Langevin simulation of scalar fields: Additive and multiplicative noises and lattice renormalization

We consider the Langevin lattice dynamics for a spontaneously broken λ?⁴$\lambda {?}^4$ scalar field theory where both additive and multiplicative noise terms are incorporated. The lattice renormalization for the corresponding stochastic Ginzburg–Landau–Langevin and the subtleties related to the multiplicative noise are investigated.     

Thermogravimetry as a Reliable tool to Estimate the Density of Silanols on a Silica Gel Surface

A method was developed to estimate the density of the silanol groups attached to silica gel surfaces from thermogravimetric data. Depending on the mechanism of condensation of silanol groups during heating, after removing physically adsorbed water, the results obtained ranged from 4.3 to 6.7 OH nm^-2 for a series of silicas. The data are in good agreement with those obtained by other techniques. Thermogravimetry proved to be a reliable tool for this kind of study, with the great advantage of being a simple, quick and inexpensive method requiring only a few mg of the silica sample. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric study of the adducts CdBr2·nL (n = 1 and 2; L = ethyleneurea and propyleneurea)

A calorimetric study was performed for adducts of general formula CdBr₂·nL (n=1 and 2; L=ethyleneurea (eu) and propyleneurea (pu)). The standard molar reaction enthalpy in condensed phase: CdBr₂(c)+nL(c)=CdBr₂·nL(c); Δ_rH_m^θ, were obtained by reaction–solution calorimetry, to give the following values for mono- and bis-adducts: −19.54 and −34.59; −7.77 and −19.05 kJ mol⁻¹ for eu and pu adducts, respectively. Decomposition (Δ_DH_m^θ) and lattice (Δ_MH_m^θ) enthalpies, as well as the mean cadmium---oxygen bond dissociation enthalpy, DCd---O, were calculated for all adducts.     

Thermogravimetric study about PVC-polyaniline blends

By dissolution of PVC and polyaniline in dimethylformamide, a series of blends PVC-polyaniline were produced which were studied by scanning electron microscopy and thermogravimetry. Special attention is focused on the kinetic study of the thermal degradation steps by using non-isothermal thermogravimetric data. The results show that the thermal stability of the synthesized blend is decreased as the total amount of polyaniline is enhanced. Furthermore, the Brřnsted acid doped blend is more stable than the corresponding undoped one. PVC and the PVC-polyaniline blends exhibit two mass loss steps which activation energy values are in the range from 176 to 283 kJ mol^-1 and 306 to 322 kJ mol^-1, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

TG and DSC investigation of gallstone samples collected from patients submitted to cholecystectomy

In the present work are performed the TG and DSC study of gallstone samples collected from patients submitted to cholecystectomy at the Hospital Universitário Onofre Lopes of Universidade Federal do Rio Grande do Norte, in Natal, Rio Grande do Norte State, Brazil. The gallstone samples were characterized by elemental analysis and infrared spectroscopy. Standard cholesterol was used for all analysis as comparison with the gallstones. Is verified that cholesterol is the main chemical component of all studied gallstone samples. The thermoanalytical study was performed on air and nitrogen atmospheres. The presence of cholesterol as the main chemical component of all gallstone samples is confirmed by TG and DSC results.     

Cathodic adsorptive stripping voltammetric behaviour of guanine in the presence of copper at the static mercury drop electrode

The cathodic adsorptive electrochemical behavior of guanine in the presence of some metal ions at the static mercury drop electrode was investigated. A 1.0×10⁻³ mol l⁻¹ NaOH or a 2.0×10⁻² mol l⁻¹ Hepes buffer at pH 8.0 solutions were used as supporting electrolytes. The reduction peak potential for guanine was found to be around −0.15 V, which is very close to the mercury reduction wave. A new peak appears at −0.60 V in the presence of copper or at −1.05 V in the presence of zinc. A square wave voltammetric procedure for electroanalytical determination of guanine in 2.0×10⁻² mol l⁻¹ Hepes buffer at pH 8.0 containing 1.6×10⁻⁵ mol l⁻¹of copper ions, was developed. An accumulation potential of −0.15 V during 270 s for the prior adsorption of guanine at the electrode surface was used. The response of the system was found to be linear in the range of guanine concentration from 6.62×10⁻⁸ to 1.32×10⁻⁷ mol l⁻¹ and the detection limit was 7.0×10⁻⁹ mol l⁻¹. The influence of DNA bases such as adenine, cytosine and thymine was also examined. Cyclic voltammetry was used to characterize the interfacial and redox mechanism.     

Synthesis, characterization and thermogravimetric study of zinc group halides adducts with imidazole

The synthesis, characterization and thermogravimetric study of the adducts ZnCl₂·2Imi, ZnBr₂·2Imi, CdCl₂·Imi, CdCl₂·2Imi, CdBr₂·2Imi, CdBr₂·3Imi, CdI₂·2.5Imi, HgCl₂·2Imi, HgBr₂·1.5Imi and HgI₂·1.5Imi (Imi = imidazole) is reported. The following sequence of thermal stability is observed for the synthesized adducts: Zn>Hg>Cd. It is also verified that larger cations, as well as larger anions, result in a smaller number of imidazole molecules in the coordination sphere of the considered cation and that hard acids exhibit stronger bonds to imidazole than soft acids, and this fact is reflected in the thermal stability sequence. ZnCl₂·2Imi behaves as a non-electrolyte in acetonitrile and ethanol, whereas ZnBr₂·2Imi is a non-electrolyte in acetonitrile and a 1:1 electrolyte in ethanol. CdI₂·2.5Imi is a non-electrolyte in acetonitrile and a 1:2 electrolyte in ethanol.     

Acetaldehyde electrooxidation: The influence of concentration on the yields of parallel pathways

Parallel pathways forming CO₂ and acetic acid occur during the electrooxidation of acetaldehyde at Pt in acid medium. The yields of products depend on potential and acetaldehyde concentration. In the whole range of concentrations investigated (2.5 × 10⁻³ – 0.5 M) and at potentials below 0.6 V, CO₂ is the only product of acetaldehyde oxidation. Acetic acid is detected at potentials higher than 0.7 V. According to the analysis of products using FTIR spectroscopy, a maximum yield of CO₂ production is obtained for an acetaldehyde concentration of 0.01 M at 0.6 V. The pathway forming CO₂ is strongly inhibited for 0.5 M of acetaldehyde. It is suggested that, at high concentrations, a competition with water for active sites occurs, which inhibits the oxidation of adsorbed species, which probably follow a Langmuir–Hinshelwood mechanism.     

Electrooxidation of isotope-labeled ethanol: a FTIRS study

In this work, we investigated some important aspects related to the electrooxidation of isotope-labeled ethanol on Pt. The central point was the effect of the adsorption potential on the formation of CO₂ produced from both alcohol and methyl groups during the electrooxidation of ethanol in acid media. As a way to follow these contributions, we used isotope-labeled ethanol (¹³CH₃CH₂OH) and Fourier transform infrared spectroscopy (FTIRS). The yield of ¹³CO₂ increased with the ethanol adsorption potential. Despite the visualization difficulties due to dipole coupling, ¹³CO was detected, indicating that the formation of ¹³CO₂ follows a mechanism analogous to the one of ¹²CO₂. Dedicated to our friend Professor Francisco Carlos Nart (in memoriam), IQSC-USP, Brazil