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  • Atrial fibrillation  (1)
  • PACS. 75.50.Lk Spin glasses and other random magnets – 75.10.Nr Spin-glass and other random models  (1)
  • 1
    Electronic Resource
    Electronic Resource
    A microscopic mechanism for rejuvenation and memory effects in spin glasses (2001)
    Springer
    The European physical journal 22 (2001), S. 203-211 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.50.Lk Spin glasses and other random magnets – 75.10.Nr Spin-glass and other random models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Aging in spin glasses (and in some other systems) reveals astonishing effects of `rejuvenation and memory' upon temperature changes. In this paper, we propose microscopic mechanisms (at the scale of spin-spin interactions) which can be at the origin of such phenomena. Firstly, we recall that, in a frustrated system, the effective average interaction between two spins may take different values (possibly with opposite signs) at different temperatures. We give simple examples of such situations, which we compute exactly. Such mechanisms can explain why new ordering processes (rejuvenation) seem to take place in spin glasses when the temperature is lowered. Secondly, we emphasize the fact that inhomogeneous interactions do naturally lead to a wide distribution of relaxation times for thermally activated flips. `Memory spots' spontaneously appear, in the sense that the flipping time of some spin clusters becomes extremely long when the temperature is decreased. Such memory spots are capable of keeping the memory of previous ordering at a higher temperature while new ordering processes occur at a lower temperature. After a qualitative discussion of these mechanisms, we show in the numerical simulation of a simplified example that this may indeed work. Our conclusion is that certain chaos-like phenomena may show up spontaneously in any frustrated and inhomogeneous magnetic system, without impeding the occurrence of memory effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510170128
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  • 2
    Electronic Resource
    Electronic Resource
    Detection of atrial-flutter and atrial-fibrillation waveforms by fetal magnetocardiogram (1992)
    Springer
    Medical & biological engineering & computing 40 (1992), S. 213-217 
    Details
    ISSN: 1741-0444
    Keywords: Fetal magnetocardiogram ; Atrial flutter ; Atrial fibrillation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Two cases of fetal tachycardia are reported: atrial flutter and fibrillation. The waveforms from each case were detected by fetal magnetocardiograms (FMCGs) using a 64-channel superconducting quantum interference device (SQUID) system. Because the magnitude of supraventricular arrhythmia signals is very weak, two subtraction methods were used to detect the fetal MCG waveforms: subtraction of the maternal MCG signal, and subtraction of the fetal QRS complex signal. It was found that atrial-flutter waveforms showed a cyclic pattern and that atrial-fibrillation waveforms showed f-waves with a random atrial rhythm. Fast Fourier transform analysis determined the main frequency of the atrial flutter to be about 7 Hz, and the frequency distribution of atrial fibrillation consisted of small, broad peaks. To visualise the current pattern, current-arrow maps, which simplify the observation of pseudo-current patterns in fetal hearts, of the averaged atrial flutter and fibrillation waveforms were produced. The map of the atrial flutter had a circular pattern, indicating a re-entry circuit, and the map of the atrial fibrillation indicated one wavelet, which was produced by a micro-re-entry circuit. It is thus concluded that an FMCG can detect supraventricular arrhythmia, which can be characterised by re-entry circuits, in fetuses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02348127
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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