bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and experimental evaluation for elastic deformation of a cold forging tool and workpiece for a sleeve cam of an automobile start motor
Authors: Kang G-J , Kim J , Kang B-S
Published: March 2008

The dimension of the final stage of cold forging a product is different from that of the die. The difference is influenced by various effects such as elastic deformation of the die and elastic recovery of the billet. In this study, in order to investigate the trend of elastic expansion of the die and elastic recovery of the billet, which is important to develop dimensional accuracy of the die, a finite element analysis was carried out using a commercial FEM code, DEFORM-3DTM. The die was designed according to the analysis results. Real elastic deformation of the die was obtained from both the rigid die model analysis and compensation by shrink fitting. Further, the forging process was evaluated by ductile fracture criteria. Finally, gear manufacturing based on the designed die is carried out. By measuring the results of the gear it was shown that the manufactured gear satisfies the JIS 6 class. The cold forging technology developed in this study to manufacture a gear part with a complicated shape is expected to be used effectively for production of other precision parts.
Geometric error measurement and compensation of a six-degree-of-freedom hybrid positioning stage
Authors: Wang F-S , Chen S-L
Published: March 2008

This paper presents the geometric error measurement and compensation of a six-degree-of-freedom (6-DOF) hybrid positioning stage consisting of a 3-DOF parallel kinematic mechanism and a 3-DOF serial mechanism. The parallel kinematic mechanism uses ball joints and wedge-shaped mechanisms to provide the required rotational and sliding movement. The advantages of this mechanism include a simple structure, easy assembly, and zero accumulated linkage errors. The study commences by describing the kinematic mechanisms of the positioning stage, and then evaluates the degrees of freedom of the parallel kinematic mechanism. Subsequently, a homogeneous transformation matrix approach is employed to perform an inverse analysis of the kinematics of the entire positioning stage. The study then discusses the effects of geometric errors caused by imprecision in the manufacturing and assembly processes on the positional accuracy of the stage. Finally, a coordinate measuring machine is used to measure the translation and orientation errors of the positioning stage. By comparing the measured data with the values derived from the inverse kinematics analysis, an error compensation model is constructed.
Improvement in microhole machining accuracy by polarity changing technique for microelectrode discharge machining on Ti—6Al—4V
Authors: Pradhan B B , Bhattacharyya B
Published: March 2008

A novel technique is presented of changing polarity for microelectrode discharge machining (micro-EDM) in a systematically designed time domain while machining titanium alloy (Ti—6Al—4V) for the fabrication of straight-through microholes. Experimental investigations were made to study precisely the effects of changing polarity in micromachining of Ti—6Al—4V. The experimental investigations revealed that the process parameters of most influence in micro-EDM are peak current Ip and pulse-on time ( Ton). These process parameters are heuristically investigated through experiments and their most suitable values are presented in this paper to achieve higher geometrical accuracy in the fabrication of straight-through microholes, which has tremendous applications in biomedical microdevices and automotive, aerospace, and microelectromechanical systems. The material removal rate (MRR), tool wear rate (TWR), overcut (OC), diameter variation at entry and exit (DVEE), and taperness are evaluated. Finally, a new technique of machining straight-through microholes with a set of machining parameters is suggested. A comparative study of constant and changing polarity is also made, and results show that Ton in the range of 1—10 μs and Ip below 1 A with changing polarity are more effective for micro-EDM in improving the machining accuracy of straight-through microholes.
Development of dimethyl ether engines for light-duty trucks using a large exhaust gas recirculation system
Authors: Lim O T , Sato Y , Oikawa H , Nozaki S , Noda T , Ushiyama D , Ishikawa T
Published: March 2008

A light-duty truck diesel engine fuelled with dimethyl ether (DME) using a jerk-type in-line DME injection system, which meets the Japan 2009 Emission Regulation, was developed. It includes lower exhaust emission technology such as a large exhaust gas recirculation system with air-throttled and inter-cooled turbocharging. The National Traffic Safety Office, Environment Laboratory, and Bosch Corporation have demonstrated low-emission engines which reduce NO x emission levels to about 50 per cent of the 2009 emissions regulation without an NO x reduction catalyst system.
Combustion and emissions of a direct-injection diesel engine during cold start under different exhaust valve closing timing conditions
Authors: Peng H-Y , Cui Y , Deng K-Y , Shi L , Li L-G
Published: March 2008

The residual gas fraction has significant effects on combustion in a diesel engine. However, few researchers have studied the effects of the residual gas on startability and emissions of a diesel engine during cold start, in which the components of the residual gas fraction were very different from those under normal operating conditions. Through experiments conducted on a single-cylinder direct-injection diesel engine, this paper investigated the combustion and emissions characteristics during cold start under different exhaust valve closing (EVC) timing conditions. The results show that an appropriate increase in the residual gas fraction could promote ignition of the first firing cycle and combustion stability significantly during cold start. Residual gas also had significant effects on the emissions during cold start. Opacity during cold start, especially during the initial phase, could be reduced significantly by properly advancing the EVC timing. Owing to the strong thermal effect of residual gas, nitrogen oxide (NO x) emissions during cold start tended to increase as the EVC timing was advanced.
Model for N2O monopropellant thruster operation
Authors: Zakirov V , Zhang H
Published: March 2008

The current paper presents a new model for the simulation of a prospective nitrous oxide (N2O) monopropellant thruster operation. The specific impulse performance expected by the N2O monopropellant is suitable for spacecraft station-keeping and small orbit manoeuvres. This thruster is presently at a lab-scale prototype firing stage of research and development. The N2O monopropellant operation is simulated during the most important, start-up transient and steady-state, thruster modes. A good fit between experiment and simulation has been achieved during model validation. This demonstrates that the assumptions made in the model are feasible for accurate representation of the processes and phenomena occurring inside the N2O monopropellant thruster during operation so that the model is applicable for practical design problem solution. Further development of the existing model is expected to provide more detailed understanding of the decomposition process along the thruster.
Solar sail attitude control using small reaction wheels and magnetic torquers
Authors: Polites M , Kalmanson J , Mangus D
Published: March 2008

The current paper describes an attitude control system that uses small reaction wheels and magnetic torquers to control the attitude of a large flexible solar sail in low-Earth orbit (LEO). This system is being proposed for the NASA New Millenium Programme Space Technology-9 solar sail technology demonstration mission. Controlling the attitude of a solar sail with these actuators in LEO was previously considered difficult and thus never proposed before. What makes it possible is choosing the right orbit and judiciously constraining the attitude of the solar sail in that orbit. Simulation results are presented that validate this design approach for solar sail attitude control in LEO.
Particle image velocimetry investigation of an aerofoil with a Gurney flap
Authors: Nožička J , Matějka M , Bárta P
Published: March 2008

The current paper reviews the research on NACA 23012 and FX66-17AII-182 aerofoils, aerodynamic performance for different angles of attack at Reynolds number Re ≍ 3 × 105, based on chord, both with clean configuration and the flaps. Flow field around the aerofoil was measured using a two-dimensional particle image velocimetry (PIV) system, and the measurement of static pressure on aerofoil surface was carried out. The current article also describes new methods in Gurney flap research, using the two-dimensional PIV system and Kutta—Joukowski lift theorem or static pressure assumption to evaluate aerofoil lift.
Reality-augmented virtual fluoroscopy for computer-assisted diaphyseal long bone fracture osteosynthesis: A novel technique and feasibility study results
Authors: Zheng G , Dong X , Gruetzner P A
Published: March 2008

In this paper, a novel technique to create a reality-augmented virtual fluoroscopy for computer-assisted diaphyseal long bone fracture osteosynthesis and feasibility study results are presented. With this novel technique, repositioning of bone fragments during closed fracture reduction and osteosynthesis can lead to image updates in the virtual imaging planes of all acquired images without any radiation. The technique is achieved with a two-stage method. After acquiring a few (normally two) calibrated fluoroscopic images and before fracture reduction, the first stage, data preparation, interactively identifies and segments the bone fragments from the background in each image. After that, the second stage, image updates, repositions the fragment projection on to each virtual imaging plane in real time during fracture reduction and osteosynthesis using an OpenGL-based texture warping. Combined with a photorealistic virtual implant model rendering technique, the present technique allows the control of a closed indirect fracture osteosynthesis in the real world through direct insight into the virtual world. The first clinical study results show the reduction in the X-ray radiation to the patient as well as to the surgical team, and the improved operative precision, guaranteeing more safety for the patient. Furthermore, based on the experiences gained from this clinical study, two technical enhancements are proposed. One focuses on eliminating the user interactions with automated identifications and segmentations of bone fragments. The other focuses on providing non-photorealistic implant visualization. Further experiments are performed to validate the effectiveness of the proposed enhancements.
Experimental set-up and sensory glove interface for microsurgery
Authors: Amirouche F , Martin J R , Gonzalez M , Fergusson L
Published: March 2008

One of the most fundamental prerequisites for successful microsurgery is thoughtful and adequate training. A combination of knowledge, technical skill, and decision making directly influences the surgical outcome. This study aims to analyse microsurgical hand coordinations quantitatively and to study the utility of a sensory glove interface in identifying the hand coordination patterns during microsurgery. A sensory glove interface used to measure the angular flexion—extension movements of the major interphalangeal joints of the hand, the grasp pressure, and the relative hand movements has been developed. Experiments of two suturing techniques were conducted with five experienced microsurgeons, and microsurgery practice was examined. The custom sensory glove interface required both signal conditioning and amplification which was directly interfaced with a custom-designed LABView software code. The sensory glove interface was calibrated using regression techniques and the set-up was validated using the Bland—Altman correlation technique.

The hand coordination patterns were analysed using principal-component analysis. Pareto plots showing the contribution of the principal components were analysed. The contributions of the first two sensory data components have also been compared with hand coordination studies. The temporal variations provided new insights into the underlying synergetic mechanisms and in particular the relation between different suture techniques on grasp pressure.
The effects of trochlear groove geometry on patellofemoral joint stability-a computer model study
Authors: Jafari A , Farahmand F , Meghdari A
Published: March 2008

The effect of the variation in the femoral groove geometry on patellofemoral joint stability was studied using a two-dimensional transverse plane model with deformable articular surfaces. The femoral and patellar bony structures were modelled as rigid bodies with their profiles expressed by splines. The articular cartilage was discretized into compression springs, distributed along the femoral and patellar profiles, based on the rigid-body spring model. The medial and lateral retinacula were modelled as linear tensile springs, and the quadriceps muscles and patellar tendon as strings with known tension. The anatomical data were obtained from the transverse plane magnetic resonance images of a normal knee flexed at 20° and from the literature. A dynamic analysis approach was employed to solve the governing equations of the model, i.e. three static equilibrium equations of the patella and a constraint equation for each cartilage spring, explicitly. The results of the model suggest that alteration of the sulcus angle from 139° to 169° causes a lateral shift and tilt of less than 3 mm and 4°. This effect increased slightly with increasing total quadriceps force, however, to significantly more than 7 mm and 18° respectively when the medial retinaculum was released. It was suggested that this might be the combined effect of the medial retinaculum deficiency and trochlear dysplasia that is responsible for patellar subluxation and, particularly, dislocation disorders.
Anatomy and biomechanics of quadratus lumborum
Authors: Phillips S , Mercer S , Bogduk N
Published: March 2008

Various actions on the lumbar spine have been attributed to quadratus lumborum, but they have not been substantiated by quantitative data. The present study was undertaken to determine the magnitude of forces and moments that quadratus lumborum could exert on the lumbar spine. The fascicular anatomy of quadratus lumborum was studied in six embalmed cadavers. For each fascicle, the sites of attachment, orientation, and physiological cross-sectional area were determined. The fascicular anatomy varied considerably, between sides and between specimens, with respect to the number of fascicles, their prevalence, and their sizes. Approximately half of the fascicles act on the twelfth rib, and the rest act on the lumbar spine. The more consistently present fascicles were incorporated, as force-equivalents, into a model of quadratus lumborum in order to determine its possible actions. The magnitudes of the compression forces exerted by quadratus lumborum on the lumbar spine, the extensor moment, and the lateral bending moment, were each no greater than 10 per cent of those exerted by erector spinae and multifidus. These data indicate that quadratus lumborum has no more than a modest action on the lumbar spine, in quantitative terms. Its actual role in spinal biomechanics has still to be determined.
Development of specimen-specific finite element models of human vertebrae for the analysis of vertebroplasty
Authors: Wijayathunga V N , Jones A C , Oakland R J , Furtado N R , Hall R M , Wilcox R K
Published: March 2008

The aim of this study was to determine the accuracy of specimen-specific finite element models of untreated and cement-augmented vertebrae by direct comparison with experimental results. Eleven single cadaveric vertebrae were imaged using micro computed tomography (mCT) and tested to failure in axial compression in the laboratory. Four of the specimens were first augmented with PMMA cement to simulate a prophylactic vertebroplasty. Specimen-specific finite element models were then generated using semi-automated methods. An initial set of three untreated models was used to determine the optimum conversion factors from the image data to the bone material properties. Using these factors, the predicted stiffness and strength were determined for the remaining specimens (four untreated, four augmented). The model predictions were compared with the corresponding experimental data. Good agreement was found with the non-augmented specimens in terms of stiffness (root-mean-square (r.m.s.) error 12.9 per cent) and strength (r.m.s. error 14.4 per cent). With the augmented specimens, the models consistently overestimated both stiffness and strength (r.m.s. errors 65 and 68 per cent). The results indicate that this method has the potential to provide accurate predictions of vertebral behaviour prior to augmentation. However, modelling the augmented bone with bulk material properties is inadequate, and more detailed modelling of the cement region is required to capture the bone—cement interactions if the models are to be used to predict the behaviour following vertebroplasty.
Towards a standard in assessment of bone cutting for total knee replacement
Authors: Barrera O A , Haider H , Garvin K L
Published: March 2008

Arthroplasty outcome is influenced by the ‘quality’ of bone preparation for implant insertion. Surgeons face increasing choices of technique and instrumentation, yet clinical scoring methods assess the overall outcome and patient satisfaction but not the bone cuts directly. ‘Quality management’ of bone reshaping is needed to evaluate different bone cutting methods and computer assisted orthopaedic surgery (CAOS) systems. Analyses and experiments in this study were formulated for measurement and computation of four quantitative characteristics of bone preparation ‘quality’ and produced a highly condensed index for each. These represented (a) surface finish of cuts, (b) implant fit/looseness possible with the cut shape, (c) implant location/misalignment, and (d) accuracy of individual planar cuts. Assessment of synthetic bone cuts verified the robustness of the method for wide application in arthroplasty intraoperatively, in vitro and for comparing navigation systems.
The internal pressure and stress environment of the scoliotic intervertebral disc — a review
Authors: Meir A , McNally D S , Fairbank J C , Jones D , Urban J P
Published: March 2008

The aetiology, in terms of both initiation and progression, of the deformity in idiopathic scoliosis is at present unclear. Even in neuromuscular cases, the mechanisms underlying progression are not fully elucidated. It is thought, however, that asymmetrical loading is involved in the progression of the disease, with evidence mainly from animal studies and modelling. There is, however, very little direct information as to the origin or mechanism of action of these forces in the scoliotic spine. This review describes the concept of intervertebral disc pressure or stress and examines possible measurement techniques. The biological and mechanical consequences of abnormalities in these parameters are described. Future possible studies and their clinical significance are also briefly discussed.

Techniques of pressure measurement have culminated in the development of ‘pressure profilometry’, which provides stress profiles across the disc in mutually perpendicular axes. A hydrated intervertebral disc exhibits mainly hydrostatic behaviour. However, in pathological states such as degeneration and scoliosis, non-hydrostatic behaviour predominates and annular peaks of stress occur. Recent studies have shown that, in scoliosis, high hydrostatic pressures are seen with asymmetrical stresses from concave to convex sides. These abnormalities could influence both disc and endplate cellular activity directly, causing asymmetrical growth and matrix changes. In addition, disc cells could be influenced via nutritional changes consequent to end-plate calcification.

Evidence suggests that the stress environment of the scoliotic disc is abnormal, probably generated by high and asymmetrical loading of non-muscular origin. If present in the scoliotic spine during daily activities, this could generate a positive feedback of cellular changes, resulting in curve progression. Future advances in understanding may rely on the development of computer models owing to the difficulties of in-vivo invasive measurements.
Tibiofemoral cartilage thickness distribution and its correlation with anthropometric variables
Authors: Connolly A , FitzPatrick D , Moulton J , Lee J , Lerner A
Published: March 2008

The objective of this study was to determine tibiofemoral cartilage thickness distribution, and to investigate the relationship between cartilage geometry and anthropometric variables.

In this study, 20 magnetic resonance examinations of the knee from normal individuals were reconstructed to provide three-dimensional models of the knee joint, including bony and cartilage surfaces. Three regions were defined on the articular surface, and the cartilage thickness distribution along each of these was determined. Statistically significant differences between femoral and tibial regions were examined using the paired Student t test in Microsoft Excel. Correlations were investigated using the correlation tool in Microsoft Excel.

The average tibial cartilage thickness was found to be 2.76 mm and the average femoral cartilage thickness was 2.75 mm. Significant correlations exist between the tibia cartilage thickness and body height ( R = 0.60; P<0.05) and weight ( R = 0.64; P < 0.05). Significant correlations exist between the femoral cartilage volume and the body height ( R = 0.736; P < 0.01) and weight ( R = 0.855; P < 0.01).

It is suggested that the distribution and correlations of cartilage distribution indicate adaptation in response to mechanical loading. Information regarding cartilage thickness and volume distribution as found in this study may be useful in diagnosing and monitoring cartilage loss in patients with degenerative joint disease.
Automatic reconfiguration of a robotic arm using a multi-agent approach
Authors: Britain S L , Gibb A J , Roberts C
Published: March 2008

There are numerous methods for solving the inverse kinematic equations for a robotic arm. This paper proposes a novel, adaptive approach based on multiagent systems (MASs). An MAS employs a distributed, decentralized approach to problem solving that is not commonly employed in conventional robotic arm control. The MAS uses patterns abstracted from various configurations of the robotic arm to provide a means of solving inverse kinematic equations where there is a changing kinematic model. Such an approach is beneficial in applications such as the maintenance of power transmission lines, welding, and providing support to handicapped people. The method is demonstrated using a case study utilizing a six-degree-of-freedom Kawasaki FS02 industrial robotic arm. The results from the case study demonstrate a solution for 95 per cent of all attainable Cartesian coordinates.
The vibration control of speed-dependent flexible rotor/magnetic bearing systems using linear matrix inequality gain-scheduled H∞ design
Authors: Schlotter M , Keogh P S
Published: March 2008

The dynamics of rotor/magnetic bearing systems are speed dependent due to gyroscopic effects and other aerodynamic influences. This paper introduces a linear matrix inequality (LMI)-based design method that enables the speed dependence to be embedded within robust gain-scheduled controllers. By utilizing an augmented plant that closely resembles the physical system, it allows for the formulation of multiple design objectives in a unified framework. In particular, a control design for minimized rotor displacements or bearing transmitted forces is considered and the importance of achieving performance over the whole speed range is addressed. If speed dependence is ignored in the controller design, system instability may occur at particular rotational speeds. However, the LMI-based gain-scheduling approach is shown to maintain closed-loop stability over the full speed range. The results are demonstrated using a system model and through measurements taken from a flexible rotor/magnetic bearing facility.
Online self-tuning fuzzy proportional—integral—derivative control for hydraulic load simulator
Authors: Ahn K K , Truong D Q , Thanh T Q , Lee B R
Published: March 2008

Hydraulic systems play an important role in modern industry owing to the fact that hydraulic actuator systems have many advantages over other technologies with electric motors, high durability, and the ability to produce large force at high speeds. Therefore, the hydraulic actuator has a wide range of application fields such as hydraulic pressing machines, moulding technology, etc. where controlled forces or pressures with high accuracy and fast response are the most significant demands. Consequently, many hybrid actuator models have been developed for research on how to control forces or pressures with the best results. The current paper presents a new kind of hydraulic load simulator for conducting performance and stability tests for control forces of hydraulic hybrid systems. In the dynamic loading process, disturbance makes the control performance (such as stability, frequency response, loading sensitivity, etc.) decrease or turn bad. In order to improve the control performance of a loading system and to eliminate or reduce the disturbance, an online self-tuning fuzzy proportional—integral—derivative (PID) controller is designed. Experiments are carried out to evaluate the effectiveness of the proposed control method applied for hydraulic systems with varied external disturbance as in real working conditions.
Model predictive control: Terminal region and terminal weighting matrix
Authors: Hu X-B , Chen W-H
Published: March 2008

Many efforts have been made for model predictive control MPC to enlarge terminal region where the stability is guaranteed by including a proper terminal weighting. This paper investigates how to maximize the ellipsoidal terminal region by using a more general method to design MPC: calculating terminal region and terminal weighting separately. With Jordan canonical form, the new ellipsoid-based method can result in terminal regions which are infinite (in certain directions) even in the case of open-loop unstable systems. Some most popular methods are just special cases of this new method. Simulation results illustrate the effectiveness of the proposed algorithms.
Thermal elastohydrodynamic lubrication of rolling/sliding line contacts using a mixture of Newtonian and power law fluids
Authors: Kumar P , Jain S C , Ray S
Published: March 2008

Thermal elastohydrodynamic lubrication (EHL) behaviour of rolling/sliding line contacts is investigated numerically using a mixed rheological fluid model. The lubricant used is a homogeneous mixture of Newtonian base oil and power law fluid with varying volume fraction, viscosity ratio (VR), and power law index. The velocity distribution across the fluid film for the mixed rheological fluid model is obtained using perturbation method to derive Reynolds and mean temperature equations. The TEHL characteristics computed for the mixture are found to depend upon the effective viscosity of the lubricant which, besides thermal effect, is governed by the superposition of shear thinning and piezo-thickening effects of the non-Newtonian fluid additive. Thermal effect is found to be a function of additive volume fraction, VR, and power law index. The mixtures yield thicker fluid films along with an increase in coefficient of friction in most of the cases. Therefore, a judicious selection of additive fluid with an appropriate volume fraction is recommended in order to achieve fairly thick fluid films at tolerable levels of friction.
Instability and surface diffusion of ultrathin liquid perfluoropolyether films on amorphous carbon surfaces
Authors: Mayeed M S , Kawaguchi M , Newaz G M , Kato T
Published: March 2008

A study is performed on the instability and surface diffusion of ultrathin liquid films of perfluoropolyethers (PFPE) on carbon-coated discs. Several carbon-coated discs have been used from the same lot, surface roughness has been measured by atomic force microscope, and average surface energy has been measured by contact angle measurements. Then, some discs are partially dip coated, producing a spreading edge of the lubricant film, using Zdol of molecular weights of about 4000 and 2000 g/mol, and used in the measurement of the spreading profiles with time. Some other discs are fully dip coated, scratched by a friction tester, and then replenishment of grooves with time has been measured by ellipsometer (calibrated verbatim by X-ray photoelectron spectroscopy (XPS)). Mono-disperse PFPE lubricant films of film thicknesses of about 0.9–3 nm have been used. Diffusion coefficients have been extracted from the spreading profiles using the Matano interface method and used in the diffusion equation to simulate the replenishment profiles of the grooves for the same initial profiles for both simulation and experiment. The diffusion equation has been observed to simulate the replenishment profiles up to the instability plane, height which creates non-linearity in the experimental replenishment profiles above it and fails to model any further.
Numerical analysis of hydrodynamic journal bearings lubricated with ferrofluid
Authors: Montazeri H
Published: March 2008

The current work focuses on studying the hydrodynamic characteristics of flow in journal bearings lubricated with ferrofluid. The bearing has an infinite length and operates under incompressible laminar flow and steady conditions. Assuming linear behaviour for the magnetic material of the ferrofluid, the magnetic force was calculated. The displaced current-carrying infinitely long wire is used as a field model. This model gives a field distribution with a gradient in the circumferential and radial directions. The analysis is based on the numerical solution of the full Navier—Stokes equations using computational fluid dynamics techniques. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid and the governing equations are transformed in the computational domain. Discretized forms of the transformed equations are obtained by control volume method and solved by the SIMPLE algorithm. In the current study, cavitation effects are also considered by an appropriate cavitation model. To validate the computational results, a modified Reynolds equation has been obtained and solved by finite‐difference method. The results indicated that comparing with a conventional lubricant, the ferrofluid as a lubricant improves the hydrodynamic characteristics of journal bearings and provides a higher load capacity and a reduced friction coefficient. It will be evident that the other bearing characteristics depend on the applied field model. Numerical results of this analysis can be used to investigate the oil flow pattern and the hydrodynamic characteristics of journal bearings lubricated with ferrofluid.
Ertel—Grubin methods in elastohydrodynamic lubrication – a review
Authors: Morales-Espejel G E , Wemekamp A W
Published: March 2008

With the arrival of powerful computers and sophisticated numerical methods the calculation of film thickness and pressure fields in elastohydrodynamically lubricated (EHL) contacts is now a common task. Complete moving-roughness solutions are easily found in literature including thermal effects, non-Newtonian rheology, and mixed-lubrication. Therefore, the pioneering days of analytical and semi-analytical EHL solutions lead by Ertel, Grubin, Crook, and others might be perceived as unfit for modern problems. However, it is important to recognise that despite their apparent simplicity these solutions have provided engineers with substantial insight of the lubrication problem. The present paper reviews Ertel—Grubin methods and shows the potential they still have in providing engineers with physical understanding and practical solutions in modern lubrication problems, including friction, transient effects, roughness, minimum film thickness, and shear thinning. The review is, however, not exhaustive.
Experimental investigation on the influence of SiC particulate reinforcement in aluminium alloy composites
Authors: Rao R N , Das S , Krishna P V
Published: March 2008

In the present study, an attempt is made to synthesize Al—Si alloy—SiC particle reinforced composite using liquid metallurgy route and to characterize the composites in terms of microstructure, mechanical properties, and sliding wear behaviour. The composite shows uniform distribution of SiC particles and good interface bonding between SiC particles and the metallic matrix. The sliding wear behaviour is studied using pin-on-disc apparatus against EN32 steel disc at different applied loads and constant sliding speed. The results show that the composite exhibits higher wear resistance, higher seizure pressure, less frictional heating, greater seizure temperature, and marginally lower coefficient of friction when compared with the alloy irrespective of applied load and sliding speed.
On the frictionless axi-symmetric contact of a thick elastic layer and the associated squeeze film problem
Authors: Jaffar M J
Published: March 2008

The problem of the frictionless axi-symmetric indentation between a thick elastic layer (the contact radius does not exceed the layer thickness) and a rigid spherical indenter is investigated. The kernel of the governing integral equation was broken down into two parts. The first corresponds to the Hertzian solution and the second represents the contribution due to the finite layer thickness. The second part was approximated by an absolute and uniform convergent series. Hence, the governing elasticity equation was reduced to a set of linear equations.

A set of simple formulae for the contact pressure, total load, and penetration depth are presented. The obtained formulae were compared with the existing numerical results where good agreement was found. Furthermore, the associated squeeze film problem is examined. Expressions for the variation of the film thickness with time were derived using two different pressure conditions.
Heterogeneity and Network Structure in the Dynamics of Diffusion: Comparing Agent-Based and Differential Equation Models
Authors: Rahmandad Hazhir , Sterman John
Published: March 2008

When is it better to use agent-based (AB) models, and when should differential equation (DE) models be used? Whereas DE models assume homogeneity and perfect mixing within compartments, AB models can capture heterogeneity across individuals and in the network of interactions among them. AB models relax aggregation assumptions, but entail computational and cognitive costs that may limit sensitivity analysis and model scope. Because resources are limited, the costs and benefits of such disaggregation should guide the choice of models for policy analysis. Using contagious disease as an example, we contrast the dynamics of a stochastic AB model with those of the analogous deterministic compartment DE model. We examine the impact of individual heterogeneity and different network topologies, including fully connected, random, Watts-Strogatz small world, scale-free, and lattice networks. Obviously, deterministic models yield a single trajectory for each parameter set, while stochastic models yield a distribution of outcomes. More interestingly, the DE and mean AB dynamics differ for several metrics relevant to public health, including diffusion speed, peak load on health services infrastructure, and total disease burden. The response of the models to policies can also differ even when their base case behavior is similar. In some conditions, however, these differences in means are small compared to variability caused by stochastic events, parameter uncertainty, and model boundary. We discuss implications for the choice among model types, focusing on policy design. The results apply beyond epidemiology: from innovation adoption to financial panics, many important social phenomena involve analogous processes of diffusion and social contagion.
Contracting and Information Sharing Under Supply Chain Competition
Authors: Ha Albert Y. , Tong Shilu
Published: March 2008

We investigate contracting and information sharing in two competing supply chains, each consisting of one manufacturer and one retailer. The two supply chains are identical, except they may have different investment costs for information sharing. The problem is studied using a two-stage game. In the first stage, the manufacturers decide whether to invest in information sharing. In the second stage, given the information structure created in the first stage, the manufacturers offer contracts to their retailers and the retailers engage in Cournot competition. We analyze the game for two different contract types. For the case of contract menus, a supply chain that does not have information sharing will lower its selling quantities because of the negative quantity distortions in the contract menus, thus creating a strategic disadvantage in Cournot competition. The value of information sharing to a supply chain is positive, and the dominant strategy of each supply chain is to invest in information sharing when the investment costs are low. We fully characterize the equilibrium information sharing decisions under different investment costs. For the case of linear price contracts, the value of information sharing to a supply chain becomes negative, and the dominant strategy of each supply chain is not to invest in information sharing regardless of investment costs. Our results highlight the importance of contract type as a driver of the value of information sharing and the role of information sharing capability as a source of competitive advantage under supply chain competition.
Truthful Double Auction Mechanisms
Authors: Chu Leon Yang , Shen Zuo-Jun Max
Published: March 2008

Following the multistage design approach, we propose two asymptotically efficient truthful double auction mechanisms, the BC-LP mechanism and the MBC mechanism, for an exchange market with many buyers and sellers. In this market, each buyer wants to procure a bundle of commodities and each seller supplies one unit of a commodity. Furthermore, various transaction-related costs will be incurred when a buyer trades with a seller. We prove that under both mechanisms, truthful bidding is a dominant strategy for all buyers and sellers when the buyers' bundle information and the transaction cost information are common knowledge. The BC-LP mechanism can be implemented by just solving two linear programs, whereas the MBC mechanism has a higher complexity. The empirical study shows that the MBC mechanism achieves higher efficiency over the BC-LP mechanism and that both outperform the KSM-TR mechanism, the only known truthful mechanism for a more restrictive exchange market.
The Optimal Time to Initiate HIV Therapy Under Ordered Health States
Authors: Shechter Steven M. , Bailey Matthew D. , Schaefer Andrew J. , Roberts Mark S.
Published: March 2008

The question of when to initiate HIV treatment is considered the most important question in HIV care today. Benefits of delaying therapy include avoiding the negative side effects and toxicities associated with the drugs, delaying selective pressures that induce the development of resistant strains of the virus, and preserving a limited number of treatment options. On the other hand, the risks of delayed therapy include the possibility of irreversible damage to the immune system, development of AIDS-related complications, and death. We use Markov decision processes to develop the first HIV optimization models that aim to maximize the expected lifetime or quality-adjusted lifetime of a patient. We prove conditions that establish structural properties of the optimal solution and compare them to our data and results. Model solutions, based on clinical data, support a strategy of treating HIV earlier in its course as opposed to recent trends toward treating it later.
Regret in the Newsvendor Model with Partial Information
Authors: Perakis Georgia , Roels Guillaume
Published: March 2008

Traditional stochastic inventory models assume full knowledge of the demand probability distribution. However, in practice, it is often difficult to completely characterize the demand distribution, especially in fast-changing markets. In this paper, we study the newsvendor problem with partial information about the demand distribution (e.g., mean, variance, symmetry, unimodality). In particular, we derive the order quantities that minimize the newsvendor's maximum regret of not acting optimally. Most of our solutions are tractable, which makes them attractive for practical application. Our analysis also generates insights into the choice of the demand distribution as an input to the newsvendor model. In particular, the distributions that maximize the entropy perform well under the regret criterion. Our approach can be extended to a variety of problems that require a robust but not conservative solution.
CAR-DEA: Context-Dependent Assurance Regions in DEA
Authors: Cook Wade D. , Zhu Joe
Published: March 2008

Assurance region (AR) restrictions on multipliers in data envelopment analysis (DEA) have been applied extensively in many performance measurement settings. They facilitate the derivation of multiplier values that reflect the reality of the problem situation under study. In measuring the operational efficiency of bank branches, for example, output multipliers would generally represent unit processing times for branch transactions such as deposits. AR restrictions on these multipliers are intended to ensure that the (multiplier) values assigned to the various outputs are relatively of the proper size. Current AR-DEA models presume that multiplier restrictions apply uniformly across all decision-making units (DMUs) in the analysis set. Such models can have severe shortcomings, however, in those situations where different circumstances prevail for some DMUs than for others. In the context of bank branches, for example, two sets of branches, whose transaction times are known to be different from each other, would generally require different sets of AR restrictions. This paper presents a methodology for incorporating multiple sets of AR restrictions, with each reflecting the context for a particular subset of DMUs. The resulting modified DEA model, referred to as CAR-DEA, evaluates performance in a manner that more accurately captures the circumstances in which the DMUs operate.
Bayesian Analysis of the Sequential Inspection Plan via the Gibbs Sampler
Authors: Chun Young H.
Published: March 2008

A complex product, such as a software system, is often inspected more than once in a sequential manner to further improve its quality and reliability. In such a case, a particularly important task is to accurately estimate the number of errors still remaining in the product after a series of multiple inspections. In the paper, we first develop a maximum likelihood method of estimating both the number of undiscovered errors in the product and the detection probability. We then compare its performance with that of an existing estimation method that has several limitations. We also propose a Bayesian method with noninformative priors, which performs very well in a Monte Carlo simulation study. As the prior knowledge is elicited and incorporated in the analysis, the prediction accuracy of the Bayesian method improves even further. Thus, it would be worthwhile to use various estimation methods and compare their estimates in a specific inspection environment.
Equity-Efficiency Bicriteria Location with Squared Euclidean Distances
Authors: Ohsawa Yoshiaki , Ozaki Naoya , Plastria Frank
Published: March 2008

A facility must be located within a given region taking two criteria of equity and efficiency into account. Equity is sought by minimizing the inequality in the facility-inhabitant distances, as measured by the sum of the absolute differences between all pairs of squared Euclidean distances from inhabitants to the facility. This measure meets the Pigou-Dalton condition of transfers and can easily be minimized. Efficiency is measured through optimizing the sum of squared inhabitant-facility distances, either to be minimized or maximized for an attracting or repellent facility, respectively. Geometric localization results are obtained for the whole set of Pareto-optimal solutions for each of the two resulting bicriteria problems within a convex polygonal region. A polynomial procedure is developed to obtain the full bicriteria plot, both trade-off curves, and the corresponding efficient sets.
TECHNICAL NOTE—Solving Linear Cost Dynamic Lot-Sizing Problems in O(n log n) Time
Authors: Ahuja Ravindra K. , Hochbaum Dorit S.
Published: March 2008

In this paper, we study capacitated dynamic lot-sizing problems with or without backorders, under the assumption that production costs are linear, that is, there are no setup costs. These two dynamic lot-sizing problems (with or without backorders) are minimum-cost flow problems on an underlying network that possess a special structure. We show how the well-known successive shortest-path algorithm for the minimum-cost flow problem can be used to solve these problems in O(n2) time, where n is the number of periods in the dynamic lot-sizing problems, and how, with the use of dynamic trees, we can solve these problems in O(n log n) time. Our algorithm also extends to the dynamic lot-sizing problem with integer variables and convex production costs with running time O(n log n log U), where U is the largest demand value.
Association of Pharmacist Presence on Compliance with Advanced Cardiac Life Support Guidelines During In-Hospital Cardiac Arrest
Authors: Draper Heather M , Eppert J Alex
Published: March 2008

BACKGROUND:

The pharmacist has many potential roles as part of the resuscitation team during cardiopulmonary arrest. Limited published research has evaluated the practice of advanced cardiac life support (ACLS) during in-hospital arrest. Recent reviews indicate that an audit of in-hospital resuscitation practices should be performed to guide future resuscitation training programs for hospital personnel.

OBJECTIVE:

To assess compliance with ACLS guidelines during in-hospital cardiopulmonary arrest in a community teaching hospital and evaluate the association of compliance with the presence of a pharmacist on the resuscitation team.

METHODS:

A retrospective analysis of the records of 74 consecutive in-hospital arrests occurring between January 1, 2003, and June 30, 2004, was conducted to evaluate compliance with American Heart Association ACLS guidelines.

RESULTS:

A total of 74 arrests were evaluated. Noncompliance was noted in 58.1% of all documented arrests; of the 650 treatment interventions identified, 10.6% were noncompliant with ACLS guidelines. The reasons cited for noncompliance included an incorrect medication dosage (20.3%), prolonged period of time between sequential interventions (26.1%), omission of an indicated treatment (17.4%), deviation from recommended treatment guidelines (26.1%), and incorrect energy for defibrillation (10.1%). A pharmacist was present at 36.5% of documented arrests. Compliance with ACLS treatment guidelines was more likely during resuscitations in which a pharmacist was present (59.3% vs 31.9%; p = 0.03).

CONCLUSIONS:

Noncompliance with resuscitation guidelines was common during in-hospital resuscitation. The presence of a pharmacist on the resuscitation team was associated with improved compliance with treatment guidelines. Despite institutional requirements for pharmacist participation during resuscitation efforts, participation rates remain low. Further evaluation of the role of the pharmacist on the resuscitation team and the impact of the pharmacist on resuscitation practices should be considered.