arXiv subjects

W. Callum Wareham

Publications and source records attributed to W. Callum Wareham.

4 recordsLinked to original sources

arXiv2026

Optimal Control of Periodic Nonequilibrium Mechanochemical Systems via Automatic Differentiation

Biological molecular machines are mesoscopic systems that act repeatedly and periodically to perform important cellular tasks while contending with strong fluctuations and operating in an overdamped regime. Optimal control theory is a tool that can be used to understand the design principles behind efficient operation of these machines; however, most studies on optimal control of classical mesoscopic systems have focused on control problems that do not repeat periodically. Here, we automatically differentiate Fokker-Planck simulations to design efficient nonequilibrium control strategies for simple models of periodic molecular machines with and without explicit changes in the machine's chemical state. The designed protocols and theoretical analysis provide insight into the design principles governing efficient driving in these nonequilibrium systems. Designed control protocols should seek to reduce mechanical heat by rotating the entire angular probability distribution at a constant speed without changing its shape, and should reduce chemical heat by reducing the proportion of chemical transitions with large heat.

cond-mat.stat-mech↗

arXiv2025

Efficiently driving F$_1$ molecular motor in experiment by suppressing nonequilibrium variation

F$_1$-ATPase (F$_1$) is central to cellular energy transduction. Forcibly rotated by another motor F$_\mathrm{o}$, F$_1$ catalyzes ATP synthesis by converting mechanical work into chemical free energy stored in the molecule ATP. The details of how F$_\mathrm{o}$ drives F$_1$ are not fully understood; however, evaluating efficient ways to rotate F$_1$ could provide fruitful insights into this driving since there is a selective pressure to improve efficiency. Here, we show that rotating F$_1$ with an angle clamp is significantly more efficient than a constant torque. Our experiments, combined with theory and simulation, indicate that the angle clamp significantly suppresses the nonequilibrium variation that contributes to the futile dissipation of input work.

physics.bio-ph↗

arXiv2024

Multiparameter optimal control of F1-ATPase

Biological molecular machines convert free energy between different forms in cells, often at high efficiency. Optimal control theory provides a framework to elucidate design principles governing energetically efficient driving. Here, we use linear-response theory to design efficient protocols exercising dynamic control of trap center and stiffness in a model of driven F1-ATPase. We find that the key design principles of an efficient protocol can be satisfied either by dynamic control of both parameters or by dynamic control of a single parameter and a good static choice for the second. These results illustrate that accessing a new degree of dynamic control provides varying performance improvements in different systems.

physics.bio-ph↗

arXiv2023

Optical conductivity of tilted higher pseudospin Dirac-Weyl cones

We investigate the finite-frequency optical response of systems described at low energies by Dirac-Weyl Hamiltonians with higher pseudospin $\mathcal{S}$ values. In particular, we examine the situation where a tilting term is applied in the Hamiltonian, which results in tilting of the Dirac electronic band structure. We calculate and discuss the optical conductivity for the cases $\mathcal{S}=1$, $3/2$, and $2$, in both two and three dimensions in order to demonstrate the expected signatures in the optical response. We examine both undertilted (type I) and overtilted (type II) as well as the critically-tilted case (type III). Along with the well-known case of $\mathcal{S} =1/2$, a pattern emerges for any $\mathcal{S}$. We note that in situations with multiple nested cones, such as happens for $\mathcal{S}>1$, the possibility of having one cone being type I while the other is type II allows for more rich variations in the optical signature, which we will label as type IV behavior. We also comment on the presence of optical sum rules in the presence of tilting. Finally, we discuss tilting in the $α$-T$_3$ model in two dimensions, which is a hybrid of the $\mathcal{S}=1/2$ (honeycomb lattice) and $\mathcal{S}=1$ (dice or T$_3$ lattice) model with a variable Berry's phase. We contrast this model's conductivity with that of $\mathcal{S}=3/2$ and $\mathcal{S}=2$ as the resultant optical response has some similarities, although there are clear distinguishing features between the these cases.

cond-mat.mes-hall↗