A note on Griffiths infinitesimal invariant for curves

Given a generic curve of genus $g\ge 4$ and a smooth point $L\in W_{g-1}^{1}(C)$ , whose linear system is base-point free, we consider the Abel–Jacobi normal function associated with $L^{\otimes 2}\otimes \omega _{C}^{-1}$ , when $(C,L)$ varies in moduli. We prove that its infinitesimal invariant reconstructs the couple $(C,L)$ . When $g=4$ , we obtain the generic Torelli theorem proved by Griffiths.     

Observation of a diamagnetic signal up to 132 K in a Tl−Ca−Ba−Cu−O compound

Tl–Ca–Ba–Cu–O compounds of the nominal composition of (1, 1, 1, 1) have been prepared from different starting materials and with the same heat treatment process. During the investigation of their properties a diamagnetic signal has been found up to the temperature of 132 K. This hints at the existence of a certain material content distributed into discrete superconducting domains. The parameters of it reflect a superstructure of the (2, 2, 2, 3) and (2, 1, 2, 2) compositions having a time-dependent behaviour. On the basis of the signal levels at 132 K and 4.2 K, the quantity of the high temperature superconducting material is about 0.01% of the total one at liquid He temperatures.     

Inner solvers for interior point methods for large scale nonlinear programming

This paper deals with the solution of nonlinear programming problems arising from elliptic control problems by an interior point scheme. At each step of the scheme, we have to solve a large scale symmetric and indefinite system; inner iterative solvers, with an adaptive stopping rule, can be used in order to avoid unnecessary inner iterations, especially when the current outer iterate is far from the solution. In this work, we analyse the method of multipliers and the preconditioned conjugate gradient method as inner solvers for interior point schemes. We discuss the convergence of the whole approach, the implementation details and report the results of numerical experimentation on a set of large scale test problems arising from the discretization of elliptic control problems. A comparison with other interior point codes is also reported. This research was supported by the Italian Ministry for Education, University and Research (MIUR) projects: FIRB Project: “Parallel Nonlinear Numerical Optimization PN ² O” (grant n. RBAU01JYPN, ) and COFIN/PRIN04 Project “Numerical Methods and Mathematical Software for Applications” (grant n. 2004012559, ).     

Electroluminescence of silicon nanocrystals in MOS structures

We have studied the structural, electrical and optical properties of MOS devices, where the dielectric layer consists of a substoichiometric SiO_x (x<2) thin film deposited by plasma-enhanced chemical vapor deposition. After deposition the samples were annealed at high temperature (>1000 °C) to induce the separation of the Si and the SiO₂ phases with the formation of Si nanocrystals embedded in the insulating matrix. We observed at room temperature a quite intense electroluminescence (EL) signal with a peak at ∼850 nm. The EL peak position is very similar to that observed in photoluminescence in the very same device, demonstrating that the observed EL is due to electron–hole recombination in the Si nanocrystals and not to defects. The effects of the Si concentration in the SiO_x layer and of the annealing temperature on the electrical and optical properties of these devices are also reported and discussed. In particular, it is shown that by increasing the Si content in the SiO_x layer the operating voltage of the device decreases and the total efficiency of emission increases. These data are reported and their implications discussed. Received: 31 August 2001 / Accepted: 3 September 2001 / Published online: 17 October 2001     

On a quadratic functional occurring in a bivariate scattered data interpolation problem

Sunto L’applicazione di noti metodi che utilizzano funzioni di tipo blending per la costruzione di funzioni bivariate C¹ per l’interpolazione di dati, richiede la conoscenza delle derivate parziali del primo ordine ai vertici di una triangolazione sottostante. In questo lavoro consideriamo il metodo proposto da Nielson, che consiste nel calcolare stime delle derivate parziali del primo ordine minimizzando un opportuno funzionale quadratico, caratterizzato da parametri di tensione non negativi. Scopo del lavoro è l’analisi di alcune proprietà particolari di questo funzionale per la costruzione di algoritmi efficienti e robusti per la determinazione delle stime suddette delle derivate quando si ha a che fare con insiemi di dati di grandi dimensioni. Abstract The application of widely known blending methods for constructingC ¹ bivariate functions interpolating scattered data requires the knowledge of the partial derivatives of first order at the vertices of an underlying triangulation. In this paper we consider the method proposed by Nielson that consists in computing estimates of the first order partial derivatives by minimizing an appropriate quadratic functional, characterized by nonnegative tension parameters. The aim of the paper is to analyse some peculiar properties of this functional in order to construct robust and efficient algorithms for determining the above estimates of the derivatives when we are concerned with extremely large data sets.      

Proton and α sequential emission in the 16O + 58Ni deep inelastic reaction: A semi-classical approach

The 132 MeV ¹⁶O + ⁵⁸Ni reaction has been experimentally investigated by using coincident charged particle techniques. A closed-form theoretical approach, describing in a simple picture the non-equilibrium component and the evaporative one of the angular correlation between light particles and reaction residues emitted in a peripheral heavy-ion collision, is applied — in the hypotesis of a sequential process — to the (C,N,O)-α and (C,N,O)-p differential multiplicities for the ¹⁶O + ⁵⁸Ni at 8.25 MeV/A deep inelastic collision. From this analysis some reaction mechanism information is deduced.