Publishing type：Research paper (scientific journal)   Publisher：EPL  

Synchronisability of limit cycle oscillators has been measured by the width of the synchronous frequency band, known as the Arnold tongue, concerning external forcing. We clarify a fundamental limit on maximizing this synchronisability within a specified extra low power budget, which underlies an important and ubiquitous problem in nonlinear science related to an efficient synchronisation of weakly forced nonlinear oscillators. In this letter, injection-locked Class-E oscillators are considered as a practical case study, and we systematically analyse their power consumption; our observations demonstrate the independence of power consumption in the oscillator from power consumption in the injection circuit and verify the dependency of power consumption in the oscillator solely on its oscillation frequency. These systematic observations, followed by the mathematical optimisation establish the existence of a fundamental limit on synchronisability, validated through systematic circuit simulations. The results offer insights into the energetics of synchronisation for a specific class of injection-locked oscillators.

DOI： 10.1209/0295-5075/ad4414

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DOI： 10.1093/pcp/pcae026

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Circadian rhythms are biological rhythms with a period of approximately 24 h that persist even under constant conditions without daily environmental cues. The molecular circadian clock machinery generates physiological rhythms, which can be transmitted into the downstream output system. Owing to the stochastic nature of the biochemical reactions and the extracellular environment, the oscillation period of circadian rhythms exhibited by individual organisms or cells is not constant on a daily basis with variations as high as 10%, as reflected by the coefficient of variation. Although the fluctuations in the circadian rhythm are measured through a reporter system such as bioluminescence or fluorescence, which is an example of output systems, experimentally confirming whether the fluctuations found in the reporter system are the same as those in the circadian clock is challenging. This study investigated a coupled system of a circadian clock and its output system numerically and analytically, and then compared the fluctuations in the oscillation period of the two systems. We found that the amount of fluctuations in the output system is smaller than that in the circadian clock, assuming the degradation rate of the molecules responsible for the output system is a typical value for protein degradation. The results indicate that the output system can improve the accuracy of the circadian rhythm without the need for any denoising processes.

DOI： 10.1016/j.jtbi.2023.111621

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press ({OUP})  

<jats:title>Abstract</jats:title>
<jats:p>The circadian clock allows plants to anticipate and adapt to periodic environmental changes. Organ- and tissue-specific properties of the circadian clock as well as shoot-to-root circadian signaling have been reported. While this long-distance signaling is thought to coordinate physiological functions across tissues, little is known about the feedback regulation of root clock on the shoot clock in the hierarchical circadian network. Here, we show that the plant circadian clock conveys circadian information between shoots and roots through sucrose and K+. We also demonstrate that K+ transport from roots suppress the variance of period length in shoots and then improve the accuracy of shoot circadian clock. Sucrose measurements and qPCR showed that root sucrose accumulation was regulated by the circadian clock. Furthermore, root circadian clock genes, including PSEUDO-RESPONSE REGULATOR7 (PRR7), were regulated by sucrose, suggesting the involvement of sucrose from the shoot in the regulation of root clock gene expression. Therefore, we performed time-series measurements of xylem sap and micrografting experiments using prr7 mutants and showed that root PRR7 regulates K+ transport and suppresses variance of period length in the shoot. Our modeling analysis supports the idea that root-to-shoot signaling contributes to the precision of the shoot circadian clock. We performed micrografting experiments that illustrated how root PRR7 plays key roles in maintaining the accuracy of shoot circadian rhythms. We thus present a novel directional signaling pathway for circadian information from roots to shoots and propose that plants modulate physiological events in a timely manner through various timekeeping mechanisms.</jats:p>

DOI： 10.1093/pcp/pcad003

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Other Link： https://academic.oup.com/pcp/article-pdf/64/3/352/49533067/pcad003.pdf

Language：Others   Publishing type：Research paper (scientific journal)  

We propose a method for designing optimal external forcings of injection-locked oscillators. This method enables to maximize the locking range of general injection-locked oscillators under certain practical constraints that encompass the power, magnitude, or area of forcing waveforms. Here, as a case study, we focus on a class-E oscillator in the injection-locked mode, for which we obtain the following systematic results. First, by using the proposed method, the optimal waveform of external forcings is obtained analytically under three different constraints, i.e., the power-(i.e., root mean square-) reduced, magnitude-reduced, and area-reduced constraints. Second, through systematic circuit simulations, those predicted optimal forcings are verified to outperform any other forcings. Third, circuits experiments confirm that the theoretical predictions and the circuit simulation results are correct and consistent, regarding lock range maximization. These findings result in a first demonstration of locking range maximization for practical electrical oscillators.

DOI： 10.1109/tcsi.2019.2960847

Language：English   Publishing type：Research paper (scientific journal)  

We investigate the formation of synchronization patterns in an oscillatory nickel electrodissolution system in a network obtained by superimposing local and global coupling with three electrodes. We explored the behavior through numerical simulations using kinetic ordinary differential equations, Kuramoto type phase models, and experiments, in which the local to global coupling could be tuned by cross resistances between the three nickel wires. At intermediate coupling strength with predominant global coupling, two of the three oscillators, whose natural frequencies are closer, can synchronize. By adding even a relatively small amount of local coupling (about 9%-25%), a spatially organized partially synchronized state can occur where one of the two synchronized elements is in the center. A formula was derived for predicting the critical coupling strength at which full synchronization will occur independent of the permutation of the natural frequencies of the oscillators over the network. The formula correctly predicts the variation of the critical coupling strength as a function of the global coupling fraction, e.g., with local coupling the critical coupling strength is about twice than that required with global coupling. The results show the importance of the topology of the network on the synchronization properties in a simple three-oscillator setup and could provide guidelines for decrypting coupling topology from identification of synchronization patterns.

DOI： 10.1063/1.5012520

Language：English   Publishing type：Research paper (scientific journal)  

Two kinds of oscillation precision are investigated for complex oscillatory dynamical systems under action of noise. The many-cycle precision determined by the variance of the times needed for a large number of cycles is closely related to diffusion of the global oscillation phase and provides an invariant property of a system. The single-cycle precision given by the variance in durations of single cycles is sensitive to the choice of an output variable and output checkpoint; it can be improved by an appropriate selection of them. A general analysis of the precision properties based on the Floquet perturbation theory is performed and analytical predictions are verified in numerical simulations of a model oscillatory genetic network.

DOI： 10.1103/PhysRevE.93.062206

Language：English   Publishing type：Research paper (scientific journal)  

Period variability, quantified by the standard deviation (SD) of the cycle-to-cycle period, is investigated for noisy phase oscillators. We define the checkpoint phase as the beginning or end point of one oscillation cycle and derive an expression for the SD as a function of this phase. We find that the SD is dependent on the checkpoint phase only when oscillators are coupled. The applicability of our theory is verified using a realistic model. Our work clarifies the relationship between period variability and synchronization from which valuable information regarding coupling can be inferred.

DOI： 10.1103/PhysRevE.87.030901

Language：English   Publishing type：Research paper (scientific journal)  

We investigate the synchronous dynamics of Kuramoto oscillators and van der Pol oscillators on Watts-Strogatz type small-world networks. The order parameters to characterize macroscopic synchronization are calculated by numerical integration. We focus on the difference between frequency synchronization and phase synchronization. In both oscillator systems, the critical coupling strength of the phase order is larger than that of the frequency order for the small-world networks. The critical coupling strength for the phase and frequency synchronization diverges as the network structure approaches the regular one. For the Kuramoto oscillators, the behavior can be described by a power-law function and the exponents are obtained for the two synchronizations. The separation of the critical point between the phase and frequency synchronizations is found only for small-world networks in the theoretical models studied.

DOI： 10.1016/j.physd.2009.04.002

Language：English   Publishing type：Research paper (scientific journal)  

Spectral properties of the Laplacian operator are studied numerically on the Watts-Strogatz-type small-world networks. The spectra on small-world networks are shown to have the characteristics that (i) the gap between the lowest frequency mode (Goldstone mode) and the second lowest frequency mode is small in contrast to that of random networks and (ii) the average participation ratio is as small as that of random networks. We also find that the highest frequency is essentially determined by the largest coordination degree.

DOI： 10.1143/JPSJ.73.3294

Language：English   Publishing type：Research paper (scientific journal)  

Percolation in random graphs is studied numerically. The strength of the largest cluster, the mean cluster size and the number of clusters are examined and the critical exponents of these quantities are shown to coincide with the classical values for percolation.

DOI： 10.1143/JPSJ.70.2485

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5

Language：Japanese  

Country：Japan  

Event date： 2019.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Snowbird, Utah, USA   Country：United States  

Event date： 2018.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Cambridge University, Cambridge, UK   Country：United Kingdom  

Event date： 2017.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan