Sample variance, source clustering and their influence on the counts of faint radio sources

The shape of the curves defined by the counts of radio sources per unit area as a function of their flux density was one of the earliest cosmological probes. Radio source counts continue to be an area of astrophysical interest as they can be used to study the relative populations of galaxy types in the Universe (as well as investigate any cosmological evolution in their respective luminosity functions). They are also a vital consideration for determining howsource confusion may limit the depth of a radio interferometer observation, and are essential for characterizing the extragalactic foregrounds in cosmicmicrowave background experiments. There is currently no consensus as to the relative populations of the faintest (sub-mJy) source types, where the counts show a turn-up. Most of the source count data in this regime are gathered from multiple observations that each use a deep, single pointing with an interferometric radio telescope. These independent count measurements exhibit large amounts of scatter (factors of the order of a few) that significantly exceeds their respective stated uncertainties. In this paper, we use a simulation of the extragalactic radio continuum emission to assess the level at which sample variance may be the cause of the scatter. We find that the scatter induced by sample variance in the simulated counts decreases towards lower flux density bins as the raw source counts increase. The field-to-field variations make significant contributions to the scatter in the measurements of counts derived from deep observations that consist of a single pointing, and could even be the sole cause at >100 μJy. We present a method for evaluating the flux density limit that a radio survey must reach in order to reduce the count uncertainty induced by sample variance to a specific value. We also derive a method for correcting Poisson errors on source counts from existing and future deep radio surveys in order to include the uncertainties due to the cosmological clustering of sources. A conclusive empirical constraint on the effect of sample variance at these low luminosities is unlikely to arise until the completion of future large-scale radio surveys with next-generation radio telescopes.Web of Scienc

Differences between elite and semi-elite Australian football conceptualised through the lens of ecological dynamics

This study explored the differences in match play between elite and semi-elite Australian football (AF) conceptualised through the lens of ecological dynamics. We sampled naturalistic constraints from match play across two AF competitions (elite and semi-elite) and heuristically classified them into task, environmental and individual classes. Data was extracted from 22 Australian Football League (AFL) games, and 18 semi-elite AF games, with a total of six constraints being sampled from each game. Match play within the AFL generated a greater percent of total disposals in general play within a processing time of 0–1s (d = 1.24 (0.64–1.80)), a greater opposition density surrounding the ball carrier (d = 0.82 (0.26–1.37)), and more disposals being performed while running (dynamic; d = 0.89 (0.33–1.45)). This data highlights differences with regards to the informational sources available to players across both competition standards to inform their movement choices. Specifically, a greater proportion of disposals within the AFL appear to be shaped by pronounced temporal and spatial constraints relative to a semi-elite competition. Coaches are encouraged to consider these results when developing representative training activities for both AFL and prospective AFL players

Multiple supermassive black hole systems: SKA's future leading role

Galaxies and supermassive black holes (SMBHs) are believed to evolve through a process of hierarchical merging and accretion. Through this paradigm, multiple SMBH systems are expected to be relatively common in the Universe. However, to date there are poor observational constraints on multiple SMBHs systems with separations comparable to a SMBH gravitational sphere of influence (<< 1 kpc). In this chapter, we discuss how deep continuum observations with the SKA will make leading contributions towards understanding how multiple black hole systems impact galaxy evolution. In addition, these observations will provide constraints on and an understanding of stochastic gravitational wave background detections in the pulsar timing array sensitivity band (nanoHz -microHz). We also discuss how targets for pointed gravitational wave experiments (that cannot be resolved by VLBI) could potentially be found using the large-scale radio-jet morphology, which can be modulated by the presence of a close-pair binary SMBH system. The combination of direct imaging at high angular resolution; low-surface brightness radio-jet tracers; and pulsar timing arrays will allow the SKA to trace black hole binary evolution from separations of a galaxy virial radius down to the sub-parsec level. This large dynamic range in binary SMBH separation will ensure that the SKA plays a leading role in this observational frontier.Comment: 11 pages, 4 figures. To be published in the proceedings of "Advancing Astrophysics with the Square Kilometre Array", PoS(AASKA14)151, in pres

Investigation of DNA adducts formed in cells and clinical tumour biopsies following exposure to platinum-containing anticancer drugs

Platinum-based anticancer drugs are believed to exert their action through chemical reactions with genomic DNA, forming adducts with DNA bases. Although the pharmacology of such adducts has been widely studied, the cytotoxic mechanism remains unclear. The possibility that non-DNA molecules have the potential to alter the types of adducts formed has received very little attention, and limited information is available on the levels of adducts formed in clinical tumours. Further understanding of platinum-DNA adduct formation may be important in explaining the efficacy of platinum-based drugs in different tumour types, providing insights into both the cytotoxic mechanism and the development of clinical resistance. The aims of the work described in this thesis were: a) to analyse the nature of DNA adducts formed by three clinically used platinum-based anticancer drugs and to investigate the potential intracellular formation of additional types of adducts to those previously characterised on pure DNA; b) to determine platinum-DNA adduct levels formed in solid ovarian cancer tissue following treatment of patients with carboplatin and test the hypothesis that these levels are comparable to the levels of DNA adducts formed in blood cells; and c) to determine whether sodium thiosulfate (STS), which is currently in clinical trials to protect against cisplatin-induced normal tissue toxicity, impacts on DNA adduct formation. Analysis of the properties of all DNA adducts formed in cells was made possible by analysing enzymatically digested DNA using anion exchange chromatography together with inductively-coupled plasma mass spectrometry (ICP-MS). Putative adducts involving deoxyguanosine monophosphate cross-linked via cisplatin to glutathione were prepared and the chromatographic properties determined. Studies were carried out to characterise the types of adducts formed following incubations of cisplatin with four cancer cell lines. No additional types of adducts were observed compared to those formed by the reaction of cisplatin with pure DNA. The chromatographic behaviour of adducts formed in cells incubated with carboplatin and oxaliplatin were comparable to those formed by cisplatin. This study is the first to investigate carboplatin-DNA adduct levels induced in solid tumours during therapy in patients. Total DNA adduct levels in tumour biopsies and blood cells were measured using ICP-MS with thallium as an internal standard. Tumour biopsies from all four patients studied showed clearly detectable levels of treatment-induced DNA adducts ranging from 1.9 - 4.2 nmoles Pt/g DNA. Blood cell adduct levels ranged from 0.15 – 3.5 nmoles Pt/g DNA. Both tumour and blood cell adduct levels were significantly above background measurements. No correlation was observed between adduct levels in DNA from biopsies and levels in DNA from peripheral blood cells. Concurrent incubation of four human tumour cell lines with cisplatin and STS caused greater than 2-fold decreases in total DNA adducts. Delayed administration of STS had no effect of adducts levels. STS did not appear to affect the chromatographic behaviour of DNA adducts formed in cells following incubation with cisplatin.EThOS - Electronic Theses Online ServiceCancer Research UK : BACRGBUnited Kingdo

Assessing low-maturity organic matter in shales using Raman spectroscopy : effects of sample preparation and operating procedure

Laser Raman spectroscopy is used to assess the thermal maturity of organic matter in sedimentary rocks, particularly organic-rich mudstones. However, discrepancies exist between quantified Raman spectral parameters and maturity values obtained by vitrinite reflectance. This has prevented the adoption of a standard protocol for the determination of thermal maturity of organic matter (OM) by Raman spectroscopy. We have examined the factors influencing the Raman spectra obtained from low-maturity OM in potential shale gas reservoir rocks. The inconsistencies in Raman results obtained are due to three main factors that are critically evaluated: (1) different operational procedures, including experiment setup and spectral processing methods; (2) different methods of sample preparation; (3) the analysis of diverse types of OM. These factors are scrutinized to determine the sources of inconsistency and potential bias in Raman results, and guidance is offered on the development of robust and reproducible analytical protocols. We present two new Raman parameters for un-deconvolved spectra named the DA1/GA ratio (area ratio of 1100–1400 cm−1/1550–1650 cm−1) and SSA (scaled spectrum area: sum of total area between 1100 and 1700 cm−1) that offer potential maturity proxies. An automated spreadsheet procedure is presented that processes raw Raman spectra and calculates several of the most commonly used Raman parameters, including the two new variables

Evolution of Atmospheric O2 Through the Phanerozoic, Revisited

An oxygen-rich atmosphere is essential for complex animals. The early Earth had an anoxic atmosphere, and understanding the rise and maintenance of high O2 levels is critical for investigating what drove our own evolution and for assessing the likely habitability of exoplanets. A growing number of techniques aim to reproduce changes in O2 levels over the Phanerozoic Eon (the past 539 million years). We assess these methods and attempt to draw the reliable techniques together to form a consensus Phanerozoic O2 curve. We conclude that O2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to ∼15–20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day. Evolutionary radiations in the Cambrian and Ordovician appear consistent with an oxygen driver, and the Devonian “Age of the Fishes” coincides with oxygen rising above 15% atm. ▪ An oxygen-rich atmosphere is essential for complex animals such as humans. ▪ We review the methods for reconstructing past variation in oxygen levels over the past 539 million years (the Phanerozoic Eon). ▪ We produce a consensus plot of the most likely evolution of atmospheric oxygen levels. ▪ Evolutionary radiations in the Cambrian, Ordovician, and Devonian periods may be linked to rises in oxygen concentration