Rapid adaptive evolution of colour vision in the threespine stickleback radiation.

Vision is a sensory modality of fundamental importance for many animals, aiding in foraging, detection of predators and mate choice. Adaptation to local ambient light conditions is thought to be commonplace, and a match between spectral sensitivity and light spectrum is predicted. We use opsin gene expression to test for local adaptation and matching of spectral sensitivity in multiple independent lake populations of threespine stickleback populations derived since the last ice age from an ancestral marine form. We show that sensitivity across the visual spectrum is shifted repeatedly towards longer wavelengths in freshwater compared with the ancestral marine form. Laboratory rearing suggests that this shift is largely genetically based. Using a new metric, we found that the magnitude of shift in spectral sensitivity in each population corresponds strongly to the transition in the availability of different wavelengths of light between the marine and lake environments. We also found evidence of local adaptation by sympatric benthic and limnetic ecotypes to different light environments within lakes. Our findings indicate rapid parallel evolution of the visual system to altered light conditions. The changes have not, however, yielded a close matching of spectrum-wide sensitivity to wavelength availability, for reasons we discuss

Noise Control Concept Verification for a Ducted Fan System

The noise level of consumer products is a growing concern for manufacturers since customers’ product sound quality expectations are increasing. The product that motivated the present work was a “bladeless” fan in which the rotor and stator module were located in the base of the unit. Direct intensity measurements were used to characterize the fan’s acoustical output, which was found to radiate primarily from the air inlet beneath the rotor in the base unit. The noise control design concept explored here is based on the dipole characteristic of axial fans. It has been shown previously that when only one side of the fan is connected to the exterior sound field, the radiation is monopole-like. But, by exposing both sides of the dipole to the exterior field, the radiation efficiency of the source is reduced, and hence the sound power is reduced compared to a situation in which only one side of the fan connects with the exterior field. That concept is applicable not just to the bladeless fan investigated in this work, but could also find application in other ducted fan systems. The monopole-to-dipole source conversion approach is demonstrated here both numerically and experimentally based on a simplified model of the fan base unit

A Desktop Procedure for Measuring the Transmission Loss of Automotive Door Seals

Due to the increasing concern with the acoustic environment within automotive vehicles, there is an interest in measuring the acoustical properties of automotive door seals. These systems play an important role in blocking external noise sources, such as aerodynamic noise and tire noise, from entering the passenger compartment. Thus, it is important to be able to conveniently measure their acoustic performance. Previous methods of measuring the ability of seals to block sound required the use of either a reverberation chamber, or a wind tunnel with a special purpose chamber attached to it. That is, these methods required the use of large and expensive facilities. A simpler and more economical desktop procedure is thus needed to allow easy and fast acoustic measurement of automotive door seals. In the present work, a desktop, four-microphone, square cross-section standing wave tube was modified by the addition of a new sample holder to make it possible to measure the transmission loss of door seals under various states of compression. In this new procedure, the sample is clamped between a sliding piston and one wall of the standing wave tube. Since the clamp partially blocks the channel, thus impacting the measured transmission loss, a correction is necessary to determine the transmission loss of the seal by itself. Therefore, an initial set of measurements was performed to identify the correction factor required to adjust the measured transmission loss of the clamp plus seal to eliminate the contribution of the clamp itself. Once the accuracy of the correction procedure was verified, a number of typical door seals were tested at various degrees of compression. The transmission losses of the seals were generally in excess of 30 dB, and the transmission loss was found to increase significantly as the seals were compressed. The latter point, in particular, indicates that careful design of the seal mounting arrangements in the vehicle is crucial to ensuring their optimal performance

Bisecting binomial coefficients

In this paper, we deal with the problem of bisecting binomial coefficients. We find many (previously unknown) infinite classes of integers which admit nontrivial bisections, and a class with only trivial bisections. As a byproduct of this last construction, we show conjectures Q2 and Q4 of Cusick and Li [7]. We next find several bounds for the number of nontrivial bisections and further compute (using a supercomputer) the exact number of such bisections for n ≤ 51

Near-Field Acoustical Holography Incorporating Compressive Sensing

To identify sound source locations by using Near-field Acoustical Holography (NAH), a large number of microphone measurements is generally required in order to cover the source region and to ensure a sufficiently high spatial sampling rate. It may be the case that hundreds of microphones are required, so such measurements are economically expensive, which has limited the industrial application of NAH to the identification of sound source locations. Recently, however, it has been shown possible to identify concentrated sound sources with a limited number of microphone measurements based on Compressive Sampling theory. In the present work, a loudspeaker was used as a sound source and a near-field intensity scan was conducted to measure the true sound field and sound power generated by the loudspeaker. Then by using exactly the same measured data, four NAH methods were used to reconstruct the sound field: i.e., Statistically Optimized Near-Field Acoustical Holography (SONAH), Wideband Holography (WBH), l1-norm minimization and a hybrid compressive sampling method. The number of microphone measurements used to reconstruct the sound field was decreased systematically by increasing the spacing between microphones. Then the reconstruction results were compared with the measured intensity results, and the benefits of the compressive sensing are illustrated

Source Identification of a Bladeless Fan by using SONAH in Cylindrical Coordinates

Near-field acoustical holography (NAH) is conventionally used to visualize sound fields in a three-dimensional space based on sound pressure measurements conducted on a surface close to a noise source. Traditional Fourier-based acoustical holography procedures require the use of a large microphone array setup to avoid spatial truncation effects: that means it is necessary that the array be large enough so that the sound pressure level measured at the edges of the array is significantly lower than that at the peak locations. To avoid the need to use large microphone arrays, a method referred to as statistically optimized near-field acoustical holography (SONAH), was proposed by Steiner and Hald, initially in planar coordinates. In that method, an extension of the measurement surface well beyond the actual source surface is not necessary since the projected sound field is calculated by using a transfer matrix defined in such a way such the propagating waves and evanescent waves are optimally represented. In the current work, the development of SONAH in cylindrical coordinates as formulated by Cho, Bolton, and Hald is first reviewed and is then applied to the observation of the sound field generated by a bladeless fan. It will be shown that the noise source locations can be clearly identified at significant frequencies by using this procedure, and that a knowledge of the source locations makes it possible to suggest effective noise control solutions targeted at specific frequencies