The embedding of the traveling salesman problem in a Markov Decision Process

In this paper we derive a new LP-relaxation of the Traveling Salesman Problem (TSP, for short). This formulation comes from first embedding the TSP in a Markov Decision Process (MDP: for short), and from perturbing this MDP appropriately

Percentile objective criteria in limiting average Markov Control Problems

Infinite horizon Markov Control Problems, or Markov Decision Processes (MDP's, for short), have been extensively studied since the 1950's. One of the most commonly considered versions is the so-called "limiting average reward" model. In this model the controller aims to maximize the expected value of the limit-average ("long-run average") of an infinite stream of single-stage rewards or outputs. There are now a number of good algorithms for computing optimal deterministic policies in the limiting average MDP's. In this paper we adopt the point of view that there are many natural situations where the controller is interested in finding a policy that will achieve a sufficiently high long-run average reward, that is, a target level with a sufficiently high probability, that is, a percentile

Excerpts from Peter Krass's Lecture "Andrew Carnegie: Ruthless Empire Builder and Pioneering Philanthropist"

“What I came to realize about Carnegie is that he is really like a flawed Shakespearean hero… he really did consider the world a stage… and when he was on that stage he wore a variety of masks and behind each mask was a distinct character and you really could not reconcile various characters.” “He would attempt to promote himself and ideas in one direction, but practically speaking it didn’t work. You get an idea that there are these two sides to Carnegie, this idealist side and this practical man.

Warfarin use in the elderly: The nurses' perspective

Objective: To explore the barriers to warfarin use from the perspective of nurses working in aged care. Design: A qualitative study, involving a semi-structured group interview, during March-April 2001. Setting and Subjects: Eleven nurses, employed within the catchment of the Northern Sydney Area Health Service, who were involved in the care of elderly warfarinised patients. Main outcome measure: Identification, via thematic analysis, of the main themes underpinning the nursing perspective on warfarin use in this setting, with regard to their perceived role/s, experiences with patients, and potential strategies for managing the therapy. Results: Five main themes were identified: perceived patient attitude toward warfarin; barriers to the use of warfarin; expressed lack of confidence in the processes involved; nurses' role in warfarin use; and strategies to improve warfarin use. Nurses were concerned about warfarin use in the elderly, but felt they had a limited capacity to intervene. Conclusion: Nurses are potentially underutilised as a resource and support for both patients and prescribers, in the management of warfarin therapy

Balancing risk versus benefit: The elderly patient's perspective on warfarin therapy

Warfarin theraphy is underused in the target at-risk elderly population. Clinicians perceive that older patients are reluctant to use this theraphy, however the perspective of patients or their carers has yet to be explored. Objective: To explore in-depth the perspectives of elderly patients and/ or their carers regarding the use of warfarin therapy. Method: A qualitative study, using semi-structured group interviews was undertaken. The audio-taped discussions were transcribed verbatim, then thematically analysed to identify emergent themes. Group discussions were conducted at a major Sydney teaching hospital, over a 2-month period. Individuals aged 65 years or older (and/or their carers) who were using long-term (6 months) warfarin therapy were recruited by voluntary response to study flyers. Results: 17 patients and carers (mean age 77.2 SD=7.5 years) participated in one of two focus groups. Five core themes emerged regarding warfarin therapy: inadequate knowledge and understanding about it, patients/carers variable experience of information provision, cycle of reactions to being on it, issues in its practical management, and the spectrum of experiences with it. Overall, participants were very accepting of the therapy, describing a high level of compliance, despite initial fears and anxieties, and a relative lack of knowledge. Patients felt somewhat abandoned in their management of warfarin due to the lack of ongoing support services in the community, and inadequate information provision. Conclusions: Elderly patients and their carers appear to be quite accepting of warfarin therapy, in contrast to the perceptions of health care professionals. More effort is needed, however, in terms of information provision, particularly in the form of community-based services, to assist patients in the long-term management of warfarin

Management of warfarin in atrial fibrillation: Views of health professionals, older patients and their carers

Objective: To identify the views of health professionals, patients and their carers on strategies to improve the use and management of warfarin in older patients with atrial fibrillation. Design: Qualitative study based on analysis of group interviews. Setting: A major metropolitan teaching hospital, from 1 March to 30 April 2003. Participants: 14 patients (≥ 65 years) with established atrial fibrillation and taking warfarin, three carers, 12 specialists, eight general practitioners, six community pharmacists, nine hospital pharmacists, and 11 nurses volunteered in response to flyers promoting the study. Results: Suggested strategies to improve warfarin management targeted support services for GPs and patients. Hospital-based clinicians felt that dissemination of trial evidence to GPs to support treatment recommendations is required, and that GPs need to enlist allied health professionals in the management of patients taking warfarin. GPs preferred access to practical advice from expert colleagues on the day-to-day management. Patients requested more information about warfarin therapy, as access to information is inadequate, particularly from primary sources (GPs, community pharmacists). Verbal and written information are equally important, but a single counselling session or supply of a booklet was viewed as inadequate. Participants identified various interventions for all levels of warfarin management; from the collective input, a framework for management strategies was developed. Conclusions: Health professionals and patients require more customised information to support warfarin use and management

Understanding the reasons behind the low utilisation of thrombolysis in stroke

Background Thrombolysis remains the only approved therapy for acute ischaemic stroke (AIS); however, its utilisation is reported to be low. Aims This study aimed to determine the reasons for the low utilisation of thrombolysis in clinical practice. Method Five metropolitan hospitals comprising two tertiary referral centres and three district hospitals conducted a retrospective, cross-sectional study. Researchers identified patients discharged with a principal diagnosis of AIS over a 12-month time period (July 2009-July 2010), and reviewed the medical record of systematically chosen samples. Results The research team reviewed a total of 521 records (48.8% females, mean age 74.4 ±14 years, age range 5-102 years) from the 1261 AIS patients. Sixty-nine per cent of AIS patients failed to meet eligibility criteria to receive thrombolysis because individuals arrived at the hospital later than 4.5 hours after the onset of symptoms. The factors found to be positively associated with late arrival included confusion at onset, absence of a witness at onset and waiting for improvement of symptoms. However, factors negatively associated with late arrival encompassed facial droop, slurred speech and immediately calling an ambulance. Only 14.7% of the patients arriving within 4.5 hours received thrombolysis. The main reasons for exclusion included such factors as rapidly improving symptoms (28.2%), minor symptoms (17.2%), patient receiving therapeutic anticoagulation (6.7%) and severe stroke (5.5%). Conclusion A late patient presentation represents the most significant barrier to utilising thrombolysis in the acute stroke setting. Thrombolysis continues to be currently underutilised in potentially eligible patients, and additional research is needed to identify more precise criteria for selecting patients for thrombolysis

Investigating How Anticipation of Object States Drives Event Comprehension

Previous literature has suggested that, when given change of state events in a visual world paradigm task, individuals anticipate either the object that can be acted upon or the goal. This study investigated under what circumstances an individual anticipates one over the other. We used reversible action verbs (e.g. open/close), destruction verbs (e.g., eat), and creation verbs (e.g., knit) in the past and future tense to investigate how anticipation differs across these conditions. Individuals heard sentences such as The woman will open the umbrella while seeing four objects on a screen: the initial state (e.g., a closed umbrella), the end state (e.g., an open umbrella), and two distractors. The eye-tracking data showed that, for reversible action verbs and creation verbs, individuals anticipated the end state significantly more than the initial state in the past tense and future tense. For destruction verbs, no significant differences were found, but participants showed numerically more looks to the end state in the past tense and the initial state in the future tense. These results suggest that, in the past tense, individuals anticipate the goal of the action, which is also the object that can be acted on. In the future tense, individuals anticipate the goal most with fewer looks to the object that can be acted on. For the destruction verbs, the goal is not depicted, so individuals look most to the object to be acted upon