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

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

Discriminative Infant Smiling to Orientations of Talking Faces of Mother and Stranger

Thirty-two infants aged 14 and 20 weeks were presented with a live face in each of eight conditions, which consisted of all combinations of (a) a 0° or 90° orientation; (b) familiar face (the infant\u27s mother) or distinctively unfamiliar face; and (c) talking or silent context. The previous findings that younger infants smile longer at 0° than at 90° faces and that this differential responsiveness to orientation wanes with increasing age were replicated; the hypothesis that older infants would smile longest at their mothers\u27 talking faces in the 0° orientation was confirmed. In addition, infants of both ages smiled more at their mothers than at the stranger, although this effect interacted with orientation and sex of the infant

PHOTOGRAMMETRIC ANALYSIS OF HISTORICAL IMAGE REPOSITORIES FOR VIRTUAL RECONSTRUCTION IN THE FIELD OF DIGITAL HUMANITIES

Historical photographs contain high density of information and are of great importance as sources in humanities research. In addition to the semantic indexing of historical images based on metadata, it is also possible to reconstruct geometric information about the depicted objects or the camera position at the time of the recording by employing photogrammetric methods. The approach presented here is intended to investigate (semi-) automated photogrammetric reconstruction methods for heterogeneous collections of historical (city) photographs and photographic documentation for the use in the humanities, urban research and history sciences. From a photogrammetric point of view, these images are mostly digitized photographs. For a photogrammetric evaluation, therefore, the characteristics of scanned analog images with mostly unknown camera geometry, missing or minimal object information and low radiometric and geometric resolution have to be considered. In addition, these photographs have not been created specifically for documentation purposes and so the focus of these images is often not on the object to be evaluated. The image repositories must therefore be subjected to a preprocessing analysis of their photogrammetric usability. Investigations are carried out on the basis of a repository containing historical images of the Kronentor ("crown gate") of the Dresden Zwinger. The initial step was to assess the quality and condition of available images determining their appropriateness for generating three-dimensional point clouds from historical photos using a structure-from-motion evaluation (SfM). Then, the generated point clouds were assessed by comparing them with current measurement data of the same object