On some Variational Problems Involving Volume and Surface Energies

We show how some problems coming from different fields of applied sciences, such as physics, engineering, biology, admit a common variational formulation characterized by the competition of two energetic terms. We discuss related problems and techniques studied by the authors and collaborators in the recent past as well open problems and further possible research directions in these topics.     

Lower Semicontinuity Properties of Functionals with Free Discontinuities

This paper is concerned with functionals with free discontinuities, considered as depending on the set variable. A splitting operation divides the sets in which the functional takes low values in the union of a noise part and a macroscopic part. Then we show lower semicontinuity results on the limit of the macroscopic parts by Hausdorff distance, along minimizing sequences.     

Effects of Field Fluctuations,Losses, and Aberrations on the Sensitivity of a Michelson GW Antenna Using Squeezed Radiation

The sensitivity of an interferometric gravitational wave (GW) antenna operating above a few hundred Hertz is shot-noise limited. Sub-shot-noise sensitivity can be achieved by superimposing squeezed light on the laser field. The benefits of this approach are reduced in nonideal interferometers having fringe visibility less than unity, as pointed out by Gea-Banacloche and Leuchs and recently discussed by Chickarmane. Here, we consider an interferometer described by a set of coefficients V_l^(k), V_sq^(k), V_lsq^(k) depending on the misalignment, mismatching, and aberrations of the optical systems, as well as on the asymmetry of the beam splitter and the two-arm losses. Due to the presence of terms proportional to the product of laser times squeezed fields, we have taken into account the amplitude fluctuations of a_l. A simple model of the squeezed vacuum light, produced by a degenerate optical parametric oscillator (OPO), is used for calculating the dependence of the spectral density of the output of a GW antenna on the fluctuations of the OPO-cavity resonance frequency, the pump amplitude fluctuation, and the nonlinear-crystal-temperature drift. A set of figures η_sq± and r_lsq±⁽²⁾ are introduced for describing the effects of the amplitude fluctuations and the relative line width γ_la on the spectral density of the quadrature phase operator X = a_la_sq⁺ h.c.     

Electrochemical behaviour of cobalta-dicarbollide sandwich complexes with different capping units

The redox aptitude of a series of cobalt(III) or cobalt(I) sandwich complexes bearing a charge compensated dicarbollide ligand ([9-L-7,8-C₂B₉H₁₀]⁻) as a constant unit and different counterparts (varying from classical [7,8-C₂B₉H₁₁]²⁻ to charge-compensated [9-L-7,8-C₂B₉H₁₀]⁻ dicarbollides, from cyclopentadienyl [C₅R₅]⁻ (R = Me, H) to cyclobutadiene [C₄Me₄]⁰ ligands) has been studied. All the Co(III) complexes display the reversible sequence Co(III)/Co(II)/Co(I). In contrast, the Co(I) complexes (namely, those capped by tetramethylcyclobutadiene) accede reversibly only to the Co(II) oxidation state, the passage to Co(III) being irreversible. When possible, the Co(II) intermediates have been characterized by EPR spectroscopy. The molecular structures of the monocation [Co(η-9-SMe₂-7,8-C₂B₉H₁₀)₂]⁺ in its DD/LL and meso diastereomeric forms as well as that of heteroleptic (η-7,8-C₂B₉H₁₁)Co(η-9-SMe₂-7,8-C₂B₉H₁₀) have been obtained by single-crystal diffraction. Presented at the 3rd Chianti Electrochemistry Meetings July 3−9, 2004, Certosa di Pontignano, Italy     

Influence of the dipping coating procedure on the mechanical strength of soda-lime glass rods

In order to investigate the effect of sol-gel coatings on the mechanical behavior of a high strength glass substrate, HF etched glass rods were used.

Coatings with different compositions (SiO₂, ZrO₂ and 20%ZrO₂---80%SiO₂) and different thicknesses were produced to study the influence of these parameters on strength.

Functions of integral probability versus strength were used to analyze data.

Coated glass rods exhibit higher strength in comparison with uncoated control rods that have undergone the same treatment. It seems evident that there is an effect of composition on strengthening. SiO₂ coated rods displayed higher strength.

A lowering in strength at thickness higher than 0.2 μ was observed, independently of composition.

The effect of a saturated Ca(OH)₂ solution was also studied.     

Novel techniques for the optical characterization of photovoltaic materials and devices

By means of newly designed optical instrumentation, mainly based on the use of integrating spheres, the fundamental optical properties of photovoltaic materials and devices (solar cells, modules) have been investigated. Relevant results concerned the optical loss (reflectance) of devices and the transmittance of semitransparent materials, used in the window sheets, under both direct and diffuse light. All the developed techniques are non-destructive and allow the characterization of selected areas of the samples. The use, however, of automatic translation stages makes easy to perform an optical and, in some cases, electrical mapping of the entire sample.     

Ion beam mixing of FeNi3 multilayers

An Fe/Ni multilayer of overall FeNi₃ composition, prepared by Joule effect deposition, has been irradiated with 200 keV krypton ions at a nominal dose of 5×10¹⁵ions/cm² to induce mixing at the interface. Depth profiling AES, RBS, XRD (glancing angle) and CEMS have been used to characterize the samples before and after irradiation and also after subsequent mild annealing. In the final structure, we have recognized the presence of embryos of an ordered FeNi₃ superlattice.     

Tailoring transition metal complexes for nonlinear optics applications. 2. A theoretical investigation of the second-order nonlinear optical properties of M(CO)(5)L complexes (M = Cr, W; L = Py, PyCHO, Pyz, PyzBF(3), BPE, BPEBF(3))

In this work, we report an ab initio investigation of second-order nonlinear optical (NLO) properties and absorption electronic spectra of push-pull transition metal chromophores of the formula [M(CO)(5)L] (M = Cr, W; L = pyridine (Py), 4-formyl-pyridine (PyCHO), pyrazine (Pyz), trans-1,2-bis(4-pyridyl)ethylene (BPE)). Pyz and BPE are considered either with one nitrogen atom free or interacting with the strong acceptor BF(3). All of the molecular properties have been calculated using two different and methodologically independent approaches: the time dependent and coupled perturbed density functional theories (TDDFT and CPDFT) and the sum-over-states (SOS) approach, where the excited states are obtained via the single configuration interaction (SCI) ab initio method. DFT results are in acceptable agreement with the experimental energy values of electronic transitions (with the exception of chromophores with the large pi-delocalization, like BPE); SCI calculations overestimate excitation energies and produce an inversion in the order of d(M) --> pi(L) and d(M) --> pi(CO) transitions. The SCI-SOS approach gives first-order hyperpolarizabilities, basically in agreement as trend and values with the experiments and seems to be a tool generally suitable for the evaluation of these properties also for transition metal complexes. On the other hand, the first-order hyperpolarizabilities computed using the CPDFT approach are consistently overestimated in comparison with the experimental results, especially in the case of a ligand with large pi-delocalization. We also show that the "two-level" approximation taking into account only the lowest energy charge transfer excitation (e.g., d(M) --> pi(L)) is not applicable to chromophores with the extended pi-delocalized ligand (BPE) coordinated to a transition metal, due to significant contributions originating from intraligand pi(L) --> pi(L) transitions. This study reports a detailed analysis and comparison of electronic NLO effects of transition metal complexes computed with DFT and ab initio SCI-SOS methodology.     

Determination of thermal diffusivity of suspended porous silicon films by thermal lens technique

An alumina suspension containing 21 vol.% solids was made to flow through a needle at rates between 10^-12–10^-11 m³s^-1 and was subjected to electrostatic atomization at different applied voltages in the range 5–13 kV. The resulting modes of atomization were studied. The stable cone-jet mode was first obtained at 7 kV and 2.2×10^-12 m³s^-1 and the effect of increasing flow rate and applied voltage on the jet diameter was investigated. Using a pointed ground electrode the alumina droplets produced by the jet in the stable cone-jet mode were printed according to a pre-determined architecture. Alumina relic diameters in the print were <35 m. PACS 81.05.Je; 81.20.Ev; 81.20.Rg; 81.15.Pq; 47.27.Wg