Influence of elastic scattering on the measurement of core-level binding energy dispersion in X-ray photoemission spectroscopy

We explore the interplay between the elastic scattering of photoelectrons and the surface core level shifts with regard to the determination of core level binding energies in Au(111) and Cu₃Au(100). We find that an artificial shift is created in the binding energies of the Au 4f core levels, that exhibits a dependence on the emission angle, as well as on the spectral intensity of the core level emission itself. Using a simple model, we are able to reproduce the angular dependence of the shift and relate it to the anisotropy in the electron emission from the bulk layers. Our results demonstrate that interpretation of variation of the binding energy of core-levels should be conducted with great care and must take into account the possible influence of artificial shifts induced by elastic scattering.     

Density functional description of the early stages of the dioxygenation of [(MeC(CH2PPh2)3)M(catecholate)]+ complexes [M = Co(III), Ir(III)]: toward a rationalization of the catalytic mechanism of ring-opening dioxygenases

Density Functional Theory (DFT) has been applied to characterize the early stages of the reaction of dioxygenation of [(triphos)M(catecholate)]+ complexes [M = Co(III), Ir(III); triphos = MeC(CH2PPh2)3], which have been considered to be models of ring-opening dioxygenases. The structural features of the starting complexes and of the intermediate complexes formed by addition of O2 to the coordinated catecholato ion are well reproduced. The calculations showed that this preliminary stage can be obtained only when the oxygen molecule attacks the molecule on the catecholato site.     

Pseudo-Goldstino in field theory

We consider two SUSY-breaking hidden sectors which decouple when their respective couplings to the visible particles are switched off. In such a scenario one expects to find two light fermions: the Goldstino and the pseudo-Goldstino. While the former remains massless in the rigid limit, the latter becomes massive due to radiative effects which we analyze from several different points of view. This analysis is greatly facilitated by a version of the Goldberger-Treiman relation, which allows us to write a universal nonperturbative formula for the mass. We carry out the analysis in detail in the context of gauge mediation, where we find that the pseudo-Goldstino mass is at least around the GeV scale and can be easily at the electroweak range, even in low scale models. This leads to interesting and unconventional possibilities in collider physics and it also has potential applications in cosmology.     

Performance of CR-39 with addition of DOP (dioctylphthalate) for fast neutron dosimetry

The ENEA fast neutron dosemeter is based on a planar poly allyl diglicol carbonate (PADC) placed in a polyethylene holder. The present paper reports the results of an experimental study of a CR-39^® material with the addition of 0.1% of dioctylphthalate (DOP) produced by the Italian company Intercast Europe S.p.A.

The etching procedure is: pre-etching with 40% KOH water solution 6.25 N and 60% ethyl alcohol at 70°C followed by 12 h of etching in 6.25 N KOH water solution. For the energy dependence of response, dosemeters have been irradiated with neutron sources (²⁴¹Am–Be, ²⁵²Cf, Pu–Li) and 14.9 MeV monoenergetic neutrons. The dosimetric performance of the material for fast neutrons is expressed in terms of sensitivity, background value, lowest detectable dose and energy dependence of response. Moreover, the results of a quality acceptance test of the material, performed on 11 sheets (980×980 mm², 1.4 mm thick) of the same production batch, are given. Therefore, the homogeneity of the neutron sensitivity and of the background signal within a sheet and the whole batch is considered. The results are compared with the acceptance test outcome for a CR39 standard material batch.     

Justifying and Proving in the Cabri Environment

This paper describes a long term teaching experiment carried out with students from the 9th–10th grades. Geometrical constructions in the Cabri environment were selected as a specific field of experience, within which the sense of theory may emerge. The idea of construction constitutes the key to accessing the idea of theorem, moving from a generic idea of justification towards the idea of validating within a geometrical system. The study aims at clarifying the role of the Cabri environment in this teaching-learning processes: analysis of protocols shows the possible evolution of a justification into a proof but at the same time indicates that this evolution is not expected to be simple and spontaneous.This revised version was published online in September 2005 with corrections to the Cover Date.     

The Legnaro Francium Magneto-Optical Trap

Hyperfine Interactions - Laser cooling and trapping of radioactive atoms represent the new frontier in atomic physics and a new powerful tool in nuclear physics. We are setting up at the...     

Vessel laser angioplastyin vitro

Summary This paper presents a set of measurements concerning the laser ability to perforate human atheromatic plaque and thrombus. Split segments of arteries were prepared under wet conditions and exposed to laser light at different power values and exposures. A multiline argon-ion laser, 5 W nominal power, coupled with a quartz fiber (600 μm diameter) was used. A dose effect correlation was found in the presence of homogeneous targets, independently of the power used. A linear fit to the data was made, which showed a very similar slope for homogeneous plaque (0.054±0.026, for a normalized χ²=0.08), as well as for organized thrombus (0.051±0.04, χ²=0.09). Such a correlation did not show up in the presence of nonhomogeneous targets.     

Optical characterization and manipulation of alkali metal nanoparticles in porous silica

Rubidium and cesium metal nanoparticles were grown in nanoporous silica samples placed in alkali vapor cells. Their size and shape were investigated by measuring the sample optical transmittance. Spectral changes due to photodesorption processes activated by weak light were also analyzed. Alkali atoms photoejected from the silica walls diffuse through and out of the nanopores, modifying both the nanoparticle distribution in the silica matrix and the atomic vapor pressure in the cell volume. The number of rubidium and cesium atoms burst out of the samples was measured as a function of photon energy and fluence. The optical absorption measurements together with the analysis of the photodesorption yield give a complete picture of the processes triggered by light inside the nanopores. We show that atomic photodesorption, upon proper choice of light frequency and intensity, induces either growth or evaporation of nanosized alkali metal clusters. Cluster size and shape are determined by the host-guest interaction.