Manipulation of speckle fringes for non-destructive testing of defects in composites

A digital speckle pattern interferometer with optical fibres is proposed for composite materials diagnostics in an operative environment. Detection of a variety of flaws, such as disbonds, delaminations and cracks in aircraft components, is reported. Additional fringes are introduced for linearizing the fringe pattern and obtaining quantitative deformation measurements by Fourier transform analysis.     

Hitting time distributions in financial markets

We analyze the hitting time distributions of stock price returns in different time windows, characterized by different levels of noise present in the market. The study has been performed on two sets of data from US markets. The first one is composed by daily price of 1071 stocks trade for the 12-year period 1987-1998, the second one is composed by high frequency data for 100 stocks for the 4-year period 1995-1998. We compare the probability distribution obtained by our empirical analysis with those obtained from different models for stock market evolution. Specifically by focusing on the statistical properties of the hitting times to reach a barrier or a given threshold, we compare the probability density function (PDF) of three models, namely the geometric Brownian motion, the GARCH model and the Heston model with that obtained from real market data. We will present also some results of a generalized Heston model.     

Mid-infrared fiber-coupled QCL-QEPAS sensor

An innovative spectroscopic system based on an external cavity quantum cascade laser (EC-QCL) coupled with a mid-infrared (mid-IR) fiber and quartz enhanced photoacoustic spectroscopy (QEPAS) is described. SF₆ has been selected as a target gas in demonstration of the system for trace gas sensing. Single mode laser delivery through the prongs of the quartz tuning fork has been obtained employing a hollow waveguide fiber with inner silver–silver iodine (Ag–AgI) coatings and internal core diameter of 300 μm. A detailed design and realization of the QCL fiber coupling and output collimator system allowed almost practically all (99.4 %) of the laser beam to be transmitted through the spectrophone module. The achieved sensitivity of the system is 50 parts per trillion in 1 s, corresponding to a record for QEPAS normalized noise-equivalent absorption of 2.7 × 10^?10 W cm^?1 Hz^?1/2.     

Photothermal detection of surface states in amorphous silicon films

A new method for the determination of surface states in amorphous silicon films is proposed. The method is based on the observation of enhancement of the interference fringe amplitude in photothermal deflection spectra, due to the presence of surface states.A theoretical approach is presented, together with the experimental results and an evaluation of the density of surface states. The method proves to be adequate, in most cases, to yield results in good agreement with those reported in literature.     

A cognitive analysis of dragging practises in Cabri environments

Dragging in Dynamical Geometry Software (DGS) is described by introducing a hierarchy of its functions. This is suitable for classifying different attitudes and aims of students who investigate a geometric problem, such as exploring, conjecturing, validating and justifying. Moreover the hierarchy has cognitive features and can be used to describe the twofold modulities namely ascending and descending in which students interact with external representations (e.g. Cabri drawings). Switching from one modality to the other through dragging often allows them to produce fruitful conjectures and to pass from the empirical to the theoretical side of the question. The genesis of such different functions in students does not happen automatically but is the consequence of specific didactical interventions of the teacher in the pupils' apprenticeship of Cabri practises. A worked-out example illustrates the theoretical concepts introduced in the paper.     

Photoacoustic measurement of the thermal effusivity of solids

A simple photoacoustic method for measuring the thermal effusivity of solids is described. The method is based on front illumination and front inspection of the sample. The experimental results are interpreted by means of the theory of layered samples.     

Dynamical spin magnetic susceptibility in the 2D Hubbard model

Magnetic properties of the two-dimensional Hubbard model are investigated by studying the imaginary part of the dynamical spin magnetic susceptibility as a function of momentum and doping. The calculations are performed by means of the composite operator method in the static approximation. It is shown that the results are in good qualitative agreement with the experimental data for LaSrCuO compounds.     

Variable temperature n.m.r. behaviour of 1,5-benzodiazepinones and 1,5-benzodiazepinthiones

The n.m.r. variable temperature behaviour of the 7-membered ring in 1,3-dihydro-2H-1,5-benzodiazepin-2-one derivatives and in the corresponding 2-thiones has been investigated. The results indicate that the ring inversion barrier is higher in the thiones and dependent on substituents bonded at N-1. The activation parameters are obtained and discussed.     

Magnetic properties of the two-band singlet-hole model for the copper-oxide plane

A two-band Hubbard-like model with highly asymmetric hopping parameters is studied by means of composite operator method. In particular, the spin magnetic susceptibility for the paramagnetic case is computed and the results are in qualitative agreement with the experimental situation in La_2?x Sr _x CuO₄ systems.