Panphasia: a user guide

We make a very large realisation of a Gaussian white noise field, called PANPHASIA, public by releasing software that computes this field. Panphasia is designed specifically for setting up Gaussian initial conditions for cosmological simulations and resimulations of structure formation. We make available both software to compute the field itself and codes to illustrate applications including a modified version of a public serial initial conditions generator. We document the software and present the results of a few basic tests of the field. The properties and method of construction of Panphasia are described in full in a companion paper Jenkins 2013.Comment: 11 pages, 2 figures. Software to calculate Panphasia is available from: http://icc.dur.ac.uk/Panphasia.ph

Centurial‐millenial ice‐rafted debris pulses from ablating marine ice sheets

We use an ice‐sheet model to show that (i) margins of marine ice‐sheets can be expected to be frozen to the bed, except where ice‐streams discharge; (ii) 20–50km retreats induced by ablation rates of 2 m/yr provide sufficient debris flux through the grounding line to produce large sedimentation events. Such ablation would reduce ice‐shelf extent markedly, permitting debris to reach the calving front and be transported by icebergs leading to ice‐rafted debris (IRD) events. Ice shelf break‐up takes around a century (start of IRD pulse), while the creation of warm‐based conditions (end of IRD pulse) due to upwards motion of warm ice takes a few more centuries. Such IRD pulses are unlikely to explain Heinrich events, which are associated with relatively cold periods within glaciations. Surges are not necessary conditions for the production of large IRD events

A simple model of the ice-shelf-ocean boundary layer and current

Ocean-forced basal melting has been implicated in the widespread thinning of Antarctic ice shelves, but our understanding of what determines melt rates is hampered by our limited knowledge of the buoyancy- and frictionally-controlled flows along the ice shelf base that regulate heat transfer from ocean to ice. In an attempt to address this deficiency, a simple model of a buoyant boundary flow, considering only the spatial dimension perpendicular to the boundary, is presented. Results indicate that two possible flow regimes exist: a weakly-stratified, geostrophic cross-slope current with upslope flow within a buoyant Ekman layer; or a strongly-stratified upslope current with a weak cross-slope flow. The latter regime, which is analogous to the steady solution for a katabatic wind, is most appropriate when the ice-ocean interface is steep. For the gentle slopes typical of Antarctic ice shelves the buoyant Ekman regime, which has similarities with the case of an unstratified density current on a slope, provides some useful insight. When combined with a background flow, a range of possible near-ice current profiles emerge as a result of arrest or enhancement of the upslope Ekman transport. A simple expression for the upslope transport can be formed that is analogous to that for the wind-forced surface Ekman layer, with curvature of the ice shelf base replacing the wind-stress curl in driving exchange between the Ekman layer and the geostropic current below

Reducing the Risk of Police Corruption in Guatemala

The country of Guatemala has always been plagued by political, security, and socio-economic conditions. These issues have contributed to the country having one of the highest violent crime rates in Central America and being ranked as the third most murderous country in the entire world (Grann, D.). This project will examine one of the factors believed to be most prominent in the country’s security problem, police corruption. The Guatemalan National Civil Police (PNC) officers are confronted with institutional corruption, a homicide rate over five times the world average, insufficient resources, poor training, and distrust from the civilian population (ghrc-usa, 2014). “The U.S. State Department 2077 Guatemala Country Report on Human Rights Practices states that “Members of the police force committed a number of unlawful killings. Corruption, intimidation, and ineffectiveness within the police department and other institutions prevented adequate investigation of many such killings, as well as the arrest and successful prosecution of perpetrators.” (ghrc-usa, 2014). Another challenge for the PNC is drug trafficking. Guatemalan President Alvaro Colom blames the drug traffickers for the corruption plaguing the PNC. Drug traffickers have been able to corrupt many PNC officers and chiefs because they have the ability to pay more than the monthly salaries these people receive. Mexican drug cartels such as the Los Zetas and the Mara Salvatrucha actively operate throughout the country. In addition, Guatemala’s geographical location makes it a key country for trafficking in cocaine and heroin from South America en route to the U.S. and Europehttps://scholarscompass.vcu.edu/uresposters/1046/thumbnail.jp

Oceanographic observations at the Amundsen sea shelf break

Introduction: The continental shelf environment of the Amundsen and Bellingshausen seas differs markedly from that of the other circumpolar seas, where water temperatures are close to the surface freezing point throughout. In the Amundsen/Bellingshausen sector near-freezing temperatures are encountered only in the upper few hundred metres of the water column. Below this surface layer a broad thermocline trends towards upper Circumpolar Deep Water (uCDW), which is found in a form that is almost unmodified from its off-shelf manifestation (Giulivi and Jacobs, 1996). This means that the ice shelves of the Amundsen and Bellingshausen seas experience ocean temperatures some three degrees warmer than those experienced by the other Antarctic ice shelves, and the rates of basal melting are correspondingly high (Jacobs et al., 1996)

Decaying dark matter: the case for a deep X-ray observation of Draco

Recent studies of M31, the Galactic Centre (GC), and galaxy clusters have made tentative detections of an X-ray line at ∼3.5keV that could be produced by decaying dark matter. We use high-resolution simulations of the Aquarius project to predict the likely amplitude of the X-ray decay flux observed in the GC relative to that observed in M31, and also of the GC relative to other parts of the Milky Way halo and to dwarf spheroidal galaxies. We show that the reported detections from M31 and the GC are compatible with each other, and with upper limits arising from high galactic latitude observations, and imply a decay time τ∼1028 s. We argue that this interpretation can be tested with deep observations of dwarf spheroidal galaxies: in 95 per cent of our mock observations, a 1.3 Ms pointed observation of Draco with XMM-Newton will enable us to discover or rule out at the 3σ level an X-ray feature from dark matter decay at 3.5keV, for decay times τ<0.8×1028

The effect of meltwater plumes on the melting of a vertical glacier face

Freshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord-terminating glaciers. The discharge of the freshwater forms upwelling plumes in front of the glacier calving face. We simulate the meltwater plumes emanated into an unstratified environment using a non-hydrostatic ocean model with an unstructured mesh and subgrid-scale mixing calibrated by comparison to established plume theory. The presence of an ice face reduces the entrainment of seawater into the meltwater plumes, so the plumes remain attached to the ice front, in contrast to previous simple models. Ice melting increases with height above the discharge, also in contrast to some simple models, and we speculate that this ‘overcutting’ may contribute to a tendency of icebergs to topple inwards toward the ice face upon calving. The overall melt rate is found to increase with discharge flux only up to a critical value, which depends on the channel size. The melt rate is not a simple function of the subglacial discharge flux, as assumed by many previous studies. For a given discharge flux, the geometry of the plume source also significantly affects the melting, with higher melt rates obtained for a thinner, wider source. In a wider channel, two plumes are emanated near the source and these plumes eventually coalesce. Such merged meltwater plumes ascend faster and increase the maximum melt rate near the center of the channel. The melt rate per unit discharge decreases as the subglacial system becomes more channelised

Dark Matter Halo Merger Histories Beyond Cold Dark Matter: I - Methods and Application to Warm Dark Matter

We describe a methodology to accurately compute halo mass functions, progenitor mass functions, merger rates and merger trees in non-cold dark matter universes using a self-consistent treatment of the generalized extended Press-Schechter formalism. Our approach permits rapid exploration of the subhalo population of galactic halos in dark matter models with a variety of different particle properties or universes with rolling, truncated, or more complicated power spectra. We make detailed comparisons of analytically derived mass functions and merger histories with recent warm dark matter cosmological N-body simulations, and find excellent agreement. We show that, once the accretion of smoothly distributed matter is accounted for, coarse-grained statistics such as the mass accretion history of halos can be almost indistinguishable between cold and warm dark matter cases. However, the halo mass function and progenitor mass functions differ significantly, with the warm dark matter cases being strongly suppressed below the free-streaming scale of the dark matter. We demonstrate the importance of using the correct solution for the excursion set barrier first-crossing distribution in warm dark matter - if the solution for a flat barrier is used instead the truncation of the halo mass function is much slower, leading to an overestimate of the number of low mass halos.Comment: 19 pages, 14 figures, MNRAS in press. Comments welcom