Experimental investigation and thermodynamic prediction of the Bi–Sb–Zn phase diagram

Phase diagram of the ternary Bi–Sb–Zn system was investigated experimentally by DTA and SEM-EDS methods and analytically by CALPHAD method. The liquidus projection, invariant equilibria, several vertical sections and isothermal section at 300 °C were predicted using COST 531 thermodynamic database. Phase transition temperatures of alloys along three predicted vertical sections of the Bi–Sb–Zn ternary system with molar ratio Bi:Sb = 1, Bi:Zn = 1 and Sb:Zn = 1, were measured by differential thermal analysis (DTA). Predicted isothermal section at 300 °C was compared with the results of the scanning electron microscope (SEM) with energy dispersive spectrometry (EDS) analysis from this work.     

Dynamic mechanical analysis study of the curing of phenol‐formaldehyde novolac resins

The curing reaction of typical commercial phenol‐formaldehyde novolac resins with hexamethylentetraamine (HMTA) was followed by dynamic mechanical analysis. The evolution of the rheological parameters, such as storage modulus G′, loss modulus G″, and tanδ (G″/G′), as a function of time, for samples of the phenolic resins on cloth, was recorded. The curing reaction, leading to the formation of a crosslinked structure, is described by a third‐order phenomenological equation. This equation takes into account a self‐acceleration effect, as a consequence not only of the chemical reaction of crosslinking after the gel point but of phase segregation as well. This rheokinetic model of the curing of phenolic novolac resins permits the determination of the numerical values of the kinetic equation constants. The influence of the composition, structure, and physical treatment on the curing kinetics of the novolac resins is evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1902–1913, 2001     

Fracture resistance of endodontically treated maxillary incisors restored with zirconia posts: effect of the internal plateau preparation

ABSTRACT

We report on a new approach to increase the fracture resistance of endodontically treated teeth. We propose a preparation of horizontal internal plateau (IP) in dentine and the use of retentive zirconia posts to achieve a more favourable load transmission. The aim of our work was to investigate the effect of the IP depth and the post diameter on the fracture resistance and the failure mode of maxillary central incisors. Seventy-two teeth were, divided into six groups of 12. IP 4?mm in diameter and 0, 1 or 2?mm in depth was prepared and zirconia posts of two diameters luted. Specimens were loaded until failure and fractures were classified as reparable or not. Two-way ANOVA, Tukey’s HSD test and Poisson regression were used for statistical analysis (α?=?0.05). Significantly improved fracture resistance and predominantly favourable failure modes were found when 2-mm deep IP is prepared.     

Intensification of Mass Transfer in the Extraction Process with a Nanofluid Prepared in a Natural Deep Eutectic Solvent

The phytotoxic residues after olive oil production and residue leaves after pruning contain valuable bioactive compounds. A natural deep eutectic solvent (NADES) and an ethanol-water mixture were used for polyphenol extraction from olive pomace and leaves. Type of solvent, extraction temperature, and particle size of the leaves were optimized. NADES demonstrated better efficiency in the extraction process than conventional solvents; with higher temperature and smaller fraction of olive leaves, a higher yield of polyphenols was obtained from leaves. Extraction with a nanofluid as solvent was carried out. A stable nanofluid was prepared from NADES by adding Al₂O₃ nanoparticles. A higher yield was obtained with nanofluid from leaves, while an improvement of polyphenol extraction was achieved after the removal of oil from olive pomace.     

Factors affecting smoking of elementary and high school children from Chile

The outcome of orthodontic treatment involving early extraction of 4 second molars was evaluated in 52 patients (29 girls, 23 boys). Computer-assisted analysis of cephalograms, casts and panoramic X-rays was performed at the start (T1, mean age 11.5 years) and at the end (T2, mean age 14.4 years) of treatment. Following treatment, mesial migration of upper and lower first molars was counteracted; however, treatment only moderately influenced normal development of the position of the incisors and the profile. At the end of treatment, the third molars had erupted in only 3 patients. Nevertheless, on average a significant mesial movement of these teeth was observed. In addition, there was a significant improvement in the axial inclination of the third molars, especially in the upper arch. This improvement was correlated with the original position of the teeth. All patients needed a longer follow-up period and it seems reasonable that some of them might require a second treatment phase to adjust the position of the third molars.     

Expression and initial characterization of a soluble glycine binding domain of the N-methyl-D-aspartate receptor NR1 subunit

Glycine is an essential co-agonist of the excitatory N-methyl-D-aspartate (NMDA) receptor, a subtype of the ionotropic glutamate receptor family. The glycine binding site of this hetero-oligomeric ion channel protein is formed by two distinct extracellular regions, S1 and S2, of the NR1 subunit, whereas the homologous domains of the NR2 subunit mediate glutamate binding. Here, segments S1 and S2 of the NR1 polypeptide were fused via a linker peptide followed by N- and C-terminally tagging with Flag and His6 epitopes, respectively. Infection of High Five insect cells with a recombinant baculovirus containing this glycine binding site construct resulted in efficient secretion of a soluble fusion protein of about 53 kDa. After affinity purification to near-homogeneity, the fusion protein bound the competitive glycine site antagonist [3H]MDL105,519 with high affinity (Kd = 5.22 +/- 0. 13 nM) similar to that determined with rat brain membrane fractions. This high affinity binding could be competed by the glycine site antagonist 7-chlorokynurenic acid as well as the agonists glycine and D-serine but not by L-glutamate. This indicates that the S1 and S2 domains of the NR1 subunit are sufficient for the formation of a glycine binding site that displays pharmacological properties similar to those of the NMDA receptor in vivo.     

Synthesis,characterisation and flame,thermal and electrical properties of poly (<Emphasis Type="Italic">n</Emphasis>-butyl methacrylate)/titanium dioxide nanocomposites

Nanocomposites based on poly (n-butyl methacrylate) (PBMA) with various concentrations of titanium dioxide (TiO₂) nanoparticles were synthesised by in situ free radical polymerisation method. The formation of nanocomposite was characterised by FTIR, UV, XRD, DSC, TGA, impedance analyser and flame retardancy measurements. FTIR and UV spectrum ascertained the intermolecular interaction between nanoparticles and the polymer chain. The XRD studies indicated that the amorphous region of PBMA decreased with the increase in content of metal oxide nanoparticles. The SEM revealed the uniform dispersion of nanoparticles in the polymer composite. The DSC and TGA studies showed that the glass transition temperature and thermal stability of the nanocomposites were increased with the increase in the concentration of nanoparticles. The conductivity and dielectric properties of nanocomposites were higher than pure PBMA and the maximum electrical property was observed for the sample with 7 wt% TiO₂. As the concentration of nanoparticles increased above 7 wt%, the electrical property of nanocomposite was decreased owing to the agglomeration of nanoparticles in the polymer. Nanoparticles could impart better flame retardancy to PBMA/TiO₂ composite and the flame resistance of the materials improved with the addition of nanoparticles in the polymer matrix.     

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters

Summary First unsaturated polyester fibers were prepared starting from stereoregular, macromolecular poly(octamethylene fumarate). Fibers obtained from octamethylene copolyesters of fumaric and terephthalic acids manifested improved mechanical properties and higher melting points. All unsaturated polyester fibers prepared in the study, based on the homopolymer and on copolymers of fumaric acid, even those containing as low as 10% of fumaric acid residues, are able to be covalently bonded to an unsaturated polyester matrix.For part 7, see Jaovi M.S., et al., Makromol. Chem. (submitted)     

Robustness of the near infrared spectroscopy method determined using univariate and multivariate approach

The robustness assessment is a part of a method validation protocol, during which several characteristics of an analytical method are also evaluated (e.g. accuracy, repeatability, reproducibility, linearity, intermediate precision, measurement uncertainty) in order to assess its fitness for purpose. The purpose of robustness assessment of the near infrared spectroscopy method (NIRS) is to indicate which factor significantly influence the obtained results, as well as to point to the potential problems that might occur in the routine application of the method. The assessment of robustness of the NIRS method included variation of certain operational and environmental factors at three level (−1, 0, 1) by applying univariate (one-variable-at-a-time, OVAT) and multivariate (multivariate-at-a-time, MVAT) approach to the experimental design. Operational and environmental factors that were varied included the number of subsamples to be measured in the NIRS measurement (1), environmental temperature (2), sample temperature (3), environmental air humidity (4), instrument voltage (5) and lamp aging (6). Regardless the applied experimental design, external factors with significant influence on obtained NIRS results were indicated, as well as pointed the potential problems that might occur in the routine application of the method. In order to avoid them, every effort should be made to stabilize instrument and sample temperature and to standardize the homogeneity and number of subsamples to be measured in NIRS measurement. Moreover, the obtained results highlighted the necessity that the NIRS instruments should work through a voltage regulator.