The Hamiltonian structure of Dirac's equation in tensor form and its Fermi quantization

Currently, there is some interest in studying the tensor forms of the Dirac equation to elucidate the possibility of the constrained tensor fields admitting Fermi quantization. We demonstrate that the bispinor and tensor Hamiltonian systems have equivalent Fermi quantizations. Although the tensor Hamiltonian system is noncanonical, representing the tensor Poisson brackets as commutators for the Heisenberg operators directly leads to Fermi quantization without the use of bispinors

Living on the edge: cosmology on the boundary of anti-de Sitter space

We sketch a particularly simple and compelling version of D-brane cosmology. Inspired by the semi-phenomenological Randall--Sundrum models, and their cosmological generalizations, we develop a variant that contains a single (3+1)-dimensional D-brane which is located on the boundary of a single bulk (4+1)-dimensional region. The D-brane boundary is itself to be interpreted as our visible universe, with ordinary matter (planets, stars, galaxies) being trapped on this D-brane by string theory effects. The (4+1)-dimensional bulk is, in its simplest implementation, adS_{4+1}, anti-de Sitter space. We demonstrate that a k=+1 closed FLRW universe is the most natural option, though the scale factor could quite easily be so large as to make it operationally indistinguishable from a k=0 spatially flat universe. (With minor loss of elegance, spatially flat and hyperbolic FLRW cosmologies can also be accommodated.) We demonstrate how this model can be made consistent with standard cosmology, and suggest some possible observational tests.Comment: LaTeX2e, 17 pages; Revised (references added, physics unchanged). To appear in Physics Letters

Nonlinear modes of the tensor Dirac equation and CPT violation

Recently, it has been shown that Dirac's bispinor equation can be expressed, in an equivalent tensor form, as a constrained Yang-Mills equation in the limit of an infinitely large coupling constant. It was also shown that the free tensor Dirac equation is a completely integrable Hamiltonian system with Lie algebra type Poisson brackets, from which Fermi quantization can be derived directly without using bispinors. The Yang-Mills equation for a finite coupling constant is investigated. It is shown that the nonlinear Yang-Mills equation has exact plane wave solutions in one-to-one correspondence with the plane wave solutions of Dirac's bispinor equation. The theory of nonlinear dispersive waves is applied to establish the existence of wave packets. The CPT violation of these nonlinear wave packets, which could lead to new observable effects consistent with current experimental bounds, is investigated

Wormhole solutions in the Randall-Sundrum scenario

In the simplest form of the Randall-Sundrum model, we consider the metric generated by a static, spherically symmetric distribution of matter on the physical brane. The solution to the five-dimensional Einstein equations, obtained numerically, describes a wormhole geometry.Comment: 10 pages, 2 figures, revtex

Crowd-powered positive psychological interventions

Recent advances in crowdsourcing have led to new forms of assistive technologies, commonly referred to as crowd-powered devices. To best serve the user, these technologies crowdsource human intelligence as needed, when automated methods alone are insufficient. In this paper, we provide an overview of how these systems work and how they can be used to enhance technological interventions for positive psychology. As a specific example, we describe previous work that crowdsources positive reappraisals, providing users timely and personalized suggestions for ways to reconstrue stressful thoughts and situations. We then describe how this approach could be extended for use with other positive psychological interventions. Finally, we outline future directions for crowd-powered positive psychological interventions

Broadening Accessibility Through Special Interests: A New Approach for Software Customization

Individuals diagnosed with autism spectrum disorder (ASD) often fixate on narrow, restricted interests. These interests can be highly motivating, but they can also create attentional myopia, preventing individuals from pursuing a broad range of activities. Interestingly, researchers have found that preferred interests can be used to help individuals with ASD branch out and participate in educational, therapeutic, or social situations they might otherwise shun. When interventions are modified, such that an individual’s interest is properly represented, task adherence and performance can increase. While this strategy has seen success in the research literature, it is difficult to implement on a large scale and therefore has not been widely adopted. This paper describes a software approach designed to solve this problem. The approach facilitates customization, allowing users to easily embed images of almost any special interest into computer-based interventions. Specifically, we describe an algorithm that will: (1) retrieve any image from the Google image database; (2) strip it of its background; and (3) embed it seamlessly into Flash-based computer programs. To evaluate our algorithm, we employed it in a naturalistic setting with eleven individuals (nine diagnosed with ASD and two diagnosed with other developmental disorders). We also tested its ability to retrieve and process examples of preferred interests previously reported in the ASD literature. The results indicate that our method was an easy and efficient way for users to customize our software programs. While we believe this model is uniquely suited for individuals with ASD, we also foresee this approach being useful for anyone that might like a quick and simple way to personalize software programs.Things That Think ConsortiumBank of Americ

Efficacy of a Web-Based, Crowdsourced Peer-To-Peer Cognitive Reappraisal Platform for Depression: Randomized Controlled Trial

Background: Self-guided, Web-based interventions for depression show promising results but suffer from high attrition and low user engagement. Online peer support networks can be highly engaging, but they show mixed results and lack evidence-based content. Objective: Our aim was to introduce and evaluate a novel Web-based, peer-to-peer cognitive reappraisal platform designed to promote evidence-based techniques, with the hypotheses that (1) repeated use of the platform increases reappraisal and reduces depression and (2) that the social, crowdsourced interactions enhance engagement. Methods: Participants aged 18-35 were recruited online and were randomly assigned to the treatment group, “Panoply” (n=84), or an active control group, online expressive writing (n=82). Both are fully automated Web-based platforms. Participants were asked to use their assigned platform for a minimum of 25 minutes per week for 3 weeks. Both platforms involved posting descriptions of stressful thoughts and situations. Participants on the Panoply platform additionally received crowdsourced reappraisal support immediately after submitting a post (median response time=9 minutes). Panoply participants could also practice reappraising stressful situations submitted by other users. Online questionnaires administered at baseline and 3 weeks assessed depression symptoms, reappraisal, and perseverative thinking. Engagement was assessed through self-report measures, session data, and activity levels. Results: The Panoply platform produced significant improvements from pre to post for depression (P=.001), reappraisal (P<.001), and perseverative thinking (P<.001). The expressive writing platform yielded significant pre to post improvements for depression (P=.02) and perseverative thinking (P<.001), but not reappraisal (P=.45). The two groups did not diverge significantly at post-test on measures of depression or perseverative thinking, though Panoply users had significantly higher reappraisal scores (P=.02) than expressive writing. We also found significant group by treatment interactions. Individuals with elevated depression symptoms showed greater comparative benefit from Panoply for depression (P=.02) and perseverative thinking (P=.008). Individuals with baseline reappraisal deficits showed greater comparative benefit from Panoply for depression (P=.002) and perseverative thinking (P=.002). Changes in reappraisal mediated the effects of Panoply, but not the expressive writing platform, for both outcomes of depression (ab=-1.04, SE 0.58, 95% CI -2.67 to -.12) and perseverative thinking (ab=-1.02, SE 0.61, 95% CI -2.88 to -.20). Dropout rates were similar for the two platforms; however, Panoply yielded significantly more usage activity (P<.001) and significantly greater user experience scores (P<.001). Conclusions: Panoply engaged its users and was especially helpful for depressed individuals and for those who might ordinarily underutilize reappraisal techniques. Further investigation is needed to examine the long-term effects of such a platform and whether the benefits generalize to a more diverse population of users.MIT Media Lab Consortiu