The X-ray properties of the merging galaxy pair NGC 4038/9 - the Antennae

We report the results of an X-ray spectral imaging observation of the Antennae with the ROSAT PSPC. 55% of the soft X-ray flux from the system is resolved into discrete sources, including components identified with the galactic nuclei and large HII regions, whilst the remainder appears to be predominantly genuinely diffuse emission from gas at a temperature ~4x10^6 K. The morphology of the emission is unusual, combining a halo which envelopes the galactic discs, with what appears to be a distorted, but well-collimated bipolar outflow. We derive physical parameters for the hot gas in both diffuse components, which are of some interest, given that the Antennae probably represents an elliptical galaxy in the making.Comment: 15 pages plus 9 figures, uuencoded encapsulated postscript file. Accepted for publication in MNRA

Super-rotating jets in a re-analysis of the martian atmosphere

Strong westerly, prograde jets have been identified in the martian atmosphere between about 10–20 km altitude throughout much of the year in a Mars Global Circulation Model (MGCM) study [2]. The development of data assimilation techniques for Mars [3, 5] now permits the analysis of super-rotation in less highly idealized cases using an atmospheric reanalysis, as would be done for the Earth. This paper reviews recent atmospheric reanalyses, in order to validate previous modeling results, to quantify jet amplitudes and to diagnose possible mechanisms supplying angular momentum to the jets. [2] Lewis, S. R., and Read, P. L.: Equatorial jets in the dusty martian atmosphere, J. Geophys. Res., Vol. 108 (E4), 5034, pp. 1–15, 2003. [3] Lewis, S. R., Read, P. L., Conrath, B. J., Pearl, J. C., and Smith, M. D.: Assimilation of Thermal Emission Spectrometer atmospheric data during the Mars Global Surveyor aerobraking period, Icarus, Vol. 192 (2), pp. 327–347, 2007. [5] Montabone, L., Lewis, S. R., Read, P. L., Hinson, D. P., Validation of Martian meteorological data assimilation for MGS/TES using radio occultation measurements, Icarus Vol. 185 (1), pp. 113–132, 2006

Nitrification-denitrification in WSP: a mechanism for permanent nitrogen removal in maturation ponds

A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N labelled nitrite (Na15NO2), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of δ15N showed that nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity

Dust-related interannual and intraseasonal variability of Martian climate using data assimilation

Data assimilation has been applied in several studies [Montabone et al., 2005; Lewis et al., 2005; Montabone et al., 2006a; Montabone et al., 2006b; Lewis et al., 2007; Wilson et al., 2008; Rogberg et al. 2010] as an effective tool with which to analyze spacecraft observations and phenomena (e.g., atmospheric tides, transient wave behavior, effects of clouds in the tropics, weather predictability, etc.) in the Martian atmosphere. A data assimilation scheme combined with a Martian Global Circulation Model (GCM) is able to provide a complete, balanced, four-dimensional solution consistent with observations. The GCM we use [Forget et al., 1999] combines a spectral dynamical solver and a tracer transport scheme developed in UK and Laboratoire de Météorologie Dynamique (LMD; Paris, France) physics package developed in collaboration with Oxford, The Open University and Instituto de Astrofisica de Andalucia (Granada, Spain). Here, we describe and discuss dust-related interannual and intraseasonal variability of the Martian climate. The results shown in this study come from a reanalysis using the Martian GCM with data assimilation scheme which assimilates Mars Global Surveyor/ Thermal Emission Spectrometer (MGS/TES) retrievals of temperature and column dust opacity. The detailed model setup was described by Montabone et al. [2006a], and the data assimilation scheme employed in this study was introduced in the work of Lewis et al. [2007]

Thermal metal in network models of a disordered two-dimensional superconductor

We study the universality class for localization which arises from models of non-interacting quasiparticles in disordered superconductors that have neither time-reversal nor spin-rotation symmetries. Two-dimensional systems in this category, which is known as class D, can display phases with three different types of quasiparticle dynamics: metallic, localized, or with a quantized (thermal) Hall conductance. Correspondingly, they can show a variety of delocalization transitions. We illustrate this behavior by investigating numerically the phase diagrams of network models with the appropriate symmetry, and for the first time show the appearance of the metallic phase.Comment: 5 pages, 3 figure

Group inquiry to aid organisational learning in enterprises

This paper describes a method for surfacing and exploring ‘situated knowledge’ in medium-sized organisations, with employee groups utilising a ‘low impact’ form of group support system (GSS), based on wireless handsets. Some results of piloting this method are summarised and one intervention is presented in detail. The method encouraged organisational members to give voice to the emotions and politics of leadership and learning in organisations, and helped to articulate how situated knowledge was ignored, as well as utilised. The method is practical, and may be used by organisations for themselves to aid the development of group as well as individual reflection, to stimulate the consideration of change

The Fractional Quantum Hall effect in an array of quantum wires

We demonstrate the emergence of the quantum Hall (QH) hierarchy in a 2D model of coupled quantum wires in a perpendicular magnetic field. At commensurate values of the magnetic field, the system can develop instabilities to appropriate inter-wire electron hopping processes that drive the system into a variety of QH states. Some of the QH states are not included in the Haldane-Halperin hierarchy. In addition, we find operators allowed at any field that lead to novel crystals of Laughlin quasiparticles. We demonstrate that any QH state is the groundstate of a Hamiltonian that we explicitly construct.Comment: Revtex, 4 pages, 2 figure

QUAGMIRE v1.3: a quasi-geostrophic model for investigating rotating fluids experiments

QUAGMIRE is a quasi-geostrophic numerical model for performing fast, high-resolution simulations of multi-layer rotating annulus laboratory experiments on a desktop personal computer. The model uses a hybrid finite-difference/spectral approach to numerically integrate the coupled nonlinear partial differential equations of motion in cylindrical geometry in each layer. Version 1.3 implements the special case of two fluid layers of equal resting depths. The flow is forced either by a differentially rotating lid, or by relaxation to specified streamfunction or potential vorticity fields, or both. Dissipation is achieved through Ekman layer pumping and suction at the horizontal boundaries, including the internal interface. The effects of weak interfacial tension are included, as well as the linear topographic beta-effect and the quadratic centripetal beta-effect. Stochastic forcing may optionally be activated, to represent approximately the effects of random unresolved features. A leapfrog time stepping scheme is used, with a Robert filter. Flows simulated by the model agree well with those observed in the corresponding laboratory experiments