Modelling the light-curves of objects tidally disrupted by a black hole

Tidal disruption by massive black holes is a phenomenon, during which a large part of gravitational energy can be released on a very short time-scale. The time-scales and energies involved during X-ray and IR flares observed in Galactic centre suggest that they may be related to tidal disruption events. Furthermore, aftermath of a tidal disruption of a star by super-massive black hole has been observed in some galaxies, e.g. RX J1242.6-1119A. All these discoveries increased the demand for tools for tidal disruption study in curved space-time. Here we summarise our study of general relativistic effects on tidal deformation of stars and compact objects.Comment: 2 pages, to appear in the proceedings of the JENAM 2008, Symposium 7: "Grand Challenges in Computational Astrophysics

The Use of Digital Video Annotation in Teacher Training: The Teachers’ Perspectives

The use of digital video offers interesting opportunities in teacher training, particularly the possibilities provided by video annotation, whereby people can add and share comments and opinions on the same videos, even from different places. This exploratory study aims to examine teachers’ perspectives of this technology, taking into account both their explicit and implicit evaluations. Different methods of using video annotation for training are compared, one based on its individual use, another supported by various types of tutorship. The data were collected and analysed first through a quantitative phase, followed by an in-depth qualitative phase. It is pointed out that to make this technology fully operational it is important to address the cultural and psychosocial aspects that control the emotional conditions which arise when one’s teaching behaviour is being observed and assessed

Do flares in Sagittarius A* reflect the last stage of tidal capture?

In recent years the case for the presence of 3-4 10^6 M_sun black hole in our Galactic Center has gained strength from results of stellar dynamics observations and from the detection of several rapid X-ray and IR flares observed in the Sagittarius A* from 2000 to 2004. Here we explore the idea that such flares are produced when the central black hole tidally captures and disrupts a small body - e.g. a comet or an asteroid.Comment: 6 pages, 9 figures, acknowledgments added, to appear in the Proceedings of the Albert Einstein's Century International Conference, Paris 200

Optical conductivity of CuO_2 infinite-layer films

The infrared conductivity of CaCuO_2, SrCuO_{2-y}, and Sr_{0.85}Nd_{0.15}CuO_2 infinite-layer films is obtained from reflectivity measurements by taking into account the substrate contribution. SrCuO_{2-y} and Sr_{0.85}Nd_{0.15}CuO_2 exhibit extra-phonon modes and structured bands in the midinfrared, not found in stoichiometric CaCuO_2. These features mirror those observed in the perovskitic cuprates, thus showing that the polaronic properties of high-T_c superconductors are intrinsic to the CuO_2 planes.Comment: File latex, 5 p. incl. 4 fig. in epsf. Submitted to Solid State Com

Tecnologie per apprendere: quale il ruolo dell’Evidence Based Education?

Se ci chiediamo se le tecnologie migliorino gli apprendimenti, la ricerca «evidence-based» ci fornisce ormai un corpus consistente di sintesi di conoscenza, ottenute prevalentemente attraverso comparazioni sistematiche tra indagini sperimentali. Nella prima parte del lavoro, si presenta lo stato dell’arte in ottica evidence based sull'efficacia delle tecnologie sugli apprendimenti scolastici (K-12), sull’e-learning / blended learning, sulla lettura digitale e sulla LIM e si sottolinea il contrasto tra tali dati e la «retorica» che accompagna da tempo l’innovazione tecnologica nella scuola. Nella seconda parte del lavoro, si sottolinea come una valutazione basata sulla evidenza, se necessaria, non rappresenta però una condizione sufficiente per le decisioni da assumere sull'innovazione tecnologica nella scuola. Le tecnologie hanno implicazioni pluridimensionali e per una loro corretta collocazione nella scuola occorre anche considerare potenzialità inespresse e integrare le informazioni «evidence-based» con altri criteri di valutazione, ispirati a motivi di utilità o di natura squisitamente etica e valoriale

Temperature dependence of the optical spectral weight in the cuprates: Role of electron correlations

We compare calculations based on the Dynamical Mean-Field Theory of the Hubbard model with the infrared spectral weight $W(\Omega,T)$ of La$_{2-x}$Sr$_x$CuO$_4$ and other cuprates. Without using fitting parameters we show that most of the anomalies found in $W(\Omega,T)$ with respect to normal metals, including the existence of two different energy scales for the doping- and the $T$-dependence of $W(\Omega,T)$, can be ascribed to strong correlation effects.Comment: 4 pages, 3 figures. Minor corrections, corrected some typos and added reference

What brakes the Crab pulsar?

Optical observations provide convincing evidence that the optical phase of the Crab pulsar follows the radio one closely. Since optical data do not depend on dispersion measure variations, they provide a robust and independent confirmation of the radio timing solution. The aim of this paper is to find a global mathematical description of Crab pulsar's phase as a function of time for the complete set of published Jodrell Bank radio ephemerides (JBE) in the period 1988-2014. We apply the mathematical techniques developed for analyzing optical observations to the analysis of JBE. We break the whole period into a series of episodes and express the phase of the pulsar in each episode as the sum of two analytical functions. The first function is the best-fitting local braking index law, and the second function represents small residuals from this law with an amplitude of only a few turns, which rapidly relaxes to the local braking index law. From our analysis, we demonstrate that the power law index undergoes "instantaneous" changes at the time of observed jumps in rotational frequency (glitches). We find that the phase evolution of the Crab pulsar is dominated by a series of constant braking law episodes, with the braking index changing abruptly after each episode in the range of values between 2.1 and 2.6. Deviations from such a regular phase description behave as oscillations triggered by glitches and amount to fewer than 40 turns during the above period, in which the pulsar has made more than 2.0e10 turns. Our analysis does not favor the explanation that glitches are connected to phenomena occurring in the interior of the pulsar. On the contrary, timing irregularities and changes in slow down rate seem to point to electromagnetic interaction of the pulsar with the surrounding environment.Comment: 11 pages, 8 figures, 3 tables; accepted for publication in Astronomy & Astrophysic

Il microteaching rinascerà a nuova vita ? Video annotazione e sviluppo della riflessività del docente.

Lo sviluppo del pensiero riflessivo è sempre più al centro del dibattito relativo alla formazione degli insegnanti. Una possibilità per favorirlo può essere rappresentata oggi dall’impiego dei video digitali che in virtù della loro flessibilità ed amichevolezza d’uso ripropongono, con funzioni e modalità del tutto nuove, metodologie ed esperienze svolte negli anni passati con la tecnica del microteaching. In questo ambito una funzionalità interessante è rappresentata dalla video an notazione, ovvero dalla possibilità di inserire commenti testuali sincronizzati a specifici momenti della registrazione di una lezione, rendendo altresì condivisibile, in rete, l’esperienza individuale all’interno di una comunità di tirocinanti in formazione. Il presente lavoro è indirizzato a valutare se l’impiego della video annotazione si differenzi da altri strumenti di supporto (scaffold) nel promuovere la riflessione degli insegnanti. A questo scopo vengono comparati tre gruppi di giovani insegnanti chiamati a riflettere e commentare una propria lezione con dispositivi diversi: il primo senza scaffold, il secondo con l’ausilio di un questionario orientativo, il terzo con l’ausilio aggiuntivo di una revisione del video della lezione e della video annotazione. I dati raccolti mostrano significative differenze nella tipologie dei commenti in rapporto ai diversi dispositivi preposti all’autoriflessione ma anche come queste differenze non si conservino quando i gruppi sono ricollocati nella condizione originaria.Increasing the quality of reflective practice in teacher training is a focal point in the current educational debate. A new opportunity has been opened up by the use of digital videos offering highly innovative functions according to procedures resembling the microteaching experiences of recent decades. An interesting tool in this context is video annotation, a function offered by various software programmes allowing the user and/or observers to add comments to the digital videos of the lessons and to share them in a community of practice This work intends to examine how video-supported reflection techniques influence teachers’ capacity for self-analysis, revealed by means of written comments, and will focus, in particular, on how the video annotation tool may influence the type of comments made. The study compared three groups of young teachers, who were asked to reflect and comment on one of their lessons in three different sets of conditions: the first without scaffolding, the second with the help of a questionnaire, the third with the additional support of a review of the lesson video using the video annotation tool. The data collected showed that types of comments made varied significantly depending on the self-reflection technique adopted but that these differences were not maintained when the groups reverted to the original conditions

Effects of Superconductivity and Charge Order on the sub-Terahertz reflectivity of La1.875_{1.875}Ba0.125−y_{0.125-y}Sry_{y}CuO4_4

The reflectivity $R (\omega)$ of both the $ab$ plane and the c axis of two single crystals of La$_{1.875}$Ba$_{0.125-y}$Sr$_{y}$CuO$_4$ has been measured down to 5 cm$^{-1}$, using coherent synchrotron radiation below 30 cm$^{-1}$. For $y$ = 0.085, a Josephson Plasma Resonance is detected at $T \ll T_c$ = 31 K in $R_{c} (\omega)$, and a far-infrared peak (FIP) appears in the optical conductivity below 50 K, where non-static charge ordering (CO) is reported by X-ray scattering. For $y$ = 0.05 ($T_c$ = 10 K), a FIP is observed in the low-temperature tetragonal phase below the ordering temperature $T_{CO}$. At 1/8 doping the peak frequency scales linearly with $T_{CO}$, confirming that the FIP is an infrared signature of CO, either static or fluctuating.Comment: v2: longer version, 9 pages, 6 color figure