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Biomedical subjects

A De Vita

Publications and source records attributed to A De Vita.

13 recordsLinked to original sources
PubMed2006

Exposure setup to study potential adverse effects at GSM 1800 and UMTS frequencies on the auditory systems of rats.

To investigate possible biological effects of exposure to electromagnetic (EM) fields at the frequencies of global system for mobile communication (GSM) 1800 system and universal mobile telecommunication system (UMTS) on the auditory system of rats, an exposure setup for in vivo experiments is presented. The study was carried out in the framework of two European research projects. The target of the investigation was the cochlea. A dosimetric study was performed, both numerically and through direct measurements, to assess the interaction of the radiated fields and the dose distribution in the biological target. For the local exposure of rats, a loop antenna operating at the frequency bands of interest was designed, realised and characterised through numerical and experimental dosimetric procedures. Moreover, an exposure apparatus was set up, consisting of three arrays of four loop antennas, placed on three levels, thus allowing simultaneous exposure of 12 rats to give statistical power to the experiments. To isolate the exposure arrays, the setup was assembled by a wooden rack with EM field absorbing panels, inserted among the levels and at the four sides of the rack. Isolation was verified by direct measurements. Two exposure arrays were simultaneously supplied, whereas the third one was used for sham exposure. Blind exposure was achieved through a black box, hiding physical connections to the microwave power supply. During exposure sessions, rats were restrained in special plastic jigs for repeatable positioning, thus assuring the fixed level of dose in the target.

Animals↗
PubMed2004

"Learn on the fly": a hybrid classical and quantum-mechanical molecular dynamics simulation.

We describe and test a novel molecular dynamics method which combines quantum-mechanical embedding and classical force model optimization into a unified scheme free of the boundary region, and the transferability problems which these techniques, taken separately, involve. The scheme is based on the idea of augmenting a unique, simple parametrized force model by incorporating in it, at run time, the quantum-mechanical information necessary to ensure accurate trajectories. The scheme is tested on a number of silicon systems composed of up to approximately 200 000 atoms.

Journal Article↗
PubMed2004

Mesoscopic chiral reshaping of the Ag(110) surface induced by the organic molecule PVBA.

We report scanning tunneling microscopy observations on the restructuring of a Ag(110) surface induced by the molecule 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA). Our data reveal that the surface undergoes a mesoscopic step faceting following exposure to submonolayer coverages and thermal activation. A sawtooth arrangement evolves implying long-range mass transport of substrate atoms and forming a regular arrangement of kink sites. Its formation is associated with the molecules' functional headgroups forming carboxylates with [100] Ag microfacets at step edges, and eventually operating to reshape the surface morphology. Interestingly, the resulting microfacets act as chiral templates for the growth of supramolecular PVBA structures. Theoretical modeling based on ab initio results indicates that chiral recognition processes discriminating between the two enantiomers of adsorbed PVBA molecules occur in this process.

Journal Article↗
PubMed2003

Adatom-vacancy mechanisms for the C6)/Al111-(6 x 6) reconstruction.

The irreversible (6x6) reconstruction of the C(60)/Al(111) system from the (2sqrt[3]x2sqrt[3])R30 degrees phase is studied by first-principles techniques. We find that C60 binds optimally to the surface if an Al vacancy is created directly underneath. The removed Al atoms form a (6x6) array of ad-dimers in the interstices below the C60 overlayer, to which they strongly bind. This spontaneous local process, rather than the compression state of the unreconstructed C60 overlayer, explains why one molecule out of three protrudes from the surface upon reconstruction.

Journal Article↗
PubMed2001

Insulator at the ultrathin limit: MgO on Ag(001).

The electronic structure and morphology of ultrathin MgO films epitaxially grown on Ag(001) were investigated using low-temperature scanning tunneling spectroscopy and scanning tunneling microscopy. Layer-resolved differential conductance (dI/dU) measurements reveal that, even at a film thickness of three monolayers, a band gap of about 6 eV is formed corresponding to that of the MgO(001) single-crystal surface. This finding is confirmed by layer-resolved calculations of the local density of states based on density functional theory.

Journal Article↗
PubMed2001

Mesoscopic correlation of supramolecular chirality in one-dimensional hydrogen-bonded assemblies.

The ordering of 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid, a two-dimensional chiral species, was studied by scanning tunneling microscopy at noble metal surfaces. Homochiral molecules self-assemble in supramolecular chiral hydrogen-bonded twin chains, which order in nanogratings where the supramolecular chirality is strictly correlated over the entire microm domains without intimate molecular contact. Model simulations indicate that the underlying mesoscopic chiral resolution is associated with twin chains acting as chiroselective templates for transient molecular attachment, which process mediates the gratings' evolution.

Journal Article↗
PubMed2001

Initial nucleation of platinum clusters after reduction of K(2)PtCl(4) in aqueous solution: a first principles study.

The initial nucleation of platinum clusters after the reduction of K(2)PtCl(4) in aqueous solution is studied by means of first principles molecular dynamics simulations. A reaction mechanism leading to a Pt dimer is revealed both by gas-phase simulations and by simulations which model the solution environment. The key step of the observed reaction process is the formation of a Pt-Pt bond between a Pt(I) complex and an unreduced Pt(II) complex. In light of this result, we discuss the reduction process leading to the formation of platinum nanoparticles. In the generally accepted model, the nucleation of Pt particles starts only when a critical concentration of Pt(0) atoms is reached. Here, we discuss a complementary mechanism where metal-metal bonds form between Pt complexes in higher oxidation states. This is consistent with a number of experimental results which show that a high concentration of zerovalent atoms is not necessary to start the nucleation.

Journal Article↗
PubMed1990

[Forme fruste of Gorlin's syndrome with a left ventricular neoplasm].

We report on a 25-year-old man, referred for atypical chest pain and negative T waves in leads V5-V6. A cardiac tumor, localized in the posterolateral left ventricular wall was diagnosed in this patient by nuclear techniques and bidimensional echocardiography. A complex form of pluridistrectual dysmorphic disorder (hypertelorism, prognathism, frontal bossing, multiple cysts of the mandible, calcification in falx cerebri, etc) was also present, suggesting a limited form of Gorlin's syndrome (nevoid basal cell carcinoma syndrome).

Adult↗
PubMed1987

Importance of showing HBsAg and HBcAg positivity in the liver for better aetiological definition of chronic liver disease.

Serum and tissue hepatitis B virus (HBV) markers were compared in 35 alcoholic and 23 non-alcoholic subjects affected by chronic liver disease. Seventeen point one per cent of alcoholic and 21.7% of non-alcoholic subjects had HBV tissue markers, but not serum markers, for this virus. It is therefore concluded that showing the presence of HBV tissue markers permits a better aetiological definition of hepatitis B surface antigen (HBsAg) negative chronic liver disease, both in alcoholic and non-alcoholic subjects.

Chronic Disease↗