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91.
Large eddy simulations of turbulent flow between shrouded co-rotating disks, representing a simplified model of a hard disk drive, are performed. The computation domain surrounds a complete disk and is bounded at top and bottom by half a disk. Therefore, it is possible to compute the fluctuating pressure field surrounding the middle disk. Also, the influence of the shroud geometry is taken into account by comparing a flat shroud wall and a wall with rib chambers. In the flat shroud case, the fluctuating pressure on the upper- and lower-surface of a disk indicates a strong correlation with fluid motion travelling across the disk-tip clearance region. However, in the ribbed shroud case the organized flow structure that is observed in the flat shroud case disappears and the fluctuating pressure acting on the surface of the disk is remarkably diminished. 相似文献
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93.
Takaya Mitsui Naohisa Hirao Yasuo Ohishi Ryo Masuda Yumiko Nakamura Hirotoshi Enoki Kouji Sakaki Makoto Seto 《Journal of synchrotron radiation》2009,16(6):723-729
An energy‐domain 57Fe‐Mössbauer spectrometer using synchrotron radiation (SR) with a diamond anvil cell (DAC) has been developed for ultrahigh‐pressure measurements. The main optical system consists of a single‐line pure nuclear Bragg reflection from an oscillating 57FeBO3 single crystal near the Néel temperature and an X‐ray focusing device. The developed spectrometer can filter the Doppler‐shifted single‐line 57Fe‐Mössbauer radiation with a narrow bandwidth of neV order from a broadband SR source. The focused incident X‐rays make it easy to measure a small specimen in the DAC. The present paper introduces the design and performance of the SR 57Fe‐Mössbauer spectrometer and its demonstrative applications including the newly discovered result of a pressure‐induced magnetic phase transition of polycrystalline 57Fe3BO6 and an unknown high‐pressure phase of Gd57Fe2 alloy placed in a DAC under high pressures up to 302 GPa. The achievement of Mössbauer spectroscopy in the multimegabar range is of particular interest to researchers studying the nature of the Earth's core. 相似文献
94.
Recently, many reports have emerged about circularly polarized luminescence (CPL) based on excimer emission of pyrenes. The intense CPL was observed from various pyrene derivatives such as pyrenes having chiral side chains, chiral oligomers bearing multiple pyrene rings, and pyrenes encapsulated by γ-cyclodextrins. The luminescence dissymmetry factor was found to be obviously higher than the absorption one in those pyrenes. In addition, several pyrenes revealed reversible “on-off” CPL switching upon the complexation/decomplexation of metal ions. 相似文献
95.
Qualitative and quantitative flow visualizations were performed on a flapping rigid plate to establish a quantitative method
for flow observation and evaluation of the force in the near field of a flapping wing. Flow visualization was performed qualitatively
with dye visualization and quantitatively with velocity measurements using stereo particle image velocimetry (PIV) on three
planes near the tip of the plate along its chord and oriented normally. By ensemble averaging the velocity fields of the same
phase angles, they represent a portion of the volume near the tip. Measurements were conducted with two flapping frequencies
to compare the flow structure. The second invariant of the deformation tensor visualized the leading edge and mid-chord vortices
around the plate appearing due to flow separation behind the plate while other vortical structures were visualized by streamlines.
These structures appear to be related to the dynamics of the leading edge vortex. Force analysis by integrating the phase-averaged
velocity field within a chosen control volume showed increases in the maxima of the magnitudes of the non-dimensional unsteady
force terms on the edge of the plate at the angles after the end of each stroke. The non-dimensional phase-averaged momentum
flux was similar for both flapping frequencies. 相似文献
96.
97.
We report what we believe to be the first demonstration of stable gain-switched 845 nm pulse generation (Er(3+): (4)S(3/2)->(4)I(13/2) transition) by a weak modulated 1550 nm seed laser, from an Er(3+)-doped fluoride fiber pumped by a cw 974 nm laser diode. When the pump power of the 974 nm laser diode is set to a certain value, the injection of a weak (<1 mW) modulated 1550 nm seed laser into the 845 nm lasing cavity can depopulate the lower state (4)I(13/2) of 845 nm lasing, switch the gain to regulate the conventionally chaotic spiking, and generate stable synchronous 845 nm pulse trains with the repetition rate up to 100 kHz. 相似文献
98.
Mechanophores with a Reversible Radical System and Freezing‐Induced Mechanochemistry in Polymer Solutions and Gels
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Dr. Keiichi Imato Atsushi Irie Takahiro Kosuge Dr. Tomoyuki Ohishi Dr. Masamichi Nishihara Prof. Atsushi Takahara Prof. Hideyuki Otsuka 《Angewandte Chemie (International ed. in English)》2015,54(21):6168-6172
Visualization and quantitative evaluation of covalent bond scission in polymeric materials are highly important for understanding failure, fatigue, and deterioration mechanisms and improving the lifetime, durability, toughness, and reliability of the materials. The diarylbibenzofuranone‐based mechanophore radical system enabled, through electron paramagnetic resonance spectroscopy, in situ quantitative evaluation of scission of the mechanophores and estimation of mechanical energy induced along polymer chains by external forces. The coagulation of polymer solutions by freezing probably generated force but did not cleave the mechanophores. On the other hand, cross‐linking led to efficient propagation of the force of more than 80 kJ mol?1 to some mechanophores, resulting their cleavage and generation of colored stable radicals. This mechanoprobe concept has the potential to elucidate other debated issues in the polymer field as well. 相似文献
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100.