Understanding how kurtosis is transferred from input acceleration to stress response and it's influence on fatigue life

High cycle fatigue of metals typically occurs through long term exposure to time varying loads which, although modest in amplitude, give rise to microscopic cracks that can ultimately propagate to failure. The fatigue life of a component is primarily dependent on the stress amplitude response at critical failure locations. For most vibration tests, it is common to assume a Gaussian distribution of both the input acceleration and stress response. In real life, however, it is common to experience non-Gaussian acceleration input, and this can cause the response to be non-Gaussian. Examples of non-Gaussian loads include road irregularities such as potholes in the automotive world or turbulent boundary layer pressure fluctuations for the aerospace sector or more generally wind, wave or high amplitude acoustic loads. The paper first reviews some of the methods used to generate non-Gaussian excitation signals with a given power spectral density and kurtosis. The kurtosis of the response is examined once the signal is passed through a linear time invariant system. Finally an algorithm is presented that determines the output kurtosis based upon the input kurtosis, the input power spectral density and the frequency response function of the system. The algorithm is validated using numerical simulations. Direct applications of these results include improved fatigue life estimations and a method to accelerate shaker tests by generating high kurtosis, non-Gaussian drive signals

Advancements in Electrochemical and Optical Detection, Quantification, and Characterization of Cosmetic/Industrial Polyelectrolytes

Polyions are polymers that contain significant numbers of positive and/or negative charges dispersed along their polymeric chains. Polyquaternary ammonium salts (i.e., polyquaterniums (PQs)) are cationic polyions (polycations) that derive their positive charges from quaternary ammonium groups. These polycations have found increased use in various cosmetic and industrial applications (e.g., hair conditioning formulations, lotion formulations, water treatment processes, etc.). As PQs are used in many applications it is imperative to develop simple devices/methods to quantitate and characterize these species. This dissertation examines the application of various electrochemical and optical sensing technologies to the study of four PQs (i.e., PQ-2, PQ-6, PQ-10, and poly(2-methacryloxyethyltrimethylammonium) chloride (PMETAC)). Chapter 1 provides an overview of the most significant advancements in electrochemical and optical polyion sensing technologies and applications over the last 25+ years. Chapter 2 explores the application of established electrochemical polyion sensing technology for the detection of PQ-10 in commercially relevant sample mixtures. These samples contain both sodium lauryl sulfate (SLS) and PQ-10. However, SLS can generate significant negative response signals when using single-use polyanion-sensitive ion-selective electrodes (ISEs) as detectors to detect PQ-10 indirectly via potentiometric titrations. However, it was determined that subjecting SLS/PQ-10 mixtures to an anion-exchange resin reduces the amount of SLS to a level at which there is negligible interference observed. Further, the remaining PQ-10 is shown to be detectable within the range of 0 – 80 µg/mL by titration with dextran sulfate (DS). Chapter 3 describes the application of single-use polyion-sensitive ISEs to the quantification and characterization of PQ-2 PQ-6, PQ-10, and PMETAC. Both direct (dose-response) and indirect (titrimetric) detection methods were explored. Limits of detection (3σ) for these species were found to be 7.7, 6.9, 21.5, and 9.0 µg/mL, respectively, using the preferred titration method. PQ-6 was also quantified in partially treated drinking water from a water treatment plant. Chapter 4 demonstrates the application of fully reversible (pulstrode) polyion-sensitive ISEs to the same PQ species discussed in Chapter 3 using direct and indirect detection methods. Limits of detection for PQ-2, PQ-6, PQ-10, and PMETAC were found to be 8.0, 7.9, 35.5, and 10.3 µg/mL, respectively, using the preferred titration method. Chapter 5 explores the application of the first polymer-/plasticizer-free polycation-sensitive ion-selective optode (ISO) for the direct detection of PQ-2, PQ-6, PQ-10, and PMETAC. Each PQ was found to yield sigmoidal response curves when average hue values were plotted against the logarithm of the PQ concentration. These polycation-sensitive ISOs were found to be useful in quantifying PQ-6 in recreational swimming pool water. Chapter 6 describes the construction and application of the first all-solid-contact paper-based polyanion-sensitive ISE to the direct detection of polyanions and the indirect detection of PQs. These sensors are found to yield similar dose-response and titration data to the single-use ISEs described in Chapter 3. Slope values for each PQ calibration curve are in excellent agreement with calibration curves reported in Chapter 3. Finally, an overview of the accomplishments of this thesis work and potential new directions for polyion sensor research/applications are discussed in Chapter 7.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147628/1/safergus_1.pd

Biomechanics of the aging spine

The human spine is composed of highly specific tissues and structures, which together provide the extensive range of motion and considerable load carrying capacity required for the physical activities of daily life. Alterations to the form and composition of the individual structures of the spine with increasing age can increase the risk of injury and can have a profound influence on the quality of life. Cancellous bone forms the structural framework of the vertebral body. Individual trabeculae are oriented along the paths of principal forces and play a crucial role in the transfer of the predominantly compressive forces along the spine. Age-related changes to the cancellous core of the vertebra includes a loss of bone mineral density, as well as morphological changes including trabecular thinning, increased intratrabecular spacing, and loss of connectivity between trabeculae. Material and morphological changes may lead to an increased risk of vertebral fracture. The vertebral endplate serves the dual role of containing the adjacent disc and evenly distributing applied loads to the underlying cancellous bone and the cortex of the vertebra. With aging, thinning of the endplate, and loss of bone mineral density increases the risk of endplate fracture. Ossification of the endplate may have consequences for the nutritional supply and hydration of the intervertebral disc. The healthy intervertebral disc provides mobility to the spine and transfers load via hydrostatic pressurization of the hydrated nucleus pulposus. Changes to the tissue properties of the disc, including dehydration and reorganization of the nucleus and stiffening of the annulus fibrosus, markedly alter the mechanics of load transfer in the spine. There is no direct correlation between degenerative changes to the disc and to the adjacent vertebral bodies. Furthermore, advancing age is not the sole factor in the degeneration of the spine. Further study is crucial for understanding the unique biomechanical function of the aging spin

Readability of Australian road safety information for the general public

This research was conducted as a result of the authors becoming aware of the Australasian College of Road Safety (ACRS) submission to the National Road Safety Strategy 2021-2030. The ACRS submission outlined six key elements, one of which suggested that the National Road Safety Strategy should include ‘Publication in easily consumable form, for the public, of infrastructure safety star ratings for all road users’ (ACRS, 2021, p.61). This prompted the researchers to consider the road safety information provided to the general public about driving behaviour. Forty excerpts from online data from one Australian State’s road safety website were assessed for readability using an online tool. Fifteen additional excerpts from another three States were assessed to ensure consistency across Australia. Results indicated that the excerpts assessed were written at a readability level that is too high for almost half of the Australian public. Recommendations include that those producing road safety information consider the level of literacy across the general public and ensure that their work becomes increasingly accessible to more Australians. The limitations of readability are acknowledged in relation to the overall communications which often include pictures and/or diagrams

BMP-2 and TGF-β3 do not prevent spontaneous degeneration in rabbit disc explants but induce ossification of the annulus fibrosus

Introduction: Different approaches for disc regeneration are currently under investigation. Beside gene therapy and tissue engineering techniques, the application of growth and differentiation factors own promising potential. Studies using reduced intervertebral disc models, such as cell or tissue fragment cultures, have limited validity and show controversial results depending on the employed experimental model. Therefore, the goal of the current study was to investigate the effect of BMP-2 and TGF-β3 on intervertebral disc degeneration using an in vitro full-organ disc/endplate culture system. Materials and methods: Intervertebral rabbit disc explants were cultured in the presence of 1μg/ml BMP-2 or TGF-β3 for 21days in DMEM/F12 media. Nucleus and annulus were analyzed for gene expression of collagen type I and II (Col I/II), aggrecan, collagenases (MMP-1/MMP-13) with RT-qPCR, histological changes with bone and proteoglycan-specific staining (von Kossa, toluidine blue) and differences in cellularity (DNA) and proteoglycan content (alcian blue binding assay). Results: The results demonstrate that disc proteoglycan concentration decreased with time in the TGF-β3 and BMP-2 groups. In the annulus fibrosus (AF), TGF-β3 and BMP-2 resulted in an up-regulation of Col I and type II, and of aggrecan gene expression. In contrast, MMP genes were inhibited. In the nucleus, the growth factors decreased gene expression of aggrecan and spontaneous Col I up-regulation was inhibited by TGF-β3, whereas expression of Col II was decreased with BMP-2. There was no effect on expression of MMP-1 and MMP-13 for most sampling points. However, TGF-β3 and BMP-2 induced ossification of the AF was demonstrated by histology. Conclusion: It can be concluded that both growth factors, at the tested concentrations, may not be suitable to regenerate the whole intervertebral disc organ but they are interesting candidates for being injected alone or in combination into a painful intervertebral disc to induce osseous fusion (spondylodesis

The long-term mechanical integrity of non-reinforced PEEK-OPTIMA polymer for demanding spinal applications: experimental and finite-element analysis

Polyetheretherketone (PEEK) is a novel polymer with potential advantages for its use in demanding orthopaedic applications (e.g. intervertebral cages). However, the influence of a physiological environment on the mechanical stability of PEEK has not been reported. Furthermore, the suitability of the polymer for use in highly stressed spinal implants such as intervertebral cages has not been investigated. Therefore, a combined experimental and analytical study was performed to address these open questions. A quasi-static mechanical compression test was performed to compare the initial mechanical properties of PEEK-OPTIMA polymer in a dry, room-temperature and in an aqueous, 37°C environment (n=10 per group). The creep behaviour of cylindrical PEEK polymer specimens (n=6) was measured in a simulated physiological environment at an applied stress level of 10MPa for a loading duration of 2000hours (12weeks). To compare the biomechanical performance of different intervertebral cage types made from PEEK and titanium under complex loading conditions, a three-dimensional finite element model of a functional spinal unit was created. The elastic modulus of PEEK polymer specimens in a physiological environment was 1.8% lower than that of specimens tested at dry, room temperature conditions (P<0.001). The results from the creep test showed an average creep strain of less than 0.1% after 2000hours of loading. The finite element analysis demonstrated high strain and stress concentrations at the bone/implant interface, emphasizing the importance of cage geometry for load distribution. The stress and strain maxima in the implants were well below the material strength limits of PEEK. In summary, the experimental results verified the mechanical stability of the PEEK-OPTIMA polymer in a simulated physiological environment, and over extended loading periods. Finite element analysis supported the use of PEEK-OPTIMA for load-bearing intervertebral implant

Communications in the time of a pandemic: The readability of documents for public consumption

© 2021 The Authors Objective: Government communications in a crisis can influence public health outcomes. This research aimed to investigate if written communications of the most commonly sought sources of COVID-19 information available on the internet have readability levels commensurate with those of the general public. Methods: Online documents from the World Health Organization (WHO), and the governments of Australia, the UK and the US were assessed for readability using an online instrument that calculated scores for the Flesch Reading Ease Score, the SMOG Index and the Readability Consensus Grade Level. Results: Similar to the previous research, most documents assessed had a readability standard that was at or above the recommended grade level, and as such inaccessible to substantial portions of the general public. A one-way ANOVA with post hoc tests revealed significant differences among the data, with Australian documents significantly more difficult to read than those from the UK and US. Conclusions: Government departments need to consider their audience and monitor readability of the documents they produce to ensure that readers can understand them. Implications for public health: Health communications need to be written at a level appropriate for the targeted population in order to be fit for purpose

Polyion Detection via All‐solid‐contact Paper‐based Polyion‐sensitive Polymeric Membrane Electrodes

The first all‐solid‐contact paper‐based single‐use polyion‐sensitive ion‐selective electrodes (ISEs) are described. These polyion‐sensitive ISEs are fabricated using cellulose filter paper coated with a carbon ink conductive layer. A polyanion sensing membrane is cast on a section of the coated paper and the sensor is insulated, resulting in a disposable, single‐use device. Various polyanions are shown to yield large negative potentiometric responses when using these disposable devices for direct polyanion detection. These new sensors are further demonstrated to be useful in indirect polycation detection when polycations (i. e., polyquaterniums (PQs)) are titrated with polyanionic dextran sulfate (DS). Titrations monitored using these paper‐based, all‐solid‐contact devices yield endpoints proportional to the given PQ concentration present in the test sample.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151253/1/elan201900155.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151253/2/elan201900155_am.pd