A Variational Principle for the Asymptotic Speed of Fronts of the Density Dependent Diffusion--Reaction Equation

We show that the minimal speed for the existence of monotonic fronts of the equation $u_t = (u^m)_{xx} + f(u)$ with $f(0) = f(1) = 0$, $m >1$ and $f>0$ in $(0,1)$ derives from a variational principle. The variational principle allows to calculate, in principle, the exact speed for arbitrary $f$. The case $m=1$ when $f'(0)=0$ is included as an extension of the results.Comment: Latex, postcript figure availabl

Propagation failure of traveling waves in a discrete bistable medium

Propagation failure (pinning) of traveling waves is studied in a discrete scalar reaction-diffusion equation with a piecewise linear, bistable reaction function. The critical points of the pinning transition, and the wavefront profile at the onset of propagation are calculated exactly. The scaling of the wave speed near the transition, and the leading corrections to the front shape are also determined. We find that the speed vanishes logarithmically close to the critical point, thus the model belongs to a different universality class than the standard Nagumo model, defined with a smooth, polynomial reaction function.Comment: 8 pages, 6 eps figures, to appear in Physica

Factors Influencing Depression and Anxiety among Black Sexual Minority Men

The primary aim of this study was to examine the relationships between depression and anxiety, and ethnic and sexual identity development, and discrimination and harassment (DH) among Black sexual minority men. Additional aims were to determine whether an interaction effect existed between ethnic and sexual identity and whether coping skills level moderated these relationships. Using an observational cross-sectional design, 54 participants recruited through snowball sampling completed self-administered online surveys. Stepwise multiple regression analysis was used. Sixty-four percent of the variance in depression scores and 53% of the variance in anxiety scores were explained by DH and internalized homonegativity together. Thirty percent of the sample had scale scores indicating likelihood of depression and anxiety. Experience of DH and internalized homonegativity explained a large portion of the variability in depression and anxiety among Black sexual minority men. The study showed high prevalence of mental distress among this sample

The Social Justice Teaching Collaborative: A Collective Turn Towards Critical Teacher Education

In this article, we share the collaborative curricular work of an interdisciplinary Social Justice Teaching Collaborative (SJTC) from a PWI university. Members of the SJTC worked strategically to center social justice across required courses pre-service teachers are required to take: Introduction to Education, Sociocultural Studies in Education, and Inclusive Education. We share our conceptualization of social justice and guiding theoretical frameworks that have shaped our pedagogy and curriculum. These frameworks include democratic education, critical pedagogy, critical race theory, critical whiteness studies, critical disability studies, and feminist and intersectionality theory. We then detail changes made across courses including examples of readings and assignments. Finally, we conclude by offering reflections, challenges, and lessons learned for collaborative work within teacher education and educational leadership.&nbsp

Passive Laser Power Stabilization via an Optical Spring

Metrology experiments can be limited by the noise produced by the laser involved via small fluctuations in the laser's power or frequency. Typically, active power stabilization schemes consisting of an in-loop sensor and a feedback control loop are employed. Those schemes are fundamentally limited by shot noise coupling at the in-loop sensor. In this letter we propose to use the optical spring effect to passively stabilize the classical power fluctuations of a laser beam. In a proof of principle experiment, we show that the relative power noise of the laser is stabilized from approximately $2 \times 10^{-5}$ Hz$^{-1/2}$ to a minimum value of $1.6 \times 10^{-7}$ Hz$^{-1/2}$, corresponding to the power noise reduction by a factor of $125$. The bandwidth at which stabilization occurs ranges from $400$ Hz to $100$ kHz. The work reported in this letter further paves the way for high power laser stability techniques which could be implemented in optomechanical experiments and in gravitational wave detectors

Promoting Community and Population Health in Public Health and Medicine: A Stepwise Guide to Initiating and Conducting Community-engaged Research

Various methods, approaches, and strategies designed to understand and reduce health disparities, increase health equity, and promote community and population health have emerged within public health and medicine. One such approach is community-engaged research. While the literature describing the theory, principles, and rationale underlying community engagement is broad, few models or frameworks exist to guide its implementation. We abstracted, analyzed, and interpreted data from existing project documentation including proposal documents, project-specific logic models, research team and partnership meeting notes, and other materials from 24 funded community-engaged research projects conducted over the past 17 years. We developed a 15-step process designed to guide the community-engaged research process. The process includes steps such as: networking and partnership establishment and expansion; building and maintaining trust; identifying health priorities; conducting background research, prioritizing “what to take on”; building consensus, identifying research goals, and developing research questions; developing a conceptual model; formulating a study design; developing an analysis plan; implementing the study; collecting and analyzing data; reviewing and interpreting results; and disseminating and translating findings broadly through multiple channels. Here, we outline and describe each of these steps

Velocity Selection for Propagating Fronts in Superconductors

Using the time-dependent Ginzburg-Landau equations we study the propagation of planar fronts in superconductors, which would appear after a quench to zero applied magnetic field. Our numerical solutions show that the fronts propagate at a unique speed which is controlled by the amount of magnetic flux trapped in the front. For small flux the speed can be determined from the linear marginal stability hypothesis, while for large flux the speed may be calculated using matched asymptotic expansions. At a special point the order parameter and vector potential are dual, leading to an exact solution which is used as the starting point for a perturbative analysis.Comment: 4 pages, 2 figures; submitted to Phys. Rev. Letter

Renormalization Group Theory And Variational Calculations For Propagating Fronts

We study the propagation of uniformly translating fronts into a linearly unstable state, both analytically and numerically. We introduce a perturbative renormalization group (RG) approach to compute the change in the propagation speed when the fronts are perturbed by structural modification of their governing equations. This approach is successful when the fronts are structurally stable, and allows us to select uniquely the (numerical) experimentally observable propagation speed. For convenience and completeness, the structural stability argument is also briefly described. We point out that the solvability condition widely used in studying dynamics of nonequilibrium systems is equivalent to the assumption of physical renormalizability. We also implement a variational principle, due to Hadeler and Rothe, which provides a very good upper bound and, in some cases, even exact results on the propagation speeds, and which identifies the transition from ` linear'- to ` nonlinear-marginal-stability' as parameters in the governing equation are varied.Comment: 34 pages, plain tex with uiucmac.tex. Also available by anonymous ftp to gijoe.mrl.uiuc.edu (128.174.119.153), file /pub/front_RG.tex (or .ps.Z

Para-adventure: A hyper-dynamic problem for the inclusive coach

Recent research has recognized sports coaching as complex, chaotic, and cognitively taxing for coaches. Against this backdrop, the present paper explores challenges faced by high-level coaches working with disabled performers. Specifically, it seeks to understand how coaches create mental models of performance in adventure sports and para-canoe. Five coaches were purposively sampled and underwent a semi-structured interview. A thematic analysis revealed conceptualizing the mental model as being mechanically-related for all and as including a social construction within the para-canoe coaches. Reflection on the coaching process and on personal characteristics were perceived as important to individualized inclusive coaching. Coach training should particularly emphasize the need for critical judgment and decision making skills within a similarly oriented social structure of coaches and support staff where applicable

The Elusive Baseline of Marine Disease: Are Diseases in Ocean Ecosystems Increasing?

Disease outbreaks alter the structure and function of marine ecosystems, directly affecting vertebrates (mammals, turtles, fish), invertebrates (corals, crustaceans, echinoderms), and plants (seagrasses). Previous studies suggest a recent increase in marine disease. However, lack of baseline data in most communities prevents a direct test of this hypothesis. We developed a proxy to evaluate a prediction of the increasing disease hypothesis: the proportion of scientific publications reporting disease increased in recent decades. This represents, to our knowledge, the first quantitative use of normalized trends in the literature to investigate an ecological hypothesis. We searched a literature database for reports of parasites and disease (hereafter “disease”) in nine marine taxonomic groups from 1970 to 2001. Reports, normalized for research effort, increased in turtles, corals, mammals, urchins, and molluscs. No significant trends were detected for seagrasses, decapods, or sharks/rays (though disease occurred in these groups). Counter to the prediction, disease reports decreased in fishes. Formulating effective resource management policy requires understanding the basis and timing of marine disease events. Why disease outbreaks increased in some groups but not in others should be a priority for future investigation. The increase in several groups lends urgency to understanding disease dynamics, particularly since few viable options currently exist to mitigate disease in the oceans