Polarization dependent Brillouin gain in randomly birefringent fibers

An extensive study of the alignment between the pump, the signal and the polarization dependent gain (PDG) vectors in stimulated Brillouin amplification in randomly birefringent fibers is realized by numerically integrating the equations governing the propagation. At the fiber output, the signal tends to align to the PDG vector for large pump power because of the nonlinear polarization pulling effect. The PDG vector, for large random birefringence, aligns to a state that has the same linear component of the pump but opposite circular component.Comment: 3 pages submitted to IEEE Photonics Technology Letter

Errori e difficoltà nella comprensione del concetto di variabile algebrica. Uno studio con ragazzi della scuola secondaria di primo grado

In questo articolo si analizzano gli errori commessi da un gruppo di 118 ragazzi italiani al termine della scuola secondaria di primo grado nell’affrontare tre diversi usi della variabile algebrica (incognita, numero generico, variabili in relazione funzionale) e nel contempo si illustra come si può utilizzare il Modello 3UV per individuare le difficoltà che si nascondono dietro tali errori. I risultati mostrano che i ragazzi sono stati in grado di manipolare espressioni lineari, risolvere equazioni, riconoscere regole o relazioni funzionali e applicarle, ma solo in casi molto semplici. Nonostante il livello elementare degli esercizi, hanno trovato difficoltà nel percepire la variazione, nell’interpretare la variabile nei suoi differenti ruoli, nello scrivere in simboli equazioni, regole e relazioni funzionali. Le loro risposte rivelano una limitata esperienza nella riflessione sul significato della variabile e la poca padronanza nel suo utilizzo.While analyzing the errors 118 Italian students made when working with three different uses of algebraic variable (unknown, general number, variables in functional relationship) at the end of the first cycle of secondary school, the way in which the 3UV Model can be used to reveal the difficulties hidden behind the errors is illustrated. Results show students’ capability in manipulating linear expressions, solving equations, and recognizing general rules and functional relationships but only for very simple cases. In spite of the elementary level of the exercises, pupils had difficulty coping with perceiving variation, interpreting the different role of variables, and writing in symbols equations, general rules and functional relationships. These results point to a limited experience in reflecting on the meaning a variable can have and a poor capability in using it

Riflessioni sulle attività del progetto “La matematica dei ragazzi: scambi di esperienze tra coetanei”

Le attività laboratoriali svolte durante la manifestazione “La matematica dei ragazzi” possono essere raggruppate, in generale, in due grandi blocchi: la finalità principale del primo di essi è la motivazione verso lo studio della matematica, quella del secondo è la didattica. Il contributo invita a riflettere su ciascuna di queste due tendenze. Si afferma che per motivare i ragazzi sarebbe auspicabile aiutarli ad assumere un atteggiamento critico verso la matematica, offrendo, ad esempio, degli elementi che li stimolino a riflettere sullo sviluppo storico delle idee matematiche. A proposito della didattica, si fornisce un esempio nel quale si mostra l’importanza di associare spiegazioni teoriche e attività pratiche per migliorare la comprensione e l’apprendimento dei concetti matematici. Infine, si evidenziano le opportunità che la manifestazione “La matematica dei ragazzi” offre non solo per avvicinare i ragazzi alla matematica, ma anche per svolgere ricerche interessanti, con i partecipanti come soggetto di studio

Il Modello 3UV: uno strumento teorico a disposizione degli insegnanti di matematica

Dopo un’introduzione, nella quale si giustifica la necessità di uno strumento teorico che permetta di analizzare le concezioni degli allievi riguardo al complesso concetto di variabile algebrica e che serva da guida per progettare strategie più efficaci per favorirne l’apprendimento, si descrive brevemente uno strumento di questo tipo, chiamato Modello 3UV. Si dà poi qualche esempio atto a illustrare la sua utilità per far comprendere meglio agli insegnanti le risposte degli alunni a quesiti che coinvolgono il concetto di variabile e per progettare strategie per superare eventuali difficoltà.The need for a theoretical model is explained in the introduction. It will allow an analysis of students’ concepts regarding algebraic variables and the formulation of strategies to help students develop a better understanding of this notion. A theoretical model with these characteristics, named 3UV Model, is briefly described. Examples are given to illustrate how it can be used by mathematics teachers who want to improve the understanding of their students’ answers concerning the notion of variables as well as the use of strategies to overcome associated difficulties.Fondazione CRTriest

Synthesis And Characterization Of Polyynes End-Capped By Biphenyl Groups ({\Alpha},{\Omega}-Biphenylpolyynes)

Stable polyyne chains terminated with biphenyl end groups (a,u-biphenylpolyynes) were synthesized in a single step through a simple procedure by using the Cadiot-Chodkiewicz reaction conditions. The a,ubiphenylpolyynes were separated through HPLC analysis and identified by means of their electronic absorption spectra. The a,u-biphenylpolyynes were studied by FT-IR and Raman spectroscopy and the spectral interpretation was supported with DFT calculations. A peculiarly low reactivity of a,u-biphenylpolyynes with ozone was observed.Comment: The research leading to these results has received funding from the European Research Council Consolidator Grant EspLORE (ERC-2016-CoG Grant No.724610

Swift/XRT- NuSTAR spectra of type 1 AGN]{Swift/XRT- NuSTAR spectra of type 1 AGN: confirming INTEGRAL results on the high energy cut-off

We present the 0.5 - 78 keV spectral analysis of 18 broad line AGN belonging to the INTEGRAL complete sample. Using simultaneous Swift-XRT and NuSTAR observations and employing a simple phenomenological model to fit the data, we measure with a good constraint the high energy cut-off in 13 sources, while we place lower limits on 5 objects. We found a mean high-energy cut-off of 111 keV (standard deviation = 45 keV) for the whole sample, in perfect agreement with what found in our previous work using non simultaneous observations and with what recently published using NuSTAR data. This work suggests that simultaneity of the observations in the soft and hard X-ray band is important but not always essential, especially if flux and spectral variability are properly accounted for. A lesser agreement is found when we compare our cut-off measurements with the ones obtained by Ricci et al. (2017) using Swift-BAT high energy data, finding that their values are systematically higher than ours. We have investigated whether a linear correlation exists between photon index and the cut-off and found a weak one, probably to be ascribed to the non perfect modelling of the soft part of the spectra, due to the poor statistical quality of the 2-10 keV X-ray data. No correlation is also found between the Eddington ratio and the cut-off, suggesting that only using high statistical quality broad-band spectra is it possible to verify the theoretical predictions and study the physical characteristics of the hot corona and its geometry.Comment: 12 pages, 11 figures, accepted for publication in Monthly Notices of the Royal Astronomical Societ

Creencias y actitudes hacia las matemáticas. Un estudio con alumnos de bachillerato

Se presentan los resultados de un estudio exploratorio, cuyo propósito es analizar las creencias y las actitudes hacia las matemáticas de estudiantes mexicanos de último año de bachillerato y, a partir de esta información explorar la intención de elección de carrera (IEC). El objetivo es obtener información que nos permita formular algunas hipótesis acerca de la relación entre creencias y actitudes hacia las matemáticas, y su relación con la IEC. Participaron 55 estudiantes que cursaban el último año de bachillerato. Para determinar las actitudes hacia las matemáticas se aplicó la escala AMMEC y para determinar las creencias se aplicaron cuatro sub-escalas del cuestionario de Fennema-Sherman. Los resultados sugieren que no hay una relación directa entre tipo de actitud y tipo de creencias, pero si se perfilan asociadas con la IEC. Próximamente este estudio se realizará con una población de estudiantes mucho más amplia

The NuSTAR view of the Seyfert Galaxy HE 0436-4717

We present the multi epoch spectral analysis of HE 0436-4717, a bright Seyfert 1 galaxy serendipitously observed by the high energy satellite NuSTAR four times between December 2014 and December 2015. The source flux shows modest variability within each pointing and among the four observations. Spectra are well modelled in terms of a weakly variable primary power law with constant photon index ($\Gamma$=2.01$\pm$0.08). A constant narrow \ion{Fe} K$\alpha$ emission line suggests that this feature has an origin far from the central black hole, while a broad relativistic component is not required by the data. The Compton reflection component is also constant in flux with a corresponding reflection fraction R=0.7$^{+0.2}_{-0.3}$. The iron abundance is compatible with being Solar (A$_{Fe}$=1.2$^{+1.4}_{-0.4}$), and a lower limit for the high energy cut-off E$_c$>280 keV is obtained. Adopting a self-consistent model accounting for a primary Comptonized continuum, we obtain a lower limit for the hot corona electron temperature kT$_e$>65 keV and a corresponding upper limit for the coronal optical depth of $\tau_e$<1.3. The results of the present analysis are consistent with the locus of local Seyfert galaxies in the kT$_e$-$\tau_e$ and temperature-compactness diagrams.Comment: accepted for publication in A&

Experiencias pre-algebraicas

Algunas de las dificultades que encuentran los alumnos que se inician en el estudio del algebra, pueden deberse a la falta de experiencia previa en tratar numéricamente problemas matemáticos de distinta naturaleza, que los lleven hacia la necesidad y aceptación de ideas algebraicas. En este artículo se muestra la factibilidad de ofrecer experiencias de este tipo. Se presenta un ejemplo que ilustra cómo la capacidad de los niños para trabajar a nivel numérico se puede usar para ayudarlos a construir la idea de número general, entendido este como un número indeterminado involucrado en un método o regla general