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  • 1995-1999  (6)
  • Human  (3)
  • Non-Gibbsian measures  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Pathological behavior of renormalization-group maps at high fields and above the transition temeprature (1995)
    Springer
    Journal of statistical physics 79 (1995), S. 969-992 
    Details
    ISSN: 1572-9613
    Keywords: Non-Gibbsian measures ; real-space renormalization ; complete analyticity ; majority-rule ; decimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We show that decimation transformations applied to high-q Potts models result in non-Gibbsian measures even for temperatures higher than the transition temperature. We also show that majority transformations applied to the Ising model in a very strong field at low temperatures produce non-Gibbsian measures. This shows that pathological behavior of renormalization-group transformations is even more widespread than previous examples already suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02181211
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Control strategies for finger movement during touch-typing The role of the extrinsic muscles during a keystroke (1998)
    Springer
    Experimental brain research 121 (1998), S. 1-6 
    Details
    ISSN: 1432-1106
    Keywords: Key words EMG ; Finger ; Typing ; Force ; Neural control ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A single keystroke during touch-typing is a rapid, goal-directed motion of the fingertip which consists of two single-direction movements. The neural control and the role of the finger extrinsic musculature during typing have not yet been explained. The fingertip motion and force, and the intramuscular electromyographic (EMG) activity (fine-wire) of the index finger extrinsic musculature were measured during touch-typing by ten experienced typists. The motions and forces were repeatable qualitatively across keystrokes. A three-burst EMG pattern was observed during a single keystroke. The three bursts were: (1) a burst of extensor activity lifted the finger before the keystroke; (2) a burst of flexor activity followed while the fingertip was moving downward; and (3) a second burst of extensor activity occurred as the fingertip reached the end of key travel. The timing of the third burst suggests the role of the extensors is to remove the fingertip from the keyswitch rather than stop the downward motion of the finger. The collision with the end of key travel stops the downward finger motion. The timing of the finger flexor EMG activity, burst 2, suggests that the flexor contraction principally overcomes the activation force of the keyswitch rather than accelerates the finger downward as expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050430
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of the muscarinic antagonist scopolamine on regional cerebral blood flow during the performance of a memory task (1995)
    Springer
    Experimental brain research 104 (1995), S. 337-348 
    Details
    ISSN: 1432-1106
    Keywords: Scopolamine ; Memory ; Positron emission tomography ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Scopolamine, a muscarinic antagonist, impairs memory performance in both humans and animals. In this study, repeated measurements of regional cerebral blood flow (rCBF) were made in normal volunteers whilst performing auditory verbal memory tasks, before and after the administration of scopolamine (0.4 mg s.c.) or placebo. Compared to placebo, scopolamine increased blood flow in the lateral occipital cortex bilaterally and the left orbitofrontal region. Scopolamine decreased rCBF in the region of the right thalamus, the precuneus and the right and left lateral premotor areas. Scopolamine attenuated memory-task-induced increases of rCBF in the left and right prefrontal cortex and the right anterior cingulate region. These data suggest that acute blockade of cholinergic neurotransmission affects diverse brain areas, including components of the visual and motor systems, and, in addition, modulates memory task activations at distinct points in a distributed network for memory function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242019
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Frequency peaks of tremor, muscle vibration and electromyographic activity at 10 Hz, 20 Hz and 40 Hz during human finger muscle contraction may reflect rhythmicities of central neural firing (1997)
    Springer
    Experimental brain research 114 (1997), S. 525-541 
    Details
    ISSN: 1432-1106
    Keywords: Key words Tremor ; Electromyogram ; Muscle vibration ; Frequency analysis ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The output from the central nervous system to muscles may be rhythmic in nature. Previous recordings investigating peripheral manifestations of such rhythmic activity are conflicting. This study attempts to resolve these conflicts by employing a novel arrangement to measure and correlate rhythms in tremor, electromyographic (EMG) activity and muscle vibration sounds during steady index finger abduction. An elastic attachment of the index finger to a strain gauge allowed a strong but relatively unfixed abducting contraction of the first dorsal interosseous (1DI). An accelerometer attached to the end of the finger recorded tremor, surface electrodes over 1DI recorded EMG signals and a heart-sounds monitor placed over 1DI recorded vibration. This arrangement enabled maintenance of a constant overall muscle contraction strength while still allowing measurement of the occurrence of tremulous movements of the finger. Ten normal subjects were studied with the index finger first extended at rest and then contracting 1DI to abduct the index finger against three different steady forces up to 50% of maximal voluntary contraction (MVC). Power spectral analysis of tremor, EMG activity and muscle vibration signals each revealed three frequency peaks occurring together at around 10 Hz, 20 Hz and 40 Hz. Coherence analysis showed that the same three peaks were present in the three signals. Phase analysis indicated a fixed time lag of tremor behind EMG of around 6.5 ms. This is compared with previous measurements of electromechanical delay. Other experiments indicated that the three peaks were of central nervous origin. Introducing mechanical perturbations or extra loading to the finger and making recordings under partial anaesthesia of the hand and forearm demonstrated preservation of all the peaks, suggesting that they did not originate from mechanical resonances or peripheral feedback loop resonances. It is concluded that, at least for a small hand muscle, there exist not one but a number of separate peak frequencies of oscillation during active contraction, and that these oscillations reflect synchronization of motor units at frequencies determined within the central nervous system. It is proposed that the multiple oscillations may be a means of frequency coding of motor commands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005662
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    (Almost) Gibbsian Description of the Sign Fields of SOS Fields (1998)
    Springer
    Journal of statistical physics 92 (1998), S. 353-368 
    Details
    ISSN: 1572-9613
    Keywords: Non-Gibbsian measures ; weak versus strong non-Gibbsianness ; robustly non-Gibbsian measures ; projected Gibbs measures ; cluster models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An example is presented of a measure on a lattice system which has a measure zero set of points (configurations) where some conditional probability can be discontinuous, but does not become a Gibbs measure under decimation (or other) transformations. We also discuss some related issues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1023024218192
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Ill-defined block-spin transformations at arbitrarily high temperatures (1996)
    Springer
    Journal of statistical physics 83 (1996), S. 761-765 
    Details
    ISSN: 1572-9613
    Keywords: Non-Gibbsian measures ; block-spin map pathology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Examples are presented of block-spin transformations which map the Gibbs measures of the Ising model in two or more dimensions at temperature intervals extending to arbitrarily high temperatures onto non-Gibbsian measures. In this way we provide the first example of this kind of pathology for very high temperatures, and as a corollary also the first example of such a pathology happening at a critical point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02183748
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    Paper (German National Licenses)
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