168 research outputs found
Quantum asymptotic phase reveals signatures of quantum synchronization
We propose a fully quantum-mechanical definition of the asymptotic phase for
quantum nonlinear oscillators. The asymptotic phase function of the system is
introduced in terms of the eigenoperator of the adjoint Liouville superoperator
associated with the fundamental frequency. This quantum asymptotic phase yields
appropriate phase values of the system even in the strong quantum regime, while
reproducing the conventional asymptotic phase in the semiclassical regime. We
analyze a quantum van der Pol oscillator with Kerr effect and show that several
dominant eigenoperators with different fundamental frequencies exist in the
strong quantum regime. Using the quantum asymptotic phase functions with
respective fundamental frequencies, we reveal that the multiple phase locking
of the system with a harmonic drive at several different frequencies, an
explicit quantum signature observed only in the strong quantum regime, can be
interpreted as synchronization on a torus rather than a simple limit cycle.Comment: 9 pages, 4 figures + Supplemental Material (6 pages 1 figure
Phase dynamics of noise-induced coherent oscillations in excitable systems
Noise can induce coherent oscillations in excitable systems without periodic
orbits. Here, we establish a method to derive a hybrid system approximating the
noise-induced coherent oscillations in excitable systems and further perform
phase reduction of the hybrid system to derive an effective,
dimensionality-reduced phase equation. We apply the reduced phase model to a
periodically forced excitable system and two-coupled excitable systems, both
undergoing noise-induced oscillations. The reduced phase model can
quantitatively predict the entrainment of a single system to the periodic force
and the mutual synchronization of two coupled systems, including the phase
slipping behavior due to noise, as verified by Monte Carlo simulations. The
derived phase model gives a simple and efficient description of noise-induced
oscillations and can be applied to the analysis of more general cases
NANOS2 promotes male germ cell development independent of meiosis suppression
AbstractNANOS2 is an RNA-binding protein essential for fetal male germ cell development. While we have shown that the function of NANOS2 is vital for suppressing meiosis in embryonic XY germ cells, it is still unknown whether NANOS2 plays other roles in the sexual differentiation of male germ cells. In this study, we addressed the issue by generating Nanos2/Stra8 double knockout (dKO) mice, whereby meiosis was prohibited in the double-mutant male germ cells. We found that the expression of male-specific genes, which was decreased in the Nanos2 mutant, was hardly recovered in the dKO embryo, suggesting that NANOS2 plays a role in male gene expression other than suppression of meiosis. To investigate the molecular events that may be controlled by NANOS2, we conducted a series of microarray analyses to search putative targets of NANOS2 that fulfilled 2 criteria: (1) increased expression in the Nanos2 mutant and (2) the mRNA associated with NANOS2. Interestingly, the genes predominantly expressed in undifferentiated primordial germ cells (PGCs) were significantly selected, implying the involvement of NANOS2 in the termination of the characteristics of PGCs. Furthermore, we showed that NANOS2 is required for the maintenance of mitotic quiescence, but not for the initiation of the quiescence in fetal male germ cells. These results suggest that NANOS2 is not merely a suppressor of meiosis, but instead plays pivotal roles in the sexual differentiation of male germ cells
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