Structural studies on lead-cadmium fluoride solid solutions

(1-x)PbF2-(x)CdF2 solid solutions (with 0.1 less than or equal to x less than or equal to 0.5) were obtained by hyper-quenching the melt. Structural characteristics have been studied by X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). A cubic solid solution was obtained in which the lattice parameter decreases with increasing CdF2 content. High anionic disorder was evidenced from EXAFS investigations, whereas cations remain in the FCC arrangement. Pb L-3-edge EXAFS results illustrate clearly the occurrence of CdxPb1-xF2 mixed crystals by the introduction of Cd atoms in the second Pb coordination shell. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Development of an experimental glass ionomer cement containing niobium and fluoride

Glass ionomer cements (GICs) are currently used for various dental applications such as luting cements or as restorative materials. The calcium fluoro-alumino-silicate system is the basis for degradable glasses used to obtain the GICs. The purpose of the present paper is to add niobium to conventional glass system because according to previous papers niobium addition improves the chemical resistance and the mechanical properties of glasses. Therefore, the GICs prepared from these glasses would result in cements with higher chemical and mechanical resistance. The niobium fluoride powders were prepared using the sol-gel process and were characterized by X-ray diffraction, differential thermal analysis (DTA) and Al-27 and Si-29 MAS NMR. The results obtained by XRD showed that the powders prepared by this method are glass-ceramic. In the DTA curve was detected the presence of T-g and T-c temperatures. The analysis of MAS NMR spectra indicated that the framework of the powders is formed by SiO4 and AlO4 linked tetrahedra which are essential structures to yield the cements. Thus, we concluded that niobium fluoride silicate powders can be used in the preparation of GICs. (c) 2005 Elsevier B.V. All rights reserved.

POSSIBLE MECHANISMS FOR REDUCTION OF CIRCULATING CONCENTRATIONS OF PROGESTERONE BY INTERFERON-ALPHA IN COWS - EFFECTS ON HYPERTHERMIA, LUTEAL CELLS, METABOLISM OF PROGESTERONE AND SECRETION OF LH

Experiments were performed to determine the mechanism by which recombinant bovine interferon-alpha(I)1 (rbIFN-alpha) causes an acute reduction in plasma concentrations of progesterone. In experiment 1, administration of a prostaglandin synthesis inhibitor blocked rbIFN-alpha-induced hyperthermia but did not prevent the decline in plasma concentrations of progesterone. The decline in progesterone concentrations caused by rbIFN-alpha was, therefore, not a direct consequence of the associated hyperthermia or of pathways mediated through prostaglandin synthesis. It is also unlikely that rbIFN-alpha acts to increase the clearance of progesterone since injection of rbIFN-alpha did not decrease plasma concentrations of progesterone in ovariectomized cows given an intravaginal implant of progesterone (experiment 2). In experiment 3, rbIFN-alpha did not affect basal and LH-induced release of progesterone from cultured luteal slices, indicating that rbIFN-alpha is unlikely to affect luteal function directly. Injection of rbIFN-alpha did, however, cause a decrease in plasma concentrations of LH in ovariectomized cows (experiment 4) that coincided temporally with the decrease in progesterone concentrations seen in cows having a functional corpus luteum. The present results strongly suggest that rbIFN-alpha acts to reduce secretion of progesterone by interfering with pituitary support for luteal synthesis of progesterone. The finding that rbIFN-alpha can inhibit LH secretion implies that interferon-alpha molecules should be considered among the cytokines that can regulate hypothalamic or pituitary function.

Prevalence of caries and developmental defects of enamel in 9-10 year old children living in areas in Brazil differing water fluoride histories

Aims To assess the prevalences of caries, of developmental defects of enamel and their interrelationship in Brazilian 9-10-year-olds from areas of contrasting fluoridation histories.Methods systematic random sampling procedures were used to select children from an area where water had been fluoridated in 1963 and from a second area where water had been fluoridated since 1998. Clinical examinations for caries were carried out using the DMFT index and WHO diagnostic criteria. Developmental defects of enamel on upper incisors were diagnosed using the DDE index.Results A difference of 40% in DMFT was observed, with a lower prevalence of disease in the area fluoridated since 1963. Diffuse opacities affected 14.3% of the children from the area fluoridated since 1963 compared with only 2.4% in the area fluoridated in 1998. Children living in the area fluoridated in 1963 who had diffuse defects had twice the chance of being free from caries compared with those living in the same area who had no defects or who had only demarcated or hypoplastic defects.Conclusions This study confirms previous ones in showing the benefits of water fluoridation. Diffuse opacities of upper incisors affected relatively few subjects in either of the two areas.

Influence of two methods of CaCl2 application and concentrations used to maintain passion fruit firmness

This is a report on the influence of the methods of postharvest application of CaCl2 in several concentrations, on the maintenance of the firmness of the sweet passion fruit (Passiflora alata Dryander). The fruits, picked in the pre-climateric stage, were selected desinfection with thiabendazol and submitted to CaCl2 in concentrations of 0% (control), 1%, 2%, 3% or 4% with two methods: immersion (for 2 h) and infiltration under vacuum and pressure (- 25 vacuum kPa, for 1 minute and, + 25 pressure kPa, for 1 min). All fruits were stored under refrigeration (9 degreesC, 85-90% RH), for 30 d. The fruits were evaluated for texture every 3 d. From the results, it is concluded that application of CaCl2 by infiltration favored the maintenance of fruit consistency during the first 18 days of storage. Fruits treated with 1% and 2% of CaCl2 were firmer than the others.

Glasses containing lutetium fluoride

Glasses containing lutetium fluoride have been prepared in the system BaF2 - SrF2 - ZnF2 - LuF3 - InF3. The composition of the phases crystalling out of these glasses suggests octahedral pre-arrangement comprising [LuF6] and [Sr(Ba)F-2 structural fragments.

Phase transition in poly(vinylidene fluoride) investigated with micro-Raman spectroscopy

The phase transition from the non-polar a-phase to the polar beta-phase of poly(vinylidene fluoride) (PVDF) has been investigated using micro-Raman spectroscopy, which is advantageous because it is a nondestructive technique. Films of alpha-PVDF were subjected to stretching under controlled rates at 80 degrees C, while the transition to P-PVDF was monitored by the decrease in the Raman band at 794 cm(-1) characteristic of the a-phase, along with the concomitant increase in the 839 cm-1 band characteristic of the P-phase. The alpha ->beta transition in our PVDF samples could be achieved even for the sample stretched to twice (2 X -stretched) the initial length and it did not depend on the stretching rate in the range between 2.0 and 7.0 mm/min. These conclusions were corroborated by differential scanning calorimetry (DSC) and X-ray diffraction experiments for PVDF samples processed under the same conditions as in the Raman scattering measurements. Poling with negative corona discharge was found to affect the a-PVDF morphology, improving the Raman bands related to this crystalline phase. This effect is minimized for films stretched to higher ratios. Significantly, corona-induced effects could not be observed with the other experimental techniques, i.e., X-ray diffraction and infrared spectroscopy.

Influence of fluoride-containing solutions on the translucency of flowable composite resins

The aim of this study was to evaluate the influence of fluoride-containing solutions on the translucency of flowable composite resins, with respect the immersion time. Flow-It! (FI) and Natural Flow (NF) composite resins and three commercial brands of fluoride-containing solutions (Fluordent, Fluorgard and Oral B) were used. Specimens were prepared and stored in the solutions at 37degreesC, until the measurements were made after the following treatments: T1 - after 1 hour in relative humidity; T2 - after 1 h in solution; T3 - 24 h; T4 - 48 h; T5 - after a week; from T9, the measurements were accomplished weekly, up to 30-day immersion. To obtain translucency values an electrophoresis equipment was employed. Data were submitted to ANOVA and Tukey tests. The results disclosed that NF showed highest values of translucency and was statistically different from FI (p < 0.001). As regards the solutions, Fluordent and Oral B presented similar values and were statistically superior to Fluorgard (p < 0.05). Concerning the immersion time, similar results were observed for the different evaluation periods. It may be concluded that the fluoride-containing solutions affected the translucency of the composite resins, independently of the materials used. Among the tested resins, NF presented the best performance. (C) 2003 Kluwer Academic Publishers.