Arrest of Domain Coarsening via Antiperiodic Regimes in Delay Systems

Motionless domains walls representing heteroclinic temporal or spatial orbits typically exist only for very specific parameters. This report introduces a novel mechanism for stabilizing temporal domain walls away from the Maxwell point opening up new possibilities to encode information in dynamical systems. It is based on anti-periodic regimes in a delayed system close to a bistable situation, leading to a cancellation of the average drift velocity. The results are demonstrated in a normal form model and experimentally in a laser with optical injection and delayed feedback.Comment: 6 pages, 5 figures, resubmitted manuscrip

Small Dollar Loans, Big Problems: How States Protect Consumers From Abuses and How the Federal Government Can Help

Across America, drivers pass twice as many payday loan storefronts as Starbucks coffee shops.2 In twenty-nine states, there are more payday lender stores than McDonald’s restaurants.3 Numerous research studies warn of the dangers associated with payday loans, including significantly higher rates of bankruptcies, evictions, utility shut-offs, and involuntary bank account closures.4 Many states have recognized the dangers posed by payday and other types of small-dollar loans with predatory features, prompting them to adopt laws to combat the abusive nature of these loans. These laws, however, offer consumers varying degrees of protection. Historically, states have used their police powers to protect consumers from predatory lending. This Article discusses the extent to which each state’s current laws protect consumers from lending abuses associated with four common small-dollar loans: payday loans, auto-title loans, six-month installment loans, and one-year installment loans.5 Specifically, this Article highlights the findings from the 2010 Small Dollar Loan Products Scorecard (Scorecard), which updated the original 2008 Scorecard. 6 Both the 2008 and 2010 Scorecard grade state laws based on the maximum annual percentage rate (APR) they allow for the four typical small-dollar loan products listed above. Since the 2008 Scorecard, there has been significant state legislative activity across the country related to small-dollar loans. Only a handful of states, however, have enacted new measures that adequately protect consumers. This Article provides policy recommendations to guide ongoing reform efforts. The Article highlights three key points. First, states should continue their longstanding good fight on behalf of American families against abusive, small dollar lending, but they need help. Congress and the Consumer Financial Protection Bureau (CFPB), which President Obama established when he signed the Dodd-Frank Wall Street Reform and Consumer Protection Act into law on July 21, 2010, should join the battle.7 Second, the states and Congress should focus their reform efforts on enacting an across-the-board usury cap of 36% APR on all small-dollar loans. Third, the states, CFPB, and Congress should impose several restrictions on high-cost (over 36% APR), small-dollar lending to help curb its abusive nature. In this Article, Part II describes the methodology used by the 2010 Scorecard. Part III reports the major changes that have occurred in the two years since the Scorecard’s original 2008 publication. Finally, Part IV proposes several policy recommendations, at the state and federal level, with the focus in the latter category on opportunities for action by the newly created CFPB

From Gatekeeping to Engagement: A Multicontextual, Mixed Method Study of Student Academic Engagement in Introductory STEM Courses.

The lack of academic engagement in introductory science courses is considered by some to be a primary reason why students switch out of science majors. This study employed a sequential, explanatory mixed methods approach to provide a richer understanding of the relationship between student engagement and introductory science instruction. Quantitative survey data were drawn from 2,873 students within 73 introductory science, technology, engineering, and mathematics (STEM) courses across 15 colleges and universities, and qualitative data were collected from 41 student focus groups at eight of these institutions. The findings indicate that students tended to be more engaged in courses where the instructor consistently signaled an openness to student questions and recognizes her/his role in helping students succeed. Likewise, students who reported feeling comfortable asking questions in class, seeking out tutoring, attending supplemental instruction sessions, and collaborating with other students in the course were also more likely to be engaged. Instructional implications for improving students' levels of academic engagement are discussed

Boundary-induced heterogeneous absorbing states

We study two different types of systems with many absorbing states (with and without a conservation law) and scrutinize the effect of walls/boundaries (either absorbing or reflecting) into them. In some cases, non-trivial structured absorbing configurations (characterized by a background field) develop around the wall. We study such structures using a mean-field approach as well as computer simulations. The main results are: i) for systems in the directed percolation class, a very fast (exponential) convergence of the background to its bulk value is observed; ii) for systems with a conservation law, power-law decaying landscapes are induced by both types of walls: while for absorbing walls this effect is already present in the mean-field approximation, for reflecting walls the structured background is a noise-induced effect. The landscapes are shown to converge to their asymptotic bulk values with an exponent equal to the inverse of the bulk correlation length exponent. Finally, the implications of these results in the context of self-organizing systems are discussed.Comment: 8 pages, 2 figure

Reentrant Behavior of the Spinodal Curve in a Nonequilibrium Ferromagnet

The metastable behavior of a kinetic Ising--like ferromagnetic model system in which a generic type of microscopic disorder induces nonequilibrium steady states is studied by computer simulation and a mean--field approach. We pay attention, in particular, to the spinodal curve or intrinsic coercive field that separates the metastable region from the unstable one. We find that, under strong nonequilibrium conditions, this exhibits reentrant behavior as a function of temperature. That is, metastability does not happen in this regime for both low and high temperatures, but instead emerges for intermediate temperature, as a consequence of the non-linear interplay between thermal and nonequilibrium fluctuations. We argue that this behavior, which is in contrast with equilibrium phenomenology and could occur in actual impure specimens, might be related to the presence of an effective multiplicative noise in the system.Comment: 7 pages, 4 figures; Final version to appear in Phys. Rev. E; Section V has been revise

Transforming triangulations on non planar-surfaces

We consider whether any two triangulations of a polygon or a point set on a non-planar surface with a given metric can be transformed into each other by a sequence of edge flips. The answer is negative in general with some remarkable exceptions, such as polygons on the cylinder, and on the flat torus, and certain configurations of points on the cylinder.Comment: 19 pages, 17 figures. This version has been accepted in the SIAM Journal on Discrete Mathematics. Keywords: Graph of triangulations, triangulations on surfaces, triangulations of polygons, edge fli

Investigation of vertical cavity surface emitting laser dynamics for neuromorphic photonic systems

We report an approach based upon vertical cavity surface emitting lasers (VCSELs) to reproduce optically different behaviors exhibited by biological neurons but on a much faster timescale. The technique proposed is based on the polarization switching and nonlinear dynamics induced in a single VCSEL under polarized optical injection. The particular attributes of VCSELs and the simple experimental configuration used in this work offer prospects of fast, reconfigurable processing elements with excellent fan-out and scaling potentials for use in future computational paradigms and artificial neural networks. © 2012 American Institute of Physics