Directed Percolation and Tandem Queues

We outline some of the connections which exist between directed site percolation and tandem queues, and show how these can be (and have been, although generally not in the language of queueing theory) used to explicit shape theorems for certain first and last passage percolation problems

Self reported aggravating activities do not demonstrate a consistent directional pattern in chronic non specific low back pain patients: An observational study

Question: Do the self-reported aggravating activities of chronic non-specific low back pain patients demonstrate a consistent directional pattern? Design: Cross-sectional observational study. Participants: 240 chronic non specific low back pain patients. Outcome measure: We invited experienced clinicians to classify each of the three self-nominated aggravating activities from the Patient Specific Functional Scale by the direction of lumbar spine movement. Patients were described as demonstrating a directional pattern if all nominated activities moved the spine into the same direction. Analyses were undertaken to determine if the proportion of patients demonstrating a directional pattern was greater than would be expected by chance. Results: In some patients, all tasks did move the spine into the same direction, but this proportion did not differ from chance (p = 0.328). There were no clinical or demographic differences between those who displayed a directional pattern and those who did not (all p > 0.05). Conclusion: Using patient self-reported aggravating activities we were unable to demonstrate the existence of a consistent pattern of adverse movement in patients with chronic non-specific low back pain

Assessment of Aeroacoustic Simulations of the High-Lift Common Research Model

This paper presents further validation of PowerFLOWR aeroacoustic simulations of the High-Lift Common Research Model through comparisons with experimental data from a recently completed wind tunnel test. Preliminary time- averaged surface pressure and microphone array data from the experiment are in reasonably good agreement with the simulations, and the slat is shown to be a dominant noise source on this model. The simulations did not predict slat tones that were very prominent in the experiment, but they did capture the broadband component of slat noise in the low-frequency range up to 1 kHz at full scale. Future tests are planned to demonstrate slat noise reduction technology, and simulations are being used to guide this development

Large deviations and overflow probabilities for the general single-server queue, with applications

We consider from a thermodynamic viewpoint queueing systems where the workload process is assumed to have an associated large deviation principle with arbitrary scaling: there exist increasing scaling functions (a_t, v_t, t ϵ R_+) and a rate function I such that if (W_t, t ϵ R_+) denotes the workload process, then lim_(t→∞) (v_t)^(-1)logP(W_t/a_t > w) = -I(w) on the continuity set of I. In the case that a_t = v_t = t it has been argued heuristically, and recently proved in a fairly general context (for discrete time models) by Glynn and Whitt [8], that the queue-length distribution (that is, the distribution of supremum of the workload process Q = sup_(t≥0) W_t) decays exponentially: P(Q > b) ~ e^(-δb) and the decay rate δ is directly related to the rate function I. We establish conditions for a more general result to hold, where the scaling functions are not necessarily linear in t: we find that the queue-length distribution has an exponential tail only if lim_(t→∞) a_t/v_t is finite and strictly positive; otherwise, provided our conditions are satisfied, the tail probabilities decay like P(Q > b) ~ e^(-δv(a^(-1)(b))). We apply our results to a range of workload processes, including fractional Brownian motion (a model that has been proposed in the literature (see, for example, Leland et al [10] and Norros [13]) to account for self-similarity and long range dependence) and, more generally, Gaussian processes with stationary increments. We also show that the martingale upper bound estimates obtained by Daley and Duffield [5], when the workload is modelled as an Ornstein-Uhlenbeck position process, are asymptotically correct

The future for African air transport: learning from Ethiopian Airlines

The African air transport market has been a laggard in development, remaining encircled by a plethora of problematic issues that curtailed its expansion and prosperity for decades. Regulatory restrictions, protectionism, inadequate infrastructure and prolonged loss making periods are regularly correlated with the plights of African carriers. Ethiopian Airlines is disrupting this negative manifestation and is exponentially expanding its African and international network footprint, enshrined in continuously profitability. The research quantifies that it is Africa’s most successful airline through a POA analysis by aggregating a series of pertinent airline indices to derive its prominence from amongst its peers. Three key pillars were deduced that specifically correlated with Ethiopian Airlines’ continued prosperity and can be used as template, which included a large intra-African network, a strong hub with multiple wave permutations for onward connecting traffic and forging a deep strategic partnership with a regional based African carrier

Functional Stroke Symptoms: A Narrative Review and Conceptual Model

Stroke services have been reconfigured in recent years to facilitate early intervention. Throughout stroke settings, some patients present with functional symptoms that cannot be attributed to a structural cause. Emphasis on fast diagnosis and treatment means that a proportion of patients entering the care pathway present with functional symptoms that mimic stroke or have functional symptoms in addition to vascular stroke. There is limited understanding of mechanisms underlying functional stroke symptoms, how the treatment of such patients should be managed, and no referral pathway or treatment. Predisposing factors vary between individuals, and symptoms are heterogeneous: onset can be acute or insidious, and duration can be short-lived or chronic in the context of new or recurrent illness cognitions and behaviors. This article proposes a conceptual model of functional symptoms identified in stroke services and some hypotheses based on a narrative review of the functional neurological disorder literature. Predisposing factors may include illness experiences, stressors, and chronic autonomic nervous system arousal. Following the onset of distressing symptoms, perpetuating factors may include implicit cognitive processes, classical and operant conditioning, illness beliefs, and behavioral responses, which could form the basis of treatment targets. The proposed model will inform the development of theory-based interventions as well as a functional stroke care pathway

Optimising Agronomic Options At The Farm Scale

Strategic planning and policy development for environmentally sustainable and economically viable management options for the rice based farming systems require the assessment of management options using mathematical models which integrate our understanding of water and salt movement with economic considerations at both the farm and regional scales. This project also had strong links with LWRRDC/MIL/CSIRO project on optimising irrigation intensities in the Murray Valley. During this project a standalone farm scale hydrological economic model SWAGMAN Farm (Salt Water and Groundwater MANagement) was developed and customised for situations in the Coleambally and Murray Irrigation Areas. The model processes were developed and refined by using feed back from irrigation managers, regulators and community groups. The following major achievements have been made: · Collection of crop, soil, irrigation, climatic and economic data sets for fourteen farms in the Murray Irrigation Districts · Rigorous validation of model processes by applying the model to fourteen farms with a range of enterprise, soil and groundwater conditions. · Development of simulation and optimisation modes in SWAGMAN Farm to assess environmental and economic impacts of existing and optimal cropping patterns · Various improvements of water and salt balance processes to suit conditions in the Murray Districts and the Coleambally Irrigation Area · Incorporation of soil water content accounting which provides flexibility in the representation of various starting soil profile water content conditions, water availability to crops and rational computation of recharge and watertable rise during the cropping and fallow periods · Development of a Windows based GAMS independent version of SWAGMAN Farm. GAMS (General Algebraic Modelling System) was an expensive software platform for the previous version with inflexible licence requirements. The new version written in C++ language uses Microsoft Access databases and will be linked with a GIS interface in near future. These sensitivity runs and model developments gained the confidence of members of the steering committee who provided vital inputs throughout this project. While considerable progress was made, they see the need for the work to continue to the stage where it can be applied to assist strategic planning and policy development, taking into account local regional conditions. Parallel to the modelling project an intensive paddock water monitoring project titled “Rigorously determined water balance benchmarks for irrigated crops and pasture’ was also initiated by the steering committee with the assistance of CSIRO, MIL, NSW Agriculture and LWRRDC. The purpose of the monitoring project was to further customise SWAGMAN Farm to local conditions and to validate the model results with the field data. Since monitoring projects take significant time in setting up and calibrating equipment, data analysis has only recently started, however initial comparisons of model results with the field results suggest that the improved SWAGMAN Farm can reasonably simulate field situations. However this work needs to continue to maximise the benefits of the paddock water balance monitoring. However, due to the wide range of groundwater, enterprise and soil conditions in the irrigation areas, SWAGMAN Farm needs to be applied to every farm to develop soundly based policy options. The need for application to individual farms is further driven by the complex regional groundwater interactions causing reversal (downward to upward and local discharge zones) of leakage rates in parts of the irrigation areas e.g. Murray Valley. This project has demonstrated that it is possible to develop methodology which helps assess optimal irrigation intensity within a multitude of biophysical and socio-economic constraints. The methods developed have scientific validity in capturing and representing key processes, and have community acceptance as a way of examining options that are important to them