Mechanical properties of As-cast and directionally solidified Nb-Mo-W-Ti-Si <Emphasis Type="Italic">in-situ</Emphasis> composites at high temperatures

To improve the high-temperature strength of Nb-Mo-Ti-Si in-situ composites, alloying with W and a directional solidification technique were employed. The alloy composition of Nb-xMo-10Ti-18Si (x=10 or 20) was used as the base, and Nb was further replaced by 0, 5, 10 and 15 mol pct W. For samples without W, the as-cast microstructure was a eutectic mixture of fine Nb solid solution (Nb _SS ) and (Nb, Me)₅ Si₃ silicide (Me = Mo, W, or Ti), while large primary Nb _SS particles appeared besides the eutectic mixture as a result of replacing Nb by W. The directionally solidified samples consisted of coarse Nb _SS and (Nb,Me)₅ Si₃ silicides, and the microstructure showed a slight orientation in the direction of growth. The maximum compressive ductility (ɛ _max) at room temperature decreased with increasing W content and was in the range of 0.8 to 2.3 pct, in contrast to the Vickers hardness (HV), which increased with W content. The 0.2 pct yield compressive strength (σ _0.2) and the specific 0.2 pct yield compressive strength (σ _0.2S ) (σ _0.2 divided by the density of sample) at elevated temperatures were markedly improved by the W addition. The directionally solidified samples always showed higher σ _0.2 and σ _0.2S values than the as-cast samples. At elevated temperatures, the directionally solidified sample with 10 mol pct Mo and 15 mol pct W had the highest σ _0.2 and σ _0.2S values; even at 1770 K, σ _0.2 was as high as 650 MPa. The directionally solidified materials alloyed with W exhibited excellent compressive creep performance. The sample with 10 mol pct Mo and 15 mol pct W had a minimum creep rate of 1.4×10⁻⁷s⁻¹ and retained steady creep deformation at 1670 K and an initial stress of 200 MPa. Under compression, the damage and failure of these in-situ composites were dominated by decohesion of interfaces between the Nb _SS and silicide matrix.     

Validation study of computer code for sodium fire safety evaluation of fast reactor

A computer code solves coupled phenomena of thermal hydraulics and sodium fire based on a multi-zone model. It deals with an arbitrary number of rooms, each of which is connected mutually by doorways and penetrations. With regard to the combustion phenomena, a flame sheet model and a liquid droplet combustion model are used for pool and spray fires, respectively, with the chemical equilibrium model based on the Gibbs free energy minimization method. The chemical reaction and mass and heat transfer are solved interactively. A specific feature of is detailed representation of thermalhydraulics of a sodium pool and a steel liner, which is placed on the floor to prevent sodium–concrete contact. The authors analyzed a series of pool combustion experiments, in which gas and liner temperatures are measured in detail. It has been found that good agreement is obtained and the code has been validated with regard to pool combustion phenomena. Further research needs are identified for pool spreading modeling considering thermal deformation of steel liner and measurement of pool fluidity property as a mixture of liquid sodium and reaction products. The code is to be used mainly in the safety evaluation of the consequence of a sodium fire accident in a liquid metal cooled fast reactor as well as fire safety analysis in general.     

Three-dimensional architecture of ribosomal DNA within barley nucleoli revealed with electron microscopy

To elucidate the topological positioning of ribosomal RNA genes (rDNA) and nucleolar structure in three dimensions, we examined the localization of rDNA using in situ hybridization (ISH) analysis by scanning electron microscopy (SEM). The rDNA genes within the three-dimensional architecture of nucleoli were detected on chromatin fibers that connect a thick strand-like structure and a protrusion of rDNA into the inner nuclear hole where the nucleolus is formed. This novel use of ISH together with SEM is useful for the analysis of nucleolar structure in detail. Furthermore, rDNA was detected at the periphery of the fibrillar centers (FCs) of the nucleolus using immuno-gold labeling together with transmission electron microscopy (TEM). In situ hybridization with TEM confirmed that rDNA is naked and thus active in the FCs of nucleoli; ISH with SEM confirmed that rDNA is not covered with ribonucleo proteins at the protruding point and is thus inactive. We also show that the distribution pattern of FCs differs from sample to sample. These results indicate that rDNA is transcribed dynamically in a time- and region-specific manner over the course of the cell cycle.     

Keratin sponge: immobilization of lysozyme

A porous wool keratin sponge was used for immobilization of lysozyme, a model bioactive substance and was demonstrated to be a unique biomaterial in terms that the activity of lysozyme linked to the sponge through disulfide bond was gradually released, while lysozyme through thioether bond was stably maintained.     

Synthesis and characterization of deoxycholyl 2-deoxyglucuronide: A water-soluble affinity labeling reagent

Acyl glucuronides, which are biosynthesized by the action of glucuronosyltransferases to material for detoxification, are water-soluble and chemically active; they produce irreversible protein adducts via both the transacylation mechanism and the imine mechanism. The acyl group at the C-1 position migrates from the anomeric carbon to the C-2 position of the glucuronic acid moiety, producing the aldehyde group at the C-1 position, where the protein easily condenses through a Schiff's base, in the open-chain aldose form. The elimination of the hydroxyl group at the C-2 position therefore may prevent a protein-bound adduct via the imine mechanism. In this paper, we describe the synthesis and characterization of an acyl 2-deoxyglucuronide of deoxycholic acid as a model compound to investigate its possible utility as a water-soluble affinity labeling reagent for lipophilic carboxylic acids. The solubility of deoxycholyl 2-deoxyglucuronide in an aqueous solution was sufficient under physiological conditions, and the desired material reacted with model peptides to produce covalently bound adducts only via the transacylation mechanism.     

Dynamics of subcellular organelles, growth hormone, Rab3B, SNAP-25, and syntaxin in rat pituitary cells caused by growth hormone releasing hormone and somatostatin

Rab3B is involved in the exocytosis of synaptic vesicles and secretory granules in the central nervous system and the anterior pituitary cells. The aim of this study was to elucidate both the role of rab3B in GH secretion and the mutual relationship of rab3B and SNARE proteins. Adult male rats were injected intravenously with 10 microg of growth hormone releasing hormone (GHRH) or 10 microg of somatostatin (SRIF). Untreated rats were used as controls, and their pituitary glands were sectioned for histochemical examination. Rab3B is localized on the limiting membrane of the secretory granules and the cytosol. Confocal laser scanning microscopic observation of immunohistochemical double staining of rab3B and GH revealed that immunoreactivity of rab3B increased in GHRH-treated rats and decreased in SRIF-treated rats. Confocal laser scanning microscopic observation of immunohistochemical double staining of SNAP-25, syntaxin, and rab3B revealed the co-localization of rab3B and these SNARE proteins in GHRH-treated rats, and their dissociation in SRIF-treated rats. These results suggest that rab3B plays a principal role in GH secretion in the anterior pituitary cells and that SNAP-25 and syntaxin act as co-workers with rab3B in the functional regulation of GH secretion.     

Computational design of solar reflection and far-infrared transmission films for a variable emittance device

A smart radiation device (SRD) that is a variable emittance radiator has been studied as a method of thermal control for spacecraft. The SRD consists of manganese oxide with a perovskite-type structure, and the total hemispherical emittance of the SRD changes considerably depending on temperature. Here we propose an optimal method of designing multilayer films for the SRD by using agenetic algorithm. The multilayer films reflect solar radiation and transmit far-infrared radiation to maintain variation of the infrared optical properties of the SRD.     

Early hospital readmission was less likely for hemodialysis patients from facilities with longer median length of stay in the DOPPS study

The length of hospital stay is considered to influence hospital readmission in general. The Dialysis Outcomes and Practice Patterns Study (DOPPS), an international prospective observational study undertaken to establish a relationship between facility practices and dialysis outcomes, started in 1996. Results suggest that the duration of hospital stay is significantly correlated with the probability of early readmission in dialysis patients. Thus, early hospital readmission was observed to be less likely for hemodialysis patients from facilities with longer median length of stay. The lengths of hospital stay for hemodialysis patients differed in the three continents studied. Although socioeconomic pressures may drive the lengths of hospital stay, the duration of hospitalization should be determined keeping in mind the safety of clinical course for each disease. In this forum, a 47-year-old female hemodialysis patient with severe secondary hyperparathyroidism, who had been treated with hemodialysis for 21 years, was hospitalized with severe clinical symptoms. Although the clinical symptoms disappeared 10 days after total parathyroidectomy with autotransplantation, severe hypocalcemia persisted despite large amounts of intravenous calcium gluconate. This patient was hospitalized for a long duration owing to the large calcium deficit in her body. Had the length of her hospital stay been shortened, either she could have needed rehospitalization or her condition could have worsened.     

Characterization of denitrifying polyphosphate-accumulating organisms in activated sludge based on nitrite reductase gene

Nitrite reductase gene (nirS) fragments in the activated sludge obtained from a sequencing batch reactor (SBR) under anaerobic-aerobic condition were cloned and classified by restriction fragment length polymorphism (RFLP) analysis, and representative fragments were sequenced. One of the nirS clones was approximately 70% of all nirS clones in anaerobic/aerobic (existing oxygen and nitrate) cycle operation in which a large amount of anoxic phosphate uptake was observed. Although the activated sludge samples analyzed might contain bacteria that did not accumulate polyphosphate, it was likely that this nirS fragment sequence was that from denitrifying polyphosphate-accumulating organisms (DNPAOs) which can utilize both oxygen and nitrate as electron acceptors. The sequence was similar to the nirS sequences of Thauera mechernichensis (83% similarity) and Azoarcus tolulyticus (83% similarity) both of which belong to the Rhodocyclus group.     

Fabrication of subwavelength structure for improvement in light-extraction efficiency of light-emitting devices using a self-assembled pattern of block copolymer

A new fabrication method to improve the optical extraction efficiency of light-emitting devices is presented. The morphology of a self-assembled block copolymer was transferred to the surface of a compound semiconductor to achieve a subwavelength columnar structure. The optical extraction efficiency of the substrates with subwavelength columnar structures of 350 nm pillar height, 130 nm diameter, and 180 nm pitch, improved 2.2 times compared to unprocessed substrates. This method does not require expensive exposure lithography tools and is therefore suitable for conventional semiconductor processes.