Optical properties of chromium-doped fluoroindate glasses

This work reports on the optical properties of Cr3+ ions in the pseudoternary system InF3-GdF3-GaF3. Linear properties, investigated through absorption and emission spectra, provide information on the crystal field, the frequency, and number of phonons emitted during the absorption to the 4T2 band and the emission to the 4A2 ground state, and the Fano antiresonance line shape in the vicinity of the 4A2→2E transition. A study of the nonlinear refractive index as a function of the wavelength, carried out with the Z-scan technique, provides spectroscopic data about electronic transitions starting from the excited state.

Some comments on the bi(tri)-Hamiltonian structure of generalized AKNS and DNLS hierarchies

We give the correct prescriptions for the terms involving ∂ -1 xδ(x - y), in the Hamiltonian structures of the AKNS and DNLS systems, necessary for the Jacobi identities to hold. We establish that the sl(2) and sl(3) AKNS systems are tri-Hamiltonians and construct two compatible Hamiltonian structures for the sl(n) AKNS system. We give a method for the derivation of the recursion operator for the sl(n + 1) DNLS system, and apply it explicitly to the sl(2) case, showing that such a system is tri-Hamiltonian. © 1998 Elsevier Science B.V.

Method for marginal measurements of restorations: accessory device for toolmakers microscope.

Standardization of measurements for marginal fit of castings is critical. This study describes the fabrication of a device that allowed fixation of specimens on a Toolmakers microscope with identical conditions according to tri-dimensional positioning of specimens, measuring location, and seating force. The device also allows mapping of the marginal discrepancies on the entire marginal perimeter of the tooth preparation.

Marginal fit of nickel-chromium copings before and after internal adjustments with duplicated stone dies and disclosing agent.

STATEMENT OF PROBLEM: Despite careful procedures, master stone dies may be damaged during laboratory procedures. The dentist routinely adjusts castings because the marginal fit of casting is not as accurate as on the dies. PURPOSE: This study evaluated the technique of internal adjustment of castings with use of duplicated stone dies and a disclosing agent to improve marginal fit discrepancy. MATERIAL AND METHODS: Thirty-two nickel-chromium copings were fabricated and simulated standard clinical and laboratory procedures with 2 variables: tooth preparation convergence angles of 6 and 18 degrees, with or without internal relief. Master stone dies and their duplicates were selected for coping construction and internal adjustment, respectively. A specimen positioning device was coupled with a Toolmakers microscope to allow reproducibility of measurements. Each coping was evaluated at 8 locations of its marginal perimeter, before and after internal adjustment. RESULTS: Marginal fit discrepancy of copings were significantly reduced with an internal adjustment technique (mean > 52%) for all experimental groups. Tooth preparations with greater convergence and internally relieved castings recorded a better marginal fit. CONCLUSION: The casting internal adjustment technique with use of duplicated stone dies and a disclosing agent substantially reduced marginal fit discrepancy.

Chromium-containing silica materials

Chromium-containing silica samples were obtained from soluble sodium silicate solutions in the presence of different chromium nitrate concentrations. Precipitation was carried out in ethanolic media. Gel precipitate was dried by liophylization and samples measured by transmission electron microscopy (TEM), X-ray energy-dispersive spectrometer, X-ray mapping, X-ray photoemission spectroscopy (XPS), and particle size analysis. Spherical chromium containing silica particles with 3.5% and 4.8% (at.%) of chromium were obtained. Particle size analysis results showed that with increased addition of chromium in sodium silicate solutions produces agglomerates whose sizes range from 1 to 0.2 μm. Chromium mapping and XPS results show that chromium oxide is preferentially segregated on particle surfaces. Chromium oxide was detected on particle surface with a binding energy of 576.77 ± 0.05 eV as obtained from XPS analysis. During the hydrolysis and condensation processes chromium oxide precipitates on the silica surface and it affects the silica chain size. © 2000 Elsevier Science B.V. All rights reserved.

Effects of tungsten carbide thermal spray coating by HP/HVOF and hard chromium electroplating on AISI 4340 high strength steel

In cases of decorative and functional applications, chromium results in protection against wear and corrosion combined with chemical resistance and good lubricity. However, pressure to identify alternatives or to improve conventional chromium electroplating mechanical characteristics has increased in recent years, related to the reduction in the fatigue strength of the base material and to environmental requirements. The high efficiency and fluoride-free hard chromium electroplating is an improvement to the conventional process, considering chemical and physical final properties. One of the most interesting, environmentally safer and cleaner alternatives for the replacement of hard chrome plating is tungsten carbide thermal spray coating, applied by the high velocity oxy-fuel (HVOF) process. The aim of this study was to analyse the effects of the tungsten carbide thermal spray coating applied by the HP/HVOF process and of the high efficiency and fluoride-free hard chromium electroplating (in the present paper called 'accelerated'), in comparison to the conventional hard chromium electroplating on the AISI 4340 high strength steel behaviour in fatigue, corrosion, and abrasive wear tests. The results showed that the coatings were damaging to the AISI 4340 steel behaviour when submitted to fatigue testing, with the tungsten carbide thermal spray coatings showing the better performance. Experimental data from abrasive wear tests were conclusive, indicating better results from the WC coating. Regarding corrosion by salt spray test, both coatings were completely corroded after 72 h exposure. Scanning electron microscopy technique (SEM) and optical microscopy were used to observe crack origin sites, thickness and adhesion in all the coatings and microcrack density in hard chromium electroplatings, to aid in the results analysis. © 2001 Elsevier Science B.V. All rights reserved.

Organophosphate induced delayed neuropathy in genetically dissimilar chickens: Studies with tri-ortho-cresyl phosphate (TOCP) and trichlorfon

Measurements of plasma cholinesterase (pl.ChE), brain cholinesterase (Br.ChE) and brain Neuropathy Target Esterase (Br.NTE) were made in three different lineages of chickens. All birds received toxicants through gavage in a single oral dose between 08:00 and 09:00 h, after overnight fast. Babcock chickens were treated with 800 mg/kg tri-ortho-cresyl phosphate (TOCP) or 80 mg/kg trichlorfon. The TOCP group had 82% Br.NTE inhibition, when compared to the control group, and no birds displayed symptoms of clinical organophosphate-induced delayed neuropathy (OPIDN). Hy-line w36 lineage chickens were given 1600 mg/kg TOCP and despite this higher dose, Br.NTE inhibition was similar that presented by Babcock chickens. Isabrown chickens were given 1600 mg/kg TOCP or 80 mg/kg trichlorfon. At 36 h all trichlorfon treated birds had from 80 to 90% inhibition of Pl.ChE and Br.ChE, when compared to controls. However, Br.NTE was inhibited less than 20%, and there were no clinical signs of OPIDN. All TOCP treated isabrown chickens had more than 80% Br.NTE inhibition while one of them exhibited just light signs of OPIDN, two chickens became totally paralyzed. This finding suggested that chicken strain was important in the appearance of OPIDN. In addition, 70-80% of NTE inhibition was necessary but was not sufficient to produce OPIDN in chickens, since babcock and hy-line w36 chickens exhibited NTE inhibition in the range of 70-80% without clinical signs of OPIDN. © 2002 Elsevier Science Ireland Ltd. All rights reserved.

Cytotoxicity of denture base resins: Effect of water bath and microwave postpolymerization heat treatments

Purpose: This study compared the effect of two postpolymerization heat treatments on the cytotoxicity of three denture base resins on L929 cells using 3H-thymidine incorporation and MTT assays. Materials and Methods: Sample disks of Lucitone 550, QC 20, and Acron MC resins were fabricated under aseptic conditions and stored in distilled water at 37°C for 48 hours. Specimens were then divided into three groups: (1) heat treated in microwave oven for 3 minutes at 500 W; (2) heat treated in water bath at 55°C for 60 minutes; and (3) no heat treatment. Eluates were prepared by placing three disks into a sterile glass vial with 9 mL of Eagle's medium and incubating at 37°C for 24 hours. The cytotoxic effect from the eluates was evaluated using the 3H-thymidine incorporation and MTT assays, which reflect DNA synthesis levels and cell metabolism, respectively. Results: The components leached from the resins were cytotoxic to L929 cells when 3H- thymidine incorporation assay was employed. In contrast, eluates from all resins revealed noncytotoxic effects as measured by MTT assay. For both MTT assay and 3H-thymidine incorporation, the heat treatments did not decrease the cytotoxicity of the materials tested. Conclusion: Resins were graded by 3H-thymidine incorporation assay as slightly cytotoxic and by MTT assay as noncytotoxic. Cytotoxicity of the denture base materials was not influenced by microwave or water bath heat treatment.

Evaluation of the genotoxic potential due to the action of an effluent contaminated with chromium, by the comet assay in CHO-K1 cultures

The comet assay technique has been considered to be more efficient in the biomonitoring of aquatic environments that the micronucleus and sister chromatid exchange techniques. The comet assay has been used to determine breaks in the DNA strands of organisms exposed to pollutants with a genotoxic potential. The comet technique was applied to CHO-K1 cells in order to evaluate the genotoxic potential of the waters of the Sapucaizinho River (Municipality of Patrocínio Paulista, State of São Paulo, Brazil), which receive tannery effluents and therefore are contaminated with chromium. The results indicated high genotoxicity of the waters collected at sites located downstream from the emission of tannery effluents, where the concentration of chromium was found to be high.

Cytotoxicity of hard chairside reline resins: Effect of microwave irradiation and water bath postpolymerization treatments

Purpose: To evaluate the influence of water bath and microwave postpolymerization treatments on the cytotoxicity of 6 hard reline acrylic resins. Materials and Methods: The materials tested were Tokuso Rebase Fast (TR), Ufi Gel Hard (UGH), Duraliner II (D), Kooliner (K), New Truliner (NT), and Light Liner (LL). LL resin was additionally tested with an air-barrier coating (LLABC). Nine disks of each material (10 × 1 mm) were made and divided into 3 groups: group 1 (no postpolymerization treatment); group 2 (postpolymerization in microwave oven); group 3 (postpolymerization in water bath at 55°C for 10 minutes). L929 cells were cultured in 96-well plates and incubated for 24 hours in Eagle's medium. Eluates prepared from the disks or medium without disks (control) replaced the medium. Cytotoxicity was assessed by both dehydrogenase succinic activity (MTT) assay and incorporation of radioactive 3H-thymidine assay. Tests were carried out in quadruplicate and repeated twice. Differences between groups were determined by analysis of variance with Tukey multiple-comparison intervals (α = .05). Results: For MTT assay, the postpolymerization treatments had no effect on the cytotoxicity of all materials (P > .05). For 3H-thymidine assay, the postpolymerization treatments significantly decreased the cytotoxicity of UGH (P < .05). The cytotoxicity of K, NT, LL, and LLABC increased after microwave irradiation (P < .05). TR, NT, and LLABC showed an increase in cytotoxicity after water bath (P < .05). Conclusion: When assessed by MTT assay, the cytotoxicity of the materials was not affected by postpolymerization treatments. 3H-Thymidine assay showed that the cytotoxicity of the resins was not improved by the postpolymerization treatments, with the exception of UGH.

Screen-printed carbon electrode modified with poly-L-histidine applied to voltammetric determination of chromium (VI)

The present work reports the use of a screen-printed carbon electrode (SPCE) modified by poly-L-histidine film to determine chromium (VI). Stable films can be formed by direct addition of PH solution 1 % (w/v) on the electrode surface, followed by heating at 80°C during 5 min. Calibration curves can be constructed for Cr(VI) from 1.0 × 10-5 mol L-1 to 7.0 × 10-5 mol L-1 Cr (VI) in acetate buffer pH 4 using a preconcentration step of 60s at open circuit potential. A relative standard deviation of 3.2% was for five determination of 4.0 × 10 -5 mol L-1 Cr (VI). The method was successful applied to determination of Cr(VI) in wastewater samples from a leather dyeing industry. copyright The Electrochemical Society.

The significance and determination by image analysis of microcrack density in hard chromium plating

It is well known that the microcrack density is a fundamental parameter in hard chromium electroplating. The chemical and mechanical properties of this coating are widely dependent on its microcrack density. In this paper a simple image analysis procedure to determine microcrack density is presented in order to demonstrate it as a fundamental tool to estimate the fatigue, corrosion and wear behavior, as well as the residual stress field of a coated component. For this purpose, the image analysis procedure was carried out on two kinds of hard chromium plating - one called accelerated (high velocity of deposition and fluoride-free) and the other conventional (with fluoride). The coatings were applied on samples of AISI 4340 aeronautical steel, which is widely used in aircraft landing gear components. To characterize the practical significance of this study, the microcrack density results were related to the fatigue, wear and corrosion behavior from previous study and to the residual stress field in the coatings.

Open urban spaces quality: A study in a historical square in Bath - UK

The quality of open urban spaces is very important for urban vitality. Nowadays urban designers have to face the great challenge of designing urban spaces able to respond to people's need for liveable spaces. The success of these spaces depends on various aspects and the microclimatic condition has been recognized as one of the most influential. However, studies on thermal comfort in open space have shown that the user's thermal sensation does not depend only on microclimate parameters but also on other local qualitative aspects. Thus, environmental quality evaluation of successful public spaces can contribute to understand this issue. This paper focuses on a case study regarding Queen Square's environmental quality, a public space of historical importance in Bath-UK. The first stage of the research, a study on local characteristics and people observations, allowed a preliminary evaluation of the space performance, their social aspects, while it characterized and quantified the hourly variation of the space use in different days and seasons. In the second stage, short microclimatic surveys were carried out simultaneously with a perception survey through a questionnaire. The results show the strong vitality of the square and socioenvironmental significance, not only for its location in the urban context, but also for its historical value. The environmental quality of the square contributes to the users' sensation of comfort even in adverse climatic conditions. This research is part of a project that aims to investigate the impact of the environmental stimuli in the use of open spaces and intend to develop design strategies that aim to maximise the use of open spaces in different weather conditions.

Retention strength of cobalt-chromium vs nickel-chromium titanium vs Cp titanium in a cast framework association of removable partial overdenture

Aim: There is little information considering the framework association between cast clasps and attachments. The aim of this study was to evaluate the retention strength of frameworks match circumferential clasps and extra resilient attachment cast in three different alloys (cobalt-chromium, nickel-chromium titanium and commercially pure titanium), using two undercut (0.25 and 0.75 mm) and considering different period of time (0, 1/2, 1, 2, 3, 4 and 5 years). Methods: Using two metallic matrices, representing a partially edentulous mandibular right hemiarch with the first molar crown, canine root and without premolars, 60 frameworks were fabricated. Three groups (n = 20) of each metal were cast and each group was divided into two subgroups (n = 10), corresponding the molar undercut of 0.25 mm and 0.75 mm. The nylon male was positioned at the matrix and attached to the acrylic resin of the prosthetic base. The samples were subjected to an insertion and removal test under artificial saliva environment. Results: The data were analyzed and compared with ANOVAs and Tukey's test at 95% of probability. The groups cast in cobaltchromium and nickel-chromium-titanium had the highest mean retention strength (5.58 N and 6.36 N respectively) without significant difference between them, but statistically different from the group cast in commercially pure titanium, which had the lowest mean retention strength in all the periods (3.46 N). The association frameworks using nickel-chromium-titanium and cobalt-chromium could be used with 0.25 mm and 0.75 mm of undercut, but the titanium samples seems to decrease the retention strength, mainly in the 0.75 mm undercut. The circumferential clasps cast in commercially pure titanium used in 0.75 mm undercuts have a potential risk of fractures, especially after the 2nd year of use. Conclusion: This in vitro study showed that the framework association between cast clasp and an extra resilient attachment are suitable to the three metals evaluated, but strongly suggest extra care with commercially pure titanium in undercut of 0.75 mm. Clinical significance: Frameworks fabricated in Cp Ti tend to decrease in retentive strength over time and have a potential risk of fracture in less than 0.75 mm of undercut.

Tri-state Space Vector Modulation for Three-phase integrated inverters

The aim of this work is to present a modified Space Vector Modulation (SVM) suitable for Tri-state Three-phase inverters. A standard SVM algorithm and the Tri-state PWM (Pulse Width Modulation) are presented and their concept are mixed into the novel SVM. The proposed SVM is applied to a three-phase tri-state integrated Boost inverter, intended to Photovoltaic Energy Applications. The main features for this novel SVM are validated through simulations and also by experimental tests. The obtained results prove the feasibility of the proposal. © 2011 IEEE.