Rapidity gaps at HERA and the Tevatron from soft colour exchanges

Models based on soft colour exchanges to rearrange colour strings in the final state provide a general framework for both diffractive and non-diffractive events in ep and hadron-hadron collisions. We study two such models and find that they can reproduce rapidity gap data from both HERA and the Tevatron. We also discuss the influence of parton cascades and multiple interactions on the results.Comment: 4 pages, 4 EPS figures, presented at UK Phenomenology Workshop on Collider Physics, Durham. Uses iopart.cl

Star cluster survival and compressive tides in Antennae-like mergers

Gravitational tides are widely understood to strip and destroy galactic substructures. In the course of a galaxy merger, however, transient totally compressive tides may develop and prevent star forming regions from dissolving, after they condensed to form clusters of stars. We study the statistics of such compressive modes in an N-body model of the galaxy merger NGC 4038/39 (the Antennae) and show that ~15% of the disc material undergoes compressive tides at pericentre. The spatial distribution of observed young clusters in the overlap and nuclear regions of the Antennae matches surprisingly well the location of compressive tides obtained from simulation data. Furthermore, the statistics of time intervals spent by individual particles embedded in a compressive tide yields a log-normal distribution of characteristic time ~10 Myr, comparable to star cluster formation timescales. We argue that this generic process is operative in galaxy mergers at all redshifts and possibly enhances the formation of star clusters. We show with a model calculation that this process will prevent the dissolution of a star cluster during the formation phase, even for a star formation efficiency as low as ~10%. The transient nature of compressive tides implies that clusters may dissolve rapidly once the tidal field switches to the usual disruptive mode.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letters. For higher resolution, see http://astro.u-strasbg.fr/~renaud/publi/mnras08.pd

Recent trends in particle size analysis techniques

Recent advances and developments in the particle-sizing technologies are briefly reviewed in accordance with three operating principles including particle size and shape descriptions. Significant trends of the particle size analysing equipment recently developed show that compact electronic circuitry and rapid data processing systems were mainly adopted in the instrument design. Some newly developed techniques characterizing the particulate system were also introduced

Carnitine metabolism to trimethylamine by an unusual Rieske-type oxygenase from human microbiota

Dietary intake of L-carnitine can promote cardiovascular diseases in humans through microbial production of trimethylamine (TMA) and its subsequent oxidation to trimethylamine N-oxide (TMAO) by hepatic flavin-containing monooxygenases. Although our microbiota are responsible for TMA formation from carnitine, the underpinning molecular and biochemical mechanisms remain unclear. In this study, using bioinformatics approaches, we first identified a two-component Rieske-type oxygenase/reductase (CntAB) and associated gene cluster proposed to be involved in carnitine metabolism in representative genomes of the human microbiota. CntA belongs to a group of previously uncharacterized Rieske-type proteins and has an unusual "bridging" glutamate but not the aspartate residue, which is believed to facilitate inter-subunit electron transfer between the Rieske centre and the catalytic mononuclear iron centre. Using Acinetobacter baumannii as the model, we then demonstrate that cntAB is essential in carnitine degradation to TMA. Heterologous overexpression of cntAB enables Escherichia coli to produce TMA, confirming that these genes are sufficient in TMA formation. Site-directed mutagenesis experiments have confirmed that this unusual "bridging glutamate" residue in CntA is essential in catalysis and neither mutant (E205D, E205A) is able to produce TMA. Together, our study reveals the molecular and biochemical mechanisms underpinning carnitine metabolism to TMA in human microbiota and assigns the role of this novel group of Rieske-type proteins in microbial carnitine metabolism

Research management of water economics in agriculture - an open agenda

It is indeed a privilege and an honour to deliver the FR Tomlinson Commemorative lecture this year. Although the invitation was quite unexpected, it is of course highly appreciated. When Prof Johann Kirsten phoned me with the request, I was initially not sure what topic I should address. The topic, which I have now formulated, is one which has fascinated me and certainly kept me busy for the most part of my career. I want to share with you some thoughts and perspectives, but will steer away from a laborious review or an abstract analysis. In doing so, I trust that this is appropriate within the spirit of the occasion, which is now a well established tradition in the Agricultural Economics Association of South Africa (AEASA). Let me start with a quotation which is at the core of the theme I want to unfold in this lecture. “Our most important resource is not land, nor capital and even less the climate. Our most important resource is not the gold under the earth’s crust, or the oil that might be there. Our most important resource is our human material. We must develop our human material and make full use of it.” (Groenewald JA, 1973a)Resource /Energy Economics and Policy,

Outstanding problems in the phenomenology of hard diffractive scattering

This paper is a summary of the discussion within the Diffractive and Low-x Physics Working Group at the 1999 Durham Collider Workshop of the interpretation of the Tevatron and HERA measurements of inclusive hard diffraction.Comment: 5 pages, 1 figure. Talks and discussions from the UK Phenomenology Workshop on Collider Physics, Durham, September 199

A coupled hydrology-biogeochemistry model to simulate dissolved organic carbon exports from a permafrost influenced catchment

Funded by Natural Environment Research Council. Grant Number: NE/K000268/1 Natural Sciences and Engineering Research Council of CanadaPeer reviewedPublisher PD