bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong Optimality of Bold Play for Discounted Dubins-Savage Gambling Problems with Time-Dependent Parameters
Authors: Yao Yi-Ching , Chen May-Ru
Published: July 2008

In the classic Dubins-Savage subfair primitive casino gambling problem, the gambler can stake any amount in his possession, winning (1 − r)/r times the stake with probability w and losing the stake with probability 1 − w, 0 ≤ w ≤ r ≤ 1. The gambler seeks to maximize the probability of reaching a fixed fortune (the goal) by gambling repeatedly with suitably chosen stakes. This problem has recently been extended in a unifying framework to account for limited playing time as well as future discounting, under which bold play is known to be optimal provided that w ≤ ½ ≤ r. This paper is concerned with a further extension of the Dubins-Savage gambling problem involving time-dependent parameters, and shows that bold play not only maximizes the probability of reaching the goal, but also stochastically minimizes the number of plays needed to reach the goal. As a result, bold play also maximizes the expected utility, where the utility at the goal is only required to be monotone decreasing with respect to the number of plays needed to reach the goal. It is further noted that bold play remains optimal even when the time-dependent parameters are random.
Bias and Overtaking Optimality for Continuous-Time Jump Markov Decision Processes in Polish Spaces
Authors: Zhu Quanxin , Prieto-Rumeau Tomás
Published: July 2008

In this paper we study the bias and the overtaking optimality criteria for continuous-time jump Markov decision processes in general state and action spaces. The corresponding transition rates are allowed to be unbounded, and the reward rates may have neither upper nor lower bounds. Under appropriate hypotheses, we prove the existence of solutions to the bias optimality equations, the existence of bias optimal policies, and an equivalence relation between bias and overtaking optimality.
Poisson Approximation for the Number of Repeats in a Stationary Markov Chain
Authors: Touyar Narjiss , Schbath Sophie , Cellier Dominique , Dauchel Hélène
Published: July 2008

Detection of repeated sequences within complete genomes is a powerful tool to help understanding genome dynamics and species evolutionary history. To distinguish significant repeats from those that can be obtained just by chance, statistical methods have to be developed. In this paper we show that the distribution of the number of long repeats in long sequences generated by stationary Markov chains can be approximated by a Poisson distribution with explicit parameter. Thanks to the Chen-Stein method we provide a bound for the approximation error; this bound converges to 0 as soon as the lengthnof the sequence tends to ∞ and the lengthtof the repeats satisfiesn2ρt= O(1) for some 0 < ρ < 1. Using this Poisson approximation,p-values can then be easily calculated to determine if a given genome is significantly enriched in repeats of lengtht.
On Negative Binomial Approximation tok-Runs
Authors: Wang Xiaoxin , Xia Aihua
Published: July 2008

The distributions of the run occurrences for a sequence of independent and identically distributed (i.i.d.) experiments are usually obtained by combinatorial methods (see Balakrishnan and Koutras (2002, Chapter 5)) and the resulting formulae are often very tedious, while the distributions for non i.i.d. experiments are generally intractable. It is therefore of practical interest to find a suitable approximate model with reasonable approximation accuracy. In this paper we demonstrate that the negative binomial distribution is the most suitable approximate model for the number ofk-runs: it outperforms the Poisson approximation, the general compound Poisson approximation as observed in Eichelsbacher and Roos (1999), and the translated Poisson approximation in Rollin (2005). In particular, its accuracy of approximation in terms of the total variation distance improves when the number of experiments increases, in the same way as the normal approximation improves in the Berry-Esseen theorem.
Growth of Integral Transforms and Extinction in Critical Galton-Watson Processes
Authors: Tokarev Daniel
Published: July 2008

The mean time to extinction of a critical Galton-Watson process with initial population size k is shown to be asymptotically equivalent to two integral transforms: one involving the kth iterate of the probability generating function and one involving the generating function itself. Relating the growth of these transforms to the regular variation of their arguments, immediately connects statements involving the regular variation of the probability generating function, its iterates at 0, the quasistationary measures, their partial sums, and the limiting distribution of the time to extinction. In the critical case of finite variance we also give the growth of the mean time to extinction, conditioned on extinction occurring by time n.
Critical Behaviors and Critical Values of Branching Random Walks on Multigraphs
Authors: Bertacchi Daniela , Zucca Fabio
Published: July 2008

We consider weak and strong survival for branching random walks on multigraphs with bounded degree. We prove that, at the strong critical value, the process dies out locally almost surely. We relate the weak critical value to a geometric parameter of the multigraph. For a large class of multigraphs (which enlarges the class of quasi-transitive or regular graphs), we prove that, at the weak critical value, the process dies out globally almost surely. Moreover, for the same class, we prove that the existence of a pure weak phase is equivalent to nonamenability. The results are extended to branching random walks on weighted graphs.
The SIS Great Circle Epidemic Model
Authors: Neal Peter
Published: July 2008

We consider a stochastic SIS model for the spread of an epidemic amongst a population ofnindividuals that are equally spaced upon the circumference of a circle. Whilst infectious, an individual,isay, makes both local and global infectious contacts at the points of homogeneous Poisson point processes. Global contacts are made uniformly at random with members of the entire population, whilst local contacts are made according to a contact distribution centred upon the infective. Individuals at the end of their infectious period return to the susceptible state and can be reinfected. The emphasis of the paper is on asymptotic results as the population sizen→ ∞. Therefore, a contact process with global infection is introduced representing the limiting behaviour asn→ ∞ of the circle epidemics. A branching process approximation for the early stages of the epidemic is derived and the endemic equilibrium of a major outbreak is obtained. Furthermore, assuming exponential infectious periods, the probability of a major epidemic outbreak and the proportion of the population infectious in the endemic equilibrium are shown to satisfy the same equation which characterises the epidemic process.
Laplace Transforms of Probability Distributions and Their Inversions are Easy on Logarithmic Scales
Authors: Rossberg A. G.
Published: July 2008

It is shown that, when expressing arguments in terms of their logarithms, the Laplace transform of a function is related to the antiderivative of this function by a simple convolution. This allows efficient numerical computations of moment generating functions of positive random variables and their inversion. The application of the method is straightforward, apart from the necessity to implement it using high-precision arithmetics. In numerical examples the approach is demonstrated to be particularly useful for distributions with heavy tails, such as lognormal, Weibull, or Pareto distributions, which are otherwise difficult to handle. The computational efficiency compared to other methods is demonstrated for an M/G/1 queueing problem.
Sales forecasting for thin film transistor liquid crystal display products with data clustering and an evolving neural network model
Authors: Chang P-C , Fan C-Y , Liu J Y-C , Huang W-H
Published: July 2008

There are specific characteristics in the thin film transistor liquid crystal display (TFT-LCD) industry, such as unexpected demand fluctuation, customized products that each customer will designate a specific key component, long lead time of procurement, and short product life cycle. This research presents a genetic algorithm integrated with a neural network model for monthly sales forecasting of TFT-LCD products in Taiwan. The practical situation and its requirements are explained and two systematic approaches are discussed: (a) a K-means clustering for historic sales data and new sales is forecasted by mapping its inputs into one of these clustered data, and (b) a neural network integrated with a genetic algorithm for supervised learning of the functional behaviour of time-series data and their approximation. The evolving neural network model is applied for modelling the system's behaviour with the possibility of exploiting expert information and systematic optimization. The model has been tested and satisfying results are shown with practical data.
Optimal tolerance design of mechanical assemblies for economical manufacturing in the presence of alternative machines — a genetic algorithm-based hybrid methodology
Authors: Singh P K , Jain P K , Jain S C
Published: July 2008

Traditional practice to tolerance design has been based on a sequential approach to design and manufacturing considerations. Integrated tolerance design involving simultaneous selection of design and manufacturing tolerances was introduced in the last decade. Choice of manufacturing processes (or machines) from among the alternatives, frequently encountered in different stages of realization of individual dimensions, is an important issue in product development. The problem becomes more complicated if the available alternative manufacturing processes (or machines) have a non-overlapping precision range. The optimal tolerance design problem formulated with these issues considering both the cases of overlapping and non-overlapping precision range, based on different stack-up conditions, such as the worst case, root sum square, and Spotts’ modified criteria is the focus of this study. The resulting optimization problem involving a combinatorial, non-linear, non-convex search space cannot be effectively solved for a global solution using conventional optimization techniques. Genetic algorithm, a non-traditional optimization technique, is useful to solve such a complex problem to obtain a near-global solution. This solution may further be improved by making subsequent use of conventional techniques appropriately. In this research a hybrid approach has been proposed based on this philosophy. In the first step, a near-global solution is obtained using the genetic algorithm; in the second step the optimal solution obtained in the first step is refined using the MATLAB-optimization-toolbox. The study has been planned to obtain a better insight into solution of the tolerance design problem, and has been demonstrated with the help of a numerical example.
An environmental assessment framework with respect to the Requirements of Energy-using Products Directive
Authors: Yung W K C , Chan H K , Choi A C K , Yue T M , Mazhar M I
Published: July 2008

From August 2007, all member states of the European Union are required to enforce a new directive, 2005/32/EC, that affects any products that rely on any forms of energy as the source for operation. These products are referred to as energy-using products (EuPs), and the said directive (EuP directive) aims to achieve a higher level of environmental benefits by considering the environmental impacts throughout their whole life cycle. The EuP directive sets out to establish an outline for the eco-design requirements for EuPs. In this regard, environmental assessment, or more specifically life-cycle assessment, is the most fundamental tool to help manufacturers comply with the directive. This paper aims to discuss the background of the EuP directive and to propose a framework for assessment with respect to the directive, based on a pilot study with four products. One of these four products will be employed to demonstrate the application of the framework.
A data mining integrated architecture for shop floor control
Authors: Srinivas  , Harding J A
Published: July 2008

The dynamics of the market are forcing shop floor control systems to enhance their intelligence and reactivity to change. The control system must also have mechanisms to process the vast amount of data, which is generated with the application of cheap data logging systems and should also incorporate a mechanism for continuous learning. Data mining provides a mechanism for analysing data and generating new knowledge. This paper presents an intelligent knowledge-based decision support system for shop floor control, which incorporates data mining techniques and intelligent agent technology to provide useful information, knowledge, and a mechanism for continuous learning. The functioning of the system is described and the architecture of different agents that constitute the system has been discussed in terms of the different modules required. A process to integrate the individual data mining agents associated with the different processes has also been described. Finally a prototype of the system is presented to demonstrate the application of this agent-based system.
Flow regime discrimination technique for gas—liquid two-phase flow in magnetic fluid
Authors: Kuwahara T , Yamaguchi H , De Vuyst F
Published: July 2008

This paper describes a new discrimination technique of flow regime (flow pattern) for gas—liquid two-phase flow in magnetic fluid. The proposed technique can identify the flow regime with simple devices by exploiting the wave patterns of signals obtained by electromagnetic induction. This utilization achieves a mechanically non-contact measuring method for objective fluids. In this study, verification experiments for practical measurement were conducted in upward gas—liquid two-phase flow. The results of the experiments have verified that the proposed measuring technique is useful as a method for flow regime discrimination.
The study of deformation and stress—strain distribution of nano-scale thin sheet copper under the biaxial tensile loads by using molecular dynamics and finite-element method
Authors: Lin Z-C , Huang J-C , Chao Y-C
Published: July 2008

This paper investigates the strain and stress distributions in a nano-scale copper thin sheet under the biaxial tensile action, within the range of elasticity, by employing the molecular dynamics (MD) and finite-element method (FEM). Each atom is regarded as a node and the lattice as an element. The nano-scale copper thin sheet model, established in this study, is based on the face centered cubic lattice structure, and divides the lattice into 24 constant strain tetrahedron elements. After MD simulation, the biaxial force is found to be almost the same during the biaxial tensile action. Simulation results reveal that the stress and strain are highly closer at the edge of the sheet. The presence of strain around the upper and lower surfaces in the central region of the thin sheet indicates that after exhibiting biaxial tensile activity, contraction occurs in the region. The FEM/MD model, constructed in this paper directly melts the FEM spirit in MD computation. This facilitates the analysis of stress and strain in the entire nano-scale range for the nano-scale copper thin sheet.
Automated failure classification for assembly with self-tapping threaded fastenings using artificial neural networks
Authors: Althoefer K , Lara B , Zweiri, Y H , Seneviratne L D
Published: July 2008

This paper presents a new strategy for the automated monitoring and classification of self-tapping threaded fastenings, based on artificial neural networks. Threaded fastenings represent one of the most common assembly methods making the automation of this task highly desirable. It has been shown that the torque versus insertion depth signature signals measured on-line can be used for monitoring threaded insertions. However, the research to date provides only a binary successful/unsuccessful type of classification. In practice when a fault occurs it is useful to know the causes leading to it. Extending earlier work by the authors, a radial basis neural network is used to classify insertion signals, differentiating successful insertions from failed insertions and categorizing different types of insertion failures. The neural network is first tested using a computer simulation study based on a mathematical model of the process. The network is then validated using experimental torque signature signals obtained from an electric screwdriver equipped with an optical shaft encoder and a rotary torque sensor. Test results are presented proving that this novel approach allows failure detection and classification in a reliable and robust way. The key advantages of the proposed method, when compared to existing methods, are improved and automated set-up procedures and its generalization capabilities in the presence of noise and component discrepancies due to tolerances.
Simulation and experimental investigations for the patch near-field acoustical holography
Authors: Yang C , Chen J , Li J Q , Xue W F
Published: July 2008

In order to reconstruct the sound field, the fast Fourier transform (FFT)-based near-field acoustical holography (NAH) demands that the measurement surface must extend to a region where the sound pressure decreases to a low level. This method is unfit for reconstructing the partial sound field in which the measurement aperture size is limited either by physical necessity or as a way of reducing the measurement cost. Statistically optimal NAH (SONAH) performs plane-to-plane calculations directly in the spatial domain, avoids all errors occurred in the FFT-based NAH and significantly increases the accuracy of the reconstruction of the partial sound field. In the present work, combined with the different regularization methods, SONAH is performed for reconstructing the partial sound field. The errors over the central and the peripheral sections of the reconstruction area are researched separately. Simulations and experiments show that SONAH is successful in reconstructing the partial sound field and the errors over the central sections are smaller than that over the peripheral sections. Experiments demonstrate that Tikhonov regularization in conjunction with Engl's criterion is suitable for the reconstruction of the practical sound field.
Development of an equation to predict radial modulus of elasticity for single-walled carbon nanotubes
Authors: Sakhaee-Pour A , Ahmadian M T , Gerami A
Published: July 2008

Finite element (FE) method is used to model radial deformation of single-walled carbon nanotube (SWCNT) under hydrostatic pressure. Elastic deformation of the nanostructure is simulated via elastic beams. Properties of the beam element are calculated by considering the stiffness of the covalent bonds between the carbon atoms in the hexagonal lattice. By applying the beam elements in a three-dimensional space, elastic properties of the SWCNT in transverse direction are obtained. In this regard, influences of diameter and tube wall thickness on the radial and circumferential elastic moduli of zigzag and armchair SWCNTs are considered. It is observed that there is a good agreement between the FE results and data available in the literatures. The FE data are employed to develop a predictive equation through a statistical non-linear regression model.
Chemical-looping combustion — a thermodynamic study
Authors: McGlashan N R
Published: July 2008

The poor performance of internal combustion (IC) engines can be attributed to the departure from equilibrium in the combustion process. This departure is expressed numerically, as the difference between the working fluid's temperature and an ideal ‘combustion temperature’, calculated using a simple expression. It is shown that for combustion of hydrocarbons to be performed reversibly in a single reaction, impractically high working fluid temperatures are required — typically at least 3500 K.

Chemical-looping combustion (CLC) is an alternative to traditional, single-stage combustion that performs the oxidation of fuels using two reactions, in separate vessels: the oxidizer and reducer. An additional species circulates between the oxidizer and reducer carrying oxygen atoms. Careful selection of this oxygen carrier can reduce the equilibrium temperature of the two redox reactions to below current metallurgical limits. Consequently, using CLC it is theoretically possible to approach a reversible IC engine without resorting to impractical temperatures. CLC also lends itself to carbon capture, as at no point is N2 from the air allowed to mix with the CO2 produced in the reduction process and therefore a post-combustion scrubbing plant is not required.

Two thermodynamic criteria for selecting the oxygen carrier are established: the equilibrium temperature of both redox reactions should lie below present metallurgical limits. Equally, both reactions must be sufficiently hot to ensure that their reaction velocity is high. The key parameter determining the two reaction temperatures is the change in standard state entropy for each reaction.

An analysis is conducted for an irreversible CLC system using two Rankine cycles to produce shaft work, giving an overall efficiency of 86.5 per cent. The analysis allows for irreversibilites in turbine, boiler, and condensers, but assumes reactions take place at equilibrium. However, using Rankine cycles in a CLC system is considered impractical because of the need for high-temperature, indirect heat exchange. An alternative arrangement, avoiding indirect heat exchange, is discussed briefly.
A parameterized numerical method for generating discrete helical gear tooth surface allowing non-standard geometry
Authors: Hedlund J , Lehtovaara A
Published: July 2008

Gear analysis is typically performed using calculation based on gear standards. Standards provide a good basis in gear geometry calculation for involute gears, but these are unsatisfactory for handling geometry deviations such as tooth flank modifications. The efficient utilization of finite-element calculation also requires the geometry generation to be parameterized. A parameterized numerical approach was developed to create discrete helical gear geometry and contact line by simulating the gear manufacturing, i.e. the hobbing process. This method is based on coordinate transformations and a wide set of numerical calculation points and their synchronization, which permits deviations from common involute geometry. As an example, the model is applied to protuberance tool profile and grinding with tip relief. A fairly low number of calculation points are needed to create tooth flank profiles where error is <1 μm.
Modelling and simulation of a novel shape memory alloy actuated compliant parallel manipulator
Authors: Sreekumar M , Nagarajan T , Singaperumal M
Published: July 2008

This paper presents the non-linear analysis of a shape memory alloy (SMA) actuated fully compliant spatial parallel mechanism. A compliant mechanism made of SMA wires as its actuators and SMA pipe as its structural member that exploits both the shape memory and superelastic effects is proposed and its static analysis using ANSYS is presented in this study. Finite element analysis in a multi-physics environment considering geometric and material non-linearities helps the user to analyse complex behaviour of a system. For the proposed mechanism, simulation results show: (a) 4 per cent strain for SMA actuation is optimal considering the geometric non-linearity of the proposed mechanism for obtaining maximum displacement; (b) buckling effect is less predominant while implementing the superelastic behaviour; and (c) the mechanism can be designed as a compliant device with one or more inflexion points by exploiting the superelasticity of the SMA pipe. The knowledge obtained from the simulation study could help in further miniaturization of the manipulator.
Investigation of torsional teeth stiffness and second moment of area calculations for an analytical model of spline coupling behaviour
Authors: Barrot A , Sartor M , Paredes M
Published: July 2008

Torque distribution from within spline coupling is an important matter for design engineers, who wish to study the behaviour of spline couplings. This distribution can be estimated because of an analytical equation, based on material, torsional teeth stiffness, and second moments of area of the shaft and sleeve. These parameters have to be determined precisely. The material properties can be readily determined but calculation of the other parameters requires finite-element calculations or complex algorithms. The aim is to propose simplified equations so as rapidly to obtain values for both teeth stiffness and second moments of area. Experimental designs were implemented to determine the most appropriate equations. Torsional stiffness is the first parameter studied in the present paper. This is the result of rotations due to various phenomena involving distortions such as bending, shear, compression, rotation of the foundation of the teeth, and the teeth sliding. Two simplified equations are finally expressed to define torsional stiffness. The first equation takes into account the first four phenomena and the second one the teeth sliding. The second topic in the present paper covers the influence on torque distribution of various formulae for calculating second moments of area. A solution, which takes into account the shear of the teeth, is highlighted.
Dimensional synthesis and dynamic manipulability of a planar two-degree-of-freedom parallel manipulator
Authors: Wu J , Wang J , Wang L , Shao H
Published: July 2008

This article deals with the dimensional synthesis and dynamic manipulability of a planar two-degree-of-freedom (DOF) parallel manipulator. The dimensional synthesis based on the workspace and velocity output ratio is presented. The dynamic formulation is derived by using the virtual work principle. Taking into account that the accelerating capabilities at a given point along all directions are more isotropic, the condition number of inertia matrix in the dynamic equation is presented as an index to evaluate the dynamic manipulability of a manipulator. Furthermore, two global performance indices, which consider the mean value and standard deviation of the condition number of inertia matrix, are proposed, respectively. The dynamic manipulability of the parallel manipulator is more isotropic in the centre than at the peripheries of the workspace. The parallel manipulator is incorporated into a four-DOF hybrid machine tool, which also includes a two-DOF worktable.
A set of new general unified fluid dynamic equations for arbitrary equation of state
Authors: Huang D G , Ke H Y , Du J Y
Published: July 2008

In flow field, the pressure, which usually drives the fluid to flow, is one of the most important variables. However, in the conventional computational method, density, velocity, and temperature or stagnation internal energy are usually used as basic unknown variables, as well as the pressure, a key factor for fluid dynamics, is usually solved indirectly by pressure correction or applying the equation of state. By rational mathematical deduction, a set of new general unified equations for fluid dynamics are deduced in this paper. In these equations, the static pressure and static enthalpy are adopted as basic unknown variables.
Surface design of roller gear cam mechanisms with a turret in both translation and rotation
Authors: Chen C-G , Chiou S-T
Published: July 2008

Roller gear cam mechanisms (RGCMs) are used extensively as automatic tool changers of machining centres or as indexing mechanisms in various machinery. However, almost all the existing RGCMs have a turret in a rotational motion only. Thus for example, when they are used as a part of automatic tool changers, the translational motions of the tools have to be given by other mechanisms. An RGCM with a turret which can move with both translation and rotation simultaneously is proposed; such an RGCM may simplify the structure of some machines.

By using D-H homogeneous coordinate transformation matrices, and applying the theory of conjugate surfaces, the model for the surface design of the RGCM is developed. Two examples are included to demonstrate the usages of the model and to verify its correctness.
An evaluation of acoustic reflectometry for leakage and blockage detection
Authors: Papadopoulou K A , Shamout M N , Lennox B , Mackay D , Taylor A R , Turner J T , Wang X
Published: July 2008

Acoustic reflectometry has been shown to be an effective technique for detecting defects, such as holes and blockages, in relatively short, single lengths of pipe. This paper discusses briefly the physical basis of the technique and then describes the results of a series of experiments that were designed to evaluate the suitability of using this approach for monitoring the health of natural gas pipelines. Such pipelines will typically be many kilometres long, have diameters of up to 1 m and may form part of a complex network of pipelines. Previous studies have demonstrated that acoustic reflectometry techniques can be used to detect pipeline defects in relatively small bore pipelines with lengths of several hundred meters. The results reported in this paper indicate that even when using fairly crude equipment, the technique can be successfully applied to detect defects in single pipelines and pipeline networks with large diameters and lengths exceeding 5 km. Although the results presented in this paper are not conclusive, they do provide the necessary justification for a second phase of experiments to be conducted to extend the scope of the technique further.
External condensation heat transfer coefficients of R22 alternative refrigerants on enhanced tubes at three saturation temperatures
Authors: Park K-J , Jung D
Published: July 2008

In this study, external condensation heat transfer coefficients (HTCs) of R22, R410A, R407C, and R134a are measured on a 1024 fins per meter (26 fins per inch) low fin tube and Turbo-C tube at saturation temperatures of 30, 39, and 50 °C with wall subcooling of 3–8 °C. Test results show that condensation HTCs of all refrigerants decrease as the saturation temperature increases from 30 to 50 °C. This trend is due to the degradation of thermophysical properties of the liquid phase with an increase in saturation temperature. For the low fin tube data, Beatty and Katz's prediction equation showed a reasonably good agreement for all fluids with less than 20 per cent deviation. The performance of Turbo-C tube is better than that of the low fin tube for R22, R410A, and R134a due to the efficient removal of the condensate. For Turbo-C tube, HTCs of R407C were much lower than those of the other three fluids due to a unique condensation phenomenon associated with non-azeotropic mixtures at vapour—liquid interface. The average heat transfer enhancement ratios for the low fin tube and Turbo-C tube against the plain tube are 4.0–5.5 and 3.0–8.1, respectively, for all refrigerants tested.
Decision support at the wheel—rail interface: The development of system functional requirements
Authors: Thanh V H , Roberts C , Tobias A M , Williams J , Stirling A , Madelin K
Published: July 2008

Railway decision support systems (DSSs) tend to address track and vehicle assets separately. This paper describes the development of a comprehensive set of high-level functional requirements for an integrated support system that optimizes the system as a whole. Interviews and workshops were held with key industry stakeholders covering regulation, infrastructure, condition monitoring, mass transit, and light rail to elicit their issues, needs, and desires. The needs were checked for relevance, duplication, and overlapping; and rephrased, decomposed, grouped, classified, and prioritized in order to achieve a consistent, complete, and unambiguous set of system stakeholder requirements. They were then used to derive a set of high-level system functional requirements for the DSS. The paper also demonstrates the importance of complete traceability between the two sets of requirements.
Simulation of traction and curving for passive steering hauling locomotives
Authors: Simson S A , Cole C
Published: July 2008

In a heavy haul train operations the ruling grades that set the tractive power requirements for train consists are often associated with tight curvatures. Past studies of passive or active bogie steering developments have been mostly directed towards high-speed rail applications or light rail and commuter rail applications and hence studies have focused on two axle bogies. Linked passive steering three axle locomotive bogies such as produced by General Motors Electric Motor Division for the SD70 class locomotive are in widespread use however, there are few publications on traction and curving, and few papers on linked passive steering bogies. This paper presents a simulation study three axle bogie locomotives on various curve radii with traction and variable rail friction conditions. Curving performance is assessed showing body linked radial bogies to have considerable advantages over axle linked bogies that are significantly better than yaw relaxation bogies at improving steering under traction. As traction adhesion approaches the rail friction coefficient steering performance of all bogies without forced steering deteriorates to the same levels as a rigid bogie.
A study of the slipstreams of high-speed passenger trains and freight trains
Authors: Sterling M , Baker C J , Jordan S C , Johnson T
Published: July 2008

As the speeds of both passenger and freight trains increase, there is increasing concern that the unsteady gusts generated in train boundary layers and wakes will become more of for a risk to passengers waiting on platforms and for trackside workers. In addition, the demands of interoperability make this a problem of growing relevance to railway operators across Europe. A number of model scale and full-scale experiments have been carried out in recent years that have provided robust experimental data to quantify these flows. This paper considers all the available datasets for high-speed passenger trains and container freight trains, and in making a comparison between them, arrives at a number of conclusions concerning the characteristics of train slipstreams. It is concluded that the identification of a number of distinct flow regions in earlier work is generally valid and forms a useful framework for the consideration of the problem. The flow characteristics are different in each region, and, depending upon the train type, the measurement distance from the train and height above ground, the observed peak gusts for a train may occur at any time during the train passage or in its wake. It is also concluded that results obtained from measurements around small scale moving models are in good agreement with the full scale measurements and reproduce all the important flow features.
Measurement of vehicle ground speed using bogie-based inertial sensors
Authors: Mei T X , Li H
Published: July 2008

This paper presents a novel technique for the measurement of vehicle ground speed using inertia sensors mounted on a bogie frame of railway vehicles. The measurement is achieved indirectly from the time shift of the dynamic motions between two wheelsets, by exploring vehicle/bogie dynamic responses to track excitations and extracting particular features of motion at the wheelsets. There is no need for the use of conventional position encoders and therefore difficulties associated with inaccuracies in wheel slip/slide conditions or limited resolutions of the encoders are eliminated. The basic principle of the proposed technique is explained and detailed development of a practical measurement scheme presented. A full performance assessment is provided to illustrate that a fast and accurate measurement of the vehicle speed can be obtained with the proposed measurement scheme. Limitations and further improvements of the new method are also discussed. The method presented in the paper may provide a reliable and accurate measurement of the absolute vehicle speed essential for railway traction and braking control systems and may be extended for automotive applications.
An investigation of the effects of corrosion on the fatigue strength of AlN axle steel
Authors: Beretta S , Carboni M , Lo Conte A , Palermo E
Published: July 2008

Corrosion fatigue is an important topic in the evaluation of the structural integrity of railway axles. In fact, several recent axle failures have been attributed to the presence of corrosion pits and axle surface corrosion. Despite the importance of this issue, existing EN standards do not precisely quantify the effect that corrosion or corrosion-fatigue might have on the fatigue strength of a railway axle. Consequently, there is a need to have a better understanding of this problem.

In this paper, two main lines of research have been adopted with a view to investigating the issues regarding the corrosion fatigue properties of AlN steel. The first line of research assesses the morphology and the statistical distribution of corrosion defects present on the surface of retired axles together with the detrimental effect of the defects detected on the in-air fatigue strength of AlN steel. The second line of research examines the fatigue properties of AlN steel in the presence of artificial rainwater. The results of the analysis show that the corrosion typically found on axles is significant from a point of view of fatigue properties and that the fatigue life of AlN steel is strongly affected by the presence of a mildly corrosive substance like rainwater. Fatigue test results are consistent with the fatigue strength reduction outlined in the BASS technical recommendations.
Development of method for assessing the current collection performance of the overhead conductor rail systems used in electric railways
Authors: Huang H-H , Chen T-H
Published: July 2008

To reduce the amount of space required for power delivery structures and to improve the convenience of maintenance of overhead contact systems (OCSs), the conductor rail OCS has been used to replace the conventional catenary OCS in many railway tunnels around the world. In this article, an efficient method able to detect the contact loss between the pantograph and both the OCS interfaces is studied and set up by analysing the traction current flowing into the locomotives. Unlike other experimental tests or methods, the method of current analysis does not require an extra experimental construction. Moreover, it is very practical, non-invasive, and can be carried out to verify the performance of the whole railway line without affecting service operation. Taiwan railway's North-Link line is used as an example to test the current collection performance of the conductor rail OCS. The results indicate that the conductor rail OCS provides a slightly poorer performance when compared with the conventional OCS in supplying power to the moving trains. Nevertheless, it still complies with European OCS regulations. The findings also point out that some specific tunnels, where the conductor rail OCS is installed, provide inferior performance in supplying power to the locomotives when compared with other tunnels.
Analysis of dynamic behaviour of low vibration track under wheel load drop by a finite element method algorithm
Authors: Zhu J-Y
Published: July 2008

According to finite-element method (FEM) analytical solution (based on penalty algorithm) and the control equations of wheel—rail contact (developed from point-to-surface contact elements), the vibration responses were simulated for the two alternative railway track structures impacted by a falling wheel-set. The dynamic behaviour of low vibration track (LVT) is investigated based on this numerical method, which is verified by the field experiments. The results show that, when compared with the conventional short sleeper buried track (SSBT), the LVT is more beneficial for the reduction of track structure vibration levels — thanks to its properly matched stiffness under rail and block. Furthermore, it is demonstrated that the proposed wheel-load-drop FEM numerical procedure and field experiment can effectively and economically study the dynamic properties of track structures.
Control design for unmanned aerial vehicle swarming
Authors: Ilaya O , Bil C , Evans M
Published: July 2008

The collective behaviour observed in many social insects and animals provides the inspiration for the development of multi-vehicle control systems. The distributed nature of the multi-vehicle control problem enhances the performance of the collective system along the dimensions of scalability, robustness, and fault tolerance. The distributed/decentralized nature of the cooperative control task introduces many sub-problems often associated with network control design. In this paper, a survey of recent results in the field of cooperative control for multi-vehicle systems is presented. Various applications are discussed and presented in a mathematical framework to illustrate the major features of the cooperative control problem. Theoretical results for various cooperative control strategies are presented by topic and applied to the multi-vehicle applications.
Unmanned aerial vehicle navigation and mapping
Authors: Lazarus S B , Tsourdos A , Silson P , White B , Żbikowski R
Published: July 2008

The unmanned aerial vehicle (UAV) has significant advantages over the ground vehicle, where it can achieve a high degree of manoeuvrability, high speed response time and the ability of large area coverage. The problem considered here is that of an UAV localization and mapping using an extended Kalman filter (EKF), interval analysis (IA), covariance intersection (CI) and Hough transform (HT) for a partially known environment. The map is known partially in the sense that the obstacles and the land-marks are known to some extent. The vehicle is localized with respect to the known obstacles and to recognise the unknown obstacles to update the map of the environment. The focus is to develop an approach which can give a guaranteed performance of sensor-based localization and mapping that would increase the safety of the aerial vehicle and to produce a better performance in building the map of the environment. The guaranteed performance is quantified by explicit bounds of the position estimate of the vehicle. Generally, the UAVs carry the required sensors such as inertial sensors, accelerometers, and gyroscopes, to measure the acceleration and the angular rate, while the obstacle detection and the map-making is carried out with time of flight sensors such as ultrasonic or laser sensors. Most of these sensors give overlapping or complementary information, which offers scope for exploiting data fusion. This task of data fusion is accomplished by combining the measurements from different sensors that are obtained from two different methods namely EKF and IA, and by processing these measurements with a data fusion algorithm using the CI principle. This fused information is used with the measurements from the time of flight sensors such as laser sensor to update the map of the environment by applying the HT technique. The algorithms are complementary in the sense that they compensate for each other's limitations, so that the resulting performance of the sensor system is better than of its individual components, which in turn, improves the accuracy and richness in updating the map of the partially known environment. This proposed intelligent sensor system can provide a mathematically provable performance guarantees that are achievable in practice.
Multi-dimensional aircraft surface pressure interpolation using radial basis functions
Authors: Rendall T C S , Allen C B
Published: July 2008

Multi-dimensional interpolation via radial basis functions is applied to the problem of using aircraft surface pressure data obtained both computationally and experimentally to obtain pressure distribution predictions through parameter space. In the most complicated cases, the data may be a function of spatial position, Mach number, Reynolds number, and angle of attack as well as other more intricate variables such as control surface deflections. Amalgamation of computational fluid dynamics and wind tunnel data for load prediction is currently a time-consuming task, especially given the large number of load cases that need to be evaluated to achieve aircraft certification, so that an efficient tool for making rapid estimates based on all the information available would be of great use. The approach, using radial basis functions, is tested on a combination of simple computational and experimental results and found to offer great flexibility, while still being capable of reproducing relatively detailed features of the pressure distribution.
High-frequency vibration of a conformal antenna structure
Authors: Chen X , Tang Y , Liu L , Zhao M , Punyamurtula V K , Chen J , Han A , Qiao Y
Published: July 2008

When the functionalities of an antenna and a load-carrying airframe are integrated into a unified structure in an unmanned aerial vehicle, they would affect each other as additional mechanical loading is caused by electromagnetic field. For a low-frequency structural motion, this coupling effect is negligible; for high-frequency vibrations, non-uniform frequency shifts and magnitude variations are predicted.
Robust gain-scheduled control for vertical/short take-off and landing aircraft in hovering with time-varying mass and moment of inertia
Authors: Wu S-L , Chen P-C , Chang K-Y , Huang C-C
Published: July 2008

This paper presents a robust gain-scheduled control approach for planar vertical take-off aircraft dynamics. The uncertain properties of the aircraft mass, moment of inertia, and the non-minimum phase parasitic coupling are all addressed by considering a reasonable range in the progress of controller design. The realized control law is not implemented as a function of the unmeasurable coupling parameter as has been done in previous works. After a system-variable scaling process for the dynamic normalization and a control input transformation to ensure the controllability of the dynamics in a linear parameter-varying representation, the composite control law is used to address all the inherent uncertainties of the mass, moment of inertia, and parasitic coupling parameter. The composite control law consists of a linear state-feedback gain-scheduled matrix, constructed from parameter-dependent linear matrix inequalities algorithms, and a non-linear control law for thrust manipulation to eliminate the effect of gravitational disturbance. The design is then demonstrated by a time response simulation.
Investigating the emissions and performance of high bypass ratio aero-engines
Authors: Sorato S , Pascovici D S , Ogaji S O T , Pilidis P
Published: July 2008

In the last decades the development of new technologies and methods of analysis has brought a continuous improvement of the performance of aeronautical jet engines among which are reductions of polluting substances and noise. In this vein, and in accordance with the general attention given environmental issues by the scientific community and governments, a first analysis has been conducted to assess the potential of new types of engines to meet the green environmental expectations. The objects of the study are two powerplants, one with bypass ratio (BPR) 5, used as baseline, and the other with BPR 12. A parametric analysis of the performance and the emissions of these engines was performed using software which directly coupled models of engine performance, emissions, and aircraft operations. Design-point (take-off) and off-design (whole of flight-mission) cases have been considered in order to show the different scenarios and information they could present. Lefebvre equations were used and calibrated to match reasonably the measured NO x and CO emissions of current combustors. Calibration method and errors are presented to clarify the approach. Trends of NO x and CO2 emissions relative to different operating parameters are presented for both cases. The principal differences in emissions for engines of high BPR are shown to be higher values of NO x associated with the off-design case.