Towards a Natural Theory of Dark Energy: Supersymmetric Large Extra Dimensions

The first part of this article summarizes the evidence for Dark Energy and Dark Matter, as well as the naturalness issues which plague current theories of Dark Energy. The main point of this part is to argue why these naturalness issues should provide the central theoretical guidance for the search for a successful theory. The second part of the article describes the present status of what I regard as being the best mechanism yet proposed for addressing this issue: Six-dimensional Supergravity with submillimetre-sized Extra Dimensions (Supersymmetric Large Extra Dimensions, or SLED for short). Besides summarizing the SLED proposal itself, this section also describes the tests which this model has passed, the main criticisms which have been raised, and the remaining challenges which remain to be checked. The bottom line is that the proposal survives the tests which have been completed to date, and predicts several distinctive experimental signatures for cosmology, tests of gravity and for accelerator-based particle physics.Comment: 33 page

Role of antioxidant supplementation and exercise regimen in handling oxidative stress from natural PM2.5 exposure due to boreal forest fire

Thesis (M.S.) University of Alaska Fairbanks, 2019Particulate matter 2.5 (PM2.5) exposure induces oxidative stress that causes many negative health outcomes such as cancer, cardiovascular disease and neurodegenerative disease. Research shows that dietary antioxidants and an up-regulated endogenous antioxidant response from exercise play key roles in the antioxidant defense against oxidative stress. This study is the first to use an animal model to investigate the cumulative effects of using lifestyle interventions of antioxidant supplementation (Arthrospira platensis) and exercise regimen on the antioxidant response before, during, and after ambient PM2.5 exposure. In a two-factorial, longitudinal design, sled dogs (n=48) were divided into four groups (exercise and supplemented, exercise, supplemented, and control) to (1) test the effects of exercise and antioxidant regimen on antioxidant response after one month of implemented exercise and supplementation protocol and (2) measure the antioxidant response of all groups during and after a natural forest fire event in 2015. Commercial assays for Total antioxidant Power (TAP) and the enzymatic antioxidant Superoxide Dismutase (SOD) were used as markers for the total antioxidant response and the endogenous response at all time points. During the forest fire, SOD was increased 5-10-fold over pre/post-exposure levels in all groups suggesting potential implication for using SOD as a marker for the acute response to environmental stress. TAP was increased in the exercise groups after one month of exercise protocol implementation, demonstrating the cytoprotective increase of antioxidants after repeated exercise.Chapter 1: Introduction -- 1.1 PM2.5 -- 1.2 Oxidative stress and exercise -- 1.3 Antioxidants -- 1.4 Significance and research hypothesis -- Chapter 2 The effects of spirulina supplementation and exercise regimen on the antioxidant response to PM2.5 exposure in sled dogs -- 2.1 Introduction -- 2.2 Materials and methods -- 2.2.1 Animals -- 2.2.2 Experimental design -- 2.2.4 Exercise -- 2.2.5 Blood sampling -- 2.2.6 Biochemical analyses -- 2.2.7 Statistics -- 2.3 Results -- 2.4 Discussion -- 2.5 Conclusions -- Chapter 3 Conclusions and future directions -- References

Large, long range tensile forces drive convergence during

Indirect evidence suggests that blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 mN during gastrulation and over 4 mN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their blastopores, produce up to 2 mN of tensile force, showing that CT alone generates forces sufficient to close the blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of blastopore closure mechanisms. © Shook et al

Supersymmetric Large Extra Dimensions and the Cosmological Constant: An Update

This article critically reviews the proposal for addressing the cosmological constant problem within the framework of supersymmetric large extra dimensions (SLED), as recently proposed in hep-th/0304256. After a brief restatement of the cosmological constant problem, a short summary of the proposed mechanism is given. The emphasis is on the perspective of the low-energy effective theory in order to see how it addresses the problem of why low-energy particles like the electron do not contribute too large a vacuum energy. This is followed by a discussion of the main objections, which are grouped into the following five topics: (1) Weinberg's No-Go Theorem. (2) Are hidden tunings of the theory required, and a problem? (3) Why should the mechanism not rule out earlier epochs of inflation? (4) How big are quantum effects, and which are the most dangerous? (5) Can the mechanism be consistent with cosmological constraints? It is argued that there are plausible reasons why the mechanism can thread the potential objections, but that a definitive proof that it does depends on addressing well-defined technical points. These points include identifying what fixes the size of the extra dimensions, checking how topological obstructions renormalize and performing specific calculations of quantum corrections. More detailed studies of these issues, which are well reach within our present understanding of extra-dimensional theories, are currently underway. As such, the jury remains out concerning the proposal, although the prospects for acquittal still seem good.Comment: 21 pages; an extended version of the contribution to the proceedings of SUSY 2003, University of Arizona, Tucson AZ, June 2003, which has also been updated to include developments since the conference. (v2 includes some updated references and corrects a minor error in the bulk loop section

First language in the classroom: the forbidden fruit?

Tesis (Profesor de Inglés para la Enseñanza Básica y Media y al grado académico de Licenciado en Educación)Over the past years, the use of students’ first language (L1) in the classroom has been a highly discussed topic in the EFL classroom as well as in the field of second language (L2) teaching/learning research. There is a tendency that advocates communicative language teaching which suggests that L1 use should forbidden in the classroom. However, research has yet to discover whether L1 use has a positive or negative impact on L2 learning. Hence, the present study aimed to examine L1 functions and the impact of L1 use on L2 development. The present study was conducted in a private school in Santiago, Chile. The participants of this study (N = 34) were engaged in two collaborative writing tasks about the book they were reading in their English literature classes, and their discussions were audio-recorded and later analyzed. A quasi-experimental method was utilized in order to observe the influence that group work had on their L2 vocabulary development. The results demonstrated that the students’ L1 played a major role in their interaction while together working on the collaborative tasks, and it served for the development of L2 vocabulary. Specifically, the results suggest that the way in which individual learners contributed to interaction affected their learning outcomes.En los últimos años, el uso de la primera lengua de los estudiantes ha sido un tema altamente discutido en las salas de clases y en la investigación de la enseñanza de inglés como Lengua Extranjera. Existe una tendencia general de prohibir el uso de la primera lengua, sin embargo, aún existen vacíos sobre la influencia positiva o negativa que esta podría tener en el aprendizaje de vocabulario. El presente estudio se realizó en una escuela privada en Santiago, Chile. El propósito del mismo fue observar las funciones que cumplía la lengua nativa en la interacción de los estudiantes y cómo esto afectaba al desarrollo de la segunda lengua en alumnos de octavo básico con alto nivel de inglés. Los participantes de este estudio fueron involucrados en dos actividades de escritura colaborativa sobre el libro que estaban leyendo en las clases de literatura inglesa, donde sus discusiones fueron grabadas en audio y luego analizadas. Se utilizó un método cuasi experimental para observar la influencia que tuvieron sus discusiones grupales –utilizando su primera lengua—en el desarrollo del vocabulario en la segunda lengua. Se aplicaron evaluaciones pre y post con el fin de tener un registro del desarrollo del vocabulario de los estudiantes y las funciones que la lengua materna cumplió fueron codificadas como sugirieron DiCamilla y Antón (2012). Los resultados demostraron que la lengua materna de los estudiantes jugó un rol mayor en su interacción mientras desarrollaban en conjunto actividades colaboración, y sirvió para el desarrollo del vocabulario de la segunda lengua. Más aun, los resultados sugieren que la forma en la que alumnos contribuyeron individualmente en las discusiones afectó los resultados en sus aprendizajes

NASA/FAA general aviation crash dynamics program

The program involves controlled full scale crash testing, nonlinear structural analyses to predict large deflection elastoplastic response, and load attenuating concepts for use in improved seat and subfloor structure. Both analytical and experimental methods are used to develop expertise in these areas. Analyses include simplified procedures for estimating energy dissipating capabilities and comprehensive computerized procedures for predicting airframe response. These analyses are developed to provide designers with methods for predicting accelerations, loads, and displacements on collapsing structure. Tests on typical full scale aircraft and on full and subscale structural components are performed to verify the analyses and to demonstrate load attenuating concepts. A special apparatus was built to test emergency locator transmitters when attached to representative aircraft structure. The apparatus is shown to provide a good simulation of the longitudinal crash pulse observed in full scale aircraft crash tests

Evaluation of exercises designed to increase children's use of descriptive words.

Thesis (Ed.M.)--Boston Universit