COLLISIONAL VERSUS COLLISIONLESS MATTER: A ONE-DIMENSIONAL ANALYSIS OF GRAVITATIONAL CLUSTERING

We present the results of a series of one-dimensional N-body and hydrodynamical simulations which have been used for testing the different clustering properties of baryonic and dark matter in an expanding background. Initial Gaussian random density perturbations with a power-law spectrum $P(k) \propto k^n$ are assumed. We analyse the distribution of density fluctuations and thermodynamical quantities for different spectral indices $n$ and discuss the statistical properties of clustering in the corresponding simulations. At large scales the final distribution of the two components is very similar while at small scales the dark matter presents a lumpiness which is not found in the baryonic matter. The amplitude of density fluctuations in each component depends on the spectral index $n$ and only for $n=-1$ the amplitude of baryonic density fluctuations is larger than that in the dark component. This result is also confirmed by the behaviour of the bias factor, defined as the ratio between the r.m.s of baryonic and dark matter fluctuations at different scales: while for $n=1,\ 3$ it is always less than unity except at very large scales where it tends to one, for $n=-1$ it is above 1.4 at all scales. All simulations show also that there is not an exact correspondence between the positions of largest peaks in dark and baryonic components, as confirmed by a cross-correlation analysis. The final temperatures depend on the initial spectral index: the highest values are obtained for $n=-1$ and are in proximity of high density regions.Comment: 7 pages Latex (MN style) + 10 figures in postscript files, uuencoded submitted to MNRA

Testing students' ability to use derivatives, integrals, and vectors in a purely mathematical context and in a physical context

In this article, we discuss the development and the administration of a multiple-choice test, which we named Test of Calculus and Vectors in Mathematics and Physics (TCV-MP), aimed at comparing students' ability to answer questions on derivatives, integrals, and vectors in a purely mathematical context and in the context of physics. The comparison between the two contexts was achieved by using parallel (isomorphic) questions in mathematics and physics. The final version of the test contains 34 items (17 in a purely mathematical context and 17 in the context of physics) involving different representations (graphs, words, numbers, and formal expressions) of the concepts covered by the test. The test was administered in Spring 2018 to 1252 first-year students enrolled in 23 different degree programs of the School of Science and the School of Engineering of the University of Padua. We assessed the validity, reliability, and discriminatory power of the test both as a whole and at the single-item level, obtaining values within the desired ranges. The analysis of students' answers to individual items and the comparison between parallel mathematics and physics items provides insights into the factors that affect students' ability to use derivatives, integrals, and vectors in the context of introductory physics. We believe that the instrument we have developed can be useful not only for research purposes, but also for instructors and for students

The role of scientific museums in physics and astronomy education courses for pre-service primary school teachers

Within the Physics Education Course for pre-service primary school teachers, in the academic year 2013-14, we have developed an educational project in collaboration with the Museum of the History of Physics of Padua University and the Museum of Astronomy of Padua Astronomical Observatory. The main goals of the project were: (a) to stimulate in pre-service teachers a reflection on how scientific museums could be used for proposing effective and motivating scientific experiences within primary school curriculum, (b) make them to experience and recognize the advantages of an historical and narrative approach in the learning of a new subject. The presentations in the Museums were focused on the relation between the construction of new instruments and the evolution of scientific knowledge. Cosmological models from the ancient times up to eighteenth century were presented using instruments, paintings and significant narratives of important astronomers and physicists of the past. The effectiveness of the experience has been evaluated through a written essay that students have been asked to do at the end of both visits

Arg206 of SNAP-25 is essential for neuroexocytosis at the Drosophila melanogaster neuromuscular junction

An analysis of SNAP-25 isoform sequences indicates that there is a highly conserved arginine residue (198 in vertebrates, 206 in the genus Drosophila ) within the C-terminal region, which is cleaved by botulinum neurotoxin A, with consequent blockade of neuroexocytosis. The possibility that it may play an important role in the function of the neuroexocytosis machinery was tested at neuromuscular junctions of Drosophila melanogaster larvae expressing SNAP-25 in which Arg206 had been replaced by alanine. Electrophysiological recordings of spontaneous and evoked neurotransmitter release under different conditions as well as testing for the assembly of the SNARE complex indicate that this residue, which is at the P 1 ′ position of the botulinum neurotoxin A cleavage site, plays an essential role in neuroexocytosis. Computer graphic modelling suggests that this arginine residue mediates protein–protein contacts within a rosette of SNARE complexes that assembles to mediate the fusion of synaptic vesicles with the presynaptic plasma membrane

General Relativistic Dynamics of Irrotational Dust: Cosmological Implications

The non--linear dynamics of cosmological perturbations of an irrotational collisionless fluid is analyzed within General Relativity. Relativistic and Newtonian solutions are compared, stressing the different role of boundary conditions in the two theories. Cosmological implications of relativistic effects, already present at second order in perturbation theory, are studied and the dynamical role of the magnetic part of the Weyl tensor is elucidated.Comment: 12 pages , DFPD 93/A/6

A cosmological hydrodynamic code based on the Piecewise Parabolic Method

We present a hydrodynamical code for cosmological simulations which uses the Piecewise Parabolic Method (PPM) to follow the dynamics of gas component and an N-body Particle-Mesh algorithm for the evolution of collisionless component. The gravitational interaction between the two components is regulated by the Poisson equation which is solved by a standard FFT procedure. In order to simulate cosmological flows we have introduced several modifications to the original PPM scheme which we describe in detail. Various tests of the code are presented including adiabatic expansion, single and multiple pancake formation and three-dimensional cosmological simulations with initial conditions based on the cold dark matter scenario.Comment: 14 pages plus 10 separated figures, Latex using MN.sty, submitted to MNRA

Understanding first-year students’ curiosity and interest about physics : Lessons learned from the HOPE project

This paper focuses on results of an interview based survey of first-year university physics students, carried out within the EU Horizons in Physics Education (HOPE) project (http://hopenetwork.eu/). 94 interviews conducted in 13 universities have been analyzed to investigate the factors that inspire young people to study physics. In particular, the main motivational factor, which was proven to consist of personal interest and curiosity, was unfolded into different categories and detailed interest profiles were produced. The results are arguably useful to help academic curriculum developers and teaching personnel in physics departments to provide guidance to students in developing and focusing their interest towards specific sub-fields and/or to design targeted recruitment and outreach initiatives.Peer reviewe

Constraints at a Hadronization Deflagration Front

Properties of a hadronization front are discussed for the case in which the transition region behaves as a deflagration. As the hydrodynamics of a deflagration front can be determined only after specifying the rate of the phase transformation, we have investigated how the inclusion of the transition rate equation together with the hydrodynamical equation constrains the fluid variables on either side of the transistion front. A relationship between the temperatures of the two phases has been found and the related behaviour of the energy flux has also been derived

Supporting development of scientific competences in pre-service primary school teachers

The talk presents the structure and the expected learning outcomes of the Physics Education course for pre-service primary school teachers at Padova University. In the course, physics concepts are introduced through everyday experiences together with possible school activities that promote scientific knowledge and skills in children. In order to change the negative attitude that most of the pre-service teachers show to have towards physics, we implement particular teaching strategies, like hands-on activities, group discussion, cooperative learning and reflective writing. At the end of the course, we observe an improvement in students\u2019 attitude and self-confidence on scientific competences and science teaching methodologies

Integrazione delle competenze didattiche e disciplinari nella formazione iniziale degli insegnanti della classe A27-matematica e fisica

Nella formazione iniziale degli insegnanti \ue8 riconosciuta l\u2019importanza di coordinare l\u2019approfondimento degli aspetti pedagogico-didattici con quelli disciplinari. Spesso per\uf2 manca una reale collaborazione tra i ricercatori nel campo pedagogico-didattico e coloro che operano nei diversi settori disciplinari. La difficolt\ue0 \ue8 ancora maggiore nelle classi di concorso che coinvolgono pi\uf9 materie. Nella presentazione verranno discussi esempi di percorsi formativi in cui i futuri insegnanti sono stati posti in situazioni di apprendimento attivo e collaborativo, e in cui \ue8 stata incoraggiata la riflessione epistemologica su alcuni temi disciplinari e sui processi cognitivi coinvolti, nonch\ue8 la sperimentazione di metodologie didattiche innovative