Fluid motion and molecular reorientation in a homeotropically orientated nematic liquid-crystal cell

The linearized Ericksen-Leslie differential equations, which couple fluid motion and director reorientation to each other, are reduced to a set of time varying differential equations for two pulsed optical waves incident at an angle upon a homeotropically orientated liquid-crystal cell. The differential equations are solved by a numerical method. The fluid velocity and the director angle are plotted as a function of space and time. It is shown that the reaction of fluid motion upon director reorientation is small.     

Convergent perturbation expansion for the anharmonic oscillator

We study the ground state as well as the first three excited states of the anharmonic oscillator with anharmonicity λx⁴ for a range of λ = (0, 10) with the first-order logarithmic perturbation iteration method (FOLPIM). This leads to convergent results. The initial choice of the wave function seems only to affect the rate of convergence in the case of the ground state but may critically affect the convergence for the excited states. For large values of λ, convergence is best obtained by choosing the asymptotic solution as the initial “unperturbed” wave function.     

Self‐organization and selection in the emergence of vocabulary

Human language may have started from a consistent set of mappings between meanings and signals. These mappings, referred to as the early vocabulary, are considered to be the results of conventions established among the agents of a population. In this study, we report simulation models for investigating how such conventions can be reached. We propose that convention is essentially the product of self‐organization of the population through interactions among the agents and that cultural selection is another mechanism that speeds up the establishment of convention. Whereas earlier studies emphasize either one or the other of these two mechanisms, our focus is to integrate them into one hybrid model. The combination of these two complementary mechanisms, i.e., self‐organization and cultural selection, provides a plausible explanation for cultural evolution, which progresses with high transmission rate. Furthermore, we observe that as the vocabulary tends to convergence there is a uniform tendency to exhibit a sharp phase transition. © 2002 Wiley Periodicals, Inc.     

Target detection in reverberation by an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

An experiment was conducted to determine the ability of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus) to detect targets in the presence of reverberation. Reverberation was induced by a clutter screen consisting of forty-eight 5.1-cm-diam cork spheres spaced 15.2 cm apart and arranged in a rectangular array, located behind the targets. Hollow aluminum cylinders having the same outer diameter and wall thickness and three different lengths were used as targets. The dolphin was trained to station in a hoop, 6 m from the targets, and to echolocate the target upon the reception of an audio cue. Only one of the targets would be presented in a target-present trial. Data were collected on the animal's detection performance as a function of the separation distance between the clutter screen and the targets. The animal's performance for the smallest cylinder varied from 91% to 55% correct as the separation distance decreased from 10.2 to 0 cm. The target strength of the clutter screen and the cylinders were measured both in terms of the energies and the maximum peak-to-peak amplitudes of the incident and reflected echoes. These measurements indicated that when the target-clutter screen separation distance was 0 cm, the dolphin's 50% correct detection occurred at an energy echo-to-reverberation ratio of approximately 0.25 dB and at peak-to-peak echo-to-reverberation ratio of 2.6 dB. The results also indicated that the dolphin's performance varied almost linearly with the echo-to-reverberation ratio. The animal's pulse emissions were monitored by a microprocessor system and the results are presented in terms of the average number of clicks and the average response latency, as a function of the separation distance.     

Source levels of clicks from free-ranging white-beaked dolphins (Lagenorhynchus albirostris Gray 1846) recorded in Icelandic waters

This study reports the source levels of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris Gray 1846). A four-hydrophone array was used to obtain sound recordings. The hydrophone signals were digitized on-line and stored in a portable computer. An underwater video camera was used to visualize dolphins to help identify on-axis recordings. The range to a dolphin was calculated from differences in arrival times of clicks at the four hydrophones, allowing for calculations of source levels. Source levels in a single click train varied from 194 to 211 dB peak-to-peak (p-p) re: 1 microPa. The source levels varied linearly with the log of range. The maximum source levels recorded were 219 dB (p-p) re: 1 microPa.     

The whistles of Hawaiian spinner dolphins

The characteristics of the whistles of Hawaiian spinner dolphins (Stenella longirostris) are considered by examining concurrently the whistle repertoire (whistle types) and the frequency of occurrence of each whistle type (whistle usage). Whistles were recorded off six islands in the Hawaiian Archipelago. In this study Hawaiian spinner dolphins emitted frequency modulated whistles that often sweep up in frequency (47% of the whistles were upsweeps). The frequency span of the fundamental component was mainly between 2 and 22 kHz (about 94% of the whistles) with an average mid-frequency of 12.9 kHz. The duration of spinner whistles was relatively short, mainly within a span of 0.05 to 1.28 s (about 94% of the whistles) with an average value of 0.49 s. The average maximum frequency of 15.9 kHz obtained by this study is consistent with the body length versus maximum frequency relationship obtained by Wang et al. (1995a) when using spinner dolphin adult body length measurements. When comparing the average values of whistle parameters obtained by this and other studies in the Island of Hawaii, statistically significant differences were found between studies. The reasons for these differences are not obvious. Some possibilities include differences in the upper frequency limit of the recording systems, different spinner groups being recorded, and observer differences in viewing spectrograms. Standardization in recording and analysis procedure is clearly needed.     

Acoustic backscattering by Hawaiian lutjanid snappers. 1. Target strength and swimbladder characteristics

The target strengths and swimbladder morphology of six snapper species were investigated using broadband sonar, x rays, and swimbladder casts. Backscatter data were obtained using a frequency-modulated sweep (60-200 kHz) and a broadband, dolphinlike click (peak frequency 120 kHz) from live fish, mounted and rotated around each of their three axes. X rays revealed species-specific differences in the shape, size, and orientation of the swimbladders. The angle between the fish's dorsal aspect and the major axis of its swimbladder ranged from 3 degrees to 12 degrees and was consistent between individuals within a species. This angle had a one-to-one relationship with the angle at which the maximum dorsal aspect target strength was measured (r2 = 0.93), regardless of species. Maximum dorsal aspect target strength was correlated with length within species. However, the swimbladder modeled as an air-filled prolate spheroid with axes measured from the x rays of the swimbladder predicted maximum target strength significantly better than models based on fish length or swimbladder volume. For both the dorsal and lateral aspects, the prolate spheroid model's predictions were not significantly different from the measured target strengths (observed power >0.75) and were within 3 dB of the measured values. This model predicts the target strengths of all species equally well, unlike those based on length.     

Demonstration of adaptation in beluga whale echolocation signals

The echolocation signals of the same beluga whale (Delphinapterus leucas) were measured first in San Diego Bay, and later in Kaneohe Bay, Oahu, Hawaii. The ambient noise level in Kaneohe Bay is typically 12-17 dB greater than in San Diego Bay. The whale demonstrated the adaptiveness of its biosonar by shifting to higher frequencies and intensities after it was moved to Kaneohe. In San Diego, the animal emitted echolocation signals with peak frequencies between 40 and 60 kHz, and bandwidths between 15 and 25 kHz. In Kaneohe, the whale shifted its signals approximately an octave higher in frequencies with peak frequencies between 100 and 120 kHz, and bandwidths between 20 and 40 kHz. Signal intensities measured in Kaneohe were up to 18 dB higher than in San Diego. The data collected represent the first quantitative evidence of the adaptive capability of a cetacean biosonar system.     

Dispersion relations and AC stark shifts

It is pointed out that AC Stark energy level shifts in a laser field can be calculated from experimental photo-absorption data via a dispersion relation. Explicit calculation is carried out for the ground state of helium.