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Condition monitoring and condition-based maintenance of railway systems is increasingly important to the train operating companies and infrastructure managers. Degraded rolling stock or infrastructure elements can lead to ineffici...
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Condition monitoring and condition-based maintenance of railway systems is increasingly important to the train operating companies and infrastructure managers. Degraded rolling stock or infrastructure elements can lead to inefficient operation, or even failures and their associated downtime and damage to the track and-or train. Condition monitoring equipment for retrofitting on high speed (HS) lines needs to be low cost and non-intrusive. Such equipment can lead to more efficient maintenance scheduling and can also be used for prognostic purposes. This paper describes the use of some recently developed on-board and lineside monitoring systems: ⅰ. Locating hunting within long tunnels using an on-board inertial measurement unit (IMU). ⅱ. Identifying railhead defects with an on-board electromagnetic acoustic monitoring system. ⅲ. An on-board energy harvesting axle bearing monitoring system, ⅳ. A lineside acoustic monitoring system for wheel and axle bearing condition. These systems address a number of issues within the HS lines in the UK. This paper also discusses the adaptations required to develop such condition monitoring systems for use in a high-speed railway environment.
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We perform an n f = 2 + 1 lattice study of a number of channels where past claims exist in the literature for the existence of strong-interaction-stable light-heavy tetraquarks. We find no evidence for any such deeply bound states...
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We perform an n f = 2 + 1 lattice study of a number of channels where past claims exist in the literature for the existence of strong-interaction-stable light-heavy tetraquarks. We find no evidence for any such deeply bound states, beyond the J P = 1 + , I = 0 u d b ˉ b ˉ and I = 1 / 2 ? s b ˉ b ˉ states already identified in earlier lattice studies. We also describe a number of systematic improvements to our previous lattice studies, including working with larger m π L to better suppress possible finite volume effects, employing extended sinks to better control excited-state contamination, and expanding the number of operators used in the GEVP analyses. Our results also allow us to rule out several phenomenological models which predict significant tetraquark binding in channels where no such binding is found.
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During the diesel engine combustion process, soot particles are produced and are either exhausted into the atmosphere or absorbed by the engine's lubricant. Soot-contaminated lubricant has been shown to produce significant amounts...
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During the diesel engine combustion process, soot particles are produced and are either exhausted into the atmosphere or absorbed by the engine's lubricant. Soot-contaminated lubricant has been shown to produce significant amounts of engine wear. The main mechanism of soot-related wear is through abrasion, but, at increased levels of soot content in the lubricant, starvation of the contact can occur, which can increase wear further. High concentrations of soot can increase the local acidic level and, around the piston where high temperatures and volatile gases coexist, corrosion may also occur. In this paper, the current understanding of engine wear due to soot contamination and the previous research performed is reviewed. The paper also discusses soot formation and its general effects within the engine (including friction and efficiency), as well as other issues including filtration or removal, effects on the lubricant, engine design and operation, and future industry targets and technologies related to soot contamination.
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A bstract We present results for the leading hadronic contribution to the muon anomalous magnetic moment due to strange quark-connected vacuum polarisation effects. Simulations were performed using RBC-UKQCD’s N ~( f ) = 2 + 1 do...
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A bstract We present results for the leading hadronic contribution to the muon anomalous magnetic moment due to strange quark-connected vacuum polarisation effects. Simulations were performed using RBC-UKQCD’s N ~( f ) = 2 + 1 domain wall fermion ensembles with physical light sea quark masses at two lattice spacings. We consider a large number of analysis scenarios in order to obtain solid estimates for residual systematic effects. Our final result in the continuum limit is a ~( μ ) _((2)had, s ) ?=?53.1(9)( ~(??3) _(+?1) )?×?10_(??10).
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In the field of railway simulation, it is a general assumption to consider the coefficient of friction as a known and constant value. This hypothesis is clearly not correct as friction is a consequence of the operating conditions ...
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In the field of railway simulation, it is a general assumption to consider the coefficient of friction as a known and constant value. This hypothesis is clearly not correct as friction is a consequence of the operating conditions (an output, not an input) and many factors can cause friction coefficient to change. In this paper, numerical algorithms based on the simplified theory of Kalker (Fastsim) and capable of modelling variable friction are studied and improved to match experimental measurements. Experimental creep curves from twin disc measurements are used to extract the friction parameters required by the numerical algorithms. Different friction functions are tested to correlate the effect of the contaminants andthe pressure on the coefficient of friction. Finally, two examples are shown to highlight the differences between modelling the wheel-rail contact with variable or constant coefficient of friction and their implications in the estimation of the interaction forces and wear.
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This paper reviews the current state of the literature surrounding methods for the general graph colouring problem and presents a broad comparison of six high-performance algorithms, each belonging to one of the main algorithmic s...
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This paper reviews the current state of the literature surrounding methods for the general graph colouring problem and presents a broad comparison of six high-performance algorithms, each belonging to one of the main algorithmic schemes identified. Unlike many previous computational studies in graph colouring, a large range of both artificially generated and real-world graphs are considered, culminating in over 40,000 individual trials that have consumed more than a decade of computation time in total. The picture painted by the comparison is complex, with each method outperforming all others on at least one occasion; however, general patterns are also observed, particularly with regards to the advantages of hybridising local-search techniques with global-based operators.
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A key driver in current research on lubricant formulation is the need to move away from older technology that is highly reliant on resources derived from industries associated with high carbon dioxide emissions. In this paper, the...
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A key driver in current research on lubricant formulation is the need to move away from older technology that is highly reliant on resources derived from industries associated with high carbon dioxide emissions. In this paper, the adoption of water based (or aqueous) lubrication is explored. This is in direct contrast with most lubricated systems that rely on oil or other petroleum products. In nature, most known biological systems employ aqueous lubrication for tribological contacts, such as those found in cartilage and more widely in mammalian joints including hips and knees giving friction coefficients as low as μ < 0.002. This is achieved very effectively without the presence of an oil or grease as a base lubricant. In most engineering applications, however, oils and greases are used to achieve desired low friction levels. While effective, this comes with the associated higher costs and carbon footprint of using petroleum derived products. In recent years, certain engineering applications have shifted to aqueous lubrication, a notable example of which is stern tube bearings in maritime applications. These are typically low pressure contacts though. Depending on speed of travel this can range from 100–400 MPa. The research detailed in this paper explores the viability of high pressure contacts lubricated with novel aqueous packages and what effects this shift may have on friction and wear profiles of the system. The work reported herein demonstrates that with some modifications, effective lubrication can be achieved using aqueous lubricant packages.
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Self-loosening of bolted joints in response to vibration can lead to the catastrophic failure of a range of engineering components and structures. Many techniques employed to study this phenomenon focus on directly measuring the p...
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Self-loosening of bolted joints in response to vibration can lead to the catastrophic failure of a range of engineering components and structures. Many techniques employed to study this phenomenon focus on directly measuring the preload remaining in the bolt itself, and offer little insight into the behaviour of the clamped interface. In this study, a non-intrusive ultrasonic reflection-based technique is used to first characterize interface pressure in the joint, and then determine the rate at which relaxation occurs. A key advantage of the technique is that it does not require the modification of the contact conditions, and rather utilizes the spring-like behaviour of a rough surface interface when subject to ultrasonic excitation. A series of different bolt torques were investigated, along with the inclusion of both plain and spring washers under the bolt head. All test samples were subjected to an oscillating fixed-displacement vibration cycle. An initial rapid reduction in interface clamping pressure was observed, followed by a more steady-state period. Increasing bolt torque was seen to enhance joint integrity, whereas both the plain and spring washers showed little improvement. The spring washer was observed to extend the secondary steady-state phase of loosening, though as the majority of pre-load was removed prior to this period any change was largely unbeneficial.
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The mathematical formulation of a three-phase, three-dimensional fluid flow and rock deformation in fractured reservoirs is presented in this paper. The present formulation accounts for the significant influence of coupling betwee...
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The mathematical formulation of a three-phase, three-dimensional fluid flow and rock deformation in fractured reservoirs is presented in this paper. The present formulation accounts for the significant influence of coupling between the fluid flow and solid deformation, an aspect usually ignored in the reservoir simulation literature. A Galerkin-based finite element method is applied to discretise the governing equations in space and a finite difference scheme is used to march the solution in time. The final set of equations, which contain the additional cross coupling terms as compared to similar existing models, are highly nonlinear and the elements of the coefficient matrices are updated implicitly during each iteration in terms of the independent variables. A field scale example is employed as an alpha case to test the validity and robustness of the currently formulation and numerical scheme. The results illustrate a significantly different behavior for the case of a reservoir where the impact of coupling is also considered.
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This paper presents an assessment of newly-developed conductive adhesion materials (Products A-E) in comparison to standard rail sand used in Britain. Current rail sand is an insulating material which can affect track circuits; ne...
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This paper presents an assessment of newly-developed conductive adhesion materials (Products A-E) in comparison to standard rail sand used in Britain. Current rail sand is an insulating material which can affect track circuits; newly-developed conductive materials could reduce the risk of this and allow for more material to be applied to further mitigate against low adhesion. The particles were characterised to determine their densities, and size and shape distributions. Bulk behaviour was assessed through three characteristics: angle of repose, bulk shear strength, and particle breakage index. Materials were then assessed using a high pressure torsion approach to measure their effects on adhesion and electrical resistance in dry, wet, and leaf contaminated conditions. It was found that all products produced better or equivalent conductivity compared to the currently used GB rail sand and that Product D and Product E should be considered for future field testing.
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