Search

We investigated the influence of growth rate and Ce concentration on colony structure variation in Al 2 O 3 /YAG:Ce eutectic systems. The distance between boundary zones in the colony structure decreased with increases in either growth rate or Ce concentration. The eutectic spacing in the coarse microstructure in the boundary zone decreased with increasing growth rate but increased with increasing Ce concentration. We conclude that the colony structure is formed by cellular growth driven by constitutional supercooling with an interface instability due to Ce atom accumulation, so that the distance between boundary zones depends on both the growth rate and Ce concentration, and the coarse microstructure in the boundary zone depends on the solidification rate perpendicular to the growth interface at the cell bottom of the microscopic growth interface shape in the cellular growth.

Al 2 O 3 /Y 3 Al 5 O 12 (YAG):Ce melt growth composites (MGCs) were grown by the vertical Bridgman (VB) method using an a -axis [1120] Al 2 O 3 seed, and the crystallographic orientations and optical properties of the grown MGCs were investigated. It was found that a crack-free MGC ingot could be grown from the Al 2 O 3 seed. In the MGC grown using the Al 2 O 3 seed, the position of the seeding interface was almost the same to the initial position of the top of the seed. By means of electron backscatter diffraction (EBSD) analysis, it was found that the crystallographic orientation of the Al 2 O 3 phase in the grown MGC corresponded to the a -axis Al 2 O 3 seed, while YAG phases with several different orientations were observed. The light-conversion properties of the MGCs grown using an a axis Al 2 O 3 seed for application to white light emitting diodes (LEDs) were quite similar to those grown using an MGC seed. It was also found that it was possible to grow larger diameter, 2-in., Ce-doped MGC ingots with similar crystallographic properties with the VB method using a small Al 2 O 3 seed.

The vertical Bridgman (VB) method was investigated as a way to grow Al 2 O 3 /YAG:Ce melt growth composite (Ce-doped MGC), an attractive candidate material for blue-to-yellow light conversion. Crucibles made from molybdenum (Mo) and iridium (Ir), whose linear thermal expansion coefficients are significantly different, were examined as potential solutions to the problem of crucible reuse in the growth of large Ce-doped MGC ingots. It was found that Ce-doped MGC ingots grown in Mo crucibles could easily be released nondestructively, while ingots grown in Ir crucible could not. We confirmed that the inside diameter of a Mo crucible is always larger than the diameter of the Ce-doped MGC ingots formed in it, at all temperatures from the melting point to room temperature during the entire cooling process. We also confirmed that larger diameter, 2- and 3-in., Ce-doped MGC ingots with the same orientation as the seed could be grown using Mo crucibles with the VB method. We conclude that Mo crucibles, with a smaller linear thermal expansion coefficient than that of Ce-doped MGC at all temperatures from the melting point to room temperature are useful for growing large ingots and allowing crucible reuse.

Involvement of iron in the development of neurodegenerative disorders has long been suggested, and iron that cannot be stored properly is suggested to induce iron toxicity. To enhance iron uptake and suppress iron storage in neurons, we generated transgenic (Tg) mice expressing iron regulatory protein 2 (IRP2), a major regulator of iron metabolism, in a neuron-specific manner. Although very subtle, IRP2 was expressed in all regions of brain examined. In the Tg mice, mitochondrial oxidative insults were observed including generation of 4-hydroxynonenal modified proteins, which appeared to be removed by a mitochondrial quality control protein Parkin. Inter-crossing of the Tg mice to Parkin knockout mice perturbed the integrity of neurons in the substantia nigra and provoked motor symptoms. These results suggest that a subtle, but chronic increase in IRP2 induces mitochondrial oxidative insults and accelerates neurodegeneration in a mouse model of Parkinson's disease. Thus, the IRP2 Tg may be a useful tool to probe the roles of iron-induced mitochondrial damages in neurodegeraration research.

Various rare-earth-doped α-SiAlON powders with high purity were prepared to study mechanical and optical properties of SiAlON-based functional materials in connection with ionic radius and electronic structure of rare-earth elements. Single phase rare-earth-doped α-SiAlON powders were obtained at a temperature as low as 1873 K by heating powder mixtures of rare-earth oxide, AlN and highly active ultrafine amorphous Si3N4. Bending strength of highly dense rare-earth-doped α/β-SiAlON-based ceramics was increased with decreasing radii of rare-earth ions, i.e., Yb-SiAlON-based ceramics exhibited excellent high-temperature strength and oxidation resistance caused by the small ionic radius of ytterbium. As for optical application, α-SiAlON is an excellent host lattice with good thermal and chemical stability for doping rare-earth element which activates photoluminescence. Europium-doped Ca-α-SiAlON phosphor formulated as CaxEuy(Si,Al)12(O,N)16 (where 0

Caspase-8, a member of the caspase family, plays an important role in apoptotic signal transduction in mammals. Here we report the identification and characterization of the caspase-8 (casp8) gene in the zebrafish Danio rerio. The zebrafish casp8 gene has a genomic organization similar to mammalian casp8 genes, consisting of 10 exons. By chromosome mapping, we found that casp8 maps on linkage group 6 (LG6), a zebrafish chromosome segment orthologous to the long arm of human Chr. 2, which carries CASP8. In contrast, the zebrafish casp10-like gene and the cflar gene separately localize on LG9 and LG11, respectively, and these genes form a cluster with CASP8 on the human chromosome. This chromosomal segregation is unique to fish but not other vertebrates. Furthermore, we examined the function of zebrafish Casp8 protein in mammalian cells, and showed that it has pro-apoptotic activity when overexpressed. In addition, this molecule was capable of transmitting apoptotic signals mediated through not only Fas but also the TNF receptor in mouse Casp8-deficient cells. Expression analysis showed that casp8 is maternally expressed, and transcripts continue to be present throughout embryogenesis and into larval stages. These results show that zebrafish casp8 has a structure and function similar to mammalian CASP8 orthologs, and our study suggests that the role of caspase-8 in the apoptotic signal pathway has been conserved over at least 450 million years of vertebrate evolution.

The strain rate-dependence of the stress–strain curve and flow stress at 1873 K of the directionally solidified eutectic alumina/YAG composite under applied compressivse stress parallel (0°) and perpendicular (90°) to the solidification direction were analyzed by a finite element model and by the isostrain and isostress models based the rule of mixtures. The experimentally measured stress–strain curve and flow stress in the steady state plastic deformation region of the composite was described by a finite element model for both 0° and 90° compression directions. The influence of the microstructural deviation of alumina and YAG from the theoretical isostrain and isostress models on the overall flow stress was discussed for both 0° and 90° compression directions, based on the calculated spatial distribution of the equivalent strain rate.

A new particle- and resin-free system composed of transparent, binary single crystals entangled with each other continuously has been successfully developed for a light source for illumination. These single crystals exist in a semi-coherent state like a block copolymer; one of these single crystals exhibits effective photoluminescence and the other plays an important role as a light guide of excitation and emitting lights. This material can have low backscattering and high quantum efficiency, resulting in twice the emission light of conventional particle-dispersed systems. Furthermore, this system shows outstanding durability, because of its thermostructural properties. This concept will be expanded into wide combinations to create incandescent systems in the future.

The deformation and fracture behavior at 1773-2023K of the unidirectionally solidified eutectic Al2O3/YAG (Yttrium-Aluminum Garnet with the composition of Y3Al5O13) ceramic composite was investigated. The stress-stain curve and strength of unnotched and notched specimens, measured by bending and tensile tests, showed that (a) both unnotched and notched specimens fractured in a brittle manner at low temperatures and at high displacement speeds, but in a ductile manner at high temperatures and at low displacement speeds, and (b) the notched strength increased, reaching maximum, and decreased with increasing temperature and decreasing displacement speed. The increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum value was accounted for by the increase in plastic zone size ahead of the notch, and the decrease with further increasing temperature and decreasing displacement speed by the loss of the stress carrying capacity of the yielded ligament, based on the finite element analysis.

A unidirectional solidified Al2O3/YAG binary melt growth composite (MGC) with 40 mm in diameter and 80 mm in length has been fabricated by the Bridgman method. In order to clarify crystallographic characteristics of the MGC fabricated, we carried out the crystal orientation analysis using pole figure measurement from two directions for two MGC ingots. The solidification directions of each ingot were almost [ 1 1 2 ¯ 0 ] Al2O3 and [1 1 0] YAG, and [ 0 1 1 ¯ 0 ] Al2O3 and [1 1 0] YAG, respectively. The same set of the crystal orientations which were [0 0 0 1] Al2O3 and [ 1 ¯ 1 2 ] YAG existed in the plane vertical to the solidification direction in two MGC ingots. Since the result of the crystal orientation analysis from two directions was corresponding, these MGC ingots were composed of a single Al2O3 crystal and a single YAG crystal. The relation of the crystal orientation between the Al2O3 phase and the YAG phase in one ingot agreed with previous studies on directionally solidified Al2O3/YAG eutectic composites.

The fracture behavior of the notched unidirectionally solidified eutectic Al 2 O 3 /YAG composite was investigated by tensile test at room temperature to 2023 K, and the results were analyzed by the finite element method. The stress–strain behavior, notched strength and the fracture toughness were strongly dependent on temperature and displacement speed. The specimens fractured in a brittle manner at low temperatures and at high displacement speeds but in a ductile manner accompanying plastic deformation at high temperatures and at low displacement speeds. The notched strength for a given displacement speed of 10 −7 m/s increased with increasing temperature from 132 MPa at 1873 K to 153 MPa at 1923 K, and then decreased to 133 and 110 MPa at 1973 and 2023 K, respectively. Also the notched strength for a given temperature of 2023 K increased with decreasing displacement speed from 67 MPa at the displacement speed of 10 −5 m/s to 124 MPa at 10 −6 m/s, and then decreased to 110 and 72 MPa at 10 −7 and 10 −8 m/s, respectively. The stress distribution and the plastic zone size ahead of the notch were calculated by a finite element method using the dependence of flow stress on temperature and displacement speed. Based on the calculation result, the experimentally observed increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum value could be accounted for by the increase in plastic zone size ahead of the notch. Also, the observed decrease in notched strength with further increasing temperature and decreasing displacement speed could be accounted for by the decrease in the stress carrying capacity of the yielded ligament.

Kit and its ligand stem cell factor (SCF) play a fundamental role in hematopoiesis, melanogenesis and gametogenesis. Homozygous W(v) mutant mice with a mutation in kit show abnormalities in these cell lineages. Fas is a member of the death receptor family inducing apoptosis. In this study, we generated double-mutant mice (W(v)/W(v):Fas(-/-)) and analyzed histologically their reproductive organs. In testes and ovaries of the double-mutant mice, testicular germ cells and oocytes were detected, respectively, whereas the same-aged W(v)/W(v) mice contained neither cells. In addition, inhibition of Kit signals by administration of anti-Kit mAb, which induces degeneration of testicular germ cells in vivo in wild-type mice, did not cause degeneration in Fas-deficient mice. In testicular germ cells of W(v)/W(v) mutant mice, an increase of Fas expression was observed in spermatogonia. Further, in vitro treatment with SCF was shown to downregulate Fas on fibroblasts expressing exogenous Kit through activation of PI3-kinase/Akt. All the results clearly indicate that Fas-mediated apoptosis is involved in germ cell degeneration accompanied by defects in Kit-mediated signals, and Kit signaling negatively regulates Fas-mediated apoptosis in vivo.

Caspase-8 plays the role of initiator in the caspase cascade and is a key molecule in death receptor-induced apoptotic pathways. To investigate the physiological roles of caspase-8 in vivo, we have generated caspase-8-deficient mice by gene targeting. The first signs of abnormality in homozygous mutant embryos were observed in extraembryonic tissue, the yolk sac. By embryonic day (E) 10.5, the yolk sac vasculature had begun to form inappropriately, and subsequently the mutant embryos displayed a variety of defects in the developing heart and neural tube. As a result, all mutant embryos died at E11.5. Importantly, homozygous mutant neural and heart defects were rescued by ex vivo whole-embryo culture during E10.5-E11.5, suggesting that these defects are most likely secondary to a lack of physiological caspase-8 activity. Taken together, these results suggest that caspase-8 is indispensable for embryonic development.

Measurements of two-photon absorption (TPA) coefficients β at 532 nm in binary Bi2O3:B2O3 glasses are reported. The β obtained ranges from 12.9 to 16.4 cm/GW with the larger value observed in higher Bi2O3 glass. The relationship between β and glass composition is discussed in terms of the electronic structure of glasses: β can be scaled with optical band gap.

The reduction-oxidation of copper ions in Cu—Pd—H3PO4/SiO2 catalysts, active in the direct oxidation of benzene to phenol, was studied by means of electron spin resonance spectroscopy. The isolated and aggregated copper (II) ions were found to exist on the Cu—Pd—H3PO4/SiO2 catalyst after evacuation at room temperature. A portion of the Cu(II) ions supported on SiO2, isolated Cu(II) ions coordinated with PO43−, was found to be reversible with alternate reduction-oxidation treatments at 200°C. When the ESR results were compared with the formation rates of phenol, the ‘reversible’ Cu(II) ions were concluded to be responsible for catalytically active sites.

Cerebellar Purkinje cells have the most elaborate dendritic trees among neurons in the brain. We examined the roles of ryanodine receptor (RyR), an intracellular Ca(2+) release channel, in the dendrite formation of Purkinje cells using cerebellar cell cultures. In the cerebellum, Purkinje cells express RyR1 and RyR2, whereas granule cells express RyR2. When ryanodine (10 µM), a blocker of RyR, was added to the culture medium, the elongation and branching of Purkinje cell dendrites were markedly inhibited. When we transferred small interfering RNA (siRNA) against RyR1 into Purkinje cells using single-cell electroporation, dendritic branching but not elongation of the electroporated Purkinje cells was inhibited. On the other hand, transfection of RyR2 siRNA into granule cells also inhibited dendritic branching of Purkinje cells. Furthermore, ryanodine reduced the levels of brain-derived neurotrophic factor (BDNF) in the culture medium. The ryanodine-induced inhibition of dendritic differentiation was partially rescued when BDNF was exogenously added to the culture medium in addition to ryanodine. Overall, these results suggest that RyRs expressed by both Purkinje and granule cells play important roles in promoting the dendritic differentiation of Purkinje cells and that RyR2 expressed by granule cells is involved in the secretion of BDNF from granule cells.

Some vanadate materials were investigated as second harmonic generation (SHG) materials for Nd: YAG lasers. Li 3 VO 4 and its derivative crystals, Li 2 ZnSiO 4 and Li 2 MgGeO 4 , were found as a new type of SHG crystal. Their crystal structure belongs to the Li 3 PO 4 type, which is formed of only MO 4 (M is Li, Zn, Si, Ge, V) oxygen tetrahedra. The SHG coefficients, d ij , of the Li 3 VO 4 single crystal was measured by the Maker fringe method and the non-linear coefficient was found to be of the same order as that of KTiOPO 4 . The origin of SHG in Li 3 VO 4 was discussed from its electronic and crystal structure. The covalency of Li 3 VO 4 is important for SHG and, further, the distorted and parallel oriented VO 4 tetrahedra enhance the SHG coefficient.

Single crystals of the low temperature phase β II Li 3 VO 4 were prepared by using a floating zone technique. Three problems, micro-cracks, accumulation of bubbles and the coloration of crystals, were faced during single crystal growth. These problems were investigated in relation with the initial molten zone composition, gas atmosphere and the purity of starting materials, respectively. The obtained crack-free, colorless and transparent β II Li 3 VO 4 single crystal had a diameter of 5 mm and was 5 mm long.

Cpdm (chronic proliferative dermatitis) mice develop chronic dermatitis and an immunodeficiency with increased serum IgM, symptoms that resemble those of patients with X-linked hyper-IgM syndrome and hypohydrotic ectodermal dysplasia (XHM-ED), which is caused by mutations in NEMO (NF-κB essential modulator; also known as IKBKG). Spontaneous null mutations in the Sharpin (SHANK-associated RH domain interacting protein in postsynaptic density) gene are responsible for the cpdm phenotype in mice. SHARPIN shows significant similarity to HOIL-1L (also known as RBCK1), a component of linear ubiquitin chain assembly complex (LUBAC), which induces NF-κB activation through conjugation of linear polyubiquitin chains to NEMO. Here, we identify SHARPIN as an additional component of LUBAC. SHARPIN-containing complexes can linearly ubiquitinate NEMO and activated NF-κB. Thus, we re-define LUBAC as a complex containing SHARPIN, HOIL-1L, and HOIP (also known as RNF31). Deletion of SHARPIN drastically reduced the amount of LUBAC, which resulted in attenuated TNF-α- and CD40-mediated activation of NF-κB in mouse embryonic fibroblasts (MEFs) or B cells from cpdm mice. Considering the pleomorphic phenotype of cpdm mice, these results confirm the predicted role of LUBAC-mediated linear polyubiquitination in NF-κB activation induced by various stimuli, and strongly suggest the involvement of LUBAC-induced NF-κB activation in various disorders.

Nuclear factor-kappaB (NF-kappaB) is a key transcription factor in inflammatory, anti-apoptotic and immune processes. The ubiquitin pathway is crucial in regulating the NF-kappaB pathway. We have found that the LUBAC ligase complex, composed of the two RING finger proteins HOIL-1L and HOIP, conjugates a head-to-tail-linked linear polyubiquitin chain to substrates. Here, we demonstrate that LUBAC activates the canonical NF-kappaB pathway by binding to NEMO (NF-kappaB essential modulator, also called IKKgamma) and conjugates linear polyubiquitin chains onto specific Lys residues in the CC2-LZ domain of NEMO in a Ubc13-independent manner. Moreover, in HOIL-1 knockout mice and cells derived from these mice, NF-kappaB signalling induced by pro-inflammatory cytokines such as TNF-alpha and IL-1beta was suppressed, resulting in enhanced TNF-alpha-induced apoptosis in hepatocytes of HOIL-1 knockout mice. These results indicate that LUBAC is involved in the physiological regulation of the canonical NF-kappaB activation pathway through linear polyubiquitylation of NEMO.

Several isoforms of protein kinase C (PKC) are degraded by the ubiquitin-proteasome pathway after phorbol ester-mediated activation. However, little is known about the ubiquitin ligase (E3) that targets activated PKCs. We recently showed that an E3 complex composed of HOIL-1L and HOIP (LUBAC) generates linear polyubiquitin chains and induces the proteasomal degradation of a model substrate. HOIL-1L has also been characterized as a PKC-binding protein. Here we show that LUBAC preferentially binds activated conventional PKCs and their constitutively active mutants. LUBAC efficiently ubiquitinated activated PKC in vitro, and degradation of activated PKCalpha was delayed in HOIL-1L-deficient cells. Conversely, PKC activation induced cleavage of HOIL-1L and led to downregulation of the ligase activity of LUBAC. These results indicate that LUBAC is an E3 for activated conventional PKC, and that PKC and LUBAC regulate each other for proper PKC signaling.

FADD is an adaptor protein that transmits apoptotic signals from death receptors such as Fas to downstream initiator caspases in mammals. We have identified and characterized the Xenopus orthologue of mammalian FADD (xFADD). xFADD contains both a death effector domain (DED) and a death domain (DD) that are structurally homologous to those of mammalian FADD. We observed xFADD binding to Xenopus caspase-8 and caspase-10 as well as to human caspase-8 and Fas through interactions with their homophilic DED and DD domains. When over-expressed, xFADD was also able to induce apoptosis in wild-type mouse embryonic fibroblasts (MEF), but not in caspase-8-deficient MEF cells. In contrast, DED-deficient xFADD (xFADDdn) acted as a dominant-negative mutant and prevented Fas-mediated apoptosis in mammalian cell lines. These results indicate that xFADD transmits apoptotic signals from Fas to caspase-8. Furthermore, we found that transgenic animals expressing xFADD in the developing heart or eye under the control of tissue-specific promoters show abnormal phenotypes. Taken together, these results suggest that xFADD can substitute functionally for its mammalian homologue in death receptor-mediated apoptosis, and we suggest that xFADD functions as a pro-apoptotic adaptor molecule in frogs. Thus, the structural and functional similarities between xFADD and mammalian FADD provide evidence that the apoptotic pathways are evolutionally conserved across vertebrate species.

The optically nonlinear Li3VO4 crystal grown by the floating-zone (FZ) method has been characterized by optical absorption and electron spin resonance (ESR) spectroscopy. The as-grown single crystals grown in gaseous argon exhibit a broad absorption extending from the uv to near-infrared light regions and an absorption band at about 3 eV. Postoxidation reduces the whole optical absorption and reveals an additional 1.9 eV band. ESR detects several signals associated with transition-metal ions in as-grown and reduced crystals, i.e., Fe3+, Mn2+ and Cr3+ ions. The Mn2+ and Cr3+ signals are absent in well-oxidized crystals, while the Fe3+ signal shows no significant change. The reduced crystals have three absorption bands associated with transition-metal impurities and oxygen vacancies. The diffuse reflectance spectra of transition-metal-doped Li3VO4 polycrystals were also measured to examine the effect of the presence of Fe3+, Mn2+ and Cr3+. The origin of the optical absorption in as-grown, oxidized and reduced Li3VO4 are discussed in terms of unexpectedly doped iron-group transition-metals and oxygen vacancies. The 3 eV and 1.9 eV absorption bands and the broad band extending from the uv to near-infrared regions are suppressed in the well-oxidized crystals subjected to repeated zone refining, indicating that multiple zone refining and complete oxidation are important in obtaining optical-quality Li3VO4 single crystals.

Li3VO4- and Li3PO4-type structure crystals are found as new types of nonlinear optical materials for second-harmonic generation (SHG). Their lattices are formed of only the MO4 oxygen tetrahedra, being different from other typical nonlinear optical materials that have previously been developed.

Titanium carbide (TiC) single-crystal tips that were sharpened by cleavage have been used to observe the atomic images of the cleaved surfaces of graphite in air. The obtained atomic images were essentially the same as those observed by the commonly used tungsten and platinum tips. However, the TiC single-crystal tips were much better than the tungsten and platinum tips in that atomic images of high resolution could almost always be observed. It was also found that the TiC single-crystal tips were resistant to the intentional and accidental touching to samples. This indicates that the TiC single-crystal tips are suitable for mechanical microlithography of materials in the nanometer scale.