Yuko Ojima  Kazuya Yamaguchi  Noritaka Mizuno 《Advanced Synthesis u0026amp; Catalysis》2009,351(9):1405-1411

    

Koji  Yamaguchi Satoshi  Nishijima 《Fatigue & Fracture of Engineering Materials & Structures》1986,9(2):95-107

Ordinary short-term creep fatigue tests were carried out on a servo-hydraulic testing machine for various heat resistant steels. From these results a life prediction method in the long-term creep-fatigue regime is proposed using creep rupture ductility data up to 10⁵ h. To verify the predicted life the authors have developed a new type of testing machine driven by thermo-actuator which can evaluate the long-term creep-fatigue behaviour of materials beyond 10⁴ h.  相似文献   

    

Chavakorn Samthong  Chutimar Deetuam  Masayuki Yamaguchi  Piyasan Praserthdam  Anongnat Somwangthanaroj 《Polymer Engineering and Science》2016,56(3):258-268

The isothermal crystallization kinetics and morphology of the poly(lactic acid) (PLA) blends containing three different sizes of both spherical and fibrous poly(butylene terephthalate) (PBT) domains have been comparatively investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The dynamic DSC measurement reveals that PBT domains significantly increase the degree of crystallinity of the PLA. Furthermore, the Avrami model is employed to evaluate the crystallization kinetics under isothermal conditions and it is found that PBT acts as nucleating agent, leading to a high overall crystallization rate constant k and shortened crystallization half time t_1/2. Furthermore, the crystallization rate of PLA is promoted with the incorporation of PBT with a large specific surface area. The average Avrami index n of all samples lies within the range of 3.3 ? 4.0, suggesting that morphologies of PBT do not affect the nucleation mechanism; however, the depression of equilibrium melting temperature in the blends ascribes the reductions of perfectness and size of the PLA crystallites. Besides, the nucleation of PLA crystallites around PBT fibers is probably faster than those around PBT spheres because the PBT chains oriented at the fiber surface as a result of flow‐induced crystallization during melt stretching may serve as the primary nuclei for PLA chains to drastically crystallize at the fiber surface. POLYM. ENG. SCI., 56:258–268, 2016. © 2015 Society of Plastics Engineers  相似文献   

    

Isao Yamaguchi  Kanako Yamauchi 《应用聚合物科学杂志》2015,132(15)

Oligo(1,5‐dialkoxynaphthalene‐2,6‐diyl)s were synthesized by Ni(cod)₂ (cod = 1,5‐cyclooctadiene)‐promoted condensation reactions of 1,5‐dialkoxy‐2,6‐dibromonaphthalenes. The UV–Vis, photoluminescence (PL), and powder X‐ray diffraction (XRD) measurements suggested that the oligomers have a self‐assembling ordered structure in the solid state. The oligomers underwent electrochemical oxidation (p‐doping), which occurred at lower potentials for films than for acetonitrile solutions containing [Et₄N]BF₄. This effect is caused by the longer π‐conjugation lengths of the oligomers in films, which was attributed to molecular self‐assembly leading to ordered structures in the solid state. The electrochemical reaction of the oligomers was accompanied by electrochromism. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41840.  相似文献   

    

Siriprumpoonthum Monchai  Naoya Mieda  Vu Anh Doan  Shogo Nobukawa  Masayuki Yamaguchi 《应用聚合物科学杂志》2012,124(1):429-435

Effect of applied processing history on flow instability at capillary extrusion is studied using a commercially available low‐density polyethylene (LDPE) having long‐chain branches. It is found that processing history in an internal mixer in a molten state depresses long‐time relaxation mechanism associated with long‐chain branches, which is known as “shear modification.” Consequently, the onset of output rate for melt fracture increases greatly. Furthermore, it should be noted that the sample having intense shear history shows shark‐skin failure without volumetric distortion, although it has been believed that LDPE exhibits gross melt fracture at capillary extrusion. The reduction of elongational viscosity by the alignment of long‐chain branches along to the main chain is responsible for the anomalous rheological response. As a result, the sample shows shark‐skin failure like a linear polyethylene at a lower output rate than the critical one for gross melt fracture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

    

Keiko Yamaguchi 《时间序列分析杂志》2011,32(3):304-314

We propose an estimator of change point in the long memory parameter d of an ARFIMA(p, d, q) process using the sup Wald test. We derive the consistency and the rate of convergence of the estimator for the time of change. The convergence rate of our change point estimator depends on the magnitude of a shift. Furthermore, we obtain the limiting distribution of our change point estimator without depending on the distribution of the process. Therefore, we can construct confidence intervals for the change point. Simulations show the validity of the asymptotic theory of our estimator if the sample size is large enough. We apply our change point estimator to the yearly Nile river minimum water level.  相似文献   

    

Miwa Tenma  Masayuki Yamaguchi 《Polymer Engineering and Science》2007,47(9):1441-1446

The relationship between the structure and the optical properties of isotactic polypropylene (PP) containing 1,3:2,4‐di‐p‐methylbenzylidene sorbitol (MDBS) has been studied. It is found that thinner injection‐molded plaques of PP/MDBS show higher levels of transparency than compression‐molded plaques. The enhanced molecular orientation in the skin layer is responsible for the depression of light scattering because of polarizability fluctuation, i.e., orientation fluctuation in the crystalline phase, because the size of the fluctuation becomes larger than the wavelength of visible light. Further, the crowded network structure of the MDBS fibers generated in molten PP prohibits spherulite formation and, as a result, depresses the spatial size of polarizability fluctuation in the core, which is smaller than the wavelength of visible light. Consequently, light scattering from the core layer is also reduced. POLYM. ENG. SCI., 47:1441–1446, 2007. © 2007 Society of Plastics Engineers  相似文献   

    

Sachiko Nitta  Tomohiro Yamaguchi  Masayoshi Ito 《应用聚合物科学杂志》2007,103(3):1791-1797

The production of high modulus and high strength poly(ethylene terephthalate) fibers was examined by using commercially available melt‐spun fibers with normal molecular weight (intrinsic viscosity = 0.6 dL/g). First, molecular weight of as‐spun fibers was increased up to 2.20 dL/g by a solid‐state polymerization, keeping the original shape of as‐spun fibers. Second, the polymerized as‐spun fibers were drawn by a conventional tensile drawing. The achieved tensile modulus and strength of as‐drawn fibers (without heat setting) were 20.0 and 1.1 GPa, respectively. A heat setting was carried out for the as‐drawn fibers. Tensile properties of the treated fibers were greatly affected by the condition of the heat setting. This was related to the increase of sample crystallinity and molecular degradation during the treatments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1791–1797, 2007  相似文献   

    

Masayuki Yamaguchi 《Polymer Engineering and Science》2006,46(9):1284-1291

The effect of molecular weight on the rheological properties in the molten state has been studied for binary blends of high‐density polyethylene obtained by the Zieglar–Natta catalyst and low‐density polyethylene produced in an autoclave process. The blends composed of high‐density polyethylene with a high molecular weight and low‐density polyethylene show a higher drawdown force than the individual pure components, whereas the blends of high‐density polyethylene with a low molecular weight and low‐density polyethylene do not exhibit anomalous behavior. The pronounced drawdown force for the former blend system is attributed to the viscous enhancement in the linear viscoelastic region as well as the nonlinear strain‐hardening behavior in the elongational viscosity. POLYM. ENG. SCI. 46:1284–1291, 2006. © 2006 Society of Plastics Engineers  相似文献   

    

Atsuhisa Mimoto  Tsuyoshi Maeda  Tsugutomi Nakajima  Takashi Tsukayoshi  Atsushi Oda  Osamu Yamaguchi  Akimasa Tasaka 《Electrochimica acta》2005,50(13):2563-2571

Nickel-oxide composites such as Ni-Co₃O₄, Ni-MnO₂, Ni-Ag₂O, Ni-Y₂O₃, Ni-La₂O₃, Ni-Nd₂O₃, and Ni-Sm₂O₃ systems were prepared from mixture of nickel and oxide powders by hot isostatic pressing (HIP). Ratios of oxide in the nickel-oxide composite were 2, 5, and 10 mol%. Anode gas evolved at every nickel-based composite electrode was composed of N₂, O₂, NF₃, N₂F₂, N₂F₄, and N₂O, and its composition was almost the same as that on a nickel sheet electrode. Current efficiency for NF₃ formation on Ni-Y₂O₃ and Ni-La₂O₃ composite anodes were almost the same as that on the nickel anode, whereas that on Ni-Co₃O₄ composite anode was very small compared with that on the nickel sheet anode. In the cases of the Ni-Co₃O₄, the Ni-MnO₂, and the Ni-Ag₂O composite anodes, the current efficiency for NF₃ formation decreased with increase in the oxide concentration in the composite anodes.Current losses caused by nickel dissolution of the Ni-La₂O₃, the Ni-MnO₂, and the Ni-Ag₂O composite anodes were small compared with that of the nickel sheet anode, while that of the Ni-Co₃O₄ composite anode was very large compared with that of the nickel sheet anode. SEM observation revealed that the surfaces of the Ni-La₂O₃, the Ni-MnO₂, and the Ni-Ag₂O composite anodes after electrolysis were covered with a dense oxidized layer with a few pores and/or some defects. Anode potential during electrolysis indicated that the oxidized layer formed on the Ni-La₂O₃ composite anode has the higher electric conductivity, presumably because of presence of both LaF₃ and NiO_1+x (0 ≤ x < 0.5) in it.  相似文献