Dr Wei Xu

Quasi-zero stiffness (QZS) isolators provide superior isolation performance than linear isolators in low-frequency vibration conditions. This paper presents a novel nonlinear vibration isolator and its optimized model based on a spring-link mechanism, which exhibits favorable QZS characteristics in a specific vibration interval. First, a uniaxial spring-link isolator (USLI) is proposed. Zero stiffness condition at the static equilibrium position is applied to achieve the optimized QZS characteristics of the system, based on which, parameter characteristics are clearly analyzed. The harmonic balance method (HBM) is employed to obtain the steady-state response under harmonic force excitations and the force transmissibility, which will be used to evaluate the vibration isolation performance. The effects of the value of independent parameters on dynamic response and system stability are clearly analyzed. Subsequently, a biaxial spring-link isolator (BSLI) which consists of multi-axis mechanisms is proposed on the basis of USLI. Through the comparative analysis of the vibration isolation performance by numerical and simulation methods between the linear isolator, three-spring QZS isolator (TSI), USLI and BSLI, it is verified that the two QZS isolators proposed in this paper can effectively suppress the peak response and force transmissibility, and exhibit significantly enhanced isolation performance than linear isolators and TSI under low-frequency excitation vibration conditions. Meanwhile, the modified BSLI performs improved isolation effectiveness and enhanced stability of the system compared with USLI. The results in this paper provide effective insights and methods for the design, analysis, and mechanism optimization of QZS isolators.

In this paper, a coupled mismatched time-lag controlled quasi-zero static stiffness vibration isolator (QZS-VI) system is investigated to enhance its vibration isolation performance. Firstly, a mathematical model of the controlled QZS-VI system is established, and the steady state response is solved analytically using the averaging method and further verified by the Runge-Kutta numerical method. Subsequently, the stability of the system is analysed in depth, and the effects of Hopf bifurcation and saddle-node bifurcation on the dynamic characteristics of the system are explored. The modulation effects of the dual time-lag parameters on the amplitude-frequency characteristics, peak amplitude and resonant frequency are further investigated, and it is found that the proper selection of the time-lag parameters can effectively control the emergence and evolution of the frequency islands. In addition, the effect of double time-lag control on the force transfer rate of the system is analysed, and the results demonstrate that an appropriately mismatched time-lag control can attenuate the resonance peak and broaden the vibration isolation frequency band. Finally, the equivalent damping effect of displacement-velocity feedback control is discussed, and it is indicated that different time-lag parameters can optimise the vibration isolation performance of the system. The results show that mismatched time-lag control can significantly improve the vibration isolation effect of the QZS-VI system, which provides theoretical guidance for the optimal design of nonlinear vibration systems.

Objective In this paper, a novel Quasi-zero stiffness (QZS) vibration isolator (VI) is proposed where the negative stiffness is realized by biaxial slider-connector-springs, which presents superior static load bearing and dynamic vibration isolation capacity compared with its uniaxial counterpart. Methodology The outperformance of the proposed VI can be guaranteed only when two independent structural parameters satisfy a certain criterion, according to static analysis. On the other hand, dynamic analysis is performed to validate the superiority of the novel QZS VI in terms of force transmissibility and isolation frequency band. Careful consideration is given to the selection of structural parameters, according to the limitation for displacement amplitude in real engineering. Finally, experimental prototype of the novel QZS VI is conducted to confirm its advantage compared to the previous VI. Application The results present inspiration for development of new high-static-low-dynamic-stiffness (HSLDS) with ultralow frequency VI characteristics.

The present study theoretically explores combined dry and wet adhesive contact between a rigid sphere and elastic semi-half substrate, in which dry contact is encircled by liquid bridge. We consider threefold effects of liquid bridge on contact behavior, namely Laplace pressure induced by the curved surface of liquid meniscus, surface tension at the triple-phase junction and alternation of adhesion energy between solid surfaces ascribed to liquid immersion. A clear novelty in this study is the investigation on the effect of surface tension at the vapor-liquid-solid junction on the adhesive contact response, in contrast to previous studies. The model solution predicts that the contact behavior and adhesive strength are strongly dependent on surface wettability (manifested by contact angle), liquid volume and the contact system’s rapidity in achieving thermodynamic equilibrium. It is found that the transition of the pull-off force is evidently different from Maugis-Dugdale model in terms of a couple of interesting characteristics. Moreover, it is unveiled that the jump instabilities and hysteresis of force-separation curves are highly affected by surface wettability and liquid volume. These theoretical results can not only shed lights on the mechanism of liquid-mediated adhesion employed by animals and plants, but also provide us inspiration for development of biomimetic adhesive devices

Human dentin is known for its hierarchical structure through long-term evolution. Dental caries, embodied by dentin demineralization, is ascribed to a different reaction between peritubular dentin (PTD) and intertubular dentin (ITD) to acid dissolution. This study sheds light on the adverse effect of acid on dentin in terms of degradation of its fracture toughness (FT) due to the acid dissolution-induced erosion of PTD. A scanning electronic microscope (SEM) is utilised to visualise the difference between normal and acid-treated dentin subjected to the same loading method in terms of crack propagation performance. 3D simulative representative volume elements (RVEs) are developed to analyse the effect of PTD missing on the performance of dentin fracture resistance (FR). The results indicate PTD plays a significant role in enhancing dentin FR capability and thus reveals the importance of structural integrity for dentin.

To investigate the effects of abutment taper angles on the fracture strength of dental implants with TIS (taper integrated screwed-in) connection. Thirty prototype cylindrical titanium alloy 5.0mm-diameter dental implants with different TIS-connection designs were divided into six groups and tested for their fracture strength, using a universal testing machine. These groups consisted of combinations of 3.5 and 4.0mm abutment diameter, each with taper angles of 6°, 8° or 10°. 3-Dimensional finite element analysis (FEA) was also used to analyze stress states at implant-abutment connection areas. In general, the mechanical tests found an increasing trend of implant fracture forces as the taper angle enlarged. When the abutment diameter was 3.5mm, the mean fracture forces for 8° and 10° taper groups were 1638.9N±20.3 and 1577.1N±103.2, respectively, both larger than that for the 6° taper group of 1475.0N±24.4, with the largest increasing rate of 11.1%. Furthermore, the difference between 8° and 6° taper groups was significant, based on Tamhane's multiple comparison test (P

A prosthetic socket used by a lower limb amputee should accommodate the patient’s geometry and biomechanical needs. The creation of a geometrically accurate subject-specific finite element model can be used to provide a better understanding of the load transfer between socket and limb. There has been a limited number of finite element studies of trans-femoral sockets with all current models only including the femur and ignoring the pelvis. This study looked to evaluate the effect that including the pelvic bone as well as the femur in a finite element model has on the contact interface between the prosthetic socket and residual limb. This was done by creating a finite element model from a computerised tomography scan of a trans-femoral amputee. This model included three-dimensional geometry, nonlinear material properties and frictional contact between the residual limb and prosthetic socket. It was found that without the pelvic bone the contact pressures peaked at the distal end region of the residual limb (peak of 95 kPa). However by including the pelvic bone the contact pressures were instead concentrated at the ischial loading region (peak of 364 kPa). The shear stresses experienced on the socket-residual limb interface were also simulated. The results obtained in this study can be used to provide more of an understanding of the loading on the residual limb for the design and creation of future trans-femoral sockets.

This present study reconsiders the effect of surface tension on the behavior of adhesive contact between a rigid sphere and an elastic half-plane, in which the adhesive interactions are supposed to follow the Dugdale laws. The adhesive contact issue is transformed into two inter coupled non-linear integral equations which are governed by two parameters: λ (Maugis adhesion parameter) and S (elastocapillary number). By means of iteration method, numeric results are obtained. Analogous to the traditional Maugis-Dugdale (M-D) model, the results provide transition of the pull-off force between JKR and DMT type contact models through the Maugis adhesion parameter λ with a fixed parameter S. On the other hand, with a fixed adhesion parameter λ, we also present the transitions of the pull-off force between four extreme models, named M-D, JKR, Bradley models and Young–Dupre equation, through adjustment of the parameter S. Finally, we find the uniformity and discontinuity of the pressure distribution are affected by the combination of three factors: applied load P, adhesion parameter λ and elastocapillary number S.

The present study explores the effect of surface tension on adhesive contact behavior where the adhesion is interpreted by long-range intermolecular forces. The adhesive contact is analyzed using the equivalent system of a rigid sphere and an elastic half space covered by a membrane with surface tension. The longrange intermolecular forces are modelled with the Lennard-Jones (L-J) potential law. The current adhesive contact issue can be represented by a nonlinear integral equation, which can be solved by Newton-Raphson method. In contrast to previous studies which consider intermolecular forces as short-range, the present study reveals more details of the features of adhesive contact with surface tension, in terms of jump instabilities, pull-off forces, pressure distribution within the contact area, etc. The transition of the pull-off force is not only consistent with previous studies, but also presents some new interesting characteristics in the current situation.

AIM To develop a new technique for rapid design of prosthetic sockets for above knee amputees with enhanced comfort.

BACKGROUND: The finite element method has been widely used in orthopedic biomechanics analysis by evaluating Max von Mises stress and stress delivery and distribution. However, due to the complex biomechanics environment in the body and significant individual differences, it is difficult to obtain clinical methods based on specific cases. OBJECTIVE: To analyze the biomechanical distribution of implants in the maxillary sinus district. METHODS: An implant model, 5.5 mm×11.0 mm, located in the second molar of the maxillary was built using Simplant. The distribution of the stress of maxillary sinus district in the conditions of normal occlusion and crossbite under loading of 300 N at 0°, 30°, 45°, 60°, and 90°, respectively, was analyzed using Abaqus finite element software. RESULTS AND CONCLUSION: In crossbite condition, the concentration stress of von Mises was evenly distributed in the junction of the neck of dental implant and cortical bone; under the 300 N equivalent loading at 0°, 30°, 45°, 60°, and 90°, Max von Mises stress was 23.43, 52.97, 61.18, 66.15, and 70.53 MPa. In normal occlusion condition, the second stress concentration zone appeared in cortex in addition to the junction of the neck of dental implant and cortical bone, and Max von Mises stress was 30.91, 71.22, 71.62, 77.65, and 73.21 MPa under the 300N equivalent loading at 0°, 30°, 45°, 60° and 90°, about 50% higher compared with crossbite. Finite element analysis demonstrates that it is better to adopt crossbite in highly absorbed maxillary sinus district.

A new distributed middleware technology 'Web Services' is applied in the proposed Healthcare Information System (HIS) to address the issue of system and language interoperability raised from existing Healthcare Information systems. With the development of HISs, hospitals and healthcare institutes have been building various HISs for processing massive healthcare data, such as, systems built up for hospitals under the NHS (National Health Service) to manage patients' records. Nowadays many healthcare providers are willing to integrate their systems' functions and data for information sharing. This has raised concerns in data transmission, data security, and network limitation. Among these issues, system and language interoperability are one of most obvious issues since data and application integration is not an easy task due to differences in programming languages, system platforms Database Management Systems (DBMS) used within different systems. As a new distributed middleware technology, Web service brings an ideal solution to the issue of system and language interoperability. Web service has been approved to be very successful in many commercial applications (e.g. Amazon.com, Dell computer, etc.), however it is different to healthcare information system. As the result, Web Service-based Integrated Healthcare Information System (WSIHIS) is proposed to address the interoperabitity issue of existing HISs but also to introduce this new technology into the healthcare environment.

By the means of finite element analysis (FEa), biomechanical behaviors of human mandible have been widely studied over decades. Many different types of simulation of muscle forces have been employed in studies to increase the reality of mastication environment. Among these studies, Cruz et al (2003)'s calculation of muscle forces was well accepted. However, these simulations have not been verified experimentally as seen in literatures. In this study, a three dimensional (3D) finite element model of human mandible was created from CT images of a cadaver mandible bone. 4 pairs of muscle forces was applied to this 3D model based on a calculation by using Cruz et al (2003)'s method. The exact cadaver bone was used in an experimental testing rig to evaluate strain distribution and, hence, to verify the results of FEa. A set of different sizes of loads which matches with the one used in FE study was applied to the cadaver bone. Strain gauges were employed to gain data of strain distribution on the bone. The experimental result shows that the trend of stress/strain during increase or decrease of muscle forces coincides with FE result. This verifies the masticator muscle force calculation of Cruz et al (2003) to be correct.

Based on the surface elasticity theory, we investigate the effect of surface tension on miniaturized contact problems of an elastic graded half-plane under plane strain and axisymmetric situations. The Fourier sine and cosine transform method is used to derive the solution for the problem under uniform pressure. The results show some interesting features in the distribution of surface elastic fields, which are different from their homogeneous counterparts. The surface Green’s functions of the nonhomogeneous half-plane are finally obtained which are verified using finite element method. The outcome of this study provides us not only as a potential method for precise nanoindentation-based analysis of elastic graded materials, but also as the investigations of surface effect-induced failure in nanomaterials and nano-devices.

This paper describes software architecture of using GPRS technique to provide wireless data communication for a traffic data collection system. The development of the communication software was based on two scenarios: Centralized Database Management (CDM) and Distributed Data Management (DDM) systems. They were used effectively to improve the current “download on demand” and post event analysis working mode. A “close to the real time” data transmission was achieved. As the essential requirement of an Intelligent Traffic System (ITS), the application of the GPRS technique enabled the user to access the real time traffic data uploaded from multiple road side traffic data collection units. In this study, the authors have successfully developed and tested the communication software of a proposed CDM system and the software architecture of the DDM system was also discussed. For the DDM system, the interface and communication software were designed using Unified Modeling Language and developed as an Object-oriented system based on the .NET platform. The database part was developed using Microsoft SQL. The reliability and the performance of the DDM system were evaluated against proposed hardware configurations.

Research on the kinetics of precipitate formation and austenite reversion in maraging steels has received great attention due to their importance to steel properties. Judging from the literature in recent years, research into maraging steels has been very active, mainly extending to new types of steels, for new applications beyond the traditional strength requirements. This chapter provides an in-depth overview of the literature in this area. In addition, the kinetics of precipitate formation are analysed using the Johnson-Mehl-Avrami (JMA) theory. © 2012 Woodhead Publishing Limited All rights reserved.

This study presents an investigation on the behavior of adhesive contact between a rigid sphere and an elastic film which is either perfectly bonded (Case I) or in frictionless contact (Case II) with a rigid substrate. By using linear fracture mechanics, we formulate an convenient semi-analytical approach to develop relations between the applied force, penetration depth and contact radius. Finite element analysis (FEA) is used to verify the relationships. Our results reveal that the interfacial boundary conditions between the film and substrate have distinct effects on the adhesive contact behavior between the sphere and the film. The aim of the present study is to provide an instructive inspiration for controlling adhesion strength of the thin film subject to adhesive contact.

Improved walking comfort has been linked with better bio-mimicking of the prosthetic ankle. This study investigated if a hydraulic ankle/foot can provide enough motion in both the sagittal and frontal planes during level and camber walking and if the hydraulic ankle/foot better mimics the biological ankle moment pattern compared with a fixed ankle/foot device. Five active male unilateral trans-femoral amputees performed level ground walking at normal and fast speeds and 2.5Ê camber walking in both directions using their own prostheses fitted with an ªEchelonº hydraulic ankle/foot and an ªEspritº fixed ankle/foot. Ankle angles and the Trend Symmetry Index of the ankle moments were compared between prostheses and walking conditions. Significant differences between prostheses were found in the stance plantarflexion and dorsiflexion peaks with a greater range of motion being reached with the Echelon foot. The Echelon foot also showed significantly improved bio-mimicry of the ankle resistance moment in all walking conditions, either compared with the intact side of the same subject or with the ªnormalº mean curve from non-amputees. During camber walking, both types of ankle/foot devices showed similar changes in the frontal plane ankle angles. Results from a questionnaire showed the subjects were more satisfied with Echelon foot.

Osseointegrated trans-femoral implant is a relatively new orthopaedic anchoring method for connecting a stump with a prosthesis. Through a follow-up study of a patient over six years, significant bone remodelling has been observed. Finite element (FE) simulations were carried out to investigate the relationship between the bone remodelling and the strain re-distribution around the trans-femoral osseointegrated implant system. An initial FE model representing the original status of the femur-implant assembly was created from CT scans of the subject prior to osseointegration. Follow-up X-ray images were acquired at various stages post-surgery, which allowed the changes in bone wall thickness to be measured. By updating the bone thickness in the initial model, a series of follow-up FE models were created. Representative load associated with the subject's body weight was applied to the models, and the strain re-distributions were calculated. The results showed that in order to minimise the adverse effect of bone remodelling, an osseointegration implant made by functionally gradient materials are preferred over homogeneous materials.

The FRP composite beam structure that is intended to represent deck prototype used in civil engineering construction is investigated. FRP composite material may have possible damage, which affect vibration structural integrity and reliability. To overcome this problem, vibration data from experiments can be used to assess such damage accurately. The FE mode updating process is demonstrated in parameter identification as well as structural damage identification. It is used to minimise the difference between experimental and numerical data. The updated parameters are the modified parameters selected in the FE model with aim of correcting modelling errors and/or damage detection. In this FE model updating procedure, model physical characteristics are changed so that the differences between experimental and numerical dynamic properties are reduced. The FE model updating is carried out using optimisation tools in ANSYS software. Only the first three natural frequencies will be considered in this work. The FE model updating procedure brings the numerical results of the FRP structure in proper correlation to the experimental results, according to an objective function, by changing the FE model parameters. The test results of the structure under intact and damage states are presented. It is suggested that there is damage at the unbounded joint when there is significant change in fixed parameters of the structure beyond acceptable degree. © The Society for Experimental Mechanics, Inc. 2012.

In this paper, a progressive approach is presented for building extraction from LIDAR combined with its co-registered bands. Carefully tuned Gabor wavelet filters are applied to LIDAR data for object detection on the earth, and to localize targeted objects in order to minimize hilly terrain effects. Object classification is then carried out in local areas where objects exist. The Dempster-Shafer (DS) theory of evidence is used to conduct initial classification by fusing LIDAR and its co-registered data sets; and a fuzzy Markov random field (FMRF) model takes the output from the DS theory of evidence, and is performed the further object classification to extract buildings. Finally the level set approach is employed for building boundary extraction. The testing experiments under this research have shown the potential of this approach in accurately extracting buildings from airborne LIDAR and its co-registered bands. © 2010 SICE.

Cellular mechanical properties (CMPs) have been frequently reported as biomarkers for cell cancerization to assist objective cytology, compared to the current subjective method dependent on cytomorphology. However, single or dual CMPs cannot always successfully distinguish every kind of malignant cell from its benign counterpart. In this work, we extract 4 CMPs of four different graded bladder cancer (BC) cell lines by AFM (atomic force microscopy)-based nanoindentation to generate a CMP database, which is used to train a cancerization-grade classifier by machine learning. The classifier is tested on 4 categories of BC cells at different cancer grades. The classification shows split-independent robustness and an accuracy of 91.25% with an AUC-ROC (ROC stands for receiver operating characteristic, and ROC curve is a graphical plot which illustrates the performance of a binary classifier system as its discrimination threshold is varied) value of 97.98%. Finally, we also compare our proposed method with traditional invasive diagnosis and noninvasive cancer diagnosis relying on cytomorphology, in terms of accuracy, sensitivity and specificity. Unlike former studies focusing on the discrimination between normal and cancerous cells, our study fulfills the classification of 4 graded cell lines at different cancerization stages, and thus provides a potential method for early detection of cancerization.

Slope ambulation is a challenge for trans-femoral amputees due to a relative lack of knee function. The assessment of prosthetic ankles on slopes is required for supporting the design, optimisation, and selection of prostheses. This study assessed two hydraulic ankle-foot devices (one of the hydraulic ankles is controlled by a micro-processor that allows real-time adjustment in ankle resistance and range of motion) used by trans-femoral amputees in ascending and descending a 5-degree slope walking, against a rigid ankle-foot device. Five experienced and active unilateral trans-femoral amputees performed ascending and descending slope tests with their usual prosthetic knee and socket fitted with a rigid ankle-foot, a hydraulic ankle-foot without a micro-processor, and a hydraulic ankle-foot with a micro-processor optimised for ascending and descending slopes. Peak values in hip, knee and ankle joint angles and moments were collected and the normalcy Trend Symmetry Index of the prosthetic ankle moments (as an indication of bio-mimicry) were calculated and assessment. Particular benefits of the hydraulic ankle-foot devices were better bio-mimicry of ankle resistance moment, greater range of motion, and improved passive prosthetic knee stability according to the greater mid-stance external knee extensor moment (especially in descending slope) compared to the rigid design. The micro-processor controlled device demonstrated optimised ankle angle and moment patterns for ascending and descending slope respectively, and was found to potentially further improve the ankle moment bio-minicry and prosthetic knee stability compared to the hydraulic device without a micro-processor. However the difference between the micro-processor controlled device and the one without a micro-processor does not reach a statistically significant level.

There are many established methods to collect traffic data used for vehicle counting, speed checking and vehicle classification, such as induction loops, piezoelectric sensor, bending plates, etc. This paper presents a new method for traffic data collection. It uses vibration signals which are generated when vehicles pass the roadside. In order to extract useful information, such as the corresponding time when the vehicle was passing the vibration sensor, wavelet analysis was employed for data mining of the vibration signal observed from accelerometers (vibration sensors). The applications of wavelet transform and decomposition for vibration signals were reviewed to identify a suitable approach for the vibration signal data mining. The paper concluded with discussing the impact of wavelet analysis on data mining and outlining potential future research directions and applications.

In this study, atomic force microscopy (AFM) is used to investigate the alterations of the poropelastic properties of hepatocellular carcinoma (SMMC-7721) cells treated with fullerenol. The SMMC-7721 cells were subject to AFM-based creep tests and a corresponding poroelastic indentation model was used to determine the poroelastic parameters by curve fitting. Comparative analyses indicated that the both permeability and diffusion of fullerenol-treated cells increased significantly while their elastic modulus decreased by a small amount. From the change trend of the determined parameter, we verified the corresponding alternations of cytoskeleton (mainly filaments actin), which was reported by the previous study using confocal imaging method. Our investigation on SMMC-7721 cell reveals that the porpelastic properties could provide a better understanding how the cancer cells are affected by fullerenol or potentially other drugs which could find possible applications in drug efficacy test, cancer diagnosis and secure therapies.