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  • 1990-1994  (4)
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Material
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Observations of Pc5 micropulsation-related electric field oscillations in the equatorial ionosphere (1994)
    Springer
    Annales geophysicae 12 (1994), S. 565-573 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5○N, 77○E, 0.5○N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (Ap=161). Simultaneous 100-nT-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6○N gm) and at Narsarsuaq, Greenland (70.6○N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730–1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV m−1 and it increases with height, while it is about 1.0 mV m−1 in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brorfelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the associated ionospheric electric field penetrating from high latitudes to the magnetic equator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-0565-7
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Elastic anomalies of barium titanate (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 945-954 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anomalies of the second-, third-, and fourth-order elastic constants have been derived for barium titanate and related compounds for the phase transition from cubic to tetragonal and from the tetragonal to the orthorhombic phases. The equilibrium values of the three components of the order parameter and the strain variables in the two phases have been obtained from the stability conditions. The fluctuations in the order parameter in the two phases have been derived from the Landau–Khalatnikov equations. Expressions have been given for the shift in the zero point energy in the tetragonal and orthorhombic phases, and these are shown to be proportional to (T−Tc)2. The anomalies for all the second-order elastic constants have been derived for both phases, and relations among them have been reported. It is shown that the elastic anomalies suffer a discontinuity at the transition temperature for both the phases. Our expressions give the temperature variation of the third-order elastic and fourth-order elastic constants for the phase transition from the tetragonal to the orthorhombic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354836
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Multinuclear nonmagnetic resonance studies of perfluoro poly ether lubricants (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6161-6161 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Commercial perfluoro poly ethers (PFPE) are available with different backbone structures and end groups and are being used as lubricants for particulate/thin film disks. Very little published information is available other than F-19 spectra for these polymers.1 In this abstract a systematic study was undertaken to study the structure of these PFPE polymers using multinuclear magnetic resonance (NMR). Backbone structural differences of Z. Fomblin, Y. Fomblin, Krytox, and Demnums could be clearly seen from F-19 NMR studies. Number average molecular weight of PFPE polymers was also determined from F-19 NMR and found to be between 2000 and 10 000. C-13 NMR was used to differentiate the end group from backbone structure. Associated proton test (APT) was used to distinguish the primary, secondary, and tertiary carbons. The proton connectivity of end group (e.g., Fomblin AM2001) was studied by two dimensional (2D) proton correlation spectroscopy (COSY). The connectivity of a hydrogen containing end group to the backbone was studied by heteronuclear shift correlation spectroscopy (HCORR). Even though these PFPE polymers have low vapor pressure, a significant amount of lube loss is found over a period of time under HDA (head disk assembly) conditions.The temperature could increase from 25 to 60 °C. Additionally under certain asperity/head interaction conditions the temperature variation could be as high as 300 °C to 500 °C. It is also reported that functionalized polymeric materials (e.g., Krytox 143 AC) can be bonded to magnetic disk surface by applying heat. The effect of temperature on lubricant volatility/stability was studied for AM 2001. The molecular weight of heat treated AM 2001 (90 min at 130 °C) changed from 2100 to 4500. This could be due to preferential volatilization of low molecular weight fragments. NMR analysis showed significant conversion of piperonyl end group to -CH2OH. Thus AM 2001 is not thermally stable. Precipitation was also found to occur when AM 2001 is stored over a period of time. The precipitate is found to be a derivative of 9,10 dihydroanthracene. Unlike other PFPE polymers AM 2001 is found to be sparingly soluble in dichloromethane (contrary to the claim by the manufacturer that it is soluble only in fluorinated solvents) and hence more polar than Fomblin Z-Dol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355443
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  • 4
    Electronic Resource
    Electronic Resource
    Smallness of fermion masses (1992)
    Springer
    The European physical journal 55 (1992), S. 171-174 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss a dynamical mechanism which may yield a natural chiral symmetry for fermions. The small fermion mass generated by various dynamical interactions is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01558302
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    Paper (German National Licenses)
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