Universal bound on the efficiency of molecular motors

The thermodynamic uncertainty relation provides an inequality relating any mean current, the associated dispersion and the entropy production rate for arbitrary non-equilibrium steady states. Applying it here to a general model of a molecular motor running against an external force or torque, we show that the thermodynamic efficiency of such motors is universally bounded by an expression involving only experimentally accessible quantities. For motors pulling cargo through a viscous fluid, a universal bound for the corresponding Stokes efficiency follows as a variant. A similar result holds if mechanical force is used to synthesize molecules of high chemical potential. Crucially, no knowledge of the detailed underlying mechano-chemical mechanism is required for applying these bounds.Comment: Invited contribution to proceedings of STATPHYS26, Lyo

Universal bounds on current fluctuations

For current fluctuations in non-equilibrium steady states of Markovian processes, we derive four different universal bounds valid beyond the Gaussian regime. Different variants of these bounds apply to either the entropy change or any individual current, e.g., the rate of substrate consumption in a chemical reaction or the electron current in an electronic device. The bounds vary with respect to their degree of universality and tightness. A universal parabolic bound on the generating function of an arbitrary current depends solely on the average entropy production. A second, stronger bound requires knowledge both of the thermodynamic forces that drive the system and of the topology of the network of states. These two bounds are conjectures based on extensive numerics. An exponential bound that depends only on the average entropy production and the average number of transitions per time is rigorously proved. This bound has no obvious relation to the parabolic bound but it is typically tighter further away from equilibrium. An asymptotic bound that depends on the specific transition rates and becomes tight for large fluctuations is also derived. This bound allows for the prediction of the asymptotic growth of the generating function. Even though our results are restricted to networks with a finite number of states, we show that the parabolic bound is also valid for three paradigmatic examples of driven diffusive systems for which the generating function can be calculated using the additivity principle. Our bounds provide a new general class of constraints for nonequilibrium systems.Comment: 19 pages, 13 figure

Classical Pendulum Clocks Break the Thermodynamic Uncertainty Relation

The thermodynamic uncertainty relation expresses a seemingly universal trade-off between the cost for driving an autonomous system and precision in any output observable. It has so far been proven for discrete systems and for overdamped Brownian motion. Its validity for the more general class of underdamped Brownian motion, where inertia is relevant, was conjectured based on numerical evidence. We now disprove this conjecture by constructing a counterexample. Its design is inspired by a classical pendulum clock, which uses an escapement to couple the motion of an oscillator to another degree of freedom (a "hand") driven by an external force. Considering a thermodynamically consistent, discrete model for an escapement mechanism, we first show that the oscillations of an underdamped harmonic oscillator in thermal equilibrium arc sufficient to break the thermodynamic uncertainty relation. We then show that this is also the case in simulations of a fully continuous underdamped system with a potential landscape that mimics an escaped pendulum

Thermodynamic cost for precision of general counting observables

We analytically derive universal bounds that describe the trade-off between thermodynamic cost and precision in a sequence of events related to some internal changes of an otherwise hidden physical system. The precision is quantified by the fluctuations in either the number of events counted over time or the times between successive events. Our results are valid for the same broad class of nonequilibrium driven systems considered by the thermodynamic uncertainty relation, but they extend to both time-symmetric and asymmetric observables. We show how optimal precision saturating the bounds can be achieved. For waiting time fluctuations of asymmetric observables, a phase transition in the optimal configuration arises, where higher precision can be achieved by combining several signals.Comment: 18 pages, 6 figure

Autonomous engines driven by active matter: Energetics and design principles

Because of its nonequilibrium character, active matter in a steady state can drive engines that autonomously deliver work against a constant mechanical force or torque. As a generic model for such an engine, we consider systems that contain one or several active components and a single passive one that is asymmetric in its geometrical shape or its interactions. Generally, one expects that such an asymmetry leads to a persistent, directed current in the passive component, which can be used for the extraction of work. We validate this expectation for a minimal model consisting of an active and a passive particle on a one-dimensional lattice. It leads us to identify thermodynamically consistent measures for the efficiency of the conversion of isotropic activity to directed work. For systems with continuous degrees of freedom, work cannot be extracted using a one-dimensional geometry under quite general conditions. In contrast, we put forward two-dimensional shapes of a movable passive obstacle that are best suited for the extraction of work, which we compare with analytical results for an idealised work-extraction mechanism. For a setting with many noninteracting active particles, we use a mean-field approach to calculate the power and the efficiency, which we validate by simulations. Surprisingly, this approach reveals that the interaction with the passive obstacle can mediate cooperativity between otherwise noninteracting active particles, which enhances the extracted power per active particle significantly.Comment: 21 pages, 8 figure

Hochschulinterne Instrumente zur Qualitätssicherung aus der Sicht von Hochschulangehörigen und aus der Perspektive der Programmakkreditierung

Das Projekt "Bologna (aus)gewertet" (SUCHANEK, PIETZONKA, KÜNZEL & FUTTERER, 2012a; 2012b; 2013; PIETZONKA, 2012) hatte eine Bestandsaufnahme zur aktuellen Umsetzung der Studienreform an den niedersächsischen Hochschulen zum Ziel. Zur Ergebnissicherung wurden sämtliche Auflagen aus den Akkreditierungsverfahren ausgewertet und Hochschulmitarbeiter/innen und Studierendenvertreter/innen zu ihren Einschätzungen und Erfahrungen gezielt befragt. Im vorliegenden Beitrag werden die Ergebnisse des o. g. Projekts für die hochschulinterne Qualitätssicherung sowie deren Implikationen isoliert und ausführlich dargestellt. Die Ergebnisse zeigen teilweise erhebliche Mängel und Schwächen bei der Durchführung und Auswertung der angewendeten Verfahren sowie bei der Verwendung der gewonnenen Daten auf. Die Programmakkreditierung ist nicht in der Lage, die Wirksamkeit der hochschulinternen Qualitätssicherung hinreichend sicherzustellen. 22.03.2013 | Manuel Pietzonka (Hannover

Digitalisierung von Hochschulen als Change-Management-Projekt. Organisationspsychologische Praxisempfehlungen

Der Beitrag verfolgt das Ziel, organisationspsychologisch begründete Empfehlungen für die Umsetzung von hochschulischen Veränderungsprozessen im Bereich Digitalisierung für die Praxis zu formulieren. Damit soll der Nutzen der Berücksichtigung entsprechender Prinzipien für die Digitalisierung von Hochschulen aufgezeigt werden. (HoF/Text übernommen