Dynamics of Silent Universes

We investigate the local non--linear dynamics of irrotational dust with vanishing magnetic part of the Weyl tensor, $H_{ab}$. Once coded in the initial conditions, this dynamical restriction is respected by the relativistic evolution equations. Thus, the outcome of the latter are {\it exact solutions} for special initial conditions with $H_{ab}=0$, but with no symmetries: they describe inhomogeneous triaxial dynamics generalizing that of a fluid element in a Tolman--Bondi, Kantowski--Sachs or Szekeres geometry. A subset of these solutions may be seen as (special) perturbations of Friedmann models, in the sense that there are trajectories in phase--space that pass arbitrarily close to the isotropic ones. We find that the final fate of ever--expanding configurations is a spherical void, locally corresponding to a Milne universe. For collapsing configurations we find a whole family of triaxial attractors, with vanishing local density parameter $\Omega$. These attractors locally correspond to Kasner vacuum solutions: there is a single physical configuration collapsing to a degenerate {\it pancake}, while the generic configuration collapses to a triaxial {\it spindle} singularity. These {\it silent universe} models may provide a fair representation of the universe on super horizon scales. Moreover, one might conjecture that the non--local information carried by $H_{ab}$ becomes negligible during the late highly non--linear stages of collapse, so that the attractors we find may give all of the relevant expansion or collapse configurations of irrotational dust.Comment: 40 pages with 4 figures, compressed and uuencoded PostScript file, submitted to ApJ, SISSA preprint Ref. 85/94/

Second-order matter perturbations in a LambdaCDM cosmology and non-Gaussianity

We obtain exact expressions for the effect of primordial non-Gaussianity on the matter density perturbation up to second order in a LambdaCDM cosmology, fully accounting for the general relativistic corrections arising on scales comparable with the Hubble radius. We present our results both in the Poisson gauge and in the comoving and synchronous gauge, which are relevant for comparison to different cosmological observables.Comment: 15 pages. LaTeX file. Invited article for CQG issue on non-linear cosmolog

An instructional experience for pre-service teachers: integrating simulations and hands-on activities in physics teaching

Simulations are a valuable tool in teaching modern science. We report on an experiment in a physics laboratory on electricity using both simulations as well as hands-on activities. The laboratory was implemented as part of a course for pre-service secondary school physics teachers. The 45 participants were divided into two groups, one performing first simulations and then hands-on activities, the other in the reversed order. The laboratory activities focused on DC circuits related to real-life situations, like a multiple socket or a chandelier modeled with simple wires, batteries and bulbs. The participants were asked to make predictions of the outcome before conducting each task and to compare their predictions with the observations and measurements they made during the activities. The participants were asked to make predictions of the outcome before conducting each task and to compare their predictions with the observations and measurements they made during the activities. No significant differences in performance were observed between the two groups, suggesting that in this experiment simulations did not help the pre-service teachers in transferring their conceptual knowledge to practical application

Student interviews on inspirational and drop-out factors progress report (Sub-Group WG1-B)

Progress report on the survey on inspirational and drop-out factors we carried out, within the activities of WG1, through individual interviews to physics students. In particular, we present: 1) the research groups involved in the survey and in the data analysis; 2) the sample; 3) the research questions; 4) the quantitative and qualitative research methods of data analysis we are designing; 4) the preliminary analysis and the problematic issues we are dealing with; 5) discussion, implications and future plans

What inspires young people to study physics? Results from the WG1 interviews survey

The talk will focus on the main results of an Interview based Survey of 1st Year University Physics Students, carried out within Working Group 1 (WG1) of the HOPE project. Among the HOPE activities, 112 interviews have been conducted in 16 universities, in order to investigate in some depth the factors that inspire young people to study physics and to identify possible critical factors which can produce the dropping out.The individual interviews have been carried out on a selection of students who had previously answered the WG1 Questionnaire on the inspirational factors, led by Gareth Jones from the Imperial College, London. In the talk, we will show how the interviews helped us to unpack the main results achieved with the questionnaire survey. In particular, we will present a comprehensive picture of \u201ccuriosity\u201d which turned out to be the predominant motivating factor and we will show how the interviews can throw extra light on reasons for comparatively low scores for factors like (i) enhancing employment prospects, (ii) effect of physics teacher, (iii) scientists in the family

The daily life of a researcher introduced with an online data analysis experience based on visual programming

A common criticism for the Italian higher education system is the gap that separates it from the employment landscape. To improve this situation, our department and schools are sponsoring internships, to expose the students to the work life. Groups of two high school students are invited to work with researchers for a week. A tutor introduces them to the research theme and proposes related activities. In order not to require previous experience with programming languages, the visual programming language Blockly is used as the development toolkit, for its suitability for educational activities. We present the development of new functionalities for Blockly purposely for the project: online reading data from a real detection system, interactive analysis, and online data visualization. The activity was successfully experienced by the students hosted in the research group. The actual implementation of the analysis algorithm was quickly achieved, even with no prior experience with data analysis. We bypassed the difficulties related to the syntax of programming languages, by employing Blockly and our added features; this allowed us to focus on the fundamental concepts. The students enjoyed the whole experience and were very proactive asking relevant questions and proposing ideas

EVAPORATION OF QUARK DROPS DURING THE COSMOLOGICAL Q-H TRANSITION

We have carried out a study of the hydrodynamics of disconnected quark regions during the final stages of the cosmological quark-hadron transition. A set of relativistic Lagrangian equations is presented for following the evaporation of a single quark drop and results from the numerical solution of this are discussed. A self-similar solution is shown to exist and the formation of baryon number density inhomogeneities at the end of the drop contraction is discussed.Comment: 12 pages Phys. Rev. format, uuencoded postscript file including 12 figure

Academic careers and educational strategies to contrast dropout: an analysis of Physics, Astronomy and Physics and Optometry bachelor degree courses at University of Padua

We studied the development of the academic careers of Physics, Astronomy and Optics and Optometry Bachelor Degree students. Groups of students from 2001/02 to 2014/15 were analysed in terms of secondary school attended, final mark obtained, geographic origins and gender, to collect results about enrolment, dropout, transfer, and graduated students. We found that increasing enrolment was accompanied by growing dropout rate. To contrast this phenomenon, a programme of formative tutoring has been activated. Weekly meetings with senior students and professors of the degree course and the university student services allow for orientation and empowerment of first-year students

FisicaMente: supporting first-year students in transferring mathematical skills and knowledge to a physical context.

Research in physics education shows that students often enter university-level physics courses lacking the prerequisite mathematics skills and knowledge and/or the ability to apply them in a physical context. To analyze these difficulties and provide students with effective feedback, we have designed two multiple-choice tests, inspired by current research in physics education and in cognitive psychology, and starting from a taxonomy of the most frequent errors made by students. We assessed the tests’ content reliability and discriminatory power both globally and at the single-item level. The tests were administered to first-year students enrolled in Science and Engineering courses

Innovating physics teaching through teachers’ learning communities and action research

The paper provides information, foundation and supporting evidence about a possible structure of a research-based in-service program for physics teachers aimed at improving their use of the laboratory. We present our model and we describe the CoLLabora project where the model was first implemented. The results suggest that the program actually produced positive changes in the participants’ ideas about the laboratory, its actual use in their teaching practice, and in students’ outcomes. We also present two case studies and we outline some research lines and the ‘teacher training cascade’ that have developed from the project