Implementation and analysis of an adaptive multilevel Monte Carlo algorithm

We present an adaptive multilevel Monte Carlo (MLMC) method for weak approximations of solutions to Itô stochastic differential equations (SDE). The work [Oper. Res. 56 (2008), 607-617] proposed and analyzed an MLMC method based on a hierarchy of uniform time discretizations and control variates to reduce the computational effort required by a single level Euler-Maruyama Monte Carlo method from ( TOL -3 )${{{\mathcal {O}}({\mathrm {TOL}}^{-3})}}$ to ( TOL -2 log( TOL -1 ) 2 )${{{\mathcal {O}}({\mathrm {TOL}}^{-2}\log ({\mathrm {TOL}}^{-1})^{2})}}$ for a mean square error of ( TOL 2 )${{{\mathcal {O}}({\mathrm {TOL}}^2)}}$ . Later, the work [Lect. Notes Comput. Sci. Eng. 82, Springer-Verlag, Berlin (2012), 217-234] presented an MLMC method using a hierarchy of adaptively refined, non-uniform time discretizations, and, as such, it may be considered a generalization of the uniform time discretization MLMC method. This work improves the adaptive MLMC algorithms presented in [Lect. Notes Comput. Sci. Eng. 82, Springer-Verlag, Berlin (2012), 217-234] and it also provides mathematical analysis of the improved algorithms. In particular, we show that under some assumptions our adaptive MLMC algorithms are asymptotically accurate and essentially have the correct complexity but with improved control of the complexity constant factor in the asymptotic analysis. Numerical tests include one case with singular drift and one with stopped diffusion, where the complexity of a uniform single level method is ( TOL -4 )${{{\mathcal {O}}({\mathrm {TOL}}^{-4})}}$ . For both these cases the results confirm the theory, exhibiting savings in the computational cost for achieving the accuracy ( TOL )${{{\mathcal {O}}({\mathrm {TOL}})}}$ from ( TOL -3 )${{{\mathcal {O}}({\mathrm {TOL}}^{-3})}}$ for the adaptive single level algorithm to essentially ( TOL -2 log( TOL -1 ) 2 )${{{\mathcal {O}}({\mathrm {TOL}}^{-2}\log ({\mathrm {TOL}}^{-1})^2)}}$ for the adaptive MLMC algorith

Selection of Flapper Valve Steel for High Efficient Compressor

Due to the environmental, energy saving and economic requirements, development of very high efficient compressors is of great importance. Consequently, flapper valve material becomes a critical issue and a limiting factor for the development of compressor. This paper provides a discussion on the material selection of the flapper valve for the compressors with very high efficiency, based mainly on a basic research on the mechanisms of impact fatigue and a FEM simulation on the formation of stress concentration in the flapper valve during the impact process. Impact fatigue initiation is caused by the initial impact stress, but the fatigue crack propagation is caused by a wavy stress propagation. This causes the formation of secondary cracks at the stress concentration points where two stress waves have the same phase. The results indicate that the flapper valve materials for the very high efficient compressors should have both high impact fatigue strength for the initial stress, and high stress damping capacity to reduce the crack propagation rate. Most recent developed flapper valve steel, Sandvik Hiflex™, shows both higher impact fatigue strength and higher damping capacity comparing with other commercial flapper valve steels available. This flapper valve steel material has successfully been used in the newly developed high efficient compressors recently. Some case stories have been discussed

A New Alloy for High Performance Valve Steel for High Efficiency Compressors

In 2018 the International Energy Association IEA reported that air conditioning will be a major contributor for future electricity consumption (Birol, F. 2018). As recently seen in China, tougher legislation on energy efficiency for air conditioning and refrigeration is being introduced all the time. It is therefore crucial that new compressor models perform at the highest levels in terms of efficiency to reduce global energy consumption. The prerequisites to fulfill this legislation vary for the different applications such as rotary, reciprocating, scroll and linear compressors. However, to succeed in developing more energy efficient compressors, the ability to improve the performance of the flapper valves will play an important role. Furthermore, the current commercial alloys available for flapper valves may not be sufficient to meet these increasing demands. In the past, to improve the material fatigue properties, the development of high-performance flapper valve material has been focused around optimizing the metallurgical cleanliness, microstructure, surface finish and mechanical properties. Now research has been completed to develop a new alloy composition aiming to develop a material with further improved fatigue properties for flapper valve applications. The results from internal and external testing of the new alloy show significantly improved fatigue properties. Within this paper, some of the critical properties of the new alloy are presented and the test results are compared with other existing flapper valve steels on the market

Risk assessment on import of Australian redclaw crayfish to Norway. Opinion of the Panel on Animal Health and Welfare of the Norwegian Scientific Committee for Food Safety

Source at https://vkm.no/english/riskassessments/allpublications/assessmentofriskstoanimalhealthandbiodiversityfromimportandfarmingofaustralianredclawcrayfish.4.2375207615dac0245aee2789.html.Main message: It seems unlikely that the Australian red claw clayfish will establish reproductive populations under Norwegian climate conditions, but hitchhiker organisms and infectious agents could potentially follow the import, and unless managed, may pose risks to biodiversity and aquatic animal health. This is the conclusion in a risk assessment from the Norwegian Scientific Committee for Food Safety (VKM)

Risk assessment on import of Australian redclaw crayfish to Norway. Opinion of the Panel on Animal Health and Welfare of the Norwegian Scientific Committee for Food Safety

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Circulating markers of extracellular matrix remodelling in severe COVID-19 patients

Background Abnormal remodelling of the extracellular matrix (ECM) has generally been linked to pulmonary inflammation and fibrosis and may also play a role in the pathogenesis of severe COVID-19. To further elucidate the role of ECM remodelling and excessive fibrogenesis in severe COVID-19, we examined circulating levels of mediators involved in various aspects of these processes in COVID-19 patients. Methods Serial blood samples were obtained from two cohorts of hospitalised COVID-19 patients (n = 414). Circulating levels of ECM remodelling mediators were quantified by enzyme immunoassays in samples collected during hospitalisation and at 3-month follow-up. Samples were related to disease severity (respiratory failure and/or treatment at the intensive care unit), 60-day total mortality and pulmonary pathology after 3-months. We also evaluated the direct effect of inactivated SARS-CoV-2 on the release of the different ECM mediators in relevant cell lines. Results Several of the measured markers were associated with adverse outcomes, notably osteopontin (OPN), S100 calcium-binding protein A12 and YKL-40 were associated with disease severity and mortality. High levels of ECM mediators during hospitalisation were associated with computed tomography thorax pathology after 3-months. Some markers (i.e. growth differential factor 15, galectin 3 and matrix metalloproteinase 9) were released from various relevant cell lines (i.e. macrophages and lung cell lines) in vitro after exposure to inactivated SARS-CoV-2 suggesting a direct link between these mediators and the causal agent of COVID-19. Conclusion Our findings highlight changes to ECM remodelling and particularly a possible role of OPN, S100A12 and YKL-40 in the pathogenesis of severe COVID-19