bluuebunny/crossref_metadata_2025 huggingface dataset:
SIGNAL-TO-NOISE RATIO GAIN IN NON-DYNAMICAL AND DYNAMICAL BISTABLE STOCHASTIC RESONATORS
Authors: MAKRA PETER , GINGL ZOLTAN , KISH LASZLO B.
Published: November 2002

It has recently been reported that in some systems showing stochastic resonance, the signal-to-noise ratio (SNR) at the output can significantly exceed that at the input; in other words, SNR gain is possible. We took two such systems, the non-dynamical Schmitt trigger and the dynamical double wellpotential, and using numerical and mixed-signal simulation techniques, we examined what SNR gains these systems can provide. In the non-linear response limit, we obtained SNR gains much greater than unity for both systems. In addition to the classical narrow-band SNR definition, we also measured the ratio of the total power of the signal to the power of the noise part, and it showed even better signal improvement. Here we present a brief review of our results, and scrutinise, for both the Schmitt-trigger and the double well potential, the behaviour of the SNR gain by stochastic resonance for different signal amplitudes and duty cycles. We also discuss the mechanism of providing gains greater than unity.
CHEMICAL REACTION DYNAMICS WITH REAL WAVE PACKETS
Authors: GRAY STEPHEN K.
Published: November 2002

An approach to carrying out accurate quantum dynamics simulations of chemical reactions, termed the real wave packet (RWP) method, is outlined. The method focuses on propagation of just the real part of a complex-valued wave packet, halving computational memory and effort requirements in comparison with comparable high accuracy quantum propagation methods. Applications to 3-atom and 4-atom chemical reactions are reviewed. Potential future directions are indicated.
CHEMICAL REACTIONS IN THE O(1D) + HCl SYSTEM I.
Authors: NANBU SHINKOH , AOYAGI MUTSUMI , KAMISAKA HIDEYUKI , NAKAMURA HIROKI , BIAN WENSHENG , TANAKA KYOSHI
Published: November 2002

New global ab initio potential energy surfaces (PES) are presented for the low-lying 11A′, 11A′′ and 21A′ electronic states which are correlated to O (1D) + HCl . These potential energy surfaces are computed by using the multi-reference configuration interaction method with the Davidson correction (MRCI+Q). The reference functions are constructed by the complete active space self-consistent field (CASSCF) calculations using the quadruple zeta + polarization basis set augmented with diffuse functions. The computations are carried out at about 5000 molecular conformations on each three-dimensional potential energy surface. The high accuracy of the computations is confirmed by a comparison with the available most accurate data for the ground state 11A′; thus the present work is the first report of the accurate potential energy surfaces for the two excited states. Three low-lying transition states on the excited surfaces, two (TS2 and TS4) on 11A′′ and one (TS3) on 21A′, are found. Since TS2 and TS3 are as low as 0.07 eV and 0.28 eV, respectively, and correlate to the OH (2Π) + Cl (2P) product, these excited surfaces are expected to play quite important roles in the reaction dynamics. Possible effects of nonadiabatic couplings among the three PESs are also briefy discussed, although the nonadiabatic couplings have not yet been estimated. The quantum reaction dynamics on these three PESs are discussed in the second accompanying paper, Paper II.
CHEMICAL REACTIONS IN THE O(1D) + HCl SYSTEM II.
Authors: KAMISAKA HIDEYUKI , NAKAMURA HIROKI , NANBU SHINKOH , AOYAGI MUTSUMI , BIAN WENSHENG , TANAKA KIYOSHI
Published: November 2002

Using the accurate global potential energy surfaces for the 11A′, 11A′′, and 21A′ states reported in the previous sister Paper I, detailed quantum dynamics calculations are performed for these three adiabatic surfaces separately for J = 0 (J: total angular momentum quantum number). Overall reaction probabilities for O + HCl → OH + Cl and H + ClO, the branching ratio between the two reactions, effects of the initial rovibrational excitation, and product rovibrational distributions are evaluated in the total energy region E tot ≤ 0.9 eV. Significant contributions to the overall reaction dynamics are found from the two excited 11A′′ and 21A′ potential energy surfaces, clearly indicating the insufficiency of the dynamics only on the ground 11A′ surface. The detailed dynamics on the excited surfaces are reported in the third paper of this series.
CHEMICAL REACTIONS IN THE O(1D) + HCl SYSTEM III.
Authors: KAMISAKA HIDEYUKI , NAKAMURA HIROKI , NANBU SHINKOH , AOYAGI MUTSUMI , BIAN WENSHENG , TANAKA KIYOSHI
Published: November 2002

Using the accurate global potential energy surfaces for the 11A′′ and 21A′ states reported in the previous sister Paper I, detailed quantum dynamics calculations are performed for these adiabatic surfaces separately for J = 0 (J: total angular momentum quantum number). In addition to the significant overall contributions of these states to the title reactions reported in the second Paper II of this series, quantum dynamics on these excited potential energy surfaces (PES) are clarified in terms of the PES topographies, which are quite different from that of the ground PES. The reaction mechanisms are found to be strongly selective and nicely explained as vibrationally nonadiabatic transitions in the vicinity of potential ridge.
CONFORMATIONAL AND DYNAMICAL PROPERTIES OF THE C(O)–CH2–S–H MOIETY IN THIOGLYCOLIC ACID AND METHYLTHIOGLYCOLATE: AN AB INITIO AND DFT STUDY
Authors: FANTONI A. C.
Published: November 2002

The results of a series of ab initio molecular orbital calculations on thioglycolic acid and methylthioglycolate are presented. Full geometry optimizations at different levels of theory have been performed for the equilibrium and transition state configurations, in order to determine the height of the inversion barriers, and to obtain information on the relaxation of some geometrical parameters.

In spite of using extended basis sets and the inclusion of electron correlation, there is an important inconsistency between the relative position of the thiolic hydrogen derived from experimental data and the ab initio predictions.

As regards the barrier height, the results more consistent with the available experimental data are obtained when the Gaussian2 compound methods [G2 and G2(MP2)] are used.

The possible influence of an –S–H⋯O = hydrogen bond on the conformational behavior has also been investigated by analyzing the topology of the electron density.
GEOMETRIC DIRECT MINIMIZATION OF HARTREE–FOCK CALCULATIONS INVOLVING OPEN SHELL WAVEFUNCTIONS WITH SPIN RESTRICTED ORBITALS
Authors: DUNIETZ BARRY D. , VAN VOORHIS TROY , HEAD-GORDON MARTIN
Published: November 2002

Recently, we have introduced a method based on geometric considerations, termed geometric direct minimization (GDM), to achieve robust convergence of self consistent field calculations. GDM was limited to calculations involving either spin-unrestricted orbitals or closed shell systems. We report the extension of the GDM method to treat open shell systems involving spin-restricted orbitals. Open shell systems pose a challenge for achieving robust convergence of the calculation. We compare the convergence using the GDM method to the convergence achieved by the well known direct inversion in the iterative space (DIIS) technique. This comparison demonstrates the ability of the GDM method to achieve robust convergence. Additionally we assess the importance of geometric considerations by comparing against an alternative direct minimization method that is not geometrically correct.
FIRST PRINCIPLES MOLECULAR DYNAMICS INVOLVING EXCITED STATES AND NONADIABATIC TRANSITIONS
Authors: DOLTSINIS NIKOS L. , MARX DOMINIK
Published: November 2002

Extensions of traditional molecular dynamics to excited electronic states and non-Born–Oppenheimer dynamics are reviewed focusing on applicability to chemical reactions of large molecules, possibly in condensed phases. The latter imposes restrictions on both the level of accuracy of the underlying electronic structure theory and the treatment of nonadiabaticity. This review, therefore, exclusively deals with ab initio "on the fly" molecular dynamics methods. For the same reason, mainly mixed quantum-classical approaches to nonadiabatic dynamics are considered.
CONTROL OF PHOTODISSOCIATION BRANCHING USING THE COMPLETE REFLECTION PHENOMENON: APPLICATION TO HI MOLECULE
Authors: FUJISAKI HIROSHI , TERANISHI YOSHIAKI , NAKAMURA HIROKI
Published: November 2002

The laser control of photodissociation branching in a diatomic molecule is demonstrated to be effectively achieved with use of the complete reflection phenomenon. The phenomenon and the control condition can be nicely formulated by the semiclassical (Zhu–Nakamura) theory. The method is applied to the branching between I (2P3/2) ( HI → H + I ) and I *(2P1/2) ( HI → H + I *) formation, and nearly complete control is shown to be possible by appropriately choosing an initial vibrational state and laser frequency in spite of the fact that there are three electronically excited states involved. Numerical calculations of the corresponding wavepacket dynamics confirm the results.
HEISENBERG MODEL AND ITS APPLICATIONS TO π-CONJUGATED SYSTEMS
Authors: LI SHUHUA , MA JING , JIANG YUANSHENG
Published: November 2002

This paper briefly reviewed the Heisenberg model and its improvement by including higher order corrections, and their applications to bond lengths, stability, and reactivity of non-benzenoids and the low-lying excitation spectra of conjugated systems. Two efficient computational methods, the Lanczos method and the density-matrix renormalization group (DMRG), for exactly and approximately solving various Heisenberg models, respectively, were briefly introduced.
TOWARDS A MOLECULAR THEORY FOR THE VAN DER WAALS–MAXWELL DESCRIPTION OF FLUID PHASE TRANSITIONS
Authors: KOVALENKO ANDRIY , HIRATA FUMIO
Published: November 2002

We briefly review developments of theories for phase transitions of molecular fluids and mixtures, from semi-phenomenological approaches providing equations of state with adjustable parameters to first-principles microscopic methods qualitatively correct for a variety of molecular models with realistic interaction potentials. We further present the generalization of the van der Waals–Maxwell description of fluid phase diagrams to account for chemical specificities of polar molecular fluids, such as hydrogen bonding. Our theory uses the reference interaction site model (RISM) integral equation approach complemented with the new closure we have proposed (KH approximation), successful over a wide range of density from gas to liquid. The RISM/KH theory is applied to the known three-site models of water, methanol, and hydrogen fluoride. It qualitatively reproduces their vapor-liquid phase diagrams and the structure in the gas as well as liquid phases, including hydrogen bonding. Furthermore, phase transitions of water and methanol sorbed in nanoporous carbon aerogel are described by means of the replica generalization of the RISM approach we have developed. The changes as compared to the bulk fluids are in agreement with simulations and experiment. The RISM/KH theory is promising for description of phase transitions in various associating fluids, in particular, electrolyte as well as non-electrolyte solutions and ionic liquids.
WHAT, IF ANYTHING, IS MAHĀYĀNA BUDDHISM? PROBLEMS OF DEFINITIONS AND CLASSIFICATIONS
Authors: Silk Jonathan
Published: November 2002

This study investigates some problems regarding the definition of Mahāyāna Buddhism. Tracing the history of the notion in modern scholarship, it pays particular attention to the question of the relation between Mahāyāna and so-called Hīnayāna or Sectarian Buddhism. Finding the commonly used methods of classification which rely on necessary and sufficient conditions to be inadequate to the task, it suggests the alternative employment of polythetic classification, a method which permits a constantly variable set of questions and data to be taken into account in the most flexible and accommodating manner.
ASPECTS DU "SACERDOCE" EN SYRIE ANCIENNE: REMARQUES METHODOLOGIQUES ET EXAMEN D'UN CAS PARTICULIER
Authors: Xella Paolo
Published: November 2002

A historico-religious study focusing on "priesthood" and "priest" has to face many difficulties, in terms of terminology and of content. On the one hand, it is methodologically incorrect to link "priesthood" to debated modern concepts such as "religion" or "cult" which, like the former, need to be (even conventionally) defined each time for every particular culture, and not to be assumed as universal keys of historical understanding. On the other hand, previous studies on the topic - where the aim has been to determine latent forms and/or particular manifestations of "priesthood" in other cultures and also to write a "general history" of this phenomenon - exhibit the total historical irrelevance of such an approach, based only on our modern (Christian) concept of "priest(hood)." In order to limit ethnocentrism and, at the same time, to employ useful conceptual categories, new heuristic parameters must be found. In addition to the criterion indicated by J. Rüpke (the religious specialist as a control-agent within the framework of symbolic systems), I propose to distinguish between professional specialisation and practical (cultic) function. The case study I present here to illustrate some aspects and problems of this research is that of ancient Syrian (Ugaritic) culture, where "priests" in our meaning are difficult to be found, whereas a fully new concept emerges if we look at the issue from a functional (and "emic") perspective.
A loose-ring lubricator model
Authors: Innes G. E. , Dowson D , Taylor C. M.
Published: November 2002

The loose-ring lubricator is used as a pump within self-contained journal bearings to deliver lubricating fluid from a reservoir or sump to the bearing. It is desired to understand its behaviour sufficiently to be able to predict the performance of new designs. An analytical model is derived that uses the balance of forces acting on the ring to predict the ring speed. The delivered flowrate is then estimated using viscous lifting theory. The results compare favourably with experimental data and published empirical models. Improvements are also suggested to account for additional influences that might affect actual lubricator operation.
A theoretical formula for calculating damping in the impact of two bodies in a multibody system
Authors: Zhu S. H. , Zwiebel S , Bernhardt G
Published: November 2002

Clearance often exists in the connections of machine parts and causes impact between the parts during machine operation. A spring damper element is usually applied to predict the impact loads acting on the parts. In this paper the impact process is modelled as a two-degrees-of-freedom vibrational system. Based on the assumption that the loss of kinetic energy of the two parts during impact should be absorbed by the damper in the spring damper element that is applied to describe the impact process, a theoretical formula for estimating damping by impact between two parts is derived for the first time. An example is given to show the application of the formula in dynamic simulation using a multibody simulation (MBS) program.
Wavelet analysis of the breakdown of a pulsed vortex flow
Authors: Addison P. S.
Published: November 2002

The paper provides an introduction to the properties and use of the continuous wavelet transform. It then describes the wavelet analysis of the breakdown of a confined vortex flow where time series data of the centre-line velocities from a pulsed vortex flow at a pipe orifice are examined using the Mexican hat wavelet transform. The development of the signal from the periodic, vortex flow via an energetic turbulent breakdown region to a flow composed of low-frequency coherent structures at intermittent temporal scales is monitored using wavelet transform plots, wavelet energy plots and wavelet power spectra.
A symmetrically piecewise linear oscillator: Design and measurement
Authors: Sin V. W. T. , Wiercigroch M
Published: November 2002

A simple piecewise linear system with symmetrical flexible constraints was designed and manufactured to carry out a wide range of experimental dynamic analysis and ultimately to validate piecewise models. The design choice was based on the following criteria: accuracy in representing the mathematical model, manufacturing simplicity, flexibility in terms of parameter changes and cost effectiveness. The system consists of a block mass attached to two leaf springs, the stiffness of which can easily be varied by changing their length. The secondary stiffness in the form of cantilever beams can be widely varied in the same way. The clearance between the mass and secondary springs can also be varied by adjusting the screws at the ends of the beams. A variable pneumatic damper is mounted on the upper surface of the mass and provides a means of changing the viscous damping coefficient. The experimental set-up, calibration procedures and typical results are discussed.
Theoretical and experimental results of the elastic—plastic response of a circular rod subjected to non-proportional combined torque and tension loadings
Authors: Ali A. R. M. , Hashmi M. S. J.
Published: November 2002

Experimental and theoretical results concerning the elastoplastic response of a circular steel rod subjected to non-proportional biaxial loadings are reported. The following loading paths were studied: elastoplastic torsion followed by tension, keeping the initial angle of twist constant, and elastoplastic tension followed by torsion, holding the initial axial displacement constant. Experimental results show that when the rod is initially subjected to a torque and then, keeping the corresponding angle of twist constant, to a gradually increasing axial load, the rod behaves as if its torque-carrying ability has been drastically reduced without in any way affecting its axial load-carrying ability. Similarly, when the rod is initially subjected to an axial load and then, keeping the corresponding axial displacement constant, to a gradually increasing torque, the rod behaves as if its load-carrying ability has been considerably reduced without in any way affecting its torque-carrying ability. The mechanisms of such reduction are discussed in relation to the theoretical predictions based on Gaydon's [1] analytical model. Numerical solution has also been obtained along the lines of the above-mentioned model. The findings of this work have a direct bearing on the relaxation of tightening torques or axial loads as experienced by critical engineering components, such as couplings, bolted joints and rotating shafts, that are subjected to similar types of biaxial loading.
A finite element analysis of steady viscous flow in triangular cavities
Authors: Gaskell P. H. , Thompson H. M. , Savage M. D.
Published: November 2002

A finite element formulation of the Navier—Stokes equations, written in terms of the stream function, ψ, and vorticity, ω, for a Newtonian fluid in the absence of body forces, is used to solve the problem of flow in a triangular cavity, driven by the uniform motion of one of its side walls. A key feature of the numerical method is that the difficulties associated with specifying ω at the corners are addressed and overcome by applying analytical boundary conditions on ω near these singularities. The computational results are found to agree well with previously published data and, for small stagnant corner angles, reveal the existence of a sequence of secondary recirculations whose relative sizes and strengths are in accord with Moffatt's classical theory. It is shown that, as the stagnant corner angle is increased beyond approximately 40°, the secondary recirculations diminish in size rapidly.
Flow characteristics inside a diffuser of complex shape
Authors: Benhamza M. E. H. , Khezzar L , Marquis A. J.
Published: November 2002

An experimental study was made of an incompressible flow through a model S-shaped semicircular to circular transition diffusing duct. The transition diffuser has a length—exit diameter ratio of 3 and a duct offset ratio of 0.3. The operating Reynolds number based on hydraulic diameter and bulk velocity is 40 000. The refraction index matching technique and laser Doppler velocimetry were used for velocity measurements. The measurements indicate that flow distortion persists at the outlet and the separation of the boundary layers is incipient. Semicircular to circular transition duct flow was studied in order to document the transition duct flow field and to provide detailed duct flow data for comparison with numerical code prediction. Experimental results also suggest that details of the near-wall flow incipient separation region and the distortion of the flow in the second half of the diffuser are likely to provide a severe test for various computational methods and turbulence models.
Comparison of experimental assessment methods to estimate the strength of gear teeth
Authors: Ahmad-Shariff A , Ashby R , Metcalfe A. V. , Swailes D. C.
Published: November 2002

Regression type methods for analysing proportions, known as probit and logit analyses, are compared with the British Standard BS 3518 (part 5) recommendations for analysis of staircase designs. All these methods are found to give similar results. Different experimental strategies, involving fixed sample sizes for load levels chosen in advance, are compared with staircase designs. Recommendations for practice are made. Finally, the versatility of the logit analysis for investigating the effects of additional variables, such as additional treatments during manufacture, is demonstrated through a case study.
Particle image velocimetry and laser Doppler anemometry experimental studies of a compressible short take-off and vertical landing ground vortex flow
Authors: Lawson N J , Eyles J M , Knowles K
Published: November 2002

A particle image velocimetry (PIV) and laser Doppler anemometry (LDA) study of a scaled short take-off and vertical landing (STOVL) ground vortex flow is presented. The scaled flow features a compressible impinging jet in cross-flow with a moving ground plane. Mean and transient PIV and LDA velocity data are recorded from the ground vortex about the jet centre-line over a range of nozzle pressure ratios (NPR s) from 2.3 to 3.7, nozzle height—diameter ratios ( h/dn) from 3 to 10 (where dn = 12.7 mm) and cross-flow velocities (V∞) from 10 to 20 m/s, corresponding to effective velocity ratios of 19 < Ve−1 < 38. For each condition, 72 PIV vector maps were taken from the ground vortex region to generate an instantaneous and time-average data set. From the instantaneous data, a cinematic sequence was used to track the ground vortex position, which was found to fluctuate longitudinally by a root mean square distance of up to 4.47 dn and vertically by up to 2.18 dn. From the time-averaged PIV measurements, selected LDA pointwise data were taken at the average ground vortex core. Subsequent spectral analysis of the PIV time series showed the ground vortex position to fluctuate at dominant frequencies of between 2.5 and 5 Hz while the LDA data showed the velocity to fluctuate by dominant frequencies ranging between 1 and 30 Hz.
Preliminary reliability design of a solar-powered high-altitude very long endurance unmanned air vehicle
Authors: Frulla G
Published: November 2002

Within the research project HELINET (network of stratospheric platforms for traffic monitoring, environmental surveillance and broadband services), a preliminary reliability design is performed in conjunction with the platform design. The aim of the discussion consists in determining the configuration of the propulsion system and in the choice of the number of propulsion units (a propulsion unit consists of one propeller and one or more motors). The reliability and the weight of different very simple systems are evaluated and compared with one another in order to indicate the best one. The analysis of the fleet reliability and a study of its standby platforms is also taken into consideration. The analysis of the reliability of the solar cell array is also an interesting issue. A parametric analysis based on well-known formulae is used. Some results are verified by means of a numerical simulation based on the Monte Carlo methodology. Some important design indications could be obtained from this effort.
Non-linear modelling of a one-degree-of-freedom twin-rotor multi-input multi-output system using radial basis function networks
Authors: Ahmad S M , Shaheed M H , Chipperfield A J , Tokhi M O
Published: November 2002

Modelling of innovative aircraft such as unmanned air vehicles (UAVs), X-wing, tilt body and delta-wing aircraft is not easy. It is argued in this paper that non-linear system identification is suitable for modelling air vehicles of complex configuration. This approach is demonstrated through a laboratory test rig. Extensive time and frequency-domain model-validation tests are employed in order to instil confidence in the estimated model. The estimated model has a good predictive capability and can be utilized for non-linear flight simulation studies. Some aspects of the modelling approach presented may be relevant to flight mechanics modelling of new generations of air vehicle.
Dynamic stability of a curved beam under sinusoidal loading
Authors: Poon W Y , Ng C F , Lee Y Y
Published: November 2002

This paper is a study of snap-through properties of a non-linear dynamic buckling response to sinusoidal excitation of a clamped—clamped buckled beam. Using a simple formula, the highly non-linear motion of snap-through and its effects on the overall vibration response have been studied. The non-linear governing equation obtained here is solved using the Runge—Kutta (RK-4) numerical integration method. Critical parameters at the onset of the snap-through motion, which vary with different damping coefficients and linear circular frequencies of a flat beam, are studied and given in terms of the excitation level and response displacement. The relationships between static and dynamic responses at the start of the snap-through motion are also predicted. The analysis brings out various characteristic features of the phenomenon, i.e. (a) small oscillations about the buckled position, (b) chaotic motion of intermittent snap-through and (c) large oscillations of continuous snap-through motion crossing the two buckled positions. The non-linear dynamic instability behaviour of the beam, changing from the softening spring type to the hardening type, is due to the snap-through motion.
Relation between mechanical stiffness and vibration transmission of fracture callus: An experimental study on rabbit tibia
Authors: Akkus O , Korkusuz F , Akin S , Akkas N
Published: November 2002

It has been suggested that the vibration transmission across a fracture is affected by the stages of healing of the fracture callus. This study aims to correlate the change in vibration transmission with mechanical stiffness of the callus measured by three-point bending. The right tibiae of male, three-month old local albino rabbits were osteotomized and stabilized by intramedullary fixation following open reduction. The intramedullary rods were removed on the 15th, 28th, 42nd and 90th days postoperatively and the tibiae were excised for vibration, three-point bending and bone mineral density analysis by quantitative computerized tomography (QCT). Optimum time for clinical weight bearing was determined by checking the convergence of the vibration parameters of the fractured tibia to those of the unfractured contralateral. The conclusions obtained from curvature analysis, based on vibration experiments, were in considerable correlation (Spearman's rank correlation coefficient r = 0.93, p = 0.003) with the conclusions obtained from the three-point bending test data which reflected the mechanical condition of the bone by direct means. However, no correlation between bone mineral density change and vibration transmission was noted.
The lubricating ability of biomembrane models with dipalmitoyl phosphatidylcholine and γ-globulin
Authors: Higaki H , Murakami T , Nakanishi Y , Miura H , Mawatari T , Iwamoto Y
Published: November 2002

Two kinds of friction tests were conducted to investigate the lubricating effect of the injection of amphiphilies on the osteoarthritic joint. The effects of the addition of Lα-dipalmitoyl phosphatidylcholine (Lα-DPPC) riposomes and γ-globulin in a saline solution of sodium hyaluronate (HA) were evaluated through pendulum friction tests. The frictional characteristics of pig shoulder joints were confirmed to depend on the viscosity of the lubricants only in the physiologically low load condition and in the condition immediately after loading. Detergent (polyoxyethylene p-t-octylphenyl ether) was successfully used to remove adsorbed films from the articular surfaces. The friction coefficient of natural synovial joints was significantly increased in a mode of mixed lubrication with the HA solution of 0.2 g/dl by the treatment of the surface with the detergent. The addition of Lα-DPPC riposomes or y-globulin significantly improved the boundary lubricating ability of the articular surfaces treated with the detergent, depending on the quantity of those additives. It appears that the Lα-DPPC riposomes and γ-globulin can form protective films on the articular surfaces like a biomembrane.

Moreover, the reciprocating frictional behaviour in sliding pairs of pig articular cartilages and glass plates was studied in order to elucidate the tribological role of those constituents in the boundary lubricating film on the articular surface. Pig synovial fluid and water solutions of HA were used as lubricants. The synovial fluid had superior lubricating ability compared to the HA solution of equivalent viscosity under a physiologically high load condition. This fact seems to be responsible for the boundary lubricating ability of constituents other than hyaluronic acid. Langmuir-Blodgett (LB) films of Lα-DPPC on the glass plate were kept at a low and stable friction coefficient, depending on the number of film layers. In conditions of mixed films with Lα-DPPC and γ-globulin, the frictional behaviour was improved by increasing the quantity of γ-globulin. A model is proposed in which the effective adsorbed films are composed of proteins, phospholipids and other conjugated constituents on the articular surfaces to be accurate in describing the boundary lubricating mechanism. The mechanism is controlled by hydrophobic groups in those amphiphilies.
Accuracy of an electromagnetic measurement device and application to the measurement and description of knee joint motion
Authors: Bull A M J , Berkshire F H , Amis A A
Published: November 2002

The aims of this study were to analyse the accuracy and sensitivity to metals of an electromagnetic motion measurement device and to use it to provide a description of motion of the human knee joint. A calibrated grid and sine bar were used to measure translational and rotational accuracy, which were found to be ±0.23 per cent of the step size (translation) and ±2.0 per cent of the step size (rotation) within an optimal operational zone of minimal positional error for which the receiver to transmitter separation was between 271 and 723 mm. The presence of multiple receivers was found to have a significant effect on the accuracy only when positioned within 30 mm of one another. Mild steel was found to have a significant detrimental effect when within 150 mm of the transmitter or receiver. A stainless steel bone screw had no effect on the accuracy of the device. A mathematical description of knee joint motion is presented which describes the motion in terms of clinical rotations. The device is a useful tool for measuring joint motion in the operating theatre and laboratory, owing to its accuracy and insensitivity to surgical alloys.
Knee joint motion: Description and measurement
Authors: Bull A M J , Amis A A
Published: November 2002

Knee joint motion has been described in various ways in the literature. These are explained and commented on. Two methods for describing knee joint motion with 6 degrees of freedom (DOF)—Euler angle and the helical axis of motion—are discussed. Techniques to measure joint motion which can either approximate the motion to less than 6 DOF or fully measure the spatial motion are identified. These include electrical linkage methods, radiographic and video techniques, fluoroscopic techniques and electromagnetic devices. In those cases where the full spatial motion is measured, the data are available to describe the motion in simpler terms (or with less DOF) than three rotations with three translations. This is necessary for clinical application and to facilitate communication between the clinician and the engineer.
The design of an optimized portable artificial kidney system using recirculation and regeneration of dialysate
Authors: Bigsby R J A , Rider R J , Blount G N
Published: November 2002

This paper is intended as an overview of the research carried out at Coventry University in the design of a portable artificial kidney system. It was seen that the key to the problem was the reduction in dialysate volume, and so it was decided to develop a prototype that would utilize the regeneration and recirculation of a small volume of dialysate. A prototype system has been produced and used to simulate a dialysis session. Activated carbon was used as a sorbent for the regeneration of the dialysate, circulating in a closed loop. For the purpose of this work, the adsorption of urea was investigated as this is, volumetrically, the major solute to be removed. Peltier effect cooling was used to vary the dialysate temperature down to 2 °C, as activated carbon will adsorb greater amounts of urea at lower temperatures. A series of tests was then carried out to investigate the effect of dialysate temperature, flowrate and volume on the amount of urea that could be dialysed.

From the experimental results, a model of the system was derived, which made it possible to determine the implications of different operating conditions on the overall mass and size of a portable dialysis system. The output of this model was then used to establish a design specification and produce an optimum design solution for the system.
Rapid prototyping for orthopaedic surgery
Authors: Potamianos P , Amis A A , Forester A J , McGurk M , Bircher M
Published: November 2002

The revision of an orthopaedic procedure can present surgeons with the challenge of a complex reconstructive process. Orthopaedic surgery can also face considerable challenges in cases presenting extensive primary injuries with multiple bone fragmentation, as well as in cases presenting bone deformities. Radiographs are used routinely for orthopaedic surgical planning, yet they provide inadequate information on the precise three-dimensional extent of bone defects. Three-dimensional reconstructions from X-ray computed tomography offer superior visualization but are not portable for consultation or readily available in the operating theatre for guidance during a procedure. A physical model manufactured from X-ray computed tomography data can offer surgeons a clear understanding of complex anatomical detail, by providing an intuitive physical relationship between patient and model. Rapid prototyping was used for the construction of an anatomical model in a case presenting with a complex shoulder injury. The model provided a definitive interpretation of joint pathology and enabled a full assessment of the degree of injury.
The frictional behaviour of explanted PCA hip prostheses
Authors: Elfick A P , Hall R M , Pinder I M , Unsworth A
Published: November 2002

The frictional characteristic of 22 explanted and two unused PCA total hip arthoplasties were assessed using the Durham hip simulator. The friction of the explanted joints was not found to be significantly different from that of the unused joints. In contrast, explanted Charnley joints often exhibit increased frictional characteristics. This discrepancy is accounted for by the lack of cement ingression in the PCA design.
A multi-station hip joint simulator study of the performance of 22 mm diameter zirconia-ultra-high molecular weight polyethylene total replacement hip joints
Authors: Goldsmith A A J , Dowson D
Published: November 2002

The commissioning of a new form of 10-station hip joint simulator is described and the results of a study of the performance of zirconia-ultra-high molecular weight polyethylene (UHMWPE) total replacement hip joints in the familiar Charnley head size of 7/8 inch (22.225 mm) diameter are presented. The head size is referred to as 22 mm for brevity and consistency throughout the paper. The simulator provided very consistent and repeatable results and the new machine, together with the methods of investigation adopted, offer an excellent facility for the further evaluation of existing and new prostheses. The findings are compared with the outcome of previous laboratory simulator and clinical studies of ceramic-polyethylene implants of similar diameter. It was found that a relatively rapid penetration of the head into the cup was followed by a very low, steady, long-term penetration rate after about two million loading cycles. The mean long-term volumetric penetration rate was 6.28 mm3/106 loading cycles. When the linear penetration rates were assessed by direct measurement on a coordinate measuring machine, or deduced from the tunnelling expression, the resulting values were very similar and small at 0.019 and 0.016 mm/106 loading cycles respectively. It is generally assumed that one million loading cycles is equivalent to about one year of service in the body and if this equivalence is accepted, these penetration rates compare very favourably with a clinical evaluation of alumina heads of the same diameter, which yielded a mean long-term penetration rate of 0.022 mm/year.
Estimation of blood perfusion using ultrasound
Authors: Jansson T , Persson H W , Lindström K
Published: November 2002

Ways to measure blood perfusion using ultrasound techniques such as continuous-wave Doppler, pulsed Doppler, colour Doppler and power Doppler will be reviewed. From a certain standpoint, blood perfusion may be defined as the difference between arterial inflow and arterial outflow from a considered volume, i.e. capillary flow. The low velocities and small blood volumes involved make the signal-to-noise ratio, dynamic range and frequency resolution critical factors in the detection system. Another limiting factor is tissue motion which obscures the blood signal. Perfusion may still under certain conditions be estimated with the first moment of the Doppler power spectrum, as obtained with any Doppler ultrasound method. Modern flow mapping techniques also make it possible to estimate perfusion by counting the number of pixels that indicate flow, but low flow velocities cannot be included in the estimate. Future high-frequency systems may, however, provide very detailed images of minute flow distributions in superficial layers. Contrast agents are widely used today to enhance the blood signal, and a technique named harmonic imaging can suppress movement artefacts from surrounding tissue. Transient signals from disrupting contrast agent particles in an ultrasound field can potentially be used for perfusion quantification. Future developments to extract the blood flow signal from its noisy environment, aside from contrast agents, may be multiple sample volumes, frequency compounding and/or improved signal processing. The lack of an adequate perfusion phantom for verification of measurements of microcirculatory flow becomes, however, more apparent with improved detectability of slow flows.
A review of metallic, ceramic and surface-treated metals used for bearing surfaces in human joint replacements
Authors: Dearnley P A
Published: November 2002

A review of established and advanced materials used for the bearing surfaces of total hip replacements (THRs), their standards, methods of manufacture and corrosion testing is presented. Some account is also taken of parallel developments in femoral components used in total knee replacements (TKRs). Metallic, ceramic and surface-modified metallic materials are separately reviewed, but wherever possible common practices are collated. Coated implant bearing surfaces are in an advanced state of development and some designs are receiving clinical evaluation. To date, however, no standard methods of manufacturing and testing these materials have been agreed. Accordingly, corrosion and other key quality test methods suitable for surface-modified implant bearing materials are reviewed.
The effects of design and configuration on the biomechanical response of an internal spinal fixator
Authors: Alkalay R N , Sharpe D , Bader D L
Published: November 2002

This study examines the biomechanical performance of an internal spinal fixator and the effects of specific design features under a range of loading modes. The commercial device was mounted on plastic vertebrae in a corpectomy injury model and attached by a series of experimental jigs to an appropriate material testing machine and tested under axial compression, torsion and flexion and extension moments. Results from the torsional tests indicated that increasing the clamp tightening torque from 5 to 15 N m significantly increased the rigidity of the fixation system. The inclusion of the transverse elements resulted in a significant increase in the torsional stiffness, with the increase largely overriding the effect of clamp tightening torque. By contrast, under compressive and both flexion and extension loads, neither of the design features of the fixator had a marked effect on the overall measured stiffness of the system. However, under extension loads, there were specific interactions between the two design parameters. The present study clearly indicates the need for the optimization of the design of the clamps and for alternative configurations of the transverse elements to enhance their performance under sagittal loads.
The role of acetabular component screw holes and/or screws in the development of pelvic osteolysis
Authors: Schmalzried T P , Brown I C , Amstutz H C , Engh C A , Harris W H
Published: November 2002

Anecdotal reporting of osteolysis around cementless modular acetabular components with holes through the metal shell and/or iliac fixation screws has raised concern that such designs may generate excessive particulate debris and/or permit direct access of particulate debris to iliac bone. To address this issue, incidence data are reported on 513 total hip replacements from six different single-surgeon series of total hip arthroplasties performed with six different porous ingrowth acetabular components. With follow-up ranging from 40 to 108 months, a total of 45 pelvic osteolytic lesions were observed (8.8 per cent).

Pelvic osteolysis was seen nearly as frequently in the ischium and pubis (21 lesions) as it was in the ilium (24 lesions). It was not possible to explain ischial and pubic osteolysis by holes and/or screws through the acetabular component shell. There was no direct correlation between the presence of screw holes or screws and the incidence of pelvic osteolysis. The incidence of pelvic osteolysis around modular components with holes through the shell was 4.5 per cent (14 of 313 hips). The incidence of pelvic osteolysis with solid-shell components was 15.5 per cent (31 of 200). The incidence of pelvic osteolysis around acetabular reconstructions with screws was 2.3 per cent (3 of 133). The incidence of pelvic osteolysis in reconstructions without screws was 11.1 per cent (32 of 380). The incidence of pelvic osteolysis in one-piece acetabular components (polyethylene pre-fixed in the metal shell) was 12.7 per cent (21 of 165) and the incidence of pelvic osteolysis with the modular components was 6.9 per cent (24 of 348). In each comparison, the incidence of pelvic osteolysis was actually lower in the group assumed to be at increased risk.

Based on this review there does not appear to be a direct relationship between holes and/or screws through an acetabular component and the development of pelvic osteolysis. The incidence of pelvic osteolysis was associated with larger head diameters and longer follow-up. While screw holes may provide an access channel in specific cases, the present data indicate that the simple elimination of holes through the acetabular shell will not eliminate pelvic osteolysis.

Regardless of other acetabular component design features, joint fluid and polyethylene wear particles from the femoral-acetabular articulation can gain access to bone behind an acetabular component via the peripheral implant-bone interface through regions without sufficient contact or tissue ingrowth. The development of pelvic osteolysis is multifactorial and includes the total volumetric wear of polyethylene as well as specific features of the acetabular component design and reconstruction technique.
The influence of lubricant on the morphology of ultra-high molecular weight polyethylene wear debris generated in laboratory tests
Authors: Besong A A , Tipper J L , Mathews B J , Ingham E , Stone M H , Fisher J
Published: November 2002

Since the implication of polyethylene wear debris as a major cause of osteolysis in total joint replacements, there has been much interest in polyethylene wear studies and in cell culture studies using ultra-high molecular weight polyethylene (UHMWPE) wear debris. Studies have shown that particles in the 0.1-10 μm size range are particularly important in causing adverse cellular reactions resulting in osteolysis. The morphology, the mass and size distributions, and the number of wear particles produced at the joint surfaces are influenced by the tribological conditions at the joint. Laboratory wear tests are used to investigate the wear properties of prosthetic joint materials and different research groups have used different lubricants in these tests. This paper shows that the volumetric wear and morphology of UHMWPE particles generated in vitro are influenced by the type of lubricant used. This study compared, quantitatively, UHMWPE wear debris generated in deionized water to debris that was generated in a system lubricated by bovine serum which was diluted to 25 per cent. The wear factors of UHMWPE in water and serum lubricants were significantly different ( p<0.05). UHMWPE wore 14 times more in water than in serum. Quantitative analysis of the wear particles showed that the debris that was generated in serum was morphologically different from debris that was produced in a water-lubricated system. Furthermore, the particles produced in serum showed a closer similarity to those found in retrieved acetabular tissues.
Cross-sectional geometry of the human femur in the mid-third region
Authors: Stephenson P , Seedhom B B
Published: November 2002

The design of a medical implant requires that the geometry and anatomy of the host region is fully understood. For any prosthesis to be located in the mid-third of the human femur it is therefore vitally important that an in-depth understanding of this region is obtained. This study focuses on the geometry of the medulla and the cortex and the relationship between them in the diaphyseal region of the human femur. Sixteen femora obtained from the Human Biology Department of the University of Leeds were sectioned at 10 mm intervals along the shaft and scaled photographs of each section were taken. These photographs then provided the raw data to enable the variation in long bone cross-sectional geometry to be evaluated. The results show that the medulla is almost cylindrical in the mid-third region, being most cylindrical between 35 and 50 per cent of the total bone length. The medullary width is found to be greater in the antero-posterior direction (>90 per cent maximum diameter) than in the medio-lateral direction (78-88 per cent maximum diameter) along the studied femoral length. The cortex is also analysed and it is found that the mean cortical thickness on the anterior side is significantly smaller than the medial cortex and the lateral cortex, with the posterior cortex being the thickest. All the above findings suggest that the medulla does not lie centrally within the femur but is positioned slightly anteriorly. Anatomical characteristics such as this can have profound effects on the design of prostheses to be implanted in this region.