Statistical comparison of clouds and star clusters

The extent to which the projected distribution of stars in a cluster is due to a large-scale radial gradient, and the extent to which it is due to fractal sub-structure, can be quantified -- statistically -- using the measure ${\cal Q} = \bar{m}/\bar{s}$. Here $\bar{m}$ is the normalized mean edge length of its minimum spanning tree (i.e. the shortest network of edges connecting all stars in the cluster) and $\bar{s}$ is the correlation length (i.e. the normalized mean separation between all pairs of stars). We show how ${\cal Q}$ can be indirectly applied to grey-scale images by decomposing the image into a distribution of points from which $\bar{m}$ and $\bar{s}$ can be calculated. This provides a powerful technique for comparing the distribution of dense gas in a molecular cloud with the distribution of the stars that condense out of it. We illustrate the application of this technique by comparing ${\cal Q}$ values from simulated clouds and star clusters.Comment: Accepted 2010 October 27. Received 2010 October 25; in original form 2010 September 13 The paper contains 7 figures and 2 table

Ransomware and reputation

open access articleRansomware is a particular form of cyber-attack in which a victim loses access to either his electronic device or files unless he pays a ransom to criminals. A criminal’s ability to make money from ransomware critically depends on victims believing that the criminal will honour ransom payments. In this paper we explore the extent to which a criminal can build trust through reputation. We demonstrate that there are situations in which it is optimal for the criminal to always return the files and situations in which it is not. We argue that the ability to build reputation will depend on how victims distinguish between different ransomware strands. If ransomware is to survive as a long term revenue source for criminals then they need to find ways of building a good reputation

Phase Transitions for Random Walk Asymptotics on Free Products of Groups

Suppose we are given finitely generated groups $\Gamma_1,...,\Gamma_m$ equipped with irreducible random walks. Thereby we assume that the expansions of the corresponding Green functions at their radii of convergence contain only logarithmic or algebraic terms as singular terms up to sufficiently large order (except for some degenerate cases). We consider transient random walks on the free product {$\Gamma_1 \ast ... \ast\Gamma_m$} and give a complete classification of the possible asymptotic behaviour of the corresponding $n$-step return probabilities. They either inherit a law of the form $\varrho^{n\delta} n^{-\lambda_i} \log^{\kappa_i}n$ from one of the free factors $\Gamma_i$ or obey a $\varrho^{n\delta} n^{-3/2}$-law, where $\varrho<1$ is the corresponding spectral radius and $\delta$ is the period of the random walk. In addition, we determine the full range of the asymptotic behaviour in the case of nearest neighbour random walks on free products of the form $\Z^{d_1}\ast ... \ast \Z^{d_m}$. Moreover, we characterize the possible phase transitions of the non-exponential types $n^{-\lambda_i}\log^{\kappa_i}n$ in the case $\Gamma_1\ast\Gamma_2$.Comment: 32 page

What Made the Ratman Sick?

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Respite and repair: how mothers of incarcerated long-term problematic drug users make prison work for them

This article considers the way a group of mothers experienced the incarceration of their problematic drug using offspring. The offspring had been imprisoned for a range of offences including theft, burglary and drug dealing with the root cause of their incarceration being connected to their long-term problematic drug use. Much of the existing literature on imprisonment identifies the separation of offenders from their family as a source of strain both for the offender and the family, with separation being one of the pains of imprisonment described in the literature. However, in contrast to this, the evidence gathered during the research that this article is based upon, highlights how the mothers of problematic drug users sought to use the periods of time their offspring were in prison as respite from their difficult and time-consuming caring responsibilities. Furthermore, the time their offspring were incarcerated was used to repair fractured relationships

Researching difficult-to-reach and vulnerable groups using grounded theory methods

This case study describes a research project that used grounded theory methods. The aim of this research was to develop new knowledge about how parents experience their offspring’s problematic drug use. Unstructured interviews were used during the data-gathering phase of the research, and data were collected in two distinct periods. The case study is divided into four sections. Section 1 outlines the approaches used to find and recruit research participants. This section also describes how I engaged with the participants in ways that I hoped would encourage participation and build a rapport. Section 2 outlines significant life events that some of the research participants experienced and the importance of working sensitively with vulnerable participants and how this can contribute to your research endeavor. This section also highlights some of the ethical issues that need to be negotiated during the fieldwork phase of a research project. Section 3 describes the methods used during the data collection and data analysis stages of the project. The processes involved are broken down with each stage being explained. The process is presented as a linear model; however, in grounded theory, it is possible to move back and forth between stages, and the benefits this may bring are explained in this section. Finally, Section 4 offers a reflexive account of the research journey. Reflexivity is an important aspect of qualitative research and this section highlights why it is important

Planning for the End of Life for People with Dementia - Part 2

This publication is a discussion about additional end-of-life options which may become legally available at some time in the future, i.e., assisted death (usually called euthanasia or assisted suicide). Alzheimer's Australia is not advocating that such options become available and takes a neutral position about them. However, there is a need for an informed debate on the issues, given that well-conducted research indicates that a significant proportion of the community supports making such options available.Some people believe that they should have the right to make decisions about their own bodies and about the way they die; in other casespeople see the current legal and medical options as inadequate. While Australia was the first place in the world to pass legislation allowing both euthanasia and physician-assisted suicide (i.e. the Northern Territory Rights of the Terminally Ill Act (1995)), that legislation was overturned by the Commonwealth's Euthanasia Laws Act (1997) and at present these options are illegal throughout Australia. However, given that assisted dying Bills are regularly presented to state/territory parliaments in Australia it is possible that, at some time in the future, legislation will be passed that allows such options. It is therefore important for the arguments for and against assisted dying to be understood and for open debate to be encouraged. We hope that the information provided in this document will contribute to that debate.Section 2 of Part 2 asks: What is doctor-assisted dying*? and identifies what isand what is not euthanasia. In Section 3, arguments for and against doctor-assisted dying are provided and in Section 4 some issues which relate specifically to assisted dying for people with dementia are considered