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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental 120-turn thin-film inductive heads have been built. The key features of this head are the 6-μm pitch helical coils and an omega-shaped, planar yoke structure having dual easy axes. Hardbaked photoresist insulator layers are used to encapsulate the yoke and to smooth out the wafer surface topography. Micro-Kerr studies show that the easy axis remains in the transverse direction in the yokes after multiple anneals. The P1/G/P2 is 3.8/0.3/3.8 μm, and the yoke length is close to 1 mm. The helical coils were built with a novel process that combines yoke/stud coplating and a photoresist planarization process. The coil resistance is 68Ω and the inductance is 5.5 μH. The yoke saturates at 5 mA. The heads were tested over disks having Mrt of 2.5 memu/cm2 and Hc of 1500 Oe. The write threshold current is 5.3 mA (peak-to-peak) and the overwrite is 30 dB. The isolated pulse amplitude Vpp is 10.3 μV/(TwV), where track width Tw is in μm and the linear velocity V in m/s.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2770-2776 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electromechanical response of a polyurethane elastomer was investigated at room temperature and in the temperature range near its glass transition. It was found that the Maxwell stress contribution to the strain response can be significant at temperatures higher than the glass transition temperature. In addition, the material exhibits a very high electrostrictive coefficient Q, about two orders of magnitude higher than that of polyvinylidene fluoride. It was also found that in a polymeric material, the chain segment motions can be divided into those related to the polarization response and those related to the mechanical response and the overlap between the two yields the electromechanical response of the material. In general, the activation energies for different types of motion can be different, resulting in different relaxation times in the dielectric, the elastic compliance, and the electrostrictive data, as observed in the polyurethane elastomer investigated. The experimental results indicate that at the temperatures investigated, the activation energy for the mechanical related segment motions is higher than that of nonmechanical related segment motions. © 1997 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 310-318 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The accelerating and focusing wake fields that can be excited by a short laser pulse in a hollow underdense plasma are examined. The evacuated channel in the plasma serves as an optical fiber to guide the laser pulse over many Rayleigh lengths. Wake fields excited by plasma current at the edge of the channel extend to the center where they may be used for ultrahigh gradient acceleration of particles over long distances. The wake field and equilibrium laser profiles are found analytically and compared to two-dimensional (2-D) particle-in-cell (PIC) simulations. Laser propagation is simulated over more than ten Rayleigh lengths. The accelerating gradients on the axis of a channel of radius c/ωp are of order of one-half of the gradients in a uniform plasma. For present high-power lasers, multi-GeV/m gradients are predicted. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3148-3162 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The modulational instability and collapse of waves in the vicinity of the lower-hybrid resonance including both magnetosonic and lower-hybrid waves are investigated by analytical and numerical methods. The mechanism leading to the modulational instability is the nonlinear coupling of lower-hybrid waves with the much lower-frequency quasineutral density perturbations via the ponderomotive force. The result is a filamentation of the high-frequency field producing elongated, cigar-shaped nonlinear wave packets aligned along the magnetic field with the plasma expelled outside (cavities). The analytical self-similar solutions describing cavity collapse are obtained and compared with the results of numerical simulation for both two- and three-dimensional cavity geometries. It is shown that in three-dimensional solutions the transverse, with respect to the magnetic field, contraction remains prevailing. The possibility of ion acceleration as the result of the lower-hybrid collapse is discussed and detailed comparison is made with the observations of the phenomena in the auroral ionosphere.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1384-1389 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The plasma physics associated with intense electron and positron beams in high-energy colliders is discussed. The focusing and plasma oscillation of these beams are studied in the presence of an externally supplied plasma (a plasma lens) and in the self-consistent fields of the interpenetrating beams. A plasma lens can provide strong focusing of a beam by shielding the beam's radial space-charge electric field and allowing it to self-pinch in its self-generated azimuthal magnetic field. The focusing force of a plasma lens can be equivalent to quadrupole magnet strengths of the order of hundreds of MG/cm. Theoretical and computational work characterizing the aberrations and final spot sizes possible with plasma lenses is presented. Furthermore, when the e+ and e− beams overlap at the interaction point (i.e., collide), they behave (temporarily) as a two-component plasma. The self-pinching or disruption of one beam by another in the e+e− plasma is modeled analytically and with two-dimensional particle-in-cell simulations.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 2480-2483 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A bimorph based dilatometer has been developed which enables one to characterize the electric field induced strain response in the out-of-plane direction in thin and soft free standing polymer film samples conveniently over a relatively wide frequency range (1 Hz to 1 kHz). The test results demonstrate that the newly developed dilatometer is capable of detecting displacement down to sub-angstrom range. The agreement between the test results from the bimorph dilatometer, the results from a laser dilatometer, and the model analysis indicates that the device can indeed be used reliably for these measurement with high sensitivity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1630-1633 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the dielectric properties of Zn1−xMnxSe(0≤x≤0.78) epilayers, by capacitance and dissipation factor measurements at temperature 5 K〈T〈475 K and frequency 20 Hz〈f〈100 kHz. A Debye-like relaxational contribution to the dielectric response is observed, which requires the presence of charge redistribution. The relaxation is found to be a thermally activated process, and the activation energies obtained from the dissipation factor and capacitance are in good agreement. The capacitance is found to increase with a decrease in test frequency. From our results it is established that the dielectric response is caused by carrier hopping among structural defects. A monotonic variation is found in the relationship between the activation energy and the Mn concentration. This monotonic variation is interpreted in terms of the four-center model, in which the number of Mn atoms appearing in the nearest-neighbor sites of the defect can have four possible configurations. The measured defect behavior reflects the overall average of all energy levels involved in the center, and the result is weighted by the relative concentrations. © 1999 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 439-441 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the study on the dielectric properties of C60 films by means of capacitance and dissipation factor measurements at temperatures between 5 and 325 K. In addition to the structural phase transition at 260 K, we have observed a clear anomaly at T=90 K, which did not show up in previous dielectric studies. This result confirms the fact that a glass transition exists due to the freezing in of orientational disorder in C60. A Debye-like relaxation in the dielectric response has also been observed, and the relaxation rate is thermally activated with an energy of about 277 meV, which is in good agreement with that obtained from other measurements. © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1607-1609 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Capacitance and dissipation factor measurements of the dielectric properties on C60 thin films are performed at a temperature between 275 and 470 K. A Debye-like relaxation in the dielectric response has been observed, and the relaxation rate is thermally activated with an energy of about 467 meV which is different from the value 277 meV obtained at a temperature below 260 K. Remarkably, both the capacitance and dissipation factor curves as a function of temperature have a pronounced feature at 435 K. It confirms the fact that above 400 K a phase transition does occur in the C60 crystal except for that detected around 260 K. We interpreted the phase transition at 435 K in terms of the disappearance of one of the spherical harmonics Ylm that describe the orientational density distribution of the C60 molecules. © 1999 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 386-388 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that the large electrical-field-induced strain response observed in certain polyurethane elastomers is a thin-film effect. Based on the frequency dispersion of the strain response in samples with different thicknesses and the thermally stimulated discharge current on samples with different processing conditions, we suggest that the charge injection, an interface effect, which results in a nonuniform space-charge distribution and, hence, a nonuniform electric-field distribution across the sample thickness, is responsible for the enhanced electromechanical response in thin polyurethane samples. © 1997 American Institute of Physics.
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