115 research outputs found

    Circadian clocks optimally adapt to sunlight for reliable synchronization

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    Circadian oscillation provides selection advantages through synchronization to the daylight cycle. However, a reliable clock must be designed through two conflicting properties: entrainability to synchronize internal time with periodic stimuli such as sunlight, and regularity to oscillate with a precise period. These two aspects do not easily coexist because better entrainability favors higher sensitivity, which may sacrifice the regularity. To investigate conditions for satisfying the two properties, we analytically calculated the optimal phase-response curve with a variational method. Our result indicates an existence of a dead zone, i.e., a time period during which input stimuli neither advance nor delay the clock. A dead zone appears only when input stimuli obey the time course of actual solar radiation but a simple sine curve cannot yield a dead zone. Our calculation demonstrates that every circadian clock with a dead zone is optimally adapted to the daylight cycle.Comment: 24 pages, 7 figure

    Fluctuating noise drives Brownian transport

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    The transport properties of Brownian ratchet was studied in the presence of stochastic intensity noise (SIN) in both overdamped and underdamped regimes. In the overdamped case, analytical solution using the matrix continued fraction method revealed the existence of a maximum current when the noise intensity fluctuates on intermediate time scale regions. Similar effects were observed for the underdamped case by Monte Carlo simulations. The optimal time-correlation for the Brownian transport coincided with the experimentally observed time-correlation of the extrinsic noise in Esherichia coli gene expression and implied the importance of environmental noise for molecular mechanisms.Comment: 22 pages, 8 figure

    Enhanced entrainability of genetic oscillators by period mismatch

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    Biological oscillators coordinate individual cellular components so that they function coherently and collectively. They are typically composed of multiple feedback loops, and period mismatch is unavoidable in biological implementations. We investigated the advantageous effect of this period mismatch in terms of a synchronization response to external stimuli. Specifically, we considered two fundamental models of genetic circuits: smooth- and relaxation oscillators. Using phase reduction and Floquet multipliers, we numerically analyzed their entrainability under different coupling strengths and period ratios. We found that a period mismatch induces better entrainment in both types of oscillator; the enhancement occurs in the vicinity of the bifurcation on their limit cycles. In the smooth oscillator, the optimal period ratio for the enhancement coincides with the experimentally observed ratio, which suggests biological exploitation of the period mismatch. Although the origin of multiple feedback loops is often explained as a passive mechanism to ensure robustness against perturbation, we study the active benefits of the period mismatch, which include increasing the efficiency of the genetic oscillators. Our findings show a qualitatively different perspective for both the inherent advantages of multiple loops and their essentiality.Comment: 28 pages, 13 figure

    Dynamics of a levitated microparticle in vacuum trapped by a perfect vortex beam : three-dimensional motion around a complex optical potential

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    We trap a single silica microparticle in a complex three dimensional optical potential with orbital angular momentum in vacuum. The potential is formed by the generation of a ``perfect vortex' in vacuum which, upon propagation, evolves to a Bessel light field. The optical gradient and scattering forces interplay with the inertial and gravitational forces acting on the trapped particle, including the rotational degrees of freedom. As a result the particle undergoes a complex trajectory, part of which is rotational motion in the plane of the "perfect vortex". As the particle explores the whole three dimensional volume and not solely restricted to one anchor point, we are able to determine the three dimensional optical potential in situ by tracking the particle. This represents the first demonstration of trapping a microparticle within a complex three dimensional optical potential in vacuum. This may open up new perspectives in levitated optomechanics with particle dynamics on complex trajectories.PostprintPeer reviewe

    Rotation of two trapped microparticles in vacuum : observation of optically mediated parametric resonances

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    Funding: Engineering and Physical Sciences Research Council (EPSRC) (EP/J01771X/1).We demonstrate trapping and rotation of two mesoscopic particles in vacuum using a spatial-light-modulator-based approach to trap more than one particle, induce controlled rotation of individual particles, and mediate interparticle separation. By trapping and rotating two vaterite particles, we observe intensity modulation of the scattered light at the sum and difference frequencies with respect to the individual rotation rates. This first demonstration of optical interference between two microparticles in vacuum leads to a platform to potentially explore optical binding and quantum friction effects.PostprintPeer reviewe
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