SciCombinator

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Journal: Materials (Basel, Switzerland)

138

The frequent instability of mandibular removable complete dentures affects patient Oral Health Related Quality of Life (OHRQoL). An innovative therapeutic strategy used to improve stability involves placing four symphyseal mini-implants. This study was aimed at assessing OHRQoL over time in subjects in which mini-implants were placed and exploring if certain parameters could predict the evolution of their OHRQoL. The OHRQoL of subjects with dentures was assessed using the Geriatric Oral Health Assessment Index (GOHAI) before (T0), 2-6 months (T1), twelve months (T2) and twenty-four or more months (T3) after mini-implant setting. Age, gender and chewing ability were tested as explanatory variables for the change in OHRQoL with time. Thirteen women and six men were included (mean age: 69 ± 10 years). After treatment, mean GOHAI scores at T1, T2 and T3 increased significantly (p < 0.001). The GOHAI-Add mean score was not affected by age or gender. Baseline chewing ability impacted the "functional" and "pain and discomfort" fields of the mean GOHAI scores (p < 0.05). The OHRQoL quickly improved after mini-implant placement in complete denture wearers and then stabilized over time. Baseline chewing ability can be used as a predictive parameter of OHRQoL.

Concepts: Future, Dentistry, Currying, Scientific method, Medicine, Removable partial denture, Dentures

1

The performance of a persistent phosphor is often determined by comparing luminance decay curves, expressed in cd/m 2 . However, these photometric units do not enable a straightforward, objective comparison between different phosphors in terms of the total number of emitted photons, as these units are dependent on the emission spectrum of the phosphor. This may lead to incorrect conclusions regarding the storage capacity of the phosphor. An alternative and convenient technique of characterizing the performance of a phosphor was developed on the basis of the absolute storage capacity of phosphors. In this technique, the phosphor is incorporated in a transparent polymer and the measured afterglow is converted into an absolute number of emitted photons, effectively quantifying the amount of energy that can be stored in the material. This method was applied to the benchmark phosphor SrAl 2 O 4 :Eu,Dy and to the nano-sized phosphor CaS:Eu. The results indicated that only a fraction of the Eu ions (around 1.6% in the case of SrAl 2 O 4 :Eu,Dy) participated in the energy storage process, which is in line with earlier reports based on X-ray absorption spectroscopy. These findings imply that there is still a significant margin for improving the storage capacity of persistent phosphors.

Concepts: Phosphorus, Electron, X-ray absorption fine structure, X-ray absorption spectroscopy, Emission spectrum, Photon, Absorption spectroscopy, Electromagnetic radiation

0

Multiferroics, showing both ferroelectric and magnetic order, are promising candidates for future electronic devices. Especially, the fundamental understanding of ferroelectric switching is of key relevance for further improvements, which however is rarely reported in literature. On a prime example for a spin-driven multiferroic, LiCuVO₄, we present an extensive study of the ferroelectric order and the switching behavior as functions of external electric and magnetic fields. From frequency-dependent polarization switching and using the Ishibashi-Orihara theory, we deduce the existence of ferroelectric domains and domain-walls. These have to be related to counterclockwise and clockwise spin-spirals leading to the formation of multiferroic domains. A novel measurement-multiferroic hysteresis loop-is established to analyze the electrical polarization simultaneously as a function of electrical and magnetic fields. This technique allows characterizing the complex coupling between ferroelectric and magnetic order in multiferroic LiCuVO₄.

Concepts: Schmitt trigger, Hysteresis, Multiferroics, Condensed matter physics, Electronics, Electricity, Magnetic field, Ferroelectricity

0

Anisotropic assembly of nanoparticles (NPs) has attracted extensive attention because of the potential applications in materials science, biology, and medicine. However, assembly control (e.g., the number of assembled NPs) has not been adequately studied. Here, the growth of anisotropic gold NP assemblies on a liposome surface is reported. Citrate-coated gold NPs adsorbed on liposome surfaces were assembled in one dimension at temperatures above the phase transition temperature of the lipid bilayer. Growth of the anisotropic assemblies depended on the heating time. Absorption spectroscopy and transmission electron microscopy revealed that the gradual growth was attributed to liposome fusion, which was strongly affected by the size of the gold NPs. This method enabled us to precisely control the number of NPs in each anisotropic assembly. These results will enable the fabrication of functional materials based on NP assemblies and enable investigations of cell functions and disease causality.

Concepts: Thermodynamics, Sol-gel, Electron, Fundamental physics concepts, Phase transition, Nanoparticle, Nanotechnology, Gold

0

In this work, calcined chitosan-supported layered double hydroxides (CSLDO) were synthesized through a co-precipitation method that restrained the particles' aggregation of LDHs and exhibited huge specific surface areas, which can enhance the fluoride adsorption capacity. CSLDOs were characterized by physical and chemical methods and used for fluoride adsorption in an aqueous solution. The results indicated that the nanoparticles were constructed first and then assembled to form a porous and layered structure, and chitosan-supported layered double hydroxides (CSLDHs) calcined at 400 °C (CSLDO400) showed the highest specific surface area of 116.98 m²·g(-1) and the largest pore volume of 0.411 cm³·g(-1). CSLDO400 exhibited excellent adsorption performance at a wide pH range from 5 to 9 for fluoride. The adsorption kinetics indicated that the adsorption reached equilibrium after 120 min, and followed a pseudo-first-order model. It agreed well with the Langmuir isotherm with maximum adsorption amounts of 27.56 mg·g(-1). The adsorption of fluoride ions was spontaneous and endothermic. Furthermore, CSLDO400 showed a high stability for fluoride removal; it could still achieve 68% removal for fluoride after repeating five times of adsorption-desorption cycles. This study demonstrated that CSLDO400 is a promising functional material to remove fluoride from surface/ground water.

Concepts: Surface area, Thermodynamics, Area, Specific surface area, BET theory, Adsorption, Surface chemistry, Chemistry

0

A kriging modeling method is proposed to conduct the temperature uncertainty analysis of an injection mechanism in squeeze casting. A mathematical model of temperature prediction with multi input and single output is employed to estimate the temperature spatiotemporal distributions of the injection mechanism. The kriging model applies different weights to the independent variables according to spatial location of sample points and their correlation, thus reducing the estimation variance. The predicted value of the kriging model is compared with the sample data at the corresponding position to investigate the influence of the temperature uncertainty of the injection mechanism on the injection process including friction. The results indicate that the significant error is observed at a few sample points in the early injection due to the impact of the uncertainty facts. The variance mean and standard deviation obtained by the model calibrated by experimental samples reduce largely in comparison to those obtained from the initial kriging model. This study indicates that model calibration produces more accurate prediction.

Concepts: Physics, Measurement, Variance, Scientific method, Statistics, Regression analysis, Standard deviation, Mathematics

0

Osteogenesis process displays a fundamental role during dental implant osteointegration. In the present work, we studied the influence of Osteon Growth Induction (OGI) surface properties on the angiogenic and osteogenic behaviors of Mesenchymal Stem cells (MSC). MSC derived from dental pulp and HUVEC (Human Umbilical Vein Endothelial Cells) were grown in on OGI titanium surfaces, and cell proliferation and DNA synthesis were evaluated by MTT [3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide] test and DNA quantification. Gene expression has been performed in order to evaluate the presence of mRNA related to endothelial and osteogenesis markers. Moreover, morphological and biochemical analyses of osteogenesis commitments has been performed. On OGI surfaces, MSC and HUVEC are able to proliferate. Gene expression profiler confirms that MSC on OGI surfaces are able to express endothelial and osteogenic markers, and that these expression are higher compared the expression on control surfaces. In conclusion On OGI surfaces proliferation, expression and morphological analyses of angiogenesis-associated markers in MSC are promoted. This process induces an increasing on their osteogenesis commitment.

Concepts: Cell, Cell nucleus, Organism, Bacteria, Gene expression, Genetics, Gene, DNA

0

Mn(4+)-activated hexafluoroaluminates are promising red-emitting phosphors for white light emitting diodes (w-LEDs). Here, we report the synthesis of Na₃AlF₆:Mn(4+), K₃AlF₆:Mn(4+) and K₂NaAlF₆:Mn(4+) phosphors through a simple two-step co-precipitation method. Highly monodisperse large (~20 μm) smoothed-octahedron shaped crystallites are obtained for K₂NaAlF₆:Mn(4+). The large size, regular shape and small size distribution are favorable for application in w-LEDs. All Mn(4+)-doped hexafluoroaluminates show bright red Mn(4+) luminescence under blue light excitation. We compare the optical properties of Na₃AlF₆:Mn(4+), K₃AlF₆:Mn(4+) and K₂NaAlF₆:Mn(4+) at room temperature and 4 K. The luminescence measurements reveal that multiple Mn(4+) sites exist in M₃AlF₆:Mn(4+) (M = Na, K), which is explained by the charge compensation that is required for Mn(4+) on Al(3+) sites. Thermal cycling experiments show that the site distribution changes after annealing. Finally, we investigate thermal quenching and show that the luminescence quenching temperature is high, around 460-490 K, which makes these Mn(4+)-doped hexafluoroaluminates interesting red phosphors for w-LEDs. The new insights reported on the synthesis and optical properties of Mn(4+) in the chemically and thermally stable hexafluoroaluminates can contribute to the optimization of red-emitting Mn(4+) phosphors for w-LEDs.

Concepts: Chemical reaction, White, Optics, Lighting, Steel, Chemical engineering, Light, Light-emitting diode

0

Mg-5wt.% Sn alloy is often used in portable electronic devices and automobiles. In this study, mechanical properties of Mg-5wt.% Sn alloy processed by Equal Channel Angular Extrusion (ECAE) were characterized. More precisely, its hardness and wear behavior were measured using Vickers hardness test and a pin-on-disc wear test. The microstructures of ECAE-processed Mg-Sn alloys were investigated by scanning electron microscope and X-ray diffraction. ECAE process refined the grain sizes of the Mg-Sn alloy from 117.6 μm (as-cast) to 88.0 μm (one pass), 49.5 μm (two passes) and 24.4 μm (four passes), respectively. Meanwhile, the hardness of the alloy improved significantly. The maximum wear resistance achieved in the present work was around 73.77 m/mm³, which was obtained from the Mg-Sn alloy treated with a one-pass ECAE process with a grain size of 88.0 μm. The wear resistance improvement was caused by the grain size refinement and the precipitate of the second phase, Mg₂Sn against the oxidation of the processed alloy. The as-cast Mg-Sn alloy with the larger grain size, i.e., 117.6 μm, underwent wear mechanisms, mainly adhesive wear and abrasive wear. In ECAE-processed Mg-Sn alloy, high internal energy occurred due to the high dislocation density and the stress field produced by the plastic deformation, which led to an increased oxidation rate of the processed alloy during sliding. Therefore, the oxidative wear and a three-body abrasive wear in which the oxide debris acted as the three-body abrasive components became the dominant factors in the wear behavior, and as a result, reduced the wear resistance in the multi-pass ECAE-processed alloy.

Concepts: Scanning electron microscope, Carbon, Materials science, Abrasion, Vickers hardness test, Wear, Rockwell scale, Hardness

0

The aim of this study is to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has not yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitations of high melting point, brittleness, and low thermal shock resistance from ceramic material properties, the key obstacle lies in the very poor absorptivity of oxide ceramics to fiber laser, which is widely installed in commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions is presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser is discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.

Concepts: Rapid prototyping, Rapid manufacturing, Ceramic engineering, Silicon carbide, Ceramic materials, Ceramic, Sintering, Selective laser sintering