Cosmology at the boundary of de Sitter using the dS/QFT correspondence

Using the dS/QFT correspondence in the context of inflation allows for the study of interesting, otherwise inaccessible physics. In particular, by studying inflation via its dual field theory at the boundary of the de Sitter space, it may be possible to study a regime of strongly coupled gravity at early times. The purpose of this work is to completely express cosmological observables in terms of the free parameters of a dual field theory and to compare them with CMB data. In this way, constraints on the observational parameters constrains the validity of the strongly coupled inflation picture by imposing limits on the parameters of the field theory. The fit with data defines a limit for the consistency and validity of the approach taken and shows that, within this limit, the model is almost unconstrained, but quite predictive, producing power spectra of density perturbations extremely near scale invariance

Development of an algebraic turbulence model for analysis of propulsion flows

A simple turbulence model that will be applicable to propulsion flows having both wall bounded and unbounded regions was developed and installed within the PARC Navier-Stokes code by linking two existing algebraic turbulence models. The first is the Modified Mixing Length (MML) model which is optimized for wall bounded flows. The second is the Thomas model, the standard algebraic turbulence model in PARC which has been used to calculate both bounded and unbounded turbulent flows but was optimized for the latter. This paper discusses both models and the method employed to link them into one model (referred to as the MMLT model). The PARC code with the MMLT model was applied to two dimensional turbulent flows over a flat plate and over a backward facing step to validate and optimize the model and to compare its predictions to those obtained with the three turbulence models already available in PARC

Gravitational waves from binary systems in circular orbits: Convergence of a dressed multipole truncation

The gravitational radiation originating from a compact binary system in circular orbit is usually expressed as an infinite sum over radiative multipole moments. In a slow-motion approximation, each multipole moment is then expressed as a post-Newtonian expansion in powers of v/c, the ratio of the orbital velocity to the speed of light. The bare multipole truncation of the radiation consists in keeping only the leading-order term in the post-Newtonian expansion of each moment, but summing over all the multipole moments. In the case of binary systems with small mass ratios, the bare multipole series was shown in a previous paper to converge for all values v/c < 2/e, where e is the base of natural logarithms. In this paper, we extend the analysis to a dressed multipole truncation of the radiation, in which the leading-order moments are corrected with terms of relative order (v/c)^2 and (v/c)^3. We find that the dressed multipole series converges also for all values v/c < 2/e, and that it coincides (within 1%) with the numerically ``exact'' results for v/c < 0.2.Comment: 9 pages, ReVTeX, 1 postscript figur

Physical Dissipation and the Method of Controlled Lagrangians

We describe the effect of physical dissipation on stability of equilibria which have been stabilized, in the absence of damping, using the method of controlled Lagrangians. This method applies to a class of underactuated mechanical systems including “balance” systems such as the pendulum on a cart. Since the method involves modifying a system’s kinetic energy metric through feedback, the effect of dissipation is obscured. In particular, it is not generally true that damping makes a feedback-stabilized equilibrium asymptotically stable. Damping in the unactuated directions does tend to enhance stability, however damping in the controlled directions must be “reversed” through feedback. In this paper, we suggest a choice of feedback dissipation to locally exponentially stabilize a class of controlled Lagrangian systems

Dissipation and Controlled Euler-Poincaré Systems

The method of controlled Lagrangians is a technique for stabilizing underactuated mechanical systems which involves modifying a system’s energy and dynamic structure through feedback. These modifications can obscure the effect of physical dissipation in the closed-loop. For example, generic damping can destabilize an equilibrium which is closed-loop stable for a conservative system model. In this paper, we consider the effect of damping on Euler-Poincaré (special reduced Lagrangian) systems which have been stabilized about an equilibrium using the method of controlled Lagrangians. We describe a choice of feed-back dissipation which asymptotically stabilizes a sub-class of controlled Euler-Poincaré systems subject to physical damping. As an example, we consider intermediate axis rotation of a damped rigid body with a single internal rotor

Leadership for Technology Integration: Computing the Reality

United States school districts continue to spend billions of dollars annually on various forms of technology equipment and services. Despite the widespread expectation that teachers routinely integrate technology into the curriculum to facilitate student achievement, there is substantial evidence that this is not occurring either in the manner or to the degree desirable. This study examined the extent to which computer-related technology is used in 12 school districts in North Louisiana from the perspectives of 214 site-based administrators in 149 schools. The findings suggest that technology integration remains problematic in that many teachers seem unwilling or unable to incorporate technology into the teaching and learning process. Furthermore, the data reveal that many school administrators consider themselves ill prepared to assume the role of technology leader. The implications of these and other findings for school improvement are discussed.Aux États-Unis, les districts scolaires dépensent des milliards de dollars à chaque année pour acheter divers équipements et services technologiques. Malgré les attentes généralisées voulant que les enseignants intègrent la technologie dans leur programme d’études pour faciliter l’apprentissage par les étudiants, des informations probantes considérables indiquent que cette intégration ne se produit pas, ni de la façon, ni au degré, prévus. Cette recherche a porté sur la mesure dans laquelle 12 districts scolaires du nord de la Louisiane intègrent la technologie informatique. Les données ont été recueillies auprès de 214 administrateurs dans 149 écoles. Les résultats indiquent que l’intégration de la technologie continue à poser des problèmes car plusieurs enseignants semblent peu enclins à intégrer la technologie dans leurs cours, ou incapables de le faire. De plus, les données révèlent que les administrateurs scolaires n’ont pas l’impression d’être en mesure d’assumer le rôle de chef de file en matière de technologie. L’article termine en exposant les conséquences de ce genre de résultats sur l’amélioration des écoles

Effective primary level science teaching in the Philippines

Early studies of educational achievement in developing countries emphasized the effects of material inputs (such as textbooks) over teaching practices and classroom organization. This paper examines how five teaching practices affected the achievements of fifth grade students in the Philippines - and what affected teachers'decisions to use effective teaching practices. With school, teacher, and classroom characteristics held constant, achievement was higher for students whose teachers used three teaching practices that show promise for applications in developing countries because they are effective, low cost, or cost effective: frequent tests or quizzes; small group instruction, including peer tutoring; and teaching through laboratory work, particularly for science. Teachers'decisions about whether to test students frequently were unrelated to their prior education of work experience, suggesting that school-level management may be more important in encouraging effective teaching than preservice education and training.Curriculum&Instruction,Educational Sciences,Primary Education,Secondary Education,Teaching and Learning