Large closed queueing networks in semi-Markov environment and its application

The paper studies closed queueing networks containing a server station and $k$ client stations. The server station is an infinite server queueing system, and client stations are single-server queueing systems with autonomous service, i.e. every client station serves customers (units) only at random instants generated by a strictly stationary and ergodic sequence of random variables. The total number of units in the network is $N$. The expected times between departures in client stations are $(N\mu_j)^{-1}$. After a service completion in the server station, a unit is transmitted to the $j$th client station with probability $p_{j}$ $(j=1,2,...,k)$, and being processed in the $j$th client station, the unit returns to the server station. The network is assumed to be in a semi-Markov environment. A semi-Markov environment is defined by a finite or countable infinite Markov chain and by sequences of independent and identically distributed random variables. Then the routing probabilities $p_{j}$ $(j=1,2,...,k)$ and transmission rates (which are expressed via parameters of the network) depend on a Markov state of the environment. The paper studies the queue-length processes in client stations of this network and is aimed to the analysis of performance measures associated with this network. The questions risen in this paper have immediate relation to quality control of complex telecommunication networks, and the obtained results are expected to lead to the solutions to many practical problems of this area of research.Comment: 35 pages, 1 figure, 12pt, accepted: Acta Appl. Mat

Research-informed design, management and maintenance of infrastructure slopes: development of a multi-scalar approach

The UK’s transport infrastructure is one of the most heavily used in the world. The performance of these networks is critically dependent on the performance of cutting and embankment slopes which make up £20B of the £60B asset value of major highway infrastructure alone. The rail network in particular is also one of the oldest in the world: many of these slopes are suffering high incidents of instability (increasing with time). This paper describes the development of a fundamental understanding of earthwork material and system behaviour, through the systematic integration of research across a range of spatial and temporal scales. Spatially these range from microscopic studies of soil fabric, through elemental materials behaviour to whole slope modelling and monitoring and scaling up to transport networks. Temporally, historical and current weather event sequences are being used to understand and model soil deterioration processes, and climate change scenarios to examine their potential effects on slope performance in futures up to and including the 2080s. The outputs of this research are being mapped onto the different spatial and temporal scales of infrastructure slope asset management to inform the design of new slopes through to changing the way in which investment is made into aging assets. The aim ultimately is to help create a more reliable, cost effective, safer and more resilient transport system

ACHILLES: reducing infrastructure whole-life costs

The ACHILLES research programme is a collaboration between six UK universities and the British Geological Survey, which aims to provide the tools to “assess, monitor, design and repair the performance of the ground” upon which infrastructure depends, to ensure that rail and other linear infrastructure provides “consistent, affordable and safe services, underpinned by intelligent design, management and maintenance.” The research programme addresses three main challenges: (i) improved understanding of material and asset deterioration processes; (ii) improved understanding of asset performance, with and without interventions; and (iii) improved forecasting of asset and network behaviour, and decision support for interventions, identifying best-value intervention strategies. These challenges are met through four complementary workstreams: (i) Performance and Deterioration (PaD); (ii) Monitoring and Measurement (MaM); (iii) Simulation and Modelling (SaM); and (iv) Design and Decisions (DaD). This paper is focussed on the SaM and, especially, DaD workstreams. It describes the development of decision support to identify the earthworks maintenance and renewal strategies, and select the designs required, to reduce and ideally minimise the whole-life costs of individual assets, routes and networks. The work is based initially upon cuttings on Britain’s Great Western Main Line railway between London and Bristol, whose individual and collective whole-life costs are being analysed to develop a route-level whole-life engineering cost model. The workstreams then extend to include the handling of uncertainty, environmental and passenger and freight end-user impacts, and the costs and potential benefits of additional asset condition data

ACHILLES: reducing earthworks failure risks and whole-life costs

Vital transport and other linear infrastructure in Britain and elsewhere depends upon an extensive set of earthworks of varying age, condition and engineering quality. These earthworks are subject to normal deterioration, and these processes are exacerbated and complicated by the variable and unpredictable effects of climate change on weather patterns, particularly in the form of increased rainfall intensity and flooding. Railway earthworks are particularly vulnerable to these effects, given their typical age and the comparatively primitive engineering techniques used in their design and construction, as well as the increasing (pre-Covid) traffic levels to which they have been subjected. This paper describes research work being undertaken to improve the understanding of earthworks condition, deterioration and remediation, and to develop methods and tools to assist with the economic assessment of, selection from and prioritisation of alternative design interventions

Canine angiostrongylosis: an emerging disease in Europe

Objective: The aim of this article is to review Angiostrongylus vasorum infection in dogs, including the life cycle, signalment, clinical signs, diagnosis, and treatment. Apparent changes in the epidemiology of this unique parasite are considered, alongside information available regarding its recent geographic spread. Etiology: A. vasorum is a metastrongyloid parasite capable of causing an array of clinical problems in dogs, including cardiorespiratory, coagulopathic, and neurologic signs. Currently, the parasite has a worldwide distribution; however, it usually arises in small pockets of enzootic foci. Recent reports suggest a changing distribution of this parasite, which has renewed interest in its epidemiology and in the risk of expansion to new areas including mainland North America. Diagnosis: A definitive diagnosis of angiostrongylosis is usually made using the modified Baermann technique either using feces or tracheobronchial secretions; however, this review also discusses novel methods such as serologic and molecular techniques. Therapy: Once a diagnosis of angiostrongylosis is made, prompt treatment should follow with anthelmintic drugs (such as moxidectin/imidacloprid, milbemycin oxime, or fenbendazole) and supportive care dependent upon the patient's clinical signs. Currently, there is no proven prophylactic regime. Prognosis: The prognosis appears to be very dependent upon the severity of clinical signs at presentation. A. vasorum can be fatal and death may be sudden. However, if a prompt diagnosis is made and appropriate treatment is administered complete clinical resolution is possibl

Weather-driven deterioration processes affecting the performance of embankment slopes

Deterioration of earthworks and the resultant implications for serviceability and increased occurrence of failures have a significant negative impact on transport networks both in the UK and internationally. There is evidence in the field that deterioration processes are occurring over the life of an asset, comprising cracking and loss of suction. These are weather-driven processes that occur in the absence of increased mechanical loads and can lead to failure many years after construction. To demonstrate the progressive loss in mechanical performance of clay fill due to a purely environmentally driven deterioration process, a programme of unsaturated triaxial testing was carried out. A new mechanism of soil deterioration driven by cyclic wetting and drying is proposed, based on an extensive laboratory and field experimental programme. The underlying cause for this is the micro-structural changes to the soil fabric leading to loss of suction generation capacity. In addition, cracking leads to changes in hydraulic conductivity and the movement of water into and out of the soil. The implications for slope stability assessment include the need for changeability of soil parameters and of the ground model, with changes occurring both seasonally and gradually over time

Emulating long-term weather-driven transportation earthworks deterioration models to support asset management

The deterioration of transport infrastructure earthworks is a global problem, with negative impacts for infrastructure resilience, becoming of increasing significance as existing infrastructure ages. Key mechanisms which affect this deterioration include seasonal pore pressure cycling driven by changing weather and climate, and the long-term dissipation of construction induced excess pore pressures. These complex processes lead to significant uncertainty in rates of deterioration and the current state of existing earthworks assets. The objective in this work was to establish a framework to emulate deterministic numerical models of slope deterioration over time using statistical (Gaussian process) emulation. A validated, physically based, deterministic modeling capability has been developed that can replicate the hydro-mechanically coupled behavior of cut and embankment slopes and their deterioration as driven by weather and climate. In parallel, a statistical (Gaussian process) emulator model was developed, and then trained with data from a deterministic modeling parametric study, using a formal experimental design approach, making use of Latin hypercube sampling. Exemplar forecasting outputs are presented to demonstrate application of the approach for use in decision-making. This information can be used in the design of new earthworks and the management of existing earthwork portfolios

Evidence for the weather-driven deterioration of ageing transportation earthworks in the UK

Seasonal, weather-driven pore pressure cycles alter and degrade the hydro-mechanical engineering properties of earthworks as they age. The accumulating effects of deterioration over many years can lead to the excessive deformation or failure of earthworks; requiring interventions to ensure their reliable performance. This paper reviews the evidence for the weather-driven deterioration of ageing transportation earthworks, with a focus on clay earthworks in the UK. These include earthworks of various ages (up to ∼200 years old), formed from a range of clay-rich strata and at various stages of deterioration. Evidence is considered for both past behaviour and projected behaviour in response to continued ageing and a changing climate. There is clear evidence that some clay earthworks are influenced by the cumulative effect of seasonal weather cycles over many decades. Simulations show that seasonal slope ratcheting will become an increasingly dominant driver of shallow failures in high-plasticity cut slopes as they age and in response to projected climate change. The evidence can inform performance curves describing the deterioration of individual earthworks in response weather-driven ageing. This can help identify earthworks with the highest likelihood of failure and inform decisions made by earthwork asset managers

The seasonal ratcheting of clay cut slopes in response to seasonal weather cycles

Many cut slopes in the UK are in the later stages of their operational life but continue to support road and rail transportation networks. Some of these slopes experienced delayed, deep-seated, first-time failures between 10 and 50 years after construction. However, some continue to seasonally deform and then fail at shallow depth due to the process of seasonal, downslope ratcheting. This paper reviews the evidence for seasonally-induced, downslope ratcheting movements in clay cut slopes, gathered from physical model tests, in-situ monitoring and numerical simulations. The evidence shows that seasonal ratcheting is an increasingly dominant mechanism of slope deformation and ultimate failure for some high-plasticity clay cut slopes as they are exposed to many seasonal weather cycles. The rate of downslope ratcheting depends on the slope age (i.e., number of seasonal weather cycles since construction), the slope geometry (i.e., slope height and angle) and the strain-softening behaviour of the slope material (e.g., as observed in stiff, high-plasticity clays). This rate, when measured, can be used to inform monitoring and management strategies for old, clay cut slopes (e.g., ageing railway and highway cuttings) by identifying the slopes that are prone to seasonally-induced, downslope ratcheting towards the end of their operational life