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  • 1990-1994  (151)
  • 1910-1914  (2)
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  • 1
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    Modelling of the electrical resistivity of ferromagnetic and paramagnetic intermetallic compounds (1992)
    Institute of Physics
    Details
    Publication Date: 1992-11-16
    Print ISSN: 0953-8984
    Electronic ISSN: 1361-648X
    Topics: Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 2
    Electronic Resource
    Electronic Resource
    New 8-(trifluoromethyl)-substituted quinolones. The benefits of the 8-fluoro group with reduced phototoxic risk (1992)
    s.l. : American Chemical Society
    Journal of medicinal chemistry 35 (1992), S. 361-367 
    Details
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jm00080a023
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Electromigration failure by shape change of voids in bamboo lines (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1563-1571 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of electromigration-induced voids in narrow, unpassivated aluminum interconnects is examined, using scanning electron microscopy. Some electromigration tests were interrupted several times in order to observe void nucleation, void growth, and finally the failure of the conductor line. It is found that voids which opened the line have a specific asymmetric shape with respect to the electron flow direction. Besides void nucleation and void growth, void shape changes can consume a major part of the lifetime of the conductor line. A first attempt to model these processes on the basis of diffusion along the void surface shows that voids with a noncircular initial shape tend to produce the fatal asymmetry due to electron wind effects, with the anisotropy of surface energy possibly playing only a minor role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357734
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  • 4
    Electronic Resource
    Electronic Resource
    Broadband heterodyne reflectometer at the W7-AS stellarator (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2284-2290 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz in extraordinary mode polarization, has been installed and operated at the Wendelstein 7-AS stellarator for the study of density fluctuations and density profile determination. At 2.5 T it covers the density range between 5×1018 and 5×1019 m−3. The system differs from the usual setup as it combines the advantages of heterodyne detection with broadband capability avoiding the limitations of phase-locked sources and permits the unambiguous determination of the phase delay independent of amplitude fluctuations in the reflected beam. After a first downconversion to an intermediate frequency of about 6 GHz, two additional mixing steps lead to an intermediate frequency of 60 MHz, which carries the phase delay from the plasma as a phase modulation. The phase information is yielded numerically from sin/cos detection at 60 MHz. Due to the balanced detection scheme, the drift as well as the broadband noise of the signal and local oscillators are canceled. The system has a dynamic range of about 60 dB and is within this range almost insensitive to amplitude fluctuations of the reflected beam. Examples are given demonstrating the potential of the system installed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144678
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  • 5
    Electronic Resource
    Electronic Resource
    The Hopkinson effect in BaFe12O19 fine particles (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5148-5148 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The samples are prepared by the coprecipitation method.1 The average particle size is 0.07 μm, which is less than critical single-domain size. Thermomagnetic curves (TMC) of thermally demagnetized samples are studied between 300 and 800 K in external fields up to 8 kOe by VSM. An experimental curve with a well-expressed maximum closely below the Curie temperature (so-called Hopkinson effect) is shown on Fig. 1 (curve 1). Curve 2 on the figure shows a TMC calculated on the basis of the Stoner–Wohlfarth model, following the method described in Ref. 2. There is a good agreement between the experimental and calculated curves. This agreement becomes better when the thermal activation processes are taken into account.3 These results can be considered as an experimental confirmation of the existence of the Hopkinson effect in systems of single-domain particles.〈ks〉
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348106
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  • 6
    Electronic Resource
    Electronic Resource
    Broadband heterodyne reflectometry on the W7-AS stellarator (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4653-4653 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz, has been installed and operated at the W7-AS Stellarator in Garching for the study of density fluctuations and fast density profile determination. Both local (LO) and signal (rf) oscillators can be swept over the whole frequency range. Due to the balanced detection scheme, all drifts, as well as the broadband noise of the BWO (rf and LO) oscillators, are canceled at the different downconversion stages. After installation on W7-AS, first results reproduced the original findings of the former homodyne system [J. Sanchez, H. J. Hartfuss, E. Anabitarte, A. P. Navarro, et al. Nucl. Fusion 30, 2383 (1990)] as well as new results on the radial distribution of density fluctuations have been obtained. A phase drift due to asymmetries in the spectrum around the last IF has been observed; this phenomenon is strongly dependent on the plasma conditions and could be caused by plasma rotation. It is presently under study. The system offers broadband operation together with the possibility to decouple phase and amplitude oscillations of the reflected beam. The high dynamic range (up to 80 dB) is able to overcome the large amplitude oscillations of the reflected beam. The reflectometer described offers a good basis for further developments on large devices, which will require a very high sensitivity due to the long waveguide runs, together with the advantage of the operation in a continuous frequency range and fast sweeping capability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143650
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  • 7
    Electronic Resource
    Electronic Resource
    Amplitude modulation reflectometry for large fusion devices : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4654-4656 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One of the main problems which arises in density profile measurements by reflectometry is the need for continuous tracking of the phase delay; fast density fluctuations and strong modulation on the amplitude of the reflected signal can cause "fringe jumps'' in the phase signal. Amplitude modulation reflectometry performs a time delay measurement by the determination of the phase delay of the modulating envelope of a millimeter wave reflected by the plasma. The phase delays involved are small, the measurement is not affected by the fluctuations and can be directly performed without complicated fringe counters; the method provides a promising possibility for real time determination of the plasma position and density profile. In the present paper the principles of the method are presented as well as the analysis on the effects of phase and amplitude fluctuations, dispersive effects, and accuracy requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143651
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  • 8
    Electronic Resource
    Electronic Resource
    Radial distribution of turbulence correlation lengths obtained by reflectometry in the TJ-I tokamak (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4657-4657 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for determination of radial correlation lengths of the electrostatic turbulence has been developed and applied to the TJ-I tokamak [T. Estrada, J. Sanchez, B. Brañas, and A. P. Navarro, Rev. Sci. Instrum. 61, 3034 (1990)]. The method uses homodyne detection and is based on the slow sweeping of one oscillator while the other remains at fixed frequency. The decay of the coherence can be observed as the distance between the two probing points increases. By the operation in the Q band (33–50 GHz) extraordinary mode, the system reaches most of the plasma radius. Correlation lengths obtained at the edge are compared with those measured at the plasma center. A critical issue for this comparison is the detailed knowledge of the local density gradient. The proposed method can provide the density profile information, avoiding the effect of lost fringes, even in the presence of turbulence. This fact can be used to determine the local density gradient which is needed to evaluate the separation between both reflecting points. Initial experimental results and a discussion on its degree of accuracy is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143652
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  • 9
    Electronic Resource
    Electronic Resource
    Swept frequency reflectometer for correlation studies in the TJ-I tokamak (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 487-491 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An improved correlation reflectometer technique has been developed and implemented on TJ-I to measure the radial correlation lengths of the density turbulence. The method uses homodyne detection and is based on the slow sweeping of one oscillator while the other remains at fixed frequency. The decay of the coherence shows maxima and minima as the distance between the two probing points increases. The maxima correspond to the relevant coherence values. The correlation length for the overall turbulence as well as the correlation length for the different frequency intervals can be directly determined in a single shot. By the operation in the Q-band (33–50 GHz) extraordinary mode, the system reaches most of the plasma radius. Correlation lengths obtained at the edge are compared with those measured at deeper positions in the plasma. The proposed method can provide the values of the differential phase delay along the sweep, avoiding the effect of lost fringes even in the presence of turbulence. This opens the possibility of obtaining the information on the density profile if several channels are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144219
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  • 10
    Electronic Resource
    Electronic Resource
    The conformational problem studied through the torsional Raman spectra of CH2DCH2D, CHD2CHD2, and CH2DCHD2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1575-1590 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The torsional Raman spectra of CH2DCH2D, CHD2CHD2, and CH2DCHD2, recorded with an improved conventional Raman spectrometer, are interpreted here in the frame of an exact rotational–torsional Hamiltonian. The kinetic and potential operators of this Hamiltonian are discussed in detail, showing that the term responsible for the existence of two distinguishable conformers is of kinetic nature. For CH2DCH2D and CHD2CHD2 it is shown how to separate the rotational and the torsional motions by means of an appropriate choice of the molecular axis system. The wave numbers and intensities of both torsional Raman spectra are satisfactorily reproduced within the limits of the experiment with the following effective potential parameters: CH2DCH2D, V3=1002 cm−1, V6=6.0 cm−1; CHD2CHD2, V3=995 cm−1, V6=7.3 cm−1. For CH2DCHD2, only partially tractable in the present approach, an approximate estimate of V3=995 cm−1 has been obtained. Besides the quantitative interpretation of the torsional spectra, a discussion of the main facts of the conformational problem in connection to the spectroscopic observation is presented. In particular, the induced conformational transitions described here may contribute to the understanding of the elementary photoisomerization processes in molecules of the type AX2Y–AX2Y.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465326
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