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Raman spectroscopy: Probing dynamics of water molecules confined in nanoporous silica glasses

In order to explore the influence of nanoscopic confinement on the vibrational properties of H-bonded liquids, we performed a detailed Raman scattering study, as a function of temperature, on water confined in 75 ? and 200 ? pores of a Gelsil glass. A detailed evaluation of the observed changes in the O-H stretching profile has been achieved by decomposing the O-H band into individual components, corresponding to those found for bulk water and associated to different levels of water connectivity. As main result, a similar effect produced by enlarging pore diameter and lowering T has been put into evidence. Again, the “structure-breaker” role of the GelSil glass on physisorbed water is confirmed and shown to be enhanced by the diminishing of the pore size.     

The Classification of Non-Local Chiral CFT with <Emphasis Type="Italic">c</Emphasis> < 1

All non-local but relatively local irreducible extensions of Virasoro chiral CFTs with c < 1 are classified. The classification, which is a prerequisite for the classification of local c < 1 boundary CFTs on a two-dimensional half-space, turns out to be 1 to 1 with certain pairs of A-D-E graphs with distinguished vertices. Dedicated to Hans-Jürgen Borchers on the occasion of his 80th birthday Supported in part by JSPS. Supported in part by EU network “Quantum Spaces - Noncommutative Geometry” HPRN-CT-2002-00280. Supported in part by GNAMPA and MIUR.     

Effect of Pr3+ Doping on the OH Content of Silica Xerogels

Pr2O3-SiO2 xerogels doped with different Pr/Si concentrations were annealed at 900°C for 120 h and then investigated by FTIR, NIR absorption, Raman and luminescence spectroscopies. It is observed that the content of surface silanol groups is lower for higher Pr3+ concentrations. Luminescence measurements indicate that the amount of the residual OH plays an important role in the spectroscopic properties of the Pr3+ ion and in particular the quantum yield of the emission from the 3P0,1 and 1D2 states.     

On-line monitoring of Au nanoparticles formation by optical spectroscopy

X-Ray Magnetic Circular Dichroism experiments have been conducted on a vanadium inorganic salt and a vanadium enamino-ketone complex. Measurements at the K edge of oxygen and nitrogen reveal the amount of magnetic moment transferred in the 2p orbitals of the ligand atoms from the magnetic V ion. Measurements at the L edge of vanadium show that the orbital moment is small and that J = L + S, contrary to the expected J = L-S coupling for a 3d metal with less than five d-electrons. This surprising inobservance of Hunds third rule emphasizes the need for more detailed studies and calculations on such hybrid molecules.Received: 19 November 2003, Published online: 20 April 2004PACS: 75.20.-g Diamagnetism, paramagnetism, and superparamagnetism - 75.70.Ak Magnetic properties of monolayers and thin films - 78.70.Dm X-ray absorption spectra     

E stereoregular 1,1 and 1,3 constitutional units from 1,3-butadiene in copolymerizations catalyzed by a highly hindered c(2) symmetric metallocene

Unprecedented 1,1 and 1,3 constitutional units from 1,3-butadiene, both presenting only the E configuration of the double bond, have been achieved by copolymerization with ethene, conducted at high temperature and low ethene concentration, when catalyzed by a highly hindered C(2) symmetric metallocene. Ethene/butadiene copolymerizations by this catalyst generally lead to prevailing methylene-1,2-cyclopropane units from butadiene. Polymer microstructures obtained for different comonomer concentrations clearly indicate that the rate-determining step leading to cyclopropanation involves ethene, while that leading to 1,1 and 1,3 constitutional units does not. A general copolymerization scheme and a molecular modeling study of the cyclopropanation reaction are presented. Molecular modeling also indicates that the E stereoselectivity for 1,1 and 1,3 constitutional units can be rationalized, in the assumption that an allyl isomerization of the terminal of the growing chain would occur.     

Search for the lepton-number-violating decay Xi(-)-->pmu(-)mu(-)

A sensitive search for the lepton-number-violating decay Xi(-)-->pmu(-)mu(-) has been performed using a sample of approximately 10(9) Xi(-) hyperons produced in 800 GeV/c p-Cu collisions. We obtain B(Xi(-)-->pmu(-)mu(-))<4.0x10(-8) at 90% confidence, improving on the best previous limit by 4 orders of magnitude.     

Structural and ferroelectric properties of Pb1-xSrxTiO3 thin films

Strontium-modified lead titanate (PST) thin films with composition Pb_1-xSr_xTiO₃ (0.10<x0.60) were grown on Pt/Ti/SiO₂/Si substrates using a soft chemical process. The crystallization of the PST thin films was achieved by heat treatment at 600 °C. The structural and microstructural modifications in the films were studied using X-ray diffraction (XRD) and atomic force microscopy, respectively. The XRD study shows that the lattice parameters of polycrystalline PST thin films calculated from X-ray data indicate a decrease in lattice tetragonality with the increase in strontium content in these films. This indicates a gradual change from tetragonal to cubic structure. By atomic force microscopy analysis, the average grain size of the thin films was systematically reduced with the increase in Sr content. The dielectric property of the thin films was found to be strongly dependent on the Sr concentration. With 60 at.% Sr content, a ferroelectric to paraelectric phase transition was observed at room temperature. PACS 61.10.Nz; 68.37.Ps; 77.55.+f; 77.84.-s; 81.15.-z     

Solitons in Affine and Permutation Orbifolds

We consider properties of solitons in general orbifolds in the algebraic quantum field theory framework and constructions of solitons in affine and permutation orbifolds. Under general conditions we show that our construction gives all the twisted representations of the fixed point subnet. This allows us to prove a number of conjectures: in the affine orbifold case we clarify the issue of fixed point resolutions; in the permutation orbifold case we determine all irreducible representations of the orbifold, and we also determine the fusion rules in a nontrivial case, which imply an integral property of chiral data for any completely rational conformal net.Supported in part by NSF.Supported in part by GNAMPA-INDAM and MIUR.Supported in part by NSF.