Forward masking in a bottlenose dolphin Tursiops truncatus : Dependence on azimuthal positions of the masker and test sources

Forward masking was investigated by the auditory evoked potentials (AEP) method in a bottlenose dolphin Tursiops truncatus using stimulation by two successive acoustic pulses (the masker and test) projected from spatially separated sources. The positions of the two sound sources either coincided with or were symmetrical relative to the head axis at azimuths from 0 to ±90°. AEPs were recorded either from the vertex or from the lateral head surface next to the auditory meatus. In the last case, the test source was ipsilateral to the recording side, whereas the masker source was either ipsi- or contralateral. For lateral recording, AEP release from masking (recovery) was slower for the ipsi- than for the contralateral masker source position. For vertex recording, AEP recovery was equal both for the coinciding positions of the masker and test sources and for their symmetrical positions relative to the head axis. The data indicate that at higher levels of the auditory system of the dolphin, binaural convergence makes the forward masking nearly equal for ipsi- and contralateral positions of the masker and test.

Optimal Passive Source Localization for Acoustic Emissions

Acoustic emission is a non-destructive testing method where sensors monitor an area of a structure to detect and localize passive sources of elastic waves such as expanding cracks. Passive source localization methods based on times of arrival (TOAs) use TOAs estimated from the noisy signals received by the sensors to estimate the source position. In this work, we derive the probability distribution of TOAs assuming they were obtained by the fixed threshold technique—a popular low-complexity TOA estimation technique—and show that, if the sampling rate is high enough, TOAs can be approximated by a random variable distributed according to a mixture of Gaussian distributions, which reduces to a Gaussian in the low noise regime. The optimal source position estimator is derived assuming the parameters of the mixture are known, in which case its MSE matches the Cramér–Rao lower bound, and an algorithm to estimate the mixture parameters from noisy signals is presented. We also show that the fixed threshold technique produces biased time differences of arrival (TDOAs) and propose a modification of this method to remove the bias. The proposed source position estimator is validated in simulation using biased and unbiased TDOAs, performing better than other TOA-based passive source localization methods in most scenarios.

Effect of the Sound Source Position Error on Distribution Characteristics of Underwater Shock Wave Bunching Sound Field

Curved reflection bunching technique of underwater plasma sound source (UPSS) uses the geometric characteristics of the curved reflector to reflect and bunching intense sound shock wave, so the center position error of the sound source is one of the important factors affecting the bunching performance of the shock wave. In this paper, the cause of the sound source position error is analyzed in detail, and nonlinear finite element software ANSYS/LS-DYNA (dynamic analysis software developed by LSTC) is used to establish the model of the shock wave bunching sound field. Through numerical simulations, the shock wave bunching sound field distribution characteristics under the influence of different position errors are comprehensively simulated, and the bunching performance of the shock wave and its influence law are deeply analyzed according to the simulation results. It provides guidance for reasonably controlling the machining error and installation error of the reflector and discharge electrode, estimating the effective discharge times of the discharge electrode, and formulating the design process.

Re-examining the New Product Paradox: How Innovation Ambidexterity Mediates the Market Orientation and New Product Development Performance Relationship

More and more well-documented failure of established companies which could not respond to rapid market changes, such as Kodak and Nokia, demonstrate the importance of transferring marketing information into real firm performance. While marketing strategy and management literature has long advocated the direct impact of strong firm market orientation (MO) on new product development (NPD) performance, limited research has discussed the mediating mechanism of this MO-NPD performance relationship. Using the traditional source–position–performance (SPP) framework, this study focuses on the innovation ambidexterity perspective to investigate the mediating mechanism between MO and NPD performance. Then, this study proposed a conceptual framework and propositions to examine the MO - NPD performance relationship further. Theoretical and practical implications of the findings are also discussed.

Characterizing the astrometric instability of extragalactic radio source positions measured with geodetic VLBI

Context. Geodetic very long baseline interferometry (VLBI) has been used to observe extragalactic radio sources for more than 40 yr. The absolute source positions derived from the VLBI measurements serve as a basis to define the International Celestial Reference Frame (ICRF). Despite being located at cosmological distances, an increasing number of these sources are found to show position instabilities, as revealed by the accumulation of VLBI data over the years. Aims. We investigate how to characterize the astrometric source position variations, as measured with geodetic VLBI data, in order to determine whether these variations occur along random or preferential directions. The sample of sources used for this purpose is made up of the 215 most observed ICRF sources. Methods. Based on the geodetic VLBI data set, we derived source coordinate time series to map the apparent trajectory drawn by the successively measured positions of each source in the plane of the sky. We then converted the coordinate time series into a set of vectors and used the direction of these vectors to calculate a probability density function (PDF) for the direction of variation of the source position. For each source, a model that matches the PDF and that comprises the smallest number of Gaussian components possible was further adjusted. The resulting components then identify the preferred directions of variation for the source position. Results. We found that more than one-half of the sources (56%) in our sample may be characterized by at least one preferred direction. Among these, about three-quarters are characterized by a unique direction, while the remaining sources show multiple preferred directions. The analysis of the distribution of these directions reveals an excess along the declination axis that is attributed to a VLBI network effect. Whether single or multiple, the identified preferred directions are likely due to source-intrinsic physical phenomena.

Locating Thunder Source Using a Large-Aperture Micro-Barometer Array

Lightning generates sound waves across a wide range of frequencies, including infrasonic waves below 20 Hz. Source mechanism for these low frequency pulses is still area for debate. Infrasound pulses detected after rapid changes of electrostatic field during the thunderstorm activity were analyzed. The measurements were done by large aperture array of absolute microbarometers located in the Western part of the Czech Republic. Distances between four measuring sites are in the range of 4–10 km. The infrasound source position was calculated from time delays between the rapid change of electrostatic field and infrasound signal arrival to the individual microbarometers assuming propagation of spherical waves from the source. Only cases with a sufficient signal-to-noise ratio on all four microbarometers were analyzed. The variation of sound speed with height due to temperature height profile was taken into account. For most of the analyzed cases, the calculated infrasound source position corresponds to the lightning location determined by European lightning detection network (EUCLID). The calculated height of infrasound source is most often 3–5 km.

Dual modulation of topological edge states from two-dimensional photonic crystals with lattice shrink

The current topological edge states lack dynamical modulation and the intense field localization effect. To solve these problems, we construct a topological edge state structure based on two-dimensional photonic crystals with lattice shrink. Through the optimization of structure parameters, a nearly flat edge state dispersion curve occurs in a wide bandgap. The topological edge states with intense field localization take on some unique properties such that the transport directions can be controlled by both the source spin and the source position. The transport modes can be dynamically switched between the two opposite unidirectional channels just through moving the source position.