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971.
We studied equilibrium conformations of ring polymers in the melt over the wide range of segment number up to 1000 by the Monte Carlo simulations and the bond fluctuation model, and estimated Flory's scaling exponent nu. The radial distribution function of segments for the ring polymers in the melt is obtained. We have found that nu for ring polymers is decreased with increasing segment number N, and nu goes down to 0.365 when N reaches 1000, whose value is apparently smaller than the theoretically predicted one, i.e., 25. Those values are in contrast to the well established nu value of 0.5 for linear polymers in the melt. This is because ring polymer chains in the melt are squeezed both by their own topological effect and the compression effect by the neighboring ring polymer coils which are also squeezed at bulk state. The difference in our result and the theory may be due to the fact that the estimation of topological entropy loss was ignored in the theoretical prediction, while it has been taken into consideration in the present study. If polymer coils repel each other in melt at N --> infinity, we have the limiting nu value of 13, so we conclude that nu is in the range of 13 < or = nu < 0.365 when the molecular weight of a ring polymer is high enough. 相似文献
972.
Morita N Fukui K Irikuchi J Sato H Takano Y Okamoto I Ishibashi H Tamura O 《The Journal of organic chemistry》2008,73(18):7164-7174
Ethyl glyoxylate O-tert-butyldimethylsilyloxime (8), on treatment with 2.2 equiv of BF3 x OEt2, generated N-boranonitrone E, which underwent intermolecular cycloaddition with alkenes 18 to afford isoxazolidines 19 in moderate to high yields. The cycloaddition of N-boranonitrone E with most of the alkenes gave 3,5-trans isoxazolidines as the major isomers via a concerted mechanism. However, in the case of 1-methylated cyclic alkenes (18j and 18l), the cycloaddition surprisingly furnished the 3,3a-cis-cycloadducts (19j and 19l) as major isomers. A possible explanation is that the reaction of 1-methylated cyclic alkenes proceeds mainly via a stepwise mechanism. This reaction of terminal alkenes is very useful for synthesis of 1,3-anti aminoalcohol derivatives by reductive cleavage of an N-O bond. 相似文献
973.
Naoaki Hayashi Shigetoshi Muranaka Mikio Takano Dong-Feng Zhang Chun-Hua Yan 《Journal of solid state chemistry》2008,181(12):3283-3286
A SnO2/α-Fe2O3 architectural nanocomposite, which was evidenced as SnO2 nanorod arrays assembled on the surface of α-Fe2O3 nanotubes in our previous study, was investigated microscopically by means of Mössbauer spectroscopic and magnetic measurements. It was found for the SnO2 nanorods that Fe3+ ions substituted slightly to Sn0.998Fe0.002O2. Concerning the α-Fe2O3 tubes, the Morin transition, which was completely suppressed in the mother, SnO2-free α-Fe2O3 nanotubes, was found to be recovered locally. We speculate that it takes place in the interface area as a result of structural modification needed for the connection with the SnO2 nanorods. 相似文献
974.
Shintaro Ishiwata Ichiro Terasaki Mikio Takano 《Journal of solid state chemistry》2008,181(5):1273-1278
A new magnetoplumbite-type hexagonal cobalt oxide, SrCo12O19, has been synthesized at a high pressure of 3 GPa and its structural and magnetic properties have been studied using single crystalline samples. Bond-valence calculations for five crystallographically independent Co sites show a rather wide charge distribution from +2.15 to +3.50. Magnetic measurements have revealed anisotropic magnetic behavior below a magnetic ordering temperature of 80 K. Comparative discussions on the structure-property relationship for SrCo12O19 and related compounds suggest the presence of localized spins with a uniaxial anisotropy at the trigonal bipyramidal site. 相似文献
975.
Murakami Y Yokoyama M Nishida H Tomizawa Y Kurosawa H 《Colloids and surfaces. B, Biointerfaces》2008,65(2):186-189
Several hemostat hydrogels are clinically used, and some other agents are studied for safer, more facile, and more efficient hemostasis. In the present paper, we proposed a novel method to evaluate local hemostat hydrogel on tissue surface. The procedure consisted of the following steps: (step 1) a mouse was fixed on a cork board, and its abdomen was incised; (step 2) serous fluid was carefully removed because it affected the estimation of the weight gained by the filter paper, and parafilm and preweighted filter paper were placed beneath the liver (parafilm prevented the filter paper's absorption of gradually oozing serous fluid); (step 3) the cork board was tilted and maintained at an angle of about 45 degrees so that the bleeding would more easily flow from the liver toward the filter paper; and (step 4) the bleeding lasted for 3 min. In this step, a hemostat was applied to the liver wound immediately after the liver was pricked with a needle. We found that (1) a careful removal of serous fluid prior to a bleeding and (2) a quantitative determination of the amount of excess aqueous solution that oozed out from a hemostat were important to a rigorous evaluation of hemostat efficacy. We successfully evaluated the efficacy of a fibrin-based hemostat hydrogel by using our method. The method proposed in the present study enabled the quantitative, accurate, and easy evaluation of the efficacy of local hemostatic hydrogel which acts as tissue-adhesive agent on biointerfaces. 相似文献
976.
Nakai M Yamanoi Y Nishimori Y Yonezawa T Nishihara H 《Angewandte Chemie (International ed. in English)》2008,47(35):6699-6702
977.
978.
Ishida N Takano H Naito S Isobe S Uemura K Haishi T Kose K Koizumi M Kano H 《Magnetic resonance imaging》2001,19(6):867-874
The architecture of baked breads made of fresh dough and frozen dough was depicted by magnetic resonance imaging (MRI). Pieces of bread (16 mm cubic cakes) were soaked in organic solvents containing various concentrations of heavy metals (Cu(2+), Co(2+) and Fe(3+)) and images of the grain structure of the breads were obtained. Of the organic solvents tested, acetone was preferable because of its single peak that prevents chemical shift effects on images, the retention of the bread structure, and the solubility of heavy metals. The heavy metals, especially Fe(3+), shortened the overly long relaxation times of acetone to practical lengths for imaging and stained the materials to provide high contrasts. The images obtained in acetone with 8 mM Fe(3+) were suitable for analyzing crumb grain structures. The bread of fresh dough showed a uniform distribution of pores of various sizes made of thin gluten sheets, whereas the pores in the bread of frozen dough were less, prominently large, non-uniformly distributed, and made of thick gluten sheets. 相似文献
979.
Dezawa M Takano M Negishi H Mo X Oshitari T Sawada H 《Micron (Oxford, England : 1993)》2002,33(1):1-6
We developed a new in vivo electroporation method to deliver genes into retinal ganglion cells (RGCs). Efficiency and degree of tissue damage were evaluated using green fluorescent protein (GFP) gene and TUNEL. Soon after the intravitreous injection of the GFP gene, electroporation (five electric pulses of 99 ms duration each and 12V/cm delivered twice 5 min apart) was carried out on the adult rat eyeball with the aid of tweezer-type disc electrodes attached to corneal (cathode) and scleral (anode) surfaces. GFP expression, exhibiting a maximum on day 7, was detectable for up to 21 days. DiI retrograde labeling of RGCs showed that 41.5% of the total ganglion cells in the electroinjected area were GFP-positive. Therefore, this new method may be a useful tool for the delivery of genes into RGCs. 相似文献
980.