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排序方式: 共有168条查询结果,搜索用时 15 毫秒
61.
Poly(vinyl alcohol) (PVAc) composite porous membrane has been prepared from PVAc latex film by extraction with acetone. The PVAc latex was prepared by emulsion polymerization of vinyl acetate in the presence of PVA, employing the hydrogen peroxide–tartaric acid systemm as an initiator. The extraction degree of PVAc could be controlled in a wide range by changing the addition method of the initiator, and, acoordingly, PVA–PVAc omposite porous membranes which had variosu void volumes were obtained. The maximum void volume attained was ca. 90%. Permation characteristics of organic solvents wre investigated on the membranes whose extraction degrees were 95.6% and 80.7%. Thge feeds were benzene, n-hexane, cyclohexane, and their mixtures. neither swelling nor shrinkage in tje appearance size of the while benzene hardly permeated even at 20 kg/cm2. The grafted PVAc in the mebrane was removed or converted into grafted PVA by treatment with sodium methylate, and then the depression of benzene permeation was lost. The grafted PVAc was suggested to be localizd on the cell wall and was found to function as a valve which closes with nenzene or a good solvent for PVAc and opens with n-haxane or a poor solvent for PVAc. 相似文献
62.
The kinetics of the ligand exchange reaction of the Cu(II)-ammine complex with poly(vinyl alcohol) (PVA) has been studied by a stopped-flow method at pH 9–10, at μ=0.1 (NH4Cl) and at 25°C. The reaction is initiated by the formation of unstable [Cu(NH3)3]2+ by the attack of H+ on Cu(II)-ammine complex, and proceeds through the mixed complex {[Cu(NH3)3(O?PVA)]2+}. This step may be rate-determining, followed by a rapid reaction. Finally, the Cu(II) ion is taken up by PVA. The rate is given by d[Cu(II)?PVA]/dt=k[H+]{[Cu(NH3)4]2+}[PVA]/[NH4Cl], where k=k1 + k′2[H+], k1=4.25× 10s?1 and k′2=5.20× 1011l mol?1s?1. 相似文献
63.
64.
SiC ceramics were prepared from nanosized β-SiC powder with different compositions of AlN and Y2O3 sintering additives by spark plasma sintering (SPS) at 1900 °C for 600 s in N2. The relative density of the sintered SiC specimens increased with increasing amount of AlN, reaching a relative density higher than 99%, while at the same time grain size decreased significantly. The smallest average grain size of 150 nm was observed for SiC sample sintered with 10 vol% of additives consisting of 90 mol% AlN and 10 mol% Y2O3. Fully dense nanostructured SiC ceramics with inhibited grain growth were obtained by the AlN additive and SPS technique. The flexural strength of the SiC body containing 70 mol% AlN and 30 mol% Y2O3 additives reached the maximum value of 1000 MPa. The SiC bodies prepared with AlN and Y2O3 additives had the fracture toughness of around 2.5 MPam1/2. 相似文献
65.
M Hojo M Hoshimaru S Miyamoto W Taki I Nagata M Asahi N Matsuura R Ishizaki H Kikuchi N Hashimoto 《Canadian Metallurgical Quarterly》1998,89(4):623-629
N-Nitroso propoxur (NP) can be synthesized from a widely used N-methylcarbamate insecticide, propoxur, in vitro in the laboratory. Because of the extensive use of aerosol propoxur, the adverse effect on cells of respiratory origin is worth elucidating. In this report, two mammalian cell cultures from respiratory tissues [a hamster lung fibroblast, V79, and a primary rat tracheal epithelial cell (RTE)], were used to investigate the genotoxicity of propoxur and NP. NP was more cytotoxic than propoxur, with LC50s (20 and six times smaller, respectively in V79 and RTE cells. NP significantly induced sister chromatid exchange (> or = 0.01 microg/ml), chromosome aberration (> or = 2.5 microg/ml) and hprt gene mutation (> or = 0.5 microg/ml) in V79 cells, and cell transformation (> or = 0.2 microg/ml) in RTE cells. Results of chromosome aberration and hprt gene mutation indicated that the major pre-mutagenic lesion induced by NP must be the O6-methylguanine adduct, which frequently mispairs with thymine and thus gives rise to a GC-->AT transition. Propoxur was not mutagenic to either type of cells. However, it inhibited gap-junctional intercellular communication in V79 cells, which indicates that propoxur could act through some epigenetic mechanisms, such as tumor promotion or cell proliferation, in the multiple process of chemical carcinogenesis. 相似文献
66.
Hideo Yonezawa Mizuho Motegi Atsushi Oishi Fuhito Hojo Seiya Higashi Eriko Nozaki Kentaro Oka Motomichi Takahashi Takako Osaki Shigeru Kamiya 《International journal of molecular sciences》2021,22(7)
Lantibiotics are a type of bacteriocin produced by Gram-positive bacteria and have a wide spectrum of Gram-positive antimicrobial activity. In this study, we determined that Mutacin I/III and Smb (a dipeptide lantibiotic), which are mainly produced by the widespread cariogenic bacterium Streptococcus mutans, have strong antimicrobial activities against many of the Gram-positive bacteria which constitute the intestinal microbiota. These lantibiotics also demonstrate resistance to acid and temperature. Based on these features, we predicted that lantibiotics may be able to persist into the intestinal tract maintaining a strong antimicrobial activity, affecting the intestinal microbiota. Saliva and fecal samples from 69 subjects were collected to test this hypothesis and the presence of lantibiotics and the composition of the intestinal microbiota were examined. We demonstrate that subjects possessing lantibiotic-producing bacteria in their oral cavity exhibited a tendency of decreased species richness and have significantly reduced abundance of the phylum Firmicutes in their intestinal microbiota. Similar results were obtained in the fecal microbiota of mice fed with S. mutans culture supernatant containing the lantibiotic bacteriocin Mutacin I. These results showed that lantibiotic bacteriocins produced in the oral cavity perturb the intestinal microbiota and suggest that oral bacteria may be one of the causative factors of intestinal microbiota dysbiosis. 相似文献
67.
T Hojo 《Canadian Metallurgical Quarterly》1994,8(2):303-313
Specimen preparation methods are very important in scanning electron microscopy (SEM) of nerve tissues. In the present study, a t-butyl alcohol freeze-drying device was used to prepare cerebellar cortex of the human and that of the rat at 15 degrees C and 160 mm Hg. This method has been previously used with success in the preparation of other tissues, such as pancreas and trachea. Relatively large specimens (about 10 mm x 15 mm x 1 mm) of formalin-fixed human and glutaraldehyde-Millonig buffer perfused (1 hour) Wistar rat were rinsed in water, dehydrated in a series of ethanols, immersed in t-butyl alcohol, and then placed in the new freeze-drying device. The specimens were cut with a razor, freeze-dried without acid or alkali digestion, mounted on stubs, and sputter-coated with gold. This new preparation method allowed a higher magnification examination of surfaces of cells and fibers of the human cerebellar cortex compared to the critical point drying method. This was valid for Purkinje cell bodies with axons, dendrites with climbing fibers and climbing fiber glomeruli, and stellate neuron cell processes connected to the Purkinje cell dendrites. Lugaro cell, basket cells with axons, Golgi II cell, mossy fiber glomerulus with granule cell dendrites, satellite Bergmann glial cells with processes, and many microtubule-like fibrous structures on the inside of Purkinje cell dendrites were observed. Furthermore with this method, the glutaraldehyde-Millonig buffer perfused cerebellar cortex of the Wistar rat shows better three-dimensional images than the formalin-fixed human cerebellar cortex. 相似文献
68.
Kiminobu Hojo Makoto Takenaka Hitoshi Kaguchi Genki Yagawa Shinobu Yoshimura 《Nuclear Engineering and Design》1993,142(1)
A probabilistic fracture mechanics code which evaluates fracture probability of a plate model with an elliptical surface crack caused by creep-fatigue crack growth has been developed. The code named PCCF (Probabilistic Fracture Mechanics Code for Creep-Fatigue Crack Growth) uses simplified methods of C* and J-integral for evaluation of creep-fatigue crack growth and a stratified sampling method for two input variables to improve the solution convergency. According to the test analyses focused on an applied stress level using PCCF code, leak probability is sensitive to a stress level and increases rapidly when an applied stress is close to a yield stress level. 相似文献
69.
T Fukushima T Tawara A Isobe N Hojo K Shiwaku Y Yamane 《Canadian Metallurgical Quarterly》1995,42(3):385-390
Paraquat was reduced to the paraquat radical via complex I in bovine cerebral mitochondria and accelerated lipid peroxidation. Thirty-kilodalton subunit of complex I was considered to be the radical formation site, because of its marked destruction by the paraquat radical. The lipid peroxidation by the paraquat radical was suppressed not only by superoxide dismutase (SOD) but also by mannitol. The destruction of complex I subunits via lipid peroxidation must have been caused by the hydroxyl radical which was formed from the superoxide radical. The same phenomenon was observed by using 1-methylnicotinamide (MNA), which contains the same partial structure as paraquat in itself and is metabolized from nicotinamide in a living body. We observed NADH oxidation by MNA via cerebral complex I (Km = 26.3 mM), and MNA destroyed some complex I subunits, especially 30-kilodalton protein. Paraquat might be useful for studying the pathogenesis of Parkinson's disease (PD) in vitro, and MNA is expected to be one of the causal substances of PD from the viewpoint of the oxidative stress theory. 相似文献
70.
H Tomita I Hojo S Yasuda T Nakamura K Takemura Y Mishima 《Canadian Metallurgical Quarterly》1993,23(12):1099-1102
We report herein the case of a 23-year-old man with Crohn's disease who was found to have a perforated small bowel following blunt abdominal trauma sustained in a traffic accident. The general findings of diffuse peritonitis were identified by physical examination, and a plain X-ray film showed free air in the abdominal cavity. An emergency laparotomy was performed which revealed three perforated ulcers in the affected intestine. An abrupt increase in intraluminal pressure due to the striking force of the steering wheel to the abdomen was assumed to have been the cause of these perforations. 相似文献