Kambiz Saber-Sheikh

Feasibility of using inertial sensors to assess human movement

The aim of this study was to determine the suitability of inertial sensors for motion analysis research. Inertial sensors (Xsens Technologies, Netherlands) consisting of 3D gyroscopes, accelerometers and a magnetometer were compared against an electromagnetic motion tracking system (Fastrak, Polhemus, USA) for measuring motions of an artificial hinge joint and random 3D motions. Subsequently, to assess the feasibility of using inertial sensors for human motion analysis, the movements of the hip joint during walking were recorded in 20 normal asymptomatic subjects. The comparative study demonstrated good agreement between the inertial and electromagnetic systems. Measurements obtained for hip joint movement during walking (flexion, extension and step length) were similar to those reported in previous studies (flexion 38.8 degrees , extension 6.6 degrees , step frequency 1.02Hz). We conclude that the inertial sensors studied have the potential to be used for motion analysis and clinical research.

Viscoelastic properties of some soft lining materials - I - effect of temperature

The time dependent, viscoelastic characteristics of a number of dental soft liners (occasionally called resilient liners) were investigated using a dynamic mechanical analyser (DMA). The materials consisted of eight commercial products including methacrylate, silicone and phosphazine-based soft polymers as well as two experimental formulations. The DMA used was of the forced vibrational variety. The test conditions, such as frequency and temperature, were chosen to mimic in use (masticatory) conditions. A wide variety of behaviour was observed and accounted for. This included a seven fold range in the storage modulus (2.79-19.7 MPa) and a 50-fold range in the loss tangent (0.029-1.52) at 37 degrees C and 1 Hz. The materials could generally be divided into either rubbery behaviour with low modulus and loss tangent, i.e. the silicones, or leathery behaviour with both higher modulus and loss tangent, i.e. the methacrylates. A search of the literature did not find a universally preferred set of properties, although a possible link with residual ridge resorption is indicated.

Measurement of lumbar spine range of movement and coupled motion using inertial sensors – A protocol validity study

Measurement of spinal lumbar range of movement is useful in clinical examination of the spine and for monitoring changes in spinal movement characteristics of individuals over time, particularly in the research context. As the spine exhibits six degrees of movement, three dimensional measurements provide additional information that could benefit the study of spinal conditions. Inertial measurement systems present an innovative method of spinal motion measurement. These systems are small and portable, and of low cost compared to laboratory based three dimensional measurement systems such as electromagnetic and opto-electronic systems. The present study aimed to validate the use of inertial measurement systems in three dimensional spinal range of movement measurement using an electromagnetic tracking system as a reference. Twenty-six healthy participants had their lumbar spine range of movement measured using both an inertial measurement system and an electromagnetic tracking system. Measurements taken by the inertial measurement system were found to be highly correlated with the electromagnetic tracking system (overall regression R(2) 0.999, p < 0.005). Measurements showed strong agreement (mean differences between -0.81° and 1.26°) and produced no significant difference from the electromagnetic tracking system (paired t-test p > 0.05). The ranges of movement measured were also highly comparable to those reported in the literature. Inertial measurement systems that consist of triaxial gyroscopes, accelerometers and magnetometers are concluded to be valid tools for three dimensional spinal range of movement measurement within or outside of the laboratory settings due to their cost, size and portability.

Viscoelastic properties of some soft lining materials. II-Ageing characteristics

A non-resonant forced vibration, dynamic mechanical analyser was employed to measure the viscoelastic characteristics of soft lining materials at 1 Hz, after storage in distilled water at mouth temperature for periods up to and including one year. The six commercial products included methacrylate, silicone, and phosphazine based polymers and the one experimental material was a methacrylate. Water sorption of the soft liners, recorded by change in sample mass, ranged from -4.39 to +48.57% and their solubilities from 0.13 to 13.58%, after one year. The heat-cured silicone was the most stable polymer in water in contrast to its autopolymerised counterpart. The excessive water uptake of this latter material resulted in a massive reduction in modulus. At the other extreme one methacrylate with a high plasticiser content hardened substantially after ageing (modulus changed from 5.87 to 72.3 MPa). Changes in loss tangent data were relatively small for all the polymers tested, even for materials with high water uptake. Reduced leaching and/or plasticiser content have led to a more stable generation of soft lining materials.

Active Flexure Compensation for the HROS Spectrograph

The Cassegrain location of the high resolution optical spectrograph (HROS) for the 8-meter Gemini telescope presents a difficult challenge in controlling mechanical flexure. This is especially the case for a high-resolution spectrography, which requires large and heavy optical components. In HROS, to achieve the required spectrum stability of 2.0 micrometers /hr, we developed a closed-loop monitoring and correction system capable of measuring the spectrograph flexure in as it happens and actively compensating for image motion.

A Gadamerian approach to interpreting pain: model-making metaphors through embodied cognitive theory

ABSTRACT This paper will discuss how the conceptualization of embodied, abstract notions such as pain, which is multi-modal, non-visual and subjective, has the potential to be communicated visually using model making, as it is traditionally understood in the fields of architecture and design. We propose a new methodological approach to research where Gadamer’s [2004. Truth and Method. Continuum International Publishing Group] understanding of intersubjective interpretation used in conjunction with Simulation theory [Gallese, V., and A. Goldman. 1998. “Mirror Neurons and the Simulation Theory of Mind-Reading.” Trends in Cognitive Sciences 2 (12): 493–501] in embodied cognitive science, provides a strong framework in which to formulate a palette of materials and forms to visualize subjective experience. This novel approach to design research is currently being undertaken within the field of Health Sciences to produce metaphorically provocative, descriptive models of the lived experience of people with Rheumatoid Arthritis (RA) to help bridge the gap in understanding between the sufferer and the public. This paper seeks to engage briefly with two questions integral to the research being undertaken: how does one understand another’s pain, and how can one conceptualize and communicate abstract notions such as pain visually using material and form as language?

Designing the Gemini high-resolution optical spectrograph structure to meet the flexural performance required at a Cassegrain focus

The HROS is a Cassegrain focus instrument for use on the Gemini South telescope at Cero Pachon, Chile. It is of novel design, using exceptionally large optical components, and subject to the normal high flexural and stability requirements of optical wavelength instrumentation. To meet these requirements while subjecting HROS to the infinite number of gravity vectors found at the Cassegrain focus has resulted in a very difficult design and analysis of the support structure. This paper describes the mechanical design approach to meting these requirements and presents the flexural performance predictions for the structure as given by Finite Element Analysis.