MFS: an Adaptive Distributed File System for Mobile Hosts

Mobility is a critical feature of computer systems, and while wireless networks are common, most applications that run on mobile hosts lack flexible mechanisms for data access in an environment with large and frequent variations in network connectivity. Such conditions arise, for example, in collaborative work applications, particularly when wireless and wired users share files or databases. In this paper, we describe some techniques for adapting data access to network variability in the context of MFS, a client cache manager for a distributed file system. We show how MFS is able to adapt to widely varying bandwidth levels through the use of modeless adaptation, and evaluate the benefit of mechanisms for improving file system performance and cache consistency using microbenchmarks and file system traces

The trade-off between taxi time and fuel consumption in airport ground movement

Environmental impact is a very important agenda item in many sectors nowadays, which the air transportation sector is also trying to reduce as much as possible. One area which has remained relatively unexplored in this context is the ground movement problem for aircraft on the airport’s surface. Aircraft have to be routed from a gate to a runway and vice versa and it is still unknown whether fuel burn and environmental impact reductions will best result from purely minimising the taxi times or whether it is also important to avoid multiple acceleration phases. This paper presents a newly developed multi-objective approach for analysing the trade-off between taxi time and fuel consumption during taxiing. The approach consists of a combination of a graph-based routing algorithm and a population adaptive immune algorithm to discover different speed profiles of aircraft. Analysis with data from a European hub airport has highlighted the impressive performance of the new approach. Furthermore, it is shown that the trade-off between taxi time and fuel consumption is very sensitive to the fuel-related objective function which is used

'A light in a very dark place' : The role of a voluntary organisation providing support for those affected by encephalitis

Voluntary organisations are seen as contributing to the ‘democratisation’ of health and social care. Little, however, is written about their role and this paper, by focusing on the work of The Encephalitis Society, provides insights into the challenges facing voluntary organisations as they manage twin roles as service providers and advocates, of people with neurological disorders. Two studies are presented: a review conducted by the Society, focusing on patient’s experiences of neurological services; and an external evaluation of the Society’s current provision. The first, based on a postal survey of its members affected by encephalitis (n = 339), illustrates the Society’s advocacy role. The survey provided support for the Association of British Neurologists’ recommendation for nationally agreed standards of care. The second study, a postal survey of recent contacts (n = 76) and in-depth telephone interviews (n = 22), illustrates the Society’s value role as a service provider and supports its role in helping rehabilitate affected individuals and their families. These studies provided the Society with information for policy and service development. Importantly, providing the basis of informed action and partnership with stakeholders and informing the organisation’s sense of purpose, in the changing context of welfare provision in the UK

A comparison of published criteria for assuming attainment of adult height in girls who have received growth hormone treatment

At least six different criteria to assume attainment of adult height in girls who have received growth hormone (GH) treatment have been published in the literature. The aim of this study was to assess whether, if applied to the same population, different criteria for assuming adult height would produce the same outcome

Bulletin No. 97 - Report on the Southern Utah Experiment Station

When, in the early part of the year 1905 , the management of the Southern Utah Experiment Farm was turned over to the officials of the Utah Agricultural Experiment Station, in compliance with an act of the legislature of that year a number of experiments were under way, principally variety tests with orchard and small fruit. The State Board of Horticulture had been in charge of this farm since its establishment in 1899, and had succeeded in making out of it not only a place that will indicate the varieties of fruits adapted to that climate and soil , but also a farm that in neatness and careful arrangement can be an instructive model to anyone contemplating engaging in that industry. The new management decided not to make any radical change in the tests that were under way , but to continue them to such a conclusion a will yield the valuable results that were to come out of them. New tests or investigations are to be started with the same crop without interfering with them as variety tests, and upon the ground still available or which has not yet been set out into orchard, vineyard, or other permanent crops. Such it is planned to do as the problems suggest themselves, and as means are available

Addressing key issues in the consanguinity-related risk of autosomal recessive disorders in consanguineous communities: lessons from a qualitative study of British Pakistanis

Currently there is no consensus regarding services required to help families with consanguineous marriages manage their increased genetic reproductive risk. Genetic services for communities with a preference for consanguineous marriage in the UK remain patchy, often poor. Receiving two disparate explanations of the cause of recessive disorders (cousin marriage and recessive inheritance) leads to confusion among families. Further, the realisation that couples in non-consanguineous relationships have affected children leads to mistrust of professional advice. British Pakistani families at-risk for recessive disorders lack an understanding of recessive disorders and their inheritance. Such an understanding is empowering and can be shared within the extended family to enable informed choice. In a three-site qualitative study of British Pakistanis, we explored family and health professional perspectives on recessively inherited conditions. Our findings suggest, first, that family networks hold strong potential for cascading genetic information, making the adoption of a family centred approach an efficient strategy for this community. However, this is dependent on provision of high quality and timely information from health care providers. Secondly, families’ experience was of ill-coordinated and time-starved services, with few having access to specialist provision from Regional Genetics Services; these perspectives were consistent with health professionals’ views of services. Thirdly, we confirm previous findings that genetic information is difficult to communicate and comprehend, further complicated by the need to communicate the relationship between cousin marriage and recessive disorders. A communication tool we developed and piloted is described and offered as a useful resource for communicating complex genetic information

Investigating novel synthesis, optical properties and applications of model 2D semiconducting nanocrystals

The successful synthesis of graphene and other atomically thin materials in 2004 marked the beginning of a period of intense research into atomically thin materials that continues to this day. A wide range of these two dimensional (2D) materials have been explored that demonstrate many novel properties. Of this new family of materials, 2D semiconducting transition metal dichalcogenides (TMDs) such as molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are especially important, owing to their potential for applications including catalysis and novel electronic and optical devices. The transition of these materials from indirect to direct band gap with the change from bulk material to monolayer is just one example of the emergence of new properties. For these reasons, research into these 2D semiconducting materials has been a particularly active area of materials science in recent years. Similarly, transition metal oxides (TMOs) have proven potential for novel applications when reduced to the monolayer, and much research has been, and continues to be, conducted on these materials. The potential for production of large-area 2D stannous oxide (SnO) has been highlighted in recent works, inspiring investigations into viable synthesis methods for the material. 2D SnO promises great potential in sensing, catalysis and transistor technology, provided a successful method of production is available. With these challenges in mind, the author addresses several important aspects of model semiconducting 2D TMDs and TMOs in this Ph.D. thesis. In the first stage of the thesis, the author addressed the existing ambiguity in reported explanations for the emergence of high-intensity emission at the edges of 2D WS2 flakes. The two main arguments were that these bright edges are the result of either differing exciton/trion concentration ratios across the 2D WS2 flake area, or the intercalation of H2O between the flake edges and the substrate. This work explains that this is the result of both ambient air H2O intercalation and exciton-dominated emission at these regions, rather than one of these factors alone. Additionally, in the process of this investigation, a previously not defined phenomenon of photoluminescence (PL) loss following high radiant exposure from an incident laser was discovered. The phenomenon was thoroughly investigated, and was found to occur only when laser exposure takes place in ambient conditions, resulting in the formation of sulphate groups on the 2D WS2 surface. In the second stage, an investigation into methods for producing hybrid 2D WS2 based nanosheets was carried out. Although the enhancement of the photocatalytic properties of 2D WS2, when hybridised with graphitic carbon dots (CDs), had been investigated to a degree, no studies had yet examined the origin of the photocatalytic effect. Another issue was the synthesis that relied on liquid phase exfoliation, In the established techniques for liquid phase exfoliation of 2D WS2, the existence of solvent residues on the nanoflake surfaces was a main challenge. High quality hybridisation requires pristine, non-functionalised surfaces. A solution to this challenge was demonstrated by the liquid phase ultrasonic exfoliation of bulk WS2 powder in a 35% H2O/ethanol solution. By limiting exposure of WS2 to H2O and ethanol only, presence of solvent residues on the exfoliated 2D WS2 was kept to a minimum. Having achieved this, hybrid nanomaterial synthesis was able to proceed. Attempts to produce a hybrid nanomaterial by creating 2D WS2 and CDs separately and later combining them failed to achieve the necessary bonding between the two components. To solve this problem, the author developed a novel method of CD hybridisation by the addition of citric acid to the 35% H2O/ethanol solution, containing exfoliated 2D WS2, and microwaving this solution to grow CDs on 2D WS2 surfaces. The resulting hybrid nanomaterial was found to have a photocatalytic efficiency approximately 30% higher than that of pristine 2D WS2, and a comparison with similar recently produced photocatalytic 2D TMDs and their hybrid nanomaterials showed this hybrid to have a significantly higher turnover frequency. In the final stage, the large-scale synthesis of 2D SnO using a novel method started from molten tin was explored. Recently reported methods of oxide exfoliation from liquid bulk metal were adapted for the synthesis of 2D SnO, and was shown to allow for the creation of very large scale 2D films of SnO. TMOs have been reported as having a superior stability in air relative to that of 2D TMDs, and could be useful in filling roles for which 2D TMDs are not optimally suited. 2D SnO , as a 2D TMO, is currently considered as a material with great potential in applications such as p-type semiconducting thin films, catalytic units, as the channel material in ferroelectric field-effect memories and complementary metal oxide semiconductor (CMOS) devices. In summary, this Ph.D. research has yielded an extensive exploration of several important aspects of model semiconducting 2D TMDs and TMOs. Specifically, the PL properties of 2D WS2 have been explored, along with a novel approach to its enhancement as a photocatalyst via hybridisation and the practicalities thereof. This research has also contributed significantly to synthesis methodology for the production of the important semiconducting 2D TMO, SnO, at large scales

Guiding and reflecting light by boundary material

We study effects of finite height and surrounding material on photonic crystal slabs of one- and two-dimensional photonic crystals with a pseudo-spectral method and finite difference time domain simulation methods. The band gap is shown to be strongly modified by the boundary material. As an application we suggest reflection and guiding of light by patterning the material on top/below the slab.Comment: 12 pages, 7 figure

Higher Order Analogues of Tracy-Widom Distributions via the Lax Method

We study the distribution of the largest eigenvalue in formal Hermitian one-matrix models at multicriticality, where the spectral density acquires an extra number of k-1 zeros at the edge. The distributions are directly expressed through the norms of orthogonal polynomials on a semi-infinite interval, as an alternative to using Fredholm determinants. They satisfy non-linear recurrence relations which we show form a Lax pair, making contact to the string literature in the early 1990's. The technique of pseudo-differential operators allows us to give compact expressions for the logarithm of the gap probability in terms of the Painleve XXXIV hierarchy. These are the higher order analogues of the Tracy-Widom distribution which has k=1. Using known Backlund transformations we show how to simplify earlier equivalent results that are derived from Fredholm determinant theory, valid for even k in terms of the Painleve II hierarchy.Comment: 24 pages. Improved discussion of Backlund transformations, in addition to other minor improvements in text. Typos corrected. Matches published versio