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121.
Takakazu Kojima Rikio Yokota Masakatsu Kochi Hirotaro Kambe 《Journal of Polymer Science.Polymer Physics》1980,18(8):1673-1683
Light scattering and viscometric studies have been carried out on dilute solutions of a polybenzimidazole in N,N-dimethylacetamide. The data, which span the molecular weight range 2.9 ≦ 10?4Mw ≦ 23.3, and the temperature range 290 ≦ T/K ≦343, yield the dependence of the mean-square radius of gyration 〈s2〉LS, the second virial coefficient A2, and the intrinsic viscosity [η] on molecular weight Mw and temperature. The unperturbed mean-square radius 〈s〉LS was calculated using experimental values of 〈s2〉LS and A2. It was found that excluded volume effects on 〈s2〉LS are very small. The unperturbed hydrodynamic chain dimension 〈s〉η was estimated by considering draining effects. A small value of the draining parameter was obtained. Analysis of the temperature dependence of A2 and [eta;] leads to the conclusion that this system approaches a lower theta temperature with increasing temperature. The steric factor σ = 〈s〉/〈s〉f, based on the value of 〈s〉f calculated for the polymer chain with free rotation, is nearly unity. Most of these properties can be interpreted in terms of long rotational units within the main chain. 相似文献
122.
123.
Nishimura K Tsumagari H Morioka A Yamauchi Y Miyashita K Lu S Jisaka M Nagaya T Yokota K 《Applied biochemistry and biotechnology》2002,102(1-6):239-250
The arachidonate cascade includes the cyclooxygenase (COX) pathway to form prostanoids and the lipoxygenase (LOX) pathway
to generate several oxygenated fatty acids, collectively called eicosanoids. Eicosanoids are suggested to play a dual role
in regulating cell survival and apoptosis in various types of cells through an unknown mechanism. We found apoptosis in cultured
Madin-Darby canine kidney (MDCK) cells treated with 12-O-tetradecanoylphorbol β-acetate (TPA), a potent tumor promoter, and nordihydroguaiaretic acid (NDGA), a LOX inhibitor. The
effect of TPA was synergistically stimulated along with NDGA. Aspirin, a COX inhibitor, was not effective. The target of NDGA
might be different from the mechanism involving a LOX activity in some kinds of carcinoma cells because the increased expression
of 12-LOX was not detected in MDCK cells treated with TPA. Caspase and poly(ADP-ribose) metabolites were found to be involved
in the signal transduction pathway of the TPA- and NDGA-induced apoptosis in MDCK cells. Alternatively, hydrogen peroxide-induced
apoptosis was not affected by NDGA. Thus, the TPA-induced response involved the mechanism independent of the oxidative stress.
Obesity is a risk factor for severe diseases including noninsulin-dependent diabetes and atherosclerosis characterized by
the changes of cell properties of adipocytes. We found that conjugated linolenic acid from bitter gourd was able to induce
apoptosis in mouse preadipogenic 3T3-L1 cells. The findings provide the potential use of conjugated fatty acids to regulate
obesity. 相似文献
124.
Total syntheses of (+/-)-methyl gummiferolate (13b), (+/-)-methyl 7beta-hydroxykaurenoate (14b), and (+/-)-methyl 7-oxokaurenoate (14d) and a formal synthesis of (+/-)-gibberellin A(12) (15) have been accomplished through the common synthetic precursor, (3aR,7aR)-3,3-dimethyl-7a-(2-propynyl)-3a,4,7,7a-tetrahydroisobenzofuranone (16). The homoallyl-homoallyl radical rearrangement reaction of the monocyclic enyne 25, derived from 16 in two steps, afforded the bicyclo[2.2.2]octane compound 26, which was converted to (+/-)-methyl gummiferolate (13b). In contrast, the radical cyclization of the bicyclic enyne 16 gave the tricyclic lactone 19, leading to (+/-)-methyl 7beta-hydroxykaurenoate (14b) and (+/-)-methyl 7-oxokaurenoate (14d). Transformation of 14d into lactone 20 was carried out in a single step under bromination conditions. This constitutes a formal total synthesis of gibberellin A(12) (15). 相似文献
125.
Few studies have been made on the fracture mechanics of polymers, their resistance to plastic failure, fatique rupture, and the adverse effects of environmental conditions, in contrast to the numerous studies conducted on metallic materials. Since fatigue is characterized by very local and cyclic fractures, in the present study a real-time fine-grid method was applied to study the fatigue rupture of polymers: to examine changes in local strain at the root of the notch during the process of crack initiation, the local strain at the tip of the crack during crack propagation and the relation between the plastic zone formed in front of the crack tip and the rate of crack propagation. As a result, strong correlation between three proposed parameters of the local crack-tip strain, the crack initiation and the propagation rate was obtained, and the mechanism of low-cycle fatigue rupture of polymers could be discussed.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10. 相似文献
126.
Takumi Yokota 《Mathematische Zeitschrift》2014,277(1-2):293-304
It was proved by F. Wilhelm that Gromov’s filling radius of closed positively curved manifolds with a uniform lower bound on sectional curvature attains the maximum with the round sphere. Recently the author proved that this is also the case for closed finite-dimensional Alexandrov spaces with a positive lower curvature bound. These were proved as a corollary of a comparison theorem for the invariant called spread of those spaces. In this paper, we extend the latter result to infinite-dimensional Alexandrov spaces. 相似文献
127.
Takashi Fukutomi Atsushi Yokota Koji Ishizu 《Journal of polymer science. Part A, Polymer chemistry》1984,22(11):2983-2991
Poly(methyl mehtacrylate)(PMMA) macromers with several vinyl groups at both chain ends were synthesized by the mechanical scission reaction of the main chain in the presence of p-divinylbenzene(p-DVB). The radical copolymerization of this macromer with styrene(St) or MMA was carried out in benzene at 60°C and the reactivity ratio of both monomers (r2) was calculated from a kinetic scheme of copolymerization. As a result, the effect of molecular weight and concentration of macromers was not observed in both copolymerization systems. The value of r2, however, decreased as the number of end vinyl groups in a macromer (N) increased. These results are discussed in some detail as we describe the construction of the kinetic model of copolymerization. 相似文献
128.
Tsutomu Kagiya Masatsune Kondo Kenichi Fukui Hisao Yokota 《Journal of polymer science. Part A, Polymer chemistry》1969,7(10):2793-2803
The γ-ray-induced copolymerization of carbon monoxide with saturated or unsaturated cyclic hydrocarbons, such as cyclohexane, cyclohexene, 4-vinyl-1-cyclohexene, and cyclopentadiene was studied at 30°C. Resinous or powdery polymers were obtained in the copolymerization. The results of elementary analysis, infrared spectra, and NMR spectra showed that copolymers containing ketone and ring structures were produced. The copolymers were confirmed to be partially crystalline by the x-ray diffraction diagram. Further, the influence of the addition of ethylenimine on the copolymerization of carbon monoxide with cyclohexane or cyclohexene was examined. A powdery polymer formed in the copolymerization was concluded to be a terpolymer of carbon monoxide with cyclic hydrocarbon and ethylenimine. On the basis of the experimental results, a mechanism of the copolymerization is proposed. 相似文献
129.
Koike T Yokota S Fujiwara H Sugimoto T Noguchi S de Caro D Valade L 《Inorganic chemistry》2008,47(16):7074-7076
Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide ( 2), in chlorobenzene (PhCl)/ethanol containing NBu 4FeCl 4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2 6.Fe 2OCl 6.2PhCl are obtained that have a different molecular formula from that of 2 2.FeCl 4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe 2OCl 6 (2-) ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi p) observed can be described by the sum of chi p obeying a Curie-Weiss law for the impurity spins and of chi p obeying a dimer model with a spin-exchange integral ( J approximately -180 K) in each Fe 2OCl 6 (2-) ion, which is also weakly coupled to neighboring Fe 2OCl 6 (2-) ions through an additional exchange interaction. 相似文献
130.
The zone-boundary LO—phonon frequencies of SmS show a “softening” in the semiconducting as well as in the valence-fluctuating metallic phase. This has been interpreted as a renormalization of the phonon frequencies due to the phonon-induced on-site ?-d hybridization interaction. Renormalized phonon frequencies, which are calculated as a function of the ?-d energy gap, show a larger “softening” in the semiconducting phase than in the metallic phase, being in qualitative agreement with experiment. 相似文献