bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of navigation errors based on ergodic processes
Authors: Jin H , Zhang H Y 
Published: October 2002

The problems of estimation and test of navigation errors are discussed in this paper. Based on Poor's estimation algorithm, the error model of a navigation system is studied from the stochastic process point of view, and the ergodicity of a stochastic process is extended to the ergodicity of a multivariate stochastic process. It is pointed out that Poor's estimation algorithm should be based on the ergodicity of a multivariate stochastic process for practical use and a sufficient condition is given for its application. In addition, Poor's estimation algorithm is extended to the case of any n navigation systems. The hypothesis test problem of a navigation system accuracy is also discussed in this paper. By using the multivariate statistical analysis theory, the hypothesis test problem of the error covariance matrix of every navigation system can be solved by testing the hypothesis of the relative error covariance matrix between two different navigation systems.
Studies on twin non-parallel unventilated high-speed jets
Authors: Elangovan S , Solaiappan A , Rathakrishnan E 
Published: October 2002

The interaction of twin high-speed jets is an important problem which is most relevant to aircraft engine exhaust systems. Many studies have been carried out on twin parallel high-speed jets, but similar studies for non-parallel configurations are almost absent. Such an investigation would be useful in understanding jet flow fields associated with V/STOL aircraft. The present work is an attempt to investigate experimentally the interaction of two high-speed axisymmetric jets obliquely oriented towards each other. Twin nozzles of exit diameter ( D) 10 mm are set on a common end wall with their axes intersecting each other at half-angles ( α) of 0, 5, 10 and 15°. The centre-to-centre spacings ( S) of the nozzles, non-dimensionalized as S/D, are varied as 3.1, 4 and 5. The nozzles are operated at fully expanded sonic and underexpanded exit conditions to yield fully expanded Mach numbers Mj of 1, 1.19, 1.41 and 1.52. Some of the conclusions arrived at were based on the experimental results and are given below. In the case of sonic jets, the variation of mean velocity along the nozzle block centre-line can be correlated with empirical equations based on the geometric intersection distance and the maximum centre- line velocity. In general, at a particular nozzle spacing and angle of interception, the merging distance decreases with increasing fully expanded Mach numbers. In most of the cases, the complete combining of the twin jets into a single jet occurs downstream of the geometric intersection point, the location of the combining point being strongly influenced by the fully expanded Mach number.
Design study of a split-torque helicopter transmission
Authors: White G 
Published: October 2002

A helicopter transmission with split-torque drive trains to the main rotor and tail rotor drive shaft is described. A design based on two 1200 kW engines supplying torque to a 350 r/min main shaft demonstrates a weight reduction of 40 per cent, extreme low height and reduced losses. Four double-helical pinions drive a combining gear and provide a 10:1 reduction ratio to the main shaft; flexible torque tubes, set by fine-difference splines, control the division of torque between pairs of pinions. Rotor loads bypass the transmission housings and pass to the fuselage through a large-diameter mast that encloses an integral sump and cooler.
Design of a surface replacement prosthesis for the proximal interphalangeal joint
Authors: Ash H E , Unsworth A 
Published: October 2002

A surface replacement finger joint prosthesis was designed specifically for the proximal interphalangeal joint (PIPJ). The two-piece design consisted of a bi-condylar proximal phalangeal head and a conforming bi-concave middle phalangeal base. The bearing surfaces were designed as close to the original anatomy of the PIPJs as possible, using detailed information obtained from a previous anatomical study of 83 PIPJs by the present authors. Four sizes of prosthesis were designed with maximum head diameters of 7, 8, 9 and 10 mm. Fixation of the joint prosthesis was achieved by an interference fit between the stems of semicircular crosssection and the phalangeal bone shafts. The main considerations for the stem designs were the offset from the centre of rotation, angle of inclination, length, and cross-sectional shape and size. It is proposed that the two components will be made from cross-linked polyethylene (XLPE) because it can be injection moulded to produce the complex shapes of the joint prosthesis. In addition, XLPE against itself has shown comparable wear rates with stainless steel against ultra-high molecular weight polyethylene from previous work by Joyce et al.
The development of a long, dual-platform triaxial walkway for the measurement of forces and temporal-spatial data in the clinical assessment of gait
Authors: Hynd D , Hughes S C , Ewins D J 
Published: October 2002

Force-plate measurement of the ground reaction force (GRF) has, for many years, been considered a vital component of the comprehensive assessment of human gait in the clinical context. For example, the data can be used in the adjustment of prostheses and orthoses and in identifying the mechanisms underlying a gait dysfunction. However, commercial force plates are usually only capable of measuring GRF data from one step in a single traverse. That can lead to problems of ‘targeting’ and, with less able subjects, fatigue before the necessary data have been collected. Previous work at the University of Surrey resulted in a prototype dual-platform force walkway capable of measuring the vertical component of the GRF and estimating the position of application of that force for multiple foot contacts in a single traverse. In addition, temporal-spatial information, e.g. speed and step length, could also be determined. This paper describes the development of a longer walkway that can measure the three orthogonal components of the GRF and provide a more accurate estimate of the position of application of that force. Software to allow the rapid reduction of gait data to useful clinical information has also been developed.
Long-term results for Kinemax and Kinematic knee bearings on a six-station knee wear simulator
Authors: Ash H E , Burgess I C , Unsworth A 
Published: October 2002

A long-term wear test was performed on Kinemax and Kinematic (Howmedica Inc.) knee bearings on the Durham six-station knee wear simulator. The bearings were subjected to flexion/extension of 65–0°, anterior-posterior translation of between 4.5 and 8.5 mm and a maximum axial load of 3 kN. Passive abduction/adduction and internal/external rotation were also permitted, however, two of the stations had a linkage system which produced ± 5° active internal/external rotation. The bearings were tested at 37 °C in a 30 per cent bovine serum solution and the test was run to 5.6 × 106 cycles. The bearings from stations 2 and 3, and stations 4 and 5 were swapped during the test to investigate the effects of interstation variability. The average wear rate and standard error was 3.00 ± 0.98 mg/106 cycles (range 1.33-4.72 mg/106 cycles) for the Kinemax bearings and 3.78 ± 1.04 mg/106 cycles (range 1.87-4.89 mg/106 cycles) for the Kinematic bearings. There were no significant differences in wear rates between the different bearing designs, the addition of active internal/external rotation or a change of stations. However, the wear tracks were different for the two types of bearings and with active internal/external rotation. The wear rates and factors were generally lower than previously published in vitro wear results; however, this may have been due to a difference in the axial loads and lubricants used. The appearance of the wear tracks with active internal/external rotation was comparable with those seen on explanted knee bearings.
Radiographic assessment of the cement mantle thickness of the femoral stem in total hip replacement: A case study of 112 consecutive implants
Authors: Isaac G H , Busch C A , Shetty V , Drabu K J 
Published: October 2002

The results are reported of a radiographic study of cement mantle thickness in 112 consecutive primary hip replacements. Measurements were made by three observers of the apparent cement thickness medially and laterally using standard anterior-posterior radiographs. The average cement thickness was 3.2 mm, which is 1.2 mm greater than the size difference between the broach and the prosthesis, and was in the range 2–5 mm in 67 per cent of all measurement points. This has significance for the design of instrumentation to prepare the femoral cavity to give a defined cement mantle thickness. There was a greater cement mantle thickness proximally than distally. In 95 cases it was possible to determine the orientation of the stem within the cement mantle, which showed an even distribution between varus and valgus orientation; 49 per cent were within 1 ° of neutral and only one case was more than 5° from neutral.
A viscoelastic analysis of the tensile weakening of deep femoral head articular cartilage
Authors: Egan J M 
Published: October 2002

Articular cartilage from below the surface of the femoral head of the hip joint shows a profound age-dependent weakening in its tensile mechanical properties. This ageing is also associated with a reduced viscoelastic response in the older tissue. A constitutive model of the viscoelastic behaviour of deep articular cartilage (as discussed by Egan in 1988) is used to generate a graphical pattern which represents the mechanical behaviour. This constitutive approach suggests that the tensile weakening of the older cartilage is due to an age-related reduction in the recruitment of load-carrying structures as the tissue is deformed. The viscoelastic constitutive model also predicts a reduction in the tensile strength of deep articular cartilage with rate of deformation. This prediction is supported by experimental fracture stress data. A weakening of the tensile integrity of the microstructure of articular cartilage could make the tissue less able to sustain normal compressive physiological loading without damage and thus make the tissue more susceptible to osteoarthritic degeneration. The constitutive approach indicates that the weakening of the older tissue may be related to changes within the microstructure which determine how applied mechanical energy is stored and dissipated.
A comparative evaluation of dental luting cements by fracture toughness tests and fractography
Authors: Ryan A K , Orr J F , Mitchell C A 
Published: October 2002

In recent years there has been a shift from traditional methods of investigating dental materials to a fracture mechanics approach. Fracture toughness (KIC) is an intrinsic material property which can be considered to be a measure of a material's resistance to crack propagation. Glassionomer cements are biocompatible and bioactive dental restorative materials, but they suffer from poor fracture toughness and are extremely susceptible to dehydration. The main objective of this study was to evaluate the fracture toughness of three types of commercially available dental cements (polyacid-modified composite resin, resin-modified and conventional glass ionomer) using a short-rod chevron-notch test and to investigate and interpret the results by means of fractography using scanning electron microscopy. Ten specimens of each cement were fabricated according to manufacturers' instructions, coated in varnish, and stored at ambient laboratory humidity, 100 per cent relative humidity, or in water at 37 °C for 7 days prior to preparation for testing. Results indicated that significant differences existed between each group of materials and that the fracture toughness ranged from 0.27 to 0.72 MN/m3/2. It was concluded that the resin-modified glass-ionomer cement demonstrated the highest resistance to crack propagation. Fractographs clearly showed areas of stable and unstable crack growth along the fractured surfaces for the three materials examined.
In vitro testing of the primary stability of the VerSys enhanced taper stem: A comparative study in intact and intraoperatively cracked femora
Authors: Monti L , Cristofolini L , Toni A , Ceroni R G 
Published: October 2002

The Zimmer VerSys enhanced taper uncemented stem was tested in vitro for primary stability. Six stems were implanted in six composite femora. Three femora were unintentionally damaged by cracking of the bone during stem insertion and press-fit. A previously validated protocol was used to load the specimens cyclically and to record locally the rotational and axial bone/implant relative motions in terms of elastic motion and permanent migration. For the undamaged femora, the VerSys stem showed excellent primary stability, in terms of both elastic motions (less than 9 μm) and permanent migrations (less than 6 μm), and in both axial and rotational directions, comparing favorably with the literature. Intraoperatively-induced proximal cracks did influence the primary stability of the stem in terms of permanent migration. As cracks may easily be produced in the diaphyseal canal during insertion of cementless stems, which rely for primary stability on conical fitting into the canal, great care must be taken in preparation of the canal and insertion of the stem.
The effect of femoral head diameter upon lubrication and wear of metal-on-metal total hip replacements
Authors: Smith S L , Dowson D , Goldsmith A A J 
Published: October 2002

It has been found that a remarkable reduction in the wear of metal-on-metal hip joints can be achieved by simply increasing the diameter of the joint. A tribological evaluation of metal-on-metal joints of 16, 22,225, 28 and 36 mm diameter was conducted in 25 per cent bovine serum using a hip joint simulator. The joints were subject to dynamic motion and loading cycles simulating walking for both lubrication and wear studies. For each size of joint in the lubrication study, an electrical resistivity technique was used to detect the extent of surface separation through a complete walking cycle. Wear of each size of joint was measured gravimetrically in wear tests of at least 2 × 106 cycles duration. Joints of 16 and 22.225mm diameter showed no surface separation in the lubrication study. This suggested that wear would be proportional to the sliding distance and hence joint size in this boundary lubrication regime. A 28 mm diameter joint showed only limited evidence of surface separation suggesting that these joints were operating in a mixed lubrication regime. A 36 mm diameter joint showed surface separation for considerable parts of each walking cycle and hence evidence of the formation of a protective lubricating film. Wear testing of 16 and 22.225mm diameter metal-on-metal joints gave mean wear rates of 4.85 and 6.30mm3/106 cycles respectively. The ratio of these wear rates, 0.77, is approximately the same as the joint diameters ratio, 16/22.225 or 0.72, as expected from simple wear theory for dry or boundary lubrication conditions. No bedding-in was observed with these smaller diameter joints. For the 28 mm diameter joint, from 0 to 2 × 106 cycles, the mean wear rate was 1.62 mm3/106 cycles as the joints bedded-in. Following bedding-in, from 2.0 × 106 to 4.7 × 106 cycles, the wear rate was 0.54mm3/106 cycles. As reported previously by Goldsmith in 2000 [1], the mean steady state wear rate of the 36 mm diameter joints was lower than those of all the other diameters at 0.07 mm3/106 cycles. For a range of joints of various diameters, subjected to identical test conditions, mean wear rates differed by almost two orders of magnitude. This study has demonstrated that the application of sound tribological principles to prosthetic design can reduce the wear of metal-on-metal joints, using currently available materials, to a negligible level.
A novel instrumented ring for the measurement of grip force adjustments during precision grip tasks
Authors: van der Kamp M , Conway B A , Nicol A C 
Published: October 2002

A wide range of scientific and clinical research studies use the measurement of grip force to quantify hand function and activities during daily living. Many applications of instrumented objects can be found in the biomechanical and neurophysiological literature. However, these were found not to be suitable for the measurement of grip force and force modulations during precision grip independently from the hand orientation. The low-cost precision grip force transducer described here is capable of recording magnitude, direction and modulation of the force exerted on a closed ring. The design is based on a standard proving ring, onto which a second set of strain gauges is applied. The outputs of both Wheatstone bridges yield a unique signature for every position under a two-point load. The tested aluminium ring had an outer diameter of 83 mm, a wall thickness of 3 mm and a height of 12mm. With eight single bending strain gauges used, the maximum load was 100N. During a grip task, tremor components from d.c. to 45 Hz could be detected. The newly developed ring might therefore find a use in many biomechanical and neurophysiological studies as a tool for measuring grip force and its fine modulations.
Hip simulator wear testing according to the newly introduced standard ISO 14242
Authors: Kaddick C , Wimmer M A 
Published: October 2002

Ultra-high molecular weight polyethylene (UHMWPE) acetabular cups were tested against alumina-ceramic femoral heads using a new type of hip joint simulator according to ISO/FDIS 14242-1. Bovine serum as well as newborn calf serum were used as test fluids. Total polyethylene wear was determined by weight loss of the cups. In addition, wear depth and its distribution were recorded by means of a coordinate measurement system. Wear particle analysis and inspection of the worn polyethylene surfaces using light and scanning electron microscopy (SEM) were performed to analyse damage and identify the acting wear mechanisms. The total wear rate was determined to be 22.07 ± 1.75 mg/106 cycles for the bovine serum group and 26.57 ± 3.55 mg/106 cycles for the calf serum group. Unexpectedly, the formation of two wear vectors corresponding to recent clinical findings was detected. Retrieved polyethylene wear debris was comparable in size and shape with clinical findings. The test method described by ISO/FDIS 14242-1 produced reliable and reproducible wear data using UHMWPE acetabular cups articulating against alumina-ceramic heads. In the authors' opinion, the lubricant composition should be described in more detail, since the protein and additive content seem to have a high impact on the wear results. It needs to be emphasized that the findings of this study cannot be regarded as a general validation of hip wear tests according to ISO/FDIS 14242-1 but are limited to the material combinations investigated herein. Further testing of other clinically relevant materials and interlaboratory ring tests must follow.
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.
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.
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.