60419 research outputs found
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CFD modelling and analysis of variable and constant wall thickness scroll expanders and their performance.
No full textHigher efficiencies and more compact designs in spite of larger expansion ratios are associated with variable wall thickness scroll expander geometries. However, the literature for these innovative scroll designs is mainly limited to theoretical studies since the research and development of scroll expanders is still in the early stages. Considering the potential benefits of less overall leakage areas, shorter residence time of the gas and less time for leakages and heat transfer, the scroll machine with variable wall thickness could be a promising candidate to further improve the efficiency and power output in organic Rankine cycle systems. It has also the opportunity of opening up new application fields such as hybrid vehicle powertrain systems in which power cycles with high pressure ratio are needed. The main aims of this PhD research were to investigate variable and constant wall thickness scroll expanders for small scale organic Rankine cycle systems using three-dimensional and transient CFD simulations. The aerodynamic performances are compared to examine the features of the novel variable wall thickness scroll expander design. This is followed by the investigation of spark-ignition scroll engines and their performance by means of a heat release rate analysis and CFD based combustion modelling tools. The evaluation of the CFD simulations of variable wall thickness scroll expanders reveals that the geometrical effects of varying wall thicknesses did not affect the characteristic scroll machine operation. The validation, verification and the findings had proven consistency with the theory of scroll expanders. The optimum performance was achieved at a pressure ratio of 3.5 regardless of the rotational speed. The decrease of radial clearance from 200μm to 75μm had a positive effect on isentropic efficiency and specific power output. The isentropic efficiency at the optimum performance point was significantly improved by 22% from 31.9% to 53.9%. It is also found that the lower number of working chambers resulted in a shorter gas residence time, associated with less time for flank leakages, in comparison to the constant wall thickness scroll expander. Thus, the fluid friction was reduced, converting less kinetic energy into enthalpy. The large-scale swirls were completely dissipated in the expansion chambers of the variable wall thickness scroll expander at the crank angle of 600°, in contrast to 672°in the expansion chambers of the constant wall thickness design. In addition, the shorter scroll profile length of the variable wall thickness scroll expander generated lower average radial and axial gas forces. Moreover, higher pressure gradients between individual working chambers contributed to a higher peak of the tangential gas moment but at the expense of higher transient radial and axial gas force and tangential gas moment variations. More significant pressure drops occurred along the local radial clearance reducing the isentropic efficiencies in spite of the shift towards higher pressure ratio. The heat release rate analysis reveals that a more thorough expansion was achieved by employing the scroll engine in the Miller/Atkinson cycle instead of the conventional Otto cycle. The highest power output of 44.5kW was achieved for a compression ratio of 10.1:1 and an expansion ratio of 17.8:1 (V=4.62dm^3) at a rotational speed of n=3000rpm. The thermal efficiency followed the same trend reaching a peak value of 43.1% but for a lower compression ratio of 8.2:1. The evaluation of the CFD based combustion model results shows that the third combustion cycle was technically not feasible because the entire domain was filled with burned gas due to the lack of flame quenching. No steady-state solution was achieved and all the results are therefore hypothetical
To what extent does UK and Irish maternity policy and guidance address integration of services to meet needs of women with comorbidity? A policy document review
No full textDespite a reduction in overall maternal mortality in the United Kingdom (UK) during recent decades, maternal mortality rates over the previous six years have started to increase (Knight et al. 2019), and maternal deaths associated with pre-existing physical and/or psychological comorbidities are increasing nationally and globally (Nair et al. 2017). Surveillance data from the UK and Ireland suggests that most women who died during or following pregnancy in the period 2015 to 2017 had multiple health problems and/or additional complex social factors (Knight et al. 2019). This is mirrored in maternal mortality case reviews in other high-income countries including United States of America (USA) (Creanga et al. 2015), Australia (Australian Institute of Health and Welfare 2017) and New Zealand (Perinatal and Maternal Mortality Review Committee 2018).
Whilst maternal mortality rates in other high-income countries have also decreased over the past two decades, ranging from 3 to 12 deaths per 100,000 live births (WHO 2018a), severe maternal morbidity rates are increasing (Gellar et al. 2018), as a consequence of pre-existing and pregnancy related health problems, often reflecting multiple complex health and social needs. In the USA for example, overall severe maternal morbidity rates increased from 74 per 10,000 hospital births in 1998–99 to 163 in 2010–11 (Creanga et al. 2014). In the UK and Ireland more than two-thirds (68%) of the women who died during or after pregnancy in the triennial period 2014-2016 were known to have pre-existing medical problems (Knight et al. 2018). Conditions associated with increased maternal morbidity include obesity (Dudenhausen 2015, NHSE 2018a) diabetes (Coton et al. 2016, Feig et al. 2018) cardiac disease (Roos-Hesselink 2019) and severe mental illness (Estrin et al. 2019, Xu et al. 2014). Increasing numbers of women have physical and/or psychological comorbidities prior to becoming pregnant (Molyneaux et al. 2014, Ruhstaller et al. 2017, Kumpulainen 2018). These women are at greater risk of adverse pregnancy outcomes than women in the general pregnant population (Mhyre et al. 2011, Nair et al. 2015) and it is imperative that maternity policy acknowledges and addresses the impact of the changing health-profile of women to consider how to prevent or at least reduce maternal morbidity.</p
Systematic Review of Research on Abusive Supervision in Hospitality
No full textPurpose: This paper aims to provide researchers and practitioners with an understanding of abusive supervision in the context of hospitality. It seeks to conduct a comprehensive review of the area and offer recommendations for future research by exploring the antecedents, consequences, mechanisms, and designs of research on abusive supervision.
Design/methodology/approach: Content analysis was conducted to review and analyze studies on abusive supervision in the context of hospitality. Previous studies were searched in the EBSCO, Scopus, Web of Science, and Google Scholar electronic databases.
Findings: Thirty-six referred articles related to abusive supervision in hospitality were reviewed across four key areas, namely, antecedents, consequences, mechanisms, and research design. After reviewing the research on abusive supervision in the context of hospitality, this paper offers future research directions with respect to research focus and research design.
Research limitations/implications: This paper only included English articles from peer-reviewed journals on abusive supervision. The number of reviewed articles was relatively small. This limitation may have arisen because abusive supervision is a new research field and is still a sensitive topic.
Practical implications: The results of this work may encourage managers to minimize or even halt abusive supervision. From an organizational perspective, formal policies may be developed to regularize supervisors’ behavior. In turn, employees could use this paper to learn further about abusive behavior and how to handle it effectively.
Social implications: The review highlighted the negative consequences of abusive supervision. Managers should urgently realize the seriousness of abusive supervision and develop effective policies to minimize its negative effect.
Originality/value: This paper contributes to the emerging literature on abusive supervision in the context of hospitality by identifying key research trends and framing the outlines of empirical studies. It identifies research gaps, and as the first review of abusive supervision in hospitality, it may encourage researchers to explore the topic on the basis of the characteristics of the sector and offer suggestions for future research.</p
Effect of reacting gas flowrates and hydration on the carbonation of anion exchange membrane fuel cells in the presence of CO2
No full textAnion exchange membrane fuel cells (AEMFCs) have been widely touted as a low-cost alternative to existing proton exchange membrane fuel cells. However, one of the limitations of this technology has been the severe performance penalty related to the introduction of CO2 to the cell – typically in the air cathode feed. Introduction of CO2 into AEMFCs results in cell carbonation, which imparts thermodynamic, kinetic and Ohmic overpotentials that can add up to hundreds of millivolts. Therefore, it is important to find strategies and operational protocols for AEMFCs that minimize these overpotentials. In this paper, we investigate the impacts of the anode and cathode flowrate, as well as the cell hydration level, on the extent of cell carbonation and cell polarization. Key findings include: (1) decreasing the cathode flowrate generally decreases the total CO2-related voltage loss while changing the anode flowrate has a minimal effect; (2) increasing cell hydration helps to mitigate the performance loss in the presence of CO2; and (3) operational combinations are found that significantly reduce the CO2 penalty compared to the present literature
On the vehicle state estimation benefits of smart tires
No full textSmart tires are systems that are able to measure temperature, inflation pressure, footprint dimensions, and, importantly, tire contact forces. The integration of this additional information with the signals ob-tained from more conventional vehicle sensors, e.g., inertial measure-ment units, can enhance state estimation in production cars. This paper evaluates the use of smart tires to improve the estimation performance of an Unscented Kalman filter (UKF) based on a nonlinear vehicle dynam-ics model. Two UKF implementations, excluding and including smart tire information, are compared in terms of estimation accuracy of vehicle speed, sideslip angle and tire-road friction coefficient, using experi-mental data obtained on a high performance passenger car
A NEW SET OF DIRECTIONAL WEIGHTS FOR ITU-R BS.1770 LOUDNESS MEASUREMENT OF MULTICHANNEL AUDIO
No full textThe ITU-R BS.1770 multichannel loudness algorithm performs a sum of channel energies with weighting coefficients
based on azimuth and elevation angles of arrival of the audio signal. In its current version, these coefficients
were estimated based on binaural summation gains and not on subjective directional loudness. Also, the algorithm lacks
directional weights for wider elevation angles (jfj � 30�). A listening test with broadband stimuli was conducted to collect subjective data on directional effects. The results were used to calculate a new set of directional weights. A modified version
of the loudness algorithm with these estimated weights was tested against its benchmark using the collected data, and
using program material rendered to reproduction systems with different loudspeaker configurations. The modified algorithm
performed better than the benchmark, particularly with reproduction systems with more loudspeakers positioned out of the
horizontal plane
The COVID-19 MS Coalition—accelerating diagnostics, prognostics, and treatment
No full textRapid and comprehensive genetic
sequencing has shed light on the
origin of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
and allowed timely implementation
of PCR tests to determine the presence
of viral RNA. PCR tests for SARS-CoV-2
are some way from being reliably
qualitative and will never indicate
how the disease might progress in
an individual. As COVID-19 becomes
endemic, there is a concomitant need
for accurate serological assays to detect
antibodies to SARS-CoV-2 antigens and
ultimately tests for prognostic markers
to target treatment options.1,2 With this
considerable genetic insight, and the
emerging structural information, comes
associated questions regarding the
molecular descriptors that contribute
to disease progression, especially when
we consider spread across different
populations. The power of mass spectrometry to generate rapid, precise, and
reproducible diagnostic information that
complements genomic information and
accelerates our understanding of the
disease, is now becoming a reality
Recovery from work: Testing the effects of chronic internal and external workload on health and wellbeing
No full text“What is already know on this subject”
The need for recovery from the demands of work has been associated with workers detachment from work and wellbeing. Recovery from work can occur both during the working day, by way of rest breaks (i.e., internal recovery), and outside or work, during leisure time, by not working in the evening (i.e., external recovery). Recovery can be compromised when workload is high. It remains unclear how the experience of exposure to persistent high workload over time effects health and wellbeing, and whether similar effects are found for internal and external workload. Most research has focused on external workload and there is a lack of studies that have examined the effects of workload longitudinally.
“What does this study add?”
This study showed that chronic workload both during the day and evening is associated with increased risk of reporting psychological fatigue, physical fatigue and sleep problems. Interestingly, the effects on health are particularly salient when recovery opportunities are not taken during the working day. These results highlight the importance of workers needing to take time away from the demands of work by taking regular recovery breaks throughout the day as a prerequisite for maintaining health and wellbeing
Exposure to Toenail Heavy Metals and Child Behavior Problems in Nine-Year-Old Children: A Cross-Sectional Study
No full textBehavioral problems are multifactorial and includes perinatal, maternal, family, parenting, socio-economic and personal risk factors, but less is known about the association of postnatal heavy metals on children’s behavioral problems in Pacific Island children. Methods: A cohort of eligible nine-year-old children within a Pacific Island Families longitudinal study were recruited for a cross-sectional study. Child behavior problems were assessed using the child behavior checklist. Heavy metals (including Ni, Cu, Pb, Al, Cr and Cd) were determined in toenails, after acid digestion and analyzed using inductively coupled plasma mass spectrometry. Other factors such as lifestyle (smoking in pregnancy), health outcomes (obesity, health status), demographics (gender, ethnicity, parents’ marital status) and socioeconomic status (household income levels) were also collected. The statistical analysis included t-tests for independent sample and Mann–Whitney U-test, and chi-square or Fisher’s exact tests of independence for comparisons of the proportions. Regression models tested the hypothesized risk factors for behavior outcomes. Results: This observational study enrolled 278 eligible Pacific Island children living in Auckland, New Zealand. The prevalence of behavioral problems in the clinical range was high (22%) but there was no significant association between heavy metals in toenails and adverse behavioral outcomes. Conclusion: Regular monitoring and assessments of children for environmental risk factors, as well as social and lifestyle factors for behavior problems, continues. Alternative indicators of exposure to heavy metal should be evaluated
Evaluating Interoceptive Crossover between emotional and physical symptoms
No full textSymptom perception is complex and influenced by a number of psychological factors. Further, a number of problems relating to symptom perception have been identified including poor interoception and a reduced ability to recognise bodily signals and alexithymia reflecting an impaired ability to identify and describe emotional symptoms. In addition, research indicates that some individuals may have difficulty distinguishing between internal signals and demonstrate an ‘Interoceptive Crossover’ of emotions and physical symptoms. To date, research in this area is sparse. The current study therefore aimed to explore the incidence and nature of Interoceptive Crossover. 239 individuals completed an online survey and reported their experiences of perceived similarity between a range of emotions (e.g., Sad, Happy, Afraid and Calm) and physical symptoms (e.g., Stomach Pain, Fatigue/Tiredness, Headache and Abnormal Heartbeat) to assess the incidence and nature of Interoceptive Crossover. Some individuals demonstrated crossover between emotions and physical symptoms. Some crossovers were more unsurprising and reported by greater proportion of the sample, such as Afraid and Abnormal Heartbeat (74.5%); Sad and Fatigue (29.4%) and Afraid and Shortness of Breath (58.5%). Other crossovers were less prevalent in the sample and more unexpected such as Satisfied with Headache (1.2%); Bored with Back Pain (5.95%) and Happy and Back Pain (0.4%). Some individuals demonstrate Interoceptive Crossover of emotions and physical symptoms. Some crossovers are more prevalent whilst others are rare and unexpected. This phenomena needs to be explored in more depth and with relation to other constructs such as alexithymia and interoception
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