Dove siamo? Ci siamo persi?…No!… Abbiamo il GPS

“Dove siamo? Ci siamo persi?… No!… Abbiamo il GPS!” è il titolo del laboratorio con cui le Classi II e III della Scuola Media “Via Roma” di Mariano del Friuli (GO) hanno partecipato alla VII edizione della manifestazione “La matematica dei ragazzi: scambi di esperienze fra coetanei”. Perché un lavoro sul GPS? Da dove l’idea? Quali le motivazioni? L’iniziativa è stata la naturale prosecuzione dello sforzo, più che ventennale, fatto dalla nostra scuola per interfacciare l’attività istituzionale con la dinamica realtà che ci circonda e ci coinvolge. Nelle edizioni precedenti di “La matematica dei ragazzi” erano stati presentati lavori relativi a fogli elettronici e “algebra arcade” (1996), calcolatrici (1998), calcolatrici grafiche e sensori on line (2002 e 2004), storia dell’informatica e Google Earth (2006). Dato l’esito decisamente positivo di queste iniziative, è sembrato proficuo proseguire le attività di sperimentazione sull’utilizzo di nuove tecnologie. L’uso dei sistemi di navigazione satellitare sta diventando un fenomeno di massa a seguito della progressiva riduzione dei costi dei loro supporti tecnologici e per il diffondersi del loro impiego nelle più svariate attività umane. Allora, cosa si poteva provare a presentare quest’anno se non il navigatore satellitare

Long Noncoding RNA GAS5: A Novel Marker Involved in Glucocorticoid Response

Glucocorticoids (GCs) exert their effects through regulation of gene expression after activation in the cytoplasm of the glucocorticoid receptor (GR) encoded by NR3C1 gene. A negative feedback mechanism resulting in GR autoregulation has been demonstrated through the binding of the activated receptor to intragenic sequences called GRE-like elements, contained in GR gene. The long noncoding RNA growth arrest-specific transcript 5 (GAS5) interacts with the activated GR suppressing its transcriptional activity. The aim of this study was to evaluate the possible role of GAS5 and NR3C1 gene expression in the antiproliferative effect of methylprednisolone in peripheral blood mononuclear cells and to correlate the expression with individual sensitivity to GCs. Subjects being poor responders to GCs presented higher levels of GAS5 and NR3C1 in comparison with good responders. We suggest that abnormal levels of GAS5 may alter GC effectiveness, probably interfering with the mechanism of GR autoregulation

Nonlinear intensity dependence of terahertz edge photocurrents in graphene

We report on the observation of terahertz radiation induced edge photogalvanic currents in graphene, which are nonlinear in intensity. The increase of the radiation intensities up to MW/cm$^2$ results in a complex nonlinear intensity dependence of the photocurrent. The nonlinearity is controlled by the back gate voltage, temperature and radiation frequency. A microscopic theory of the nonlinear edge photocurrent is developed. Comparison of the experimental data and theory demonstrates that the nonlinearity of the photocurrent is caused by the interplay of two mechanisms, i.e. by direct inter-band optical transitions and Drude-like absorption. Both photocurrents saturate at high intensities, but have different intensity dependencies and saturation intensities. The total photocurrent shows a complex sign-alternating intensity dependence. The functional behaviour of the saturation intensities and amplitudes of both kinds of photogalvanic currents depending on gate voltages, temperature, radiation frequency and polarization is in a good agreement with the developed theory.Comment: 10 Figure

Edge photocurrent in bilayer graphene due to inter-Landau-level transitions

We report the observation of the resonant excitation of edge photocurrents in bilayer graphene subjected to terahertz radiation and a magnetic field. The resonantly excited edge photocurrent is observed for both inter-band (at low carrier densities) and intra-band (at high densities) transitions between Landau levels (LL). While the intra-band LL transitions can be traced to the classical cyclotron resonance (CR) and produce strong resonant features, the inter-band-LL resonances have quantum nature and lead to the weaker features in the measured photocurrent spectra. The magnitude and polarization properties of the observed features agree with the semiclassical theory of the intra-band edge photogalvanic effect, including its Shubnikov-de-Haas oscillations at low temperatures.Comment: 11 pages, 11 figure

THz radiation induced circular Hall effect in graphene

We report on the observation of the circular transversal terahertz photoconductivity in monolayer graphene supplied by a back gate. The photoconductivity response is caused by the free carrier absorption and reverses its sign upon switching the radiation helicity. The observed dc Hall effect manifests the time inversion symmetry breaking induced by circularly polarized terahertz radiation in the absence of a magnetic field. For low gate voltages, the photosignal is found to be proportional to the radiation intensity and can be ascribed to the alignment of electron momenta by the combined action of THz and static electric fields as well as by the dynamic heating and cooling of the electron gas. Strikingly, at high gate voltages, we observe that the linear-in-intensity Hall photoconductivity vanishes; the photoresponse at low intensities becomes superlinear and varies with the square of the radiation intensity. We attribute this behavior to the interplay of the second- and fourth-order effects in the radiation electric field which has not been addressed theoretically so far and requires additional studies

Edge photocurrent driven by terahertz electric field in bilayer graphene

We report on the observation of edge electric currents excited in bilayer graphene by terahertz laser radiation. We show that the current generation belongs to the class of second order in electric field phenomena and is controlled by the orientation of the THz electric field polarization plane. Additionally, applying a small magnetic field normal to the graphene plane leads to a phase shift in the polarization dependence. With increasing the magnetic field strength, the current starts to exhibit 1/B-magneto-oscillations with a period consistent with that of the Shubnikov-de Haas effect and amplitude by an order of magnitude larger as compared to the current at zero magnetic field measured under the same conditions. The microscopic theory developed shows that the current is formed in the edge's vicinity limited by the mean-free path of carriers and the screening length of the high-frequency electric field. The current originates from the alignment of the free carrier momenta and dynamic accumulation of charge at the edges, where the P-symmetry is naturally broken. The observed magneto-oscillations of the photocurrent are attributed to the formation of Landau levels

Clima e piogge acide

Il contributo delinea le modalità con cui è stato affrontato in classe, attraverso il ricorso a un approccio di natura sperimentale, lo studio del fenomeno delle piogge acide e vuole mostrare un esempio di integrazione di saperi e di abilità multidisciplinari. Con tale contributo si intende evidenziare l’efficacia di iniziative che comportino una seppur “dosata” applicazione del metodo scientifico