Tree LANS with collision avoidance : protocol, switch architecture, and performance

Packet collisions and their resolution create a performance bottleneck in random access LANs. A hardware solution to this problem is to use collision avoidance switches. These switches allow the implementation of random access protocols without the penalty of collisions among packets. We review and compare the designs of some tree LANs that use collision avoidance switches. They have the potential of combining the benefits of random access (low delay when traffic is light, simple and distributed, and therefore robust, protocols) with excellent network utilization and concurrency of transmission. The collision avoidance LANs we review are broadcast star, Hubnet-like tree, Tinker-Tree, and a treenet that allows concurrent broadcasts within non-intersecting subtrees. After this review, we present a slotted-time, infinite user analysis of the broadcast star network

Longitudinal investigation of medical student perceptions of a video-based guided study resource used to facilitate an eight week module in medicine

We use an action research approach to evaluate three successive cohorts of medical student perceptions of using a multi-faceted video-based guided study resource which provides academic (skills-based), social (motivation-based) and professional (clinical-based) interventions aimed at facilitating and enriching learning across an eight week module in the second year of the MBChB medical degree. Our findings show that whilst students value these video resources both as a revision tool and an aid to learning during the semester, they have specific critiques about several areas which would improve the project. We interpret our data to evidence a tangible beneficial argument for the use video-based learning objects to support student learning that is reliably reaffirmed by our longitudinal data

Early changes in credibility of therapies offered in child and family work

The aim of the research was to quantify some changes in families' beliefs about therapies that can occur very early on in the therapeutic relationship (Hardy et al, 1995). Brief descriptions were developed of the three main therapies offered at a child and family clinic to help families with reported difficulties with their children. Prior to being seen for an assessment interview, 33 mothers and 18 fathers rated the credibility of each of the therapy types by reading therapy descriptions and answering questions adapted from Borkovec & Nau (1972) in a postal questionnaire. Psychological mindedness was also assessed by administering a questionnaire adapted from Conte et al.'s (1990) Psychological Mindedness Scale. The credibility of the therapies was re-assessed by each mother and father immediately after the assessment interview using the same measure. At the same time, the main therapist involved in the interview also assessed the credibility of the therapies, according to how suitable they felt each of the therapies would be for the family just seen. The direction of changes in beliefs was measured, to see if there was a convergence towards the therapists' beliefs, as Atkinson et al. (1991) had shown. The research also investigated whether psychological mindedness affected the convergence of beliefs. The main finding was that mothers' therapy ratings all increased after assessment, significantly so for parent and family therapies. Some evidence was also found that mothers' therapy ratings began to converge towards those of the therapists - Mothers rated child therapy highest before assessment and then lowest after assessment. This change corresponded with the therapists' ratings since the therapists rated child therapy significantly lower than the other two therapies. - The group of more psychologically-minded mothers were significantly more pro-therapies than the other mothers. Finally, the therapists who assessed the more psychologically-minded mothers were more optimistic about the benefits of therapy for them than for the other mothers

Does the cap fit? The case for contextualised Initial Teacher Training for vocational teachers

This case study of UK teacher-training for vocational trainers highlights the tensions between the professionalization of the teaching workforce and the skills and expectations of vocational trainers

Integration of physiological responses of crustaceans to environmental challenge

Brachyuran crustaceans are useful models for physiological studies because of their intermediate size and since they occupy a spectrum of habitats requiring widely varied behaviour. In this paper we examine the physiological responses to environmental fluctuations, extremes of habitat and consequent behaviours, with special emphasis on the adoption of air-breathing. It is established that metabolic end products such as lactate, intermediates including urate, and monoamine and peptide neurohormones can have important regulatory roles. These include effects on ventilation and heart function, blood perfusion, respiratory gas transport, as well as water and salt homeostasis providing an integrated suite of control mechanisms to regulate responses to environmental or behaviourally induced stress. A separate body of work has long suggested that the regulation of energy metabolism and provision of metabolic fuel for glycolysis is influenced by similar effectors. Most recently, metabolic end-products have been implicated as effectors of behaviour and thereby metabolic state. Thus, there is strong, emerging evidence for integration of physiological control mechanisms at the organismal level. We present new information, both mechanistic and from eco-physiological laboratory simulations, and from field studies of terrestrial crabs, that strengthens and extends the scope of this integration. Branchial chamber ventilation, cardiovascular function, relative perfusion of gills v. lungs, gas transport in the blood, the mobilisation of energy reserves, ion transport and water balance are all apparently influenced by similar messengers which coordinate and optimise these functions to meet specific requirements

On the Transition and Migration of Flight Functions in the Airspace System

Since ~400 BC, when man first replicated flying behavior with kites, up until the turn of the 20th century, when the Wright brothers performed the first successful powered human flight, flight functions have become available to man via significant support from man-made structures and devices. Over the past 100 years or so, technology has enabled several flight functions to migrate to automation and/or decision support systems. This migration continues with the United States NextGen and Europe s Single European Sky (a.k.a. SESAR) initiatives. These overhauls of the airspace system will be accomplished by accommodating the functional capabilities, benefits, and limitations of technology and automation together with the unique and sometimes overlapping functional capabilities, benefits, and limitations of humans. This paper will discuss how a safe and effective migration of any flight function must consider several interrelated issues, including, for example, shared situation awareness, and automation addiction, or over-reliance on automation. A long-term philosophical perspective is presented that considers all of these issues by primarily asking the following questions: How does one find an acceptable level of risk tolerance when allocating functions to automation versus humans? How does one measure or predict with confidence what the risks will be? These two questions and others will be considered from the two most-discussed paradigms involving the use of increasingly complex systems in the future: humans as operators and humans as monitors