Demand uncertainty and lot sizing in manufacturing systems: the effects of forecasting errors and mis-specification

This paper proposes a methodology for examining the effect of demand uncertainty and forecast error on lot sizing methods, unit costs and customer service levels in MRP type manufacturing systems. A number of cost structures were considered which depend on the expected time between orders. A simple two-level MRP system where the product is manufactured for stock was then simulated. Stochastic demand for the final product was generated by two commonly occurring processes and with different variances. Various lot sizing rules were then used to determine the amount of product made and the amount of materials bought in. The results confirm earlier research that the behaviour of lot sizing rules is quite different when there is uncertainty in demand compared to the situation of perfect foresight of demand. The best lot sizing rules for the deterministic situation are the worst whenever there is uncertainty in demand. In addition the choice of lot sizing rule between ‘good’ rules such as the EOQ turns out to be relatively less important in reducing unit cost compared to improving forecasting accuracy whatever the cost structure. The effect of demand uncertainty on unit cost for a given service level increases exponentially as the uncertainty in the demand data increases. The paper also shows how the value of improved forecasting can be analysed by examining the effects of different sizes of forecast error in addition to demand uncertainty. In those manufacturing problems with high forecast error variance, improved forecast accuracy should lead to substantial percentage improvements in unit costs

Optimisation of scheduling and routing for offshore wind farm maintenance

The growing increase in the size and scope of offshore wind farms motivates the need for industry to have access to mathematical tools that reduce costs by efficiently performing daily operations and maintenance activities. Key offshore activities require the transportation of technicians to and within offshore wind farms to complete corrective and preventive maintenance tasks to keep turbines operating efficiently. We provide a new deterministic mixed integer linear programming formulation for deciding the optimal vessel routes for transporting technicians around a wind farm and the scheduling of crew transfers, by minimising downtime, travel and technician costs. The model contains sufficient flexibility to account for multiple vessels, shifts and task profiles, whilst being able to prioritise and omit tasks in environments containing limited resources. Computational experiments are performed which quantify and confirm the impact of key instance characteristics such as technician availability, task profiles and weather conditions. We implement and evaluate the impact of a novel industry safety constraint. The complexity of larger instances motivates a second continuous time formulation, in which preventive maintenance again requires no minimum duration of work before it can provide benefit. We employ a specific decomposition structure to take advantage of variable preventive maintenance and utilise an adaptive large neighbourhood search procedure to solve instances. We evaluate several distinct acceptance criteria in conjunction with random and adaptive operator selection to determine the best option for our model. We produce a statistical model of offshore weather conditions to help quantify the likelihood of limited vessel accessibility to offshore wind farms. We model the joint distribution of key meteorological and oceanographic variables over time whilst accounting for seasonal trends using multivariate kernel density estimation. Our method generates alternative metocean realisations from historical data and reproduces the important long term persistence statistics of good and adverse offshore conditions

Multicast communications in distributed systems

PhD ThesisOne of the numerous results of recent developments in communication networks and distributed systems has been an increased interest in the study of applications and protocolsfor communications between multiple, as opposed to single, entities such as processes and computers. For example, in replicated file storage, a process attempts to store a file on several file servers, rather than one. MUltiple entity communications, which allow one-to-many and many-to-one communications, are known as multicast communications. This thesis examines some of the ways in which the architectures of computer networks and distributed systems can affect the design and development of multicast communication applications and protocols.To assist in this examination, the thesis presents three contributions. First, a set of classification schemes are developed for use in the description and analysis of various multicast communication strategies. Second, a general set of multicast communication primitives are presented, unrelated to any specific network or distributed system, yet efficiently implementable on a variety of networks. Third, the primitives are used to obtain experimental results for a study ofintranetwork and internetwork multicast communications.Postgraduate Scholarship, The Natural Sciences and Engineering Research Council of Canada: Overseas Research Student Award: the Committee of Vice-Chancellors and Principals of the Universities of the Uni ted Kingdom

EHRaS: Electronic Healthcare Record Management for Ad Hoc Settlements

Providing reliable and accurate healthcare to refugees in an ad hoc setting can be challenging for a variety of reasons, and most settlements currently utilize little to no record keeping for patients. EHRaS, our mobile-first electronic healthcare record management system, can provide an inexpensive electronic healthcare record (EHR) solution that is flexible in last-mile applications where infrastructure and technical support is at a minimum. By utilizing NFC technology, novel caching practices, and an extensible interface, our system not only securely identifies patients and authorizes staff to access sensitive medical data, but generally provides a competitive, low-overhead alternative to other open source EHR systems

Somali immigrants and social capital formation : a case study of spaza shops in the Johannesburg township of Cosmo City

Text in EnglishThe aim of this research is to assess the impact social capital has had on Somali businesses. It argues against the perception that Somali business expertise is derived solely from the principles of economics. It argues that social capital plays a pivotal role in shaping the Somali spirit of entrepreneurship. The role of social capital in the creation of Somali human and financial capital is examined. This thesis, being a qualitative study, used semi-structured, unstructured interviews and direct observation as data collection methods.SociologyM.A. (Sociology

Performance criteria and assessment of vendors in government sponsored entrepreneur development programme

In Entrepreneur Development Programme, vendor rating is important not only in supplier selection and in deciding how to allocate business but also determine where scare development effort is best-applied. The paper reviews current methods for vendor rating and finds them wanting. It illustrates a new approach based on the use of Saaty’s Analytic Hierarchy process method, which was developed to assist in multi-criteria decision problems. The new method overcomes the difficulties associated with the categorical and simple linear weighted criteria ranking methods. It provides a more systematic way of deriving the weights to he used and for scoring the performance of vendors

Innovation and opportunity: review of the UK’s national AI strategy

The publication of the UK’s National Artificial Intelligence (AI) Strategy represents a step-change in the national industrial, policy, regulatory, and geo-strategic agenda. Although there is a multiplicity of threads to explore this text can be read primarily as a ‘signalling’ document. Indeed, we read the National AI Strategy as a vision for innovation and opportunity, underpinned by a trust framework that has innovation and opportunity at the forefront. We provide an overview of the structure of the document and offer an emphasised commentary on various standouts. Our main takeaways are: Innovation First: a clear signal is that innovation is at the forefront of UK’s data priorities. Alternative Ecosystem of Trust: the UK’s regulatory-market norms becoming the preferred ecosystem is dependent upon the regulatory system and delivery frameworks required. Defence, Security and Risk: security and risk are discussed in terms of utilisation of AI and governance. Revision of Data Protection: the signal is that the UK is indeed seeking to position itself as less stringent regarding data protection and necessary documentation. EU Disalignment—Atlanticism?: questions are raised regarding a step back in terms of data protection rights. We conclude with further notes on data flow continuity, the feasibility of a sector approach to regulation, legal liability, and the lack of a method of engagement for stakeholders. Whilst the strategy sends important signals for innovation, achieving ethical innovation is a harder challenge and will require a carefully evolved framework built with appropriate expertise

HIV p24-Specific Helper T Cell Clones From Immunised Primates Recognize Highly Conserved Regions of HIV-l

We have investigated Th cell recognition of the HIV core protein p24 by using CD4+ T cell clones derived from cynomolgus macaques immunized with hybrid HIV p24:Ty virus-like particles (VLP). T cell lines from two immunized animals responded to p24:Ty-VLP, control Ty-VLP, purified p24, and whole inactivated HIV, indicating the presence of T cells specific for p24 as well as the Ty carrier protein. The HIV determinants recognized by the T cell lines were identified by using a series of overlapping peptides synthesized according to the sequence of p24. Both T cell lines recognized peptide 11 (amino acids 235-249) and peptide 14 (amino acids 265- 279). In addition, one T cell line also responded to peptide 9 (amino acids 215-229). Definitive identification of two T cell epitopes on p24 was confirmed at the clonal level: from a total of four T cell clones generated from one of the T cell lines, two respond specifically to peptide 11 and two to peptide 14. The T cell clones were CD4' and MHC class 11-restricted and secreted IL-2 in response to stimulation with purified p24, inactivated HIV or a single synthetic peptide. The specificityof the Th clones for variant peptides demonstrated cross-reactivity with two simian immunodeficiency virus isolates, but only limited responses to HIV-2 sequences. However, the Th cell epitopes identified on p24 are highly conserved between 12 HIV-1 isolates and were recognized by both of the immunized primates. These sequences may therefore be useful for priming a broadly reactive immune response to HIV-1

Editing of HIV-1 RNA by the double-stranded RNA deaminase ADAR1 stimulates viral infection

Adenosine deaminases that act on dsRNA (ADARs) are enzymes that target double-stranded regions of RNA converting adenosines into inosines (A-to-I editing) thus contributing to genome complexity and fine regulation of gene expression. It has been described that a member of the ADAR family, ADAR1, can target viruses and affect their replication process. Here we report evidence showing that ADAR1 stimulates human immuno deficiency virus type 1 (HIV-1) replication by using both editing-dependent and editing-independent mechanisms. We show that over-expression of ADAR1 in HIV-1 producer cells increases viral protein accumulation in an editing-independent manner. Moreover, HIV-1 virions generated in the presence of over-expressed ADAR1 but not an editing-inactive ADAR1 mutant are released more efficiently and display enhanced infectivity, as demonstrated by challenge assays performed with T cell lines and primary CD4+ T lymphocytes. Finally, we report that ADAR1 associates with HIV-1 RNAs and edits adenosines in the 5′ untranslated region (UTR) and the Rev and Tat coding sequence. Overall these results suggest that HIV-1 has evolved mechanisms to take advantage of specific RNA editing activity of the host cell and disclose a stimulatory function of ADAR1 in the spread of HIV-1