A darkless space-time

In cosmology it has become usual to introduce new entities as dark matter and dark energy in order to explain otherwise unexplained observational facts. Here, we propose a different approach treating spacetime as a continuum endowed with properties similar to the ones of ordinary material continua, such as internal viscosity and strain distributions originated by defects in the texture. A Lagrangian modeled on the one valid for simple dissipative phenomena in fluids is built and used for empty spacetime. The internal "viscosity" is shown to correspond to a four-vector field. The vector field is shown to be connected with the displacement vector field induced by a point defect in a four-dimensional continuum. Using the known symmetry of the universe, assuming the vector field to be divergenceless and solving the corresponding Euler-Lagrange equation, we directly obtain inflation and a phase of accelerated expansion of spacetime. The only parameter in the theory is the "strength" of the defect. We show that it is possible to fix it in such a way to also quantitatively reproduce the acceleration of the universe. We have finally verified that the addition of ordinary matter does not change the general behaviour of the model.Comment: 13 pages, 7 figures Typos; section V on Newtonian limit adde

Spherical symmetry in a dark energy permeated space-time

The properties of a spherically symmetric static space-time permeated of dark energy are worked out. Dark energy is viewed as the strain energy of an elastically deformable four dimensional manifold. The metric is worked out in the vacuum region around a central spherical mass/defect in the linear approximation. We discuss analogies and differences with the analogue in the de Sitter space time and how these competing scenarios could be differentiated on an observational ground. The comparison with the tests at the solar system scale puts upper limits to the parameters of the theory, consistent with the values obtained applying the classical cosmological tests.Comment: 14 pages, 1 figure, in press on Classical and Quantum Gravit

Cosmological constraints for the Cosmic Defect theory

The Cosmic Defect theory has been confronted with four observational constraints: primordial nuclear species abundances emerging from the big bang nucleosynthesis; large scale structure formation in the universe; cosmic microwave background acoustic scale; luminosity distances of type Ia supernovae. The test has been based on a statistical analysis of the a posteriori probabilities for three parameters of the theory. The result has been quite satisfactory and such that the performance of the theory is not distinguishable from the one of the Lambda-CDM theory. The use of the optimal values of the parameters for the calculation of the Hubble constant and the age of the universe confirms the compatibility of the Cosmic Defect approach with observations.Comment: 13 pages, 1 figure, in press on IJMP

Pulsars as celestial beacons to detect the motion of the Earth

In order to show the principle viability of a recently proposed relativistic positioning method based on the use of pulsed signals from sources at infinity, we present an application example reconstructing the world-line of an idealized Earth in the reference frame of distant pulsars. The method considers the null four-vectors built from the period of the pulses and the direction cosines of the propagation from each source. Starting from a simplified problem (a receiver at rest) we have been able to calibrate our procedure, evidencing the influence of the uncertainty on the arrival times of the pulses as measured by the receiver, and of the numerical treatment of the data. The most relevant parameter turns out to be the accuracy of the clock used by the receiver. Actually the uncertainty used in the simulations combines both the accuracy of the clock and the fluctuations in the sources. As an evocative example the method has then been applied to the case of an ideal observer moving as a point on the surface of the Earth. The input have been the simulated arrival times of the signals from four pulsars at the location of the Parkes radiotelescope in Australia. Some substantial simplifications have been made both excluding the problems of visibility due to the actual size of the planet, and the behaviour of the sources. A rough application of the method to a three days run gives a correct result with a poor accuracy. The accuracy is then enhanced to the order of a few hundred meters if a continuous set of data is assumed. The method could actually be used for navigation across the solar system and be based on artificial sources, rather than pulsars. The viability of the method, whose additional value is in the self-sufficiency, i.e. independence from any control from other operators, has been confirmed.Comment: 11 pages, 3 eps figures; revised to match the version accepted for publication in IJMP

Gravitomagnetism, clocks and geometry

New techniques to evaluate the clock effect using light are described. These are based on the flatness of the cylindrical surface containing the world lines of the rays constrained to move on circular trajectories about a spinning mass. The effect of the angular momentum of the source is manifested in the fact that inertial observers must be replaced by local non rotating observers. Starting from this an exact formula for circular trajectories is found. Numerical estimates for the Earth environment show that light would be a better probe than actual clocks to evidence the angular momentum influence. The advantages of light in connection with some principle experiments are shortly reviewed.Comment: TCI Latex, 12 pages, 2 figures. To appear in European Journal of Physic

Einstein-Cartan theory as a theory of defects in space-time

The Einstein-Cartan theory of gravitation and the classical theory of defects in an elastic medium are presented and compared. The former is an extension of general relativity and refers to four-dimensional space-time, while we introduce the latter as a description of the equilibrium state of a three-dimensional continuum. Despite these important differences, an analogy is built on their common geometrical foundations, and it is shown that a space-time with curvature and torsion can be considered as a state of a four-dimensional continuum containing defects. This formal analogy is useful for illustrating the geometrical concept of torsion by applying it to concrete physical problems. Moreover, the presentation of these theories using a common geometrical basis allows a deeper understanding of their foundations.Comment: 18 pages, 7 EPS figures, RevTeX4, to appear in the American Journal of Physics, revised version with typos correcte

The Potential Impact of Online Learning on Economically Disadvantaged Students

Opportunity gaps have consistently been prevalent in the United States’ education system and that continues today. The struggle to provide economically disadvantaged students the equity necessary to ensure opportunities exist, similar to those present for students of economic advantage, remains a pervasive dilemma for which there are few solutions. As technology continually changes the global marketplace, it is doing the same to education. Educators have an enormous impact on the lives of their students, both in and out of the classroom and through their instruction, there are techniques available to ensure that students remain engaged. One such method is by using technology, specifically online/virtual learning to not only captivate student interest, but to reduce the already wide chasm that exists between students with and without the means to an equitable education. This action research study sought to determine any possible correlation that may be present between students that are economically disadvantaged who enroll in online courses and the effect it may have on their ability to complete those courses. Several theoretical viewpoints framed the study, including critical theory, social learning theory, ecological systems theory and online learning theory. The study was completed using data from online course enrollments from a southeastern Pennsylvania school district from a three-year time period. The online course data was further examined based on several defining characteristics, such as required as opposed to elective and the location in which students partook in the course; onsite or offsite. Online students were also delineated into whether they were considered economically disadvantaged based on eligibility for the Free and Reduced Lunch Program. Teachers from the school district’s middle school and high school were surveyed for their perceptions about online/virtual learning and the instruction of economically disadvantaged students. Drawing on all of the compiled data, the study showed that students who completed online, required courses in an onsite capacity passed them more frequently than those who took online, required courses offsite. The study also revealed that there are discrepancies between teachers and students in their perceptions of the effectiveness and usefulness of online/virtual learning

A Qualitative Multi-site Case Study: Components, Strengths, & Benefits of Studio Production in Traditional Public High Schools

My own experiences in the visual arts lead me to a personal understanding of their importance and an interest in arts education advocacy. In order to advocate for the visual arts one must know what the arts teach and how to talk about those benefits. The lack of research on what is taught in the visual arts makes discussing the benefits difficult. Hetland, Winner, Veenema, & Sheridan (2007) began to close this gap with their findings of eight Studio Habits of Mind (develop craft, engage and persist, envision, express, observe, reflect, stretch and explore, understanding the art world) being taught in visual arts classrooms. However, their data was only collected from art magnet schools of the Boston area. My qualitative multisite case study builds on Hetland‘s et al. (2007) findings by focusing on the extent to which the Studio Habits of Mind are present within traditional public high schools. Analysis of the data collected in this study began with reflective notes during data collection, and continued with reading and re-reading of field notes, transcriptions of teacher interviews, and course documents. What was done and said in the classrooms were put into categories based on what they were teaching or encouraging students to learn. In addition to the eight Studio Habits of Mind I also found responsibility and confidence being taught. As the data was collected and analyzed differences in the extent to which each Studio Habit of Mind was taught began to surface between the schools, the teachers, and the class levels. Demonstrations, language, time, and emersion were found to support the teaching of the Studio Habits of Mind when used in a balanced teaching approach