Zirconium-substituted isopolytungstates: structural models for zirconia-supported tungsten catalysts

The synthesis and characterization of a series of mixed W-Zr polynuclear Lindqvist-type complexes, deriving from hexatungstate [W6O19]2-, are described in this work. This family of compounds is built from {W5O18Zr}2- moieties as shown by the X-ray structures of the monomeric [W5O18Zr(H2O)(3-n)(DMSO)n]2- (n = 1 and 2) and dimeric [{W5O18Zr(mu-OH)}2]6- anions. A comprehensive spectroscopic study (183W NMR, FTIR, Raman, EXAFS, and EPR) of these compounds is presented. The goal of incorporating Zr(IV) cations into an oxotungstic core is to obtain spectroscopic models that could mimic the interactions that develop in supported catalysts between the active phase and the supporting oxide. This work tends to show that these molecular compounds can be regarded as soluble structural analogues of WOx/ZrO2 catalysts, which are interesting candidates for the skeletal isomerization of light n-alkanes.     

Self-affine analysis of protein energy

We study the time series of the total energy of polypeptides and proteins. These time series were generated by molecular dynamics methods and analyzed by applying detrended fluctuation analysis to estimate the long-range power-law correlation, i.e. to measure scaling exponents α. Such exponents were calculated for all systems and their values follow environment conditions, i.e., they are temperature dependent and also, in a continuum medium approach, vary according to the dielectric constants (we simulated ?=2 and ?=80). The procedure was applied to investigate polyalanines, and other realistic models of proteins (Insect Defensin A and Hemoglobin). The present findings exhibit results that are consistent with previous ones obtained by other methodologies.     

Influence of light guide tip used in the photo-activation on degree of conversion and hardness of one nanofilled dental composite

The aim of this study was to evaluate the degree of conversion and hardness of a dental composite resin Filtek™ Z-350 (3M ESPE, Dental Products St. Paul, MN) photo-activated for 20 s of irradiation time with two different light guide tips, metal and polymer, coupled on blue LED Ultraled LCU (Dabi Atlante, SP, Brazil). With the metal light tip, power density was of 352 and with the polymer was of 456 mW/cm², respectively. Five samples (4 mm in diameter and 2mm in thickness—ISO 4049), were made for each Group evaluated. The measurements for DC (%) were made in a Nexus-470 FT-IR, Thermo Nicolet, E.U.A. Spectroscopy (FTIR). Spectra for both uncured and cured samples were analyzed using an accessory of reflectance diffuse. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm⁻¹ resolution, 300–4000 cm⁻¹ wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm⁻¹) against internal standard before and after curing of the sample: aromatic C-C (peak at 1610 cm⁻¹). The Vickers hardness measurements (top and bottom surfaces) were performed in a universal testing machine (Buehler MMT-3 digital microhardness tester Lake Bluff, Illinois USA). A 50 gf load was used and the indenter with a dwell time of 30 s. The data were submitted to the test t Student at significance level of 5%. The mean values of degree of conversion for the polymer and metal light guide tip no were statistically different (p = 0.8389). The hardness mean values were no statistically significant different among the light guide tips (p = 0.6244), however, there was difference between top and bottom surfaces (p < 0.001). The results show that so much the polymer light tip as the metal light tip can be used for the photo-activation, probably for the low quality of the light guide tip metal.     

Anisotropic tight-binding model applied to zigzag ultra-small nanotubes

A single-wall carbon nanotube (SWCNT) can be visualized as a graphene rolled into a cylinder. Tight-binding band structure calculations, with hopping between nearest-neighbor π orbitals only (NNTB), established rules by which both the mode in which the graphene is rolled up and the diameter determine whether the SWCNT is a metal or a semiconductor. However, when the diameter of the SWCNT is ultra-small its large curvature results in the breakage of these rules. In this work, we studied zigzag (n, 0) SWCNTs with diameters smaller than 0.7 nm using a π orbital-only tight-binding model including anisotropy in the hopping between next-nearest-neighbor sites (ANNNTB). Band overlaps were found in the electronic band structures of the zigzag SWCNTs for n=3, 4, 5, and 6, indicating that they are metals. The reason why the band structures of armchair and chiral SWCNTs are less affected by curvature effects becomes clear with the ANNNTB model, as does the reason why non-degenerate states cause band overlaps of the zigzag SWCNTs for n=3, 4, 5, and 6. Our results show that a π orbital-only tight-binding model is able to describe both the band overlaps and gaps obtained by ab initio calculations for zigzag SWCNTs.     

Using phonon resonances as a route to all-angle negative refraction in the far-infrared region: the case of crystal quartz

We consider how all-angle negative refraction may be induced in anisotropic crystals by making use of the phonon response. We investigate the example of crystal quartz at far-infrared wavelengths. Reflection and transmission measurements confirm the expected behavior, and show relatively high transmission efficiency at frequencies at which negative refraction occurs.     

Study of spectroscopic properties of Europium (III) Tris(β-diketonate) complex and α-Cyclodextrin in aqueous medium

The solubilization of an europium (III) β-diketonate chelate in aqueous medium and the changes in its photophysical properties upon its inclusion into an α-cyclodextrin hydrophobic cavity are described. The complex [Eu(tta)₃·(H₂O)₂] (tta = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione) was synthesized, characterized, and incorporated into the hydrophobic cavity by stirring in an α-cyclodextrin aqueous solution. The inclusion was confirmed by ¹H NMR, and the stoichiometry of association was obtained by the Job method. The maximum in the excitation spectrum of the α-CD inclusion compound in aqueous solution was shifted 28 nm compared with the maximum of non α-CD complex. The emission spectrum of the association is similar to that of the free solid complex and displays the characteristic ⁵D₀ → ⁷F_0-4 Eu³⁺ transitions.     

Active planar waveguides based on sol–gel Er3+-doped SiO2–ZrO2 for photonic applications: Morphological,structural and optical properties

Er³⁺-doped glass-ceramic SiO₂–ZrO₂ optical planar waveguides were prepared by the sol–gel route using different SiO₂:ZrO₂ molar ratios (90:10, 85:15, 80:20 and 75:25). Multilayered films were deposited onto Si(1 0 0) substrates by the dip-coating technique. Structural characterization was performed using vibrational spectroscopy and X-ray diffraction. Some optical properties, densification and surface morphology of these films were investigated as a function of the SiO₂:ZrO₂ ratio, annealing temperature and time. Optical properties such as refractive index, number of propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm, by the prism coupling technique. Uniform surface morphology with roughness less than 0.5 nm. Low losses, less than 0.9 dB/cm at 612.8 nm in the TE₀ mode, were measured for the planar waveguides containing up to 25 mol% zirconium oxide. Luminescence of Er³⁺ in the near infrared was observed for the active nanocomposite.     

A bundle-filter method for nonsmooth convex constrained optimization

For solving nonsmooth convex constrained optimization problems, we propose an algorithm which combines the ideas of the proximal bundle methods with the filter strategy for evaluating candidate points. The resulting algorithm inherits some attractive features from both approaches. On the one hand, it allows effective control of the size of quadratic programming subproblems via the compression and aggregation techniques of proximal bundle methods. On the other hand, the filter criterion for accepting a candidate point as the new iterate is sometimes easier to satisfy than the usual descent condition in bundle methods. Some encouraging preliminary computational results are also reported.     

Estimation of uncertainty in the determination of nitrogen oxides emissions

This paper presents a methodology for estimation of uncertainty on a reference test method for the determination of nitrogen oxides concentration in gaseous emissions from stationary sources. As a first stage for identification of uncertainty sources, the test method is carefully reviewed in detail. Afterwards, these sources are quantified, bearing in mind its partial uncertainty, allowing the determination of the combined uncertainty and, finally, the expanded uncertainty. The calculation procedure was implemented into an excel calculation file. Using this file and considering several numerical applications from real situations, uncertainities around 15 mg/Nm³ over determined concentrations of 350 mg/Nm³ of NO _x (expressed as NO₂) were obtained.