Leave blank (2009/2010)

Leave blank (2009/2010

Erratum: The chemistry of transient molecular cloud cores

We assume that some, but not all, of the structure observed in molecular clouds is associated with transient features which are not bound by self-gravity. We investigate the chemistry of a transient density fluctuation, with properties similar to those of a core within a molecular cloud. We run a multipoint chemical code through a core's condensation from a diffuse medium to its eventual dispersion, over a period of ∼1 Myr. The dynamical description adopted for our study is based on an understanding of a particular mechanism, involving slow-mode wave excitation, for transient structure formation which so far has been studied in detail only with plane-parallel models in which self-gravity has not been included. We find a significant enhancement of the chemical composition of the core material on its return to diffuse conditions, whilst the expansion of the core as it disperses moves this material out to large distances from the core centre. This process transports molecular species formed in the high-density regions out into the diffuse medium. Chemical enrichment of the cloud as a whole also occurs, as other cores of various sizes, life-spans and separations evolve throughout. Enrichment is strongly affected by freeze-out on to dust grains, which takes place in high-density, high visual extinction regions. As the core disperses after reaching its peak density and the visual extinction drops below a critical value, grain mantles are evaporated back into the gas phase, initiating more chemistry. The influence of the sizes, masses and cycle periods of cores will be large both for the level of chemical enrichment of a dark cloud and ultimately for the low-mass star formation rate. The cores in which stars form are almost certainly bound by their self-gravity and are not transient in the sense that the cores on which most of our study is focused are transient. Obviously, enrichment of the chemistry of low-density material will not take place if self-gravity prevents the re-expansion of a core. We also consider the case of a self-gravitating core, by holding its peak density conditions for a further 0.4 Myr. We find that the differences near the peak densities between transient and gravitationally bound cores are generally small, and the resultant column densities for objects near the peak densities do not provide definitive criteria for discriminating between transient and bound cores. However, increases in fractional abundances due to reinjection of mantle-borne species may provide a criterion for detection of a non-bound core

Digital unreason: Jordan Wolfson’s ‘Evil Jew’

This article privileges an analysis of the artwork Animation, masks (2011) by the Jewish-American contemporary artist Jordan Wolfson. This animated film is over 10 minutes long and features only one character, based on a collection of references Wolfson found under the Google search terms ‘evil Jew’ and ‘Shylock’. One of the key references for this ‘evil Jew’ stereotype, ‘Le Happy Merchant’, is a popular meme circulating on the 4chan media network and has become a mascot of the so called ‘alt-right’ – a loose network of racists and anti-Semites that became militant supporters of the 2016 Donald Trump presidential campaign and presidency. In Wolfson’s version of the meme, professional American animators were hired to give this stereotype the illusion of life. The result is a fascist stereotype restaged as an endearing Dreamworks character, unpredictable and incoherent, lurching between violent and placatory gestures. Rather than attempt a close analysis, this article argues that Wolfson’s social link to stereotype, conspiracy theory and fascist rebellion requires greater interrogation in light of the Donald Trump campaign, Brexit and the Le Pen candidacy. In all these campaigns, a vitalistic critique of metropolitan ‘elites’ or ‘globalists’ became the anti-establishment pretext for verbal assaults on immigrants, people of colour and Muslims. Alberto Toscano and Jeff Kinkle in Cartographies of the Absolute (2015) connect a popular upsurge in conspiratorial thinking to an absented critique of capitalism. They claim that if the abstract and impersonal character of capitalism is never awarded popular interrogation, conspiracy theory is an easy substitute, leaving the door open to anti-Semitic and racist projections. In turn, they call for art and popular culture that creates a systematic link to the bewildering movements of late capitalism, rather than fall into conspiratorial thinking. In this article, the author suggests that Wolfson in Animation, masks is using animation and caricature to bear witness to the circulation of anti-Semitic conspiracy and the narcissistic social networks that have been emboldened by the rise of the international far Right. However, by ambivalently playing around with stereotype, Wolfson also risks falling into complicity with forces of unreason that are indifferent to ironic treatment. This article discusses the critical contributions and limitations of this artwork, leading to an evaluation of Wolfson’s conceptual performance as a whole

Clouds, Clumps, Cores & Comets - a Cosmic Chemical Connection?

We discuss the connection between the chemistry of dense interstellar clouds and those characteristics of cometary matter that could be remnants of it. The chemical evolution observed to occur in molecular clouds is summarized and a model for dense core collapse that can plausibly account for the isotopic fractionation of hydrogen, nitrogen, oxygen and carbon measured in primitive solar system materials is presented.Comment: to be published in Advances in Geoscience

A hybrid moment equation approach to gas-grain chemical modeling

[Context] The stochasticity of grain chemistry requires special care in modeling. Previously methods based on the modified rate equation, the master equation, the moment equation, and Monte Carlo simulations have been used. [Aims] We attempt to develop a systematic and efficient way to model the gas-grain chemistry with a large reaction network as accurately as possible. [Methods] We present a hybrid moment equation approach which is a general and automatic method where the generating function is used to generate the moment equations. For large reaction networks, the moment equation is cut off at the second order, and a switch scheme is used when the average population of certain species reaches 1. For small networks, the third order moments can also be utilized to achieve a higher accuracy. [Results] For physical conditions in which the surface reactions are important, our method provides a major improvement over the rate equation approach, when benchmarked against the rigorous Monte Carlo results. For either very low or very high temperatures, or large grain radii, results from the rate equation are similar to those from our new approach. Our method is faster than the Monte Carlo approach, but slower than the rate equation approach. [Conclusions] The hybrid moment equation approach with a cutoff and switch scheme is applicable to large gas-grain networks, and is accurate enough to be used for astrochemistry studies. The layered structure of the grain mantle could also be incorporated into this approach, although a full implementation of the grain micro-physics appears to be difficult.Comment: 11 pages, 4 figures. Accepted for publication in Astronomy and Astrophysic

On the master equation approach to diffusive grain-surface chemistry: the H, O, CO system

We have used the master equation approach to study a moderately complex network of diffusive reactions occurring on the surfaces of interstellar dust particles. This network is meant to apply to dense clouds in which a large portion of the gas-phase carbon has already been converted to carbon monoxide. Hydrogen atoms, oxygen atoms, and CO molecules are allowed to accrete onto dust particles and their chemistry is followed. The stable molecules produced are oxygen, hydrogen, water, carbon dioxide (CO2), formaldehyde (H2CO), and methanol (CH3OH). The surface abundances calculated via the master equation approach are in good agreement with those obtained via a Monte Carlo method but can differ considerably from those obtained with standard rate equations.Comment: 13 pages, 5 figure

Recognizing aboriginal oral tradition through blended learning: a success story

The Aboriginal Health and Community Administration Program (AHCAP) is a certificate program developed through the partnership of the Institute for Aboriginal Health and Continuing Studies at the University of British Columbia. This paper examines factors in the program’s blended design and development which have contributed to the exceptionally high completion rate and the strongly positive responses and outcomes for widely diverse learner cohorts. Factors which appear to contribute to the program success include: 1) a holistic approach compatible with traditional Aboriginal oral traditions of teaching and learning; 2) a university partnership that taps into unique networks and capacities; 3) incorporating the 4 R’s of Aboriginal education: relevance, reciprocity, respect and responsibility generated throughout the learning and teaching, both online and face-to-face; and 4) making the program accessible to geographically and technologically diverse communities of learners.\u

Chemical and Hydrodynamical Models of Cometary Comae

Multi-fluid modelling of the outflowing gases which sublimate from cometary nuclei as they approach the Sun is necessary for understanding the important physical and chemical processes occurring in this complex plasma. Coma chemistry models can be employed to interpret observational data and to ultimately determine chemical composition and structure of the nuclear ices and dust. We describe a combined chemical and hydrodynamical model [1] in which differential equations for the chemical abundances and the energy balance are solved as a function of distance from the cometary nucleus. The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of 1P/Halley. The anions O(-), OH(-), C(-), CH(-) and CN(-) have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu [2]. Organic molecular anions such as C4H(-) and C6H(-) are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas-phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been fully explored. We present details of new models for the chemistry of cometary comae that include atomic and molecular anions and calculate the impact of these anions on the coma physics and chemistry af the coma