An experimental study of airfoil instability tonal noise with trailing edge serrations

This paper presents an experimental study of the effect of trailing edge serrations on airfoil instability noise. Detailed aeroacoustic measurements are presented of the noise radiated by an NACA-0012 airfoil with trailing edge serrations in a low to moderate speed flow under acoustical free field conditions. The existence of a separated boundary layer near the trailing edge of the airfoil at an angle of attack of 4.2 degree has been experimentally identified by a surface mounted hot-film arrays technique. Hot-wire results have shown that the saw-tooth surface can trigger a bypass transition and prevent the boundary layer from becoming separated. Without the separated boundary layer to act as an amplifier for the incoming Tollmien-Schlichting waves, the intensity and spectral characteristic of the radiated tonal noise can be affected depending upon the serration geometry. Particle Imaging Velocimetry (PIV) measurements of the airfoil wakes for a straight and serrated trailing edge are also reported in this paper. These measurements show that localized normal-component velocity fluctuations that are present in a small region of the wake from the laminar airfoil become weakened once serrations are introduced. Owing to the above unique characteristics of the serrated trailing edges, we are able to further investigate the mechanisms of airfoil instability tonal noise with special emphasis on the assessment of the wake and non-wake based aeroacoustic feedback model. It has been shown that the instability tonal noise generated at an angle of attack below approximately one degree could involve several complex mechanisms. On the other hand, the non-wake based aeroacoustic feedback mechanism alone is sufficient to predict all discrete tone frequencies accurately when the airfoil is at a moderate angle of attack

Similarity measures for mid-surface quality evaluation

Mid-surface models are widely used in engineering analysis to simplify the analysis of thin-walled parts, but it can be difficult to ensure that the mid-surface model is representative of the solid part from which it was generated. This paper proposes two similarity measures that can be used to evaluate the quality of a mid-surface model by comparing it to a solid model of the same part. Two similarity measures are proposed; firstly a geometric similarity evaluation technique based on the Hausdorff distance and secondly a topological similarity evaluation method which uses geometry graph attributes as the basis for comparison. Both measures are able to provide local and global similarity evaluation for the models. The proposed methods have been implemented in a software demonstrator and tested on a selection of representative models. They have been found to be effective for identifying geometric and topological errors in mid-surface models and are applicable to a wide range of practical thin-walled designs

Observer-based networked control for continuous-time systems with random sensor delays

This is the post print version of the article. The official published version can be obtained from the link - Copyright 2009 Elsevier LtdThis paper is concerned with the networked control system design for continuous-time systems with random measurement, where the measurement channel is assumed to subject to random sensor delay. A design scheme for the observer-based output feedback controller is proposed to render the closed-loop networked system exponentially mean-square stable with H∞ performance requirement. The technique employed is based on appropriate delay systems approach combined with a matrix variable decoupling technique. The design method is fulfilled through solving linear matrix inequalities. A numerical example is used to verify the effectiveness and the merits of the present results.This paper was not presented at any IFAC meeting. This paper was recommended for publication in revised form by Associate Editor George Yin under the direction of Editor Ian R. Petersen. This work was supported in part by the Royal Society of the UK, the National Natural Science Foundation of China (60774047, 60674055) and the Taishan Scholar Programs Foundation of Shandong Province, China

3D thermal analysis of a permanent magnet motor with cooling fans

Overheating of permanent magnet (PM) machines has become a major technical challenge as it gives rise to magnet demagnetization, degradation of insulation materials, and loss of motor efficiency. This paper proposes a state-of-the-art cooling system for an axial flux permanent magnet (AFPM) machine with the focus on its structural optimization. A computational fluid dynamics (CFD) simulation with thermal consideration has been shown to be an efficient approach in the literature and is thus employed in this work. Meanwhile, a simplified numerical approach to the AFPM machine with complex configuration in 3D consisting of conduction, forced convection, and conjugate heat transfer is taken as a case study. Different simplification methods (including configuration and working conditions) and two optimized fans for forced convection cooling are designed and installed on the AFPM machine and compared to a natural convection cooling system. The results show that the proposed approach is effective for analyzing the thermal performance of a complex AFPM machine and strikes a balance between reasonable simplification, accuracy, and computational resource

The Microglial Sensome Revealed by Direct RNA Sequencing

Microglia, the principal neuroimmune sentinels of the brain, continuously sense changes in their environment and respond to invading pathogens, toxins and cellular debris. Microglia exhibit plasticity and can assume neurotoxic or neuroprotective priming states that determine their responses to danger. We used direct RNA sequencing, without amplification or cDNA synthesis, to determine the quantitative transcriptomes of microglia of healthy adult and aged mice. We validated our findings by fluorescent dual in-situ hybridization, unbiased proteomic analysis and quantitative PCR. We report here that microglia have a distinct transcriptomic signature and express a unique cluster of transcripts encoding proteins for sensing endogenous ligands and microbes that we term the “sensome”. With aging, sensome transcripts for endogenous ligand recognition are downregulated, whereas those involved in microbe recognition and host defense are upregulated. In addition, aging is associated with an overall increase in expression of microglial genes involved in neuroprotection

A review of size and geometrical factors influencing resonant frequencies in metamaterials

Although metamaterials and so-called left-handed media have originated from theoretical considerations, it is only by their practical fabrication and the measurement of their properties that they have gained credibility and can fulfil the potential of their predicted properties. In this review we consider some of the more generally applicable fabrication methods and changes in geometry as they have progressed, exhibiting resonant frequencies ranging from radio waves to the visible optical region

The 1.24–1.21 Ga Licheng large igneous province in the North China Craton: Implications for paleogeographic reconstruction

Detailed geochronological, geochemical, and paleomagnetic studies of mafic dyke swarms, often associated with mantle plumes, can provide unique constraints on paleogeographic reconstructions. Mafic dykes with baddeleyite U-Pb ages of 1,233 27 Ma (SIMS), 1,206.7 1.7 Ma (TIMS), 1,214.0 4.9 Ma (TIMS), and 1,236.3 5.4 Ma (TIMS) have been identified in the eastern North China Craton. Geochemical data indicate subalkaline to alkaline basalt compositions with OIB-like trace element signatures and an intraplate tectonic setting. In addition to these geochemical signatures, the radiating geometry of these dykes also suggests a 1.24-1.21 Ga large igneous province caused by a mantle plume event. A new similar to 1.24 Ga paleomagnetic pole at 2.0 degrees N, 165.1 degrees E, A(95) = 11.0 degrees, N = 9 and an similar to 1.21 Ga VGP at -23.0 degrees N, 92.5 degrees E, dp/dm = 4.7 degrees/7.8 degrees have been obtained from these dykes, with the 1.24 Ga pole supported by positive baked contact test. Our paleomagnetic analyses suggest that the North China Craton and the proto-Australian continent could have been separated by 1.24-1.21 Ga from an established Nuna connection at ca. 1.32 Ga. By comparison with Laurentia paleopoles, we present the paleogeography of dispersing North China, proto-Australian, and Laurentia cratons in the late Mesoproterozoic during the breakup of the supercontinent Nuna.Peer reviewe

Transition to adult care of young people with congenital heart disease: Impact of a service on knowledge and self-care skills, and correlates of a successful transition

Aims Less than one-third of adolescents with congenital heart disease (CHD) successfully transition to adult care, missing out on education of their cardiac condition, and risking loss to follow-up. We assessed the efficacy of our transition clinic on patient education and empowerment and identified correlates of successful transition. Methods and results Overall, 592 patients were seen at least once in our transition service between 2015 and 2022 (age 15.2 ± 1.8 years, 47.5% female). Most adolescents (53%) had moderate CHD, followed by simple (27.9%) and severe (19.1%) CHD. Learning disability (LD) was present in 18.9% and physical disability (PD) in 4.7%. In patients without LD, knowledge of their cardiac condition improved significantly from the first to the second visit (naming their condition: from 20 to 52.3%, P 0.05). Treatment adherence and management involvement, self-reported anxiety, and dental care awareness did not change over time. Successful transition (attendance of ≥ 2 clinics) was achieved in 49.3%. Younger age at the first visit, simpler CHD, and absence of PD were associated with successful transition. Conclusion A transition service positively impacts on patient education and empowerment in most CHD adolescents transitioning to adult care. Strategies to promote a tailored support for patients with LD should be sought, and earlier engagement should be encouraged to minimize follow-up losses

Host Suitability of a Gregarious Parasitoid on Beetle Hosts: Flexibility between Fitness of Adult and Offspring

Behavioral tactics play a crucial role in the evolution of species and are likely to be found in host-parasitoid interactions where host quality may differ between host developmental stages. We investigated foraging decisions, parasitism and related fitness in a gregarious ectoparasitoid, Sclerodermus harmandi in relation to two distinct host developmental stages: larvae and pupae. Two colonies of parasitoids were reared on larvae of Monochamus alternatus and Saperda populnea (Cerambycidae: Lamiinae). Paired-choice and non-choice experiments were used to evaluate the preference and performance of S. harmandi on larvae and pupae of the two species. Foraging decisions and offspring fitness-related consequences of S. harmandi led to the selection of the most profitable host stage for parasitoid development. Adult females from the two colonies oviposited more quickly on pupae as compared to larvae of M. alternatus. Subsequently, their offspring development time was faster and they gained higher body weight on the pupal hosts. This study demonstrates optimal foraging of intraspecific détente that can occur during host-parasitoid interactions, of which the quality of the parasitism (highest fitness benefit and profitability) is related to the host developmental stage utilized. We conclude that S. harmandi is able to perfectly discriminate among host species or stages in a manner that maximizes its offspring fitness. The results indicated that foraging potential of adults may not be driven by its maternal effects, also induced flexibly with encountering prior host quality