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Enhanced diffusion, swelling and slow reconfiguration of a single chain in non-Gaussian active bath
A prime example of non-equilibrium or active environment is a biological
cell. In order to understand in-vivo functioning of biomolecules such as
proteins, chromatins, a description beyond equilibrium is absolutely necessary.
In this context, biomolecules have been modeled as Rouse chains in Gaussian
active bath. However, these non-equilibrium fluctuations in biological cells
are non-Gaussian. This motivates us to take a Rouse chain subjected to a series
of pulses of force with finite duration, mimicking run and tumble motion of a
class of micro-organisms. Thus by construction, this active force is
non-Gaussian. Our analytical calculations show that the mean square
displacement (MSD) of center of mass (COM) grows faster and even shows
superdiffusive behavior at higher activity, supporting recent experimental
observation on active enzymes (A.-Y. Jee, Y.-K. Cho, S. Granick, and T. Tlusty,
Proc. Natl. Acad. Sci. 115, 10812 (2018)), but chain reconfiguration is slower.
The reconfiguration time of a chain with N monomers scales as N^sigma, where
the exponent sigma=2. In addition, the chain swells. We compare this
activity-induced swelling with that of a Rouse chain in a Gaussian active bath.
In principle, our predictions can be verified by future single molecule
experiments
Entropy production and work fluctuation relations for a single particle in active bath
A colloidal particle immersed in a bath of bacteria is a typical example of a
passive particle in an active bath. To model this, we take an overdamped
harmonically trapped particle subjected to a thermal and a non-equilibrium
noise arising from the active bath. The harmonic well can be attributed to a
laser trap or to the small amplitude motion of the sedimented colloid at the
bottom of the capillary. In the long time, the system reaches a non-equilibrium
steady state that can be described by an effective temperature. By adopting
this notion of effective temperature, we investigate whether fluctuation
relations for entropy hold. In addition, when subjected to a deterministic time
dependent drag, we find that transient fluctuation theorem for work cannot be
applied in conventional form. However, a steady state fluctuation relation for
work emerges out with a renormalized temperature
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