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251.
Dielectric properties of vinyl acetate and methyl methacrylate oligomers having chemically different end groups were compared. Dielectric measurements were carried out over the frequency range between 23 and 3 MHz and the temperature range between +50 and ?50°C. The static dielectric constants of these oligomers are between 10 and 20. The relaxations were analyzed with the Havriliak–Negami equation. The dielectric properties depend on the chain end groups on the oligomers. The distribution of relaxation times of the vinyl acetate oligomers was wider than that of poly(vinyl acetate). It was concluded that two cooperative motions, that of the principal chain and that of the chain and that of the chain end group, take part in the dielectric relaxation of these short chain molecules. 相似文献
252.
A simple noncollinear SHG autocorrelator for monitoring the time behavior of single subpicosecond laser pulses is described. A new CCD image-line sensor with high sensitivity in the UV range is used to measure the second-harmonic (SH) spatial distribution which gives information on the duration of the fundamental light pulses. An input energy of only 10 μJ is enough to obtain the SH spatial beam patterns in this highly sensitive autocorrelation system. 相似文献
253.
Inoue Y Nomura Y Nakaoka T Watanabe M Kiryu S Okubo T Ohtomo K 《Magnetic resonance imaging》2005,23(5):641-645
The aim of this study was to investigate the effect of temporal resolution on the estimation of left ventricular (LV) function by cardiac magnetic resonance (MR) imaging using a steady-state free precession (SSFP) sequence. Left ventricular function was assessed by cine MR imaging using a segmented SSFP sequence in 10 healthy volunteers. Views per segment (VPS) were set at 8 and 20, resulting in high and low true temporal resolution, respectively. Irrespective of VPS, images were reconstructed at 40 cardiac phases, providing high apparent temporal resolution. Data were analyzed using 40, 20 and 10 phases to simulate different apparent temporal resolutions. Increasing the cardiac phases used for analysis slightly decreased mean end-systolic volume (ESV) and slightly increased mean ejection fraction (EF). No substantial difference in estimates of end-diastolic volume (EDV) was found between VPSs of 8 and 20. Imaging with a VPS of 20 yielded a larger ESV and smaller EF than imaging with a VPS of 8 when 40 phases were used. In conclusion, low true temporal resolution causes overestimation of ESV and underestimation of EF. Improvement of apparent temporal resolution mildly reduces but does not eliminate the errors caused by low true temporal resolution. 相似文献
254.
Nakayama M Goto S Uchimoto Y Wakihara M Kitajima Y Miyanaga T Watanabe I 《The journal of physical chemistry. B》2005,109(22):11197-11203
Changes in the electronic structure of olivine Li(1-x)CoPO(4), 4.8 V positive electrode material for lithium ion batteries, were investigated using the X-ray absorption spectroscopy (XAS) technique. The threshold energy in the Co K-edge increased with electrochemical Li removal, indicating the oxidation of cobalt ions due to charge compensation. Moreover, P and O K-edge XAS showed a slight shift in threshold energy with Li removal. Although it is generally believed that the electrons of PO(4) polyanion do not contribute to the oxidation process, present experimental results indicate changes in the electronic structure around PO(4) units. Such results would be interpreted by the idea of the hybridization effect between the Co 3d and O 2p orbitals and of the polarization effect introduced by Li ions. 相似文献
255.
The effect of molecular vibrations on electronic transport is investigated with the smallest fullerene C20 bridge, utilizing the Keldysh nonequilibrium Green's function techniques combined with the tight-binding molecular-dynamics method. Large discontinuous steps appear in the differential conductance when the applied bias voltage matches particular vibrational energies. The magnitude of the step is found to vary considerably with the vibrational mode and to depend on the local electronic states besides the strength of electron-vibration coupling. On the basis of this finding, a novel way to control the molecular motion by adjusting the gate voltage is proposed. 相似文献
256.
We report the first experimental results showing transition-specific anisotropy of molecular frame (e, 2e) cross sections. Vector correlations between the two outgoing electrons and the fragment ion have been measured for specific ionization-excitation processes of H2. The results enable us to obtain molecular frame (e, 2e) cross sections for transitions to the 2ssigma(g) and 2psigma(u) excited states of H(2)(+), thereby making stereodynamics of the electron-molecule collisions directly visible. 相似文献
257.
Robert G.?PaytonEmail author Kazumi?Watanabe 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2004,55(4):658-677
The two-dimensional wave front shape caused by a point impulse excitation in a
cylindrically anisotropic elastic solid is considered. The elastic parameters of the solid are
constrained such that
E
=
G
This constraint allows the parametric equations of
the wave front to be expressed exactly in terms of elementary transcendental functions. The precise
location of double and cusp points on the front is treated in detail. Time histories of several
wave front patterns are presented and an interesting feature of the front is generalized to the
unconstrained solid. 相似文献
258.
The hydrodynamic instability of surfactant solutions between two coaxial cylinders was investigated by using a laser-induced-fluorescence flow visualization technique to clarify the effect of drag-reducing additives on vortex formation in Taylor-Couette flow. The test fluids were Ethoquad O/12 surfactant solutions, which have a gel-like structure called “shear-induced structurer” (SIS). Photographs of the formation of Görtler vortices were taken and compared with these of tap water. In the Taylor number range of 1.2×105≤Ta≤7.1×105, tap water and 10 ppm surfactant solution flows consisted of Taylor vortices and much smaller Görtler vortices at the rotating inner wall. However, for 50 and 100 ppm surfactant solutions, Taylor vortices were not apparent and Görtler vortices were collapsed. Measurements of the wavelength of Görtler vortices lead to the conclusion that surfactant solutions have a stabilizing effect on Görtler instabilities. This effect depends on surfactant concentration and becomes considerable with increasing acceleration of the inner cylinder. 相似文献
259.
Takayama H 《Chemical & pharmaceutical bulletin》2004,52(8):916-928
The leaves of a tropical plant, Mitragyna speciosa KORTH (Rubiaceae), have been traditionally used as a substitute for opium. Phytochemical studies of the constituents of the plant growing in Thailand and Malaysia have led to the isolation of several 9-methoxy-Corynanthe-type monoterpenoid indole alkaloids, including new natural products. The structures of the new compounds were elucidated by spectroscopic and/or synthetic methods. The potent opioid agonistic activities of mitragynine, the major constituent of this plant, and its analogues were found in in vitro and in vivo experiments and the mechanisms underlying the analgesic activity were clarified. The essential structural features of mitragynines, which differ from those of morphine and are responsible for the analgesic activity, were elucidated by pharmacological evaluation of the natural and synthetic derivatives. Among the mitragynine derivatives, 7-hydroxymitragynine, a minor constituent of M. speciosa, was found to exhibit potent antinociceptive activity in mice. 相似文献
260.
Kitajima M Hashimoto K Sandoval M Aimi N Takayama H 《Chemical & pharmaceutical bulletin》2004,52(10):1258-1261
A new oleanan-type triterpene and three new cincholic acid glycosides were isolated from Peruvian "Una de Gato" (Cat's claw, plant of origin: Uncaria tomentosa), a traditional herbal medicine in Peru. Their structures were determined by spectroscopic analysis. 相似文献