJMSSC, updated to
accepted versio
Why does low intensity, long-day lighting promote growth in Petunia, Impatiens, and tomato?
Numerous reports demonstrate that low intensity, long-day (LD) lighting treatments can promote growth. However,
there are conflicting suggestions as to the mechanisms involved. This study examines the responses of Petunia,
Impatiens, and tomato to LD lighting treatments and concludes that no single mechanism can explain the growth
promotion observed in each case. Petunia showed the most dramatic response to photoperiod; up to a doubling in dry
weight (DW) as a result of increasing daylength from 8 h d–1 to 16 h d–1.This could be explained by an increase in specific leaf area (SLA) comparable to that seen with shading. At low photosynthetic photon flux densities (PPFD), the increased leaf area more than compensated for any loss in photosynthetic capacity per unit leaf area. In Petunia, the response may, in part, have also been due to changes in growth habit. Impatiens and tomato showed less dramatic increases in DW as a result of LD lighting, but no consistent effects on SLA or growth habit were observed. In tomato, increased growth was accompanied by increased chlorophyll content, but this had no significant effect on
photosynthesis. In both species, increased growth may have been due to a direct effect of LD lighting on photosynthesis.
This is contrary to the generally held view that light of approx. 3 – 4 μmol m–2 s–1 is unlikely to have any significant impact on net photosynthesis. Nevertheless, we show that the relationship between PPFD and net photosynthesis is non-linear at low light levels, and therefore low intensity LD lighting can offset respiration very efficiently.
Furthermore, a small increase in photosynthesis will have a greater impact when ambient light levels are low
Dismissive incomprehension: a use of purported ignorance to undermine others
This paper analyses a particular social phenomenon whereby a speaker purports ignorance of the meaning of another speaker’s speech in order to undermine that other speaker: dismissive incomprehension. It develops a speech act theory of the phenomenon, and develops its distinctive, and sometimes problematic perlocutionary character. After taking a look at some of the issues surrounding the phenomenon, the paper compares it to more fully studied features of our social lives, including epistemic injustice and gaslighting. It ends with some thoughts on counteracting the problematic cases of dismissive incomprehension
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