Approximate Bayesian Computation for astronomical model analysis : a case study in galaxy demographics and morphological transformation at high redshift

Approximate Bayesian Computation’ (ABC) represents a powerful methodology for the analysis of complex stochastic systems for which the likelihood of the observed data under an arbitrary set of input parameters may be entirely intractable – the latter condition rendering useless the standard machinery of tractable likelihood-based, Bayesian statistical inference [e.g. conventional Markov chain Monte Carlo (MCMC) simulation]. In this paper, we demonstrate the potential of ABC for astronomical model analysis by application to a case study in the morphological transformation of high-redshift galaxies. To this end, we develop, first, a stochastic model for the competing processes of merging and secular evolution in the early Universe, and secondly, through an ABC-based comparison against the observed demographics of massive (Mgal > 1011 M⊙) galaxies (at 1.5 < z < 3) in the Cosmic Assembly Near-IR Deep Extragalatic Legacy Survey (CANDELS)/Extended Groth Strip (EGS) data set we derive posterior probability densities for the key parameters of this model. The ‘Sequential Monte Carlo’ implementation of ABC exhibited herein, featuring both a self-generating target sequence and self-refining MCMC kernel, is amongst the most efficient of contemporary approaches to this important statistical algorithm. We highlight as well through our chosen case study the value of careful summary statistic selection, and demonstrate two modern strategies for assessment and optimization in this regard. Ultimately, our ABC analysis of the high-redshift morphological mix returns tight constraints on the evolving merger rate in the early Universe and favours major merging (with disc survival or rapid reformation) over secular evolution as the mechanism most responsible for building up the first generation of bulges in early-type discs.

Metal Skin and the cinema of noise

In traditional communication and information theory, noise is the demon Other, an unwelcome disruption in the passage of information. Noise is "anything that is added to the signal between its transmission and reception that is not intended by the source...anything that makes the intended signal harder to decode accurately". It is in Michel Serres' formulation, the "third man" in dialogue who is always assumed, and whom interlocutors continually struggle to exclude. Noise is simultaneously a condition and a by-product of the act of communication, it represents the ever present possibility of disruption, interruption, misunderstanding. In sonic or musical terms noise is cacophony, dissonance. For economists, noise is an arbitrary element, both a barrier to the pursuit of wealth and a basis for speculation. For Mick (Jeremy Sims) and his mate Kev (Ben Mendelsohn) in David Caesar's Idiot Box (1996), as for Hando (Russell Crowe) and his gang of skinheads in Geoffrey Wright's Romper Stomper (1992), or Dazey (Ben Mendelsohn) and Joe (Aden Young) in Wright's Metal Skin (1994) and all those like them starved of (useful) information and excluded from the circuit - the information poor - their only option, their only point of intervention in the loop, is to make noise, to disrupt, to discomfort, to become Serres' "third man", "the prosopopoeia of noise" (5).

Significance of drying periods on nitrate removal in experimental biofilters

Nitrogen is an important nutrient that can impact the quality of aquatic environments when present in high concentration. Even though low concentration levels of ammonium-nitrogen have been observed in laboratory studies in bioretention basins, poor removal or even the production of nitrate-nitrogen within the filter is often recorded in such studies. Ten Perspex biofilter columns of 94 mm (internal diameter) were packed with a filter layer, transition layer and a gravel layer. While the filter layer was packed to a height of 800 mm, transition and gravel layers were packed to a composite height of 220 mm and operated with simulated stormwater in the laboratory. The filter layer contained 8% organic material by weight. A free board of 350 mm provided detention storage and head to facilitate infiltration. The columns were operated with different antecedent dry days (0 d to 21 d) and constant inflow concentration at a feed rate of 100 mL/min. Samples were collected from the outflow at different time intervals, between 2 min and 150 min from the start of outflow, and were tested for nitrate-nitrogen and total organic carbon. Washoff of organic carbon from the filter layer was observed to occur for 30 min of outflow. This indicated washoff of organic carbon from the filter itself. At the same time, a very low concentration of nitrate-nitrogen was recorded at the beginning of the outflow, indicating the effective removal of nitrate-nitrogen. We conclude that the removal of nitrate-nitrogen is insignificant during the wetting phase of a rainfall event and the process of denitrification is more pronounced during the drying phase of a rainfall event. Thus intermittent wetting and drying is crucial for the removal of nitrate-nitrogen in bioretention basins.

The management of venereal disease in New South Wales, 1871 to 1916

Practical techniques to manage the dangers associated with sexually transmitted diseases have varied considerably both cross culturally and historically. Adopting a Foucauldian perspective, this article examines sociohistorical aspects of the governance of venereal disease in New South Wales between 1871 and 1916. Public debates and official documents are analysed to identify strategic shifts in practices associated with venereal disease management , especially in relation to prostitution. Particular attention is paid to the development of contagious disease legislation and its role in the regulation of venereal disease . It is argued that during the period in question, two distinct governmental regimes of disease control can be identified. In the first, medical policing managed venereal disease through the mobilisation of repressive controls, requiring the isolation and detention of polluting bodies. In the second, liberal governance adopted pedagogic practices to train populations perceived as either healthy or unhealthy. It is further argued that as liberal strategies of governance came to dominate the management of venereal disease , the association of prostitution with venereal disease began to weaken. Instead, authorities became increasingly concerned with populations whose behaviour was not traditionally linked with venereal disease , such as the young and the sexually inexperienced.

'A slap on the wrist'? The conservative agenda in Queensland, Australia

Recent amendments to youth justice legislation in Queensland include opening Children’s Court proceedings, removing the Principle of Detention as a Last Resort, facilitating transfers of 17 year-old offenders to adult prisons, instigating new bail offences, and introducing mandatory boot camp orders. This article examines the context of these changes including the inadequacies of the public policy process, and the impassioned political rhetoric imbued with simplistic slogans. This is a case study of regressive youth justice policy and the article reflects on the many causes underlying the reactive winding back of reform.

Navigating uncertainty in Australia : fostering informed citizenship through teaching controversial issues with pre-service teachers

Australia is a multicultural immigrant society created by public policy and direct state action over a period of two hundred years. It is now one of the world’s most diverse societies. However, like many nations, Australia faces challenges to managing ‘unauthorized arrivals’ who claim to be refugees. The issue of how to deal with unauthorized arrivals is controversial and highly emotive as it challenges public policy and government capacity to manage the multicultural ‘mix’ of Australia’s population. It also raises questions about border security. Given that it is impossible to discern beforehand who is a ‘proper’ refugee and who is not, claims to refugee status by unauthorised arrivals in Australia need to be tested against international convention criteria devised by the United Nations High Commissioner for Refugees (UNHCR). There are no simple solutions to controversial questions such as how and where should unauthorised arrivals, and the children accompanying them, be housed whilst their claims are investigated? Moreover, as this issue continues to prompt division and heated debate in Australian society, teachers new to the profession are often reluctant to explore it in the classroom. However, there are opportunities in national and state curriculum documents for the values dimensions of curriculum inquiries into controversial issues such as this to be addressed. For example, the most recent national statement on the goals for schooling in Australia, the Melbourne Declaration (MCEETYA, 2008), makes clear that Australian students need to be prepared for the challenges of the 21st century and to develop the capacity for innovation and complex problem-solving. The Melbourne Declaration informs the first national curriculum to be implemented in the Australian states and territories, and all other national and state initiatives. Its focus on developing active and informed citizens who can contribute to a socially cohesive society implies a capacity to deal with a range of issues associated with cultural diversity, This chapter explores the ways in which pre-service and early career teachers in one Australian state reflect upon curriculum opportunities to address controversial issues in the social sciences and history classroom. As part of their pre-service education, all the participants in this study completed a final year social science curriculum method unit that embedded a range of controversial issues, including the placement of children in Australian Immigration Detention Centres (IDCs), for investigation. By drawing from interviews and focus groups conducted with different cohorts of pre-service teachers in their final year of university study and beginning years of teaching, this chapter analyses the range of perceptions about how controversial issues can be examined in the secondary classroom as part of fostering informed citizenship. The discussion and analysis of the qualitative data in this study makes no claims for the representativeness of its findings, rather, a range of beginner teacher insights into a complex and important facet of teaching in a period of change and uncertainty is offered.

A Hybrid Queue-based Bayesian Network framework for passenger facilitation modelling

This paper presents a novel framework for the modelling of passenger facilitation in a complex environment. The research is motivated by the challenges in the airport complex system, where there are multiple stakeholders, differing operational objectives and complex interactions and interdependencies between different parts of the airport system. Traditional methods for airport terminal modelling do not explicitly address the need for understanding causal relationships in a dynamic environment. Additionally, existing Bayesian Network (BN) models, which provide a means for capturing causal relationships, only present a static snapshot of a system. A method to integrate a BN complex systems model with stochastic queuing theory is developed based on the properties of the Poisson and exponential distributions. The resultant Hybrid Queue-based Bayesian Network (HQBN) framework enables the simulation of arbitrary factors, their relationships, and their effects on passenger flow and vice versa. A case study implementation of the framework is demonstrated on the inbound passenger facilitation process at Brisbane International Airport. The predicted outputs of the model, in terms of cumulative passenger flow at intermediary and end points in the inbound process, are found to have an R2 goodness of fit of 0.9994 and 0.9982 respectively over a 10 h test period. The utility of the framework is demonstrated on a number of usage scenarios including causal analysis and ‘what-if’ analysis. This framework provides the ability to analyse and simulate a dynamic complex system, and can be applied to other socio-technical systems such as hospitals.

Cryptographic hash functions

Cryptographic hash functions are an important tool of cryptography and play a fundamental role in efficient and secure information processing. A hash function processes an arbitrary finite length input message to a fixed length output referred to as the hash value. As a security requirement, a hash value should not serve as an image for two distinct input messages and it should be difficult to find the input message from a given hash value. Secure hash functions serve data integrity, non-repudiation and authenticity of the source in conjunction with the digital signature schemes. Keyed hash functions, also called message authentication codes (MACs) serve data integrity and data origin authentication in the secret key setting. The building blocks of hash functions can be designed using block ciphers, modular arithmetic or from scratch. The design principles of the popular Merkle–Damgård construction are followed in almost all widely used standard hash functions such as MD5 and SHA-1.

FaceXpress : an integrated software suite for facial emotion stimulus manipulation and facial measurement

The characterisation of facial expression through landmark-based analysis methods such as FACEM (Pilowsky & Katsikitis, 1994) has a variety of uses in psychiatric and psychological research. In these systems, important structural relationships are extracted from images of facial expressions by the analysis of a pre-defined set of feature points. These relationship measures may then be used, for instance, to assess the degree of variability and similarity between different facial expressions of emotion. FaceXpress is a multimedia software suite that provides a generalised workbench for landmark-based facial emotion analysis and stimulus manipulation. It is a flexible tool that is designed to be specialised at runtime by the user. While FaceXpress has been used to implement the FACEM process, it can also be configured to support any other similar, arbitrary system for quantifying human facial emotion. FaceXpress also implements an integrated set of image processing tools and specialised tools for facial expression stimulus production including facial morphing routines and the generation of expression-representative line drawings from photographs.

Making the fun stop : youth justice reform in Queensland

In 2013 the newly elected conservative Liberal National Party government instigated amendments to the Youth Justice Act 1992 (Qld). Boot camps replaced court ordered youth justice conferencing. In 2014 there were more drastic changes, including opening the Children’s Court proceedings to the public, permitting publication of identifying information of repeat offenders, removing the principle of ‘detention as a last resort’, facilitating prompt transferral of 17 year olds to adult prisons and instigating new bail offences and mandatory boot camp orders for recidivist motor vehicle offenders in Townsville. This article compares these amendments to the legislative frameworks in other jurisdictions and current social research. It argues that these amendments are out of step with national and international best practice benchmarks for youth justice. Early indications are that Indigenous children are now experiencing increased rates of unsentenced remand. The article argues that the government’s policy initiatives are resulting in negative outcomes and that early and extensive evaluations of these changes are essential.

The suffix-free-prefix-free hash function construction and its indifferentiability security analysis

In this paper, we observe that in the seminal work on indifferentiability analysis of iterated hash functions by Coron et al. and in subsequent works, the initial value (IV) of hash functions is fixed. In addition, these indifferentiability results do not depend on the Merkle–Damgård (MD) strengthening in the padding functionality of the hash functions. We propose a generic n -bit-iterated hash function framework based on an n -bit compression function called suffix-free-prefix-free (SFPF) that works for arbitrary IV s and does not possess MD strengthening. We formally prove that SFPF is indifferentiable from a random oracle (RO) when the compression function is viewed as a fixed input-length random oracle (FIL-RO). We show that some hash function constructions proposed in the literature fit in the SFPF framework while others that do not fit in this framework are not indifferentiable from a RO. We also show that the SFPF hash function framework with the provision of MD strengthening generalizes any n -bit-iterated hash function based on an n -bit compression function and with an n -bit chaining value that is proven indifferentiable from a RO.

Cryptanalysis of Tav-128 Hash Function

Many RFID protocols use cryptographic hash functions for their security. The resource constrained nature of RFID systems forces the use of light weight cryptographic algorithms. Tav-128 is one such 128-bit light weight hash function proposed by Peris-Lopez et al. for a low-cost RFID tag authentication protocol. Apart from some statistical tests for randomness by the designers themselves, Tav-128 has not undergone any other thorough security analysis. Based on these tests, the designers claimed that Tav-128 does not posses any trivial weaknesses. In this article, we carry out the first third party security analysis of Tav-128 and show that this hash function is neither collision resistant nor second preimage resistant. Firstly, we show a practical collision attack on Tav-128 having a complexity of 237 calls to the compression function and produce message pairs of arbitrary length which produce the same hash value under this hash function. We then show a second preimage attack on Tav-128 which succeeds with a complexity of 262 calls to the compression function. Finally, we study the constituent functions of Tav-128 and show that the concatenation of nonlinear functions A and B produces a 64-bit permutation from 32-bit messages. This could be a useful light weight primitive for future RFID protocols.

Further development of discrete computational techniques for calculation of restricted diffusion propagators in porous media

Magnetic resonance is a well-established tool for structural characterisation of porous media. Features of pore-space morphology can be inferred from NMR diffusion-diffraction plots or the time-dependence of the apparent diffusion coefficient. Diffusion NMR signal attenuation can be computed from the restricted diffusion propagator, which describes the distribution of diffusing particles for a given starting position and diffusion time. We present two techniques for efficient evaluation of restricted diffusion propagators for use in NMR porous-media characterisation. The first is the Lattice Path Count (LPC). Its physical essence is that the restricted diffusion propagator connecting points A and B in time t is proportional to the number of distinct length-t paths from A to B. By using a discrete lattice, the number of such paths can be counted exactly. The second technique is the Markov transition matrix (MTM). The matrix represents the probabilities of jumps between every pair of lattice nodes within a single timestep. The propagator for an arbitrary diffusion time can be calculated as the appropriate matrix power. For periodic geometries, the transition matrix needs to be defined only for a single unit cell. This makes MTM ideally suited for periodic systems. Both LPC and MTM are closely related to existing computational techniques: LPC, to combinatorial techniques; and MTM, to the Fokker-Planck master equation. The relationship between LPC, MTM and other computational techniques is briefly discussed in the paper. Both LPC and MTM perform favourably compared to Monte Carlo sampling, yielding highly accurate and almost noiseless restricted diffusion propagators. Initial tests indicate that their computational performance is comparable to that of finite element methods. Both LPC and MTM can be applied to complicated pore-space geometries with no analytic solution. We discuss the new methods in the context of diffusion propagator calculation in porous materials and model biological tissues.

Hosting an asylum seeker in Australia: A nationwide exploratory study

In recent years, there has been a rise in the number of people seeking asylum in Australia, resulting in over-crowded detention centres in various parts of the country. Appropriate management and assistance of asylum seekers has been an issue of major socio-political concern. In mid-2012, the Australian ruling government introduced a ‘first of its kind’ community placement initiative, which involved relocating low-risk asylum seekers from detention centres to homes of those Australian families who volunteered for this program. The present study investigated host families’ motivations for volunteering into this scheme and their resulting experiences. Twenty-four men and women from all over Australia were interviewed in person or over the telephone. Consistent with theoretical frameworks of altruism, acculturation, and intergroup contact, thematic analysis indicated participants’ interest in diversity/humanitarian issues were major factors that motivated them to host asylum seekers. Language and cultural barriers were reported as challenges, but generally, participants found the experience positive and rewarding. The initiative was regarded as an excellent avenue of learning about new cultures. The hosts played a strong role in promoting the English language proficiency and intercultural settlement of the asylum seekers. The scheme was considered as one way of diffusing fear/biases against asylum seekers prevalent amongst the Australian community at-large. Participants also provided suggestions to improve the scheme.

‘Only a pawn in their game’ : crime, risk and politics in the case of Robert Fardon

In 2003 Robert Fardon was the first prisoner to be detained under the Dangerous Prisoners (Sexual Offenders) Act 2003 (Qld), the first of the new generation preventive detention laws enacted in Australia and directed at keeping sex offenders in prison or under supervision beyond the expiry of their sentences where a court decides, on the basis of psychiatric assessments, that unconditional release would create an unacceptable risk to the community. A careful examination of Fardon’s case shows the extent to which the administration of the regime was from the outset governed by politics and political calculation rather than the logic of risk management and community protection. In 2003 Robert Fardon was the first person detained under the Dangerous Prisoners (Sexual Offenders) Act 2003 (Qld) (hereafter DPSOA), a newly enacted Queensland law aimed at the preventive detention of sex offenders. It was the first of a new generation of such laws introduced in Australia, now also in force in NSW, Western Australia and Victoria. The laws have been widely criticized by lawyers, academics and others (Keyzer and McSherry 2009; Edgely 2007). In this article I want to focus on the details of how the Queensland law was administered in Fardon’s case, he being perhaps the most well-known prisoner detained under such laws and certainly the longest held. It will show, I hope, that seemingly abstract rule of law principles invoked by other critics are not simply abstract: they afford a crucial practical safeguard against the corruption of criminal justice in which the ends both of community protection and of justice give way to opportunistic exploitation of ‘the mythic resonance of crime and punishment for electoral purposes’ (Scheingold 1998: 888).