Hexagonal dielectric resonators and microcrystal lasers

We study long-lived resonances (lowest-loss modes) in hexagonally shaped dielectric resonators in order to gain insight into the physics of a class of microcrystal lasers. Numerical results on resonance positions and lifetimes, near-field intensity patterns, far-field emission patterns, and effects of rounding of corners are presented. Most features are explained by a semiclassical approximation based on pseudointegrable ray dynamics and boundary waves. The semiclassical model is also relevant for other microlasers of polygonal geometry.Comment: 12 pages, 17 figures (3 with reduced quality

Spectral properties of quantized barrier billiards

The properties of energy levels in a family of classically pseudointegrable systems, the barrier billiards, are investigated. An extensive numerical study of nearest-neighbor spacing distributions, next-to-nearest spacing distributions, number variances, spectral form factors, and the level dynamics is carried out. For a special member of the billiard family, the form factor is calculated analytically for small arguments in the diagonal approximation. All results together are consistent with the so-called semi-Poisson statistics.Comment: 8 pages, 9 figure

Biodiversity, International Tourism and Development

We analyze whether biodiversity is increasing the receipts of tourism and beneficial for Least Developed Countries (LDCs). The underlying assumption is that a rich biodiversity provides a comparative advantage for most LDCs. We use a simple trade theory framework. The model is supported by an empirical analysis. The main findings are that first LDCs seem to have a comparative advantage in (sustainable) tourism, that second incidence of birds as the probably best explored taxonomic group has a positive impact on inbound tourism receipts per capita, and that third the rate of endangered to total birds is negatively influencing tourism receipts

Newborn Habituation to Visual Stimuli: A Sex Difference in Novelty Detection

Thirty-six newborn human infants were repeatedly exposed to one of two visual stimuli, a four-square or 144-square black and white checkerboard target, until a set criterion of habituation was demonstrated, as measured by a decrement in visual fixation time. When the habituation criterion was reached, independent groups of Ss were either presented with the same target or with a target of either moderate or large discrepancy from the standard habituation stimulus. Results indicated that (1) there was habituation of visual attention, which replicated previous findings, and suggests that some infants soon after birth are capable of storing simple visual information, and (2) following habituation female infants displayed greater recovery of attention than male infants when the moderate stimulus change was introduced

Bidimensional Sorting in Preschoolers with An Instrumental Learning Task.

74 lower- and middle-class children aged 2 1/2, 3 1/2, and 4 1/2 years who were successful at unidimensional sorting of 2 objects by either color or form were given feedback for correct bidimensional sorting of 3 objects, 2 of which had been used in unidimensional testing. Four of the 10 2 1/2-year-olds and 58 of the 64 3 1/2- and 4 1/2-year-olds reached criterion on the bidimensional sorting task. Neither social class nor performance on a verbal comprehension test (the Peabody Picture Vocabulary Test) was significantly correlated with success on either unidimensional or bidimensional sorting, although social class and test scores were significantly correlated. The results indicate that Piagetian centration (i.e., the inability to transcend unidimensional attention) is a task- or situation-specific phenomenon, and biodimensional responding is the rule rather than the exception for 3 1/2- and 4 1/2-year-olds in an instrumental situation involving a limited number of stimuli

Response-Contingent Stimulation as a Treatment for Developmental Failure in Infancy

An 8-month-old infant with a developmental quotient of 1 1 2 months was given response-contingent stimulation using a pressure-sensitive pillow which turned an overhead mobile. The subject learned to control the mobile by kicking the pillow, and concurrently began smiling at both the mobile and her mother for the first time. After mastering three contingencies on arm, head, and leg movement, she displayed what appeared to be a Piagetian coordinated secondary circular reaction, in which one response provided 4 seconds of access to another contingency. Although the subject remains severely retarded, the results suggest that some forms of developmental delay may be treated at least in part as a failure to develop contingency awareness

Infant Sex Differences in Operant Fixation with Visual and Auditory Reinforcement

Forty-eight 14-week-old infants were reinforced for fixation of either a left or right circle with an auditory or visual stimulus. Each subject was tested for a baseline period, and three conditioning-extinction phases, during which three intensities were presented in one of three orders. Subjects performed significantly better during the final two conditioning periods than during baseline or the first conditioning period. There was a significant interaction between sex, intensity and modality during the first conditioning period, indicating that males performed better than females with the visual stimulus across intensities, while females performed better than males with low intensity auditory stimuli