45,631 research outputs found

    Hydrogen embrittlement processes in microalloyed steel notched tensile samples

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    ABSTRACT: In this work, two microalloyed steels, one used for oil&gas pipelines and the other one for structural components in hydrotreating reactors in petrochemical industries, have been studied under hydrogen embrittlement (HE) conditions. They have been cathodically charged with hydrogen under different aggressive conditions, its hydrogen content being determined afterwards. In order to know the effect of triaxiality on the HE behaviour of this steel, two different types of axisymmetric round notched tensile specimens have been tested under continuous hydrogen charging processes, whilst varying cathodic charging conditions and loading rate. The effects on the global mechanical characterization have been analysed, as well as the correlation between the observed fracture micromechanisms with both local environmental (as hydrogen concentration) and mechanical conditions (as hydrostatic stress and plastic strain determined with a finite elements analysis). Also, subcritical cracking due to embrittlement has been analysed and compared with those obtained by fracture mechanics standardised specimens

    Development of a phenomenological constitutive model for fracture resistance degradation of asphalt concrete with damage growth due to repeated loading

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    Discontinuous areas under the asphalt concrete (AC) layer, such as joints and cracks in an underlying layer, induce higher stress concentration than the designed strength. Stress concentration in the vicinity of discontinuities accelerates distress on the AC layer. Repeated traffic and environmental loading applied to the AC layer also induce degradation of the layer’s strength as microcracks grow at stress levels lower than the layer’s designed strength. In addition, this could be magnified when combined with low temperature cracking, one of the main distresses in AC pavements resulting from extreme temperature changes. When loading is applied near the joints or discontinuity, it amplifies the tensile stress at the bottom of the AC layer as well as the shear stress when the Portland cement concrete (PCC) slab or discontinuity moves vertically. Repetitive traffic loading and environmental changes cause continuous damage accumulations which consequently results in the acceleration of movement in the AC layer at the localized area close to the discontinuity region, thus leading to mechanical degradation of the AC materials which become less resistant to fracture. Even a small load can result in fracture failure of AC pavements when the loss of strength in AC pavements progresses significantly through repeated loading. The current approach to determine the critical properties of AC materials is to conduct laboratory testing under monotonic loading and cyclic loading separately. The fatigue testing under cyclic loading can only provide bulk material properties without consideration to any discontinuities, such as cracks in underlying pavement or joints. On the other hand, the current fracture tests conducted under monotonic loading fail to capture the loss of material strength as repeated loading is applied on pavements. For an accurate estimation of pavement life, it is essential to consider the effect of repeated traffic and thermal loading on the fracture resistance of the AC materials. This study investigates the degradation of the fracture resistance of AC materials as a result of the progressive damages caused by repeated loading application. The study develops the phenomenological constitutive model for fracture resistance degradation with damage growth caused by repeated loading. An experimental program was designed to apply monotonic and cyclic loading to the same test geometry and to examine the degradation of fracture properties with damage growth at the crack tip. Fracture and fatigue tests were implemented using semi-circular bending (SCB) test geometry with notched specimens at various temperatures, loading frequencies, and loading amplitudes. It is observed that damage functions and proposed parameters reflect the degradation rate of fracture resistance with respect to damage growth at the notch tip region. A presented constitutive model accurately predicts the remaining service life of existing pavements. It is further observed that the model coefficient distinguishes AC materials in terms of sensitivity to cracking resistance under both monotonic and cyclic loading.U of I OnlyGraduate College 2-year Extension For

    Osteoporosis in men

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    Osteoporosis in men is a common but often overlooked disorder by clinicians. The criterion for osteoporosis diagnosis in men is similar to that in women—namely, a bone mineral density (BMD) that is 2·5 standard deviations or more below the mean for the young adult population (aged 20–29 years; T-score –2·5 or lower), measured at the hip or lumbar spine. Sex steroids are important for bone health in men and, as in women, oestrogens have a key role. Most men generally have bigger and stronger bones than women and typically have less bone loss during their lifetime. Men typically fracture less often than women, although they have a higher mortality rate after a fracture. Secondary osteoporosis is more common in men than in women. Lifestyle changes, adequate calcium, vitamin D intake, and exercise programmes are recommended for the management of osteoporosis in men. Bisphosphonates, denosumab, and teriparatide have been shown to increase BMD and are used for pharmacological treatment. In this Review, we report an updated overview of osteoporosis in men, describe new treatments and concepts, and discuss persistent controversies in the area

    Exploring the effects of spinal cord stimulation for freezing of gait in parkinsonian patients

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    Dopaminergic replacement therapies (e.g. levodopa) provide limited to no response for axial motor symptoms including gait dysfunction and freezing of gait (FOG) in Parkinson’s disease (PD) and Richardson’s syndrome progressive supranuclear palsy (PSP-RS) patients. Dopaminergic-resistant FOG may be a sensorimotor processing issue that does not involve basal ganglia (nigrostriatal) impairment. Recent studies suggest that spinal cord stimulation (SCS) has positive yet variable effects for dopaminergic-resistant gait and FOG in parkinsonian patients. Further studies investigating the mechanism of SCS, optimal stimulation parameters, and longevity of effects for alleviating FOG are warranted. The hypothesis of the research described in this thesis is that mid-thoracic, dorsal SCS effectively reduces FOG by modulating the sensory processing system in gait and may have a dopaminergic effect in individuals with FOG. The primary objective was to understand the relationship between FOG reduction, improvements in upper limb visual-motor performance, modulation of cortical activity and striatal dopaminergic innervation in 7 PD participants. FOG reduction was associated with changes in upper limb reaction time, speed and accuracy measured using robotic target reaching choice tasks. Modulation of resting-state, sensorimotor cortical activity, recorded using electroencephalography, was significantly associated with FOG reduction while participants were OFF-levodopa. Thus, SCS may alleviate FOG by modulating cortical activity associated with motor planning and sensory perception. Changes to striatal dopaminergic innervation, measured using a dopamine transporter marker, were associated with visual-motor performance improvements. Axial and appendicular motor features may be mediated by non-dopaminergic and dopaminergic pathways, respectively. The secondary objective was to demonstrate the short- and long-term effects of SCS for alleviating dopaminergic-resistant FOG and gait dysfunction in 5 PD and 3 PSP-RS participants without back/leg pain. SCS programming was individualized based on which setting best improved gait and/or FOG responses per participant using objective gait analysis. Significant improvements in stride velocity, step length and reduced FOG frequency were observed in all PD participants with up to 3-years of SCS. Similar gait and FOG improvements were observed in all PSP-RS participants up to 6-months. SCS is a promising therapeutic option for parkinsonian patients with FOG by possibly influencing cortical and subcortical structures involved in locomotion physiology

    The effects of cultural dimensions on algorithmic news: How do cultural value orientations affect how people perceive algorithms?

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    How do cultural values influence/are influenced by algorithms? A comparative study was conducted between the United States (US) and the United Arab Emirates (UAE) to investigate how users in the different cultures perceive the features of chatbot-driven news and how they view ethical issues concerning chatbot journalism. Different models of chatbot news perception reveal that the acceptance of chatbots involves a cultural dimension as the algorithms reflect the values and interests of their constituencies. How users perceive chatbot news and how they consume and interact with the chatbots depend on the cultural and social contexts in which the interaction is taking place. Our results suggest the algorithms reflect cultural values and algorithms are implicitly situated in social contexts, mediated by cultural artifacts and activities. The results resonate with ongoing debates on whether and how algorithms reinforce cultural and social values implying the co-evolving nature of algorithms and humans

    Farm fatalities in Northern Ireland agriculture: What fifty years of data tell us

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    Publication history: Accepted - 8 March 2022; Published online - 10 March 2022.Agriculture is one of the most hazardous sectors in terms of fatal and non-fatal accidents. This paper utilises an administrative dataset that recorded farm fatalities in Northern Ireland over a 50 year timeframe (1968–2017) to undertake an age-period analysis of accident related mortality rates by sex, cause of death, season, and day of the week. Public policies aimed to improve farm safety should consider that fatalities due to animals have increased while the incidence of deaths due to vehicles and equipment has substantially decreased over the years although it is still the primary cause of death. With respect to age, elderly still actively involved in farming and children in the spring and at week-ends are most exposed to the risk of a fatal accident. Overall, men die on farms five times more than women.This research was supported by the Department of Agriculture, Environment, and Rural Affairs of Northern Ireland, grant number E-I 18-01-19

    Posicionamento atual sobre vitamina D na prática clínica: Posicionamento da Associação Brasileira de Nutrologia (Abran)

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    Objective: To establish a position statement to standardize the recommendations of the Brazilian Association of Nutrology related to vitamin D deficiency management in the clinical practice with an emphasis on the diagnosis, treatment and prevention. Methods: We present an update on the diagnosis, prevention and treatment of vitamin D deficiency, based on the most recent scientific evidence, including an extensive data review of PubMed, Lilacs and SciELO. Results: Based on the recent information obtained in contrast to previous published Brazilian and American guidelines, the authors drafted the agreement, which was approved by the scientific board of the Brazilian Association of Nutrology. Conclusion: After a critical analysis of the most recent data, a scientific update regarding vitamin D management was presented resulting in the present institutional guide from the Brazilian Association of Nutrology about the prevention, diagnosis and treatment of this condition in Brazil
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