Effects of age on autobiographical memory

Six experiments investigate the effects of healthy ageing on autobiographical memory (AM). Previous work in this area has shown that older adults exhibit a deficit in recall of specific episodes from their personal past, yet there is evidence in the literature of exceptions to this rule. As yet, there have been few replications and little systematic exploration of the factors and processes that contribute to age effects in AM. Chapter 1 begins with an examination of age differences in memory for prospectively sampled recent everyday events – an area which, despite the growing interest in AM research, has remained largely unstudied. The results showed similar event memory for younger and older adults, and demonstrated both replicability and dissociation from more typical measures of AM (Experiment 2). Subsequent investigations focused on ways of cueing AM by manipulating the need for generative retrieval processing (Chapter 3), and the effect of increasing experimental control and measuring memory for the same staged event (Chapter 4). On all other tasks older adults performed more poorly than younger adults. However, a reanalysis of the data suggested that younger adults exhibit an elderly-like deficit on measures of memory for mundane, everyday events. Moreover, analysis of semantic memory within autobiographical narratives suggested that older adults recall more temporally abstracted information than younger adults (Chapter 5). The findings are interpreted within a framework which suggests that accumulating experience drives a shift from specific episodic memory representation towards a more abstracted schematic form. A parallel line of research investigated the effect of a wearable camera, SenseCam (SC), on memory for recently experienced events (Experiments 1, 4 and 5). SC use provided a general retrieval benefit, but the effect was the same for both younger and older adults, which supports the notion that poor memory performance in older adults is related to altered memory representation rather than deficient retrieval processes

Numerical analysis of pitting corrosion fatigue in floating offshore wind turbine foundations

The mooring system of offshore floating wind foundations, which anchors the floating foundations to the seabed, sustains large dynamic loads during operation. The mooring chains are connected to the floating foundation below the water level through fairleads and chain-stoppers. The corrosive marine environment and the cyclic loading make the mooring connection prone to corrosion pitting and fatigue crack initiation and propagation from the pits, particularly in the weld zones. In this study, a finite element analysis of the crack growth from corrosion pits has been performed and the results are presented in order to provide an estimate of the extent of damage after the crack is detected. A Python script have been developed which generates the pit profiles based on a non-uniform random distribution of pit dimensions. 3D pits and elliptical cracks are embedded at critical points of weldment on the mooring point and analysed using ABAQUS XFEM. The Walker's model has been applied in the model to examine the effect of realistic R ratios in floating structures on pitting corrosion fatigue crack propagation along with direct cyclic solver. The numerical results obtained from this study are discussed in terms of the corrosion pitting effects on fatigue crack propagation behaviour in Spar-type floating offshore wind turbine foundations

Structural integrity assessment of floating offshore wind turbine support structures

Floating offshore wind turbines are becoming more attractive to the wind industry due to their capability to operate larger turbines in deeper waters. The floating support structures are anchored to the seabed via mooring chains to impede the structure's unwanted movements. The combination of cyclic stresses and the corrosive marine environment makes the floating support structures vulnerable to corrosion pitting and subsequently fatigue crack initiation and propagation. In this study a framework is proposed to simulate fatigue crack growth from multiple corrosion pits at critical spots of the Spar-type floating support structures to examine the status of the crack during several years of operation. The proposed advanced fracture mechanics based approach provides a methodology to assess the integrity of the structure and subsequently plan for preventive or curative maintenance. The crack growth rate is examined for both singular and multiple cracks at different R ratios and for different stress levels using ABAQUS XFEM. Following numerical simulations, a sensitivity analysis is carried out using Crackwise software for different values of plate thickness, R ratio and initial crack size. The numerical results are discussed in terms of the corrosion pitting effects on fatigue life assessment of floating offshore wind turbine

Improved Calibration Functions of Three Capacitance Probes for the Measurement of Soil Moisture in Tropical Soils

Single capacitance sensors are sensitive to soil property variability. The objectives of this study were to: (i) establish site-specific laboratory calibration equations of three single capacitance sensors (EC-20, EC-10, and ML2x) for tropical soils, and (ii) evaluate the accuracy and precision of these sensors. Intact soil cores and bulk samples, collected from the top 20 and 80 cm soil depths at five locations across the Upper Mākaha Valley watershed, were analyzed to determine their soil bulk density (ρb), total porosity (θt), particle size distribution, and electrical conductivity (EC). Laboratory calibration equations were established using soil packed columns at six water content levels (0–0.5 cm3 cm−3). Soil bulk density and θt significantly varied with sampling depths; whereas, soil clay content (CC) and EC varied with sampling locations. Variations of ρb and θt at the two depths significantly affected the EC-20 and ML2x laboratory calibration functions; however, there was no effect of these properties on calibration equation functions of EC-10. There was no significant effect of sampling locations on the laboratory calibration functions suggesting watershed-specific equations for EC-20 and ML2x for the two depths; a single watershed-specific equation was needed for EC-10 for both sampling depths. The laboratory calibration equations for all sensors were more accurate than the corresponding default equations. ML2x exhibited better precision than EC-10, followed by EC-20. We conclude that the laboratory calibration equations can mitigate the effects of varying soil properties and improve the sensors’ accuracy for water content measurements

Supporting older and younger adults’ memory for recent everyday events: a prospective sampling study using SenseCam

This study measured the effect of a wearable camera, SenseCam, on older and younger adults’ memories of recently experienced everyday events. Participants used SenseCam to prospectively sample events from a typical week, which they recalled two weeks later. Recall was cued by a self-generated title only (control condition), by the title and forward-order SenseCam images, or by the title and random-order SenseCam images. In the control condition, older and younger adults’ memories were comparably episodic, but older adults recalled more semantic details. Both forward- and random-order SenseCam images were associated with increased episodic and semantic recall in both groups, and there was a small but significant effect of temporal order favouring the forward-order condition. These findings suggest that SenseCam is effective in supporting retrieval of memory for recent events, and the results of the temporal order manipulation also shed light on the mechanism of SenseCam’s effect

Sex and Death: The Effects of Innate Immune Factors on the Sexual Reproduction of Malaria Parasites

Malaria parasites must undergo a round of sexual reproduction in the blood meal of a mosquito vector to be transmitted between hosts. Developing a transmission-blocking intervention to prevent parasites from mating is a major goal of biomedicine, but its effectiveness could be compromised if parasites can compensate by simply adjusting their sex allocation strategies. Recently, the application of evolutionary theory for sex allocation has been supported by experiments demonstrating that malaria parasites adjust their sex ratios in response to infection genetic diversity, precisely as predicted. Theory also predicts that parasites should adjust sex allocation in response to host immunity. Whilst data are supportive, the assumptions underlying this prediction – that host immune responses have differential effects on the mating ability of males and females – have not yet been tested. Here, we combine experimental work with theoretical models in order to investigate whether the development and fertility of male and female parasites is affected by innate immune factors and develop new theory to predict how parasites' sex allocation strategies should evolve in response to the observed effects. Specifically, we demonstrate that reactive nitrogen species impair gametogenesis of males only, but reduce the fertility of both male and female gametes. In contrast, tumour necrosis factor-α does not influence gametogenesis in either sex but impairs zygote development. Therefore, our experiments demonstrate that immune factors have complex effects on each sex, ranging from reducing the ability of gametocytes to develop into gametes, to affecting the viability of offspring. We incorporate these results into theory to predict how the evolutionary trajectories of parasite sex ratio strategies are shaped by sex differences in gamete production, fertility and offspring development. We show that medical interventions targeting offspring development are more likely to be ‘evolution-proof’ than interventions directed at killing males or females. Given the drive to develop medical interventions that interfere with parasite mating, our data and theoretical models have important implications

Order recall in verbal short-term memory: The role of semantic networks

In their recent article, Acheson, MacDonald, and Postle (Journal of Experimental Psychology: Learning, Memory, and Cognition 37:44-59, 2011) made an important but controversial suggestion: They hypothesized that (a) semantic information has an effect on order information in short-term memory (STM) and (b) order recall in STM is based on the level of activation of items within the relevant lexico-semantic long-term memory (LTM) network. However, verbal STM research has typically led to the conclusion that factors such as semantic category have a large effect on the number of correctly recalled items, but little or no impact on order recall (Poirier & Saint-Aubin, Quarterly Journal of Experimental Psychology 48A:384-404, 1995; Saint-Aubin, Ouellette, & Poirier, Psychonomic Bulletin & Review 12:171-177, 2005; Tse, Memory 17:874-891, 2009). Moreover, most formal models of short-term order memory currently suggest a separate mechanism for order coding-that is, one that is separate from item representation and not associated with LTM lexico-semantic networks. Both of the experiments reported here tested the predictions that we derived from Acheson et al. The findings show that, as predicted, manipulations aiming to affect the activation of item representations significantly impacted order memory

An Upstream Open Reading Frame Controls Translation of var2csa, a Gene Implicated in Placental Malaria

Malaria, caused by the parasite Plasmodium falciparum, is responsible for substantial morbidity, mortality and economic losses in tropical regions of the world. Pregnant women are exceptionally vulnerable to severe consequences of the infection, due to the specific adhesion of parasite-infected erythrocytes in the placenta. This adhesion is mediated by a unique variant of PfEMP1, a parasite encoded, hyper-variable antigen placed on the surface of infected cells. This variant, called VAR2CSA, binds to chondroitin sulfate A on syncytiotrophoblasts in the intervillous space of placentas. VAR2CSA appears to only be expressed in the presence of a placenta, suggesting that its expression is actively repressed in men, children or non-pregnant women; however, the mechanism of repression is not understood. Using cultured parasite lines and reporter gene constructs, we show that the gene encoding VAR2CSA contains a small upstream open reading frame that acts to repress translation of the resulting mRNA, revealing a novel form of gene regulation in malaria parasites. The mechanism underlying this translational repression is reversible, allowing high levels of protein translation upon selection, thus potentially enabling parasites to upregulate expression of this variant antigen in the presence of the appropriate host tissue

A plasmid DNA-launched SARS-CoV-2 reverse genetics system and coronavirus toolkit for COVID-19 research

The recent emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the underlying cause of Coronavirus Disease 2019 (COVID-19), has led to a worldwide pandemic causing substantial morbidity, mortality, and economic devastation. In response, many laboratories have redirected attention to SARS-CoV-2, meaning there is an urgent need for tools that can be used in laboratories unaccustomed to working with coronaviruses. Here we report a range of tools for SARS-CoV-2 research. First, we describe a facile single plasmid SARS-CoV-2 reverse genetics system that is simple to genetically manipulate and can be used to rescue infectious virus through transient transfection (without in vitro transcription or additional expression plasmids). The rescue system is accompanied by our panel of SARS-CoV-2 antibodies (against nearly every viral protein), SARS-CoV-2 clinical isolates, and SARS-CoV-2 permissive cell lines, which are all openly available to the scientific community. Using these tools, we demonstrate here that the controversial ORF10 protein is expressed in infected cells. Furthermore, we show that the promising repurposed antiviral activity of apilimod is dependent on TMPRSS2 expression. Altogether, our SARS-CoV-2 toolkit, which can be directly accessed via our website at https://mrcppu-covid.bio/, constitutes a resource with considerable potential to advance COVID-19 vaccine design, drug testing, and discovery science