Constraining the mass density of free-floating black holes using razor-thin lensing arcs

Strong lensing of active galactic nuclei in the radio can result in razor-thin arcs, with a thickness of less than a milli-arcsecond, if observed at the resolution achievable with very long baseline interferometry (VLBI). Such razor-thin arcs provide a unique window on the coarseness of the matter distribution between source and observer. In this paper, we investigate to what extent such razor-thin arcs can constrain the number density and mass function of `free-floating' black holes, defined as black holes that do not, or no longer, reside at the centre of a galaxy. These can be either primordial in origin or arise as by-products of the evolution of super-massive black holes in galactic nuclei. When sufficiently close to the line of sight, free-floating black holes cause kink-like distortions in the arcs, which are detectable by eye in the VLBI images as long as the black hole mass exceeds $\sim 1000$ Solar masses. Using a crude estimate for the detectability of such distortions, we analytically compute constraints on the matter density of free-floating black holes resulting from null-detections of distortions along a realistic, fiducial arc, and find them to be comparable to those from quasar milli-lensing. We also use predictions from a large hydrodynamical simulation for the demographics of free-floating black holes that are not primordial in origin, and show that their predicted mass density is roughly four orders of magnitude below the constraints achievable with a single razor-thin arc.Comment: 17 pages, 13 figures, 1 table, comments welcom

Government Promotion of eCommerce through Seed Funding: A Review of the Australian Government,s ITOL Program

12 page(s

Understanding Information Systems Outsourcing: why multiple perspectives are essential

Over recent years, many forms of inter-organisational collaboration have gained in popularity. IT outsourcing is a particular form of collaboration and, while cost savings and other benefits forecast in the early days of the outsourcing boom have not always eventuated, the approach has retained much of its popularity. It is becoming increasingly apparent, however, that we still have some way to go in understanding how outsourcing arrangements actually work in practice. In particular the many failed ventures indicate that managing these partnerships is no trivial matter. Here, we report on an IT outsourcing venture, where interface management’s failure to take into account the needs of one of its most successful Divisions destroyed a major source of that Division’s competitive advantage – its information systems support function. We describe how that Division developed and attempted to employ a system dynamics model to protect its operations and functions. We then use a further model based on the same paradigm to illustrate how power/ political considerations meant that its efforts were always likely to fail

On the Assembly Bias of Cool Core Clusters Traced by Hα\alpha Nebulae

Do cool-core (CC) and noncool-core (NCC) clusters live in different environments? We make novel use of H$\alpha$ emission lines in the central galaxies of redMaPPer clusters as proxies to construct large (1,000's) samples of CC and NCC clusters, and measure their relative assembly bias using both clustering and weak lensing. We increase the statistical significance of the bias measurements from clustering by cross-correlating the clusters with an external galaxy redshift catalog from the Sloan Digital Sky Survey III, the LOWZ sample. Our cross-correlations can constrain assembly bias up to a statistical uncertainty of 6%. Given our H$\alpha$ criteria for CC and NCC, we find no significant differences in their clustering amplitude. Interpreting this difference as the absence of halo assembly bias, our results rule out the possibility of having different large-scale (tens of Mpc) environments as the source of diversity observed in cluster cores. Combined with recent observations of the overall mild evolution of CC and NCC properties, such as central density and CC fraction, this would suggest that either the cooling properties of the cluster core are determined early on solely by the local (<200 kpc) gas properties at formation or that local merging leads to stochastic CC relaxation and disruption in a periodic way, preserving the average population properties over time. Studying the small-scale clustering in clusters at high redshift would help shed light on the exact scenario.Comment: 17 pages, 9 figures, 2 tables, to be submitted to ApJ; comments welcom

Space Warps: I. Crowd-sourcing the Discovery of Gravitational Lenses

We describe Space Warps, a novel gravitational lens discovery service that yields samples of high purity and completeness through crowd-sourced visual inspection. Carefully produced colour composite images are displayed to volunteers via a web- based classification interface, which records their estimates of the positions of candidate lensed features. Images of simulated lenses, as well as real images which lack lenses, are inserted into the image stream at random intervals; this training set is used to give the volunteers instantaneous feedback on their performance, as well as to calibrate a model of the system that provides dynamical updates to the probability that a classified image contains a lens. Low probability systems are retired from the site periodically, concentrating the sample towards a set of lens candidates. Having divided 160 square degrees of Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) imaging into some 430,000 overlapping 82 by 82 arcsecond tiles and displaying them on the site, we were joined by around 37,000 volunteers who contributed 11 million image classifications over the course of 8 months. This Stage 1 search reduced the sample to 3381 images containing candidates; these were then refined in Stage 2 to yield a sample that we expect to be over 90% complete and 30% pure, based on our analysis of the volunteers performance on training images. We comment on the scalability of the SpaceWarps system to the wide field survey era, based on our projection that searches of 10$^5$ images could be performed by a crowd of 10$^5$ volunteers in 6 days.Comment: 21 pages, 13 figures, MNRAS accepted, minor to moderate changes in this versio

Space Warps II. New Gravitational Lens Candidates from the CFHTLS Discovered through Citizen Science

We report the discovery of 29 promising (and 59 total) new lens candidates from the CFHT Legacy Survey (CFHTLS) based on about 11 million classifications performed by citizen scientists as part of the first Space Warps lens search. The goal of the blind lens search was to identify lens candidates missed by robots (the RingFinder on galaxy scales and ArcFinder on group/cluster scales) which had been previously used to mine the CFHTLS for lenses. We compare some properties of the samples detected by these algorithms to the Space Warps sample and find them to be broadly similar. The image separation distribution calculated from the Space Warps sample shows that previous constraints on the average density profile of lens galaxies are robust. SpaceWarps recovers about 65% of known lenses, while the new candidates show a richer variety compared to those found by the two robots. This detection rate could be increased to 80% by only using classifications performed by expert volunteers (albeit at the cost of a lower purity), indicating that the training and performance calibration of the citizen scientists is very important for the success of Space Warps. In this work we present the SIMCT pipeline, used for generating in situ a sample of realistic simulated lensed images. This training sample, along with the false positives identified during the search, has a legacy value for testing future lens finding algorithms. We make the pipeline and the training set publicly available.Comment: 23 pages, 12 figures, MNRAS accepted, minor to moderate changes in this versio

A HACCP-based approach to mastitis control in dairy herds. Part 1: Development

Hazard Analysis and Critical Control Points (HACCP) systems are a risk based preventive approach developed to increase levels of food safety assurance. This is part 1 of a pilot study on the development, implementation and evaluation of a HACCP-based approach for the control of good udder health in dairy cows. The paper describes the use of a novel approach based on a deconstruction of the infectious process in mastitis to identify Critical Control Points (CCPs) and develop a HACCP-based system to prevent and control mastitis in dairy herds. The approach involved the creation of an Infectious Process Flow Diagram, which was then cross-referenced to two production process flow diagrams of the milking process and cow management cycle. The HACCP plan developed, may be suitable for customisation and implementation on dairy farms. This is a logical, systematic approach to the development of a mastitis control programme that could be used as a template for the development of control programmes for other infectious diseases in the dairy herd

Influence of Inner Shell Structure on the Encapsulation Behavior of Dexamethasone and Tacrolimus

We here present the synthesis and characterization of a set of biodegradable core–multishell (CMS) nanocarriers. The CMS nanocarrier structure consists of hyperbranched polyglycerol (hPG) as core material, a hydrophobic (12, 15, 18, 19, and 36 C-atoms) inner and a polyethylene glycol monomethyl ether (mPEG) outer shell that were conjugated by ester bonds only to reduce the toxicity of metabolites. The loading capacities (LC) of the drugs, dexamethasone and tacrolimus, and the aggregate formation, phase transitions, and degradation kinetics were determined. The intermediate inner shell length (C15) system had the best overall performance with good LCs for both drugs as well as a promising degradation and release kinetics, which are of interest for dermal deliver