Infra-red properties of bulk heavily doped silicon

Summary In this work reflectance (R) and thermoreflectance (TR) spectra in the infra-red of bulk P and B heavily doped silicon samples are reported and discussed. The values of the scattering time and of the effective mass, as well as the temperature derivative of the plasma frequency, scattering time and high-frequency dielectric constant are extracted from the data and analysed in terms of free-carrier-photon and free-carrier-impurity interaction.

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Riassunto In questo lavoro sono riportati e discussi gli spettri di riflettanza (R) e termoriflettanza (TR) in infrarosso di campioni di silicio drogati pesantemente per diffusione con P e B. Dai dati sono ricavati i valori dei tempi di rilassamento e della massa effettiva, come pure la derivata in temperatura della frequenza di plasma, del tempo di rilassamento e della costante dielettrica ad alta frequenza, che sono analizzati sulla base delle interazioni fra portatori liberi e fononi e fra portatori liberi e impurezze.

     

CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

A new active layer for CO₂ sensing based on semiconducting CuO-Cu_xFe_3−xO₄ (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO₂ target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 °C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (Rair/RCO₂=1.9) at 250 °C and 700 Hz for a CO₂ concentration of 5000 ppm.     

Synchronized abandonments in a single server unreliable queue

We consider a single server unreliable queue represented by a 2-dimensional continuous-time Markov chain. At failure times, the present customers leave the system. Moreover, customers become impatient and perform synchronized abandonments, as long as the server is down. We analyze this model and derive the main performance measures using results from the basic q-hypergeometric series.     

Bridging the Gap Between the Dense and the Discrete: The Number Line and the “Rubber Line” Bridging Analogy

In two experiments we explored the instructional value of a cross‐domain mapping between “number” and “line” in secondary school students' understanding of density. The first experiment investigated the hypothesis that density would be more accessible to students in a geometrical context (infinitely many points on a straight line segment) compared to a numerical context (infinitely many numbers in an interval). The participants were 229 seventh to eleventh graders. The results supported this hypothesis but also showed that students' conceptions of the line segment were far from that of a dense array of points. We then designed a text-based intervention that attempted to build the notion of density in a geometrical context, making explicit reference to the number-to-points correspondence and using the “rubber line” bridging analogy (the line as an imaginary unbreakable rubber band) to convey the no-successor principle. The participants were 149 eighth and tenth graders. The text intervention improved student performance in tasks regarding the infinity of numbers in an interval; the “rubber line” bridging analogy further improved performance successfully conveying the idea that these numbers can never be found one immediately next to the other.     

Polyhedral models for generalized associahedra via Coxeter elements

Motivated by the theory of cluster algebras, F. Chapoton, S. Fomin, and A. Zelevinsky associated to each finite type root system a simple convex polytope, called generalized associahedron. They provided an explicit realization of this polytope associated with a bipartite orientation of the corresponding Dynkin diagram. In the first part of this paper, using the parametrization of cluster variables by their g-vectors explicitly computed by S.-W. Yang and A. Zelevinsky, we generalize the original construction to any orientation. In the second part we show that our construction agrees with the one given by C. Hohlweg, C. Lange, and H. Thomas in the setup of Cambrian fans developed by N. Reading and D. Speyer.     

Running of neutrino parameters and the Higgs self-coupling in a six-dimensional UED model

We investigate a six-dimensional universal extra-dimensional model in the extension of an effective neutrino mass operator. We derive the β  -functions and renormalization group equations for the Yukawa couplings, the Higgs self-coupling, and the effective neutrino mass operator in this model. Especially, we focus on the renormalization group running of physical parameters such as the Higgs self-coupling and the leptonic mixing angles. The recent measurements of the Higgs boson mass by the ATLAS and CMS Collaborations at the LHC as well as the current three-flavor global fits of neutrino oscillation data have been taken into account. We set a bound on the six-dimensional model, using the vacuum stability criterion, that allows five Kaluza–Klein modes only, which leads to a strong limit on the cutoff scale. Furthermore, we find that the leptonic mixing angle _θ12${\theta }_{12}$ shows the most sizeable running, and that the running of the angles _θ13${\theta }_{13}$ and _θ23${\theta }_{23}$ are negligible. Finally, it turns out that the findings in this six-dimensional model are comparable with what is achieved in the corresponding five-dimensional model, but the cutoff scale is significantly smaller, which means that it could be detectable in a closer future.     

Direct and Regioselective Di-α-fucosylation on the Secondary Rim of β-Cyclodextrin

A straightforward glycosylation method is described to regio- and stereoselectively introduce two α-l -fucose moieties directly to the secondary rim of β-cyclodextrin. Using NMR and MS fragmentation studies, the nonasaccharide structure was determined, which was also visualized using molecular dynamics simulations. The reported glycosylation method proved to be robust on gram-scale, and may be generally applied to directly glycosylate β-cyclodextrins to make well-defined multivalent glycoclusters.     

Interface Fluctuations for the D = 1 Stochastic Ginzburg–Landau Equation with Nonsymmetric Reaction Term

We consider a Ginzburg–Landau equation in the interval [?ε^?1, ε^?1], ε>0, with Neumann boundary conditions, perturbed by an additive white noise of strength $\sqrt {\varepsilon } $ and reaction term being the derivative of a function which has two equal–depth wells at ±1, but is not symmetric. When ε=0, the equation has equilibrium solutions that are increasing, and connect ?1 with +1. We call them instantons, and we study the evolution of the solutions of the perturbed equation in the limit ε→0⁺, when the initial datum is close to an instanton. We prove that, for times that may be of the order of ε^?1, the solution stays close to some instanton whose center, suitably normalized, converges to a Brownian motion plus a drift. This drift is known to be zero in the symmetric case, and, using a perturbative analysis, we show that if the nonsymmetric part of the reaction term is sufficiently small, it determines the sign of the drift.     

A reassessment of the association between azulene and [60]fullerene. Possible pitfalls in the determination of binding constants through fluorescence spectroscopy

We show here that the recently reported surprisingly large association constant (K = 7.6 x 10(4) M(-1)) between azulene and [60]fullerene is due to experimental artifacts, pointing out potential errors in the characterization of association equilibria by fluorescence spectroscopy, and suggesting the best experimental practices.