Theoretical analysis on microwave heating of oil–water emulsions supported on ceramic, metallic or composite plates

A detailed theoretical analysis has been carried out to study efficient heating due to microwaves for one-dimensional (1D) oil–water emulsion samples placed on various ceramic, metallic (reflective) and ceramic–metallic composite supports. Two typical emulsion systems are considered such as oil-in-water (o/w) and water-in-oil (w/o). A preliminary study has been carried out via average power vs emulsion thickness diagram to estimate microwave power absorption within emulsion samples for various cases. The maxima in average power, also termed as ‘resonances’, are observed for specific emulsion thicknesses and the two consecutive resonances of significant magnitudes are termed as R1 and R2 modes. For both o/w and w/o emulsions, it is observed that microwave power absorption is enhanced in presence of metallic and composite supports during both R1 and R2 modes. The efficient heating strategies characterized by ‘large heating rates’ with ‘minimal thermal runaway’ i.e. uniform temperature distributions within the sample have been assessed for each type of emulsion. Based on the detailed spatial distributions of power and temperature for various cases, SiC-metallic composite support may be recommended as an optimal heating strategy for o/w samples with higher oil fractions (0.45) whereas metallic and Alumina-metallic composite supports may be favored for samples with smaller oil fractions (=0.3) during R1 mode. For w/o samples, SiC-metallic composite support may be suitable heating strategy for all ranges of water fractions during R1 mode. During R2 mode, metallic and Alumina-metallic composite supports are favored for both o/w and w/o emulsion samples. Current study recommends the efficient way to use microwaves in a single mode waveguide and the heating strategy can be suitably extended for heating of any other emulsions for which dielectric properties are easily measurable or available in the literature.

Micro-scale abrasion behaviour of electroless Ni-P-SiC coating on aluminium alloy

Electroless nickel (EN) and electroless nickel composite (ENC) coatings were deposited on aluminium alloy substrate, LM24. The micro abrasion test was conducted to study the wear behaviour of the coatings with the effect of SiC concentration. Microhardness of the coatings was tested also. The wear scars were analysed using optical microscope and scanning electron microscope (SEM). The wear resistance was found to be improved in composite coating that has higher microhardness as compared to particles free and the bare aluminium substrate. In as-deposited condition for the composite coating, the wear volume increases on increase in SiC percentage in the coating but is found to be minimum for lower SiC percentage. The increase in hardness on heat treatment at 400°C is due to the hardening or grain coarsening with the formation Ni3P.

Análisis del gen adra2a receptor alfa 2a adrenergico en pacientes con trastorno de hiperactividad y déficit de atención

El trastorno de hiperactividad y déficit de atención (THDA), es definido clínicamente como una alteración en el comportamiento, caracterizada por inatención, hiperactividad e impulsividad. Estos aspectos son clasificados en tres subtipos, que son: Inatento, hiperactivo impulsivo y mixto. Clínicamente se describe un espectro amplio que incluye desordenes académicos, trastornos de aprendizaje, déficit cognitivo, trastornos de conducta, personalidad antisocial, pobres relaciones interpersonales y aumento de la ansiedad, que pueden continuar hasta la adultez. A nivel global se ha estimado una prevalencia entre el 1% y el 22%, con amplias variaciones, dadas por la edad, procedencia y características sociales. En Colombia, se han realizado estudios en Bogotá y Antioquia, que han permitido establecer una prevalencia del 5% y 15%, respectivamente. La causa específica no ha sido totalmente esclarecida, sin embargo se ha calculado una heredabilidad cercana al 80% en algunas poblaciones, demostrando el papel fundamental de la genética en la etiología de la enfermedad. Los factores genéticos involucrados se relacionan con cambios neuroquímicos de los sistemas dopaminérgicos, serotoninérgicos y noradrenérgicos, particularmente en los sistemas frontales subcorticales, corteza cerebral prefrontal, en las regiones ventral, medial, dorsolateral y la porción anterior del cíngulo. Basados en los datos de estudios previos que sugieren una herencia poligénica multifactorial, se han realizado esfuerzos continuos en la búsqueda de genes candidatos, a través de diferentes estrategias. Particularmente los receptores Alfa 2 adrenérgicos, se encuentran en la corteza cerebral, cumpliendo funciones de asociación, memoria y es el sitio de acción de fármacos utilizados comúnmente en el tratamiento de este trastorno, siendo esta la principal evidencia de la asociación de este receptor con el desarrollo del THDA. Hasta la fecha se han descrito más de 80 polimorfismos en el gen (ADRA2A), algunos de los cuales se han asociado con la entidad. Sin embargo, los resultados son controversiales y varían según la metodología diagnóstica empleada y la población estudiada, antecedentes y comorbilidades. Este trabajo pretende establecer si las variaciones en la secuencia codificante del gen ADRA2A, podrían relacionarse con el fenotipo del Trastorno de Hiperactividad y el Déficit de Atención.

A thirty months clinical evaluation of a posterior composite resin in primary molars

The purpose of this in vivo study was to evaluate the clinical performance of a posterior composite resin TRH (Caulk Dentisply) in class I restorations in primary molars. A total of 30 children aged 5 to 8 years old with 49 class I dental lesions in primary molars participated in the study. The cavity preparations involved removal of carious lesion only and the enamel margins were beveled. The results showed after 30 months that, 82% (32/39) of Alfa ratings and 18% (7/39) of Bravo ratings. We concluded that the composite resin TP-H could be used in conservative restorations in primary molars, particularly in the late mixed dentition.

Influence of filler charge on gloss of composite materials before and after in vitro toothbrushing

Objectives: This study evaluated the gloss behaviour of experimental resin composites loaded with different filler percentages, immediately after polishing and after toothbrushing simulation. Methods: Sixteen disc-shaped specimens were fabricated for each different-charged composite (40%, 50%, 60%, 70% and 75%) and polished with SiC abrasive papers. Gloss measurements were made prior to simulated toothbrushing. The specimens were subjected to the simulation for 5, 15, 30 and 60 min using an electrical toothbrush with a standardized pressure while being immersed in a toothpaste/artificial saliva slurry. Results: Baseline composite gloss values ranged from 69.7 (40%) to 81.3 (75%) GU (gloss units) and from 18.1 (40%) to 32.3 (75%) GU after 1 h of brushing. Highest gloss values were obtained by 75%-charged resin, while the lowest values were obtained by the 40%-charged one. Conclusions: All tested materials showed a gloss decrease. However, the higher filler load a composite resin has, the higher gloss it can achieve. Clinical significance: Gloss of resin composite materials is an important factor in determining aesthetic success of anterior restorations, and this property may vary according to the filler charge of the restorative material. Higher filler load of a composite resin results in higher gloss values. © 2013 Elsevier Ltd. All rights reserved.

Resistência ao microcisalhamento de diferentes sistemas adesivos no esmalte dental humano

Pós-graduação em Odontologia Restauradora - ICT

Seven-Year Clinical Performance of Resin Composite Versus Resin-Modified Glass lonomer Restorations in Noncarious Cervical Lesions

Purpose: The purpose of this study was to comparatively assess the seven-year clinical performance of a one-bottle etch-and-rinse adhesive with resin composite (RC) and resin-modified glass ionomer (RMGI) restorations in noncarious cervical lesions.Methods and Materials: One operator placed 70 restorations (35 restorations in each group) in 30 patients under rubber dam isolation without mechanical preparation. The restorations were directly assessed by two independent examiners, using modified US Public Health Service criteria at baseline and 6, 12, 24, 60, and 84 months. The obtained data were tabulated and statistically analyzed using the Fisher and McNemar tests. A difference was significant if p<0.05.Results: Twenty patients were available for recall after seven years (66.6%), and 25 RC and 26 RMGI restorations out of 70 restorations were evaluated. Excellent agreement was registered for all criteria between examiners (kappa >= 0.85). Alfa and bravo scores were classified as clinically acceptable. The McNemar test detected significant differences within RC restorations between baseline and seven-year evaluations for anatomic form, marginal integrity, and retention (p<0.05). For RMGI restorations, a significant difference was identified for marginal integrity (p<0.05). As to material comparison, the Fisher exact showed a better retention performance for RMGI restorations than for RC restorations (p<0.05). Twelve composite restorations were dislodged (52.0% retention) and three ionomer restorations were lost (88.5% retention). The cumulative success rate for RC and RMGI was 30% and 58.1%, respectively.Conclusions: After seven years of service, the clinical performance of RMGI restorations was superior to that of the adhesive system/resin composite restorations in this study.

Sealing composite with defective margins, good care or over treatment? results of a 10-year clinical trial

Purpose: The objective of this study was to clinically evaluate sealed composite restorations after 10 years and compare their behavior with respect to controls. Methods and Materials: The cohort consisted of 20 patients aged 18 to 80 years with 80 composite restorations. All participants in the sealing and no-treatment groups presented with clinical features for the marginal adaptation that deviated from the ideal and were rated Bravo (United States Public Health Service criteria). Composites with Alfa values for the marginal adaptation were used as the positive control. Results: The marginal adaptation behavior was similar between the sealing and control (+) groups, with a high frequency of Bravo values in the 10th year (80% and 51%, respectively). Most of the no-treatment (-) group maintained the Bravo values (91%) for 10 years, although some restorations (9%) progressed to Charlie values. The anatomy parameter differed significantly between the first and 10th years, with deterioration in all three groups (p,0.05). The secondary caries parameter had a similar behavior in the three groups (p.0.05). Conclusions: Sealing the margins of the composite resin restorations had no significant effect compared with the control groups, under the conditions of this study. Sealing the restorations substantially improved the marginal staining and marginal adaptation parameters, although by the tenth year they were similar to the group without intervention.

Anodization mechanism on SiC nanoparticle reinforced al matrix composites produced by power metallurgy

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

High temperature, low cycle fatigue of a hybrid particulate/fiber aluminum metal-matrix composite

The effect of shot particles on the high temperature, low cycle fatigue of a hybrid fiber/particulate metal-matrix composite (MMC) was studied. Two hybrid composites with the general composition A356/35%SiC particle/5%Fiber (one without shot) were tested. It was found that shot particles acting as stress concentrators had little effect on the fatigue performance. It appears that fibers with a high silica content were more likely to debond from the matrix. Final failure of the composite was found to occur preferentially in the matrix. SiC particles fracture progressively during fatigue testing, leading to higher stress in the matrix, and final failure by matrix overload. A continuum mechanics based model was developed to predict failure in fatigue based on the tensile properties of the matrix and particles. By accounting for matrix yielding and recovery, composite creep and particle strength distribution, failure of the composite was predicted.

CNT and PDCs: A fruitful association? Study of a polycarbosilane–MWCNT composite

The effect of MWCNT introduction in a polycarbosilane based ceramic on its electrical properties is presented. The electrical conductivity of two MWCNT powders was measured under dynamic compaction up to 20 MPa when it reached 3–5 S/cm. The compaction behavior was also analyzed and modeled. A composite was then realized using allylhydridopolycarbosilane SMP10® and divinylbenzene as matrix. Intact 10 mm MWCNT-SiC ceramic discs samples with 2 wt.% filler load were produced pressure-less via liquid route despite the linear shrinkage of about 30%. Nanotubes microstructure and distribution in the matrix were confirmed after pyrolysis with TEM and SEM analysis. Anyhow similar electrical conductivity values after pyrolysis between the loaded and unloaded samples were measured. The microstructure analysis via XRD and TEM revealed that the percolative carbon network formed through the use of divinylbenzene improves the electric conductivity more than that of MWCNT addition and also simplifies the whole process.

Microstructure and mechanical properties at high temperature of SiC-matrix by electrophoretic deposition and polymer infiltration and pyrolysis process

The EFDA-ITER programme for materials wants to develop new structural materials for future nuclear magnetic fusion reactors. In this context, special attention must be paid in the development of new composite materials that could support the hard working conditions of the nuclear fusion reactors: high temperature, high stresses, and high radiation.

Effect of layer thickness on the high temperature mechanical properties of Al/SiC nanolaminates

Composite laminates on the nanoscale have shown superior hardness and toughness, but little is known about their high temperature behavior. The mechanical properties (elastic modulus and hardness) were measured as a function of temperature by means of nanoindentation in Al/SiC nanolaminates, a model metal–ceramic nanolaminate fabricated by physical vapor deposition. The influence of the Al and SiC volume fraction and layer thicknesses was determined between room temperature and 150 °C and, the deformation modes were analyzed by transmission electron microscopy, using a focused ion beam to prepare cross-sections through selected indents. It was found that ambient temperature deformation was controlled by the plastic flow of the Al layers, constrained by the SiC, and the elastic bending of the SiC layers. The reduction in hardness with temperature showed evidence of the development of interface-mediated deformation mechanisms, which led to a clear influence of layer thickness on the hardness.

D. Aurelii Augustini ... Sermones : quorum seriem & numeru[m] sic habeto De verbis Domini, De verbis Apostoli, Homiliae L. Homiliae de tempore Homiliae de Sanctis, Ad fratres in eremo, Decem & septem Sermones, nonnullique alij : tomus decimus ...

Mode of access: Internet.

Tensile properties of as fabricated, aged, and stretched SiC whisker and particle reinforced 2009 aluminium alloy

Tensile tests were carried out using specimens of 2009 aluminium alloy reinforced by either SiC whiskers or particles. The size distributions of the whiskers and particles in the matrix were obtained by image analysis. It was found that failure was a result of uniform void nucleation and coalescence in the as fabricated composites, or a result of fast crack propagation initiated by a flaw developed at clusters of SiC in the aged or stretched and aged composites. The strengths of the as fabricated composites were estimated based on the results of image analysis using continuum mechanics and dislocation theories. The estimation indicated that the tensile strengths are largely contributed to by composite strengthening, supplemented by residual dislocation strengthening and work hardening. Owing to the flaw controlled failure, the tensile strengths of the aged or stretched and aged composites were independent of aging time, aging temperature, and the amount of stretching. The elastic moduli of the composites were estimated using the Halpin-Tsai model and a good correlation was found between the measured and estimated moduli. © 1996 The Institute of Materials.