添加合金元素对奥氏体不锈钢等离子渗氮和渗碳的影响

奥氏体不锈钢众所周知有良好的耐蚀性,但是在工业上没有用于承受摩擦的工件上,因为它的硬度低,摩擦磨损性能差。奥氏体不锈钢经低温等离子体渗氮或渗碳能生成一层特殊的氮化物或碳化物层,称为S相,它具有高的硬度和优良的耐蚀性。这项研究中各种奥氏体不锈钢都经低温等离子体渗氮或渗碳,用各种分析技术研究了添加合金元素对S相特性的影响,用了光学显微镜和电子显微镜观察,做了X射线衍射分析,在5%H2SO4溶液中测量阳极极化,用球对平面摩擦装置做摩擦磨损测试。氮化物或碳化物层厚度随处理温度增加而加厚,AISI316钢上生成的渗层厚度是所有的基体钢材中最厚的。超过临界温度,由于氮化铬工碳化铬沉淀使耐蚀性降低。临界温度由渗氮的基材决定。另一方面,在渗碳层中临界温度不随基材变化。大部分样品上S相层的耐蚀性比没有处理的不锈钢的低。但是,AISI316和JIS-SUS304J3钢在400℃渗碳后都有和未处理钢一样优良的耐蚀性。每种不锈钢经渗氮或渗碳后耐磨性都有明显的改进。     

Influence of Slurry Flocculation on the Character and Compaction of Spray-Dried Silicon Nitride Granules

The effect of slurry flocculation on the characteristics of silicon nitride granules prepared by the spray drying process is investigated. The flocculation state of an aqueous silicon nitride slurry is controlled by adding nitric acid and evaluated as a function of pH. Dense and hard silicon nitride granules result from a well-dispersed slurry having a high pH (e.g., 10.8). These hard granules retain their shape in green compacts and form detrimental defects. Lowering the pH of the slurry to a certain value (e.g., pH 7.9) results in slurry flocculation. Granules prepared from this flocculated slurry have low density and low diametral compression strength and contribute to the elimination of large pores in green compacts.     

Enhanced growth inhibition of hepatic multicellular tumor spheroids by lactosylated poly(ethylene glycol)-siRNA conjugate formulated in PEGylated polyplexes

PEGylated polyplexes (lac-PEGylated polyplexes) composed of poly(L-lysine) and lactosylated poly(ethylene glycol)-small interfering RNA conjugate, which inhibits the RecQL1 gene product, were revealed to show an appreciable growth inhibition of multicellular HuH-7 spheroids (human hepatocarcinoma cell lines) for up to 21 days (IC(50)=6 nM); this system used as an in vitro three-dimensional (3D) model mimicking the in vivo biology of tumors. The PEGylated polyplexes thus prepared had a size of approximately 110 nm with clustered lactose moieties on their periphery as targeting ligands for the asialoglycoprotein-receptor-expressing HuH-7 cells. In contrast, OligofectAMINE/siRNA (cationic lipoplex) was observed to have almost no growth-inhibitory effect against HuH-7 spheroids, even though the lipoplex showed a stronger growth-inhibitory effect than the lac-PEGylated polyplexes on conventional monolayer-cultured HuH-7 cells. The FITC-tagged conjugate in the lac-PEGylated polyplexes showed smooth penetration into the HuH-7 spheroids compared with that in the lipoplexes, as observed by confocal fluorescence-scanning microscopy. This indicates that the small size of approximately 100 nm and the reduced nonspecific interaction due to the nonionic and hydrophilic lactosylated PEG layer contributes to the smooth penetration of the PEGylated polyplexes into the spheroid interior, eventually facilitating their uptake into the cells composing the spheroids. Cellular apoptosis indicating programmed cell death was also observed in the HuH-7 spheroids treated with the PEGylated polyplexes, revealing that the observed growth inhibition was indeed induced by the RNAi of the RecQL1 siRNA. These data suggest that the smart PEGylated polyplexes can indeed penetrate into the multiple cell layers of 3D tumor masses in vivo, exerting therapeutic effects through the RNAi.     

Dissolution and wet spinning of silk fibroin using phosphoric acid/formic acid mixture solvent system

Regenerated silk fibroin (SF) filaments could be prepared by wet spinning in common solvent/coagulation system. SF was directly dissolved in mixture solvent of phosphoric acid and formic acid (20/80–30/70 ratio) and coagulated in methanol bath. The concentration and stability of SF dope solution have been studied by varying the mixture ratios of these solvents in accordance with elucidating the role of formic acid in the mixture solvent system. Morphological structure as well as crystalline structure of the regenerated filament was examined using SEM and XRD analyses. As a result of tensile test, the regenerated SF filament, which was made by one‐step dissolution and coagulation process, had good mechanical properties, 2.3 gf/d tenacity and 18% breaking strain. In this study, a simple wet spinning method which enables to apply to practical production has been reported for the preparation of the regenerated SF filament. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Electrospun three‐dimensional silk fibroin nanofibrous scaffold

Practical application to three‐dimensional (3‐D) tissue culture has been limited by the structural restriction of two‐dimensional (2‐D) nature of electrospun nanofiber mat. In this study, for constructing 3‐D nanofibrous structure as real 3‐D tissue engineering scaffold, we developed new fabrication process with silk fibroin (SF) by electrospinning and evaluated the features of this SF nanofiber scaffold (SFNS) through morphological and cell‐culture analyses. Foam type of the SFNS exhibited high porosity as well as large pores and its cell proliferation well occurred inside (inner spaces of pores), which makes this suitable for 3‐D cell‐culture scaffold. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Dehydration of d-glucose in high temperature water at pressures up to 80 MPa

Reaction of d-glucose in water to yield 5-hydroxymethylfurfural (5-HMF), 1,2,4-benzenetriol (BTO) and furfural was studied at high temperatures (up to 400 °C) and high pressures (up to 80 MPa) using a continuous flow reactor. Maximum temperature and pressure conditions gave maximum furfural yield. Increasing pressure from 40 to 70 and 80 MPa enhanced dehydration reactions to 5-HMF, but also enhanced hydrolysis of 5-HMF leading to the production of BTO and thus lead to lower yields of 5-HMF (below 10%). Remarkably, the dehydration reaction to 5-HMF and the hydrolysis of 5-HMF were both enhanced by the increase in water density at 400 °C.     

Myosin is solubilized in a neutral and low ionic strength solution containing l-histidine

Myosin, one of the major myofibrillar proteins, is insoluble at low and physiological ionic strength and soluble at high ionic strength. In this study, the behavior and morphology of myosin solubilized in a low ionic strength solution containing l-histidine (l-His) was investigated. More than 80% of myosin was solubilized in a low ionic strength solution with dialysis against a solution containing 1 mM KCl and 5 mM l-His. Transmission electron microscopy with rotary shadowing demonstrated that the rod of myosin in a low ionic strength solution containing l-His is longer than that of myosin in a high ionic strength solution. The elongation of the myosin rod in a low ionic strength solution containing l-His would inhibit the formation of a filament, resulting in the solubilization of myosin.     

Novel expansion/shrinkage modulation of 2D layered MOF triggered by clathrate formation with CO(2) molecules

Crystal-to-crystal transformation from a 3D interpenetrated-type MOF {[Cu(BF(4))(2)(bpy)(H(2)O)(2)] (bpy)} (1) to a 2D square-grid-type [Cu(BF(4))(2)(bpy)(2)] (2) (bpy = 4,4'-bipyridine) was observed. It was derived from dehydration and confirmed by in situ FT-IR, TG, and elemental analysis. Moreover, we elucidate the novel expansion/shrinkage dynamic modulation of 2 triggered by clathrate formation with gas molecules.     

Phenotypic abnormalities observed in aged cloned mice from embryonic stem cells after long-term maintenance

Somatic/embryonic stem cell cloning has made it possible to produce an individual genomically identical to another individual. However, the cloned animals have a variety of abnormalities caused by the aberrant gene modification, with insufficient reprogramming in cloning. We previously reported abnormalities in cloned mice at birth. In this study, we examined what abnormalities could be seen in cloned mice after long-term maintenance. The aged cloned mice showed multiple abnormalities: increase of body weight, some phenotypic abnormalities in the kidneys, testes and thymus, and lower urea nitrogen in their serum biochemical values. The kidneys of all cloned mice were hypertrophied, with a metamorphic or whitish appearance. The multiple lesions, including the enlarged renal pelvis and distension of the renal veins in histology, might be the result of urine accumulation by urinary tract obstruction. The testes of the cloned mice were atrophied, and showed no sperm formation in histology. In contrast, the thymus was rather hypertrophied, and a comparably increased number of lymphocytes were observed in the medulla, consisting mainly of T cells. By conducting a progeny test between the cloned mice, it was confirmed that these abnormalities in the aged cloned mice were not transmitted to their offspring, indicating that the incomplete reprogramming in clones might be in part responsible for the abnormalities detected in aged clones. These results indicate that the postnatal abnormalities observed in aged cloned mice are varied and can be restored through the germ line.