58622 research outputs found
Sort by
Flow and Heat Transfer in Rotating Compressor Cavities with Inverted Shroud-Throughflow Temperature Differences
Get PDFIn an aero-engine compressor, co-rotating discs form cavities that interact with an axial throughflow of secondary air at low radius. In the high-pressure (HP) compressor the shroud is hotter than the throughflow (directed downstream to the turbine) and the radial temperature gradient creates buoyancy-induced flow at Grashof numbers 1013. Such flows can be unstable and typically take the form of counter-rotating vortex pairs separated by radial hot and cold plumes. However, in low pressure (LP) and intermediate pressure (IP) compressors the secondary air is directed upstream. In this inverse scenario, the axial throughflow is hotter than the compressor discs, reversing the disc temperature gradient and eliminating the fundamental driver for buoyancy. Despite its practical application and importance, this inverse scenario has not been previously investigated. The University of Bath Compressor Cavity Rig has been uniquely designed to simulate such flows, measuring temperature, and unsteady pressure in the frame of reference of the rotating discs. Bayesian and spectral analysis have determined the radial distribution of disc heat flux, as well as the asymmetry of the rotating vortex structures and their slip relative to the discs. Unexpectedly, the new data reveal the flow structure in cavities with positive and inverted temperature differences are fundamentally similar (albeit with reversed radial-Temperature profiles). Isothermal cases identified a critical Rossby number (Ro), above which the flow structure in the cavity was dominated by a toroidal vortex. At subcritical Ro, the flow structure for the inverted temperature gradient continued to be governed by buoyancy due to disc heat transfer. Momentum exchange with the axial throughflow and the gradient of circumferential pressure combine to vary the slip and vortex symmetry. This paper provides the first data and analysis of flow and heat transfer during inverse throughflow conditions in LP and IP compressors. The new insights are of importance for the determination of the thermal stresses in discs, engine life, compressor blade clearance and efficiency.</p
Reducing the spread of retracted pain research
Get PDFHighlights Retracted literature continues to be cited despite its withdrawalAuthors are key stakeholders to reduce to spread of retracted pain literatureChanges to manuscript submission instructions may reduce citation of retractionsKeywordsretractionmisconducttrustworthinessresearch qualit
Improving the predictive capability of empirical heat transfer correlations for hydrogen internal combustion engines
Get PDFHydrogen internal combustion is widely considered a viable technology to achieve near-zero tailpipe CO2 and NOx emissions for difficult-to-electrify applications due to the maturity of ICE technology and production facilities. One-dimensional/zero-dimensional (0D) modeling is a valuable tool for engine development due to its relatively low computational requirements, but hydrogen combustion models still require further development. A large factor is gas-to-wall heat transfer, which is higher for hydrogen combustion due to higher flame temperatures and shorter quenching distance. For accurate prediction of in-cylinder temperatures, and therefore combustion rates and knock propensity, a well calibrated heat transfer model is essential. This paper evaluates existing heat transfer models against previously published experimental cylinder pressure and heat flux data from a Cooperative Fuel Research (CFR) engine with hydrogen Port Fuel Injection (PFI). A new heat transfer correlation is developed, utilizing a new fluid properties correlation to better represent the change in viscosity and conductivity with changing hydrogen concentration. Recent developments in 0D turbulence models improve the characteristic velocity calculation, which is augmented with a combustion term. This model is tested against a second dataset from the CFR engine with lambda from 1.0 to 4.0 and compression ratios of 9–13, showing improved performance versus previously published models. Whilst the new model provides more consistent results during combustion for variations in lambda and compression ratio, it requires improvement in its prediction of heat loss during expansion, and further validation at higher engine speeds and different engine configurations
Reviewing human-robot collaboration in manufacturing:Opportunities and challenges in the context of industry 5.0
Get PDFIndustry 4.0 (I4.0) has been characterized by the increasing use of automation, artificial intelligence, and big data in manufacturing. It has brought different machines, tools, robots and devices together through integration with cyber physical systems as well as Internet of Things and computer systems. This has dramatically improved efficiency, productivity, and flexibility of automated systems, but it has also raised concerns about the impact of automation on jobs, the ethical considerations and the future of work in general. Industry 5.0(I5.0) is the next manufacturing paradigm evolution and builds on I4.0 with the addition of ‘people’, in which robots will be designed to work alongside humans in a safe and efficient manner. Human-robot collaboration (HRC) is its key enabler. In manufacturing, HRC has the potential to improve safety, efficiency, and productivity by allowing humans to focus on tasks that require creativity, judgment, and flexibility, while robots perform more repetitive and dangerous tasks. This paper explores the concept of HRC and its advancement within 21st century industry. It identifies the opportunities and challenges arising from the interactions between robots and humans in manufacturing applications, assembly, and inspection. It also highlights the significance of HRC in I4.0 and its potential in I5.0. In addition, the role of artificial intelligence, machine learning, large language models, information modelling (ontologies) and new emerging digital technologies (augmented reality, virtual reality, digital twins, cyber-physical system) in the development of HRC and I5.0 is documented and discussed adding new perspectives to the growing literature in this area. This investigation sheds light on the emerging paradigms that have come about asparts of I5.0 and the transformative role of human-robot interaction in shaping the future of manufacturing. This critical review provides a realistic picture of manufacturing automation and the benefits and weaknesses of current HRC systems. It presents a researched view on the concept, needs, enabling technologies and system frameworks of human-robot interaction in manufacturing, providing a practical vision and research agenda for future work in this area and its associated systems.<br/
A new approach to children’s work that prioritises resilience, wellbeing, and agency:emerging findings from a ‘cash plus’ intervention in Bangladesh
Get PDFBackground Criticism of mainstream approaches to child labour is widespread and well-established. The Child Labour Action Research in South and Southeast Asia (CLARISSA) Cash Plus pilot sought to address these critiques through an innovative programme that prioritised the development of household resilience and well-being, and through increasing household capacity to make alternative choices around children’s work.Research Funded by the UK’s Foreign, Commonwealth and Development Office, this pilot delivered unconditional cash transfers (UCTs) and needs-based case management and community mobilising across an entire slum neighbourhood in Dhaka, Bangladesh. Cash worth about 20% of household monthly income was delivered to all households for 7 months, with case work and community organising wrapped around for 21 months. The intended outcomes were that families would be able to increase their economic resilience and develop alternative capacities to meet their needs, with the intended goals of increasing well-being and the ability to make choices other than difficult or dangerous work for children. Research into impact was rooted in contribution analysis and combined bimonthly monitoring surveys administered by the community mobilisers; surveys at multiple time points; three rounds of targeted focus group discussions; three rounds of key informant interviews with case study households; community mobiliser diaries; and ethnographic observation.Results and conclusions The results strongly suggest that UCTs reduce poverty, increase economic resilience; improve well-being; and generate various household-level improvements that relate directly and indirectly to children’s work. They further suggest that case work and community organising act as a beneficial form of social protection and a tool for developing locally appropriate micro-responses to collective problems that commonly impact directly on well-being and indirectly on children’s work. These results point to the potential for this intervention to be scaled-up in efforts to achieve the eighth Sustainable Development Goal of ensuring decent work for all, including the elimination of child labour
Adopting a Systemic Design Approach to Cyber Security Incident Response
Get PDFComputer security incident response teams (CSIRTs) are critical to maintaining business continuity in the face of cyber-attacks. Yet there has been little research conducted in the last decade to understand the root causes of the challenges they face to sustain their effectiveness. Moreover, they operate in complex sociotechnical multiteam systems, making it challenging to understand the causes of problems and how to bring about improvements. This paperproposes the use of a Systemic Design approach to develop a more in-depth understanding of the complex sociotechnical system(s) of cyber security incident response, in order to find intervention points that can be leveraged in one area to transition the whole system into a better state. We present the first steps of a case study that uses Gigamap workshops and in-depth interviews with a range ofstakeholders to frame the system and understand its effectiveness
Efficient Multi-Task Reinforcement Learning via Task-Specific Action Correction
Get PDFMulti-task reinforcement learning (MTRL) holds potential for building general-purpose agents, enabling them to generalize across a variety of tasks. However, MTRL may still be susceptible to conflicts between tasks. A primary reason for this problem is that a universal policy struggles to balance short-term and dense learning signals across various tasks, e.g. , distinct reward functions in reinforcement learning. In social cognitive theory, internalized future goals, as a form of cognitive representations, can effectively mitigate potential short-term conflicts in multitask settings. Considering the benefits of future goals, we propose a novel and general framework called Task-Specific Action Correction (TSAC) from the goal perspective as an orthogonal research to previous MTRL methods. Specifically, to avoid myopia, TSAC introduces goal-oriented sparse rewards and decomposes policy learning into two separate policies: a shared policy (SP) and an action correction policy (ACP). The SP outputs a short-term perspective action based on guiding dense rewards. To alleviate conflicts resulting from excessive focus on specific tasks' details in SP, the ACP incorporates goal-oriented sparse rewards, enabling an agent to adopt a long-term perspective to output a correction action and achieve generalization across tasks. Finally, the actions output by SP and ACP are combined based on the action correction function to form a final action that interact with the environment. Extensive experiments conducted on Meta-World and multi-task StarCraft II multi-agent scenarios demonstrate that TSAC outperforms existing state-of-the-art methods, achieving significant improvements in sample efficiency, generalization and effective action execution across tasks.</p
Supersonic Gravitational Collapse for Nonisentropic Gaseous Stars
Get PDFWe show the existence of a new class of initially smooth spherically symmetric self-similar solutions to the non-isentropic Euler--Poisson system. These solutions exhibit supersonic gravitational implosion in the sense that the density blows-up in finite time while the fluid velocity remains supersonic. In particular, they occupy a portion of the phase space that is far from the recently constructed isentropic self-similar implosion. At the heart of our proof is the presence of a two-parameter scaling invariance and the reduction of the problem to a non-autonomous system of ordinary differential equations. We use the requirement of smoothness of the flow as a selection principle that constrains the choice of scaling indices. An important consequence of our analysis is that for all the solutions we construct, the polytropic index \ga is strictly bigger than , which is in sharp contrast to the known results in the isentropic case
A geological timescale for bacterial evolution and oxygen adaptation
Get PDFMicrobial life has dominated Earth's history but left a sparse fossil record, greatly hindering our understanding of evolution in deep time. However, bacterial metabolism has left signatures in the geochemical record, most conspicuously the Great Oxidation Event (GOE). We combine machine learning and phylogenetic reconciliation to infer ancestral bacterial transitions to aerobic lifestyles, linking them to the GOE to calibrate the bacterial time tree. Extant bacterial phyla trace their diversity to the Archaean and Proterozoic, and bacterial families prior to the Phanerozoic. We infer that most bacterial phyla were ancestrally anaerobic and adopted aerobic lifestyles after the GOE. However, in the cyanobacterial ancestor, aerobic metabolism likely predated the GOE, which may have facilitated the evolution of oxygenic photosynthesis.</p
Quantum Geometric Injection and Shift Optical Forces Drive Coherent Phonons
Get PDFWe identify {\em injection} and {\em shift} rectified Raman forces, which are phononic counterparts of the photogalvanic effect, that drive lattice vibrations and trigger transient emergent properties. These forces are governed by the {\em quantum geometric tensor}, a {\em phononic shift vector}, and interband asymmetries in the electron-phonon coupling. The injection force acts displacively, while -- unlike conventional impulsive mechanisms -- the shift force emerges impulsively in the resonant interband absorbing regime when time-reversal symmetry is broken. Using the bilayer Haldane model, we quantify the injection and shift forces acting on interlayer shear phonons through both analytical and numerical methods. Strikingly, we reveal strong tunability, both in magnitude and direction, of the rectified forces by varying the driving frequency and magnetic flux, uncovering a distinct quantum geometric mechanism for ultrafast and coherent manipulation of quantum materials
Access Repository Dashboard
Do you manage Open Research Online? Become a CORE Member to access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard! 👇