Search

The article discusses a study which described a technique that may be used in the freeform fabrication of alumina dental-crown models through stereolithography. Due to their desirable aesthetics and biocompatibility, ceramic materials have been popular in the area of dental restoration for dentures and crowns. Glass infiltration has been used to improve the flexural strength of sintered specimens used in the study.

Dense three-dimensional (3D) microdevices of ZrO2-toughened Al2O3 (ZTA) were fabricated using microstereolithography and a subsequent sintering process. Using microstereolithography, 3D green bodies could be formed from a 40 vol% ZTA ceramic–resin paste. After sintering, the fabricated 3D devices are converted into dense ceramic devices without deformation. In this study, a gear (with a tooth edge of 25 μm) and a photonic crystal (with a lattice constant of 500 μm) were designed and fabricated. The dimensional accuracy of the fabrication process is within 20 μm and the sintering shrinkage is around 26% for these microdevices. The relative density of the sintered ZTA ceramics reached 96.5% of theoretical value. The measured hardness and toughness were about 14 GPa and 11 MPa m1/2, respectively, in both the top and side surfaces. A band gap between 320 and 420 GHz was observed in the ZTA photonic crystal. The microstereolithography process can be easily applied to other ceramic materials and devices. [ABSTRACT FROM AUTHOR]

Dense three-dimensional microphotonic crystals of SiO2–Al2O3 ceramics were fabricated using microstereolithography and successive sintering process. The forming dimensional tolerance for a 50 vol% ceramic paste is 10 μm and sintering shrinkage is around 12%. Diamond-type photonic crystals with lattice constants of 500 and 125 μm were formed and sintered successfully. The band gaps of the samples were measured and compared with the theoretically calculated band diagram. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) metallodielectric photonic crystals with a diamond structure were fabricated in order to investigate the formation of stop bands and the absorption ability for microwaves with the dielectric absorbing media embedded into the 3D metal lattice. First, the metallic photonic crystals were prepared by filling the epoxy molds formed by stereolithography with a metal alloy having a low melting point of 70°C, followed by removal of the molds. The metallodielectric photonic crystals were then fabricated by infiltrating the porous metal crystal with a SiC/polyester mixture. The lattice constant of photonic crystals was 15 mm. The effects of different aspect ratios of diamond lattice rods, number of metallic lattice units along Γ-L 〈1 1 1〉, Γ-X 〈1 0 0〉, and Γ-K 〈1 1 0〉 directions, and metallodielectric samples along the Γ-X 〈1 0 0〉 direction on the formation of stop band and microwave absorption ability were investigated in the frequency range from 3 to 30 GHz. Metallodielectric photonic crystals formed showed good absorption ability. The measured transmission spectra of the metallic and metallodielectric crystals agreed well with the simulation of the transmission line modeling method. [ABSTRACT FROM AUTHOR]

A genetic association of knee osteoarthritis (OA) and a C/T transition single nucleotide polymorphism (SNP) (rs912428) located in intron 1 of the LRCH1 gene has recently been reported in European Caucasians; however, the results are inconsistent. Our objective was to evaluate the association in different knee OA populations. Three case-control association studies were conducted in Han Chinese, Japanese, and Greek Caucasian populations. The LRCH1 SNP was genotyped in patients who had primary symptomatic knee OA with radiographic confirmation and in matched controls, and the association was examined. We performed a meta-analysis for the studies together with results of two previous papers using the DerSimonian–Laird procedure and calculated the power of the pooled studies by the software R. A total of 1,145 OA patients and 1,266 controls were genotyped. No significant difference was detected in genotype or allele frequencies between knee OA and control groups in the three populations (all P > 0.05). Association was not observed even after stratification by gender and Kellgren/Lawrence (K/L) scores. Meta-analysis also supported the lack of association between LRCH1 and knee OA. The strong heterogeneity between original and replication studies was detected in Caucasian populations. However, a tendency for the increase of TT genotype was observed in the European populations (OR = 1.46, P = 0.06). The powers for European and Asian replication studies were less than 0.8. Our results suggest that there is no association between LRCH1 and knee OA. However, lack of association should be concluded by further replication studies. [ABSTRACT FROM AUTHOR]

Dense Al2O3-based composites (≥99.0% of theoretical) dispersed with carbon nanofibers (CNFs) were fabricated using the pulsed electric-current pressure sintering (PECPS) for 5 min at 1300°C and 30 MPa in a vacuum. The dispersion of CNFs into the matrix depended much on the particle size of the starting Al2O3 powders. Mechanical properties of the composites were evaluated in relation with their microstructures; high values of three-point bending strength σb (∼800 MPa) and fracture toughness K IC (∼5 MPa·m1/2) were attained at the composition of CNF/Al2O3 = 5:95 vol%, which σb and K IC values were ∼25% and ∼5%, respectively, higher than those of monolithic Al2O3. This might be due to the small Al2O3 grains (1.6 μm) of dense sintered compacts compared with that (4.4 μm) for the pure Al2O3 ceramics, resulting from the suppression of grain growth during sintering induced by uniformly dispersed CNFs in the matrix. Electrical resistivity of CNF/Al2O3 composites decreased rapidly from >1015 to ∼2.1 × 10−2 Ωm (5vol%CNF addition), suggesting the machinability of Al2O3-based composites by electrical discharge machining. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) photonic crystals with a diamond structure made of a dense SiO2 ceramic were successfully fabricated using a CAD/CAM micro-stereolithography and sintering process. The designed lattice constant of the diamond unit cell was 500 μm and the forming tolerance from 50 vol% SiO2 paste (before sintering) was around 15 μm. After the SiO2-resin photonic crystals were formed via micro-stereolithography, they were converted to pure SiO2 ceramic photonic crystals of 99% theoretical density by sintering at 1400°C. The electromagnetic wave propagation in these dense SiO2 photonic crystals was measured by terahertz-time-domain spectroscopy. The results showed that the band gap appeared between 470 and 580 GHz in the Γ– X〈100〉 direction, between 490 and 630 GHz in the Γ– K〈110〉 direction, and between 400 and 510 GHz in the Γ– L〈111〉 direction, resulting in the formation of a common band gap in all directions between 490 and 510 GHz. These results agreed well with the band gaps calculated by the plane wave expansion method. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) photonic crystals with a diamond structure made from 40 vol% TiO2–acrylate dielectric composites were formed by means of a CAD/CAM micro-stereolithography system. The lattice constant of the diamond unit cell was 500 μm and the forming accuracy was 10 μm. The photonic band gap in the Γ–X 〈100〉 direction measured by terahertz-time-domain spectroscopy appeared at 280–360 GHz, which agreed fairly well with the band gap calculated by the plane wave expansion method. [ABSTRACT FROM AUTHOR]

Three-dimensional photonic crystals were fabricated by infiltrating an epoxy mold with a SiC/polyester mixture. The epoxy molds with normal or inverse diamond structures were formed by stereolithography. The size of the mold was 45 mm × 18 mm × 18mm, and the lattice constant of the photonic crystals was 18 mm. The effects of the epoxy mold type, aspect ratio (the ratio of height and diameter of a diamond lattice rod), and number of sample units on the formation of photonic band gap (PBG) and microwave absorption ability along the 〈100〉 direction were studied. The attenuations of microwave transmission and reflection were measured through the photonic crystal samples at a frequency range of 3–12 GHz with a network analyzer. The results obtained suggest that the combination of the absorbing material SiC and diamond structure has a dual effect to form a PBG with a high absorption ability. [ABSTRACT FROM AUTHOR]

Oto-spondylo-megaepiphyseal dysplasia (OSMED) is a skeletal dysplasia characterized by severe sensorineural hearing loss, enlarged epiphyses and early onset of osteoarthritis. COL11A2 has been reported as a causative gene for OSMED. We have identified a novel COL2A1 mutation at a splice-acceptor site within intron 10 (c.709–2A>G) in an OSMED patient. This mutation caused the skipping of exon 11, and of exons 11 and 13. These exon-skipping events are presumed to cause an in-frame deletion of the triple helical region of the COL2A1 product. Thus, our findings highlight the genetic heterogeneity of OSMED and extend the phenotypic spectrum of type II collagenopathy, as well as confirming the overlap between type II and type XI collagenopathies. [ABSTRACT FROM AUTHOR]

Intergenic splicing, the joining of exons from separate genes, has been observed only rarely in mammals. While the matrilin (MATN) and lysosomal-associated protein transmembrane (LAPTM) genes comprise distinct gene families, we have demonstrated intergenic splicing between two sets of family genes, the matrilin-3 (MATN3) and lysosomal-associated protein transmembrane 4α (LAPTM4A), and the matrilin-2 (MATN2) and lysosomal-associated protein transmembrane 4β (LAPTM4B). The expression pattern and sub-cellular localization of the MATN–LAPTM hybrid transcripts differ from those of the original genes, suggesting unique functions for the products. Our observations indicate that intergenic splicing is a common and well-regulated phenomenon and underscore the fundamental challenges in defining the gene (transcriptional unit). Given these findings, the number of gene in the human genome may be smaller than present estimates suggest. [ABSTRACT FROM PUBLISHER]

Ceramic photonic crystals with diamond structure were fabricated using stereolithography and successive sintering. The green body of an epoxy resin incorporating 10 vol% TiO2–SiO2 was formed by stereolithography and then heated in air at 1100°–1400°C for 2 h. The sintered products maintained the diamond structure with a linear shrinkage ratio of about 57% and a porosity of 38%. The ceramic photonic crystal with eight unit cells showed a photonic band gap at the center frequency of 23.5 GHz. This fabrication method of three-dimensional (3D) ceramic photonic crystals is applicable to other 3D structural ceramics and does not require any molding techniques. [ABSTRACT FROM AUTHOR]

A new concept of smart processing is proposed that can produce advanced materials and components by finely controlling processing energy and engineering structures. New functional components of 3D photonic crystals and fractals are demonstrated, which are constructed of dielectric ceramics and a polymer using a CAD/CAM stereolithography system. By modifying the structure of diamond-like photonic crystals using free-form fabrication, electromagnetic waves can be controlled, opening the way for new applications in communication and sensing technology. The photonic fractal, a new material that can strongly localize electromagnetic waves without reflection and transmission, will also lead to new applications in the energy and medical fields. [ABSTRACT FROM AUTHOR]

Millimeter-order photonic crystals with the periodic arrangement of the dielectric constant were fabricated by infiltrating the mixed slurry of ceramics and polyester into the epoxy molds with an inverse form of a diamond structure. The epoxy molds are designed and processed by using a CAD/CAM process of stereolithography. The photonic crystals were prepared to have the diamond structure of the ceramic/polyester composite lattice, which is embedded in the epoxy matrix. The ceramic powders mixed with polyester are TiO2, SrTiO3, and BaTiO3 with high dielectric constant. It is possible to control more freely and widely the dielectric constant of the photonic crystals by this method. These ceramic/resin photonic crystals formed the complete photonic band gaps in the microwave band of 7–11 GHz, which can totally reflect the electromagnetic wave for all crystal directions. Attenuation profiles of the transmission amplitude in the band gaps were controlled with the dielectric constant of the composite lattice. The obtained results fairly agreed with the theoretical simulation of the electromagnetic wave propagation through photonic crystals. [Copyright &y& Elsevier]

Presents a study which investigated the electromagnetic properties of photonic crystals with diamond structure containing defects. Types of lattice defects in a diamond structure; Calculation of resonant frequencies in the defects; Properties of photonic crystals.

TiAl/Ti2AlC composites were produced by spark plasma sintering technology from mixed powders of Ti, Al and TiC. X-ray diffraction (XRD) patterns showed that the sintered products mainly consisted of TiAl and Ti2AlC phases. Electric probe microcosmic analysis (EPMA) photos indicated different microstructures depending on composition. In one case, when 7 vol.%TiC was mixed in the starting powders, the produced Ti2AlC particles were uniformly dispersed in the TiAl matrix with the partial lamellar structure containing γ and lamellar phases (duplex structure). In another case, while 15 vol.%TiC was added, the composites consisted of interpenetrating networks of Ti2AlC and TiAl phases. After the annealing, however, all of them changed to that of Ti2AlC particles dispersed uniformly in the γ(TiAl) matrix. The fracture toughness and bending strength of the composites were tested, respectively. [Copyright &y& Elsevier]

Interdiffusion of copper and zinc alloys of Cu-28.5 at. pct Zn and Cu-4.9 at. pct Zn has been investigated under pressures from 0.101 to 3240 MPa in the temperature range from 1256 to 1377 K. The diffusion coefficients decrease with increasing pressure. The activation energy for impurity diffusion of zinc in copper increases with pressure. The ratio of the activation volume to the molar volume of copper is between 0.75 and 0.90. It is concluded that the impurity diffusion of zinc in copper occurs predominantly by the monovacancy mechanism at temperatures near the melting point of the alloy. [ABSTRACT FROM AUTHOR]