X-ray colour-colour selection for heavily absorbed AGN

We present a method for the identification of heavily absorbed AGN (NH>10^23 cm^-2) from X-ray photometric data. We do this using a set of XMM-Newton reference spectra of local galaxies for which we have accurate NH information, as described in Brightman & Nandra. The technique uses two rest-frame hardness ratios which are optimised for this task, which we designate HR1 (2-4/1-2 keV) and HR2 (4-16/2-4 keV). The selection method exploits the fact that while obscured AGN appear hard in HR2 due to absorption of the intrinsic source flux below ~4 keV, they appear soft in HR1 due to excess emission originating from scattered source light, thermal emission, or host galaxy emission. Such emission is ubiquitous in low redshift samples. The technique offers a very simple and straight forward way of estimating the fraction of obscured AGN in samples with relatively low signal-to-noise ratio in the X-ray band. We apply this technique to a moderate redshift (z~1) sample of AGN from the Chandra Deep Field North, finding that 61% of this sample has NH> 10^23 cm^-2. A clear and robust conclusion from our analysis, is that in deep surveys the vast majority of sources do not show hardness ratios consistent with a simple absorbed power-law. The ubiquity of complex spectra in turn shows that simple hardness ratio analysis will not yield reliable obscuration estimates, justifying the more complex colour-colour analysis described in this paper. While this method does very well at separating sources with NH> 10^23 cm^-2 from sources with lower NH, only X-ray spectroscopy can identify Compton thick sources, through the detection of the Fe Ka line. This will be made possible with the high throughput X-ray spectral capabilities of ATHENA.Comment: 5 pages, 4 figures, accepted for publication by MNRA

Sulphur Induced Degradation of Nickel-Based Solid Oxide Fuel Cell Anodes

Solid Oxide Fuel Cells (SOFCs) are high temperature solid-state electrochemical devices that convert fuel into electricity and heat with high efficiency. Many fuels suitable for SOFCs derive from hydrocarbon sources, such as natural gas or biogas; however, these contain significant impurities, most notably compounds containing sulphur, which can poison the nickel electrocatalyst in the anode of the fuel cell. Sulphur removal is usually carried out but it is complicated and expensive to achieve levels below 1 part per million (ppm). An enhanced scientific understanding of chemical interactions on the surface of SOFC electrodes is critical to the development of robust nickel-based anodes, but the mechanisms and effects of sulphur poisoning are not fully understood. The scope of this thesis is to advance the field of sulphur-poisoning research by studying the effect of current density on the sulphur-induced degradation, and focuses on intermediate-temperature (IT) conditions with nickel-gadolinia doped ceria (Ni-CGO), which is the most promising anode material for IT-SOFCs, operating between 600–800 °C. The work of this thesis is aimed at (i) investigating the kinetics of sulphur poisoning, and the effect of current density, by use of a specially built three-electrode electrochemical test rig; (ii) analysis of structural modifications to the anode microstructure as a result of exposure to fuel cell conditions and (iii) development and prototype testing of a miniature SOFC test rig with optical access for in situ Raman spectroscopy. Fuel cell operation at higher current density was found to partially mitigate the sulphur poisoning of up to 3 ppm H2S in H2 fuel, while microstructural analysis found that the presence of as little as 0.5 ppm H2S accelerated restructuring of nickel grain surfaces. Finally, preliminary proof-of-concept results were obtained for the in situ Raman rig, and suggestions for a future design are discussed

Differential disease restriction of Moloney and Friend murine leukemia viruses by the mouse Rmcf gene is governed by the viral long terminal repeat.

Neonatal CxD2 (Rmcfr) and Balb/c (Rmcfs) mice inoculated with Moloney murine leukemia virus (M-MuLV) exhibited approximately equivalent time course and pathology for disease. CxD2 mice showed only slightly reduced presence of Moloney mink cell focus-forming virus (M-MCF) provirus as seen by Southern blot analysis compared to Balb/c mice. This lack of restriction for disease and spread of MCF was in sharp contrast to that seen for CxD2 mice inoculated with Friend murine leukemia virus (F-MuLV), where incidence of disease and propagation of MCFs were severely restricted, as previously reported. Inoculation of CxD2 mice with FM-MuLV, a recombinant F-MuLV virus containing M-MuLV LTR sequences (U3 and R), resulted in T cell disease of time course equal to that seen in Balb/c mice; there also was little restriction for propagation of MCFs. This indicated that presence of the M-MuLV long terminal repeat (LTR) was sufficient for propagation of MCFs in CxD2 mice. Differing restriction for F-MuLV vs. M-MuLV in CxD2 mice was explained on the basis of different "MCF propagator cells" for the two viruses. It was suggested that cells propagating F-MCF (e.g., erythroid progenitors) are blocked by endogenous MCF-like gp70env protein, whereas cells propagating M-MCF (e.g., lymphoid) do not express this protein on their surface. F-MuLV disease in CxD2 mice was greatly accelerated when neonates were inoculated with a F-MuLV/F-MCF pseudotypic mixture. However, F-MCF provirus was not detectable or only barely detectable in F-MuLV/F-MCF-induced tumors, suggesting that F-MCF acted indirectly in induction of these tumors

CRCJ 361-D1

A theory-based comparison of the American criminal justice system with a number of selected criminal justice systems from around the world. Emphasis will be placed on how the social organization of a specific society affects the definition of crime and the administration of justice

Constraining the fraction of Compton-thick AGN in the Universe by modelling the diffuse X-ray background spectrum

This paper investigates what constraints can be placed on the fraction of Compton-thick (CT) AGN in the Universe from the modeling of the spectrum of the diffuse X-ray background (XRB). We present a model for the synthesis of the XRB that uses as input a library of AGN X-ray spectra generated by the Monte Carlo simulations described by Brightman & Nandra. This is essential to account for the Compton scattering of X-ray photons in a dense medium and the impact of that process on the spectra of obscured AGN. We identify a small number of input parameters to the XRB synthesis code which encapsulate the minimum level of uncertainty in reconstructing the XRB spectrum. These are the power-law index and high energy cutoff of the intrinsic X-ray spectra of AGN, the level of the reflection component in AGN spectra and the fraction of CT AGN in the Universe. We then map the volume of the space allowed to these parameters by current observations of the XRB spectrum in the range 3-100 keV. One of the least constrained parameters is the fraction of CT AGN. Statistically acceptable fits to the XRB spectrum at the 68% confidence level can be obtained for CT fractions in the range 5-50%. This is because of degeneracies among input parameters to the XRB synthesis code and uncertainties in the modeling of AGN spectra (e.g. reflection). The most promising route for constraining the fraction of CT AGN in the Universe is via the direct detection of those sources in high energy (>10keV) surveys. It is shown that the observed fraction of CT sources identified in the SWIFT/BAT survey, limits the intrinsic fraction of CT AGN, at least at low redshift, to 10-20% (68% confidence level). We also make predictions on the number density of CT sources that current and future X-ray missions are expected to discover. Testing those predictions will constrain the intrinsic fraction of CT AGN as a function of redshift.Comment: To appear in A&

Trust and Distrust Approaches in the Constitutional Lawmaking of Rural Land Rights in Ethiopia: Nature, Drafting and Implications

Although rural land rights are recognized in the 1995 Constitution of the Federal Democratic Republic of Ethiopia (FDRE), the academic discourse and policy dialogues on the issue are still underway. However, these dialogues do not comprehensively cover the provisions in the Constitution concerning rural land rights, the modus operandi in the drafting approaches of the provisions and their legal implications. Hence, by analyzing the different sections and articles of the Constitution, this article seeks to examine the extent to which rural land rights are defined in the Constitution and the legal implications of its constitutional recognition. This article examines the compatibility of the approach adopted by Ethiopian Constitution makers with the Trust and Distrust approaches propounded by Rosalind Dixon for drafting of constitutional provisions on rural land rights. Dixon’s view is reviewed before considering it in relation with compatibility issues.Key termsRural land rights · Constitutional drafting · Nature of land rights · Ethiopi

Mending The Broken Bridges: An Analysis of Familyhood in Zakes Mda’s Ways of Dying (1995)

This paper examines South African literature’s paradigm shift through Zakes Mda’s disruption of the dominant trope of apartheid by his focusing on black ordinary lives in Ways of Dying. The novel foregrounds the broken bridges of love and unity that used to link families before colonisation. Mda demonstrates how the rise of the city engendered the demise of the village where blacks lived as a unified community before migrating to the city whence they sink into individualism. The discussion focuses on family units during the period of death and dying to reveal broken links that happen to have a bearing to black familyhood. The focus of the argument is on how Mda depicts and mends the lost spirit of oneness among the blacks during the final stages of the anti-apartheid struggle and the transition to a democratic South Africa. The discussion highlights a new traditional African community built on forgiveness, care and unity

The NuSTAR View of the Seyfert 2 Galaxy NGC 4388

We present analysis of NuSTAR X-ray observations in the 3-79 keV energy band of the Seyfert 2 galaxy NGC 4388, taken in 2013. The broadband sensitivity of NuSTAR, covering the Fe K$\alpha$ line and Compton reflection hump, enables tight constraints to be placed on reflection features in AGN X-ray spectra, thereby providing insight into the geometry of the circumnuclear material. In this observation, we found the X-ray spectrum of NGC 4388 to be well described by a moderately absorbed power law with non-relativistic reflection. We fit the spectrum with phenomenological reflection models and a physical torus model, and find the source to be absorbed by Compton-thin material (N$_{H} = (6.5\pm0.8)\times10^{23}$ cm$^{-2}$) with a very weak Compton reflection hump (R $<$ 0.09) and an exceptionally large Fe K$\alpha$ line (EW $= 368^{+56}_{-53}$ eV) for a source with weak or no reflection. Calculations using a thin-shell approximation for the expected Fe K$\alpha$ EW indicate that an Fe K$\alpha$ line originating from Compton-thin material presents a possible explanation.Comment: 5 pages, 2 figures. Accepted for publication in Ap

The Block Signal System

A history of the railroad system, different types of railroads, their current stopping methods and suggested stopping methods which would ensure passenger safety