Development of solution techniques for nonlinear structural analysis

Nonlinear structural solution methods in the current research literature are classified according to order of the solution scheme, and it is shown that the analytical tools for these methods are uniformly derivable by perturbation techniques. A new perturbation formulation is developed for treating an arbitrary nonlinear material, in terms of a finite-difference generated stress-strain expansion. Nonlinear geometric effects are included in an explicit manner by appropriate definition of an applicable strain tensor. A new finite-element pilot computer program PANES (Program for Analysis of Nonlinear Equilibrium and Stability) is presented for treatment of problems involving material and geometric nonlinearities, as well as certain forms on nonconservative loading

Selective coupling of optical energy into the fundamental diffusion mode of a scattering medium

We demonstrate experimentally that optical wavefront shaping selectively couples light into the fundamental diffusion mode of a scattering medium. The total energy density inside a scattering medium of zinc oxide (ZnO) nanoparticles was probed by measuring the emitted fluorescent power of spheres that were randomly positioned inside the medium. The fluorescent power of an optimized incident wave front is observed to be enhanced compared to a non-optimized incident front. The observed enhancement increases with sample thickness. Based on diffusion theory, we derive a model wherein the distribution of energy density of wavefront-shaped light is described by the fundamental diffusion mode. The agreement between our model and the data is striking not in the least since there are no adjustable parameters. Enhanced total energy density is crucial to increase the efficiency of white LEDs, solar cells, and of random lasers, as well as to realize controlled illumination in biomedical optics.Comment: 5 pages, 5 figure

Bridging Thought Communities: Implications of Membership in Degree-Completion Program Groups for the Self-Concepts of Adult Students

This study assesses the impact that an alternative delivery model in higher education may have for adult undergraduates who return to college. In trying to adapt their institutions to the needs of adult students, and reduce barriers facing them, some colleges and universities have developed degree-completion programs. In addition to offering convenient class times, some programs utilize what is known as a “group” or “cohort” model that provides a context within which students can find support, and which allows them to retain important outside-the-classroom statuses and identities. The purpose of the study was to determine whether close identification with a group of relatively like others plays a role in elevating the self-concepts of adult students. The research proposes that the group model utilized by some degree-completion programs may result in the creation of thought communities. The study explores whether this delivery model has the potential to transform cohorts of adult students into thought communities from which learning cultures may emerge. When groups become thought communities, learning environments can become places where students are less dependent on professors’ supervision, and are more empowered to recognize the depth of their own skill and experience, and the relevance of that experience to the ongoing task of learning. Data for the study were obtained from nine program groups in the Covenant College Quest program. A pretest-posttest quasi-experimental design was used to assess the impact of several features of small group process and structure on the self-concepts of adult students. The pretest was administered when students first enrolled in the program, and the posttest was given when they entered their second semester (approximately seven months later). Dependent variables were measured using the Tennessee Self-concept Scale (second version: TSCS:2). Data for independent variables were obtained using a questionnaire designed by the researcher. Complete pretest and posttest data were obtained from 109 Quest students (n = 109). Results from multiple regression analysis suggested statistically significant relationships between “influence of instructor” and an increase in student “total” self-concept scores, and between the “group supplying imagery for a possible self” and an increase in total self-concept scores. In addition, support was found for a positive relationship between a “student’s describing his/her group as cohesive” and an increase in “social” self-concept scores. This study demonstrates that the program group does play a role in elevating the self-concepts of adult students in degree-completion programs. It suggests that the program group provides a “context of possibility” from which thought communities may develop. These thought communities may help bridge the gulf between the temporary world of higher education and the outside worlds which adult students inhabit. This research raises questions about universalistic approaches to higher education and suggests that if education is to be made meaningful for adult students, the institutions that deliver education must develop programs that account for the mental memberships their students hold in worlds outside the academy

3D spatially-resolved optical energy density enhanced by wavefront shaping

We study the three-dimensional (3D) spatially-resolved distribution of the energy density of light in a 3D scattering medium upon the excitation of open transmission channels. The open transmission channels are excited by spatially shaping the incident optical wavefronts. To probe the local energy density, we excite isolated fluorescent nanospheres distributed inside the medium. From the spatial fluorescent intensity pattern we obtain the position of each nanosphere, while the total fluorescent intensity gauges the energy density. Our 3D spatially-resolved measurements reveal that the local energy density versus depth (z) is enhanced up to 26X at the back surface of the medium, while it strongly depends on the transverse (x; y) position. We successfully interpret our results with a newly developed 3D model that considers the time-reversed diffusion starting from a point source at the back surface. Our results are relevant for white LEDs, random lasers, solar cells, and biomedical optics