bluuebunny/crossref_metadata_2025 huggingface dataset:
Rule-Based Control of Weld Bead Width in Pulsed Gas Tungsten Arc Welding (GTAW)
Authors: Wu C S , Liu Y C
Published: February 2007

A rule-based control system of weld bead width is established for realizing in-process control of pulsed gas tungsten arc welding. The system consists of a microprocessor-controlled power supply and working table, a solid state television camera, a high-speed analogue-to-digital converter and an image processing and control computer. Considering the characteristic of arc light and its influence on vision sensing, special measures were taken for image capturing, processing and weld bead width extraction. The rule-based model was combined with the principle of PID (proportional integral derivative) control, and a parameter-changing PID controller was designed. The bead-on-plate welding experiments were carried out. The results show that the system is of good adaptablity for in-process control of weld bead width in pulsed gas tungsten arc welding (GTAW).
A Framework for Modelling the Coincident Flow of Workpieces and Cutting Tools
Authors: Newnes L B , Bell R
Published: February 2007

This paper describes a framework for the concurrent modelling of workpieces and cutting tools (dual flow) and introduces a computer aided tool, the dual-flow emulator, for use in the initial investment phase of high-cost flexible machining cells (FMC) and their subsequent short-term scheduling. This facility enables designers to make decisions based on the economic performance and enhancement of proposed designs. The focus of the work is on machining cells, where an individual machining centre's cost can be in excess of one million pounds, with the tooling being three/four times more expensive than conventional tooling. With these high-cost investments, where there is a small number of expensive machines, it is essential that designers are assured a greater chance of economic success. This makes it necessary to model both the flow and management of the workpieces and cutting tools. A framework for the concurrent modelling of workpieces and cutting tools (dual flow) is introduced and the dual-flow emulator described. This dual-flow emulator can be used to explore the relative merits of alternative operating strategies and, finally, as a short-term scheduling tool as an operational performance aid. An industrial-based study has been undertaken and the economic performance of two strategies is discussed in terms of the overall specification and operational performance.
Business Strategy and the Role of Engineering Product Data Management: A Literature Review and Summary of the Emerging Research Questions
Authors: Harris S B
Published: February 2007

This paper seeks to review the business strategy and product data management literature in an attempt to establish the nature of the relationship between them. One obvious linking theme is that of information systems strategies and their alignment with business processes, and therefore attention has also been given to this body of literature. The conclusions are that there is little well-researched understanding about the nature of the relationship and little concrete evidence of the relative importance of product data management in achieving overall business objectives. Therefore, if manufacturing organizations are to be able to invest wisely in product data management, substantial research is required to address the fundamental business and technical issues that have emerged as a result of this review.
Study into the Effect of Beam Waist Position on Hole Formation in the Laser Drilling Process
Authors: Yilbas B S , Sami M
Published: February 2007

Laser drilling may improve by proper selection of the laser parameters. One of the important parameters in laser hole drilling is the focus setting of the focusing lens. In the present study, the effect of the beam waist position on the resulting hole exit/entry diameter ratio is investigated experimentally. An Nd-YAG laser is used to drill the holes in stainless steel and mild steel sheets at different thicknesses. The study was conducted to include the physical processes involved at different beam waist positions during the drilling operations. It is shown that altering the beam waist positions tends to produce converging and diverging hole walls for negative and positive positions respectively. The drilling improves at a certain beam waist position for a given workpiece thickness.
Tolerance Stack Analysis for Assembly
Authors: Ngoi B K A , Tan K C K
Published: February 2007

Studies have indicated that design for manufacture and design for assembly have a significant impact on the success of a product. One of the key issues is tolerance specification and thus it is important for the designer to consider tolerance analysis thoroughly in the early stages of product development. With minor modifications and if used properly, tolerance charting can be a valuable tool to the product designer.

This paper illustrates two methods used to tackle tolerance balancing for assembly and provides an insight into the considerations to be taken into account. A manual method first demonstrates the fundamental concepts while a computer aided version further enhances the charting process. The latter is easy to apply and renders greater flexibility during problem formulation. Consequently, what–if analysis is possible and thus better results can be achieved. However, it should be cautioned that tolerance charts are merely tools; the results they produce can only be as good as the inputs they receive and thus a ‘perfect’ solution cannot be guaranteed. Nonetheless, tolerance charting is an effective diagnostic tool as it provides tolerance analysis in the early stage of products development.
Tool Management and Job Allocation in Flexible Machining Cells Part 1: Work-Oriented Strategies
Authors: Coleman P , Ozbayrak M , Bell R
Published: February 2007

In many flexible machining cells, total priority is given to meeting a scheduled list of work orders. The management of the tooling resource required to process these work schedules is also important. This paper presents and investigates strategies for tool management and job allocation in such a demand-driven system, and are termed work oriented. These generic strategies are described, forecasting the required level of tool exchange activity at individual machines according to different sets of issue and return rules. A computational study using industrial data has been conducted to assess the effectiveness of the strategies over a range of different system characteristics and under the influence of two job allocation rules. The model, data and range of parameters are discussed and results are presented and compared. Conclusions are drawn regarding the success of the study, the nature of the data used and the relative performance of the strategies.
Sensor Fusion Techniques Used for Learning/Identifying Features of Robot's Part Assembly Tasks
Authors: Son C , Ahn T
Published: February 2007

In this paper, sensor fusion techniques, fused vision/optical sensors and tactile/vision sensors are introduced, which are used for learning/identifying features of tasks related to a robot's part-bringing procedure from a part position to a position over a hole for the purpose of a micro-part insertion in partially unstructured environments. An entropy function, which is a useful measure of the variability and the information in terms of uncertainty, including learning, is introduced to measure the overall performance of a task execution related to a part assembly. By employing a learning approach, the uncertainty associated with the part-bringing task is reduced. The above tools are necessary for a robot manipulator to perform complex assembly, material handling, manufacturing or machining tasks, for example remote maintenance and hazardous material handling, in an unstructured environment.
Sensing Free Surface of Arc Weld Pool Using Specular Reflection: Principle and Analysis
Authors: Kovacevic R , Zhang Y M
Published: February 2007

The weld pool surface provides important information for understanding arc welding processes. In this study, a novel vision sensor is proposed to measure the three-dimensional shape of the free weld pool surface. A pulsed laser is projected on to the weld pool through a specific grid. Specular reflection from the pool surface is sensed using a high shutter speed camera. The three-dimensional weld pool surface shape is clearly shown by the specular reflection. To determine the shape of the pool surface, an image processing technology has been developed to extract the skeleton of the specular reflection from the acquired image. The imaging principle is analysed to determine the correlation between the reflection and the weld pool surface. If the weld pool surface is known, the corresponding specular reflection can be directly calculated using the imaging model which is derived based on the reflection law. However, no explicit models can be obtained to determine the weld pool surface using the reflection and sensor parameters. To solve this difficulty, an iterative algorithm is proposed. The weld pool surface can now be calculated in 1 second from the specular reflection of the weld pool surface. A higher calculation speed is currently being pursued.
A Case Study in Quality Improvement of Precision Turned Components
Authors: Carter L , Butler C
Published: February 2007

The company participating in this study had recently reorganized its factory layout, moving from a traditional layout to machining cells. The company was a light engineering company; the cells consisted of turning centres, each cell catering for a different family grouping of components. An associated change in production methods was the move to ‘just-in-time manufacture’. The consequences of these changes were that the batch sizes had reduced considerably so that now the maximum batch size was 20 and the average only 3 or 4. The company had previously used statistical process control (SPC), but with such small batch sizes the practice had fallen into disuse as the traditional software was no longer appropriate. The general objective of the study was therefore to investigate their current situation and recommend a systematic approach to quality improvement. The study employed non-conformance analysis, measurement capability studies and analysis of variance leading to an appropriate statistical process control methodology. The company initially employed near to 100 per cent inspection; nevertheless, significant quality improvement was achieved.
Analysis of Force Distribution in Grasps Using Augmentation
Authors: Dai J S , Kerr D R
Published: February 2007

A new approach to the analysis of statically indeterminate restraint of a rigid body with any arrangement of point contact is presented in this paper. The paper associates the elasticity at restraint contacts with geometric compatibility of the contact points and constructs elastic compatibility equations, which are complementary to the restraint equations. The equations so obtained are then used to augment the restraint equations and lead to an agumented Jacobian matrix. The new approach enables grasps to be analysed and synthesized in a constraint of combined elasticity and geometric compatibility, in addition to the force equilibrium condition. This gives a mathematical basis for the analysis of force distribution of the statically indeterminate restraint. Detailed reasoning and derivations are given followed by both planar and spatial examples.
Effects of Spatial Repeatability On Long-Term Flexible Pavement Performance
Authors: Collop A C , Cebon D , Cole D J
Published: February 2007

The effects of spatial repeatability of dynamic tyre forces on the long-term performance of three typical British pavement constructions are investigated. Long-term pavement performance is calculated using a ‘whole-life pavement performance Model’ (WLPPM). The WLPPM is capable of predicting deterministic pavement damage due to realistic traffic and environmental loading, throughout the life of the pavement. Particular attention is given to modelling dynamic tyre forces and patterns of loading applied to the pavement by a typical fleet of heavy vehicles. A method is described for simulating vehicle fleets with varying degrees of spatial repeatability using a small number of dynamic tyre force histories. Results indicate that thinner pavements are most sensitive to the level of spatial repeatability exhibited by the vehicle fleet. Pavement damage predictions made without assuming an appropriate level of spatial repeatability can be in error by 20–150 per cent, the higher values being for thinner pavements that fail by fatigue damage.
Identification of Damping Characteristics of Viscoelastically Damped Structures Using Vibration Test Results
Authors: Lin R M , Ling S-F
Published: February 2007

Damping plays an important role in structural stability and vibration control and so frequently special efforts are taken to increase structural damping, of which the most effective measure to date is the viscoelastic damping treatment. However, damping properties, especially those of viscoelastic damping, are the most difficult to model analytically but can only be revealed by vibration test. This paper examines the feasibility of identifying damping characteristics of viscoelastically damped structures whose damping and stiffness characteristics are frequency dependent by correlating finite element modelling with vibration test results and presents an effective method for achieving such an objective. Measured frequency response function data are used instead of conventional modal data, since in the case of viscoelastically damped structures that are frequency dependent modal data are not defined while frequency response functions can be easily measured. The method is developed based on the practical assumption that the measured coordinates are incomplete and the identified damping matrix is physically meaningful and possesses the same physical connectivity as that of the stiffness matrix. Computational aspects regarding the practical application of the proposed method are discussed. Several numerical case studies are given to demonstrate the practical applicability of the proposed method.
The Hodograph and the Balancer of any Frequency Term of the Shaking Force of Spatial Mechanisms
Authors: Chiou S-T , Tzou J-C
Published: February 2007

It is proved in this paper that the hodograph of a frequency term (for example the kth frequency term) of the shaking force of spatial mechanisms is an ellipse. Furthermore, expressions are provided for the lengths and attitudes of the semi-axes of this ellipse in terms of Fourier coefficients of the shaking force. Accordingly, a pair of counterweights, contra-rotating at k times of cycle frequency with their axes parallel to the unit normal vector of the hodograph plane, can be installed for eliminating the frequency term of the shaking force of spatial mechanisms. An example of a seven-link 7-R spatial linkage is included.
Bearing Condition Monitoring by Pattern Recognition Based on Bicoherence Analysis of Vibrations
Authors: Li C J , Ma J , Hwang B
Published: February 2007

For automatic detection and diagnosis of localized defects in rolling element bearings, bicoherence spectra are used to derive features that signify the condition of a bearing. These features quantitatively describe the degree of phase correlation among any three harmonics of bearing characteristic defect frequencies. Employing these features, a linear discriminant classifier is implemented to detect localized defects on a roller and the outer race of a bearing. Experimental results show that the proposed scheme is effective in bearing defect detection and sensitive to incipient defects.
Flow Properties and Passive Scalar Transport in a Model Room With Relevance to Ventilation Efficiency
Authors: Özdemir İ B , Whitelaw J H , Biçen A F
Published: February 2007

This paper describes an experimental investigation of air flow patterns and related passive scalar transport inside a model room with emphasis on the statistical time-scales of the dispersion process and the local ventilation effectiveness. Time-averaged and instantaneous structures of the turbulent flow were examined by local measurements inside a negatively pressurized cubic enclosure of 2 m side dimension and ventilated through single-supply and exhaust registers at an extract flowrate of 1.81 m3/min with a corresponding air change of 13.6 per hour. Sulphur hexafluoride was introduced at the centre of the enclosure and used to mark the flow. The distributions of its time-averaged concentration inside the room were used to deduce the degree of mixing and passive scalar transport.

The measurements of the time-averaged flow field showed that the arrangement with no sources of forced internal mixing resulted in the ventilating flow occurring in a channel connecting the supply and exhaust. Outside this jet-like main stream and particularly in corners, the flow stagnated with high concentrations of the tracer gas in these regions.

Time variations of the instantaneous local concentration values at different locations inside the room for a process of purging following steady injection were used to estimate the probability density function of the local residence age whose shape provided further experimental evidence of the prolonged dilution due to pollutant fluid which entered stagnation zones. The results also showed that the statistical time-scales of the dispersion and the mixing efficiency are independent of the level of the steady pollutant generation.

The ratio of the mean age to its standard deviation is recommended as a local mixedness factor and comparison with the mixing efficiency defined on the basis of integral time-scales and the exponential decay model revealed that it represents better the local variations, which is essential to assessing local indoor air quality. The extent of validity of the exponential decay model was also evaluated by comparing the time constant of this model with model-independent integral time-scales and it is shown that the underlying assumptions of the exponential decay model precludes the representation of spatial gradients.
Dynamic Analysis of Flexible Multi-Body Mechanical Systems
Authors: Davison P , Longmore D K , Burrows C R
Published: February 2007

The use of only the free component modes as coordinates when computing the motion of mechanisms involving flexible component structures connected together by driven or undriven joints has been further developed, with the constraint errors being controlled by penalty parameters related to both the errors and their time rate of change. Symbolic computation is used to incorporate the constraint equations into the solution program. The degenerate rigid-body modes may be indefinitely large, with Euler parameters being used for rotation, but the other free modes of the individual components, which involve structural deformation, are assumed small. The approach is examined in two examples in which the computed results are compared with experimental measurements.
On the Plastic Buckling Paradox for Cylindrical Shells
Authors: Blachut J , Galletly G D , James S
Published: February 2007

Previous investigations have raised some doubts about the accuracy of flow theory predictions for a few plate and shell plastic buckling problems. The present series of buckling experiments on machined, mild steel, cylindrical shell models under non-proportional biaxial loading (axial tension plus external pressure) was designed to provide additional data for the evaluation of the J2 plasticity theories. Numerical calculations were carried out with the BOSOR 5 shell buckling program, using the J2 deformation and flow theories, and these were compared with the test results. Neither theory can be said to predict plastic buckling accurately. However, deformation theory predicted the bifurcation buckling loads reasonably well, whereas flow theory was often incorrect.
A Novel Worm Gear of High Efficiency
Authors: French M J
Published: February 2007

This note describes a novel form of worm gear, in which the worm pinion has teeth that run straight round it and join up with themselves, so that they form rings (‘ring teeth’). These rings are free to turn on bearings whose axes are parallel to the axis of rotation of the whole pinion, but eccentric to it by a small amount r, such that the centres of the rings lie on a helix, radius r.

The teeth of the worm wheel are formed in the inside of a torus, so that they embrace the pinion somewhat. They have a small helical angle so that as a ring tooth rolls round the space between two worm teeth it forces them forward. Before that ring tooth disengages at one side of that worm wheel tooth space, the next ring tooth has engaged with the next wheel tooth space, and so on.

Because the ring teeth roll on the wheel teeth, with only a little spin and transverse sliding, the efficiency is very high. However, the construction of the pinion is elaborate and the load capacity of the drive is limited by that of the bearings on which the ring teeth rotate, which in turn is small because of the limits on space.
Possibilities for Future Developments in Primary Safety Requirements
Authors: Breen J , Condon R
Published: February 2007

Primary safety measures offer great potential for accident reduction. This paper highlights priority areas outlined in the 1993 European Transport Safety Council review (1) which could be addressed by such measures. The authors also assess the current knowledge with a view to the research-based possibilities for future developments in accident prevention which can be made through key aspects of car design.
The Torque–Tension Behaviour of 22 × 1.5 mm Bolts for Fixing Spigot-Located Wheels on Heavy Commercial Vehicles
Authors: Morgan R C , Henshall J L
Published: February 2007

Threaded fasteners are generally used to secure wheels on to vehicles. However, in the case of heavy commercial vehicles, in recent years there has been a problem of ensuring the integrity of wheel fixings (1, 2). Notwithstanding a change of wheel centring from conically ended nuts to a central hub spigot, essentially the same wheel fixing system is used nowadays as was developed when the operational duty cycles were much lower, for example 80 kN versus 130 kN maximum regular axle loads, increased mileages, markedly improved braking performance, higher speeds, better tyre/road coefficients and greater cornering forces. Consequently a new British Standard concerned with quality control of the components used for commercial vehicle wheel fixings has been published (3). The purpose of the present work is to report the results of an investigation into some of the factors which can affect the performance of the main type of commercial vehicle wheel fastener, in particular the effects of fastener friction on the pre-load.

Experiments have been performed on 22 × 1.5 mm wheel bolts and nuts under four different conditions, namely ‘as received’, degreased, heat-cycled and re-lubricated, at torques up to 800 N m. The results showed a substantial decrease, of up to 60–70 per cent, in axial tension for both degreased and heat-cycled conditions, when compared with the ‘as received’ performance. Full recovery was found to be achievable simply by re-lubricating with engine oil. The theoretical torque-tension model (4) was modified to account for the nut–washer geometry and used to determine effective friction coefficients. These, and the other limited published data (5–7) were used to define performance boundaries. A comparison is made between the data presented herein and the quality determining performance as specified in the new British Standard (3).
Assessment of a New Technique for Measuring Flow Properties of Powdered Materials Stored in Hoppers
Authors: Marjanović P , Jones M G
Published: February 2007

Particulate materials stored in silos and hoppers still cause problems during discharge, spanning from unacceptable flow patterns and inadequate flowrates to arching or rat-holing formation that may even stop the flow. All these problems relating to the flow of bulk material from hoppers and silos are very complex in nature as they are highly influenced by both bulk material properties and hopper characteristics. The major breakthrough in the understanding of this phenomenon was made more than 30 years ago with Jenike's rational approach. Ever since then a number of new techniques and methods have been developed in order to improve the reliability of hopper design. One of the latest techniques in this field is the Johanson Indicizer System. An initial assessment of the results obtained with this new technique are presented in this paper.
Pressurized Piping Elbows under Simulated Seismic Bending: Design Code Implications
Authors: Yahiaoui K , Moffat D G , Moreton D N
Published: February 2007

A series of 16 pairs of carbon and stainless steel, long and short radius 90° piping elbows, 2 inch NPS, schedule 40 and 80 (60.3 mm outside diameter, 3.91 mm and 5.54 mm thick respectively) have been tested under conditions of steady internal pressure and either in-plane or out-of-plane resonant bending to simulate seismic conditions. Experimental conditions are reviewed before some comments are made about the ASME Code Section III design stress indices. Next the stress limits achieved in the described tests are presented and compared with newly proposed allowable stresses. Ratios of applied dynamic moment to calculated limit moment in excess of unity and up to 2.11 have been consistently obtained. Finally, a summary of the experimentally obtained ratchet strain accumulation is presented and assessed against a recently proposed ‘strain control approach'.
Tolerance of Composite Pipes to Local Impact Damage
Authors: Reid S R , Peng C , Ashton J N
Published: February 2007

The results of an extensive experimental programme on local loading of composite pipes are presented. Particular attention is directed to the influence of projectile nose shape on the damage tolerance of the pipes. Both filament wound pipes and lined chopped-strand mat pipes are considered.
The Use of Centre Bodies and De-Swirl Vanes in the Exhaust of Cyclone Dust Separators
Authors: Griffiths A J , Yazdabadi P , Syred N
Published: February 2007

This study arises from vibration problems that have been encountered in cyclones operated at high pressure. Work has shown that such vibrations can be triggered by the complex flow process and regular fluid dynamic periodicities that can occur especially in the exhaust nozzle. One such phenomenon is the precessing vortex core (PVC); this is where the central forced vortex region of the flow precesses about the central axis of the system.
Measures to Reduce the Lateral Vibration of the Tail Car in a High Speed Train
Authors: Fujimoto H , Miyamoto M
Published: February 2007

From the vibration data obtained simultaneously on several cars in the same Shinkansen train, it was observed that the vibration amplitude of the tail car is greater than those of the other cars in a train. The authors' analysis arrived at the conclusion that the vibration mode of a train has a tendency for the tail car to vibrate more than the others, when the carbody hunting characteristics of a train for the yawing mode are likely to emerge, and when aerodynamic forces work in a tunnel section. Referring to those results, by simulation analysis etc., it was found that two longitudinal dampers installed parallel between the car ends (Fig. 1) with their forces depending on the angular velocity between cars, are effective in decreasing the train vibration including the tail car's vibration. Then, the prototype of the longitudinal dampers between the cars for Shinkansen was designed by obtaining the proper damping coefficient through simulation. The effectiveness of the installed damper was verified when it was tested up to 310 km/h in the Shinkansen train.
Global Stability of a Shielded Dual-Spin Satellite
Authors: Ge Z-M , Chen H-K
Published: February 2007

Sufficient conditions for the global stabilities of equilibrium positions of a dual-spin satellite equipped with a cylindrical electrostatic screen normal to the circular equatorial orbital plane system under the action of moments induced by the gravitational and Lorentz forces are obtained by Liapunov's direct method. The problem is then studied with respect to all variables, including the angular velocity of the rotor. The instabilities of the problem are solved by the first approximation theorem. Furthermore, sufficient conditions for the global stability of rotation with arbitrary angular velocity for an axisymmetric dual-spin satellite equipped with an electrostatic screen are presented by applying Liapunov's direct method.
Flow Characteristics in a Large Area Ratio Curved Diffuser
Authors: Majumdar B , Singh S N , Agrawal D P
Published: February 2007

Flow characteristics in a large area ratio curved diffuser (AR = 3.4, Δβ = 90°, AS = 0.685) have been experimentally evaluated with splitter vanes installed at different angles to the flow at the inlet of the diffuser. The splitter vanes deflect the flow towards the convex wall and simultaneously increase the turbulence intensity. A marked improvement in flow distribution inside the diffuser and a significant increase in the static pressure recovery coefficient are obtained with splitter vanes at a 10° angle.
A Modified Surface Spline for Expansion and Smoothing of Frequency Response Functions
Authors: Waters T P , Lieven N A J
Published: February 2007

Measured frequency response functions (FRFs) are becoming more widely used to correlate finite element (FE) models with test structures. However, most model updating techniques require measured data at every degree of freedom (DOF) in the FE model, a necessity that is rarely met by experiment. Furthermore, the sensitivity of updating techniques to noise measurement demands experimental data of the highest attainable quality, and often beyond. A modified surface spline is presented which can expand measured FRFs to unmeasured DOFs and also apply smoothing to reduce noise contamination.
Fatigue of Composite Materials under Aircraft Service Loading
Authors: Farrow IR
Published: February 2007

Fatigue damage accumulation and analysis methods are considered for composites and contrasted with metals. The failure of current analysis methods is illustrated and explained by the information missing in load idealization data. Detailed local strain operational monitoring with local strain fatigue data is proposed as a future approach to fatigue life assessment of composite materials under aircraft service loading.
Physical Modelling of Hip Joint Forces in Stair Climbing
Authors: Shelley F J , Anderson D D , Kolar M J , Miller M C , Rubash H E
Published: February 2007

A test device has been developed and validated to simulate physiologic loading of the hip during stair climbing. Forces about the hip joint were measured in static simulations of stair climbing using simulated extensor, abductor and adductor muscle groups to support the joint. Femoral flexion angle (to model step length and height) and applied hip flexion moment (to model trunk lean) were varied to examine the effects of different loading conditions on the hip. In stair climbing the maximum total joint force was six times body weight at 34° of femoral flexion and 60 N m of hip flexion moment. Joint forces increased with hip flexion moment and varied little with femoral flexion angle, except for the posteriorly directed force. This component, which twists implants about the femoral shaft, increased with femoral flexion angle but changed little with hip flexion moment.
Fibre Recruitment and Shape Changes of Knee Ligaments during Motion: As Revealed by a Computer Graphics-Based Model
Authors: Lu T-W , O'Connor J J
Published: February 2007

A computer graphics-based model of the knee ligaments in the sagittal plane was developed for the simulation and visualization of the shape changes and fibre recruitment process of the ligaments during motion under unloaded and loaded conditions. The cruciate and collateral ligaments were modelled as ordered arrays of fibres which link attachment areas on the tibia and femur. Fibres slacken and tighten as the ligament attachment areas on the bones rotate and translate relative to each other. A four-bar linkage, composed of the femur, tibia and selected isometric fibres of the two cruciates, was used to determine the motion of the femur relative to the tibia during passive (unloaded) movement. Fibres were assumed to slacken in a Euler buckling mode when the distances between their attachments are less than chosen reference lengths. The ligament shape changes and buckling patterns are demonstrated with computer graphics. When the tibia is translated anteriorly or posteriorly relative to the femur by muscle forces and external loads, some ligament fibres tighten and are recruited progressively to transmit increasing shear forces. The shape changes and fibre recruitment patterns predicted by the model compare well qualitatively with experimental results reported in the literature. The computer graphics approach provides insight into the micro behaviour of the knee ligaments. It may help to explain ligament injury mechanisms and provide useful information to guide the design of ligament replacements.
Wear in Retrieved Charnley Acetabular Sockets
Authors: Hall R M , Unsworth A , Siney P , Wroblewski B M
Published: February 2007

One hundred and twenty-nine Charnley acetabular components were acquired at the time of revision surgery and a tribological investigation undertaken. The relative occurrence of pitting in the unworn and worn regions of the sockets suggest that most of the cement ingress occurs during the early part of the service life. The penetration depth of the explanted sockets was determined using the shadowgraph technique. Observation of the profiles in the wear planes suggest that, in general, the creep component was not a significant proportion of the overall change in the inner bore of the socket. Using weighted ordinary least squares regression, in which the intercept was not assumed to be zero, mean penetration and wear volume rates of 0.20 (SE = 0.02) mm/year and 55 (SE = 5) mm3/year, respectively, were recorded and are in agreement with other retrieval studies. In neither case was the intercept found to be significantly different from zero. A mean clinical wear factor, kclinical, equal to 2.1 (SE = 0.2) × 10-6 mm3/N m was calculated which is considerably larger than that found in laboratory experiments which purport to reflect in vivo conditions. In this analysis, a significant positive intercept was observed [96 (SE = 36) mm3] and may be evidence of the small initial penetration due to creep reported in simulator experiments. A strong positive association between kclinical and the arithmetical mean roughness, Ra, of the femoral head was also demonstrated although the rate of change was not as great as that cited for laboratory experiments.
Intervertebral Disc Response to Cyclic Loading—An Animal Model
Authors: Ekström L , Kaigle A , Hult E , Holm S , Rostedt M , Hansson T
Published: February 2007

The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 per cent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the intitial elastic response.
Optimal Control of an n-Legged Robot
Authors: Channon P H , Hopkins S H , Pham D T
Published: February 2007

This paper presents a method for controlling the dynamic balance of legged robots using optimal state feedback. Rather than being restricted to a specific number of legs, the method considers the general case of a machine with n legs. The analysis starts with a non-linear dynamic model of a general robot and a set of equations representing the constraints on motion imposed by those feet in contact with the ground. These equations are used to derive a state-space model of order proportional to the number of degrees of freedom of the system, which will vary with the current constraint conditions. An optimal feedback gain matrix is then calculated for the linear model using standard techniques. The choice of operating point and optimization parameters is discussed. The effectiveness of the method is illustrated through simulation responses obtained for a biped model under both single and double support constraint conditions.
Measurement of Positive Displacement Pump Flow Ripple and Impedance
Authors: Johnston D N , Drew J E
Published: February 2007

The secondary source method forms the British Standard for pump fluid-borne noise testing. This is a powerful technique but requires care in order to produce accurate results. This paper describes practical aspects for implementing the method. The requirements for the test rig, data acquisition system and analysis are detailed.

The British Standard specifies that either mathematical modelling or linear interpolation is used on the source impedance measurements. A method for smoothing the impedance results is described in this paper, which is shown to give more repeatable results than linear interpolation. Some physically realistic mathematical models of pump impedance are described, and their use in determining the internal flow ripple discussed.
A Unifying Theory of Least-Squares Padé Model Reduction Methods
Authors: Smith I D , Lucas T N
Published: February 2007

The apparently different approaches of least-squares parameter-matching Podé model reduction methods are shown to be related via a unifying theory. From the formulation it is possible to show several interesting features of the least-squares approach which lead to a fuller understanding of exactly how the reduced model approximates the system. An error index is derived for the general case and it is shown that a range of system parameter preservation options are available to the user. A numerical example illustrates the main points of the paper.
A Combination of Fuzzy Logic and Neural Network Algorithms for Active Vibration Control
Authors: Huang S-J , Lian R-J
Published: February 2007

The construction of a dynamic absorber incorporating active vibration control is described. The absorber is a 2 degree of freedom spring-lumped mass system sliding on a guide pillar, with two internal vibration disturbance sources. Both the main mass and the secondary absorber mass were acted on by direct current (d.c.) servo motors, respectively, to suppress the vibration amplitude. In this paper, a new control approach is proposed by combining fuzzy logic and neural network algorithms to control the multi-input/multi-output (MIMO) system. Firstly, the fuzzy logic controller was designed for controlling the main influence part of the MIMO system. Secondly, the coupling neural network controller was employed to take care of the coupling effect and refine the control performance of the MIMO system. The experimental results show that the control system effectively suppresses the vibration amplitude and with good position tracking accuracy.
Thermal-Hydraulic Performance Prediction in Fluid Power Systems
Authors: Sidders J A , Tilley D G , Chappie P J
Published: February 2007

This paper presents a modelling approach to the study of thermal-hydraulic performance in fluid power systems. A set of lumped parameter mathematical models are developed which are based on conservation of mass and energy for the system. The theoretical basis and modelling strategy are discussed for an open circuit containing a hydraulic pump, loading valve, heat exchanger and reservoir. Simulation results are presented which show a comparison of model/rig performance, and the agreement obtained demonstrates the validity of the modelling approach. It is shown that the thermal response is dominated by the reservoir heat capacity and that close correspondence between the model and rig is only achievable with accurate hydraulic performance models.
Dynamic Characteristics of a Rolling Mill
Authors: Evans P R , Hill D E , Vaughan N D
Published: February 2007

This paper describes an investigation into the dynamic characteristics of a rolling mill. Those characteristics representing limitations, to both productivity and gauge accuracy, are clearly identified with reference to results from a recently installed rolling mill. A linearized mathematical model is developed that conceptually describes these limitations. This model highlights the significance of gauge tension interactions, the second natural frequency of the mill stack dynamic system and the first natural frequency of the entry coil dynamic system.
Computation of the Lasserre Ranks of Some Polytopes
Authors: Cheung Kevin K. H.
Published: February 2007

Over the years, various lift-and-project methods have been proposed to construct hierarchies of successive linear or semidefinite relaxations of a 0–1 polytope P ⫅ ℝn that converge to P in n steps. Many such methods have been shown to require n steps in the worst case. In this paper, we show that the method of Lasserre also requires n steps in the worst case.
Topological Uniqueness of the Nash Equilibrium for Selfish Routing with Atomic Users
Authors: Richman Oran , Shimkin Nahum
Published: February 2007

We consider the problem of selfish routing in a congested network shared by several users, where each user wishes to minimize the cost of its own flow. Users are atomic, in the sense that each has a nonnegligible amount of flow demand, and flows may be split over different routes. The total cost for each user is the sum of its link costs, which, in turn, may depend on the user’s own flow as well as the total flow on that link. Our main interest here is network topologies that ensure uniqueness of the Nash equilibrium for any set of users and link cost functions that satisfy some mild convexity conditions. We characterize the class of two-terminal network topologies for which this uniqueness property holds, and show that it coincides with the class of nearly parallel networks that was recently shown by Milchtaich [Milchtaich, I. 2005. Topological conditions for uniqueness of equilibrium in networks. Math. Oper. Res. 30 225–244] to ensure uniqueness in nonatomic (or Wardrop) routing games. We further show that uniqueness of the link flows holds under somewhat weaker convexity conditions, which apply to the mixed Nash-Wardrop equilibrium problem. We finally propose a generalized continuum-game formulation of the routing problem that allows for a unified treatment of atomic and nonatomic users.
Competition and Efficiency in Congested Markets
Authors: Acemoglu Daron , Ozdaglar Asuman
Published: February 2007

We study the efficiency of oligopoly equilibria (OE) in congested markets. The motivating examples are the allocation of network flows in a communication network or of traffic in a transportation network. We show that increasing competition among oligopolists can reduce efficiency, measured as the difference between users’ willingness to pay and delay costs. We characterize a tight bound of 5/6 on efficiency in pure strategy equilibria when there is zero latency at zero flow and a tight bound of 2√2 − 2 with positive latency at zero flow. These bounds are tight even when the numbers of routes and oligopolists are arbitrarily large.
Pain Assessment in the Perspective of Action Science
Authors: Kim Hesook Suzie , Sjöström Björn , Schwartz-Barcott Donna
Published: February 2007

Pain assessment is examined in the perspective of action science with the aim to discover espoused theories and theories-in-use for pain assessment. In action science there are 2 sets of theories of action: espouse theories and theories-in-use, which often exist in practice inconsistently with each other resulting in haphazard actions. Espoused theories of pain and pain assessment and a set of theories-in-use were revealed. Alignments between the espoused theories and the theories-in-use, and disparities between these theories were found in the pain assessment situations. The findings point to possible explanations regarding problems in pain assessment, and provide insights into our understanding of nursing practice especially in relation to pain assessment.
Having a Sibling With Schizophrenia: A Phenomenological Study
Authors: Barnable Alexia , Gaudine Alice , Bennett Lorna , Meadus Robert
Published: February 2007

Limited attention has been paid to experiences of individuals with siblings diagnosed with schizophrenia. The purpose of this article is to address this gap by exploring the impact of having a brother or sister with schizophrenia. The lived experience of 6 individuals with a sibling with schizophrenia was explored using van Manen’s (1997) Hermeneutic Phenomenology. Four themes were identified: struggling to understand, struggling with the system, caring for the sibling, and seeing beyond the illness. Health care providers need to re-evaluate current approaches for assisting individuals to cope with having a sibling with schizophrenia. Inclusion in the plan of care and recognition of their struggle is essential for individuals having a sibling with schizophrenia.
Grassed buffer strips as nitrate diffuse pollution remediation tools: management impact on the denitrification enzyme activity
Authors: Cors M. , Tychon B.
Published: February 2007

The management of grassed buffer strips proved to be an efficient remediation technique in controlling nitrogen losses to surface water. In south Belgium, agri-environmental policies have encouraged farmers to seed buffer strips along rivers, in zones where the soil was previously devoted to agricultural production.

We wanted to assess how important denitrification is in a buffer strip in comparison with a cropped field. The study investigated the denitrifiying enzyme activity (DEA) of two contiguous buffer strips with different management stories. The eastern part of the buffer strip was seeded in 1999. The western part of the buffer strip is a piece of crop field abandoned by the farmer 20 years ago and not managed for the last 10 years.

This experimental study demonstrates that the denitrification enzyme activity in a riparian buffer strip is significantly higher than in the adjacent cropped field (3.67 and 2.12 mgNkg–1d−1 respectively). The DEA was significantly different between the two buffer strips under comparison, assessing that the management of the buffer strips has a dominant effect on DEA. The old unmown buffer strip is potentially more efficient in the nitrate removal process than the 6-year-old seeded buffer strip.