We numerically investigated current-induced dynamical phases of a geometrically constrained magnetic wall (GCMW) confined in a magnetic nano-scale contact. We clarified that the dynamical phase depend on the value of current j and there exist three dynamical phases which are separated by two threshold currents of jc1 and jc2. For j < jc1, we confirmed that the GCMW is deconfined from the contact because of the current induced displacement of the GCMW. On the other hand, we found that the GCMW is confined in the contact for jc1 < j < jc2. For j > jc2, we also found an oscillation where nucleation and annihilation of a magnetic domain are alternately repeated.
The heart of ascidians (marine invertebrate chordates) has a tubular structure, and heartbeats propagate from one end to the other. The direction of pulsation waves intermittently reverses in the heart of ascidians and their relatives; however, the underlying mechanisms remain unclear. We herein performed a series of experiments to characterize the pacemaker systems in isolated hearts and their fragments, and applied a mathematical model to examine the conditions leading to heart reversals. The isolated heart of Ciona robusta autonomously generated pulsation waves at ∼20 to 25 beats min-1 with reversals at ∼1 to 10 min intervals. Experimental bisections of isolated hearts revealed that independent pacemakers resided on each side and also that their beating frequencies periodically changed as they expressed bimodal rhythms, which comprised an ∼1.25 to 5.5 min acceleration/deceleration cycle of a beating rate of between 0 and 25 beats min-1. Only fragments including 5% or shorter terminal regions of the heart tube maintained autonomous pulsation rhythms, whereas other regions did not. Our mathematical model, based on FitzHugh-Nagumo equations applied to a one-dimensional alignment of cells, demonstrated that the difference between frequencies expressed by the two independent terminal pacemakers determined the direction of propagated waves. Changes in the statuses of terminal pacemakers between the excitatory and oscillatory modes as well as in their endogenous oscillation frequencies were sufficient to lead to heart reversals. These results suggest that the directions of pulsation waves in the Ciona heart reverse according to the changing rhythms independently expressed by remotely coupled terminal pacemakers.
The mechanisms driving the collective movement of cells remain poorly understood. To contribute toward resolving this mystery, a model was formulated to theoretically explore the possible functions of polarized cell-cell adhesion in collective cell migration. The model consists of an amoeba cell with polarized cell-cell adhesion, which is controlled by positive feedback with cell motion. This model cell has no persistent propulsion and therefore exhibits a simple random walk when in isolation. However, at high density, these cells acquire collective propulsion and form ordered movement. This result suggests that cell-cell adhesion has a potential function, which induces collective propulsion with persistence.
Nitrided InAs quantum dots (QDs) have been shown to suppress In-segregation in QDs and achieve emission at 1.3 mum. Effects of strain on structural and optical properties of QDs have been demonstrated through transmission electron microscope and photoluminescence analyses
In this study, we examine the emergence of cell flow induced by a tension gradient on a tissue interface, as in the case of the Marangoni flow at liquid interfaces. We consider the molecular density polarity of the heterophilic adhesion between tissues as the origin of the tension gradient. Applying the cellular Potts model, we demonstrate that polarization in concentrations (i.e., intracellular localization) of heterophilic adhesion molecules can induce cell flows similar to the conventional Marangoni flow. In contrast to the conventional Marangoni flow, this flow is oriented in the direction opposite to that of the tension gradient. The optimal range of adhesion strength for the existence of this flow is also identified.
ABSTRACT The heart of ascidians, marine invertebrate chordates, exhibits a tubular structure, and heartbeats propagate from one end to the other. The direction of pulsation waves intermittently reverses in the heart of ascidians and their relatives; however, the underlying mechanisms remain unclear. We herein performed a series of experiments to characterize the pacemaker systems in isolated hearts and their fragments and applied a mathematical model to examine the conditions leading to heart reversals. The isolated heart of Ciona sufficiently performed heart reversals, and experimental bisections of isolated hearts revealed that independent pacemakers resided on each side and also that their beating frequencies periodically changed as they expressed bimodal rhythms. Only fragments including 5% or shorter terminal regions of the heart tube maintained autonomous pulsation rhythms, whereas other regions did not. Our mathematical model, based on FitzHugh-Nagumo equations applied to a one-dimensional alignment of cells, demonstrated that the difference between frequencies expressed by the two independent terminal pacemakers determined the direction of propagated waves. Changes in the statuses of the terminal pacemakers between the excitatory and oscillatory modes as well as in their endogenous oscillation frequencies were sufficient to lead to heart reversals. These results suggest that the directions of pulsation waves in the Ciona heart reverse according to the changing rhythms independently expressed by remotely coupled terminal pacemakers. Summary statement Pulsation waves traveling along the heart tube of the ascidian Ciona intermittently reverse because of autonomous and periodical changes in beating frequencies at a pair of terminal pacemakers.
