Simulating Radiative Magnetohydrodynamical Flows with AstroBEAR: Implementation and Applications of Non-equilibrium Cooling

Radiative cooling plays a crucial role in the dynamics of many astrophysical flows, and is particularly important in the dense shocked gas within Herbig-Haro (HH) objects and stellar jets. Simulating cooling processes accurately is necessary to compare numerical simulations with existing and planned observations of HH objects, such as those from the Hubble Space Telescope and the James Webb Space Telescope. In this paper we discuss a new, non-equilibrium cooling scheme we have implemented into the 3-D magnetohydrodynamic (MHD) code AstroBEAR. The new cooling function includes ionization, recombination, and excitation of all the important atomic species that cool below 10000 K. We tested the routine by comparing its predictions with those from the well-tested 1-D Cox-Raymond shock code (Raymond 1979). The results show thatAstroBEAR accurately tracks the ionization fraction, temperature, and other MHD variables for all low-velocity (.90 km/s) magnetized radiative shock waves. The new routine allows us to predict synthetic emission maps in all the bright forbidden and permitted lines observed in stellar jets, including H{\alpha}, [NII], [OI], and [SII]. We present an example as to how these synthetic maps facilitate a direct comparison with narrowband images of HH objects.Comment: 8 figure

Recherche littéraire / Literary Research

Franca Bellarsi Olga Beloborodova Lidia Morales Benito Jean Bessière Eury Colin Chang Véronique Corinus Santanu Das Subhraleena Deka Elke D'hoker Brahim El Guabli Marlene Hansen Esplin Massimo Fusillo Claudio Gigante Gerald Gillespie Stefan Helgesson Yvon Houssais Višnja Krstić Marie Laureillard Marc MaufortYana Meerzon Kai Mikkonen Florian Mussgnug Anzazi Joan Mwangovya Birgit Neumann Wen-chin Ouyang Daniel-Henri Pageaux Yolaine Parisot Danielle Perrot-Corpet Yannick Preumont E.V.Ramakrishnan Hubert Roland Karen-Margrethe Simonsen Vijaya Singh Daria Tunca Dirk Van Hulle Roberto Vecchi Cyril Vettorato Luke Walker Jenny Webb Robert J.C. Young

Recent Developments on the Role of Ethylene in the Ripening of Climacteric Fruit

It has long been recognised that ethylene plays a major role in the ripening process of climacteric fruit. A more thorough analysis, however, has revealed that a number of biochemical and molecular processes associated with climacteric fruit ripening are ethylene-independent. One of the crucial steps of the onset of ripening is the induction of autocatalytic ethylene production. In ethylene-suppressed melons, ACC synthase activity is induced at the same time as in control melons, indicating that ACC biosynthesis during the early stages of ripening seems to be a developmentally-regulated (ethylene-independent) process. The various ripening events exhibit differential sensitivity to ethylene. For instance, the threshold level for degreening of the rind is 1ppm, while 2.5 ppm are required to trigger some components of the softening process. The saturating level of ethylene producing maximum effects is less than 5 ppm, which is by far lower than the internal ethylene concentrations found in the fruit at the climacteric peak (over 100 ppm). In many fruit chilling temperatures hasten ethylene production and ripening and in some late season pear varieties, exposure to chilling temperatures is even absolutely required for the attainment of the capacity to synthesize autocatalytic ethylene. This is correlated with the stimulation of expression of ACC oxidase and of members of the ACC synthase gene family. Ethylene operates via a perception and transduction pathway to induce the expression of genes responsible for the biochemical and physiological changes observed during ripening. However, only a few genes induced via the ethylene transduction pathway have been described so far. We have used a differential display method to isolate novel ethylene-reponsive (ER) cDNA clones of tomato that potentially play a role in propagating the ethylene response and in regulating fruit ripening. Collectively, these data permit a general scheme of the molecular mechanisms of fruit ripening to be proposed

To swim or not to swim: an interpretation of farmed mink's motivation for a water bath

How an animal’s behavioural (ethological) needs can be met is a pivotal issue in the assessment of welfare for captive animals. The value of swimming water for farmed mink is an example how scientific and societal questions relating to animal welfare can be answered. A number of studies have addressed the issue of the indispensability of swimming water for mink; however, so far with inconclusive evidence. In this paper, the results of these studies and related literature are reviewed. First, the biological definition of need is discussed. Subsequently, attention is paid to the effects of the presence, absence and the removal of swimming water on behavioural and physiological correlates of well-being including stereotypic and anticipatory behaviour and urinary cortisol. Thereafter we discuss individual differences in the use of swimming water, the price animals pay for access to a water bath, and the effect of access to swimming water on juvenile play. The main conclusions of the literature review are that 1) the use of a water bath for mink is most likely related to foraging behaviour (foraging areas: land and water); 2) absence of swimming water, without prior experience, does not lead to consistent changes in level of stereotypic behaviour, or anticipatory responses; 3) removal of a previously experienced water bath may induce short-term stress as indicated by behavioural parameters and elevated cortisol responses; 4) mink work hard for access to a swimming bath and running wheel in consumer demand studies. Other cage modifications such as tunnels and biting objects, may also provide environmental enrichment, if they are added to otherwise impoverished conditions; 5) There are individual differences in the use of swimming water: these are related in part to variation in prior experience of aquatic resources.; 6) As prior experience is important both with respect to individual use of swimming water and the response to deprivation, swimming water can not be described as biological need in the sense of a fixed requirement for survival. As swimming water appears to act as an incentive that induces its own motivation a more accurate term may be an “incentive induced or environmentally facilitated need”. Given the available evidence, it is not possible to conclude whether mink that have never experienced swimming water, suffer as a consequence of its absence. However, it is possible to predict that mink with access to water have improved quality of life, due to increased behavioural opportunities, in comparison to farmed mink without access to swimming water. In practical terms, it is still open to debate whether mink should be provided with swimming water, or if alternative, less valued, but easier to install and maintain forms of environmental enrichment, should be provided in mink housing. To clarify these issues a number of future studies would be valuable. These include; 1) whether specific environmental cues affect motivation to swim, such as the form of drinking water delivery systems ; 2) whether prior experience of swimming water affects its incentive value; in other words “can you miss what you never experienced?”; 3) do behavioural parameters such as stereotypic behaviour; rebound effects and vacuum activity have any general utility in assessing the value of absent resources; 4) what are preferences for and the value of alternative resources which may act as substitutes for swimming water. In addition we would recommend further work investigating: relationship between access to swimming water and positive indicators of welfare such as play and/or anticipatory behaviour; the effects of preventing the performance of rewarding behaviours and deprivation of a previous experienced resource; and health and hygeine issues related to provision of a water bath. In future work, it would be desirable to present be the actual percentages of animals using a water bath during the experiment and the use of power analyses, to aid their interpretation

Sequence stratigraphy and architectural elements of the Giant Foresets Formation, northern Taranaki Basin, New Zealand

The modern continental margin in northern Taranaki Basin is underlain by a thick, mud-dominated, Pliocene and Pleistocene succession (Giant Foresets Formation, GFF) clearly imaged in seismic reflection datasets. A study focusing on the geometry and internal reflection character of the GFF has revealed structural, sedimentological, and eustatic controls on its accumulation. Isopach maps prepared for northern Taranaki Basin show shifts through time in the main loci of sediment accumulation of the Mangaa Formation and Giant Foresets Formation. During the Early Pliocene (Opoitian Stage) deposition was focused in the southern part of the Northern Graben. The prograda¬tional front moved into the vicinity of Arawa-1 and Taimana-on the Western Platform during the early-Late Pliocene (Waipipian and Mangapanian Stages), forming large mounded slope fans. Through the latest Pliocene (Mangapanian - lower Nukumaruan Stages) the progradational front moved rapidly to the north and west through and across the Northern Graben to form a distinct shelf-slope depositional front. During the Pleistocene (upper Nukumaruan Stage – Recent), the progradational front straightened out, reaching the present position of the shelf-slope break. Even during the Pleistocene, broad subsidence persisted in the Northern Graben, trapping a proportion of the sediment flux being delivered to this part of the basin. The Late Pliocene part of the GFF, particularly where it prograded on to the Western Platform, displays classic clinoform profiles, with over steepening having resulted in mass-failure of paleoslopes. Major degradation of the shelf edge and slope occurred during the Early Pleistocene, reflecting a change in the calibre and flux of sediment sourced to the continental margin. Detailed examination of part of the GFF not significantly affected by mass-failure indicates that small-scale channel levee and overbank deposits dominate slope deposition, while basin floor deposits are characterised by slope-disconnected muddy and silty basin floor fans, with little lateral continuity between systems. In a sequence stratigraphic context, many of the dominant components of each seismic unit (slumps, fans, and channel-levee complexes) were deposited during the falling (RST) and low (LST) sea level parts of a relative sea level cycle, resulting in highly asymmetric sequences. While the GFF is considered to have minor reservoir potential in terms of containing sandstone-dominated stratigraphic traps, it does afford the opportunity to study in detail how deep-water clastic systems evolved in response to the various factors that control depositional architectures, particularly in a rapidly prograding muddy continen¬tal margin system

Comment on "Long-range electrostatic interactions between like-charged colloids: Steric and confinement effects"

In a recent study [Phys. Rev. E 60, 6530 (1999)], Trizac and Raimbault showed that the effective pair interaction between like charged colloids immersed in a cylindrically confined electrolyte remains repulsive even when the size of the micro-ions or the finite longitudinal extension of the confining cylinder are taken into account. Contrary to their claim, we argue that the case of finite longitudinal confinement doesn't always generate repulsive interactions and to illustrate this point we also provide a simple example.Comment: 3 pages, 1 figure. Accepted for publication in Phys. Rev. E 200