Aeroacoustics of musical instruments

Musical sound can be generated from numerical solutions obtained from simple physical models of wind-instruments. We call such synthesizers virtual instruments. Crude caricatures capture the global oscillation behaviour of original instruments, providing the musician with a means of expression comparable to that obtained when playing real instruments. Music is, however, produced by details of the flow which correspond to much smaller temporal and spatial scales than the control of the global oscillation. This suggests that one has to split the physical model into two distinct parts: a simple numerical oscillator followed by a complex sound production module, driven by the output of the first module. We illustrate the background of this idea by a discussion of the clarinet, the human voice, and the trombone.General invited lecture presented by A. Hirschberg at the 12th Italian Congress on Theoretical and Applied Mechanics AIMETA '95, Napoli, 3–6 October 1995.     

Sialic acid uptake by BHK cells and subsequent incorporation into glycoproteins and glycolipids

BHK cells can be grown in the presence of growth medium to which radiolabeled sialic acid has been added. After 24 h, 85 percent of the radioactivity in the cells is covalently bound to glycoproteins and glycolipids. No metabolism of the radiolabeled sialic acid could be detected.     

Whistling of a pipe system with multiple side branches: Comparison with corrugated pipes

Corrugated pipes are widely used because they combine local rigidity with global flexibility. Whistling induced by flow through such pipes can lead to serious environmental and structural problems. The whistling of a multiple side branch system is compared to the whistling behavior of corrugated pipes. The study has been restricted to cavities with sharp edges which are convenient for theoretical modeling. The side branch depth is chosen to be equal to the side branch diameter, which corresponds to cavity geometries in typical corrugated pipes. The low frequency resonance modes of the multiple side branch system have been predicted by means of acoustic models, of which the validity has been tested experimentally. Several experiments have been carried out for characterizing the whistling behavior of the system. While the behavior of a multiple side branch system is interesting on its own it can be compared to that of corrugated pipes. These experiments show that the multiple side branch system is in many aspects a reasonable model for corrugated pipes. Advantage of the multiple side branch system is that it is an experimental setup allowing easy modification of cavity depth. We used this feature to identify the pressure nodes of the acoustic standing wave along the main pipe as the regions where sound is produced. This contradicts recent publications on corrugated pipes. Another interesting aspects is that the system appears to whistle at the second hydrodynamic mode of the cavities rather than at the first hydrodynamic mode. A prediction model for the whistling behavior is proposed, consisting of an energy balance, based on the vortex sound theory. The model predicts the observed Strouhal number but overestimates the acoustic fluctuation amplitude by a factor four.     

Spurious counts in gas volume flow measurements by means of turbine meters

Acoustical oscillations can induce a rotation of a turbine flow meter in the absence of main flow, which leads to spurious counts. A simplified model is presented which explains the occurrence of spurious counts in the limit of very thin turbine blades and high Strouhal numbers. The predicted threshold for the occurrence of spurious counts is compared to experimentally obtained data at various gas pressures in the range from 1 to 8 bar. The simplified model provides a reasonable prediction of the occurrence of spurious counts and can be used as an useful engineering tool in the prediction of the occurrence of spurious counts.     

Helical supramolecular aggregates based on ureidopyrimidinone quadruple hydrogen bonding

A series of mono- and bifunctional compounds 2-7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepared to study the mode of aggregation of these compounds in the bulk and in solution. Compounds 2-7 exhibit thermotropic liquid crystalline properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (D(ho)) phase of 2 a was confirmed by X-ray diffraction on an aligned sample. In chloroform, the bifunctional compounds form cyclic dimers at millimolar concentrations, and these dimers exist in equilibrium with linear species above a critical concentration, which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. Circular dichroism measurements in chloroform did not show a Cotton effect. Dodecane solutions of compounds 3, 4 b, and 7 b display a Cotton effect at the absorption band of the phenyl-pyrimidinone unit. Amplification of chirality was observed in mixtures of 7 a and 7 b, but not in mixtures of 4 a and 4 b, indicating that 7 a and 7 b form mixed polymeric aggregates with a helical architecture in dodecane solution, whereas 4 a and 4 b do not. The Cotton effect is lost upon increasing the temperature. Half of the helicity is lost at 25 degrees C for 3 and at 60 degrees C for 4 b, suggesting that 3, bearing the shorter spacer, forms less stable columns than 4 b. Compound 7 b loses half of its helicity at 45 degrees C. Compounds 2 b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effects.     

Polyvalent perfluoroorgano- and selected polyfluoroorgano-halogen(III and V) compounds

This review compiles important aspects of the chemistry of polyvalent perfluoroorganohalogen(III and V) compounds of the last three decades and reports on distinctions which are worth mentioning in comparison with non-fluorinated polyvalent organohalogen(III and V) analogues. Besides general synthetic paths to neutral (R_FHalX₂, (R_F)₂IX, (R_F)₃I, and R_FHalX₄), cationic ([R_F(R′)Hal]Y and [R_F(R′)HalF₂]Y), and anionic (M[R_FHalX₃] and M[(R_F)₂HalX₂]) derivatives of iodine and bromine, transformations at the halogen centre of those polyvalent compounds and selected applications and their use as reagents are referred. Trends of ¹⁹F and ¹³C NMR spectroscopic properties of prototypes of polyvalent perfluoroorgano-iodine and -bromine compounds are compiled and interpreted. Structural features of characteristic perfluoroalkyl-, pentafluorophenyliodine(III and V), and few -bromine(III) compounds are presented and compared.     

Zigzag and varicose instabilities of a localized stripe

A localized stripe solution to a reaction-diffusion equation can lose stability simultaneously to zigzag and varicose perturbations at a codimension-two point. The resulting mode interaction is described by O(2)xZ(2) equivariant amplitude equations. Stationary mixed-mode solutions are found which can undergo instabilities to breathing modes or to patterns which travel along the stripe.