An ab initio periodic study of NiO supported at the Pd(100) surface. Part 2: The nonstoichiometric Ni3O4 phase

The present computational study describes the structure and properties of a substoichiometric 2D monatomic in the height phase of nickel oxide, c(4 x 2)-Ni(3)O(4), which has been newly found to epitaxially grow under special deposition conditions on the (100) face of palladium. A slab model is adopted where palladium is simulated by a thin film covered on both sides by epilayers, in combination with a DFT hybrid-exchange Hamiltonian; to make convergence of the SCF procedure easier, a thermal smearing technique is used, whose consequences on the results are critically analyzed. Three adsorbed systems are considered and characterized: (i) RH, that is, the c(4 x 2)-Ni(3)O(4) phase with a rhombic distribution of Ni vacancies, as is experimentally observed; SQ, or p(2 x 2)-Ni(3)O(4), which differs from the previous one for a square, instead of a rhombic distribution of vacancies; (iii) OX, or p(2 x 2)-O, that is, a surface oxidized phase of Pd(100) which is believed to be the precursor for the formation of RH. For a better understanding of the interaction of the metal with the adlayers, the isolated substoichiometric oxides, i-RH and i-SQ, have also been studied. It is shown that RH is more stable than SQ by a few tenths of electronvolts per Ni(3)O(4) unit, which justifies its preferential formation and that the surface reaction, OX + 3NiO(ads) --> RH, is thermodynamically possible. Special attention has been devoted to characterize RH from an energetic, geometric, electronic, and magnetic viewpoint. The strong bond which is formed between surface Pd and O ions in the adlayer is responsible for some peculiar aspects of the electronic and magnetic structures of that phase.     

An ab initio periodic study of NiO supported at the Pd(100) surface. Part 1: The perfect epitaxial monolayer

The epitaxial monolayer of NiO on Pd(100) has been theoretically simulated using a hybrid-exchange GGA-DFT Hamiltonian and a slab model, periodic in two dimensions. This "perfect" system is an essential reference for the simulation of nonstoichiometric two-dimensional phases which are formed during the deposition of nickel on palladium in the presence of oxygen. The adequacy of the computational procedure is discussed, especially as concerns the use of a thermal smearing technique which has been adopted to improve the convergence properties of the SCF procedure and to prevent the onset of nonphysical spin-polarized solutions. The equilibrium configuration corresponds to antiferromagnetic order in the overlayer, with oxygens on top of the surface Pd atoms; the ad-film is slightly corrugated with Ni closer to the surface by 0.1 A with respect to O. The interaction energy is quite small, 0.20 eV/NiO unit (about 5 kcal mol(-1)); correspondingly, the electronic and magnetic properties of the Pd slab and the isolated NiO monolayer are only marginally affected by the interaction.     

Impact of Peels Extracts from an Italian Ancient Tomato Variety Grown under Drought Stress Conditions on Vascular Related Dysfunction

Background: Tomato by-products contain a great variety of biologically active substances and represent a significant source of natural antioxidant supplements of the human diet. The aim of the work was to compare the antioxidant properties of a by-product from an ancient Tuscan tomato variety, Rosso di Pitigliano (RED), obtained by growing plants in normal conditions (-Ctr) or in drought stress conditions (-Ds) for their beneficial effects on vascular related dysfunction. Methods: The antioxidant activity and total polyphenol content (TPC) were measured. The identification of bioactive compounds of tomato peel was performed by HPLC. HUVEC were pre-treated with different TPC of RED-Ctr or RED-Ds, then stressed with H₂O₂. Cell viability, ROS production and CAT, SOD and GPx activities were evaluated. Permeation of antioxidant molecules contained in RED across excised rat intestine was also studied. Results: RED-Ds tomato peel extract possessed higher TPC than compared to RED-Ctr (361.32 ± 7.204 mg vs. 152.46 ± 1.568 mg GAE/100 g fresh weight). All extracts were non-cytotoxic. Two hour pre-treatment with 5 µg GAE/mL from RED-Ctr or RED-Ds showed protection from H₂O₂-induced oxidative stress and significantly reduced ROS production raising SOD and CAT activity (* p < 0.05 and ** p < 0.005 vs. H₂O₂, respectively). The permeation of antioxidant molecules contained in RED-Ctr or RED-Ds across excised rat intestine was high with non-significant difference between the two RED types (41.9 ± 9.6% vs. 26.6 ± 7.8%). Conclusions: RED-Ds tomato peel extract represents a good source of bioactive molecules, which protects HUVECs from oxidative stress at low concentration.     

Water-Based Aerosol for Book Deacidification: Experimental Apparatus and Theoretical Interpretation of Results

One of the major problems in book conservation is the long-term deconstructive effect of acidity introduced into the paper by several additives, which, in the presence of humidity, generates a hydrogen cation with a strong catalytic role in cellulose depolymerization. Many types of treatment have been used in the past, but up to now, research for less-invasive, fast and cheap methods is still vividly ongoing. In this study, an approach to book deacidification is presented, where alkaline water solutions are administered to bound books in the form of micrometer-sized aerosol droplets, without using vacuum apparatus accessories. Alkaline clouds treatments were alternated with gentle air fluxes of drying steps. Few cycles are required to achieve uniform deacidification of books. The treatment could be conducted with proper apparatus on large volumes, resulting in rapid treatment time and low cost. The titration curve reporting the variation of book pH, with respect to the amount of absorbed alkaline aerosol, was built and interpreted in terms of a chemical model for the neutralization process. FTIR, PXRD and XRF spectroscopies were used to characterize the book chemistry. The effects of the treatment on the book were evaluated by measuring the degree of polymerization (DP) of the paper and the colorimetric coordinates of the paper and ink. Artificial aging tests revealed a general increase in the aging stability of the deacidified paper samples with respect to the untreated samples. Finally, the alkaline reserve data are discussed.     

A Remark on the Hörmander Inequality

A sufficient condition is given in order to ensure the Hörmander inequality for a (formally) self-adjoint transversally elliptic pseudodifferential operator P in the case of the symplectic form changing rank on the characteristic manifold.     

Spectral density method in quantum nonextensive thermostatistics and magnetic systems with long-range interactions

Motived by the necessity of explicit and reliable calculations, as a valid contribution to clarify the effectiveness and, possibly, the limits of the Tsallis thermostatistics, we formulate the Two-Time Green Functions Method in nonextensive quantum statistical mechanics within the optimal Lagrange multiplier framework, focusing on the basic ingredients of the related Spectral Density Method (SDM). Besides, to show how the SDM works, we have performed, to the lowest order of approximation, explicit calculations of the low-temperature properties for a quantum d-dimensional spin-1/2 Heisenberg ferromagnet with long-range interactions decaying as 1/r^p ( r is the distance between spins in the lattice).     

A toolbox for the fast information analysis of multiple-site LFP, EEG and spike train recordings

Background  

Information theory is an increasingly popular framework for studying how the brain encodes sensory information. Despite its widespread use for the analysis of spike trains of single neurons and of small neural populations, its application to the analysis of other types of neurophysiological signals (EEGs, LFPs, BOLD) has remained relatively limited so far. This is due to the limited-sampling bias which affects calculation of information, to the complexity of the techniques to eliminate the bias, and to the lack of publicly available fast routines for the information analysis of multi-dimensional responses.     

Dynamical behaviour of holographic gratings with a nematic film --Polymer slice sequence structure

We have studied the dynamical response of a new kind of holographic grating to a pulsed electric field. The structure, named POLICRYPS, consists of a sequence of homogeneous polymer slices separated by liquid-crystal films. We have found that both the rise and fall response times depend on the pulse duration and amplitude of the applied electric field. We propose a phenomenological explanation for this behaviour, outlining the possibility of getting response times of the order of 100 s by properly choosing the pulse shape. Results are very interesting for developments in which POLICRYPS gratings could be proposed as basic elements in photonic devices for telecom applications, and induce to a deeper analysis of the microscopic interaction between liquid crystal and polymer interfaces in these samples.Received: 5 February 2004, Published online: 14 September 2004PACS: 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems - 42.40.Eq Holographic optical elements; holographic gratings - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions     

Observation of two-wave coupling during the formation of POLICRYPS diffraction gratings

We report on the experimental observation of two-wave mixing that occurs inside a sample between the beams used for the fabrication of polymer-liquid-crystal-polymer slices (POLICRYPS) diffraction gratings. The effect depends on the phase shift between the curing interference pattern and the grating being cured. This shift can be mechanically induced by accidental vibrations of the experimental setup; thus a high setup stability is needed. We devised a mechanism that enables us to control setup vibrations in situ and used it to monitor the experiment. When the mechanically induced shift was significantly small, wave mixing was observed only if the initial intensities of the two curing beams were different from each other.     

Enantioselective conjugate addition of phenylboronic acid to enones catalysed by a chiral tropos/atropos rhodium complex at the coalescence temperature

A highly enantioselective rhodium-catalysed conjugate addition of phenylboronic acid to cyclic enones has been achieved using a dynamic library of chiral phosphorus ligands; the tropos/atropos nature of the ligands in the rhodium complex has been characterised via 31P-NMR.