Articular human joint modelling

Copyright @ Cambridge University Press 2009.The work reported in this paper encapsulates the theories and algorithms developed to drive the core analysis modules of the software which has been developed to model a musculoskeletal structure of anatomic joints. Due to local bone surface and contact geometry based joint kinematics, newly developed algorithms make the proposed modeller different from currently available modellers. There are many modellers that are capable of modelling gross human body motion. Nevertheless, none of the available modellers offer complete elements of joint modelling. It appears that joint modelling is an extension of their core analysis capability, which, in every case, appears to be musculoskeletal motion dynamics. It is felt that an analysis framework that is focused on human joints would have significant benefit and potential to be used in many orthopaedic applications. The local mobility of joints has a significant influence in human motion analysis, in understanding of joint loading, tissue behaviour and contact forces. However, in order to develop a bone surface based joint modeller, there are a number of major problems, from tissue idealizations to surface geometry discretization and non-linear motion analysis. This paper presents the following: (a) The physical deformation of biological tissues as linear or non-linear viscoelastic deformation, based on spring-dashpot elements. (b) The linear dynamic multibody modelling, where the linear formulation is established for small motions and is particularly useful for calculating the equilibrium position of the joint. This model can also be used for finding small motion behaviour or loading under static conditions. It also has the potential of quantifying the joint laxity. (c) The non-linear dynamic multibody modelling, where a non-matrix and algorithmic formulation is presented. The approach allows handling complex material and geometrical nonlinearity easily. (d) Shortest path algorithms for calculating soft tissue line of action geometries. The developed algorithms are based on calculating minimum ‘surface mass’ and ‘surface covariance’. An improved version of the ‘surface covariance’ algorithm is described as ‘residual covariance’. The resulting path is used to establish the direction of forces and moments acting on joints. This information is needed for linear or non-linear treatment of the joint motion. (e) The final contribution of the paper is the treatment of the collision. In the virtual world, the difficulty in analysing bodies in motion arises due to body interpenetrations. The collision algorithm proposed in the paper involves finding the shortest projected ray from one body to the other. The projection of the body is determined by the resultant forces acting on it due to soft tissue connections under tension. This enables the calculation of collision condition of non-convex objects accurately. After the initial collision detection, the analysis involves attaching special springs (stiffness only normal to the surfaces) at the ‘potentially colliding points’ and motion of bodies is recalculated. The collision algorithm incorporates the rotation as well as translation. The algorithm continues until the joint equilibrium is achieved. Finally, the results obtained based on the software are compared with experimental results obtained using cadaveric joints

Airy wave packets accelerating in space-time

Although diffractive spreading is an unavoidable feature of all wave phenomena, certain waveforms can attain propagation-invariance. A lesser-explored strategy for achieving optical selfsimilar propagation exploits the modification of the spatio-temporal field structure when observed in reference frames moving at relativistic speeds. For such an observer, it is predicted that the associated Lorentz boost can bring to a halt the axial dynamics of a wave packet of arbitrary profile. This phenomenon is particularly striking in the case of a self-accelerating beam -- such as an Airy beam -- whose peak normally undergoes a transverse displacement upon free-propagation. Here we synthesize an acceleration-free Airy wave packet that travels in a straight line by deforming its spatio-temporal spectrum to reproduce the impact of a Lorentz boost. The roles of the axial spatial coordinate and time are swapped, leading to `time-diffraction' manifested in self-acceleration observed in the propagating Airy wave-packet frame.Comment: 5 pages, 4 figure

Gender issues in the university research environment

Recruiting and retaining females within science, engineering and technology continues to challenge many European Higher Education Institutions. This study looks at female self-perceptions relating to effective research work and career progression. Focus groups are used to examine the attitudes and experiences of females, and a questionnaire used to explore perceptions in four main skills areas: group work; communication; personal awareness; and project planning and management. The study indicates consistent female concerns on issues pertaining to effective female role models, negative work-role stereotypes and the work-life balance of an academic career. For all four skills areas, the average confidence scores of the female participants fell below that of males, but these differences were only statistically significant for perceptions on group work and communication skills, and prior to an intense skills development course. Based on these findings, a student workshop on gender issues has been developed, an outline of which is presented

Süleymaniye Camii

Taha Toros Arşivi, Dosya No: 102-Camilerİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

Kelepçe Center

Taha Toros Arşivi, Dosya No: 3-Eminönü-Sirkeciİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) Istanbul Development Agency (TR10/14/YEN/0033

İstanbul kütüphaneleri

Taha Toros Arşivi, Dosya No: 111-Kütüphanelerİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

A curvilinear snake arm robot with gripper-axis fibre-optic image processor feedback

The official version of this article can be found at the link below.A curvilinear robot constructed from a number of modular flexible sections of fixed length and diameter but independently controlled radius and direction of curvature has been equipped with an optical fibre image guide transmitting images from between the gripper jaws to the remote TV camera of Microvision-100, a microcomputer controlled real-time DMA-based vision System that is easily trained to recognise the shape, position and orientation of components. The gripper position and orientation is controlled by feedback from the vision System, the action taken depending on component recognition and inspection for defects. Redundant degrees of freedom enable the curvilinear robot to avoid obstacles and work in confined spaces.The research programme described in this paper is supported by the U.K. Science and Engineering Research Council