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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 3 (1993), S. 51-62 
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of a hard oscillator with analytic solution is presented. Its behavior under periodic kicking, for which a closed form stroboscopic map can be obtained, is studied. It is shown that the general structure of such an oscillator includes four distinct regions; the outer two regions correspond to very small or very large amplitude of the external force and match the corresponding regions in soft oscillators (invertible degree one and degree zero circle maps, respectively). There are two new regions for intermediate amplitude of the forcing. Region 3 corresponds to moderate high forcing, and is intrinsic to hard oscillators; it is characterized by discontinuous circle maps with a flat segment. Region 2 (low moderate forcing) has a certain resemblance to a similar region in soft oscillators (noninvertible degree one circle maps); however, the limit set of the dynamics in this region is not a circle, but a branched manifold, obtained as the tangent union of a circle and an interval; the topological structure of this object is generated by the finite size of the repelling set, and is therefore also intrinsic to hard oscillators.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Photochemistry 38 (1987), S. 345-355 
    ISSN: 0047-2670
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 3 (1984), S. 436-446 
    ISSN: 0392-6737
    Keywords: Electronic conduction in metals and alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si sono effettuate misure di resistività, di effetto Hall e di magnetoresistività in alcuni campioni di Fe−Ni, con contenuto di nichel variabile dal 29 al 32% in peso e sottoposti a transformazione martensitica. I risultati sono stati interpretati, da una parte, tenendo conto delle modalità con cui si attua la trasformazione martensitica, diverse nelle leghe al 29 ed al 30% di Ni rispetto a quelle nelle leghe al 31 e al 32% di Ni e, dall’altra, estendendo alle suddette leghe la teoria di Smith e di Berger per l’effetto Hall nelle leghe ferromagnetiche diluite. Confrontando i dati Hall con quelli magnetoresistivi presentati alla maniera di Kohler è stato anche possibile individuare con buona approssimazione il meccanismo di scattering dei portatori di carica prevalente nelle leghe studiate, diverso nelle leghe al 29 ed al 30% di Ni (skew scattering) da quello nelle leghe al 31 e al 32% di Ni (side jump scattering).
    Abstract: Резюме Проведены измерения сопротивления, эффекта Холла и мчгнитосопротивления в образцах сплава Fe−Ni с содержанием никеля от 29 до 32 весовых процентов и подвергнутых мартенситному преобразованию. Предлагается интерпретация полученных результатов, рассматривая оба механизма мартенситного преобразования, которые различаются для сплавов с содержанием никекя 29 и 30% (по весу) и для сплавов с содержанием никеля 31 и 32% (по весу), и используя теории Смитта и Бергера для эффекта Холла в разбавленных ферромагнитных сплавах, которые применяются для описанных выше сплавов. Анализ данных по эффекту Холла, с помощью кривых Кохлера, позволяет понятв механизмы рассеяния носителей заряда, которые превалируют в различных сплавах.
    Notes: Summary Resistivity, Hall effect and magnetoresistivity measurements in Fe−Ni alloy specimens with Ni content ranging from 29 to 32 wt.% and subjected to martensitic transformation have been performed. The results have been interpreted by considering both the mechanisms of the martensitic transformation, different in 29 and 30 wt.% Ni alloys from that in 31 and 32 wt.% Ni ones, and the theories of Smith and Berger on the Hall effect in dilute ferromagnetic alloys, which have been applied to the above-described alloys. The Hall data, analysed by means of Kohler polts, have allowed us to identify the charge carrier scattering mechanisms prevailing in the different alloys,i.e. the skew scattering in 29 and 30 wt.% Ni alloys and the side jump scattering in 31 and 32 wt.% Ni ones.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0649
    Keywords: PACS: 86.70.L; 93.85
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 2 fluxes of the order of 1000, 100, and 10 tonnes/day were measured for Mt. Etna, Stromboli, and Vulcano, respectively.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 5 (1985), S. 473-482 
    ISSN: 0392-6737
    Keywords: Electronic conduction in metals and alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Leghe di ferro-nichel, con contenuto in Ni variabile dal 29% al 32%, sono state irradiate con un fascio di neutroni avente flusso integrale di 3·1018 n cm−2 a 80°C e sono state successivamente sottoposte a trasformazione martensitica mediante raffreddamento. Le misure di resistività, di magnetoresistenza e di effetto Hall compiute sui campioni irradiati consentono di fare l'ipotesi della presenza nella fase supersatura γ di microstrutture ordinate, ricche di Fe o di Ni, oltre ad una fase α addizionale. Dal comportamento dell'effetto Hall anomalo nei campioni irradiati si è valutato il contenuto di Ni presente nelle regioni ordinate.
    Notes: Summary Iron-nickel alloys in the range from 29 to 32 wt.% Ni have been irradiated with an integral flux of 3·1018 n cm−2 and then subjected to martensitic transformation. the resistivity, magnetoresistivity and Hall-effect measurements performed on the irradiated samples allow us to support the formation of iron-rich or nichel-rich ordered microstructures and additional α-phase from the supersaturated γ-matrix. The nickel content of the above-ordered region, is evaluated from the behaviour of the anomalous Hall effect in the irradiated specimens with different composition.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 381 (1979), S. 71-74 
    ISSN: 1432-2013
    Keywords: Muscle Fibre ; Force-Velocity Relation ; Activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The force-velocity relation was determined at preset times after the beginning of the stimulus volley, either at low isometric tensions, during the raising phase of tetanus and the recovery after a quick release imposed at the plateau, or at the steady state. It is concluded that the characteristics of the force-velocity relation may be used to express the actual level of activation at any time during the contractile process and that the mechanical output of frog twitch muscle fibres implies two distinct steps: (i) activation of the contractile machinery; (ii) production of force.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-2013
    Keywords: Muscle contraction ; Force-stiffness relation ; Activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1. Stiffness measurements were performed during the rise, the plateau and the relaxation of tetanic contractions both in whole single muscle fibres and in tendonfree fibre segments under either fixed-end or length-clamp conditions. Fibres were isolated from the tibialis anterior muscle of the frog. Experiments were performed at 2–6° C. Changes in length of tendon-free fibre segments were monitored by means of a “striation follower”, an optoelectronic device which, during contraction, measured sarcomere displacement at the level of two selected regions of a fibre. 2. Fast length perturbations imposed at one tendon end of a fibre during the plateau of tetanic contractions distribute uniformly along its length. 3. During the tetanus rise stiffness led isometric tension in whole fibres under fixed conditions as well as in tendon-free fibre segments under length-clamp conditions. 4. It was confirmed that a significant part of the unlinearity ofT 1 relations is determined by tendon compliance. 5. During the isometric phase of relaxation in fixed-end tetani, the decline of tension led that of stiffness both in whole fibres and in tendon-free fibre segments. 6. It is concluded that the shift observed between stiffness and tension during tetanus rise and relaxation represents a true specific event in the contractile process.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-2013
    Keywords: Frog-heart myocytes ; Force transducer ; Length-ramp generator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An apparatus for studying the mechanics of isolated frog heart myocytes is described. The cells are held horizontal in a through of Ringer solution by means of two suction micropipettes. Myocyte force is measured with an opto-electronic system recording the deflection of the tip of one micropipette, which acts as a cantilever force probe. The force probes are selected for compliance according to the force a myocyte is expected to develop in a given condition, so as to limit myocyte shortening during force development to no more than 1% of the slack cellular length (l 0). The other micropipette, which is stiff relative to the forces measured, is mounted on an electromagnetic-loudspeaker motor by which controlled-velocity length changes, of preset size and in either direction, are imposed on myocytes. The force transducer has a sensitivity of 5–10 mV/nN, with a frequency response of 700–900 Hz in Ringer solution and a resolution of 0.5–1 nN. The motor with a suction micropipette can complete controlled-velocity length ramps within 1.5–2.0 ms, across a range of ±100 μm at a resolution of 8.0 nm. These values correspond, for frog-heart myocytes 200 μm and 400 μm long, to 25%–50% l 0 and 0.002%–0.004% l 0 respectively.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2013
    Keywords: Muscle mechanics ; Muscle activation ; Force-velocity relation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The time course of the contractile process was investigated in the presence of AR-L 115BS, a twitch potentiator which is thought to increase the rate of the Ca2+ binding by troponin and to improve the Ca2+ mobilization from the sarcoplasmic reticulum. AR-L 115BS increased markedly the rate of development of the force-velocity (T-V) relation and of the isometric tetanic tension. The effect on the rate of development of theT-V relation was however substantially more intense than that on the speed of rise of tetanic tension, thus reducing considerably the isometric tension level at which theT-V relation attained its final characteristics. The velocity of shortening under zero load and the degree of curvature of theT-V relation were not affected by AR-L 115BS. These findings support the view that the development of theT-V relation and the rise of the isometric tetanic tension measure the time course of two different processes.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of muscle research and cell motility 11 (1990), S. 371-377 
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Stiffness measurements in activated skeletal muscle fibres are often used as one means of estimating the number of attached crossbridges on the assumption that myofilament compliances do not contribute significantly to the fibre compliance. This assumption was tested by studying the effects of sarcomere length on fibre stiffness in the plateau region of the length-tension diagram (from 1.96 to 2.16μm sarcomere length in the tibialis anterior muscle of the frog). Lengthening of the sarcomere across this region in fact, produces only an increase in the proportion of actin filament free from cross-bridges without altering the amount of effective overlap; no change in fibre stiffness is therefore expected if actin filaments are perfectly rigid. The results show that while tetanic tension remained constant within 1.5%, as the sarcomere length was increased from 1.96 to 2.16μm fibre stiffness decreased by about 4%, indicating that a significant proportion of sarcomere compliance is localized in the actin filaments. A simple model based on the sliding filament theory was used in order to calculate the relative contribution of actin filaments to fibre compliance. In the model it was assumed that fibre compliance resulted from the combination of crossbridge compliance (distributed over the overlap zone) in series with thin filament and tendon compliances. The calculations show that the experimental data could be adequately predicted only assuming that about 19% of sarcomere compliance is due to actin filament compliance.
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