319 research outputs found
Dynamics of Silent Universes
We investigate the local non--linear dynamics of irrotational dust with
vanishing magnetic part of the Weyl tensor, . 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 , 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 . 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 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 testsâ 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 teachersâ 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 participantsâ ideas about the laboratory, its actual use in their teaching practice, and in studentsâ outcomes. We also present two case studies and we outline some research lines and the âteacher training cascadeâ that have developed from the project
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