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

Examining the role of mental health and clinical issues within talent development

Although significant research supports the association between physical activity and mental wellbeing, current literature acknowledges that athletes are no less susceptible to mental illness than the general population. Despite welcomed initiatives aimed at improving mental health within elite sport, these programs often fail to target young athletes; an important concern given that the genesis of many mental illnesses are recognized to occur during this critical period. Given the importance of early intervention and effective treatment, and the potentially devastating consequences of clinical issues going undiagnosed, the implications for talent identification and development become obvious. With this in mind, this study sought to examine the range of mental health issues that may impact upon developing athletes and potential consequences for the development process, specific risk and protective factors associated with talent development, along with an examination of current practices concerning the identification of mental health issues in such environments. Qualitative interviews were conducted with purposively sampled clinicians (n = 8) experienced in working with adolescents and/or young athletes. Inductive content analysis was undertaken, identifying four main themes: key behavioral indicators; associated risk factors; associated protective factors; and issues around identification and diagnosis. Key behavioral indicators included behavioral change, along with behaviors associated with eating disorders, anxiety and depression. Risk factors centered on family background, the performance environment, and issues surrounding adolescence. Protective factors were primarily social in nature. Finally, a lack of awareness and understanding of clinical issues, multiple causes of symptoms, non-disclosure and the need for triangulation of assessment were identified. The need for improved identification and intervention strategies was apparent, with coaches identified as well placed to detect general ‘warning signs’ such as behavioral change. Short of integrating trained clinicians into talent development environments, as part of a triangulation process, ecologically validated assessment tools – coupled with appropriate training and signposting – could offer a practical way of flagging potential issues in developing athletes. The need for the development of such an instrument is therefore apparent. Finally, education around the influential role of family is also recommended in order to promote the protective elements and mitigate risk factors

Using stable isotope tracers to assess hydrological flow paths, residence times and landscape influences in a nested mesoscale catchment

International audience?18O measurements in precipitation and stream waters were used to investigate hydrological flow paths and residence times at nested spatial scales in the mesoscale (233 km2) River Feugh catchment in the northeast of Scotland over the 2001-2002 hydrological year. Precipitation ?18O exhibited strong seasonal variation, which although significantly damped within the catchment, was reflected in stream water at six sampling sites. This allowed ?18O variations to be used to infer the relative influence of soil-derived storm flows with a seasonally variable isotopic signature, and groundwater of apparently more constant isotopic composition. Periodic regression analysis was then used to examine the sub-catchment difference using an exponential flow model to provide indicative estimates of mean stream water residence times, which varied between approximately 3 and 14 months. This showed that the effects of increasing scale on estimated mean stream water residence time was minimal beyond that of the smallest (ca. 1 km2) headwater catchment scale. Instead, the interaction of catchment soil cover and topography appeared to be the dominant controlling influence. Where sub-catchments had extensive peat coverage, responsive hydrological pathways produced seasonally variable ?18O signatures in runoff with short mean residence times (ca. 3 months). In contrast, areas dominated by steeper slopes, more freely draining soils and larger groundwater storage in shallow valley-bottom aquifers, deeper flow paths allow for more effective mixing and damping of ?18O indicating longer residence times (>12 months). These insights from ?18O measurements extend the hydrological understanding of the Feugh catchment gained from previous geochemical tracer studies, and demonstrate the utility of isotope tracers in investigating the interaction of hydrological processes and catchment characteristics at larger spatial scales

Chemical chronology of the Southern Coalsack

We demonstrate how the observed H2O ice column densities toward three dense globules in the Southern Coalsack could be used to constrain the ages of these sources. We derive ages of ~10^5 yr, in agreement with dynamical studies of these objects. We have modelled the chemical evolution of the globules, and show how the molecular abundances are controlled by both the gas density and the initial chemical conditions as the globules formed. Based on our derived ages, we predict the column densities of several species of interest. These predictions should be straightforward to test by performing molecular line observationsComment: 10 pages, 4 figures, in press at MNRA

Nitrogen superfractionation in dense cloud cores

We report new calculations of interstellar 15N fractionation. Previously, we have shown that large enhancements of 15N/14N can occur in cold, dense gas where CO is frozen out, but that the existence of an NH + N channel in the dissociative recombination of N2H+ severely curtails the fractionation. In the light of recent experimental evidence that this channel is in fact negligible, we have reassessed the 15N chemistry in dense cloud cores. We consider the effects of temperatures below 10 K, and of the presence of large amounts of atomic nitrogen. We also show how the temporal evolution of gas-phase isotope ratios is preserved as spatial heterogeneity in ammonia ice mantles, as monolayers deposited at different times have different isotopic compositions. We demonstrate that the upper layers of this ice may have 15N/14N ratios an order of magnitude larger than the underlying elemental value. Converting our ratios to delta-values, we obtain delta(15N) > 3,000 per mil in the uppermost layer, with values as high as 10,000 per mil in some models. We suggest that this material is the precursor to the 15N `hotspots' recently discovered in meteorites and IDPsComment: accepted by MNRA

Short Distance Expansion from the Dual Representation of Infinite Dimensional Lie Algebras

We compute the short distance expansion of fields or operators that live in the coadjoint representation of an infinite dimensional Lie algebra by using only properties of the adjoint representation and its dual. We explicitly compute the short distance expansion for the duals of the Virasoro algebra, affine Lie Algebras and the geometrically realized N-extended supersymmetric GR Virasoro algebra.Comment: 19 pages, LaTeX twice, no figure, replacement has corrected Lie algebr

Using stable isotope tracers to identify hydrological flow paths, residence times and landscape controls in a mesoscale catchment

International audience?18O tracer measurements of precipitation and stream waters were used to investigate hydrological flow paths and residence times at nested spatial scales in the mesoscale (233 km2 River Feugh catchment in the northeast of Scotland over the 2001-2002 hydrological year. Precipitation ?18O exhibited strong seasonal variation, which although significantly damped by catchment mixing processes, was reflected in stream water outputs at six sampling sites. This allowed ?18O variations to be used to infer the relative influence of soil-derived storm flows with a seasonally variable isotopic signature, and groundwater of more constant isotopic composition. Periodic regression analysis was then used to examine the sub-catchment differences in the mixing of these two main hydrological sources processes more quantitatively, using an exponential flow model to provide preliminary estimates of mean stream water residence times, which varied between 0.4-2.9 years. This showed that the effects of increasing scale on estimated mean stream water residence time was minimal beyond the smallest (ca. 1 km2 headwater catchment scale. Instead, the interaction of catchment soil cover and topography acted as the dominant influence. Responsive hydrological pathways, associated with peat soils in the headwater sub-catchments, produced seasonally variable ?18O signatures in runoff with short mean residence times (0.4-0.8 years). In contrast, areas dominated by more freely draining soils and larger groundwater storage in shallow aquifers appear to provide effective mixing and damping of variable precipitation inputs implying longer residence times (1.4-2.9 years). These insights from ?18O measurements extend the hydrological understanding of the Feugh catchment gained from previous geochemical tracer studies, and demonstrate the utility of isotope tracers in investigating the interaction of hydrological processes and catchment characteristics at the mesoscale

The Anisotropic Bak-Sneppen model

The Bak-Sneppen model is shown to fall into a different universality class with the introduction of a preferred direction, mirroring the situation in spin systems. This is first demonstrated by numerical simulations and subsequently confirmed by analysis of the multitrait version of the model, which admits exact solutions in the extremes of zero and maximal anisotropy. For intermediate anisotropies, we show that the spatiotemporal evolution of the avalanche has a power law `tail' which passes through the system for any non-zero anisotropy but remains fixed for the isotropic case, thus explaining the crossover in behaviour. Finally, we identify the maximally anisotropic model which is more tractable and yet more generally applicable than the isotropic system

Gas phase production of NHD2 in L134N

We show analytically that large abundances of NH2D and NHD2 can be produced by gas phase chemistry in the interiors of cold dense clouds. The calculated fractionation ratios are in good agreement with the values that have been previously determined in L134N and suggest that triply-deuterated ammonia could be detectable in dark clouds. Grain surface reactions may lead to similar NH2D and NHD2 enhancements but, we argue, are unlikely to contribute to the deuteration observed in L134N.Comment: 6 pages, 2 figures, uses psfig.sty and emulateapj.sty, to appear in Astrophysical Journal, vol 55