Jennifer Rowson

Bayesian sensitivity analysis of a model of the aortic valve.

Understanding the mechanics of the aortic valve has been a focus of attention for many years in the biomechanics literature, with the aim of improving the longevity of prosthetic replacements. Finite element models have been extensively used to investigate stresses and deformations in the valve in considerable detail. However, the effect of uncertainties in loading, material properties and model dimensions has remained uninvestigated. This paper presents a formal statistical consideration of a selected set of uncertainties on a fluid-driven finite element model of the aortic valve and examines the magnitudes of the resulting output uncertainties. Furthermore, the importance of each parameter is investigated by means of a global sensitivity analysis. To reduce computational cost, a Bayesian emulator-based approach is adopted whereby a Gaussian process is fitted to a small set of training data and then used to infer detailed sensitivity analysis information. From the set of uncertain parameters considered, it was found that output standard deviations were as high as 44% of the mean. It was also found that the material properties of the sinus and aorta were considerably more important in determining leaflet stress than the material properties of the leaflets themselves.

Assessment of the Sheffield Support Snood, an innovative cervical orthosis designed for people affected by neck muscle weakness

BACKGROUND This study aimed at quantifying the biomechanical features of the Sheffield Support Snood, a cervical orthosis specifically designed for patients with neck muscle weakness. The orthosis is designed to be adaptable to a patients level of functional limitation using adjustable removable supports, which contribute support and restrict movement only in desired anatomical planes. METHODS The snood was evaluated along with two commercially available orthoses, the Vista and Headmaster, in a series of flexion, extension, axial-rotation and lateral flexion movements. Characterization was performed with twelve healthy participants with and without the orthoses. Two inertial-magneto sensors, placed on the forehead and sternum, were used to quantify the necks range of motion. FINDINGS In its less supportive configuration, the snood was effective in limiting movements to the desired planes, preserving free movement in other planes. The Headmaster was only effective in limiting flexion. The range of motion achieved with the snood in its rigid configuration was equivalent (P>0.05, effect size<0.4) to that achieved with the Vista, both in trials performed reaching the maximum amplitude (range of motion reduction: 25%-34% vs 24%-47%) and at maximum speed (range of motion reduction: 24%-29% vs 25%-43%). INTERPRETATION The Sheffield Support Snood is effectively adaptable to different tasks and, in its most supportive configuration, offers a support comparable to the Vista, but providing a less bulky structure. The chosen method is suitable for the assessment of range of motions while wearing neck orthoses and is easily translatable in a clinical context.

Husband, daughter, son and postman, hot-water, knife and towel: Assistive Strategies for Jar Opening

Society is ageing and this demographic shift creates significant hurdles for designers, engineers, manufacturers and health practitioners. Not least is the development of a society where the majority of people will have some issues related to a loss of strength, dexterity and, possibly, locomotion, sight and cognition. Public acknowledgement of people with disabilities has changed significantly over recent years with three parallel drivers: legislation such as the Disability Discrimination Act (1995), advances in assistive technology and rehabilitation and lastly the understanding in the design community of the need for a change in the way products are designed. With this change in demographics it is assumed that the elderly will become drivers for change, demanding changes in infrastructure, products and services. Of particular interest in the design community has been the development of a concept called ‘Inclusive’ or ‘Universal’ design, promoted by various organisations, notably the Royal College of Art, in the UK. The British Standards Institute (BSi, 2005) defines inclusive design as “The design of mainstream products and/or services that are accessible to, and usable by, as many people as reasonably possible....without the need for special adaptation.”

Squeezability. Part 2: Getting stuff out of a bottle

Abstract Western Europe, the USA, and Japan are experiencing rapidly ageing societies. That ageing brings with it a host of issues, not least a society in which a large proportion is likely to have relative difficulties with strength, dexterity, and cognition. One specific area that stimulates a significant amount of controversy is the accessibility and functionality of product packaging. Newspapers and television frequently report on consumer frustration with regard to ‘over’ packaged or poorly accessible goods. In response, researchers, designers, brand-owners, and manufacturers have been undertaking significant work to address these concerns. Developments in ‘easy to open’ packaging are all around. However, the question remains ‘how easy is easy?’ In a previous study, the authors used analytical and experimental techniques to look at accessibility of the contents of ‘squeezy’ bottles; bottles that have, in essence, been specifically designed to improve physical access to the product. This work demonstrated that ease of access is affected by a complex combination of several factors, not least of these are bottle stiffness, shape, and orifice type. This article outlines a continuation of this study, using thin-film force sensors to study grip forces applied when squeezing a bottle and assessing how that force changes with gender and age. The article goes further to derive what the authors term bottle ‘efficiency’ and illustrates that this varies significantly with the bottle design.

Comparison of tack of pressure-sensitive adhesives (PSAs) at different temperatures

Pressure-sensitive adhesives (PSAs) have applications in the fields of packaging, joining, wound care, and personal care. Depending on the application of the PSA, different performance tests are carried out when new products are developed or the quality of the existing products is checked. Tack is the property of an adhesive that enables it to form instant bond on the surface under light pressure. The tack of a PSA strongly depends on the way the bond is created. Parameters such as the bonded area, contact time and the nature of tack materials all affect the tack force measured. In the development of any PSA, it is desirable to correlate the performance related properties such as tack and peel strength to the rheological behaviour. Finding these correlations would make it possible to evaluate the performance of a PSA using its rheological characteristics. In this investigation we have studied the influence of rheological behaviour of three different PSAs on their tackiness. The three different PSAs used in this study are a low molecular weight rosin ester, high molecular weight rosin ester, and dicyclopentadiene. Various rheological properties such as viscosity, phase angle, and elastic and viscous moduli are measured versus the frequency and temperature. Also the tack properties at various removal speeds and temperatures are evaluated. Analysis of the results indicates different performances of the three PSAs which could be related to their rheological properties, especially the phase angle, at different frequencies and temperatures. The PSA with high molecular weight rosin ester is more sensitive to temperature changes and showed drastic changes in tackiness from high temperature to low temperature. On the other hand, rosin ester with low molecular weight is less sensitive to temperature changes.

Squeezability. Part 1: a pressing issue

Abstract Within the UK it is estimated that by 2020 over half the adult population will be over 50. A society in which the majority are aged poses some interesting questions, not least how that society will use and access goods and services, when the majority are likely to experience some loss of strength and dexterity. One such issue, the openability or accessibility of packaging, is becoming a major issue for brand owners, manufacturers, designers, and engineers due to the rapid ageing of much of the developed world. The authors have previously undertaken a significant amount of work on understanding the openability of vacuum lug closures (jam or sauce jars). This work looked at the forces to keep the system closed, the forces a human could apply and used experimental, numerical, and analytical analysis to understand these systems. Packaging, however, comes in many varied and differing forms and little or no previous work has been undertaken in this field on other forms of packaging such as thin film packets or bottles. The work in this article applies the principles used in the earlier studies to the squeezable bottle pack format. The article describes initial experimental and analytical work undertaken from first principals to establish the factors that contribute to the ease of use along with various laboratory tests carried out in order to determine the design rules for developing bottle styles and nozzle designs, for specific fluid contents. The work suggested several things that may be important for designers and manufacturers of squeezable bottles. Fundamental analysis shows that bottle material and shape generally dominate the squeezeability of and access to bottle contents. Bottle shape was seen to affect performance with the conditioner bottle having the best volume—deflection performance. Work also showed that hole size and Borda length can be calculated to determine specific flow characteristics with a relatively simple set of equations.

Some Recent Developments in SHM Based on Nonstationary Time Series Analysis

Many of the algorithms used for structural health monitoring (SHM) are based on, or motivated by, time series analysis. Quite often, detection methods are variants of approaches developed within the statistical process control (SPC) community. Many of the algorithms used represent mature theory and have a rigorous probabilistic or mathematical basis. However, one of the main issues facing SHM practitioners is that the structures of interest rarely respect the assumptions inherent in deriving algorithms. In the case of time series data, SPC-based approaches usually require the data to be stationary and, unfortunately, SHM data are often nonstationary because of benign variations in the environment of the structure of interest, or because of deliberate operational changes in the use of the structure. This nonstationarity can manifest itself as slowly varying trends on the data or in abrupt switches between regimes. Recent work in nonstationary time series methods for SHM has made considerable progress in accommodating nonstationarity and some of that work is discussed within this paper: in terms of understanding slowly varying trends, the cointegration algorithm from econometrics is presented; for understanding abrupt switches, Bayesian mixtures of experts are presented. Another issue in time series analysis is indirectly related to the assumption of linear behavior of structures and the impact of this assumption is briefly considered in terms of its effects on detection thresholds in SPC-like methods; again, progress has been made recently. Some issues still remain, and these are discussed also.

Computational model of an infant brain subjected to periodic motion simplified modelling and bayesian sensitivity analysis

Non-accidental head injury in infants, or shaken baby syndrome, is a highly controversial and disputed topic. Biomechanical studies often suggest that shaking alone cannot cause the classical symptoms, yet many medical experts believe the contrary. Researchers have turned to finite element modelling for a more detailed understanding of the interactions between the brain, skull, cerebrospinal fluid (CSF), and surrounding tissues. However, the uncertainties in such models are significant; these can arise from theoretical approximations, lack of information, and inherent variability. Consequently, this study presents an uncertainty analysis of a finite element model of a human head subject to shaking. Although the model geometry was greatly simplified, fluid-structure-interaction techniques were used to model the brain, skull, and CSF using a Eulerian mesh formulation with penalty-based coupling. Uncertainty and sensitivity measurements were obtained using Bayesian sensitivity analysis, which is a technique that is relatively new to the engineering community. Uncertainty in nine different model parameters was investigated for two different shaking excitations: sinusoidal translation only, and sinusoidal translation plus rotation about the base of the head. The level and type of sensitivity in the results was found to be highly dependent on the excitation type.

Analyzing finger interdependencies during the Purdue Pegboard Test and comparative activities of daily living

Study Design: Bench and cross‐sectional study. Introduction: Information obtained from dexterity tests is an important component of a comprehensive examination of the hand. Purpose of the Study: To analyze and compare finger interdependencies during the performance of the Purdue Pegboard Test (PBT) and comparative daily tasks. Methods: A method based on the optoelectronic kinematic analysis of the precision grip style and on the calculation of cross‐correlation coefficients between relevant joint angles, which provided measures of the degree of finger coordination, was conducted on 10 healthy participants performing the PBT and 2 comparative daily living tasks. Results: Daily tasks showed identifiable interdependencies patterns between the metacarpophalangeal joints of the fingers involved in the grip. Tasks related to activities of daily living resulted in significantly higher cross‐correlation coefficients across subjects and movements during the formation and manipulation phases of the tasks (0.7–0.9), whereas the release stage produced significantly lower movement correlation values (0.3–0.7). Contrarily, the formation and manipulation stages of the PBT showed low finger correlation across most subjects (0.2–0.6), whereas the release stage resulted in the highest values for all relevant movements (0.65–0.9). Discussion: Interdependencies patterns were consistent for the activities of daily living but differ from the patterns observed from the PBT. Conclusions: The PBT does not compare well with the whole range of finger movements that account for hand performance during daily tasks. Level of evidence: Not applicable.

Understanding the use of tools for opening packaging

Various tools are available to improve the accessibility or ‘openability’ of packaging for those that may have potential difficulty. In this paper, the authors undertake an assessment of some of the common tools that have been designed to aid the aged in opening common packaging items with the aim of understanding their effectiveness. The study used a purpose built torque testing device embedded in a standard glass jar and asked participants to twist the lid of the device both unaided and with a tool and the maximum torque produced was noted. The study indicated that whilst some tools are effective, most however offer little or no benefit, as they do not overcome issues such as loss of dexterity and strength amongst the aged population.