OAK (Online Access to Knowledge) Commons (Young Harris College)
Not a member yet
33676 research outputs found
Sort by
Experimental investigation on the fatigue crack growth behaviour of Q420C
No full textThe lack of test data on the fatigue crack growth behaviour of Q420C steel affects its application in the field of wind power engineering. To fill this gap, this paper carried out an experimental study and theoretical analysis of the fatigue crack propagation behaviour of Q420C steel under constant amplitude. Six compact tension specimens were separately tested under six loading conditions comprising two maximum loads (𝐹𝑚𝑎𝑥=8 𝑘𝑁 𝑜𝑟 10 𝑘𝑁) and three load ratios (𝑅=0.1,0.3,𝑜𝑟 0.5). The Back-Face Strain method was used to calculate the crack length, and a complete cycle of strain values was recorded for every 1 mm of crack extension. The crack growth rate and crack opening load were calculated according to the ASTM E647-15. The test results show that for the two crack growth rate calculation methods given by the ASTM E647-15, the secant method provides large discrete results, while the incremental polynomial method can obtain a relatively smooth rate curve. In addition, for the incremental polynomial method, the normalisation of the number of cycles in the ASTM E647-15 should not be used to achieve acceptable results. The rate curves of Q420C steel show a clear load ratio effect, for the same stress intensity factor range Δ𝐾, the higher the load ratio, the faster the crack grows. Quantitative analysis of the effect of load ratios has shown that two-parameter models based on 'unified theory', such as Walker’s model, can accurately describe the effect of load ratios. However, the theory of plasticity-induced crack closure cannot account for the effect of load ratios, as the crack opening load 𝐹𝑜𝑝 is less than the minimum load 𝐹𝑚𝑖𝑛 for load ratios greater than 0.1. Finally, a comparison is carried out against the predictions by BS7910; results verify the applicability of BS7910 to Q420C steel material and demonstrate the different degrees of conservatism of all recommended design curves in BS7910
Students’ views about alternates to traditional dissertation for Master in Public Health: results of a virtual focus group
No full textA traditional dissertation remains a component of most Master in Public Health programmes, but there is increasing interest and use of alternatives. A virtual focus group of six students studying an online distance Master in Public Health explored their perceptions about dissertations and preferences for alternatives. Students value the dissertation as a means of consolidating learning and focusing in-depth on chosen topics. Alternatives were viewed as attractive but not always practical. Participants felt that additional options need to be accompanied by guidance to ensure students make the most appropriate choice for their future. Three types of students with different needs emerged; students aspiring to progress to a PhD should do a traditional dissertation, students already employed in a relevant role may choose a work-based dissertation or replace the dissertation with taught units, and students doing the master to increase their employability could choose a placement-based dissertation or replace the dissertation with work experience reflection. Innovations that introduce alternatives to the traditional dissertation would be welcomed by MPH students studying online, but they would need to be accompanied by suitable career advice to ensure students choose the most appropriate route for their future aspirations
The effects of smoothing length on the onset of wave breaking inSmoothed Particle Hydrodynamics (SPH) simulations of highlydirectionally spread waves
No full textOcean wave breaking is a difficult-to-model oceanographic process, which has implications forextreme wave statistics, the dissipation of wave energy, and air-sea interaction. Numerical methods capable of reliably simulating real-world directionally spread breaking waves are useful for investigating the physics of wave breaking and for the design of offshore structures and floating bodies. Smoothed Particle Hydrodynamics (SPH) is capable of modelling highly steep and overturning free surfaces, which makes it a promising method for simulating breaking waves. This paper investigates the effect of smoothing length on simulated wave breaking in both following and crossing seas. To do so, we reproduce numerically the experiments of highly directionally spread breaking waves in McAllister et al. [J. Fluid Mech. vol. 860, 2019, pp. 767{786] using a range of normalised smoothing lengths: h=dp =1.4, 1.7, 2.0, 2.3, with h smoothing length and dp particle spacing. The smallest smoothing length we use appears to adversely affect the fidelity of the simulated surface elevation, so that the tallest wave crest observed in experiments is not fully reproduced (coefficient of determination r2 ≈ 0:7). For smoothing lengths h=dp = 1:7, 2:0, and 2:3, the experiments are well reproduced (r2 ≥ 0:88); in these simulations smoothing length predominantly affects the spatial extent and duration of breaking. Qualitative and quantitative comparison of our simulations show that values of h=dp in the range 1:7 - 2 best reproduce the wave breaking phenomena observed in experiments
Denotational and Algebraic Semantics for Cyber-physical Systems
No full textThe cyber-physical system (CPS) is a dynamic system that contains both continuous and discrete behaviors. It has a wide range of applications in fields such as healthcare equipment, intelligent traffic control and environmental monitoring. However, the combination of continuous physical behaviorand discrete control behavior may complicate the design of systems further. It is of great necessity to give an explicit formal language and its semantics for CPS. In this paper, we elaborate the modeling language for CPS based on our previous work.This language supports shared variables to model the interaction between the physical and the cyber. Additionally, we give it denotational semantics and algebraic semantics, especially focus on the continuous behavior and its composition with the discrete behavior. Throughout this paper, we also present some examples to illustrate the feasibility of the language and its semantics intuitively.Index Terms—Cyber-physical system (CPS), Unifying Theories of Programming (UTP), Denotational semantics, Algebraic semantic
Governance choice misfit and firm performance in offshoring innovation: The role of institutional environment
No full textIn this paper, we analyse the effect of institutional factors on the relationship between governance choices and business outcomes when offshoring innovation. Grounded in an institutional theory perspective, we use survey data from the ORN database to estimate regression models and identify governance modes related to specific drivers of offshore innovation. We then analyse the effect on firm performance of choosing a governance mode not in line with the one predicted by the model. We find that choosing a fully owned offshoring operation when theory would predict selecting offshore outsourcing has a negative effect on performance, but not vice versa. We also find that institutional factors of rule of law and IPR protection strength in host countries negatively affect firm performance when offshoring innovation activities
Numerical Stability of Algorithms at Extreme Scale and Low Precisions*
No full textThe largest dense linear systems that are being solved today are of order 𝑛 = 107. Single precision arithmetic, which has a unit roundoff 𝑢 ≈ 10-8, is widely used in scientific computing, and half precision arithmetic, with 𝑢 ≈ 10−4, is increasingly being exploited as it becomes more readily available in hardware. Standard rounding error bounds for numerical linear algebra algorithms are proportional to 𝑝(𝑛)𝑢, with 𝑝 growing at least linearly with 𝑛. Therefore we are at the stage where these rounding error bounds are not able to guarantee any accuracy or stability in the computed results for some extreme-scale or low-accuracy computations. We explain how rounding error bounds with much smaller constants can be obtained. Blocked algorithms, which break the data into blocks of size 𝑏, lead to a reduction in the error constants by a factor 𝑏 or more. Two architectural features also reduce the error constants: extended precision registers and fused multiply–add operations, either at the scalar level or in mixed precision block form. We also discuss a new probabilistic approach to rounding error analysis that provides error constants that are the square roots of those of the worst-case bounds. Combining these different considerations provides new understanding of the numerical stability of extreme scale and low precision computations in numerical linear algebra.<br/
Prognostic impact of late gadolinium enhancement at the right ventricular insertion points in non-ischemic dilated cardiomyopathy.
No full textAimsTo evaluate the baseline characteristics and the prognostic implications associated with late gadolinium enhancement limited to the right ventricular insertion points (IP-LGE) or present at both the right ventricular insertion points and the left ventricle (IP&LV-LGE) in non-ischemic dilated cardiomyopathy (DCM). Methods and results Retrospective observational multicenter cohort study including 1165 consecutive patients with DCM evaluated by cardiac magnetic resonance. The primary endpoint included appropriate defibrillator therapies, sustained ventricular tachycardia, resuscitated cardiac arrest or sudden death. The secondary outcome encompassed heart failure hospitalizations, heart transplant, left ventricular assist device implantation and end-stage heart failure death. IP-LGE was found in 72 patients (6%), who had clinical characteristics closer to LGE- than to LGE+ patients. During follow-up (median 36 months), none of the IP-LGE patients experienced the primary endpoint. The cumulative incidence of the primary endpoint was similar between IP-LGE and LGE- patients (p=1) while IP-LGE had significantly lower cumulative incidence as compared to LGE+ patients (p<0.001). As compared to IP-LGE patients, the cumulative incidence of the secondary endpoint was similar in LGE- cases (p=0.86) but tended to be higher in LGE+ patients (p=0.06). Both clinical characteristics and outcomes were similar between IP&LV-LGE patients and the rest of LGE+ cases. ConclusionsIn a large cohort of DCM patients, IP-LGE was associated with similar outcome as compared to LGE- patients and with significant lower risk of ventricular arrhythmias and sudden death as compared to LGE+ cases. Patients with IP&LV-LGE had clinical characteristics and outcomes similar to the rest of LGE+ cases
Photocatalytic biomass reforming: what role will the technology play in future energy systems
No full textPhotocatalytic biomass reforming has emerged as an area of significant interest within the last decade. The number of papers published in the literature has been steadily increasing with keywords such as ‘hydrogen’ and ‘visible’ becoming prominent research topics. There are likely two primary drivers behind this, the first of which is biomass represents a more sustainable photocatalytic feedstock for reforming to value-added products and energy. The second is the transition towards achieving net zero emission targets, which has increased focus on the development of technologies that could play a role in future energy systems. Therefore, this review provides a perspective on not only the current state of the art of research but also a future outlook on the potential roadmap for photocatalysis biomass reforming. Producing energy via photocatalytic biomass reforming is very desirable due to the ambient operating conditions and potential to utilise renewable energy (e.g. solar) with a wide variety of biomass resources. As both interest and development within this field continues to grow, however, there are challenges being identified that are paramount to further advancement. In reviewing both the literature and trajectory of the field, research priorities can be identified and utilised to facilitate fundamental research alongside whole systems evaluation. Moreover, this would underpin the enhancement of photocatalytic technology with a view towards improving the Technology Readiness Level and promoting engagement between academic and industry
Embodied Attention in Word-Object Mapping: A Developmental Cognitive Robotics Model
No full textDevelopmental Robotics models provide useful tools to study and understand the language learning process in infants and robots. These models allow us to describe key mechanisms of language development, such as statistical learning, the role of embodiment, and the impact of the attention payed to an object while learning its name. Robots can be particularly well suited for this type of problems, because they cover both a physical manipulation of the environment and mathematical modeling of the temporal changes of the learned concepts. In this work we present a computational representation of the impact of embodiment and attention on word learning, relying on sensory data collected with a real robotic agent in a real world scenario. Results show that the cognitive architecture designed for this scenario is able to capture the changes underlying the moving object in the field of view of the robot. The architecture successfully handles the temporal relationship in moving items and manages to show the effects of the embodied attention on word-object mapping
Pore-scale Large Eddy Simulation of Turbulent Flow and Heat Transfer over Porous Media
No full textThis paper investigates turbulent fluid flow and heat transfer over a porous medium in a channel using pore-scale large eddy simulation. Special attention is placed on the exchange of heat and flow between the porous and non-porous regions through the interface between the two regions. For this purpose, two different porous systems made of a packed bed of spheres and rectangular rods are analysed and the results are compared against a solid block case of the same size. Flow visualization shows that a significant portion of the fluid entering the porous blocks leaks from the porous region to the non-porous region through the porous-fluid interface. To discuss the effects of this flow leakage on the flow features and heat transfer, discussions are made regarding velocity, pressure, and temperature fields, as well as coherent structures, and turbulence production. The flow pattern inside the porous region indicates that the flow leakage clogs the pore channels inside the porous medium which induces a significant reduction in the streamwise momentum of the pore flow. In addition, coherent structures show that flow leakage leads to the creation of counter-rotating vortex pairs of fluid flow within and above the porous block that results in the formation of organized hairpin structures. Finally, the comparison of turbulence production for the porous and solid cases together with the onset growth of the Kelvin-Helmholtz instability on the porous-fluid interface show a reduction in turbulent kinetic energy above the leading edge of porous blocks. This observation implies that for the porous cases the transition to turbulence is postponed to the downstream of the porous block and it is not achieved as fast as the solid block