Scheduling in the manufacture of evaporative air conditioners

The MISG examined the problem of scheduling production of air conditioners at Seeley International. Seeley's objective was to meet their demand in a more cost-effective way. Two models are proposed to achieve this objective. A long term master production schedule with a yearly planning horizon was formulated to give Seeley a broad based schedule for planning production to meet forecast demands and production constraints. Output from this model is designed to provide the appropriate number of units of each product type or sub-assembly item to be produced in the following week. This output is then designed to be the input to a more detailed short term model for scheduling production at the machine level. The short term model is formulated to handle a mixture of both finished products and sub-assemblies. The objective of the short term model is to minimise total production time to free up the use of resources in order to allow for external orders. Directions for further work are discussed

Optimisation of work flow

AeroSpace Technologies of Australia (ASTA) is a supplier of aircraft components for several of the world's major aircraft manufacturers. Its anticipation of a substantial increase in demand has led to concern as to its ability to satisfy customer imposed schedules. ASTA's main concern is scheduling at its five autoclaves. The autoclaves, which are large pressurised ovens in which components are cured before non destructive testing and final assembly, appear to be the bottlenecks in ASTA's manufacturing process. ASTA came to the Australian Mathematics-in-Industry Study Group (MISG) with the objective of developing an optimised loading plan for the autoclaves to improve their utilisation while meeting demand for final components. This report discusses the results of an intensive three day study by the MISG group working on the ASTA problem. Its findings were that: • Modifying the way in which Materials Requirements Planning (MRP) is used may usefully increase autoclave utilisation. • A single product which will account for 60% of factory hours could and should be scheduled separately. • It is feasible and very helpful to group products into a small number of sets with common autoclave processing requirements. • Integer programming models modelling the production line show considerable promise and should be developed further

Bubble-Driven Inertial Micropump

The fundamental action of the bubble-driven inertial micropump is investigated. The pump has no moving parts and consists of a thermal resistor placed asymmetrically within a straight channel connecting two reservoirs. Using numerical simulations, the net flow is studied as a function of channel geometry, resistor location, vapor bubble strength, fluid viscosity, and surface tension. Two major regimes of behavior are identified: axial and non-axial. In the axial regime, the drive bubble either remains inside the channel or continues to grow axially when it reaches the reservoir. In the non-axial regime the bubble grows out of the channel and in all three dimensions while inside the reservoir. The net flow in the axial regime is parabolic with respect to the hydraulic diameter of the channel cross-section but in the non-axial regime it is not. From numerical modeling, it is determined that the net flow is maximal when the axial regime crosses over to the non-axial regime. To elucidate the basic physical principles of the pump, a phenomenological one-dimensional model is developed and solved. A linear array of micropumps has been built using silicon-SU8 fabrication technology, and semi-continuous pumping across a 2 mm-wide channel has been demonstrated experimentally. Measured variation of the net flow with fluid viscosity is in excellent agreement with simulation results.Comment: 18 pages, 18 figures, single colum

Equation-Free Dynamic Renormalization: Self-Similarity in Multidimensional Particle System Dynamics

We present an equation-free dynamic renormalization approach to the computational study of coarse-grained, self-similar dynamic behavior in multidimensional particle systems. The approach is aimed at problems for which evolution equations for coarse-scale observables (e.g. particle density) are not explicitly available. Our illustrative example involves Brownian particles in a 2D Couette flow; marginal and conditional Inverse Cumulative Distribution Functions (ICDFs) constitute the macroscopic observables of the evolving particle distributions.Comment: 7 pages, 5 figure

Secure Proximity-Based Identity Pairing using an Untrusted Signalling Service

New protocols such as WebRTC promise seamless in-browser peer-to-peer communications that in theory remove the need for third-party services. In practice, widespread use of Firewalls, NATS and dynamic IP addresses mean that overlay addressing or use of some fixed rendezvous point is still needed. In this paper we describe a proximity-based pairing scheme that uses a signalling service to minimise the trust requirements on the third party, achieving anonymity and avoiding the need for PKI, while still requiring only a simple asymmetric pairing protocol

ESBL-producing Enterobacteriaceae in 24 neonatal units and associated networks in the south of England: no clustering of ESBL-producing Escherichia coli in units or networks.

OBJECTIVES: The objectives of this study were to characterize ESBL-producing Enterobacteriaceae present in 24 neonatal units (NNUs) in eight networks participating in a multicentre probiotic study and to test the hypothesis that specific strains would cluster within individual units and networks. METHODS: We performed analysis of stool samples for the presence of ESBL-producing Enterobacteriaceae at 2 weeks post-natal age and 36 weeks post-menstrual age. ESBL-producing Enterobacteriaceae were characterized and typed using molecular methods. RESULTS: ESBL-producing Enterobacteriaceae (n = 71) were isolated from 67/1229 (5.5%) infants from whom we received a sample at either sampling time or both sampling times, and from infants in 18 (75%) of the 24 recruiting NNUs. Thirty-three Escherichia coli, 23 Klebsiella spp. and 6 Enterobacter spp. strains were characterized. ESBL-producing E. coli were all distinguishable within individual NNUs by antibiotic resistance genotype, serogroup (O25b), phenotype, phylotype or ST. Ten of the 33 were ST131 and 9 of the 10 ST131 isolates were ciprofloxacin resistant. Seven of the 10 ST131 isolates carried genes encoding CTX-M group 1 enzymes. ST131 isolates were isolated from centres within five of the eight NNU networks. There were clusters of indistinguishable ESBL-producing Klebsiella and Enterobacter isolates associated with specific NNUs. CONCLUSIONS: Strains of E. coli ST131 were distributed across neonatal networks in the south of England. There was no evidence of clustering of clonally related ESBL-producing E. coli strains, by contrast with Klebsiella spp. and Enterobacter spp., which did cluster within units. The possibility that ESBL-producing E. coli strains are spread by vertical transmission requires further investigation

Levels of complexity in financial markets

We consider different levels of complexity which are observed in the empirical investigation of financial time series. We discuss recent empirical and theoretical work showing that statistical properties of financial time series are rather complex under several ways. Specifically, they are complex with respect to their (i) temporal and (ii) ensemble properties. Moreover, the ensemble return properties show a behavior which is specific to the nature of the trading day reflecting if it is a normal or an extreme trading day.Comment: 14 pages, 5 figures, to appear on Physica A, Proceedings of the NATO Advanced Research Workshop on Application of Physics in Economic Modeling, Prague February 8-10 200

Correlation based networks of equity returns sampled at different time horizons

We investigate the planar maximally filtered graphs of the portfolio of the 300 most capitalized stocks traded at the New York Stock Exchange during the time period 2001-2003. Topological properties such as the average length of shortest paths, the betweenness and the degree are computed on different planar maximally filtered graphs generated by sampling the returns at different time horizons ranging from 5 min up to one trading day. This analysis confirms that the selected stocks compose a hierarchical system progressively structuring as the sampling time horizon increases. Finally, a cluster formation, associated to economic sectors, is quantitatively investigated.Comment: 9 pages, 8 figure