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  • 1
    Electronic Resource
    Electronic Resource
    Detailed dynamics of electron beams self-trapped and accelerated in a self-modulated laser wakefield (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4739-4749 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron beam generated in a self-modulated laser-wakefield accelerator is characterized in detail. A transverse normalized emittance of 0.06 π mm mrad, the lowest ever for an electron injector, was measured for 2 MeV electrons. The electron beam was observed to have a multicomponent beam profile and energy distribution. The latter also undergoes discrete transitions as the laser power or plasma density is varied. In addition, dark spots that form regular modes were observed in the electron beam profile. These features are explained by analysis and test particle simulations of electron dynamics during acceleration in a three-dimensional plasma wakefield. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873761
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  • 2
    Electronic Resource
    Electronic Resource
    A connection between the Camassa–Holm equations and turbulent flows in channels and pipes (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 2343-2353 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we discuss recent progress in using the Camassa–Holm equations to model turbulent flows. The Camassa–Holm equations, given their special geometric and physical properties, appear particularly well suited for studying turbulent flows. We identify the steady solution of the Camassa–Holm equation with the mean flow of the Reynolds equation and compare the results with empirical data for turbulent flows in channels and pipes. The data suggest that the constant α version of the Camassa–Holm equations, derived under the assumptions that the fluctuation statistics are isotropic and homogeneous, holds to order α distance from the boundaries. Near a boundary, these assumptions are no longer valid and the length scale α is seen to depend on the distance to the nearest wall. Thus, a turbulent flow is divided into two regions: the constant α region away from boundaries, and the near wall region. In the near wall region, Reynolds number scaling conditions imply that α decreases as Reynolds number increases. Away from boundaries, these scaling conditions imply α is independent of Reynolds number. Given the agreement with empirical and numerical data, our current work indicates that the Camassa–Holm equations provide a promising theoretical framework from which to understand some turbulent flows. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870096
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  • 3
    Electronic Resource
    Electronic Resource
    Study of efficiency enhancement through magnetic field profiling in cyclotron autoresonance maser (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 959-964 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phase control and the increase of the available free energy are two basic mechanisms that enhance the efficiency of a cyclotron autoresonance maser (CARM) device through linearly tapering the externally applied magnetic field. Based on these two mechanisms, a nonlinearly profiled magnetic field, as formed by adding a positively three-quarter sine profile onto a uniform magnetic field, applied on CARM is proposed in this study. Numerical results show that applications of the nonlinearly profiled magnetic field can raise the efficiency of CARM to around 50% over a wide range of frequency detunings. The reduction of efficiency sensitivity to the beam velocity spread can also be achieved for the increase of the available free energy with the use of the nonlinearly profiled magnetic field. Furthermore, the nonlinearly profiled magnetic field is also far more effective and practical than the linearly tapered magnetic field in efficiency enhancement. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871375
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  • 4
    Electronic Resource
    Electronic Resource
    Flow visualization of Taylor-mode breakup of a viscous liquid jet (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 1331-1341 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We recently reported a new spray technique called ultrasound-modulated two-fluid (UMTF) atomization and the pertinent "resonant liquid capillary wave (RLCW) theory" based on linear models of Taylor-mode breakup of capillary waves. In this article, flow visualizations of liquid jets near the nozzle tip are presented to verify the central assumption of the RLCW theory that the resonant liquid capillary wave in UMTF atomization is initiated by the ultrasound at the nozzle tip. Specifically, a bright band beneath the nozzle tip was seen in ultrasonic and UMTF atomization separately, but not in two-fluid atomization. The bright band can be attributed to scattering of laser light sheet by the capillary waves generated by the ultrasound on the intact liquid jet. As the capillary wave travels downstream in the direction of airflow, it is amplified by the air blowing around it and eventually collapsed into drops. Therefore, the jet breakup time can be determined by dividing the measured band length with the capillary wave velocity. The breakup times thus determined for water and glycerol/water jets are twice the values predicted by the modified Taylor's model with a sheltering parameter, and are one order of magnitude shorter than those in conventional two-fluid atomization. Furthermore, the images of the spray in the proximity of the nozzle tip obtained by 30 ns laser pulses are consistent with the drop sizes obtained 2.3–6 cm downstream from the nozzle tip by 13 s time average of continuous laser light. Also reported in this article is the good agreement between the measured viscosity effects on the drop-size and size distribution in UMTF atomization and those on the relative amplitude growth rates of capillary waves at different wavelengths predicted by Taylor's model as a result of its inclusion of higher order terms other than the first in viscosity. These new findings have led to the conclusion that UMTF atomization occurs via Taylor-mode breakup of capillary waves; secondary atomization and drop coalescence are negligible. Further, UMTF atomization offers a means to control the drop-size and size distribution of two-fluid atomization for uniform drop formation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869998
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  • 5
    Electronic Resource
    Electronic Resource
    Controllable fabrication of bent near-field optical fiber probes by electric arc heating (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3843-3845 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the construction of a high voltage electric arc puller for controllable fabrication of bent near-field optical fiber probes. Various probes with bent angles ranging from 30° to 75° and bent lengths between 600 and 900 μm were successfully produced. The tip diameters achieved are between 100 and 200 nm. These bent type probes can be made into cantilevered probes that can be used for any dynamic mode atomic force microscope, and make the construction of a scanning near-field optical microscope easily attainable.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149188
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  • 6
    Electronic Resource
    Electronic Resource
    Construction of a dual mode scanning near-field optical microscope based on a tapping mode atomic force microscope (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3840-3842 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present the modification of a commercial tapping mode atomic force microscope into a reflection and transmission dual mode scanning near-field optical microscope. In the configuration, the normal force detection unit is replaced by a shear force detection module and an interfacing circuit. The tip-sample distance control is therefore similar to tapping mode operation. Detection of the near-field signals is based on photodiodes and the lock-in technique, and the resolutions obtained for the topography and the near-field signal are around 80 and 150 nm, respectively.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149187
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  • 7
    Electronic Resource
    Electronic Resource
    A low coherence "white light'' interferometric sensor for eye length measurement (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 5464-5468 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article discusses the use of low coherence interferometric techniques, employing the so-called "white light interferometer,'' for axial eye length measurement. This system utilizes two Michelson interferometers, each of which locates one of the surfaces of the eye, the cornea and the retina, respectively, and thus a simultaneous determination of the two surface positions of the eye gives the value of eye length. The experimental results carried out on a simulated eye are presented, showing that the proposed system is simple, easy to align, suitable for measuring different kinds of eyes, tolerant to transverse eye movement, and worth further exploration. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146070
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  • 8
    Electronic Resource
    Electronic Resource
    An analytical moderate inversion drain current model for polycrystalline silicon thin-film transistors considering deep and tail states in the grain boundary (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1961-1967 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper presents an analytical moderate inversion drain current model for polycrystalline silicon thin-film transistors based on localized deep and tail states in the grain boundary regions. As verified by the published data, using the analytical model, that as compared to the subthreshold region in the bulk iliccon metal-oxide-silicon (MOS) devices, the less steep slope of the moderate inversion region has been explained as due to the lowering in the potential barrier height. In addition, the analytical model provides an accurate prediction that with a smaller average trap state density from the grain boundary regions, the polysilicon thin-film transistor shows a sharper moderate inversion behavior. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361046
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  • 9
    Electronic Resource
    Electronic Resource
    Nanocomposite Sm2Co17/Co permanent magnets by mechanical alloying : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5964-5966 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanically alloyed magnets SmCox (x=6.0–11.0) have been prepared using starting materials of commercial SmCo5 and Co powders. X-ray diffraction data indicate that the equilibrium Sm2Co17 phase can be achieved in a nanocomposite Sm2Co17/Co system at x=8.5–11.0, while a Sm2Co17/SmCo5 structure occurs at x=6.0–8.0. The best magnetic properties obtained at x=10.0 are as follows: (BH)max=10.2 MGOe, Br=9.4 kG, Hc=4.0 kOe, and S=0.82. Wohlfarth's remanence analysis indicates that the high remanence can be attributed to the intergranular interaction between neighboring cobalt and Sm2Co17 grains. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362121
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  • 10
    Electronic Resource
    Electronic Resource
    Structural and magnetic studies of Er2Fe17−xMxCy (M=Ga and Al) compounds : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5533-5535 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of Ga and Al substitution for Fe on the structural and magnetic properties of the Er2Fe17−xMxCy (M=Ga, Al; x=0–4, y=0–2) compounds was investigated. It was found that Ga is superior to Al in stabilizing the single-phase Er2Fe17−xMxCy compounds. The hexagonal Th2Ni17-type structure persisted in almost all alloys with the exception of Er2Fe13Ga4C and Er2Fe13Ga4C2. These two compounds exhibited a rhombohedral Th2Zn17 structure. Both the Curie temperature and magnetization can be enhanced with a certain amount of Ga or Al substitution. But they decreased almost monotonically with the increase of Ga or Al content in Er2Fe17−xMxCy (x(approximately-greater-than)1, y(approximately-greater-than)0). The spin reorientation temperature, Tsr, was influenced by both carbon interstitial and Ga or Al substitution for Fe and ascribed to the increase of the c-axis uniaxial anisotropy of the Er3+ sublattice by the modification of electron structure around it. The highest Tsr of 241 K appears in the compound Er2Fe14Ga3C. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362300
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