bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic Epidemic Models in Structured Populations Featuring Dynamic Vaccination and Isolation
Authors: Ball Frank , O'Neill Philip D. , Pike James
Published: October 2007

We consider a stochastic model for the spread of an SEIR (susceptible → exposed → infective → removed) epidemic among a population of individuals partitioned into households. The model incorporates both vaccination and isolation in response to the detection of cases. When the infectious period is exponential, we derive an explicit formula for a threshold parameter, and analytic results that enable computation of the probability of the epidemic taking off. These quantities are found to be independent of the exposure period distribution. An approximation for the expected final size of an epidemic that takes off is obtained, evaluated numerically, and found to be reasonably accurate in large populations. When the infectious period is not exponential, but has an increasing hazard rate, we obtain stochastic comparison results in the case where the exposure period is fixed. Our main result shows that as the exposure period increases, both the severity of the epidemic in a single household and the threshold parameter decrease, under certain assumptions concerning isolation. Corresponding results for infectious periods with decreasing hazard rates are also derived.
A Stochastic Maximin Fixed-Point Equation Related to Game Tree Evaluation
Authors: Alsmeyer Gerold , Meiners Matthias
Published: October 2007

After suitable normalization the asymptotic root value W of a minimax game tree of order b ≥ 2 with independent and identically distributed input values having a continuous, strictly increasing distribution function on a subinterval of R appears to be a particular solution of the stochastic maximin fixed-point equation W ξ max1≤i≤bmin1≤j≤bWi,j, where Wi,j are independent copies of W and denotes equality in law. Moreover, ξ= g'(α) > 1, where g(x) := (1 − (1 − x)b)b and α denotes the unique fixed point of g in (0, 1). This equation, which takes the form F(t) = g(F(t/ξ)) in terms of the distribution function F of W, is studied in the present paper for a reasonably extended class of functions g so as to encompass more general stochastic maximin equations as well. A complete description of the set of solutions F is provided followed by a discussion of additional properties such as continuity, differentiability, or existence of moments. Based on these results, it is further shown that the particular solution mentioned above stands out among all other ones in that its distribution function is the restriction of an entire function to the real line. This extends recent work of Ali Khan, Devroye and Neininger (2005). A connection with another class of stochastic fixed-point equations for weighted minima and maxima is also discussed.
Generalized Pólya urn Designs with Null Balance
Authors: Baldi Antognini Alessandro , Giannerini Simone
Published: October 2007

In this paper we propose a class of sequential urn designs based on generalized Pólya urn (GPU) models for balancing the allocations of two treatments in sequential clinical trials. In particular, we consider a GPU model characterized by a 2 x 2 random addition matrix with null balance (i.e. null row sums) and replacement rule depending upon the urn composition. Under this scheme, the urn process has a Markovian structure and can be regarded as a random extension of the classical Ehrenfest model. We establish almost sure convergence and asymptotic normality for the frequency of treatment allocations and show that in some peculiar cases the asymptotic variance of the design admits a natural representation based on the set of orthogonal polynomials associated with the corresponding Markov process.
Asymptotic Expansions for Distributions of Compound Sums of Random Variables with Rapidly Varying Subexponential Distribution
Authors: Barbe Ph. , McCormick W. P. , Zhang C.
Published: October 2007

We derive an asymptotic expansion for the distribution of a compound sum of independent random variables, all having the same rapidly varying subexponential distribution. The examples of a Poisson and geometric number of summands serve as an illustration of the main result. Complete calculations are done for a Weibull distribution, with which we derive, as examples and without any difficulties, seven-term expansions.
Ruin Probability for the Integrated Gaussian Process with Force of Interest
Authors: He Xiaoxia , Hu Yijun
Published: October 2007

In this paper we obtain the exact asymptotics of the ruin probability for the integrated Gaussian process with force of interest. The results obtained are consistent with those obtained for the case in which there is no force of interest.
Discounted Optimal Stopping for Maxima of Some Jump-Diffusion Processes
Authors: Gapeev Pavel V.
Published: October 2007

In this paper we present closed form solutions of some discounted optimal stopping problems for the maximum process in a model driven by a Brownian motion and a compound Poisson process with exponential jumps. The method of proof is based on reducing the initial problems to integro-differential free-boundary problems, where the normal-reflection and smooth-fit conditions may break down and the latter then replaced by the continuous-fit condition. We show that, under certain relationships on the parameters of the model, the optimal stopping boundary can be uniquely determined as a component of the solution of a two-dimensional system of nonlinear ordinary differential equations. The obtained results can be interpreted as pricing perpetual American lookback options with fixed and floating strikes in a jump-diffusion model.
A Lévy Process whose Jumps are Dragged by a Spherical Dynamical System
Authors: Franke Brice
Published: October 2007

We investigate the large scale behaviour of a Lévy process whose jump magnitude follows a stable law with spherically inhomogenous scaling coefficients. Furthermore, the jumps are dragged in the spherical direction by a dynamical system which has an attractor.
Asymptotic Behavior ofk-Word Matches Between two Uniformly Distributed Sequences
Authors: Kantorovitz M. R. , Booth H. S. , Burden C. J. , Wilson S. R.
Published: October 2007

Given two sequences of lengthnover a finite alphabetAof size |A| =d, theD2statistic is the number ofk-letter word matches between the two sequences. This statistic is used in bioinformatics for EST sequence database searches. Under the assumption of independent and identically distributed letters in the sequences, Lippert, Huang and Waterman (2002) raised questions about the asymptotic behavior ofD2when the alphabet is uniformly distributed. They expressed a concern that the commonly assumed normality may create errors in estimating significance. In this paper we answer those questions. Using Stein's method, we show that, for large enoughk, theD2statistic is approximately normal asngets large. Whenk= 1, we prove that, for large enoughd, theD2statistic is approximately normal asngets large. We also give a formula for the variance ofD2in the uniform case.
Counts of Failure Strings in Certain Bernoulli Sequences
Authors: Holst Lars
Published: October 2007

In a sequence of independent Bernoulli trials the probability for success in thekth trial ispk,k= 1, 2, …. The number of strings with a given number of failures between two subsequent successes is studied. Explicit expressions for distributions and moments are obtained for the case in whichpk=a/(a+b+k− 1),a> 0,b≥ 0. Also, the limit behaviour of the longest failure string in the firstntrials is considered. Forb= 0, the strings correspond to cycles in random permutations.
A Note on Planar Random Motion at Finite Speed
Authors: Kolesnik Alexander D.
Published: October 2007

A simple derivation of the explicit form of the transition density of a planar random motion at finite speed, based on some specific properties of the wave propagation on the plane R2, is given.
RANBP1 localizes a subset of mitotic regulatory factors on spindle microtubules and regulates chromosome segregation in human cells
Authors: Tedeschi Antonio , Ciciarello Marilena , Mangiacasale Rosamaria , Roscioli Emanuele , Rensen Wilhelmina M. , Lavia Patrizia
Published: October 2007

The GTPase RAN has an established role in spindle assembly and in mitotic progression, although not all mechanisms are fully understood in somatic cells. Here, we have downregulated RAN-binding protein 1 (RANBP1), a RAN partner that has highest abundance in G2 and mitosis, in human cells. RANBP1-depleted cells underwent prolonged prometaphase delay often followed by apoptosis. Cells that remained viable assembled morphologically normal spindles; these spindles, however, were hyperstable and failed to recruit cyclin B1 or to restrict the localization of HURP (DLG7), a microtubule-stabilizing factor, to plus-ends. RANBP1 depletion did not increase the frequency of unattached chromosomes; however, RANBP1-depleted cells frequently showed lagging chromosomes in anaphase, suggesting that merotelic attachments form and are not efficiently resolved. These data indicate that RANBP1 activity is required for the proper localization of specific factors that regulate microtubule function; loss of this activity contributes to the generation of aneuploidy in a microtubule-dependent manner.
Activin increases the number of synaptic contacts and the length of dendritic spine necks by modulating spinal actin dynamics
Authors: Shoji-Kasai Yoko , Ageta Hiroshi , Hasegawa Yoshihisa , Tsuchida Kunihiro , Sugino Hiromu , Inokuchi Kaoru
Published: October 2007

Long-lasting modifications in synaptic transmission depend on de novo gene expression in neurons. The expression of activin, a member of the transforming growth factor β (TGF-β) superfamily, is upregulated during hippocampal long-term potentiation (LTP). Here, we show that activin increased the average number of presynaptic contacts on dendritic spines by increasing the population of spines that were contacted by multiple presynaptic terminals in cultured neurons. Activin also induced spine lengthening, primarily by elongating the neck, resulting in longer mushroom-shaped spines. The number of spines and spine head size were not significantly affected by activin treatment. The effects of activin on spinal filamentous actin (F-actin) morphology were independent of protein and RNA synthesis. Inhibition of cytoskeletal actin dynamics or of the mitogen-activated protein (MAP) kinase pathway blocked not only the activin-induced increase in the number of terminals contacting a spine but also the activin-induced lengthening of spines. These results strongly suggest that activin increases the number of synaptic contacts by modulating actin dynamics in spines, a process that might contribute to the establishment of late-phase LTP.
Mammalian diaphanous-related formin Dia1 controls the organization of E-cadherin-mediated cell-cell junctions
Authors: Carramusa Letizia , Ballestrem Christoph , Zilberman Yuliya , Bershadsky Alexander D.
Published: October 2007

The formin-homology protein Dia1 is a target of RhoA and a potent activator of nucleation and elongation of actin filaments. Here, we demonstrate that short-hairpin (sh) RNA-mediated downregulation of Dia1 in human MCF7 epithelial cells disrupts adherens junctions, as manifested by the significantly decreased localization of E-cadherin and associated proteins to cell-cell contacts. Expression of mouse Dia1, which is insensitive to the human Dia1-specific shRNA, rescued the junctional integrity. Coexpression of GFP-tagged Dia1 and a constitutively active RhoA mutant, RhoA-V14, resulted in localization of the exogenous GFP-Dia1 to the cell-cell junctions. This localization was accompanied by a strong increase in the width of the adhesion zone and augmentation of the actin, E-cadherin and β-catenin content of the junctions. A constitutively active Dia1 mutant lacking the N-terminal portion was unable to localize to cell-cell junctions and did not show any junction-strengthening effect. The adherens junction enhancement induced by Dia1 and active RhoA did not require microtubules, but depended on the activity of myosin II. Inhibition of myosin II activity abolished the Dia1-mediated reinforcement of cell-cell junctions and instead induced the formation of numerous actin-rich filopodia at the contact zone. Thus, Dia1 localizes to and controls cadherin-mediated junctions in a RhoA-dependent manner.
Non-linear analysis and modelling of the cellular mechanisms that regulate arterial vasomotion
Authors: Griffith T M , Parthimos D , Edwards D H
Published: October 2007

Non-linearity intrinsic to the ion transport systems that regulate intracellular [Ca2+] and smooth muscle tone allows the emergence of fluctuations in vascular diameter and resistance in isolated arteries (vasomotion) that can be classified as chaotic. Correlation analysis suggests an underlying low dimensional system and a four-dimensional model of vasomotion has been formulated to simulate the effects of pharmacological manipulation of smooth muscle tone or nitric oxide (NO) synthesis by the vascular endothelium. The oscillatory patterns observed experimentally and in modelling studies may be considered ‘universal’ in the sense that they also occur in many physico-chemical systems and include: (a) period-doubling, a feature of the Feigenbaum route to chaos; (b) mode-locking and quasiperiodicity, which reflect the interaction of two nonlinear oscillatory subsystems; and (c) intermittency, in which segments of nearly periodic oscillations of variable duration are interrupted by short chaotic bursts. Low dimensionality allows the construction of iterative maps that confirm the existence of types I and III Pomeau-Manneville intermittency in vascular dynamics, with attractor reconstructions indicating that the reinjection mechanism underlying the type III scenario involves a Shil'nikov-type homoclinic trajectory. Dimensional analysis of experimental data and corresponding surrogate time series generated by randomization of Fourier phase also provide evidence for underlying nonlinear structure in fluctuations in red cell velocity and arteriolar calibre in vivo.
Non-linear dynamic simulation of mechanical periodicity of end-diastolic volume of left ventricle under the influence of baroreflex
Authors: Wang Q , Xu S , Chen D , Collins M
Published: October 2007

Mechanical periodicity (MP) of the end-diastolic volume (EDV) of the left ventricle (LV) is closely associated with cardiovascular pathophysiology. On the basis of the Starling's law of the LV and Burattini and Gnudi's four-element model of the vascular system, and considering baroreceptor reflex, a non-linear dynamic lumped-parameter model is proposed. This simulates the MP phenomena of the EDV by solving a series of one-dimensional discrete non-linear dynamic equations. The results demonstrate that excessive deviations of some physiological parameters often induce MP - the unstable phenomena of EDV - and verify that the effects of baroreceptor reflex enhance the ability of the human physiological system to maintain stability.
Chaotic dynamics and hysteresis in thermal convection
Authors: Vadasz P
Published: October 2007

The weak turbulence regime associated with non-steady and non-periodic free convection, in models allowing temporal irregular (i.e. chaotic) solutions is reviewed, and the conditions for its validity are specified. The rich dynamics linked to the transition from steady convection to chaos is demonstrated and explained analytically as well as computationally.
Analysis of an aerodynamic grooved journal bearing with plain sleeve
Authors: Wang C-C
Published: October 2007

This article studies the non-linear behaviour of a herringbone-grooved rigid rotor supported by a gas film bearing. A numerical method is employed to a time-dependent mathematical model for herringbone-grooved gas journal bearings. The finite difference method with successive over-relation method is employed to solve the Reynolds equation. The system state trajectory, Poincaré maps, power spectra, and bifurcation diagrams are used to analyse the dynamic behaviour of the rotor centre in the horizontal and vertical directions under different operating conditions. The analysis reveals a complex dynamic behaviour comprising periodic and quasi-periodic responses of the rotor centre. This article shows how the dynamic behaviour of this type of system varies with changes in rotor mass and bearing number. The results of this study contribute to a further understanding of the non-linear dynamics of aerodynamic-grooved journal bearing systems.
Overstrain in flush optimal-chamfered cross-bored cylinders
Authors: Kihiu J M , Rading G O , Mutuli S M
Published: October 2007

A three-dimensional finite-element method computer program was developed to establish the elastic—plastic, residual, and service stress distributions in cylinders with flush and non-protruding optimal-chamfered cross-bores under internal pressure. Eight-noded brick and four-noded tetrahedral isoparametric elements and the displacement formulation were used. The incremental theory of plasticity with a 5 per cent yield condition and von Mises yield criterion were assumed. The incipient and 5 per cent overstrain (ov) pressures were established for various thickness ratios and cross-bore to main bore radius ratios. For the optimum chamfer angle geometrical configuration, the stresses were determined for varying ov. The maximum and minimum effective stresses were located 7.5° from the meridional and transverse planes, respectively. Meridional plane through thickness yielding occurred at an ov of 41 per cent. The service stress gradients at the cross-bore chamfer end increased with ov for ovs >30 per cent. Stress reversals were eliminated for overstrain >27 per cent. Alternative autofrettage and yield condition procedures were proposed.
Laser short-pulse heating: A theoretical analysis of electron excess energy dissipation in the early heating period
Authors: Yilbas B S , Boran K
Published: October 2007

Laser short-pulse heating of a gold surface is considered. In order to examine the influence of electron-phonon collision on electron and lattice temperature rise, two cases are accommodated in the analysis. In case 1, excess energy dissipation through electron—phonon collision is omitted during the initiation of the laser pulse and the electron—phonon collision time, and in case 2, electron excess energy dissipation from the initiation of the laser pulse is accommodated in the analysis. It is found that electron temperature rise is higher while lattice site temperature is lower for case 1 than that corresponding to case 2. However, the electron temperature difference due to case 1 and case 2 is small, particularly during late heating periods.
Conjugate heat transfer from surface-mounted finite blunt plates
Authors: Yaghoubi M , Velayati E
Published: October 2007

Numerical studies of fluid flow and heat transfer are made in the separated, reattached, and redeveloped regions of the three-dimensional air flow on an array of finite plates with blunt leading edge. The flow reattachment occurs at a place downstream from the leading edge and the heat transfer coefficient becomes maximum around this region. The heat transfer coefficient is found to increase sharply near the leading edge and reduces in the wake. For the range of the parameters investigated in this study, some correlations have been developed for the length of reattachment region and variation of overall heat transfer coefficient for the considered bluff obstacles with various geometry and flow Reynolds number. For such blunt plates, when they are acting like fins, fin efficiency is determined and a relation based on flow Reynolds number and geometric parameters is developed to predict variation of the overall fin efficiency.
Delta robot: Inverse, direct, and intermediate Jacobians
Authors: López M , Castillo E , García G , Bashir A
Published: October 2007

In the context of a parallel manipulator, inverse and direct Jacobian matrices are known to contain information which helps us identify some of the singular configurations. In this article, we employ kinematic analysis for the Delta robot to derive the velocity of the end-effector in terms of the angular joint velocities, thus yielding the Jacobian matrices. Setting their determinants to zero, several undesirable postures of the manipulator have been extracted. The analysis of the inverse Jacobian matrix reveals that singularities are encountered when the limbs belonging to the same kinematic chain lie in a plane. Two of the possible configurations which correspond to this condition are when the robot is completely extended or contracted, indicating the boundaries of the workspace. Singularities associated with the direct Jacobian matrix, which correspond to relatively more complicated configurations of the manipulator, have also been derived and commented on. Moreover, the idea of intermediate Jacobian matrices have been introduced that are simpler to evaluate but still contain the information of the singularities mentioned earlier in addition to architectural singularities not contemplated in conventional Jacobians.
Chaotic dynamics of microbubbles in ultrasonic fields
Authors: Macdonald C A , Gomatam J
Published: October 2007

Chaos is present in non-linear systems that describe temporal phenomena in the physical and life sciences. Well-known instances of chaos include the logistic map, the Lorenz equations, and forced non-linear oscillators. The regular and chaotic dynamics of free gas bubbles and gas-encapsulated microbubbles (contrast agents) are of immense importance in the efficient implementation of ultrasonic contrast imaging. A modification of the Keller-Herring model, which takes into account the elastic properties of the encapsulating shell, is investigated with respect to the bifurcation structure of the time-dependent microbubble radius. Numerical simulations show that the radial oscillations can be periodic as well as chaotic in appropriate parameter domains. Several investigations on chaotic aspects of dynamics presented here are new and highlighted appropriately. The influence of the acoustic field and shell parameters are investigated to identify values where the oscillations undergo bifurcations and the bubble response becomes chaotic. An analysis of chaotic behaviour in multiple-bubble systems completes the investigation and reveals the significant influence the free gas bubbles have on the acoustic response of their encapsulated counterparts.
An analytical formula for estimating the bending angle by laser forming
Authors: Shen H , Yao Z , Shi Y , Hu J
Published: October 2007

Laser forming of metal plates offers the advantages of requiring no external forces and thus reduced cost and increased flexibility. It also enables forming of some materials and shapes that are impossible by using the traditional methods. Based on the conventional equilibrium and compatibility conditions used in solid mechanics, a simple analytical formula for predicting the bending angle is derived. The present model is compared with other models and available experimental data, from which the superiority of the present model is demonstrated.
Effect of temperature and strain rate on the shear properties of Ti–6Al–4V alloy
Authors: Lee W-S , Lin C-F , Huang S-Z
Published: October 2007

This study uses the torsional split-Hopkinson bar to investigate the dynamic shear deformation and fracture behaviour of Ti–6Al–4V alloy under strain rates of 1800, 2300, and 2800 s−1 at temperatures ranging from −100 to 300 °C. It is found that both the strain rate and the temperature have a strong influence on the dynamic shear properties and fracture characteristics of the alloy. An increased strain rate and a reduced temperature cause the strain rate sensitivity to increase and the activation volume to decrease. However, the activation energy increases with decreasing shear stress and is found to attain a maximum value of 15 kJ/ mol under the current test conditions. The failure of the tested alloy is dominated by the formation of an adiabatic shear band. The characteristics of the adiabatic shear band and the fracture surface depend significantly on both the strain rate and the temperature.
Bifurcations, transitions, and attractors of real open flows
Authors: Xie X L , Ma W W , Zhou H L
Published: October 2007

In this study, some dynamics that can be referred to as bifurcations, transitions, and attractors of real open flows, including axisymmetric shear flows, variable density jets, and wakes, have been presented. All of them can be considered as the experimental evidences of the quite abundant dynamics of the Navier-Stokes equations. A concept termed as physical territorial attractor (PTA) is proposed according to the properties of real open flows. Spatial evolutions of open flows, subsequently, can be described by different kinds of PTAs. Global relations through which global dynamics within one PTA or different PTAs can be studied are briefly introduced.
Computational fluid dynamics modelling of a static mixer
Authors: Clifford M J , Simmons K A , Roberts J , Truscot T D
Published: October 2007

In this paper, the data from physical experiments are used to quantify the mixing efficiency of a static mixer injected with two coloured streams of fluid. Two image analysis techniques are investigated - counting striations and a modified mixing index approach based on creating a histogram of greyscale values from the digitized image. The histogram approach is identified as the more promising and establishes the method for a future, more detailed study Data from a computational fluid dynamics (CFD) model of the mixer were analysed using the modified mixing index approach. Comparison to experimental results suggests that the bulk behaviour of the static mixer can be adequately captured by the deterministic CFD approach, despite the chaotic nature of the original mixing process.
Regular and chaotic oscillations of friction force
Authors: Stefański A , Wojewoda J , Wiercigroch M , Kapitaniak T
Published: October 2007

In this paper, several friction features and models are discussed in the context of the dynamical nature of friction force observed during experiments. On the basis of experimental and theoretical analysis, the authors show that such behaviour can be considered as a certain representation of the system dynamics. According to this approach, a classification of friction models with respect to their sensitivity on the system motion character is introduced. Next, the results of experimental research are reported. Friction characteristics reconstructed experimentally for various types of the system response, i.e. periodic, quasi-periodic, and chaotic, are demonstrated. Finally, these results are compared with numerical simulations using the proposed friction model.
Wavelet domain control of rotor vibration
Authors: Cole M O T , Keogh P S , Burrows C R , Sahinkaya M N
Published: October 2007

This paper describes a novel application of the real-time wavelet transform in the control of rotor vibration. Vibration signal wavelet coefficients that relate to different time scales provide direct information on the system dynamic state, and can thus be used for feedback in a closed-loop control strategy that attenuates both transient and steady-state vibration components. Control force signals are synthesized from basis functions having a characteristic frequency and spacing interval closely matched to the rotational frequency. The control signal basis coefficients are generated by integral feedback of the wavelet coefficients such that under steady-state conditions the control forces eliminate measured rotor vibration. The controller synthesis problem is solved by iterative solution of a linear matrix inequality to obtain a gain matrix that satisfies H∞ norm-bound specifications for transient vibration attenuation. It is demonstrated experimentally that wavelet coefficients from multiple scale levels can be used in direct feedback to reduce levels of transient vibration caused by instantaneous changes in unbalance.
Experimental comparison of condensers and evaporators for use in both bottom-mount and side-by-side refrigerator/freezer units
Authors: Chamra L M , Mago P J , Zdaniuk G J
Published: October 2007

The performance characteristics of several evaporators and condensers with different geometries for use in both bottom-mount and side-by-side refrigerator/freezer units are discussed and compared. This comparison was performed on the basis of the units' material, the type of fins, the fin spacing, and the overall length of the tubes. The condenser that showed the best performance for the bottom-mount and side-by-side refrigerator/freezer applications was made with copper-rifled tubes with sine-wave aluminium fins. Similarly, the evaporator that showed the best performance for the bottom-mount and side-by-side refrigerator/freezer units was made with copper-rifled tubes with plain aluminium fins.
The scattering of the harmonic anti-plane shear stress waves by two collinear interface cracks between two dissimilar functionally graded piezoelectric/piezomagnetic material half-infinite planes dynamic loading
Authors: Zhou Z-G , Wang B
Published: October 2007

In this paper, the dynamic behaviour of two collinear interface cracks between two dissimilar functionally graded piezoelectric/piezomagnetic material half-infinite planes subjected to the harmonic anti-plane shear stress waves is investigated. To make the analysis tractable, it is assumed that the material properties vary exponentially with coordinate vertical to the crack. By using the Fourier transform technique, the problem can be solved with the help of a pair of triple integral equations, in which the unknown variable is the jump of the displacements across the crack surfaces. These equations are solved by using the Schmidt method. The relations among the electric field, the magnetic flux field, and the dynamic stress field near the crack tips can be obtained. Numerical examples are provided to show the effect of the functionally graded parameter, the distance between two interface cracks, and the circular frequency of the incident waves upon the stress, the electric displacement, and the magnetic flux intensity factors of cracks.
A passively adaptive screwdriver: A novel concept for controlling off-diagonal stiffness
Authors: Ilanko S , Aitchison D R , McCallion H
Published: October 2007

A concept for an automated screw driving mechanism is presented. The proposed mechanism has a self-adjusting axial stiffness that depends on the torsional resistance against screwing. It delivers a greater axial thrust when the torsional resistance is greater, for example, towards the final stage of a screwing operation.
Development of a multipiston temperature telemetry system using Bluetooth networks
Authors: Lee H-W , Oh C-H , Kauh S K , Ha K-P
Published: October 2007

The engines in vehicles today are smaller in size and lighter in weight but are still required to produce high output power. These characteristics have been found to induce thermal problems in the engine. In solving this thermal problem, temperature measurement in the piston of the engine plays an important role. However, owing to the environment of the piston, it is difficult to measure the temperature in the piston. Thus, developing a method to measure the temperature of the piston is currently an important research topic. This paper presents a piston temperature telemetry system that was developed using Bluetooth. This system is advantageous in that it makes it possible to measure multipiston temperature using a Bluetooth wireless network, which is an area that has yet to be investigated in more depth. The telemetry system is composed of the piston part and the data acquisition part. To evaluate the performance of the telemetry system, experiments were conducted using a 2359 cm31 DOHC engine produced by the Hyundai Motor Company. The experimental results show that the piston telemetry system is applicable to real commercial engines for measuring piston temperature.
Multidisciplinary optimization of an automotive door with a tailored blank
Authors: Song S-I , Park G-J
Published: October 2007

The automotive door has many design requirements such as stiffness, natural frequency, side impact, etc. Thus, various related governing equations should be solved for systematic analysis and design. It is almost impossible to solve them simultaneously. Instead, they are separately handled and the analysis results are incorporated into the design separately. Multi-disciplinary optimization (MDO) can be exploited well to include various analysis disciplines.

Firstly, single optimization methods are carried out by considering one discipline for the automobile door design. Various optimization formulations are defined and the formulated problems are solved to determine the topology, shape, and size of the door with a tailored blank. The design is expanded to MDO to consider multiple disciplines. Although existing MDO methods are mathematically excellent, they are only adequate for the design of airplane wings. In this research, a few MDO methods are proposed to solve problems that share design variables among disciplines. This idea is from the fixed-point root finding method for multidiscipline analysis. Firstly, optimization of the entire system is divided into multiple domains according to the required analysis methods. Secondly, design variables are assigned to one domain according to the contribution or sensitivity. An optimization formulation is defined for each domain. Thirdly, optimization is performed at each domain where only the assigned variables are regarded as design variables and others are constant. If all the design variables are updated, then the single optimizations are iteratively conducted until the design is not changed.

The developed method is verified by a standard mathematical problem. Then the developed methods are applied to the design of an automobile door. The design considers the stiffness, the natural frequency, and the side impact of the door. Most of the optimization processes use mathematical optimization. When mathematical optimization is too complicated, an approximation method such as the response surface method (RSM) is utilized. The developed methods show stable convergence and the weight of the door is reduced by 15 per cent. Since commercial systems are employed for analysis and design by coding the interfacing parts, the developed methods can be easily utilized in design practice.
Modelling and control of the dynamics of bubbling fluidized beds
Authors: Harrison A. J. L. , Lim C-N , Gilbertson M. A.
Published: October 2007

An image analysis system has been developed, capable of determining the size and locations of bubbles or ‘voids’ in a planar gas-fluidized bed. From this, the bubble voidage fraction of the bed (the fraction occupied by bubbles) is calculated. Transfer functions relating this to the gas flowrate into the bed are developed theoretically and show good agreement with those obtained from experiments on the bed. PID and adaptive controllers are then implemented, enabling the bubble voidage fraction to be successfully controlled.
Design of an autofrettaged high-pressure vessel, considering the Bauschinger effect
Authors: Alegre J. M. , Bravo P , Preciado M
Published: October 2007

High-pressure processing is a method by which food products are subjected to a high level of hydrostatic pressure for a certain period of time. To achieve this process, it is necessary to correctly design high-pressure vessels capable of supporting at least 100 000 loading—unloading high-pressure cycles. The autofrettage technique is commonly used to produce compressive tangential residual stresses near the bore, which improve the fatigue life of the pressure vessel. This article shows the design of an autofrettaged thick-walled vessel that works at an internal pressure of 500 MPa, with an internal diameter of 300 mm and a length of 4500 mm. A finite element (FE) analysis was performed to obtain the residual stresses after the autofrettage at an internal pressure of 925 MPa. The material of the vessel was a 15–15 PH stainless steel hardened by precipitation, which shows a strong Bauschinger effect. For FE simulations, the material has been modelled considering an elastic—perfectly plastic behaviour for the loading phase and a Ramberg—Osgood behaviour for the unloading phase, with its coefficients depending on the previous equivalent plastic strain reached during the loading process. The simulation procedure is explained in detail and the results allow it to be applied for other autofrettage designs that need the Bauschinger effect of the material to be considered.
On non-linear methods of bogie stability assessment using computer simulations
Authors: Polach O
Published: October 2007

Stability assessment of rail vehicles is probably the most widespread form of dynamic analysis in railway vehicle engineering. The computer simulations using fully non-linear three-dimensional vehicle models constructed in a modern multi-body simulation tool allow detailed non-linear stability analysis for the specified conditions. However, high sensitivity to the wheel/ rail contact conditions and different definitions of stability in mechanics and in railway practise can lead to significant differences between prediction and the measurement. Different methods of non-linear stability analysis, which may be used in industrial applications, are introduced and compared on selected examples of contact geometry wheel set/track with high equivalent conicity. The comparisons show that the linearization of the contact geometry wheel set/track can enable a better assessment of the non-linear stability analyses. A decreasing equivalent conicity function in the range of amplitudes below ∼ 3 mm leads to supercritical Hopf bifurcation with small limit cycles and consequently to largest differences between the methods compared. When excluding the contact geometries leading to supercritical Hopf bifurcation, the results achieved are closer each other, but still with differences in the range of up to 10 per cent. This uncertainty in the stability prediction caused by the method applied must be taken into consideration, in addition to other uncertainties related to vehicle parameters, modelling, etc.
Wear at the wheel/rail interface when sanding is used to increase adhesion
Authors: Lewis R , Dwyer-Joyce R S
Published: October 2007

Sanding is used in train operation to improve adhesion at the wheel/rail interface during both braking and traction. An experimental study has been carried out to determine the effect of sanding on the wear of wheel and rail materials. Static tests were performed using actual wheel and rail sections. Dynamic tests were carried out with and without sand on a twin disc machine, where wheel and rail steel discs are loaded together and driven under controlled conditions of rolling and sliding. Sand was fed into the disc contact through a standard compressed air sanding valve.

In both static and dynamic tests, sand caused severe surface damage. During the dynamic tests, because of the application of sand, wear increased by factors between 2 and 10. The wheel steel wear rates showed the largest increases. Wear in wet conditions was higher than that in dry conditions because the wet discs entrained a larger amount of sand through the contact that otherwise was ejected when the discs were run dry.

The mechanisms of sanding wear have been investigated. Severe plastic flow as well as a high material removal rate and surface corrugation takes place. The rail discs are scored by sand particles that embed and stick in the softer wheel disc. As well as wear by abrasion, the discs were subject to a rapid fatigue process and large chunks of material fractured from the surface.

A simple abrasive wear model has been developed to predict wear of rail material caused by sand in the wheel/rail contact, which shows good correlation with test results.

There are a number of idealizations inherent in the test simulations that lead to increased severity over the actual wheel/rail contact. These include the amount of sand entering the contacts in both types of test and the disc geometry and motion in the dynamic tests. While the twin disc specimens have been scaled down, the sand is as used on the railway network, which may lead to surface damage appearing more severe than it would be in an actual wheel/rail contact. Results are therefore only to be taken as a guide to what happens in the full size wheel/rail interface.
Two-level numerical optimization of ride comfort in railway vehicles
Authors: Enblom R
Published: October 2007

This article addresses the interaction between and tuning of different mechanical subsystems in railway vehicle design. Application of numerical methods in a two-level optimization process, involving multi-body vehicle dynamics simulation and finite-element structural analysis, is proposed. The focus is on vibration ride comfort and tuning of dynamic properties of the vehicle, running gear, and carbody structure. As a background, a brief overview of multi-disciplinary and structural optimization methods is given. The selected solution based on the loosely coupled collaborative optimization approach, here implemented as a two-level structure, is presented. Numerical examples are provided to illustrate the choice of optimization algorithms suitable for this type of resonant systems and to demonstrate the performance of the numerical procedures on a realistic engineering problem. The leading coach of a three-car train-set is successfully optimized in terms of mass reduction and reduced natural frequency requirements, despite an infeasible initial design.
On the effect of varying stiffness under the switch rail on the wheel—rail dynamic characteristics of a high-speed turnout
Authors: Zhu J Y
Published: October 2007

Using models of vertical geometric and stiffness irregularities in turnouts, the dynamic effect of a high-speed train on a turnout is investigated using vehicle-track dynamic interaction theory. The ordinary slide base plate under the switch rail used today in highspeed turnouts is welded to two pieces of steel plate. To avoid the vertical uneven stiffness along the railway track's longitudinal direction, an elastic slide base plate is developed. A layer of an elastic rubber is inserted between an upper sliding plate and the base plate. After the switch rail is laid elastically, the turnout's dynamic characteristics are investigated and compared with the characteristic of the ordinary plate. The results show that the elasticity under the switch rail could effectively improve the vertical wheel—rail interaction dynamics when the train passes from the stock rail to the switch rail. The dynamic performance of the turnout improves and the life of the turnout as well as of the plates are extended.
Static wheel/rail contact isolation due to track contamination
Authors: Lewis R , Masing J
Published: October 2007

An experimental study has been carried out to investigate the effect of contaminants such as sand and leaves on the electrical isolation of a wheel/rail contact. Train detection, for signalling purposes, can be by means of track circuits. Signalling block occupancy is triggered by the wheelset of the train ‘shorting out’ the track circuit. Contaminants in the wheel/rail interface mean that contact between the wheelsets and the track may be compromised, inhibiting train identification.

Tests were performed using sections cut from wheels and rail sections loaded together hydraulically with different combinations of contaminants in wet and dry conditions. The electrical circuit used was a simplified simulation of the TI21 track circuit.

The sand results indicated that a transition exists in the amount of sand in the contact above which isolation occurred. This amount is higher than the specified sand application rate for train operation at 4.5 m/s (10 mile/h), much of which will not actually make it into the contact. At lower speeds, down to zero, however, if the applied sand rate is not reduced, there is a possibility that this amount could enter the contact leading to isolation.

Dead leaves were found to present the greatest problem in terms of isolation. The addition of sand used to mitigate the problem of adhesion loss caused by leaf fall made the likelihood of isolation greater. With water, breakdown loads were lower and partial conductance was seen to occur, although it is not clear whether these levels of conductance could be detected by a track circuit. This needs further investigation. Leaves with a higher level of sclerophylly (leatheriness) were found to be harder to break down.

Loads used represented an average value for the tread contact. It was clear that for tests with dead leaves, particularly, the breakdown loads were around this level. With train masses gradually reducing leading to lower wheel/rail contact forces, the problem could get worse.

At the present stage of development, the test method is best used as a means to qualitatively assess relative effects on electrical isolation of different contaminants, but can provide information that may be able to help in assessing where greater attention to leaf clearance may be necessary.
Routing for the Pennsylvania Maglev system by a genetic algorithm
Authors: Cao Y-Y , Lin Z , Giras T C , Disk D R
Published: October 2007

The scheduling of vehicle movement activities is an important component in highspeed railway transit operations planning process. This paper presents a mathematical programming approach to vehicle routing for the Pennsylvania Transrapid Maglev Train System. A mathematical model of the routing procedure is first derived. Based on this model, the vehicle routing problem is formulated into a constrained optimization problem, in which the train miles travelled are maximized subject to various operational and safety requirements. This large scale non-linear optimization problem is then solved by a genetic algorithm.
Tribological principles in metal-on-metal hip joint design
Authors: Dowson D
Published: October 2007

An analysis of some 100 published and communicated findings on running-in volumetric wear and steady state wear rates from simulator tests carried out in eight laboratories in three countries has been undertaken. Powerful indications have emerged of the dominant role of mixed lubrication in current metal-on-metal hip replacements, with elastohydrodynamic film thickness controlling wear.

The background to the calculation of film thickness in the elastic-isoviscous mode of lubrication has been outlined and graphs of representative film thickness and lambda ratio have been presented. For minimum wear and wear rate the diameter of the femoral component should be as large as possible, while the clearance should be as small as is practicable. The findings are valid for both monolithic and surface replacement implants.

A tentative proposal is made for the prediction of lifetime wear in metal-on-metal total hip replacements.
Development and problems of metal-on-metal hip arthroplasty
Authors: Shetty V D , Villar R N
Published: October 2007

For over 40 years, the metal-on-polyethylene bearing has dominated the field of total hip replacement. Problems of wear, osteolysis (dissolution of bone), and ultimately failure of prostheses have led to the development of alternative bearing surfaces. Metal-on-metal hip resurfacing has taken current orthopaedic surgery almost by storm. However, metal ion release following metal-on-metal hip resurfacing remains a major cause for concern. This article looks into the development and examines problems and issues surrounding metal-on-metal resurfacing arthroplasty.