A structural approach to matching problems with preferences

This thesis is a study of a number of matching problems that seek to match together pairs or groups of agents subject to the preferences of some or all of the agents. We present a number of new algorithmic results for five specific problem domains. Each of these results is derived with the aid of some structural properties implicitly embedded in the problem. We begin by describing an approximation algorithm for the problem of finding a maximum stable matching for an instance of the stable marriage problem with ties and incomplete lists (MAX-SMTI). Our polynomial time approximation algorithm provides a performance guarantee of 3/2 for the general version of MAX-SMTI, improving upon the previous best approximation algorithm, which gave a performance guarantee of 5/3. Next, we study the sex-equal stable marriage problem (SESM). We show that SESM is W[1]-hard, even if the men's and women's preference lists are both of length at most three. This improves upon the previously known hardness results. We contrast this with an exact, low-order exponential time algorithm. This is the first non-trivial exponential time algorithm known for this problem, or indeed for any hard stable matching problem. Turning our attention to the hospitals / residents problem with couples (HRC), we show that HRC is NP-complete, even if very severe restrictions are placed on the input. By contrast, we give a linear-time algorithm to find a stable matching with couples (or report that none exists) when stability is defined in terms of the classical Gale-Shapley concept. This result represents the most general polynomial time solvable restriction of HRC that we are aware of. We then explore the three dimensional stable matching problem (3DSM), in which we seek to find stable matchings across three sets of agents, rather than two (as in the classical case). We show that under two natural definitions of stability, finding a stable matching for a 3DSM instance is NP-complete. These hardness results resolve some open questions in the literature. Finally, we study the popular matching problem (POP-M) in the context of matching a set of applicants to a set of posts. We provide a characterization of the set of popular matchings for an arbitrary POP-M instance in terms of a new structure called the switching graph exploited to yield efficient algorithms for a range of associated problems, extending and improving upon the previously best-known results for this problem

Therapeutic and educational objectives in robot assisted play for children with autism

“This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.” DOI: 10.1109/ROMAN.2009.5326251This article is a methodological paper that describes the therapeutic and educational objectives that were identified during the design process of a robot aimed at robot assisted play. The work described in this paper is part of the IROMEC project (Interactive Robotic Social Mediators as Companions) that recognizes the important role of play in child development and targets children who are prevented from or inhibited in playing. The project investigates the role of an interactive, autonomous robotic toy in therapy and education for children with special needs. This paper specifically addresses the therapeutic and educational objectives related to children with autism. In recent years, robots have already been used to teach basic social interaction skills to children with autism. The added value of the IROMEC robot is that play scenarios have been developed taking children's specific strengths and needs into consideration and covering a wide range of objectives in children's development areas (sensory, communicational and interaction, motor, cognitive and social and emotional). The paper describes children's developmental areas and illustrates how different experiences and interactions with the IROMEC robot are designed to target objectives in these areas.Final Published versio

Mirror-grating tuning arrangement for high resolution lasers

A tuning arrangement (10) for a tunable laser comprises a single holographic grating (12) and two flat surface reflective mirrors (13 and 14). The beam (15) from the laser cavity is incident on the grating at a grazing angle for optimum beam expansion. The diffracted beam propogates from the grating to the first mirror (13), therefrom to the second mirror (14) and is reflected at the Littrow angle to the grating, whereat it is diffracted a second time and returned to the second mirror (14) for reflection to the first mirror (13). Therefrom it is reflected back to the grating. After undergoing a third diffraction it is directed back into the cavity for further amplification

Towards operational measures of computer security

Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of ‘the ability of the system to resist attack’. That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit ‘more secure behaviour’ in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behaviour will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working towards measures of ‘operational security’ similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches (cf rate of occurrence of failures in reliability), or the probability that a specified ‘mission’ can be accomplished without a security breach (cf reliability function). This new approach is based on the analogy between system failure and security breach. A number of other analogies to support this view are introduced. We examine this duality critically, and have identified a number of important open questions that need to be answered before this quantitative approach can be taken further. The work described here is therefore somewhat tentative, and one of our major intentions is to invite discussion about the plausibility and feasibility of this new approach

Developing resilience: Stories from novice nurse academics

© 2016 . Background: It is acknowledged that novice nurse academics face many challenges on commencement of their new role. Most are recruited from the clinical arena, with little understanding of the academic triumvirate of teaching, research and service. They struggle with role expectation and experience feelings of isolation and anxiety. Aim: The aim of this paper is to report on an exploration of 14 new nurse academics from two major nursing education institutions as they utilised and developed resilience building strategies. Method: The paper is drawn from a qualitative study that sought to see the world through the eyes of the participants through storytelling. Data was collected using semi-structured, conversational style interviews. Interviews were audio recorded and revealed themes that captured resilience strategies. Results: These themes were: Developing supportive collegial relationships; Embracing positivity; and Reflection and transformative growth. The first theme, developing supportive relationships, provides insight into the mentoring process and the relationships developed with peers and colleagues. The second theme, embracing positivity, describes the factors that assisted them to face the adversity and challenges in the new role. The final theme, reflection and transformative growth, demonstrated participants' reflecting on difficult situations and demonstrating the ability to learn from the experiences and move forward. Conclusions: The strategies utilised by the participants in this study were key factors in the development of resilience which assisted in the transition from clinical nurse to academic. These strategies were often tacit and it is imperative that in a time of acute nurse academic shortages where retention is paramount, that employing organisations support employees and contribute to resilience development. Education on resilience building strategies is fundamental for all new academics and is essential in the transition from clinical nurse to academic

Challenges in Improving Information Security Practice in Australian General

The status of information security in Australian medical general practice is discussed together with a review of the challenges facing small practices that often lack the technical knowledge and skill to secure patient information by themselves. It is proposed that an information security governance framework is required to assist practices in identifying weaknesses and gaps and then to plan and implement how to overcome their shortcomings through policies, training and changes to processes and management structure

Late-type galaxies observed with SAURON. Two-dimensional stellar and emission-line kinematics of 18 spirals

We present the stellar and gas kinematics of a sample of 18 nearby late-type spiral galaxies (Hubble types ranging from Sb to Sd), observed with the integral-field spectrograph SAURON at the 4.2-m William Herschel Telescope. SAURON covers the spectral range 4800-5380 A, allowing us to measure the Hbeta, Fe, Mgb absorption features and the emission in the Hbeta line and the [OIII], and [NI] doublets over a 33x41 arcsec field of view. The maps cover the nuclear region of these late-type galaxies and in all cases include the entire bulge. In many cases the stellar kinematics suggests the presence of a cold inner region, as visible from a central drop in the stellar velocity dispersion. The ionised gas is almost ubiquitous and behaves in a complicated fashion: the gas velocity fields often display more features than the stellar ones, including wiggles in the zero-velocity lines, irregular distributions, ring-like structures. The line ratio [OIII]/Hbeta often takes on low values over most of the field, probably indicating a wide-spread star formation.Comment: 34 pages, 24 figures. Accepted for publication in MNRAS. A version with full resolution figures is available at http://www.strw.leidenuniv.nl/sauron/papers/ganda2005_late_types.pd