A Critical Audit of Accuracy and Demographic Biases within Toxicity Detection Tools

The rise of toxicity and hate speech on social media has become a cause for concern due to their effects on politics and the growth of extremist internet communities. The tools currently used to identify and eliminate harmful content have received widespread criticism from both the public and the academic community for their inaccuracies and biases. In our research, we set out to audit the performance of Perspective API, a toxicity detector created by research teams at Google and Jigsaw, on the language of users across a variety of demographic categories. We draw from Crenshaw\u27s framework of intersectionality to discuss the unique harms that result from existing at the intersections of marginalization and examine existing computational models of disparate impact and proxy discrimination. In addition, we conduct A/B testing on Amazon\u27s Mechanical Turk, a popular crowd-sourcing platform for data annotation within research communities, to identify and discuss biases that arise from human demographic prediction

X-ray Studies of the Innermost Regions of Black Hole Accretion

In this thesis, I present the results of my research on the X-ray spectra of accreting black holes. The content of this thesis can be broadly separated into two parts: Chapter 2-3 for stellar-mass black holes in X-ray binaries (XRBs) and Chapter 4-6 for supermassive black holes in active galactic nuclei (AGN). This work mainly focuses on the X-ray spectral shape and the spectral variability of these accreting black hole systems. By studying the broad band spectra of XRBs and AGN, we are able to extract some information about the innermost regions of the discs from their X-ray observations. For example, we are able to 1) constrain the size of the coronal region that illuminates the disc; 2) estimate some properties of the discs, such as the density in the disc surface; 3) measure the spin parameters of the accreting black holes. In the meantime, I also study the variability of the innermost regions by comparing different observations or different flux states of individual sources. For example, Chapter 2-3 compare different accretion states of black hole XRBs. Chapter 4 discusses the extreme and fast flux variability on a timescale less than one kilo-second in the narrow-line Seyfert 1 galaxy IRAS 13224−3809. Chapter 5 studies the long-term spectral variability of the Seyfert 1 galaxy 1H0419−577. The main spirit of this thesis is to test for high density discs. A disc reflection model with a variable disc density parameter is used for each source in this work. In the last chapter, I apply the same model to a large sample of Seyfert 1 galaxies in order to compare the disc densities at different black hole mass scales and different accretion rates.Cambridge Trust Chinese Scholarship Counci

Testing the Kerr black hole hypothesis: comparison between the gravitational wave and the iron line approaches

The recent announcement of the detection of gravitational waves by the LIGO/Virgo collaboration has opened a new window to test the nature of astrophysical black holes. Konoplya & Zhidenko have shown how the LIGO data of GW 150914 can constrain possible deviations from the Kerr metric. In this letter, we compare their constraints with those that can be obtained from accreting black holes by fitting their reflected X-ray spectrum, the so-called iron line method. We simulate observations with eXTP, a next generation X-ray mission, finding constraints much stronger than those obtained by Konoplya & Zhidenko. Our results can at least show that, contrary to what is quite commonly believed, it is not obvious that gravitational waves are the most powerful approach to test strong gravity. In the presence of high quality data and with the systematics under control, the iron line method may provide competitive constraints.Comment: 5 pages, 3 figures. v2: updated some references as in the published versio

The Ultra-Fast Outflow of WKK 4438: Suzaku and NuSTAR X-ray Spectral Analysis

Previous X-ray spectral analysis has revealed an increasing number of AGNs with high accretion rates where an outflow with a mildly relativistic velocity originates from the inner accretion disk. Here we report the detection of a new ultra-fast outflow (UFO) with a velocity of $v_{\rm out}=0.319^{+0.005}_{-0.008}c$ in addition to a relativistic disk reflection component in a poorly studied NLS1 WKK~4438, based on archival \nustar and \suzaku observations. The spectra of both \suzaku and \nustar observations show an Fe~\textsc{xxvi} absorption feature and the \suzaku data also show evidence for an Ar~\textsc{xviii} with the same blueshift. A super-solar argon abundance ($Z^{\prime}_{\rm Ar}>6Z_{\odot}$) and a slight iron over-abundance ($Z^{\prime}_{\rm Fe}=2.6^{+1.9}_{-2.0}Z_{\odot}$) are found in our spectral modelling. Based on Monte-Carlo simulations, the detection of the UFO is estimated to be around at 3$\sigma$ significance. The fast wind most likely arises from a radius of $\geq20r_g$ away from the central black hole. The disk is accreting at a high Eddington ratio ($L_{\rm bol}=0.4-0.7L_{\rm Edd}$). The mass outflow rate of the UFO is comparable with the disk mass inflow rate ($\dot M_{\rm out}>30\%\dot M_{\rm in}$), assuming a maximum covering factor. The kinetic power of the wind might not be high enough to have influence in AGN feedback ($\dot E_{\rm wind}/L_{\rm bol}\approx 3-5\%$) due to a relatively small column density ($12^{+9}_{-4}\times10^{22}$~cm$^{-2}$). However note that both the inferred velocity and the column density could be lower limits owing to the low viewing angle ($i=23^{+3}_{-2}$$^{\circ}$).Comment: 7 pages, 3 figures, accepted by MNRA