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  • 1
    Electronic Resource
    Electronic Resource
    A new flow regime in a Taylor–Couette flow (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 3233-3235 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this Brief Communication, we report a new finding on a Taylor–Couette flow in which the outer cylinder is stationary and the inner cylinder is accelerated linearly from rest to a desired speed. The results show that when the acceleration (dRe/dt) is higher than a critical value of about 2.2 s−1, there exists a new flow regime in which the flow pattern shows remarkable resemblance to regular Taylor vortex flow but is of shorter wavelength. However, when the acceleration is lower than 2.2 s−1, a wavy flow is found to occur for the same Reynolds number range. To our knowledge, this is probably the first time that such a phenomenon has been observed. For completeness, the case of a decelerating cylinder is also investigated, and the results are found to be almost the same. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869851
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  • 2
    Electronic Resource
    Electronic Resource
    Active control of 2/1 magnetic islands in a tokamak : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1855-1863 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Closed and open loop control techniques were applied to growing m/n=2/1 rotating islands in wall-stabilized plasmas in the High Beta Tokamak-Extended Pulse (HBT-EP) [J. Fusion Energy 12, 303 (1993)]. HBT-EP combines an adjustable, segmented conducting wall (which slows the growth or stabilizes ideal external kinks) with a number of small (6° wide toroidally) driven saddle coils located between the gaps of the conducting wall. Two-phase driven magnetic island rotation control from 5 to 15 kHz has been demonstrated powered by two 10 MW linear amplifiers. The phase instability has been observed and is well modeled by the single-helicity predictions of nonlinear Rutherford island dynamics for 2/1 tearing modes including important effects of ion inertia and finite Larmor radius, which appear as a damping term in the model equations. The closed loop response of active feedback control of the 2/1 mode at moderate gain was observed to be in good agreement with the theory. Suppression of the 2/1 island growth has been demonstrated using an asynchronous frequency modulation drive which maintains the inertial flow damping of the island by application of rotating control fields with frequencies alternating above and below the natural mode frequency. This frequency modulation control technique was also able to prevent disruptions normally observed to follow giant sawtooth crashes in the plasma core. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872856
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  • 3
    Electronic Resource
    Electronic Resource
    Observation of wall stabilization and active control of low-n magnetohydrodynamic instabilities in a tokamak (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1926-1934 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The High Beta Tokamak-Extended Pulse (HBT-EP) experiment [J. Fusion Energy 12, 303 (1993)] combines an internal, movable conducting wall with a high-power, modular saddle coil system to provide passive and active control of long wavelength magnetohydrodynamic (MHD) instabilities. Systematic adjustment of the radial position, b, of the conducting wall elements in relation to the surface of the plasma (minor radius a) resulted in the suppression of β-limiting disruptions for discharges in which b/a〈1.2 and a positive plasma current ramp was maintained. Conducting wall stabilization of kink instabilities was observed in discharges with strong current ramps and in plasmas with β values near the Troyon stability boundary. The frequency of slowly growing modes that persisted in wall-stabilized discharges was controlled by applying oscillating m=2, n=1 resonant magnetic perturbations. A compact, single-phase saddle coil system permitted modulation of the rotation velocity of internal m/n=2/1 instabilities by a factor of 2. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871988
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  • 4
    Electronic Resource
    Electronic Resource
    Crystallographic transformations of rapidly quenched Nd10Fe90−xTix (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4226-4231 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural transformations from amorphous, metastable-to-equilibrium phases during annealing treatment of rapidly quenched Nd10Fe90−xTix (x=0, 2, 4, 6, 8, and 10) alloys have been studied systematically. By means of ac initial susceptibility and x-ray diffraction, a CaCu5-type metastable phase was observed for 0≤x≤10 as the crystallization of the amorphous alloys occurs below 700 °C. The CaCu5-type structure transforms into a TbCu7-type one with increasing the annealing temperature (above 700 °C). These melt-spun alloys have different structures including Th2Zn17 type for 0≤x≤4 and TbCu7 and ThMn12 types for 6≤x≤10, when annealed at high temperature (above 1000 °C). Nitrogenation was carried out at 400 °C for 10 h. Both Nd(Fe,Ti)5 and its nitride are soft-magnetic phases, like Nd(Fe,Ti)7 and Nd2(Fe,Ti)17. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290736
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  • 5
    Electronic Resource
    Electronic Resource
    Remanence enhancement and coercivity in two-phase CoPt bulk magnets (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 304-307 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effect of the atomic disorder–order transformation on remanence enhancement and coercivity in CoPt ingots by isothermal annealing at various temperatures well below the transformation point. The relative amount of the low-temperature hard-magnetic face-centered-tetragonal (fct) phase precipitated in the high-temperature magnetically soft face-centered-cubic (fcc) phase was determined by means of x-ray diffraction. As a function of annealing temperature, the mean grain size and the relative amount of the fct phase increase at the cost of the fcc phase. These changes were followed by means of magnetic measurements. We observed a continuous increase in coercivity with increasing annealing temperature, eventually reaching a maximum. The Kneller–Hawig model was used to explain the occurrence of remanence enhancement and the continuously changing degree of exchange coupling between the magnetically soft and hard phases. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1418419
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  • 6
    Electronic Resource
    Electronic Resource
    Cold neutron microprobe for materials analysis using tapered capillary optics (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3247-3253 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A prototype monolithic capillary lens for focusing neutrons produced by thermally drawing straight multicapillary bundles has been characterized with cold neutrons, and gives an intensity gain of a factor of 25 at a focal distance of 8 mm, over the focal spot area of width 87 μm. This is over an order of magnitude smaller in area than for the multifiber capillary lens. The spatial resolution available with the lens has been tested with prompt gamma measurements on slivers of dysprosium. Background problems that can affect the spatial resolution of measurements taken at the focal position of the lens are addressed. The boron glass of the tapered monolithic lens provides good shielding from unfocused neutrons in the vicinity of the lens focus. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288262
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  • 7
    Electronic Resource
    Electronic Resource
    Neutron focusing optic for submillimeter materials analysis (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3399-3402 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A neutron lens constructed with polycapillary glass fibers is used to focus a 50×45 mm2 beam exiting a cold neutron guide onto a spot of 0.53 mm (full width at half maximum) with a current density gain of 80. The characteristics of the lens are presented. This lens is designed to enhance the detection limit and lateral resolution for prompt gamma activation analysis using cold neutron beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144513
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  • 8
    Electronic Resource
    Electronic Resource
    A comparison of experiment and simulation for neutron guidance through glass polycapillary fibers (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3252-3257 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The transmission efficiency and exit divergence of cold neutrons guided through straight and bent polycapillary fibers made of borosilicate glass have been measured. Experimental results have been compared with a ray-tracing simulation. Good agreement between the two has been obtained by considering in the simulation only reflectivity losses due to absorption. Therefore, we conclude that the influence of other loss mechanisms on reflectivity, such as surface roughness and waviness, are not significant compared with absorption loss for the borosilicate polycapillary fibers we have measured. Using the same simulation program, we have characterized the performance of a neutron focusing lens placed at the end of a 58Ni guide tube and optimized for a neutron spectrum from a cold source at a temperature of 65 K. An order of magnitude increase in neutron intensity within a submillimeter focal spot is predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144337
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  • 9
    Electronic Resource
    Electronic Resource
    Structure and magnetic properties of mechanical alloyed Nd–Fe–Ti compounds and their nitrides : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5525-5527 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Nd–Fe–Ti intermetallic compounds with a ThMn12 structure have been successfully prepared by mechanical alloying and then annealed. It has been found that the phase of the hexagonal TbCu7 structure is formed in Nd8Fe84Ti8 mechanical alloy powders annealed at temperatures ranging from 650 to 850 °C. With an increase in the annealing temperature Ta, the metastable TbCu7 structure transforms into a ThMn12 structure at Ta=900 °C. Consequently, the Curie temperature increases from 180 °C of TbCu7 structure at Ta=650 to 300 °C of ThMn12 structure at Ta=1050 °C. In the series of NdxFe92−xTi8 annealed at 960 °C for 30 min, it has been observed that the ThMn12 structure exists only over the range of compositions of 5≤x〈11, and the structure of the type Th2Zn17 is formed for x≥11. All the compounds are nitrited at 400 °C for 15 h, and the Curie temperatures are raised from 400 to 450 °C. The Nd9Fe83Ti8 powder, annealed at 960 °C for 30 min, and nitrided at 400 °C for 15 h, has a coercivity iHc=2.3 kOe. The low coercivity perhaps mainly results from an excessive growth of α-Fe grains due to the high annealing temperature necessary for forming the hard magnetic phase Nd(Fe,Ti)12Nδ. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362298
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  • 10
    Electronic Resource
    Electronic Resource
    Columnar epitaxy of PtSi on Si (111) (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 686-688 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Columnar grains of PtSi surrounded by high quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and Pt in an 8:1 ratio on Si(111) substrates heated to 610–810 °C. The areal density of columns varies from 120 to 3.8 μm−2, and layers with thicknesses from 100 nm to 1 μm have been demonstrated. This result is similar to that found previously for CoSi2 (a nearly lattice-matched cubic-fluorite crystal) on Si(111), in spite of the orthorhombic structure of PtSi. The PtSi grains are also epitaxial and have one of three variants of the relation defined by PtSi(010)//Si(111), with PtSi[001]//Si〈110〉.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103592
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