In laboratories and high-tech manufacturing applications, passive vibration isolators are often used to isolate vibration sensitive equipment from ground-borne vibrations. However, in traditional ...passive isolation devices, where the payload weight is supported by elastic structures with finite stiffness, a design trade-off between the load capacity and the vibration isolation performance is unavoidable. Low stiffness springs are often required to achieve vibration isolation, whilst high stiffness is desired for supporting payload weight. In this paper, a novel design of a six degree of freedom (six-dof) vibration isolator is presented, as well as the control algorithms necessary for stabilising the passively unstable maglev system. The system applies magnetic levitation as the payload support mechanism, which realises inherent quasi-zero stiffness levitation in the vertical direction, and zero stiffness in the other five dofs. While providing near zero stiffness in multiple dofs, the design is also able to generate static magnetic forces to support the payload weight. This negates the trade-off between load capacity and vibration isolation that often exists in traditional isolator designs. The paper firstly presents the novel design concept of the isolator and associated theories, followed by the mechanical and control system designs. Experimental results are then presented to demonstrate the vibration isolation performance of the proposed system in all six directions.
On size-dependent mechanics of nanoplates Farajpour, Ali; Howard, Carl Q.; Robertson, William S.P.
International journal of engineering science,
November 2020, 2020-11-00, 20201101, Letnik:
156
Journal Article
Recenzirano
In this paper, a two-dimensional stress-driven nonlocal integral model is introduced for the bending and transverse vibration of rectangular nanoplates for the first time. An appropriate kernel ...function, which satisfies all essential properties, is proposed for two-dimensional problems in the Cartesian coordinate system. Using Leibniz integral rule and Hamilton's principle, the curvature-moment relations, classical and constitutive boundary conditions, as well as the equations of motion of rectangular small-scale plates are derived. Two differential quadrature techniques are utilised to implement both classical and non-classical boundary conditions and obtain an accurate numerical solution. The solution is used to simulate the bending and vibration of nanoplates. The Laplacian-based nonlocal strain gradient model of plates is also developed for the sake of comparison. It is found that the stress-driven integral model can better estimate the size-dependent mechanical characteristics of small-scale rectangular plates with various boundary conditions.
Well characterised mechanical response of the normal head-neck complex during passive motion is important to inform and verify physical surrogate and computational models of the human neck, and to ...inform normal baseline for clinical assessments. For 10 male and 10 female participants aged 20 to 29, the range of motion (ROM) of the neck about three anatomical axes was evaluated in active-seated, passive-lying and active-lying configurations, and the neck stiffness was evaluated in passive-lying. Electromyographic signals from the agonist muscles, normalised to maximum voluntary contractions, were used to provide feedback during passive motions. The effect of sex and configuration on ROM, and the effect of sex on linear estimates of stiffness in three regions of the moment–angle curve, were assessed with linear mixed models and generalised linear models. There were no differences in male and female ROM across all motion directions and configurations. Flexion and axial rotation ROM were configuration dependent. The passive-lying moment–angle relationship was typically non-linear, with higher stiffness (slope) closer to end of ROM. When normalising the passive moment–angle curve to active lying ROM, passive stiffness was sex dependent only for lateral bending region 1 and 2. Aggregate moment–angle corridors were similar for males and females in flexion and extension, but exhibited a higher degree of variation in applied moment for males in lateral bending and axial rotation. These data provide the passive response of the neck to low rate bending and axial rotation angular displacement, which may be useful for computational and surrogate modelling of the human neck.
Walking gait data acquired with force platforms may be used for person re-identification (re-ID) in various authentication, surveillance, and forensics applications. Current force platform-based ...re-ID systems classify a fixed set of identities (IDs), which presents a problem when IDs are added or removed from the database. We formulated force platform-based re-ID as a deep metric learning (DML) task, whereby a deep neural network learns a feature representation that can be compared between inputs using a distance metric. The force platform dataset used in this study is one of the largest and the most comprehensive of its kind, containing 193 IDs with significant variations in clothing, footwear, walking speed, and time between trials. Several DML model architectures were evaluated in a challenging setting where none of the IDs were seen during training (i.e., zero-shot re-ID) and there was only one prior sample per ID to compare with each query sample. The best architecture was 85% accurate in this setting, though an analysis of changes in walking speed and footwear between measurement instances revealed that accuracy was 28% higher on same-speed, same-footwear comparisons, compared to cross-speed, cross-footwear comparisons. These results demonstrate the potential of DML algorithms for zero-shot re-ID using force platform data, and highlight challenging cases.
The aim of the LITHOSCREEN project was to construct a comprehensive screening program and database for recording and assessing the various risk factors for stone-formation in patients with ...urolithiasis. It is intended for use in Stone Clinics and is now being made available free of charge to researchers in the field who wish to maintain a comprehensive record of their patients’ medical histories, demographic backgrounds, lifestyle activities, metabolic abnormalities, biochemical risk of forming stones of various types, diet histories, stone analysis and long-term treatment records. From the recorded data for each patient, the program automatically calculates numerous functions important in the understanding of the clinical and chemical risk factors for stone-formation, including the renal handling of the ions involved, various metabolic functions, the biochemical risk of forming kidney stones (P
SF
), the Tiselius Indices of the supersaturation of urine with respect to calcium oxalate and calcium phosphate, the projected effects of changing the composition of each patient’s urinary composition on the risk of stone recurrence, and a program for analysing the diet of patients. It automatically produces one-page Summaries of each patient’s biochemical and dietary records with abnormal values highlighted according to a “traffic-light” colour-coding system and generates charts designed to improve patient compliance with treatment in the form of colour-coded “Target Diagrams” showing (a) the patient’s 24-h urine composition, (b) the patient's biochemical risk of forming stones of different types and (c) the composition of the patient’s diet. The Summary pages and “Target Diagrams” are suitable for inclusion in the patient’s Case Notes. LITHOSCREEN also produces charts projecting the effect of changing the composition of urine on the patient's biochemical risk of forming further stones. These graphs provide clues as to which urinary risk factors to target to reduce the patient’s risk of stone recurrence.
Understanding of human neck stiffness and range of motion (ROM) with minimal neck muscle activation ("passive") is important for clinical and bioengineering applications. The aim of this study was to ...develop, implement, and evaluate the reliability of methods for assessing passive-lying stiffness and ROM, in six head-neck rotation directions. Six participants completed two assessment sessions. To perform passive-lying tests, the participant's head and torso were strapped to a bending (flexion, extension, lateral bending) or a rotation (axial rotation) apparatus, and clinical bed, respectively. The head and neck were manually rotated by the researcher to the participant's maximum ROM, to assess passive-lying stiffness. Participant-initiated ("active") head ROM was also assessed in the apparatus, and seated. Various measures of apparatus functionality were assessed. ROM was similar for all assessment configurations in each motion direction except flexion. In each direction, passive stiffness generally increased throughout neck rotation. Within-session reliability for stiffness (ICC > 0.656) and ROM (ICC > 0.872) was acceptable, but between-session reliability was low for some motion directions, probably due to intrinsic participant factors, participant-apparatus interaction, and the relatively low participant number. Moment-angle corridors from both assessment sessions were similar, suggesting that with greater sample size, these methods may be suitable for estimating population-level corridors.
A Tale of Two Shitties Robertson, William
Journal of Extreme Anthropology,
12/2020, Letnik:
4, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Based on 12 months of ethnographic data collection in an anal cancer prevention clinic, this article uses the extreme examples of patients involuntarily defecating through the anoscope during the ...procedure to highlight the relationship between the extreme and the everyday. Despite the rarity of this occurrence, I argue that these extreme examples shed light on the ways the daily clinical routines are embodied as an expert habitus. High Resolution Anoscopy procedures are specialized, highly routinized practices that are performed hundreds of times per month at the clinic. These routines result in the development of a clinical habitus that guides physicians in deploying techniques to efficiently conduct the invasive examination. Exemplary examples of ordinary procedures certainly help explain how this expert habitus is enacted through routine clinical practices; however, this expertise becomes especially observable in moments when habituated practices are disrupted, forcing clinicians to react and respond in unscripted ways. I discuss the only two instances of patients defecating through the anoscope that occurred while conducting my research, each with a different clinician. These extreme examples provide rich opportunities to analyze how clinicians with similar procedural habits navigate extraordinary situations in expert and professional but idiosyncratic ways. Whereas exemplary examples of everyday routinized procedures can show the process of developing an expert clinical habitus, these extreme examples more clearly demonstrate how this habitus enacts expertise and professionalism by highlighting the clinicians’ abilities to deftly navigate the technical and sociocultural aspects of such extraordinary disruptions.
Dielectric multilayer structures with a grating profile on the top-most layer adds an additional degree of freedom to the phase matching conditions for Bloch surface wave excitation. The conditions ...for Bloch surface wave coupling can be achieved by rotating both polar and azimuthal angles. The generation of Bloch surface waves as a function of azimuthal angle has similar characteristics to conventional grating coupled Bloch surface waves. However, azimuthally generated Bloch surface waves have enhanced angular sensitivity compared to conventional polar angle coupled modes, which makes them appropriate for detecting tiny variations in surface refractive index due to the addition of nano-particles such as protein molecules.
Purpose
To evaluate the effect of the braced arm-to-thigh technique (BATT) (versus self-selected techniques) on three-dimensional trunk kinematics and spinal loads for three common activities of ...daily living (ADLs) simulated in the laboratory: weeding (gardening), reaching for an object in a low cupboard, and car egress using the
two-legs out
technique.
Methods
Ten young healthy males performed each task using a self-selected technique, and then using the BATT. The pulling action of weeding was simulated using a magnet placed on a steel plate. Cupboard and car egress tasks were simulated using custom apparatus representing the dimensions of a kitchen cabinet and a medium-sized Australian car, respectively. Three-dimensional trunk kinematics and L4/L5 spinal loads were estimated using the Lifting Full-Body OpenSim model and compared between techniques. Paired t-tests were used to compare peak values between methods (self-selected vs BATT).
Results
The BATT significantly reduced peak extension moments (13–51%), and both compression (27–45%) and shear forces (31–62%) at L4/L5, compared to self-selected techniques for all three tasks (
p
< 0.05). Lateral bending angles increased with the BATT for weeding and cupboard tasks, but these changes were expected as the BATT inherently introduces asymmetric trunk motion.
Conclusion
The BATT substantially reduced L4/L5 extension moments, and L4/L5 compression and shear forces, compared to self-selected methods, for three ADLs, in a small cohort of ten young healthy males without prior history of back pain. These study findings can be used to inform safe procedures for these three ADLs, as the results are considered representative of a mature population.
This paper presents a comparison of passive and active stability analyses of a six degree of freedom (DOF) quasi-zero stiffness magnetic levitation vibration isolation system. The passive rotational ...stability of the system is varied by changing lever arms, and its effects on the vibration isolation performance and control cost are investigated via static and dynamic simulations. The practicality of the design is also discussed by simulating off-centred load scenarios. It is shown that the vibration isolation bandwidth reduces with increasing passive stiffness when such (passively) stable DOFs are close to being uncontrolled, and that the passively unstable rotational DOF benefits from an optimal control action. In practice, the effect of increasing the passive stability on the isolation performance is insignificant as the controller would typically be designed with a relatively large stability margin to account for uncertainties, thus dominating the closed-loop response. In contrast, the control does benefit from the improved passive stability. The robustness of the designed control system to probable time delay, sensor measurement noise, and actuation error is simulated and verified. Additionally, the importance of taking cross-coupling into consideration when designing a stabilising control through a decentralised control scheme is highlighted.
PDF
