NUMERICAL SIMULATIONS OF BURST PROCESSES IN FIBER-BUNDLES

We discuss a very effective numerical method for simulating fibre-bundle models with equal load-sharing and with local load-sharing. Particular attention is paid to the case of the local load-sharing model, in which the critical load x(c) is defined as the average load per fibre that causes the final complete failure. It is shown that x(c) --> 0 when the size of the system N --> infinity. We also show analytically that the power law of the burst size distribution, D(Delta) alpha Delta(-xi), is approximately correct. The exponent xi in the local load-sharing case is not universal, since it depends on the strength distribution as well on as the size of the system.

CHEMICAL PROCESSES IN DARK INTERSTELLAR CLOUDS - THE EFFECTS OF CNO DEPLETION

We have investigated the effects of depletion of the elements C, N and O on the chemical composition of dark clouds, using both isothermal and isochoric cloud models. Our work differs from previous approaches in that we have considered a much larger range of CNO depletions. We have included the chemistry of the ortho-and para-forms of H2 and the exothermic reaction between N+ and ortho-H2, which synthesizes NH3. In the isothermal models, the ortho:para ratio is very small at large depletions, but NH3 formation is still efficient owing to reactions between He+ and CN or HCN. In the isochoric models, the equilibrium temperature of the gas is larger, and a thermal ortho:para ratio, which is large enough to drive NH3 formation, results. In all cases, the fractional abundance of NH3 is close to 10(-8) and this may help to explain the puzzling observation that, in dark clouds, the column density of NH3 is always close to 10(15) cm-2.

Chemical processes in protoplanetary disks. II. On the importance of photochemistry and X-ray ionization

We investigate the impact of photochemistry and X-ray ionization on the molecular composition of, and ionization fraction in, a protoplanetary disk surrounding a typical T Tauri star. We use a sophisticated physical model, which includes a robust treatment of the radiative transfer of UV and X-ray radiation, and calculate the time-dependent chemical structure using a comprehensive chemical network. In previous work, we approximated the photochemistry and X-ray ionization; here, we recalculate the photoreaction rates using the explicit UV wavelength spectrum and wavelength-dependent reaction cross sections. We recalculate the X-ray ionization rate using our explicit elemental composition and X-ray energy spectrum. We find that photochemistry has a larger influence on the molecular composition than X-ray ionization. Observable molecules sensitive to the photorates include OH, HCO+, N2H+, H2O, CO2, and CH3OH. The only molecule significantly affected by the X-ray ionization is N2H+, indicating that it is safe to adopt existing approximations of the X-ray ionization rate in typical T Tauri star-disk systems. The recalculation of the photorates increases the abundances of neutral molecules in the outer disk, highlighting the importance of taking into account the shape of the UV spectrum in protoplanetary disks. A recalculation of the photoreaction rates also affects the gas-phase chemistry due to the adjustment of the H/H2 and C+/C ratios. The disk ionization fraction is not significantly affected by the methods adopted to calculate the photochemistry and X-ray ionization. We determine that there is a probable "dead zone" where accretion is suppressed, present in a layer, Z/R lsim 0.1-0.2, in the disk midplane, within R ˜ 200 AU.

“Voices, Spaces and Processes in Constitutionalism - Editorial"

(With C. Harvey, J. Shaw .)

Biodiversity and ecosystem processes in shallow coastal waters: an experimental approach

The relationship between biodiversity and ecological processes is currently the focus of considerable research effort, made all the more urgent by the rate of biodiversity loss world-wide. Rigorous experimental approaches to this question have been dominated by terrestrial ecologists, but shallow-water marine systems offer great opportunities by virtue of their relative ease of manipulation, fast response times and well-understood effects of macrofauna on sediment processes. In this paper, we describe a series of experiments whereby species richness has been manipulated in a controlled way and the concentrations of nutrients (ammonium, nitrate and phosphate) in the overlying water measured under these different treatments. The results indicate variable effects of species and location on ecosystem processes, and are discussed in the context of emerging mainstream ecological theory on biodiversity and ecosystem relations. Extensions of the application of the experimental approach to species-rich, large-scale benthic systems are discussed and the potential for novel analyses of existing data sets is highlighted. (C) 2002 Elsevier Science B.V. All rights reserved.

Microscopic theory for random processes in weakly-coupled open systems

In order to relate macroscopic random motion (described e.g. by Langevin-type theories) to microscopic dynamics, we have undertaken the derivation of a Fokker-Planck-type equation from first microscopic principles. Both subsystems are subject to an external force field. Explicit expressions for the diffusion and drift coefficients are obtained, in terms of the field.

Primed, constant infusion with [H-2(3)]serine allows in vivo kinetic measurement of serine turnover, homocysteine remethylation, and transsulfuration processes in human one-carbon metabolism

Background: One-carbon metabolism involves both mitochondrial and cytosolic forms of folate-dependent enzymes in mammalian cells, but few in vivo data exist to characterize the biochemical processes involved.

Objective: We conducted a stable-isotopic investigation to determine the fates of exogenous serine and serine-derived one carbon units in homocysteine remethylation in hepatic and whole-body metabolism.

Design: A healthy man aged 23 y was administered [2,3,3 H-2(3)]serine and [5,5,5-H-2(3)]leucine by intravenous primed, constant infusion. Serial plasma samples were analyzed to determine the isotopic enrichment of free glycine, serine, leucine, methionine, and cystathionine. VLDL apolipoprotein B-100 served as an index of liver free amino acid labeling.

Results: [H-2(1)]Methionine and [H-2(2)]methionine were labeled through homocysteine remethylation. We propose that [H-2(2)]methionine occurs by remethylation with [H-2(2)]methyl groups (as 5-methyltetrahydrofolate) formed only from cytosolic processing of [H-2(3)]serine, whereas [H-2(1)]methionine is formed with labeled one-carbon units from mitochondrial oxidation of C-3 serine to [H-2(1)]formate to yield cytosolic [H-2(1)]methyl groups. The labeling pattern of cystathionine formed from homocysteine and labeled serine suggests that cystathionine is derived mainly from a serine pool different from that used in apolipoprotein B-100 synthesis.

Conclusions: The appearance of both [H-2(1)]- and [H-2(2)]methionine forms indicates that both cytosolic and mitochondrial metabolism of exogenous serine generates carbon units in vivo for methyl group production and homocysteine remethylation. This study also showed the utility of serine infusion and indicated functional roles of cytosolic and mitochondrial compartments in one-carbon metabolism.

Low temperature conditions in building sandstone: the role of extreme events in temperate environments

Data on rock temperatures has previously been collected to characterise typical diurnal regimes, and more recently to describe short-term variability in extreme locations. However, there is also the case that little is understood concerning the impact of extreme events in otherwise temperate environments. Internal stone temperatures (5?cm) collected during the atypical cold extreme experienced, throughout the UK, in December 2010 show a difference between ambient air temperatures and aspect-related thermal differences, particularly concerning temperature lows and the influence of radiative heating. In this case, debris release was not visible; however, laboratory simulations have shown that under such conditions, surface loss does not necessarily negate the occurrence of internal stone modifications. This preparatory sequence of change demonstrates that surface loss is not the result of one process, but rather many operating over time to sufficiently decrease stone strength to facilitate obvious damage.

Centres, Peripheries and Party Systems: nested secession processes in Great Britain and Ireland

The seminal work of Lipset and Rokkan, which explores how party systems evolved organically from nineteenth-century roots, has generally been applied in states which have enjoyed a long-standing territorial identity. Their model's emphasis on stability and predictability can, however, be reconciled with circumstances where the very identity of the state itself is an issue. This article explores the capacity of the model to explain party divisions in three nested contexts: the pre-1922 United Kingdom, which encountered problems with its Celtic peripheries, and especially with Ireland; independent Ireland, where a unique party system developed, largely in response to a broader historical and geographical context; and Northern Ireland, where party politics fossilised in the 1880s, and began to unfreeze only in the 1970s. The article argues that the Lipset–Rokkan model casts valuable light on these processes, which in turn contribute to the theoretical richness of the model.

'Sometimes I wish I was an "ex" ex-prisoner': identity processes in the collective action participation of former prisoners in Northern Ireland

Since the signing of the Northern Ireland peace agreement a plethora of community based prisoner self-help organisations have been established wherein former prisoners staff, manage and deliver services to colleagues. By forging and maintaining their collective identities through community based mutual aid, members of these self-help organisations have progressed to create not only individual change/assistance but have also developed and evolved to tackle serious wider social issues which impact on the members of their organisations. This article critically analyses how the conditions of a post conflict society can influence both the development and evolution of these organisations and also how members situate their claims about the self in the organisation and beyond. Using the social movement framework it is argued that the work of these self-help organisations have given rise to a new politics of identity … that is the ‘politically motivated’ ex-prisoner. ©2013 Taylor & Francis