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  • American Institute of Physics (AIP)  (6)
  • American Chemical Society  (1)
  • 2015-2019  (2)
  • 2010-2014  (1)
  • 2000-2004  (4)
  • 1
    Publication Date: 2015-02-19
    Description: This paper reports the experimental results on the instability and associated roll structures (RSs) of Marangoni convection in liquid bridges formed under the microgravity environment on the International Space Station. The geometry of interest is high aspect ratio ( AR = height/diameter ≥ 1.0) liquid bridges of high Prandtl number fluids ( Pr = 67 and 207) suspended between coaxial disks heated differentially. The unsteady flow field and associated RSs were revealed with the three-dimensional particle tracking velocimetry. It is found that the flow field after the onset of instability exhibits oscillations with azimuthal mode number m = 1 and associated RSs traveling in the axial direction. The RSs travel in the same direction as the surface flow (co-flow direction) for 1.00 ≤ AR ≤ 1.25 while they travel in the opposite direction (counter-flow direction) for AR ≥ 1.50, thus showing the change of traveling directions with AR . This traveling direction for AR ≥ 1.50 is reversed to the co-flow direction when the temperature difference between the disks is increased to the condition far beyond the critical one. This change of traveling directions is accompanied by the increase of the oscillation frequency. The characteristics of the RSs for AR ≥ 1.50, such as the azimuthal mode of oscillation, the dimensionless oscillation frequency, and the traveling direction, are in reasonable agreement with those of the previous sounding rocket experiment for AR = 2.50 and those of the linear stability analysis of an infinite liquid bridge.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
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  • 2
    Publication Date: 2014-08-27
    Description: Microbial fuel cells (MFCs) are promising devices for capturing biomass energy. Although they have recently attracted considerable attention, their power densities are too low for practical use. Increasing their electrode surface area is a key factor for improving the performance of MFC. Carbon nanotubes (CNTs), which have excellent electrical conductivity and extremely high specific surface area, are promising materials for electrodes. However, CNTs are insoluble in aqueous solution because of their strong intertube van der Waals interactions, which make practical use of CNTs difficult. In this study, we revealed that CNTs have a strong interaction with Saccharomyces cerevisiae cells. CNTs attach to the cells and are dispersed in a mixture of water and S. cerevisiae , forming a three-dimensional CNT conductive network. Compared with a conventional two-dimensional electrode, such as carbon paper, the three-dimensional conductive network has a much larger surface area. By applying this conductive network to MFCs as an anode electrode, power density is increased to 176  μ W/cm 2 , which is approximately 25-fold higher than that in the case without CNTs addition. Maximum current density is also increased to approximately 8-fold higher. These results suggest that three-dimensional CNT conductive network contributes to improve the performance of MFC by increasing surface area.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 3
    Publication Date: 2015-02-07
    Description: Rectification properties of boron nitride/silicon p-n heterojunction diodes fabricated under low-energy ion impact by plasma-enhanced chemical vapor deposition are studied in terms of the resistive sp 2 -bonded boron nitride (sp 2 BN) interlayer. A two-step biasing technique is developed to control the fraction of cubic boron nitride (cBN) phase and, hence, the thickness of the sp 2 BN interlayer in the films. The rectification ratio at room temperature is increased up to the order of 10 4 at ±10 V of biasing with increasing the sp 2 BN thickness up to around 130 nm due to suppression of the reverse leakage current. The variation of the ideality factor in the low bias region is related to the interface disorders and defects, not to the sp 2 BN thickness. The forward current follows the Frenkel-Poole emission model in the sp 2 BN interlayer at relatively high fields when the anomalous effect is assumed. The transport of the minority carriers for reverse current is strongly limited by the high bulk resistance of the thick sp 2 BN interlayer, while that of the major carriers for forward current is much less affected.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1734-1737 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 11B and 10B magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was conducted to characterize cubic boron nitride films prepared by plasma chemical vapor deposition. Similarities and differences between cubic boron nitride films and polycrystals synthesized at high pressure and high temperature were clarified by chemical shift and linewidth. The same local structure and tetrahedral symmetry of boron atoms in both forms was demonstrated, and a higher defective density appeared to exist in the film form, agreeing well with results from Raman measurements. Noncubic-phase impurities, i.e., amorphous, turbostratic, and hexagonal phases, in films were also detected in 11B MAS NMR spectra, and the possibility of removing these impurities by chemical etching was demonstrated. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flicker noise measurements for n-metal–oxide–semiconductor field-effect transistors have been carried out under a wide range of bias conditions. The experiments show excess noise over an ideal 1/f noise spectrum at around 1–10 kHz frequency range, which is independent of the drain voltage. The origin of the additional noise is the Shockley–Read–Hall generation–recombination process occurring near the drain in the channel. Monte Carlo device simulations confirmed the excess noise origin as well as the observed reduction of its magnitude with increasing gate voltage. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 7627-7633 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotator phase transition in n-alkane was recently found to show a characteristic pattern of preferred growth along the b-axis (shorter axis) of the unit cell. In order to investigate the origin of this anisotropic growth, a pattern formation in n-alkane crystal is studied during the transition between the low temperature orthorhombic (LO) phase and the rotator (R) phase by use of the Monte Carlo method. Of possible factors that will influence the growth pattern, we here concentrate on the mode of chain packing by assuming that the chains have rigid planar zigzag conformation and are placed in a regular orthohexagonal lattice. The herringbone order in the LO phase is found to develop rather quickly resulting characteristic domains with the (100) and (110) boundaries. The domain boundaries run preferentially along the b-axis at lower temperatures and are considered as a stacking fault or antiphase boundary. The transition between the LO phase and the R phase is found to exhibit a characteristic pattern, where the R phase domains grow preferentially along the b-axis. All these behaviors are shown to originate from different energies of the (100) and (110) boundaries. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
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