8,137 research outputs found
Carbon monoxide in the solar atmosphere I. Numerical method and two-dimensional models
The radiation hydrodynamic code CO5BOLD has been supplemented with the
time-dependent treatment of chemical reaction networks. Advection of particle
densities due to the hydrodynamic flow field is also included. The radiative
transfer is treated frequency-independently, i.e. grey, so far. The upgraded
code has been applied to two-dimensional simulations of carbon monoxide (CO) in
the non-magnetic solar photosphere and low chromosphere. For this purpose a
reaction network has been constructed, taking into account the reactions which
are most important for the formation and dissociation of CO under the physical
conditions of the solar atmosphere. The network has been strongly reduced to 27
reactions, involving the chemical species H, H2, C, O, CO, CH, OH, and a
representative metal. The resulting CO number density is highest in the cool
regions of the reversed granulation pattern at mid-photospheric heights and
decreases strongly above. There, the CO abundance stays close to a value of 8.3
on the usual logarithmic abundance scale with [H]=12 but is reduced in hot
shock waves which are a ubiquitous phenomenon of the model atmosphere. For
comparison, the corresponding equilibrium densities have been calculated, based
on the reaction network but also under assumption of instantaneous chemical
equilibrium by applying the Rybicki & Hummer (RH) code by Uitenbroek (2001).
Owing to the short chemical timescales, the assumption holds for a large
fraction of the atmosphere, in particular the photosphere. In contrast, the CO
number density deviates strongly from the corresponding equilibrium value in
the vicinity of chromospheric shock waves. Simulations with altered reaction
network clearly show that the formation channel via hydroxide (OH) is the most
important one under the conditions of the solar atmosphere.Comment: 15 pages, 6 figures, final version will contain online materia
Shooting Down the More Guns, Less Crime Hypothesis
John Lott and David Mustard have used regression analysis to argue forcefully that 'shall-issue' laws (which give citizens an unimpeded right to secure permits for concealed weapons) reduce violent crime. While certain facially plausible statistical models appear to generate this conclusion, more refined analyses of more recent state and county data undermine the more guns, less crime hypothesis. The most robust finding on the state data is that certain property crimes rise with passage of shall- issue laws, although the absence of any clear theory as to why this would be the case tends to undercut any strong conclusions. Estimating more statistically preferred disaggregated models on more complete county data, we show that in most states shall- issue laws have been associated with more crime and that the apparent stimulus to crime tends to be especially strong for those states that adopted in the last decade. While there are substantial concerns about model reliability and robustness, we present estimates based on disaggregated county data models that on net the passage of the law in 24 jurisdictions has increased the annual cost of crime slightly -- somewhere on the order of half a billion dollars. We also provide an illustration of how our jurisdiction-specific regression model has the capacity to generate more nuanced assessments concerning which states might profit from or be harmed by a particular legal intervention.
There is little basis for viewing migrants in the Mediterranean as a threat to the ‘indigenous’ population of Europe
Figures released in June by the International Organisation for Migration estimate that over 100,000 migrants have made the journey across the Mediterranean since the start of 2015. Christopher J. Ayres argues that while some actors have sought to portray this situation as a case of ‘indigenous Europeans’ coming under threat from large-scale migration, there is little to justify this narrative in practice. He writes that Europeans should do more to appreciate the human dimension to the crisis, particularly given their own ancestors once pursued the same route from Africa
The EU’s law on conflict minerals could well end up hurting the people it is intended to help
A proposed law to tighten regulations on the trade of so called ‘conflict minerals’ was backed in the European Parliament on 20 May. Christopher J. Ayres writes that while the legislation may be well-intentioned, the net effect could be to damage the interests of some of the people it is aimed at helping
Measuring the muon's anomalous magnetic moment to 0.14 ppm
The anomalous magnetic moment (g-2) of the muon was measured with a precision
of 0.54 ppm in Experiment 821 at Brookhaven National Laboratory. A difference
of 3.2 standard deviations between this experimental value and the prediction
of the Standard Model has persisted since 2004; in spite of considerable
experimental and theoretical effort, there is no consistent explanation for
this difference. This comparison hints at physics beyond the Standard Model,
but it also imposes strong constraints on those possibilities, which include
supersymmetry and extra dimensions. The collaboration is preparing to relocate
the experiment to Fermilab to continue towards a proposed precision of 0.14
ppm. This will require 20 times more recorded decays than in the previous
measurement, with corresponding improvements in the systematic uncertainties.
We describe the theoretical developments and the experimental upgrades that
provide a compelling motivation for the new measurement.Comment: 5 pages, 1 figure, presented at International Nuclear Physics
Conference 2010 (INPC 2010
It is time for the European Union to redefine what it means to be a ‘refugee’
Christopher J. Ayres writes that the migration crisis has prompted discussions over whether individuals seeking to enter the EU should be classified as ‘refugees’ or simply ‘migrants’. He argues that in light of these debates it is time for the EU to drop the requirement for an individual to have a ‘well-founded fear of persecution’ to be labelled a refugee, noting that this definition is 65 years old, antiquated, and was articulated by the United Nations Refugee Agency before the EU existed
On a new species of Squirrel Monkey, Genus Saimiri, from Brazilian Amazônia (Primates, Cebidae)
51 Pegasi - a planet-bearing Maunder minimum candidate
We observed 51 Peg, the first detected planet-bearing star, in a 55 ks
XMM-Newton pointing and in 5 ks pointings each with Chandra HRC-I and ACIS-S.
The star has a very low count rate in the XMM observation, but is clearly
visible in the Chandra images due to the detectors' different sensitivity at
low X-ray energies. This allows a temperature estimate for 51 Peg's corona of
T<1MK; the detected ACIS-S photons can be plausibly explained by emission lines
of a very cool plasma near 200eV. The constantly low X-ray surface flux and the
flat-activity profile seen in optical CaII data suggest that 51 Peg is a
Maunder minimum star; an activity enhancement due to a Hot Jupiter, as proposed
by recent studies, seems to be absent. The star's X-ray fluxes in different
instruments are consistent with the exception of the HRC Imager, which might
have a larger effective area below 200eV than given in the calibration.Comment: accepted by A&
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