Compositional inhomogeneity of an unusual Selinunte coin

EDXRF and XPS characterizations of a recently found Selinunte ancient coin are presented. Such a coin was found as essentially made up by a Sn-Pb alloy and its types have a very strong similarity with those shown by a silver set issued in the same historical period. It has been also studied by means of a SEMEDXRF coupled apparatus in order to have information about the compositional inhomogeneity of the alloy. XPS measurements have been used to provide a more surface sensitive analysis. The different probing depths of the adopted techniques have been found useful in evidencing volume inhomogeneities of the sample, at least in the first few microns above its surface. From an archaeological point of view, the coin may be ascribed to a coinage for funerary use or, more probably, to a coin production carried out during the difficult economic period of the history of Selinunte, immediately preceding the year 409 b.C., when the city was destroyed by Carthaginian armies

Chiral patterns arising from electrostatic growth models

Recently, unusual and strikingly beautiful seahorse-like growth patterns have been observed under conditions of quasi-two-dimensional growth. These `S'-shaped patterns strongly break two-dimensional inversion symmetry; however such broken symmetry occurs only at the level of overall morphology, as the clusters are formed from achiral molecules with an achiral unit cell. Here we describe a mechanism which gives rise to chiral growth morphologies without invoking microscopic chirality. This mechanism involves trapped electrostatic charge on the growing cluster, and the enhancement of growth in regions of large electric field. We illustrate the mechanism with a tree growth model, with a continuum model for the motion of the one-dimensional boundary, and with microscopic Monte Carlo simulations. Our most dramatic results are found using the continuum model, which strongly exhibits spontaneous chiral symmetry breaking, and in particular finned `S' shapes like those seen in the experiments.Comment: RevTeX, 12 pages, 9 figure

S/N ratio improvement in the phase sensitive technique for low frequency measurements

This paper illustrates the operational principles of a phase sensitive tuned amplifying arrangement built up to improve the signal to noise ratio in the range of the low frequencies where the flicker noise is very troublesome. It is particularly useful when thermo-modulated absorption or reflection measurements must be carried out.Nous présentons les principes de fonctionnement d'un dispositif amplificateur synchrone à sensibilité de phase réalisé dans le but d'améliorer le facteur de bruit dans l'intervalle des basses fréquences où le bruit flicker est tres fastidieux. Il est particulièrement utile lorsqu'on doit exécuter des mesures d'absorption ou réflexion thermomodulées

S/N ratio improvement in the phase sensitive technique for low frequency measurements

This paper illustrates the operational principles of a phase sensitive tuned amplifying arrangement built up to improve the signal to noise ratio in the range of the low frequencies where the flicker noise is very troublesome. It is particularly useful when thermo-modulated absorption or reflection measurements must be carried out

Infrared and UV-visible spectra of layer semiconductors Gas, GaSe and GaTe

Wavelength derivative and thermomodulated reflectivity spectra of gallium telluride in the UV-visible range (1.0-6.0 eV), and infrared (15-80 meV) derivative absorption spectra of gallium sulphide and selenide at room temperature are presented and interpreted as due to three-dimensional or two-dimensional critical points and one or two phonons absorption respectively A new model for the complex dielectric constant is used to identify the nature of the observed structures in the range of the interband transitions.On présente les spectres de réflectivité thermomodulée et dérivée du tellurure de gallium dans la région UV-visible (1-6 eV) et les spectres d'absorption dérivée du sulfure et du séléniure de gallium dans l'infrarouge (15-80 meV) à température ambiante. Nous avons interprété les premiers comme dus aux points critiques bidimensionnels ou tridimensionnels et les seconds à l'absorption d'un ou de deux phonons. On a même utilisé un modèle nouveau pour la constante diélectrique dans le but d'identifier la nature des structures observées dans l'intervalle des transitions interbande

Studio degli spettri di perdita di energia di ellettroni alla soglia di core M_2_3 del rame

Electron Energy Loss measurements in reflection geometry, taken at three primary beam energies, are reported with the aim to investigate the possibility of isolating dipole and non-dipo1e contributions to the cross-section for the $3p_1/2,3/2$ scattering in $Cu$, in the near edge range. We notice that even at a primary energy relatively as high as 2.0 keV, monopole and quadrupole structures cannot be neglected when considering the absorption cross section just above the shallow M_2_3 core edge. An attempt is reported to identify spectral dipole and non-dipo1e features in our experimental spectra