Search

Diatoms are single-celled microalgae with silica-based cell walls (frustules) that are abundantly present in aquatic habitats, and form the basis of the food chain in many ecosystems. Many benthic diatoms have the remarkable ability to glide on all natural or man-made underwater surfaces using a carbohydrate- and protein-based adhesive to generate traction. Previously, three glycoproteins, termed FACs (Frustule Associated Components), have been identified from the common fouling diatom Craspedostauros australis and were implicated in surface adhesion through inhibition studies with a glycan-specific antibody. The polypeptide sequences of FACs remained unknown, and it was unresolved whether the FAC glycoproteins are indeed involved in adhesion, or whether this is achieved by different components sharing the same glycan epitope with FACs. Here we have determined the polypeptide sequences of FACs using peptide mapping by LC-MS/MS. Unexpectedly, FACs share the same polypeptide backbone (termed CaFAP1), which has a domain structure of alternating Cys-rich and Pro-Thr/Ser-rich regions reminiscent of the gel-forming mucins. By developing a genetic transformation system for C. australis, we were able to directly investigate the function of CaFAP1-based glycoproteins in vivo. GFP-tagging of CaFAP1 revealed that it constitutes a coat around all parts of the frustule and is not an integral component of the adhesive. CaFAP1-GFP producing transformants exhibited the same properties as wild type cells regarding surface adhesion and motility speed. Our results demonstrate that FAC glycoproteins are not involved in adhesion and motility, but might rather act as a lubricant to prevent fouling of the diatom surface.

Biological systems are robust to perturbations at both the genetic and environmental levels, although these same perturbations can elicit variation in behaviour. The interplay between functional robustness and behavioural variability is exemplified at the organellar level by the beating of cilia and flagella. Cilia are motile despite wide genetic diversity between and within species, differences in intracellular concentrations of ATP and calcium, and considerable environment fluctuations in temperature and viscosity. At the same time, these perturbations result in a variety of spatio-temporal patterns that span a rich behavioural space. To investigate this behavioural space we analysed the dynamics of isolated cilia from the unicellular algae Chlamydomonas reinhardtii under many different environmental and genetic conditions. We found that, despite large changes in beat frequency and amplitude, the space of waveform shapes is low-dimensional in the sense that two features account for 80% of the observed variation. The geometry of this behavioural space accords with the predictions of a simple mechanochemical model in the low-viscosity regime. This allowed us to associate waveform shape variability with changes in only the curvature response coefficients of the dynein motors.

A detailed experimental study on the aerodynamic performance and noise emission of airfoils and fan blades with permeable leading edges under disturbed inflow conditions was performed. The airfoils...

The advent of electrified propulsion systems for civil aircraft promises not only notable reductions of CO2 and NOx emissions, but also of perceived noise. In an attempt to estimate the noise reduction potential of fully electric aircraft engines, the current study compares the noise generated by classical turboprop and turbofan engines with noise spectra calculated for electrified engines. The calculation is based on published far-field sound pressure level spectra at different noise certification points, which are then modified to account for the absence of combustion-related noise sources. In addition to the overall sound pressure level, changes to the effective perceived noise level are also taken into account. The results clearly show that the electrification of the engine alone will not lead to the notable noise reductions that are required in order to achieve the goals for future aviation set by the European Commission. Instead, continued research is necessary to further reduce noise sources that will continue to be present in novel electrified aircraft systems, such as fan noise and airframe noise.

Dissipative mufflers are often used for the reduction of broadband noise transmitted in ducts. Many common calculation procedures for the transmission loss of such mufflers require conventional shapes like rectangular or circular cross-sectional areas. In an effort to analyze the effect of the cross-sectional area of dissipative mufflers on the resulting noise reduction, the transmission loss of axially uniform mufflers with polygonal cross-sectional areas was investigated using the finite element method. The mufflers are designed to have the same open area, and hence in a practical application would lead to a similar pressure drop. The results were compared to those obtained with the well known approximative method of Piening. Good agreement between simulation and estimation was found regarding basic trends at low frequencies, while notable differences were revealed regarding the maximum transmission loss.

Cilia and flagella are slender cylindrical organelles whose bending waves propel cells through fluids and drive fluids across epithelia. The bending waves are generated by dynein motor proteins, ATPases whose force-generating activity changes over time and with position along the axoneme, the motile structure within the cilium. A key question is: where, in an actively beating axoneme, are the force-generating dyneins located? Answering this question is crucial for determining which of the conformational states adopted by the dynein motors generate the forces that bend the axoneme. The question is difficult to answer because the flagellum contains a large number of dyneins in a complex three-dimensional architecture. To circumvent this complexity, we used a molecular-mechanics approach to show how the bending moments produced by single pairs of dynein motors work against elastic and hydrodynamic forces. By integrating the individual motor activities over the length of the axoneme, we predict the locations of the force-generating dyneins in a beating axoneme. The predicted location depends on the beat frequency, the wavelength, and the elastic and hydrodynamic properties of the axoneme. To test these predictions using cryogenic electron microscopy, cilia with shorter wavelengths, such as found in Chlamydomonas, are more suitable than sperm flagella with longer wavelengths because, in the former, the lag between force and curvature is less dependent on the specific mechanical properties and experimental preparation.

The aerodynamic noise generated by a circular cylinder in a crossflow is a classical problem in aeroacoustics, which can be found in various practical applications, such as parts of the landing gea...

The sparse layouts of radio interferometers result in an incomplete sampling of the sky in Fourier space which leads to artifacts in the reconstructed images. Cleaning these systematic effects is essential for the scientific use of radiointerferometric images. Established reconstruction methods are often time-consuming, require expert-knowledge, and suffer from a lack of reproducibility. We have developed a prototype Deep Learning-based method that generates reproducible images in an expedient fashion. To this end, we take advantage of the efficiency of Convolutional Neural Networks to reconstruct image data from incomplete information in Fourier space. The Neural Network architecture is inspired by super-resolution models that utilize residual blocks. Using simulated data of radio galaxies that are composed of Gaussian components we train Deep Learning models whose reconstruction capability is quantified using various measures. The reconstruction performance is evaluated on clean and noisy input data by comparing the resulting predictions with the true source images. We find that source angles and sizes are well reproduced, while the recovered fluxes show substantial scatter, albeit not worse than existing methods without fine-tuning. Finally, we propose more advanced approaches using Deep Learning that include uncertainty estimates and a concept to analyze larger images., Accepted for publication in Astronomy & Astrophysics

This paper presents an experimental investigation of tip vortex formation noise produced by wall-mounted finite airfoils. Acoustic measurements were taken in the open jet anechoic wind tunn...

Data availability: Data will be made available on request. Copyright © 2022 The Author(s). This paper is a predominantly experimental study into the use of porosity located downstream of an aerofoil leading edge for the reduction of turbulence interaction noise. Locating the porosity downstream of the leading edge has been shown to be beneficial in reducing the aerodynamic performance penalty compared with locating it directly at the leading edge [1], where most of the lift is generated. Noise measurements on a flat plate with downstream porosity are compared against the case of two flat plates in a tandem configuration. In both cases, the noise reduction spectra exhibit peaks of strong noise reduction at non-dimensional frequencies of fld/Uc = n, where ld is the distance between the leading edge and the downstream edge, Uc is the convection velocity and n is an integer. To explain this behaviour requires a mechanism to be present in which a phase shift of 180◦ is introduced in the interaction process. In the paper we argue that the origin of this phase shift is due to secondary vorticity generated at the leading edge. Another key finding of this paper is that overall noise reductions are due to an effective shortening of the chord in which most of the radiation is produced by the section of the flat plate upstream of the porous section, leading to generally weaker radiation. Neither of these mechanisms have been reported previously in the literature. The paper concludes with noise measurements on a thin aerofoil with downstream porosity included, in which overall noise reductions of up to 2.8 dB are achieved. EPSRC (EP/V00686X/1) QUADPORS project; Royal Academy of Engineering (RF\201819 \ 18 \ 194); EPSRC DTP EP/N509620/1; Christ’s College, University of Cambridge; EPSRC Early Career Fellowship EP/P015980/1; Oscar Propulsion; Rolls-Royce.

Otto F. Geyer und Manfred P. Gwinner: Geologie von Baden-Württemberg. 5., völlig neu bearbeitete Auflage, herausgegeben von Matthias Geyer, Edgar Nitsch und Theo Simon. Verlag Schweizerbart Stuttgart 2011. X, 627 Seiten mit 185 teilweise farbigen Abbildungen und 4 Tabellen. Gebunden € 68,–. ISBN 978-3-510-65267-9

The application of a porous coating to a smooth cylinder placed in uniform flow can reduce its vortex shedding tone and overall sound pressure level. The responsible noise generation mechanisms are not fully understood nor has an optimal porous coating type been presented. Structured Porous Coated Cylinders (SPCCs) have been recently investigated as an alternative to randomized porous coated cylinders that use metal foam or polyurethane. SPCCs possess similar noise reduction characteristics to randomized porous coated cylinders, yet their porosity can be modified in circumferential and spanwise directions. An acoustic investigation was conducted in a small anechoic wind tunnel using SPCCs constructed in four spanwise segments, yielding varying spanwise and circumferential porosities. Acoustic signals were recorded using two microphone arc arrays symmetric about the flow axis. Each SPCC revealed a reduced vortex shedding tone, a primary harmonic, and a high frequency broadband contribution. For each SPCC, the vortex shedding tones were weaker than the equivalent bare cylinder shedding tone and presented decreased overall sound pressure level. Variations in circumferential and spanwise porosity were shown to have little effect on tonal noise reduction yet influence high frequency contributions.

This paper is concerned with the flow characteristics and noise generation at the finite wing–wall junction. To characterize junction flow noise, acoustic measurements were taken in the aco...

Microtubule-associated proteins (MAPs) are a functionally highly diverse class of proteins that help to adjust the shape and function of the microtubule cytoskeleton in space and time. For this purpose, MAPs structurally support microtubules, modulate their dynamic instability, or regulate the activity of associated molecular motors. The microtubule-binding domains of MAPs are structurally divergent, but often depend on electrostatic interactions with the negatively charged surface of the microtubule. This suggests that the surface exposure of positive charges rather than a certain structural fold is sufficient for a protein to associate with microtubules. Consistently, positively charged artificial objects have been shown to associate with microtubules and to diffuse along their lattice. Natural MAPs, however, show a more sophisticated functionality beyond lattice-diffusion. Here, we asked whether basic electrostatic interactions are sufficient to also support advanced MAP functionality. To test this hypothesis, we studied simple positively charged peptide sequences for the occurrence of typical MAP-like behavior. We found that a multivalent peptide construct featuring four lysine-alanine heptarepeats (starPEG-(KA7)4)—but not its monovalent KA7-subunits—show advanced, biologically relevant MAP-like behavior: starPEG-(KA7)4 binds microtubules in the low nanomolar range, diffuses along their lattice with the ability to switch between intersecting microtubules, and tracks depolymerizing microtubule ends. Further, starPEG-(KA7)4 promotes microtubule nucleation and growth, mediates depolymerization coupled pulling at plus ends, and bundles microtubules without significantly interfering with other proteins on the microtubule lattice (as exemplified by the motor kinesin-1). Our results show that positive charges and multivalency are sufficient to mimic advanced MAP-like behavior.

Steel sheet metal is important for architecture, for mechanical engineering and vehicle construction due to its various usability and the fact that it is relatively easy to manufacture. When a regular structure is applied to such metal plates, their stiffness can be increased significantly in order to meet higher static requirements while keeping the same mass as an unstructured plate. Therefore, such structured metal plates are often used in lightweight constructions. However, at the same time any structuring of isotropic plates could lead to anisotropic characteristics, which, in turn, will affect the acoustic properties.In the study described in the present paper, the modal behavior of hexagonally structured metal plates was examined, which have been produced via a hydro-forming process. To this end, the eigenfrequencies and the shape of the corresponding eigenmodes were determined both experimentally and via finite element method (FEM). Then, the modal density as well as the driving point mobility obtained from the simulations were analyzed as a measure for the acoustical properties of the structured plates. Thereby, the influence of potential internal stresses due to the hydro-forming process, the effect of an unstructured edge as well as that of the boundary conditions were of particular interest. Keywords: Structured metal sheets, Hydro-forming, Modal analysis

Abstract One known method to reduce vortex shedding from the tip of a blade is the use of end plates or winglets. Although the aerodynamic impact of such end plates has been investigated in the past, no studies exist on the effect of such end plates on the far-field noise. The aeroacoustic noise reduction of three different end-plate geometries is experimentally investigated. The end plates are applied to the free end of a wall-mounted symmetric NACA 0012 airfoil and a cambered NACA 4412 airfoil with an aspect ratio of 2 and natural boundary layer transition. Microphone array measurements are taken in the aeroacoustic open-jet wind tunnel at BTU Cottbus-Senftenberg for chord-based Reynolds numbers between 75,000 and 225,000 and angles of attack from 0$$^\circ$$ ∘ to 30$$^\circ$$ ∘ . The obtained acoustic spectra show a broad frequency hump for the airfoil base configurations at higher angles of attack that is attributed to tip noise. Hot-wire measurements taken for one configuration show that the application of an end plate diffuses the vorticity at the tip. The aeroacoustic noise contribution of the tip can be reduced when the endplates are applied. This reduction is most effective for higher angles of attack, when the tip vortex is the dominant sound source. Graphic abstract

Aerofoil noise reduction is a topic of great interest at the present time and as such many strategies have been presented, in previous literatures whether they are trailing edge serrations, leading edge undulations or porous aerofoils, to name a few. The present study investigates a bio-inspired solution where an array of passive flexible elements, known as flaplets, are extended over the trailing edge of the aerofoil and are allowed to oscillate freely in the flow field. The aerofoil in used in the present study is a NACA 0012 and has been analysed by using both time resolved particle image velocimetry (TR-PIV), in a close circuit wind tunnel, and aeroacoustic measurements in an open jet wind tunnel at moderate chord based Reynolds numbers; ranging from 50,000 to 350,000. The results show a clear reduction in tonal noise with a clear region of maximum noise reduction scaled with \(u_\infty ^\text {1.5}\).

This paper presents an acoustic study of a standard NACA 0012 aerofoil with additional self-oscillating passive flaplets deployed from the trailing edge for self-noise reduction, putting special emphasis on the potential reduction of tonal noise generated by the periodic shedding of vortices from the trailing edge. The flaplets protruding out of the trailing edge act as rectangular thin cantilever beams exited by the surrounding flow to oscillate in their dominant flexural bending mode. The noise attenuation performance is studied for different deployment length, width and inter-spacing to find the most dominant contributions at chord based Reynolds numbers Re c from 100,000 to 900,000 and three geometric angles of attack α g = 0 ° , 10 ° and 15 ° . It was observed that all flaplet configurations oscillate and thereby reduce the tonal noise. The range of the highest noise reduction in the low frequency range scales with the Strouhal number based on chord length, whereby this range can be set specifically by how far the flaplets protrude out of the trailing edge. This determines the free vibrating length and therefore the natural frequency of the oscillators. Laser-based measurements of the flaplet oscillations confirm the occurrence of a lock-in mechanism observed in previous studies, which effectively describes the oscillating flaplets as pacemaker to keep the fundamental instabilities of the flow in their linear state. It is concluded that this contributes mainly to the tonal noise reduction while the more broadband noise reduction stems from the geometry of the flaplets acting as ‘slitted-serrations’. A larger width of the flaplets is most effective in the low-frequency range, while narrower flaplets are best addressing high-frequency noise components. The results further show that a smaller inter-spacing also benefits the noise reduction. The study paves the way for novel morphing techniques to target specific noise ranges during different flight manoeuvres.

An aeroacoustic investigating looking into the effect of changing the inter-spacing of passive self-oscillating trailing edge flaplets has been carried out using a NACA 0012 aerofoil. Clear differences can be observed between each of the different cases. Where a reduction in low frequency noise, an increase in high frequency noise and a reduction in turbulence intensity in the wake can be seen for each case. As the inter-spacing is reduced, the differences become more prominent, when compared to the reference aerofoil.

Abstract The tonal noise generation of a circular cylinder in a uniform flow is an important source of aerodynamic noise. It can be found at parts of the landing gear of airplanes, at pantographs of trains, at antennas and basically all other protruding parts of vehicles. This noise is due to the periodic shedding of vortices along the cylinder span. One method to reduce this noise is the use of flow permeable covers around the cylinders. In the present study, measurements were performed in an aeroacoustic wind tunnel on a large set of porous covered cylinders. In addition to varying the porous material, which is characterized by its air flow resistivity and its porosity, the thickness of the porous layer was varied as well. The measurements were performed at Reynolds numbers between 14,000 and 103,000 using microphones located in the acoustic far field. It was found that the porous covers lead to a notable narrowing of the vortex shedding tonal peak in the sound pressure level spectra, an effect that increases with increasing porosity and thickness and decreasing air flow resistivity of the porous layer. Based on the large set of experimental data, basic trends were derived for the estimation of the vortex shedding Strouhal number and the reduction in the energy in the vortex shedding peak using the method of linear regression. Constant temperature anemometry measurements in the wake of selected cylinders basically showed a similar narrowing of the vortex shedding peak in the spectra of the turbulent velocity fluctuations. In addition, the measurement of wake profiles showed a reduction in the mean velocity and the turbulence in the wake as well as a widening of the wake region, while an analysis of the spanwise coherence revealed that the cause of the overall noise reduction is not a breakup of spanwise turbulent structures. Rather, the results imply that viscous damping of turbulent flow pressure amplitudes by the porous material strongly contributes to the noise reduction. Graphic abstract

Airfoil tip vortex formation noise is a significant noise source in many aerodynamic applications such as aircraft, fans, rotors and propellers. The data collection presented in this paper examines the effects of sinusoidal geometry and porosity on the tip vortex formation noise produced by finite length airfoils. The use of serrated and porous materials is inspired by silent owl-wings and is a promising approach to control flow-induced noise. Noise measurements have been taken using a 47-channel planar microphone array in the anechoic wind tunnel at the Brandenburg University of Technology. Over 2600 unique test cases with variations in sinusoidal tip geometry (amplitude and wavelength) and flat tip porosity were measured during the experimental campaign for a NACA0012 and NACA614 airfoil. The microphone data have been processed using acoustic beamforming software named Acoular to produce one-third-octave band tip noise spectra.

The interaction of a turbulent flow with the leading edge of a blade is a main noise source mechanism for fans and wind turbines. Motivated by the silent flight of owls, the present paper describes an experimental study performed to explore the noise-reducing effect of comb-like extensions, which are fixed to the leading edge of a low-speed airfoil. The measurements took place in an aeroacoustic wind tunnel using the microphone array technique, while the aerodynamic performance of the modified airfoils was captured simultaneously. It was found that the comb structures lead to a noise reduction at low frequencies, while the noise at high frequencies slightly increases. The most likely reasons for this frequency shift are that the teeth of the combs break up large incoming turbulent eddies into smaller ones or that they shift turbulent eddies away from the airfoil surface, thereby reducing pressure fluctuations acting on the airfoil. The aerodynamic performance does not change significantly.