Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’ polysaccharides

Dreischmeier K, Budke C, Wiehemeier L, Kottke T, Koop T. Boreal pollen contain ice-nucleating as well as ice-binding ‘antifreeze’ polysaccharides. Scientific Reports. 2017;7(1): 41890.Ice nucleation and growth is an important and widespread environmental process. Accordingly, nature has developed means to either promote or inhibit ice crystal formation, for example ice-nucleating proteins in bacteria or ice-binding antifreeze proteins in polar fish. Recently, it was found that birch pollen release ice-nucleating macromolecules when suspended in water. Here we show that birch pollen washing water exhibits also ice-binding properties such as ice shaping and ice recrystallization inhibition, similar to antifreeze proteins. We present spectroscopic evidence that both the ice-nucleating as well as the ice-binding molecules are polysaccharides bearing carboxylate groups. The spectra suggest that both polysaccharides consist of very similar chemical moieties, but centrifugal filtration indicates differences in molecular size: ice nucleation occurs only in the supernatant of a 100 kDa filter, while ice shaping is strongly enhanced in the filtrate. This finding may suggest that the larger ice-nucleating polysaccharides consist of clusters of the smaller ice-binding polysaccharides, or that the latter are fragments of the ice-nucleating polysaccharides. Finally, similar polysaccharides released from pine and alder pollen also display both ice-nucleating as well as ice-binding ability, suggesting a common mechanism of interaction with ice among several boreal pollen with implications for atmospheric processes and antifreeze protection

Comparative regulomics supports pervasive selection on gene dosage following whole genome duplication

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Array Measurements in Wind Tunnels with open Test Sections

Acoustically optimized wind tunnels usually have an anechoic chamber around an open test section. For array measurements in this type of tunnels the acoustic array is typically placed outside the flow field - beside or above the test section. The sound emitted from sources in the flow has to propagate through a turbulent shear layer to reach the microphones. During their passage through the shear layer the sound waves interact with turbulent structures. The higher the frequency of the wave, the more significant the effect of the shear layer is. In the present paper these interaction of sound waves with a turbulent shear layer is investigated. It is analyzed which effects can occur when sound waves propagate through a turbulent shear layer and how these effects can influence the results of array measurements. Experiments with a test source in a wind tunnel with open test section are performed. It is shown that turbulent structures in the shear layer lead to systematic phase fluctuations. These phase fluctuations have a certain spectrum and a distinct spatial correlation. Beside these effects the spectral broadening of tones due to the propagation trough the shear layer is investigated

Schallquellenlokalisation mit Mikrofonarrays in Windkanälen

Microphone-Arrays have been widely used to localize and quantify aeroacoustic sound-sources in wind-tunnel tests during the last years. Especially in the field of aircraft noise they are often applied to wind tunnel measurements in closed test-sections in order to detect dominant airframe noise sources. These wind tunnels usually have a very good characteristic in terms of aerodynamics but are very noisy in return. Microphone array measurements in these non-acoustic test facilities are challenging and require special hardware and data analysis. In the lecture the setup of a microphone array measurement in a closed test-section wind-tunnel will be described to exemplify the main challenges in this kind of measurements including wind-tunnel background noise, array self-noise and limited spatial resolution. In addition, recent developments with respect to high Reynolds number measurements will be presented