Combined effect of staining substances on the discoloration of esthetic Class V dental restorative materials

The purpose of this study was to determine the combined effect of an organic substance (mucin as a substitute for salivary organic substances), chlorhexidine, and an iron compound/tea solution on the changes in the color of esthetic Class V dental restorative materials. Color of a glass ionomer, resin-modified glass ionomer, compomer and flowable resin composite of A2 shade, respectively, was determined according to the CIELAB color scale relative to the standard illuminant D65. Color was measured at baseline, and after sequential immersion in the following substances: Step-1, mucin in PBS (MCP) for 48 h; Step-2, chlorhexidine (CHX) for 24 h; Step-3, iron compound (IRN) or tea solution (TEA) up to 7 days; and Step-4, ultrasonic cleaning for 1 h. Color change (ΔE _ab *) was calculated by the equation: Δ E _ab* = [(Δ L*)² + (Δ a*)² + (Δ b*)²]^1/2, of which ΔL ^∗ indicates changes in value, Δa ^∗ indicates changes in red-green parameter and Δb ^∗ indicates changes in yellow-blue parameter. Δ E _ab* values after immersion in MCP and CHX were compared, and Δ E _ab* values after immersion in IRN or TEA, and subsequent ultrasonic cleaning were compared with respect to the restorative material and immersion substance. Δ E _ab* and changes in the color parameters (ΔL ^∗, ΔC _ab* and ΔH _ab*) were analyzed by repeated measures, analysis of variance and a post-hoc test at the 0.05 level of significance. Color changes after immersion in MCP were acceptable (Δ E _ab* < 3.3), and those after immersion in CHX were generally acceptable. The range of Δ E _ab* values after immersion in IRN was 3.1–19.6, and that after ultrasonic cleaning was 2.4–9.6. The range of Δ E _ab* values after immersion in TEA was 10.7–21.1, and that after ultrasonic cleaning was 11.9–14.5. Color changes of four Class V restorative materials after combined treatment with mucin, chlorhexidine and an iron compound/tea solution were not acceptable. Colors did not recover to their original values after ultrasonic cleaning. Modifications on the surface of a restoration should be considered to reduce stain accumulation.     

The structural efficiency of orthotropic stalks,stems and tubes

An optimised structure is one which uses the smallest quantity of the best material to perform its function, with adequate safety factor or margin for error. Structural optimisation occurs not only in mechanical engineering, but also in nature: plants with hollow stems or stalks gain a height advantage, and are thus more efficient, by approaching the optimum shape. Here we consider the optimisation of orthotropic tubes, typifying, in a mechanical sense, stalk and stem. The stiffness and strength of orthotropic tubes of initially circular section are reviewed, and diagrams are proposed which allow the optimum section shape to be selected.     

Development and characterization of magnesium composites containing nano-sized silicon carbide and carbon nanotubes as hybrid reinforcements

Magnesium based hybrid composites containing nano-sized silicon carbide and carbon nanotubes reinforcements with minimal porosity were successfully fabricated using powder metallurgy technique with microwave sintering and hot extrusion. It was found that the addition of nano-sized silicon carbide and carbon nanotubes reinforcements lowered the coefficient of thermal expansion of magnesium. Moreover, increasing presence of silicon carbide particles led to a progressive reduction in coefficient of thermal expansion for a constant overall amount of reinforcements indicating that carbon nanotubes lowered the coefficient of thermal expansion to a lesser extent when compared to silicon carbide. Micro-hardness, 0.2% YS and UTS (except for Mg+1%CNT) showed improvement, while failure strain decreased when nano-sized silicon carbide and carbon nanotubes were added to magnesium. The failure mode of magnesium and magnesium composites was predominantly brittle exhibiting the presence of cleavage steps.     

Facile and rapid synthesis of multiferroic TbMnO3 single crystalline

The pure single phase of multiferroic material TbMnO₃ powders were successfully synthesized by one-step molten salt synthesis (MSS) method in the NaCl–Na₂SO₄ eutectic salts at the temperature as low as 800 °C for 1 h. The temperature of synthesized high purity TbMnO₃ is limited in a very narrow range. Prolonging the sintering time will not have an effect on the purity of samples, and either lower or higher salt concentration is not conducive to form pure TbMnO₃. The obtained TbMnO₃ was indexed to an orthorhombically distorted perovskite phase. The as-prepared crystals exhibit uniform and regular rhombic-like morphology with an average size of about 2 μm in edge length and 1–2 μm in thickness. The elements Mn and Tb in TbMnO₃ exist dominantly as Mn³⁺ and Tb³⁺, respectively. The magnetic measurements of the TbMnO₃ powders exhibit antiferromagnetism. Because of the simplicity and generalizability of the MSS method, it is reasonable to expect that the MSS method could also be exploited in future works which involves the nanoscale investigation of ferroelectric, ferromagnetic and multiferroic materials.     

Chirped-cavity dispersion-compensation filter design

A new basic structure of a dispersive-compensation filter, called a chirped-cavity dispersion-compensator (CCDC) filter, was designed to offer the advantages of small ripples in both reflectance and group-delay dispersion (GDD). This filter provides a high dispersion compensation, like the Gires-Tournois interferometer (GTI) filter, and a wide working bandwidth, like the chirped mirror (CM). The structure of the CCDC is a cavity-type Fabry-Perot filter with a spacer layer (2 mH or 2 mL) and a chirped high reflector. The CCDC filter can provide a negative GDD of -50 fs2 over a bandwidth of 56 THz with half the optical thickness of the CM or the GTI.     

Rasch analysis of a new construct: functional caregiving for adult children with intellectual disabilities

This research examined empirical evidence for a new construct, Functional Caregiving, which is a theory about mothers' caregiving of their adult children with intellectual disabilities. A sample of 108 biological mothers and primary caregivers rated survey items about their confidence to perform caregiving tasks. Rasch rating scale analysis found 61 items defined an empirical construct with three caregiving levels: Advocacy, Personal Caregiving, and Community. Results show item separation was 3.11 with high reliability, .91, and mother separation was 2.93 and reliability, .90. Both items and mothers showed adequate INFIT and OUTFIT values. Item invariance was confirmed between older and younger mothers, and principle components analysis of item residuals did not reveal any major dimensionality threats. Item decomposition analysis showed FC content theory to account for 58 percent of item calibration variance (R2 = .58, F = 42.3, p < .001). These results have important practical implications for health and social services, as well as family caregiving, interdisciplinary practices, and health policy development.     

Efficient corner-pumped Yb:YAG/YAG composite slab laser

A high efficiency Yb:YAG/YAG composite slab laser is presented, in which the corner-pumped scheme is adopted. The slab is a composite crystal of Yb:YAG bonded thermally with undoped YAG at both edges. The pump light from diode arrays is coupled into the slab through four chamfers at the four corners independently. The pump absorption efficiency is studied, and an analysis method has been developed as a guide to optimize the geometric parameters of the composite slab, to obtain higher pump absorption efficiency and uniformity. The influence of the internal thermal lens on the laser resonator is analyzed. A 1016 W continuous-wave output has been obtained with the slope efficiency and optical-to-optical efficiency of 42.8% and 34.4%, respectively.     

Synthesis of CdS nanoplates by PAA-assisted hydrothermal approach

Triangular and hexagonal CdS nanoplates, with average size about 100 nm and average thickness range from 10 to 30 nm, have been synthesized in the presence of poly (acrylic acid) (PAA) assisted hydrothermal process at 180 °C. The structural characteristics, morphology, and optical properties of the as-prepared CdS products were investigated. UV–vis spectroscopy measurement reveals that the products show a strong quantum size effect. Based on the experiment results, the possible formation mechanism of CdS nanoplates has been proposed.     

Model-based simulation of normal grain growth in a two-phase nanostructured system

To systematically study normal grain growth in a two-phase volume-conserved system, a modified Potts model is proposed, in which the driving forces for grain boundary migration are the interfacial energy between two phases and the boundary energy inside each phase. Model-based simulation results show that the grain growth kinetics follows a power law with a temperature-independent exponent and that the normalized grain size distribution is lognormal and time invariant. Also, a simple theoretical model is used to predict the potential microstructure in a two-phase system due to the competition between interfacial and grain boundary energies. A critical ratio (2.6) of the grain boundary energy to the interfacial energy is found for a common two-phase system.     

Assessment of durability of recycled aggregate concrete produced by two-stage mixing approach

As more than 50% construction and demolition (C&D) wastes are composed of concrete debris in Hong Kong, recycling this debris into Recycled Aggregate (RA) for production of Recycled Aggregate Concrete (RAC) is an efficient way to alleviate the burden on landfill areas. Since RA is generated from concrete debris which has undergone years of services, the resulting RAC bears the weaknesses of lower density, higher water absorption, and higher porosity that limit them to lower-grade applications. Pinpointing to these weaknesses, Tam et al. [2005, Cement Concrete Res 35(6):1195–1203] developed the Two-Stage Mixing Approach (TSMA) for improving the strength of RAC, leading to the possibility in applying RAC for higher-grade applications. While the improvement in strength by TSMA has been proven in Tam et al.’s work [2005, Cement Concrete Res 35(6):1195–1203], the durability, in terms of deformation (shrinkage and creep) and permeability (water, air and chloride permeability), remains to be verified. In this paper, 0%, 20% and 100% of RA substitutions have been experimented to compare the durability performance of the Normal Mixing Approach (NMA) and the TSMA. Experiment results highlight that: (i) the higher the substitutions of RA, the weaker the performance of RAC; and (ii) the deformation and permeability of RAC can be enhanced when adopting TSMA. Therefore, it demonstrates that TSMA can help to improve the durability of RAC, on top of the previously verified strength improvement, and thus opening up wider applications of RAC.