Giant Goos–Hänchen shifts and radiation-induced trapping of Helmholtz solitons at nonlinear interfaces

Giant Goos–Hänchen shifts and radiation-induced trapping are studied at the planar boundary separating two focusing Kerr media within the framework of the Helmholtz theory. The analysis, valid for all angles of incidence, reveals that interfaces exhibiting linear external refraction can also accommodate both phenomena. Numerical evidence of these effects is provided, based on analytical predictions derived from a generalized Snell’s law

Black and gray Helmholtz Kerr soliton refraction

efraction of black and gray solitons at boundaries separating different defocusing Kerr media is analyzed within a Helmholtz framework. A universal nonlinear Snell’s law is derived that describes gray soliton refraction, in addition to capturing the behavior of bright and black Kerr solitons at interfaces. Key regimes, defined by beam and interface characteristics, are identified and predictions are verified by full numerical simulations. The existence of a unique total non-refraction angle for gray solitons is reported; both internal and external refraction at a single interface is shown possible (dependent only on incidence angle). This, in turn, leads to the proposal of positive or negative lensing operations on soliton arrays at planar boundaries

A study of social rank development in captive African painted dog (Lycaon pictus) pups.

African painted dogs, Lycaon pictus, are an endangered social carnivore native to sub-Saharan Africa. Their historic range and population densities have been reduced due to habitat fragmentation, conflict with humans, and infectious disease. Captive populations of African painted dogs are found worldwide and are maintained in social groups to encourage natural pack behaviors. Specifically, Association of Zoos and Aquariums (AZA) populations are managed by Species Survival Plans. The foci of species management in these zoos are to maintain genetic diversity, promote species-specific social behavior, and maintain a self-sustaining population. Challenges faced by zoos include failed breeding recommendations, variable litter sizes, and pack instability due to the complexity of social dynamics. Minimal research efforts have focused on captive African painted dogs. Although the species currently is self-sustaining in captivity, some packs are unstable, displaying injurious aggression, failure to reproduce, or failure to raise offspring. Thus, there is a need to better understand how to form new packs, so that welfare and reproductive success are improved. The goal of my research was to determine methods that can be used to evaluate social rank within a litter of African painted dog pups. This included evaluations of behaviors displayed by individuals as well as interactions between conspecifics. I also explored ways zoo care staff could assess individuals for transfer recommendations to a different facility. I performed this study on a litter of African painted dog pups at the Oklahoma City Zoo. I used focal observations to assess individual behaviors based on an African painted dog ethogram. Novel object presentations were used to assess responses on a bold/shy continuum. Latency to approach, first to approach, and other occurrences were documented during novel object presentations. There were significant differences among pups for the observed behaviors. Although there were no differences for submissive behaviors, there were differences among pups for dominant behaviors. There also were significant differences among pups for first to approach, as well as differences in latency to approach novel objects based on pack composition and type of object. F-flat was the subject that displayed the most first approaches and the most dominant behaviors. There were differences between behaviors of interest among individuals, but my data was insufficient for determining social rank. After evaluating the results of each observational method, the method that zoo care staff could most easily utilize would be novel object presentations. My study represents a preliminary analysis of social pack dynamics in captive populations. Further research recommendations include further defined behaviors of interests, and evaluation of the social ranks over time through changes in pack composition. For conservation efforts by zoos to continue successfully, it is essential to gain as much understanding as possible of the social structure and social development of captive-housed African painted dogs