Characterization of LiNbO3 waveguides fabricated by proton exchange in water

Proton exchange of LiNbO₃ substrates has been achieved by immersing the samples in distilled water in sealed ampoules at temperatures between 190 °C and 300 °C. The samples have been studied by infrared spectra analysis, dark mode reflectivity and X-ray rocking curve diffraction. The results obtained show that exchange rates as high as with common acids (85%) are easily reached. The structure of the exchanged waveguides varies from the low index -phase to the high index -phases depending on the temperature and time length of the exchange process, as well as on the distilled water amount used. Optical waveguides made up of phases of high, sharp index jump (n_e0.12) as well as of low index jump and very low propagation losses (0.5 dB/cm) have been obtained and characterized. PACS 42.82.Et; 42.70.Mp     

Measurement of charged-particle multiplicities in gluon and quark jets in pp collisions at square root of s = 1.8 TeV

We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of theta(c) = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejet theta c varies in the range from 12 to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = Ng/Nq is found to be 1.64+/-0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations.     

Superlinear photovoltaic currents in LiNbO<Subscript>3</Subscript>: analyses under the two-center model

Superlinear photovoltaic currents in LiNbO₃ are theoretically studied by using a two active center model, with Fe²⁺/Fe³⁺ as primary center and Nb_Li⁴⁺/Nb_Li⁵⁺ as secondary center. Analytical instead of numerical results are provided, including close-form expressions for most common experimental situations. Recent photovoltaic parameters obtained for -phase proton-exchanged LiNbO₃ waveguides (very similar to the substrate) are used for applying the model and comparing with published experimental results. Thoroughly studied aspects are: the redistribution of donor/acceptor states for each species as a function of the light intensity, their contribution to the photovoltaic current density, the effect of the temperature, and the role of the center concentrations and their reduction state. This provides a detailed understanding of the photovoltaic current function shapes versus light intensity, predicts new features of interest for experimentalists and suggests further experiments to better determine the material parameters. Photovoltaic measurements and modeling appear a simpler and safer way of understanding the role of the two-center photovoltaic effect in photorefractive phenomena as well as for determining important photorefractive parameters. PACS 42.70.Nq; 72.40.+w.     

Exclusion limits on the WIMP-nucleon cross section from the cryogenic dark matter search

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV/c2 WIMP mass and, at >75% C.L., the entire 3sigma allowed region for the WIMP signal reported by the DAMA experiment.     

Highly enantioselective copper(I)-fesulphos-catalyzed 1,3-dipolar cycloaddition of azomethine ylides

The catalyst system formed by Cu(CH3CN)4ClO4 and the planar chiral P,S-ligand Fesulphos behaves as a very efficient chiral Lewis acid in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. This catalyst shows a remarkable reactivity at low catalyst loading (0.5-3 mol %), affording in good yields the endo adducts with exceptional levels of enantioselectivity (up to >99% ee). This catalytic asymmetric procedure has a broad structural scope with regard to both azomethine and dipolarophile substitution. The first examples of catalytic asymmetric 1,3-dipolar cycloaddition with ketimine-derived azomethines are reported.     

Mössbauer study of Sn(Fe)O2 prepared by mechanosynthesis

This work deals with first-principles investigation of the electronic structure of the BF₃??H₂O complex which is important in catalysis of organic reactions and polymerization. The dissociation energy of the BF₃??H₂O complex and the nuclear quadrupole interaction parameters for the excited nuclear state ¹⁹F* (I = 5/2) of the fluorine nuclei have been studied. Our investigation shows that the complexation bond BO between the BF₃ and H₂O units is strongly influenced by the larger electronegativity of Oxygen as compared to Nitrogen in BF₃??NH_3. The quadrupole coupling constants of ¹⁹F* and the asymmetry parameter are however quite close to those for BF₃??NH₃. The likely reasons for these features of these two important catalytic systems are suggested.     

Composition assessment of ferric oxide by accurate peak fitting of the Fe 2p photoemission spectrum

A quantitative study of the surface composition of ferric oxide employing photoemission spectra is presented. It was possible to accurately reproduce the expected composition (Fe_2.00±0.05O₃) by modeling the background as a combination of Shirley‐type (Shirley–Vegh–Salvi–Castle) and slope backgrounds through the active approach. The line‐shape employed to fit apparent peak asymmetries was the double‐Lorentzian. It was possible to resolve a previously unreported satellite located at ~729 eV. Copyright © 2016 John Wiley & Sons, Ltd.     

Indoor radon levels and gamma-radiation in dwellings of the Metropolitan Zone of Guadalajara

The present study in the Metropolitan Zone of Guadalajara (MZG) in the state of Jalisco was carried out along 2007. ²²²Rn (radon) and ²²⁰Rn (thoron) levels were measured in single-family dwellings in normal living conditions (open house condition). Measurements were accomplished by Electret Passive Environmental Radon Monitors (E-PERM) in different configurations. At the same time and for the same period, the gamma dose rate was measured by a LiF: Mg, Cu, P+PTFE thermoluminiscent dosimeter. A Quality Assurance Program was improved. Results show a lognormal distribution of annual concentrations and seasonal variations. Mean annual concentrations of radon were lower than US EPA and EEC action values. ²²⁰Rn levels appear to be higher than the typical value determined by the UNSCEAR Reports (1993 and 2000). Performance of different E-PERM configurations accomplishes the US EPA guidelines and yield useful results for diverse situations. Gamma rate dose was higher than that of the Metropolitan Zone of Mexico.