bluuebunny/crossref_metadata_2025 huggingface dataset:
Titanium in Medicine
Authors: Tanner K E
Published: October 2002

Edited by D M Brunette, P Tengvall, M Textor and P Thomsen, Springer Verlag: 2001. Cost £147.00 (ISBN 3-540-66936-1)

My first response just looking at the flyer for this book was that it was expensive. However, I began to realise the reason for this cost when I picked the book up: it is large, heavy (1.58kg) and extremely well produced. The subtitle is ‘materials science, surface science, engineering, biological responses and medical applications’ and all of these areas are covered in excellent detail. I also started by wondering how the editors and authors could fill nearly 1000 pages without duplication, but found that anything one could want to know about titanium as a biomaterial is covered. The main sections cover the metallurgy and fabrication, surface engineering, biological performance and finally medical applications. The chapters are extremely well referenced, with between 30 and 288 references per chapter. The editors come from three different countries with four different specialisms and the chapter authors they have assembled work in three additional countries, both sides of the Atlantic, and with expertise from clinicians through engineers and materials scientists to biological scientists. Despite more than half the authors being non-native English speakers, I found the writing and editing such that as a reader I was not aware of their native language.
Ride quality evaluation of an actively-controlled stretcher for an ambulance
Authors: Sagawa K , Inooka H
Published: October 2002

This study considers the subjective evaluation of ride quality during ambulance transportation using an actively-controlled stretcher (ACS). The ride quality of a conventional stretcher and an assistant driver's seat is also compared. Braking during ambulance transportation generates negative foot-to-head acceleration in patients and causes blood pressure to rise in the patient's head. The ACS absorbs the foot-to-head acceleration by changing the angle of the stretcher, thus reducing the blood pressure variation. However, the ride quality of the ACS should be investigated further because the movement of the ACS may cause motion sickness and nausea. Experiments of ambulance transportation, including rapid acceleration and deceleration, are performed to evaluate the effect of differences in posture of the transported subject on the ride quality; the semantic differential method and factor analysis are used in the investigations. Subjects are transported using a conventional stretcher with head forward, a conventional stretcher with head backward, the ACS, and an assistant driver's seat for comparison with transportation using a stretcher. Experimental results show that the ACS gives the most comfortable transportation when using a stretcher. Moreover, the reduction of the negative foot-to-head acceleration at frequencies below 0.2 Hz and the small variation of the foot-to-head acceleration result in more comfortable transportation. Conventional transportation with the head forward causes the worst transportation, although the characteristics of the vibration of the conventional stretcher seem to be superior to that of the ACS.
Subsidence in impaction grafting: The effect of adding a ceramic bone graft extender to bone
Authors: Blom A W , Grimm B , Miles A W , Cunningham J L , Learmonth I D
Published: October 2002

The incidence of revision total hip arthroplasty is increasing dramatically and the associated demand for allograft bone is likely to exceed the available supply. In addition, allograft presents potential problems with regard to infection, antigenicity, availability, reproducibility and cost. It is therefore desirable to develop an alternative to allograft. This study investigated BoneSave, a porous tricalcium phosphate-hydroxyapatite ceramic for use in impaction grafting of the femur at revision total hip arthroplasty. The findings of an in vitro mechanical study comparing the initial stability of pure allograft, a volume mixture of 50 per cent allograft and 50 per cent BoneSave, and a volume mixture of 10 per cent allograft and 90 per cent BoneSave are reported. The BoneSave-allograft mixtures exhibit both much greater mechanical stability and reproducibility than the pure allograft (p < 0.05) at all tested loads (200-800 N). At high peak loads the high volume (90% v/v) BoneSave mix also provided higher mechanical stability than the medium volume (50 per cent BoneSave-50 per cent allograft) mix (p < 0.05). These results demonstrate that from a mechanical standpoint the tested ceramic provides adequate initial stability to be used as a bone graft extender with allograft in impaction grafting of the femur.
Application of numerical descriptors to the characterization of wear particles obtained from joint replacements
Authors: Stachowiak G W , Stachowiak G B , Campbell P
Published: October 2002

The application of image analysis techniques to the characterization of wear particles from failed joint replacements has been described. Wear particles were extracted from periprosthetic tissues collected during revision surgery. Chemical digestive methods were used to separate the wear particles from the biological soft material. The particles isolated were examined by optical and scanning electron microscopy. Digitized particle images were analysed on a Macintosh computer by a specially developed software and by the image analysis program ‘Prism’. The following numerical descriptors were used to characterize the particles: particle size, boundary fractal dimension and shape parameters such as form factor, roundness, convexity and aspect ratio. Elemental composition of the particles was determined by energy dispersive X-ray spectroscopy. Three selected types of wear particles were analysed and compared: titanium (Ti)-based and calcium (Ca)-based particles from a hip prosthesis and ultra-high molecular weight polyethylene (UHMWPE) particles from a knee prosthesis. The particles exhibited significantly different sizes and their shape numerical descriptors were also different. From the results obtained it appears that computer image analysis of wear particle morphology can be employed to determine the wear processes occurring in the joints. In some cases, the condition of the joint can also be assessed based on this analysis.
On an ambulance stretcher suspension concerned with the reduction of patient's blood pressure variation
Authors: Sagawa K , Inooka H , Ino-oka E , Takahashi T
Published: October 2002

The design process and control of an ambulance stretcher suspension to reduce patient's blood pressure variation (BPV) is discussed. The BPV caused by applying the vehicle brakes may lead to deterioration of a patient's condition. The proposed method can reduce BPV by tilting the stretcher and counterbalancing back-to-front acceleration of the ambulance with gravity. The experimental results obtained when using a manually controlled stretcher confirm that BPV is reduced by tilting the stretcher. A continuous control method that varies the tilting angle is investigated through simulation analysis. The results show that this control method reduces the BPV effectively and achieves safe transport of the patient.
Parameter sensitivity of a mathematical model of the anterior cruciate ligament
Authors: Toutoungi D E , Zavatsky A B , O'Connor J J
Published: October 2002

This paper presents the results of an investigation into parameter sensitivity of a mathematical model of the human anterior cruciate ligament (ACL). The model ACL comprised a continuous array of fibres mapped between part-elliptical attachment areas on the femur and tibia. Relative motion of the two bones was controlled by a planar four-bar linkage. Parameter modifications were: (a) an alternative set of values for the coordinates of the four-bar linkage joints; (b) rotation of the attachment areas of the ligament by ±30°; and (c) variation of some mechanical properties. The alternative four-bar linkage parameter set produced extremely large changes in ACL force values, up to 130 per cent. Rotating the tibial attachment changed forces by less than 20 per cent, whereas rotating the femoral attachment changed forces by up to 100 per cent. Altering the mechanical parameters produced the smallest differences in force, under 15 per cent. These results highlight the importance, when using a theoretical model, of establishing the values of the parameters defining the model as accurately as possible and of carrying out a parameter sensitivity study. From a clinical viewpoint, they also suggest that, when reconstructing a ruptured ACL, one of the most important considerations must be to position the femoral attachment of the graft as accurately as is feasible.
Simultaneous measurement of stiffness and energy absorptive properties of articular cartilage and subchondral trabecular bone
Authors: Røhl L , Linde F , Odgaard A , Hvid I
Published: October 2002

The purpose of this study was to develop a method for simultaneous measurement of the mechanical properties of articular cartilage and underlying trabecular bone. Cylindrical bone-cartilage specimens from human cadaver knees were tested under non-destructive axial compression. The specimens were mounted in a cage by three screws fixed to the subchondral bone plate to create a reference plane between the cartilage and the bone. Each test was carried out as a single test cycle between a 0.12 MPa (4N) pre-stress and 0.5 per cent bone strain. Twenty conditioning cycles were performed prior to each test cycle. In order to determine the reproducibility of the test method, the test procedure was repeated after turning the cage through 90°. The specimens were then kept at + 5°C for 24 hours, and the procedure was repeated.

The normalized stiffness and energy absorptive properties were calculated from each test cycle. No significant difference was found between the results obtained on the first and on the second day. Both days the stiffness of cartilage was significantly larger during the second test, indicating that 20 conditioning cycles may not provide a viscoelastic steady state.
A non-invasive patient registration and reference system for interactive intraoperative localization in intranasal sinus surgery
Authors: Hauser R , Westermann B , Probst R
Published: October 2002

A basic problem common to all systems for computer assisted surgery (CAS) is patient referencing, or the transfer of preoperative image data to the intraoperative pathology. The authors describe a highly precise CAS system with non-invasive referencing that can be used in ear, nose and throat (ENT) surgery of the paranasal sinuses. It is based on optical digitizing with several custom-made self-localizing surgical instruments. The accuracy of the system was tested in an experimental model using a plastic head. Measurements of repositioning the reference bow had a mean error of 0.81 mm + 0.31 mm. The system was evaluated clinically with 11 patients who received surgery for different pathologies of the paranasal sinuses. These trials met with a high rate of success and specific results are reported.
Biomechanics of the Gazi type pelvis external skeletal fixator
Authors: Korkusuz F , Kaymak Ö , çitipitioglu E , Akkas N
Published: October 2002

External skeletal fixation is an alternative method of treatment to conventional therapy and open surgical procedures in pelvis fractures. The appropriate type of frame and the configuration of the connecting bars of these fixators are under investigation. In the Gazi type pelvis external fixator (GPEF) which has been developed, a 70° angulation is applied to the connecting bars of the anterior quadrangular frame. This configuration, which is expected to improve the stability of the posterior column of the pelvis, was evaluated biomechanically on a phantom with various types of pelvic fractures and separations. The results suggest that the GPEF effectively controls anterior column pelvis fractures such as unilateral pubic ramus fractures, unilateral ischium pubis rami fractures and symphysis pubis separations under vertical loads. The fixator is partially capable of stabilizing the posterior column; however, loads above 700 N cause separation at the fracture site. Further studies and clinical trials are essential to determine the GPEF's effectiveness in reducing blood loss and in providing stability at the posterior column.
Development of a six station knee wear simulator and preliminary wear results
Authors: Burgess I C , Kolar M , Cunningham J L , Unsworth A
Published: October 2002

In order to assess the wear performance of different designs of total knee replacements (TKR), a six station multi-axis knee simulator has been designed, built and commissioned. The most important features of a knee simulator are representative angles of flexion-extension synchronized with a dynamically applied load, and a combination of rolling and sliding motion. The simulator typically applies flexion-extension of 0-65°, anterior-posterior translation of up to 15 mm, a dynamic load of up to 5.0 kN, and operates at 1.0 Hz. The loads and motions are applied using computer controlled servohydraulic actuators and hence their profiles are easily modified. A preliminary wear test has been conducted using a Kinemax (Howmedica, United Kingdom) TKR. The test was conducted in 30 per cent bovine serum which was changed every 150 000 cycles, at which time the bearing surfaces were examined and the UHMWPE tibial component was weighed. Over eight million cycles, a tibial wear rate of 2.62 mg/106 cycles was measured. The mild wear observed was characterized by burnishing and slight scratching in the anterior-posterior direction. These observations are broadly in line with both in vitro and ex vivo studies reported in the literature for this type of prosthesis. Delamination wear sometimes observed in vivo was not seen.
Development of standards for orthopaedic implants
Authors: Paul J P
Published: October 2002

This article reviews the need for standards for orthopaedic implants and illustrates the differences in approach of the European Standard Organization compared to National and International Standards. The areas where new work is being undertaken are outlined.
Adaptive multimode lubrication in natural synovial joints and artificial joints
Authors: Murakami T , Higaki H , Sawae Y , Ohtsuki N , Moriyama S , Nakanishi Y
Published: October 2002

To examine the lubrication mechanisms in both natural synovial joints and artificial joints with artificial cartilages, pendulum tests of pig shoulder joints and simulator tests of sliding pairs of a stainless steel spherical component and natural articular cartilage or artificial cartilage have been conducted.

Firstly, it was shown in pendulum tests of pig shoulder joints that both concentration of hyaluronic acid or viscosity and adsorbed film formation of proteins and phospholipids exerted a significant effect on frictional behaviour in swinging motion immediately after a loading of 100 N. Under a high load of 1 kN, low friction was observed under wide-ranging viscosity conditions, since a high load similar to body weight probably enhanced the squeeze film effect due to improved congruity.

Next, frictional behaviour of sliding pairs in knee joint models, consisting of a stainless steel spherical surface and either specimens of pig tibial cartilage or polyvinylalcohol (PVA) hydrogel, was examined during walking in simulator tests. In these tests, the influences of lubricant viscosity and addition of protein on frictional behaviour were evaluated. For both compliant materials, the appropriate addition of γ-globulin to sodium hyaluronate (HA) solution maintained low friction and protected rubbing surfaces under thin film conditions. These phenomena are discussed from the viewpoint of adaptive multimode lubrication.
Ultrasonic evaluation of ultra-high molecular weight polyethylene used in medical prostheses
Authors: Ong C S , Saffari N
Published: October 2002

An ultrasonic non-destructive evaluation process is established to observe cracks and delaminations that occur below the surface of retrieved ultra-high molecular weight polyethylene joints. The result from the ultrasonic evaluation is compared with destructive (optical) test results of the actual cracks. Feasibility of characterizing different grades of bulk polyethylene is also established by means of ultrasonic attenuation measurements in the materials. This ultrasonic data can be used to give a better understanding of the failure mechanisms in the UHMWPE material.
Calcium phosphate coatings for medical implants
Authors: de Groot K , Wolke J G C , Jansen J A
Published: October 2002

In surgical disciplines where bone has to be repaired, augmented or improved, bone substitutes are essential. Although bone banks, such as Eurotransplant, are founded to supply such substitutes, natural bone is not always adequate. For example, frequently these so-called bone grafts resorb after implantation (1). Further, they cannot be used for joint and tooth replacement, and recently worries have been raised about the transfer of infectious diseases. Therefore, interest has dramatically increased in the use of synthetic materials for replacement of lost or damaged bone tissue. The generic name of these tissue alternatives is biomaterials. A special class of these biomaterials is composed of metallic devices with coatings to improve bone bonding. These specialized coatings used to improve the metallic implant are the topic of this paper.
Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis
Authors: Simões J A O , Taylor M , Marques A T , Jeronimidis G
Published: October 2002

Previous studies have suggested that a controlled stiffness prosthesis is required to address the conflicting requirements of minimizing stress shielding and micromotion. The design for a controlled stiffness prosthesis is proposed and a preliminary analytical investigation performed to assess its predicted performance before fabrication of a prototype component. The novel prosthesis consisted of a cobalt-chrome core and a flexible composite outer layer. Varying the composite layer thickness allowed the prosthesis stiffness to be controlled. Three variants of the controlled stiffness prosthesis were critically assessed using the finite element method and their predicted performance compared with those of conventional prosthesis designs. The potential for stress shielding was assessed by examining the periosteal strain energy and the potential for migration assessed by examining the endosteal minimum principal cancellous bone stresses.

Both the conventional and controlled stiffness implants performed poorly as press-fit prostheses. All the press-fit prostheses generated high cancellous bone stresses, suggesting that excessive migration of these implants would be likely. The controlled stiffness implants performed better than the conventional implants when bonded to the surrounding bone. Although the controlled stiffness implants did not eliminate stress shielding of the calcar, they produced higher strain energies than the conventional designs.

The findings of this study are that osseointegrated controlled stiffness implants may perform better than current osseointegrated cementless prostheses and therefore it is worth while progressing to the next stage, of prototyping an implant.
Drilling of bone: A robust automatic method for the detection of drill bit break-through
Authors: Ong F R , Bouazza-Marouf K
Published: October 2002

The aim of this investigation is to devise a robust detection method for drill bit breakthrough when drilling into long bones using an automated drilling system that is associated with mechatronic assisted surgery. This investigation looks into the effects of system compliance and inherent drilling force fluctuation on the profiles of drilling force, drilling force difference between successive samples and drill bit rotational speed. It is shown that these effects have significant influences on the bone drilling related profiles and thus on the detection of drill bit break-through. A robust method, based on a Kalman filter, has been proposed. Using a modified Kalman filter, it is possible to convert the profiles of drilling force difference between successive samples and/or the drill bit rotational speed into easily recognizable and more consistent profiles, allowing a robust and repeatable detection of drill bit break-through.
Dependence of broadband ultrasound attenuation on the elastic anisotropy of trabecular bone
Authors: Han S-M , Rho J-Y
Published: October 2002

The effect of trabecular elastic anisotropy on broadband ultrasound attenuation (BUA) and bone mineral density (BMD) was investigated with human and bovine cubic cancellous bones. Ultrasonic parameters describing trabecular anisotropy were found from the three orthogonal ultrasound velocities. BMD was measured using quantitative computed tomography. Three elastic anisotropy ratios were compared to BUA in all three directions and to BMD. The combined effect of anisotropic characteristics and BMD was also correlated with BUA. The results showed that the anisotropy ratios were significantly related to BUA (p<0.05). There was, however, no correlation between BMD and the elastic anisotropy ratios. The combination of BMD and the anisotropy produced a significantly enhanced relationship with BUA.
Quantitative assessment of anterior cruciate ligament deficiency: Applied load versus applied displacement
Authors: Grimshaw P N , Bowker P
Published: October 2002

The Salford static knee instrument (SSKI) was developed to determine the quantitative assessment of the human knee joint in vivo by utilizing the technique of applied displacement and measurement of resistive load as proposed by Butler et al. (1). The instrument was used in parallel with the device developed by Al-Turaiki (2) which utilized the opposite method of assessment. The objective of the research was to examine which of the two techniques provided the more reliable and accurate method of knee assessment. Fourteen patients with suspected isolated rupture of the anterior cruciate ligament (ACL) were subjected to anterior-posterior drawer testing on both devices. The results showed that each instrument produced results which confirmed the clinical diagnosis by indicating a significant decrease in anterior stiffness when comparing the injured and uninjured knees. [SSKI device ( p = 0.000) and Al-Turaiki (2) device ( p = 0.002) statistical significant difference testing with Bonferonni Alpha correction p = 0.0125]. The results showed the Salford static knee instrument indicated a 58 per cent decrease in anterior stiffness and the Al-Turaiki (2) device a 35 per cent decrease when comparing the injured and uninjured knees. In conclusion it is suggested that the application of displacement and measurement of load as proposed by Butler et al. (1) may be the most appropriate technique for precise clinical diagnosis of pathological human knee joint instability.

load, displacement, knee, anterior, stiffness
Effect of phospholipidic boundary lubrication in rigid and compliant hemiarthroplasty models
Authors: Foy J Rogers , Williams P F , Powell G L , Ishihara K , Nakabayashi N , LaBerge M
Published: October 2002

Hemiarthroplasty may benefit from materials which produce lower friction and improved boundary lubrication protection during start-up conditions. The purpose of this study was to evaluate the effect of phospholipidic boundary lubrication in both rigid and compliant hemiarthroplasty. An in vitro model was designed to dissociate the relative contribution of implant material compliance and the presence of phospholipid to the overall friction of a hemiarthroplasty contact using bovine articular cartilage. Normal bovine articular cartilage was articulated against four flat materials using reciprocating motion: (a) borosilicate glass; (b) borosilicate glass coated with dipalmitoylphosphatid-ylcholine (DPPC); (c) polyurethane (PU) elastomer (Tecoflex®SG93A, a medical-grade aliphatic thermoplastic PU, Thermedics Incorporated, Woburn, Massachusetts); and (d) surface-coated PU (Tecoflex®SG93A substrate coated with lipid-attracting copolymer poly[methacryloyloxyethyl phosphorylcholine (MPC)-co-butyl methacrylate (BMA)]). Tests were conducted in physiologically simulated tribological conditions for a non-conformal point contact. Friction and lubrication analysis was performed using both static and kinetic coefficients of friction μ measured for each group as a function of time for a sliding distance of up to 60 m.

Results showed that the inclusion of supplemental phospholipid, DPPC, on a rigid substrate significantly decreased μ in comparison with the control (cartilage-glass). Additionally, removal of phospholipid components from the articular cartilage surface produced a significantly greater start-up μ in comparison with normal cartilage at the test onset. The use of a material with a lower modulus resulted in lower μ for the entire duration of the test. Polyurethane elastomer coated with the lipid-attracting copolymer, poly(MPC-co-BMA), resulted in the lowest frictional response. As seen in this study, the improvement of low-modulus hemiarthroplasty may involve the optimization of chemical modification and incorporation of lipid-attracting MPC copolymers onto compliant materials. However, further tests are warranted to determine whether lipid-attracting MPC copolymers perform as well during long-time, in vivo wear studies.
The use of low-frequency vibration measurement in orthopaedics
Authors: Nokes L D M
Published: October 2002

This paper reviews the literature regarding the use of applying conventional low-frequency vibration analysis as a possible diagnostic tool in the orthopaedic field. Although a considerable number of investigations have been carried out, including the effects of soft tissue, the technique has not been widely accepted clinically. The application of ultrasound appears to be a more realistic alternative.
Integration of non-linear cellular mechanisms regulating microvascular perfusion
Authors: Griffith T M , Edwards D H
Published: October 2002

It is becoming increasingly evident that interactions between the different cell types present in the vessel wall and the physical forces that result from blood flow are highly complex. This short article will review evidence that irregular fluctuations in vascular resistance are generated by non-linearity in the control mechanisms intrinsic to the smooth muscle cell and can be classified as chaotic. Non-linear systems theory has provided insights into the mechanisms involved at the cellular level by allowing the identification of dominant control variables and the construction of one-dimensional iterative maps to model vascular dynamics. Experiments with novel peptide inhibitors of gap junctions have shown that the coordination of aggregate responses depends on direct intercellular communication. The sensitivity of chaotic trajectories to perturbation may nevertheless generate a high degree of variability in the response to pharmacological interventions and altered perfusion conditions.
A review of the measurement of blood velocity and related quantities using Doppler ultrasound
Authors: Hoskins P R
Published: October 2002

Ultrasound systems can be used to investigate blood flow by use of the Doppler effect. The flow information may be displayed as either a real-time sonogram or a two-dimensional colour image. Estimates of maximum velocity using commercial systems are in error by typically 10–100 per cent; this is associated with the inability of the single-beam Doppler method to measure the true direction of flow, and with geometric spectral broadening. Vector Doppler systems acquire Doppler information along two beam directions and are able to measure accurately the velocity and direction of motion within the scan plane. The small beam width of modern Doppler systems means that the condition of uniform insonation, required for estimation of mean velocity from mean frequency shift, is not valid except for the very smallest vessels. Other quantities related to the velocity may also be estimated, such as the volumetric flow and wall shear stress. Flow visualization using colour flow imaging suffers from dependence of the displayed colour on the direction of blood motion. The vector Doppler technique may be extended to colour flow to give improved visualization of flow, in which there is no angle dependence within the scan plane.
Evaluation of a hip joint simulator
Authors: Smith S L , Burgess I C , Unsworth U
Published: October 2002

To evaluate the functioning of the Durham hip joint wear simulator, the wear rates of ultra high molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE) acetabular cups articulating against 22 mm diameter cobalt-chromium-molybdenum (CoCrMo) femoral heads were studied. A wear test was conducted in a lubricant of distilled water at 37°C for a duration of 4.8 million cycles. The average penetration rate for the CoCrMo femoral heads against UHMWPE acetabular cups was 0.03mm/106 cycles, while penetration rate for PTFE cups was some twenty times greater. These results are of a similar order of magnitude to other simulator studies in distilled water and are in a similar ratio to clinical data.
A comparison between gravimetric and volumetric techniques of wear measurement of UHMWPE acetabular cups against zirconia and cobalt-chromium-molybdenum femoral heads in a hip simulator
Authors: Smith S L , Unsworth A
Published: October 2002

Five cobalt-chromium-molybdenum (CoCrMo) and five zirconia femoral head components have been wear tested against 28 mm diameter ultra high molecular weight polyethylene (UHMWPE) acetabular cups for 5 million cycles in the Durham hip joint wear simulator using bovine serum as a lubricant. Wear measurements used gravimetric and volumetric techniques and no statistically significant difference was found between the measurement methods. The wear rates of the acetabular cups against both femoral heads are presented for both measurement methods. The UHMWPE acetabular cups showed a statistically significant higher linear wear rate for the first 2 million cycles than the lower linear wear rate from 2 million cycles to the end of the test, against both femoral head materials. Over the full duration of the wear test, the wear rates of acetabular cups articulating against zirconia femoral heads were lower than against CoCrMo femoral heads. The wear rates up to 2 million cycles and from 2 to 5 million cycles for both femoral head materials were consistent with other studies.
Analysis of debris from brushing the femoral canal with a plastic brush—a potential cause of loosening in total hip replacement
Authors: Germain M A , Tipper J L , Ingham E , Makarem R , Wroblewski B M , Fisher J
Published: October 2002

The generation of submicrometre sized polyethylene particles has been shown to be one of the major causes of osteolysis, loosening and failure of total replacement joints. It has been reported that intramedullary brushing of the femoral canal with polymer brushes prior to total hip arthroplasty results in the release of polymer particles into the femoral canal. The aim of this study was to isolate and characterize these particles on the basis of morphology and size and to determine whether these particles may play a role in osteolysis and loosening of the total hip prostheses. It was found that the majority of the particles shed by the polymer brushes were submicrometre in size and were similar in morphology to UHMWPE wear particles isolated from periprosthetic tissues. In addition, the majority of the particles released by the brushes were in the biologically active size range (0.1-10μm), and may contribute to osteolysis and loosening of hip prostheses.
An axisymmetric contact model of ultra high molecular weight polyethylene cups against metallic femoral heads for artificial hip joint replacements
Authors: Jin Z M , Heng S M , Ng H W , Auger D D
Published: October 2002

Contact mechanics of ultra high molecular weight polyethylene (UHMWPE) cups against metallic femoral heads for artificial hip joints is considered in this study. Both the experimental measurement of the contact area and the finite element prediction of the contact radius, maximum contact pressure and maximum Von Mises stress have been carried out for a wide range of contemporary artificial hip joints. Good agreement of the contact radius has been found between the experimental measurements and the finite element predictions based upon an elastic modulus of 1000 MPa and a Poisson's ratio of 0.4 for UHMWPE material under various loads up to 2.5 kN. It has been shown that the half contact angle for all the cup/head combinations considered in this study is between 40° and 50° under a load of 2.5 kN. The importance of this result has been discussed with respect to the anatomical position of the cup when placed in the body and the selection of a simple wear-screening test for artificial hip joints.

The predicted contact radius and maximum contact pressure from the finite element model have also been compared with a simple elasticity analysis. It has been shown that the difference in the predicted contact radius between the two methods is reduced for more conforming contacts between the femoral head and the acetabular cup and smaller UHMWPE cup thickness. However, good agreement of the predicted maximum contact pressure has been found for all the combinations of the femoral head and the acetabular cup considered in this study. The importance of contact mechanics on the clinical performance of artificial hip joint replacements has also been discussed.
Quantification of interdigitation at bone cement/cancellous bone interfaces in cemented femoral reconstructions
Authors: Maher S A , McCormack B A O
Published: October 2002

The mechanical interlock created at the cement/cancellous bone interface in cemented femoral reconstructions is crucial to the longevity of the replacement. To accurately model the mechanics of the interface, its morphological features must be quantified. This paper applies a semi-automated procedure to the analysis of the cement/bone interdigitation characteristics of six cemented femora: two which have been prepared in vivo and later retrieved, and four which were prepared in vitro. A parameter which combines the undulations of the cement/bone interface in a transverse slice into one value, is used to explore the trends in the interlock along the length of the femur. The differences in the interdigitation produced in the in vivo and in vitro groups are also explored.
An investigation of the performance of Biostop G and Hardinge bone plugs
Authors: Prendergast P J , Birthistle P , Waide D V , Kumar Girish N V
Published: October 2002

Although distal plugging is a common procedure to prevent distal flow of polymethylmethacrylate (PMMA) cement during cementing of femoral prostheses, there is little biomechanical testing to confirm that (a) the plugs do not displace under cementing pressure, and (b) they do in fact occlude cement flow. Two designs of femoral intramedullary plugs, the Biostop G (Bioland, France) and Hardinge (De Puy, Leeds, UK) were examined to determine their performance under cement pressurization in a biomechanical test. A testing rig was fabricated in which distal migration could be measured as a function of cement pressurization. Sectioning of the samples after polymerization of the cement revealed the extent of cement flow. The results show that, even in this well controlled test, there is significant variability in plug performance. It is shown that the Biostop G displaces less than the Hardinge for similar cement pressures. Sectioning reveals that cement can escape around the Hardinge plug at high pressures. Furthermore, a pore forming effect of the Biostop G plug was occasionally observed indicating that design improvements may be possible for this plug.
Evaluation of the forced outage length contribution of critical nuclear power systems in an extended operating cycle
Authors: Kang C W
Published: October 2002

The work presented here presents an evaluation method for the question of how reliably the system (or component), responsible for the dominant plant availability loss, will run in an extended 48 month operating cycle. As major contributors to the total plant forced outage time in pressurized water reactors (PWRs), reactor coolant pumps (RCPs) and main feed pumps (MFPs) are chosen as specific example systems for a case study. The method proposed estimates the expected forced outage length contribution of each system to the maximum allowed outage length given a certain plant capacity factor. Based upon the current reliability level estimated from the Nuclear Regulatory Commission plant performance database, the assessment of each system impact shows that 14.2 and 2.2 per cent of the maximum allowed outage length are expected to be taken by RCPs and MFPs respectively in the PWR regardless of other systems. In order to meet a 97 per cent goal capacity factor to be envisaged in a 48 month operating cycle, it is recommended that various possible actions be devised for achieving the higher RCP and MFP operational availability through design, monitoring and maintenance.
The thermo-acoustic response of a premixed swirl burner
Authors: Lawn C. J.
Published: October 2002

Application of the theory of thermo-acoustic excitation of flames requires a detailed knowledge of the flame response to plane-wave velocity fluctuations of a given frequency through the burner. A model of the type of swirl burner used in some designs of industrial gas turbine is investigated, chemiluminescent emission being used as a marker of the hear release from both methane and propane premixed flames. The effects of the equivalence ratio and the withdrawal of the swirler so as to allow an annulus of unswirled premixture are also examined.

It is found that there are two distinct modes of self-excitation. The response of different burner configurations in the mode with the higher frequency is analysed in terms of four parameters. These characterize the position and spread of the axial distribution of heat release fluctuations, and the origin and effective velocity of convection of disturbances.

From these parameters, the Rayleigh integral can be calculated and this defines the frequency range over which excitation is possible. If the acoustic conditions require that the flame is lengthened, retracting the swirler, reducing the equivalence ratio or changing from propane to methane are all shown to be possible control measures for this particular burner.
Mathematical modelling of turbulent combustion for gas turbines
Authors: Jones W. P.
Published: October 2002

The paper reviews progress in the development of methods for calculating the properties of gas turbine combustion chambers, with particular attention being devoted to combustion and turbulence-combustion interactions. For conventional combustion chambers with non-premixed combustion it is argued that a conserved scalar approach, where burning is presumed to be ‘fast’, is capable of providing an accurate representation of heat-releasing processes. The approach can also be extended to include NO2 formation, at least under conditions where it is formed under high-temperature conditions. However, if carbon monoxide and unburnt hydrocarbon emissions or partially premixed combustion is to be considered, then a more complete description of combustion is needed and the probability density function (PDF) transport equation method here represents a promising approach. It is demonstrated that the method, when combined with a simple chemical reaction mechanism, is capable without modification of reproducing the major properties of non-premixed, partially premixed and premixed turbulent flames.
An ecological exergy analysis for an irreversible Brayton engine with an external heat source
Authors: Huang Y-C , Hung C-I , Chen C-K
Published: October 2002

Brayton cycles have been used extensively in gas turbine power plants and aircraft propulsion systems. In this paper, an exergy analysis, based on an ecological optimization criterion, has been carried out for an irreversible Brayton engine with an external heat source. A cycle pressure ration is solved to yield optimum work done and reduced entropy production. Even though the work output and thermal efficiency are reduced by a certain amount, the ecological exergy analysis results in a better performance than that obtained with the maximum power (or work) output conditions.
Design and analysis of a water-ammonia absorption refrigeration system
Authors: Koç A , Bulgan A. T. , Öztürk N. A.
Published: October 2002

A water-ammonia absorption refrigeration (AAR) system is preferred to classical vapour compression when a heat source is available cheaply. This study deals with the analysis of an AAR system operating with a low-temperature heat source. Eleven design variables were chosen for this purpose. The analysis showed that the use of a low temperature heat source imposes some restrictions on the system design, but an economically operating AAR system may be designed by a careful process optimization study.
Experimental study on the performance of a compact heat sink for LSI packages
Authors: Ishizuka M , Yokono Y , Biswas D
Published: October 2002

The cooling performance of compact heat sinks composed of small fins, investigated in conditions of both natural and forced air convection, should also be explored in designing the heat sink on an LSI package. An experimental study was performed with respect to natural air convection and forced air convection. Several kinds of compact heat sink which have different base areas, fin intervals and fin heights were heated by an attached electrical heater, which could supply a specific heat flux. The increase in fin temperature was measured by small thermocouples. In natural air convection experiments, the effect of the supplied wattage on the temperature rise of the heat sink was examined for different fin intervals and fin heights. In forced air convection experiments, a wind tunnel was used. The heat sink was set downstream in the wind tunnel and a specific heat flux was applied to it. The correlation between supplied air velocity and temperature rise in the heat sinks was explored. Furthermore, from these results, non-dimensional expressions to evaluate the cooling performance of compact heat sinks were examined.
The effects of free stream air velocity on water droplet size and distribution for an impaction spray nozzle
Authors: Walton D , Spence M. K. , Reynolds B. T.
Published: October 2002

Fog generation for ingestion by gas turbine engines is a method by which the amount of work done during compression can be reduced by evaporative cooling of the inlet air and can improve the engine's efficiency by as much as 15 per cent. Generating fog produces problems if the droplet size is too high which can result in erosion and possibly corrosion damage to the compressor and stator blades. This study examines the water droplet spray characteristics of an impaction-type atomizer over a range of free stream air velocities, water pressures and fluid viscosities.
On appraising alternative power plant investment proposals: Part 1: Economic model
Authors: Bohn D , Roy-Aikins J E A
Published: October 2002

Combined energy plants operating on the Brayton-Rankine cycle have gained wide acceptance as the most efficient energy conversion system. The technology is well proven and numerous research activities are underway to develop it further past its present plateau of performance. In developed and emerging economies alike, the current situation in the global economic market has caused the liberalization of the energy industry in some countries, and in others it is causing a rethink of economic and energy policies. A result is that electric utility companies that have enjoyed a monopoly in power generation and distribution are seeing this privilege being eroded. This is opening up opportunities for independent power production and, consequently, for gas/steam turbine plants because of the technical merits of the technology and its ability to fill the vacuum being created in the energy industry. An economic model has been developed for carrying out life cycle costs analysis of energy investment proposals involving gas and steam turbines in combined power and combined heat and power. A computer program for the economic analysis of combined energy systems (PEACES) was developed with a capability to evaluate the economic merits of individual and competing energy investment proposals. This paper describes the economic medel around which the computer code was structured.
Temperature and gas concentration profiles in a circulating fluidized-bed combustor burning an Indian coal
Authors: De S , Nag P K
Published: October 2002

An experimental investigation has been carried out to study the bed temperature and gas concentration profiles due to combustion of an Indian coal in a laboratory-scale circulating fluidizedbed (CFB) combustor of 102 mm x 102mm cross-section and 5.25 m high, made of insulating firebricks. As the sulphur content of the coal burned was low, no sorbent was used. Sand acted as the bed material. The results are discussed for four different superficial velocities at a constant coal feed rate. The temperature of the bed was essentially uniform for each of the superficial velocities used. The oxygen concentration decreases along the riser height showing that combustion continues over its entire length. The carbon monoxide concentration decreases along the riser except only near the top. The carbon dioxide concentration, however, increases along the riser except near the top. The of NOx is also discussed, as it is a significant pollutant from coal combustion. The results are explained to obtain some insight into the combustion of coal in a CFB.
A theoretical and experimental study of a novel recompression absorption refrigeration cycle
Authors: Eames I. W. , Wu S
Published: October 2002

This paper describes a novel vapour absorption refrigeration cycle which uses a steam ejector to enhance the concentration process of the cycle. The paper provides a complete description of the cycle and presents the results of a theoretical study before going on to describe and evaluate the outcomes of an experimental programme. The results of this investigation showed that with the addition of a steam ejector as described the coefficient of performance (COP) of the single-effect lithium bromide absorption cycle can be increased from about 0.7 to at least 1.0 without any increase in corrosion rates often associated with high temperature vapour generators used in conventional machines of this type.
Exergy analysis of the United Kingdom energy system
Authors: Hammond G. P. , Stapleton A. J.
Published: October 2002

The exergy method has been used to analyse changes in the structure of the UK energy system over a period of more than 30 years from 1965. A sectoral approach was employed, with the supply side examined in terms of themain energy sources, while final demand was separated into four energy end-use groups: the domestic, service, industrial and transport sectors. Estimates of sector-weighted or ‘lumped’ parameters, such as exergy efficiencies, were obtained from the particular characteristics of each sector. These were employed to determine the exergetic ‘improvement potential’ for critical elements of the energy system. Electricity generation together with final energy demand in the domestic sector and in transport are shown to account for nearly 80 per cent of the Second Law improvement potential. This poor thermodynamic performance is principally due to exergy losses in combustion and heat transfer processes associated with power generation, space heating and main transport modes. The results of the exergy analysis are placed in the context of recent developments in energy market liberalization and of the need to achieve environmental sustainability. They are also contrasted with proposals for new or improved energy technologies to meet the requirements of a sustainable energy strategy. Finally, the role of the exergy method is contrasted with the various other approaches to energy technology assessment.