Experimental Accessibility of Generalized Fluctuation-Dissipation Relations for Nonequilibrium Steady States

We study the fluctuation-dissipation theorem for a Brownian particle driven into a nonequilibrium steady state experimentally. We validate two different theoretical variants of a generalized fluctuation-dissipation theorem. Furthermore, we demonstrate that the choice of variables crucially affects the accuracy of determining the nonequilibrium response from steady state nonequilibrium fluctuations

Relaxation of a Colloidal Particle into a Nonequilibrium Steady State

We study the relaxation of a single colloidal sphere which is periodically driven between two nonequilibrium steady states. Experimentally, this is achieved by driving the particle along a toroidal trap imposed by scanned optical tweezers. We find that the relaxation time after which the probability distributions have been relaxed is identical to that obtained by a steady state measurement. In quantitative agreement with theoretical calculations the relaxation time strongly increases when driving the system further away from thermal equilibrium

Role of Hidden Slow Degrees of Freedom in the Fluctuation Theorem

The validity of the fluctuation theorem for entropy production as deduced from the observation of trajectories implicitly requires that all slow degrees of freedom are accessible. We experimentally investigate the role of hidden slow degrees of freedom in a system of two magnetically coupled driven colloidal particles. The apparent entropy production based on the observation of just one particle obeys a fluctuation theorem-like symmetry with a slope of 1 in the short time limit. For longer times, we find a constant slope, but different from 1. We present theoretical arguments for a generic linear behavior both for small and large apparent entropy production but not necessarily throughout. By fine-tuning experimental parameters, such an intermediate nonlinear behavior can indeed be recovered in our system as well

Role of External Flow and Frame Invariance in Stochastic Thermodynamics

For configurational changes of soft matter systems affected or caused by external hydrodynamic flow, we identify applied work, exchanged heat, and entropy change on the level of a single trajectory. These expressions guarantee invariance of stochastic thermodynamics under a change of frame of reference. As criterion for equilibrium \textit{vs.} nonequilibrium, zero \textit{vs.} nonzero applied work replaces detailed balance \textit{vs.} nonvanishing currents, since both latter criteria are shown to depend on the frame of reference. Our results are illustrated quantitatively by calculating the large deviation function for the entropy production of a dumbbell in shear flow

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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Driven colloidal particles

Die Entwicklung neuer Experimentaltechniken, wie der optischen Pinzette Anfang der 1970er und der Kraftmikroskopie Mitte der 1980er, hatte für das Forschungsgebiet der weichen Materie erhebliche Konsequenzen. Insbesondere biologische und kolloidale Systeme konnten von nun an auf ihren intrinsischen Längenskalen untersucht und manipuliert werden. Infolgedessen rückten diese, bis dahin eher den Biologen und Chemikern vorbehaltenen Domänen, in den Fokus der Forschung vieler physikalischer Arbeitsgruppen. Als ungemein fruchtbar stellte sich dabei das interdisziplinäre Zusammenspiel der Bio-und Kolloidphysik heraus, denn biologische und kolloidale Systeme teilen sich etliche charakteristische Merkmale. Allen voran erstreckt sich ihre Längenskala über den mesoskopischen Bereich und damit von einem Nanometer bis zu einem Mikrometer. Darüber hinaus ist ihr Energieaustausch mit dem sie umgebenden Wärmebad von der Größenordnung der thermischen Energie, sodass wegen ihrer im Allgemeinen geringen Anzahl an Freiheitsgraden Fluktuationen beobachtbar sind. Aufgrund dessen werden beide Arten von Systemen auch der Klasse der kleinen Systeme zugeordnet. Kolloidale Systeme erweisen sich somit als ideale Kandidaten, um gezielt die Eigenschaften von biologischen Systemen zu studieren, zumal ihr Phasenraum mittels optischer Mikroskopie direkt zugänglich ist. In den letzten zwei Jahrzehnten konnten somit vor allem große Fortschritte im Verständnis über die Beschaffenheit von molekularen Motoren und Makromolekülen errungen werden. Wenn nicht schon durch ihre natürliche Umgebung, so werden kleine Systeme spätestens durch eine externe Manipulation aus dem thermodynamischen Gleichgewicht in ein Nichtgleichgewicht getrieben. Im Gegensatz zur Gibbs-Boltzmann-Statistik, die eine vollständige Beschreibung von Gleichgewichtssystemen ermöglicht, mangelt es bislang an einer umfassenden Theorie für Nichtgleichgewichtssysteme. Parallel zu der aufkommenden Vielzahl an bahnbrechenden Experimenten wurden deshalb in den letzten zwei Jahrzehnten vermehrt Anstrengungen unternommen, einen beschreibenden Formalismus für getriebene kleine Systeme zu entwickeln. Als besonders vielversprechender Anwärter gilt dabei die stochastische Energetik oder vielmehr die stochastische Thermodynamik. Innerhalb dieser werden Notationen wie die innere Energie, Arbeit, Wärme und Entropie aufgrund der omnipräsenten Fluktuationen zu stochastischen Größen. Obwohl nun durch eine Verteilung mit endlicher Breite beschrieben, erfüllen sie äquivalent zur klassischen Thermodynamik den ersten und zweiten Hauptsatz. Für stationäre Nichtgleichgewichte, eine spezielle Klasse von Nichtgleichgewichtssystemen, weist die stochastische Thermodynamik über das Konzept der stochastischen Entropie zwei besonders starke Gesetzmäßigkeiten aus. Zum einen das Fluktuationstheorem und zum anderen das Fluktuations-Dissipations-Theorem. Im Zuge der Auseinandersetzung mit diesen bilden kolloidale Teilchen den Mittelpunkt der vorliegenden Arbeit. Im Sinne eines reduktionistischen Ansatzes eignen sie sich im Besonderen, um die Eigenschaften kleiner Systeme zu studieren und die Gesetzmäßigkeiten der stochastischen Thermodynamik zu überprüfen.The development of new experimental techniques, like optical tweezers in the early 1970's or atomic force microscopy in the mid 1980's, was crucial for a deeper understanding of soft matter. Precipitously, scientists became able to investigate and manipulate biological and most notably colloidal systems on their intrinsic length scales. That marked the beginning of a revitalization of bio- and colloidal physics. Since both systems share a number of properties it soon emerged, that the interplay between both fields is particularly promising. First of all, they possess length scales in the range of one nanometer to one micrometer. Second, they exchange energy of the order of the thermal energy with the surrounding heat bath. And third, they generally have a small number of degrees of freedom, so that energy fluctuations must not be neglected. Accordingly, colloidal systems seem to be tailor-made to study the features of biological systems in a controlled manner, especially since their phase space is directly accessible by optical microscopy. Following this interdisciplinary approach, important progress in the perception of molecular motors and macromolecules has been made. Owing to the natural environment these small systems are embedded in, most of them are driven out of thermal equilibrium. Therefore, their behavior cannot be described by the Gibbs-Boltzmann statistics. Although, theoretical predictions which are valid beyond thermal equilibrium have become apparent, a comprehensive theory for small systems driven into non-equilibrium is still lacking. One promising candidate bridging this gap is stochastic energetics or more precisely stochastic thermodynamics. Within its framework, because of the ubiquitous fluctuations, familiar and well-defined thermodynamic quantities like inner energy, work, heat, and entropy have to be replaced by their stochastic counterparts. Consistent with classical thermodynamics, these quantities permit the formulation of the laws of energy conversation and mean entropy increase on a mesoscopic scale. For non-equilibrium steady states, a special class of non-equilibrium situations, even stronger relations originate from the concepts of stochastic thermodynamics, namely the fluctuation theorem and the fluctuation-dissipation theorem. The following thesis attends to colloidal particles driven into non-equilibrium steady states. As paradigmatic model systems they open the possibility for fundamental studies of small driven systems and tests of the concepts of stochastic thermodynamics

Non-equilibrium work distribution for interacting colloidal particles under friction

Weexperimentally investigate the non-equilibrium steady-state distribution of the work done by an external force on a mesoscopic system with many coupled degrees of freedom: a colloidal crystal mechanically driven across a commensurate periodic light field. Since this system mimics the spatiotemporal dynamics of a crystalline surface moving on a corrugated substrate, our results show general properties of the work distribution for atomically flat surfaces undergoing friction.Weaddress the role of several parameters which can influence the shape of the work distribution, e.g. the number of particles used to locally probe the properties of the system and the time interval to measure the work.Wefind that, when tuning the control parameters to induce particle depinning from the substrate, there is an abrupt change of the shape of the work distribution. While in the completely static and sliding friction regimes the work distribution is Gaussian, non-Gaussian tails show up due to the spatiotemporal heterogeneity of the particle dynamics during the transition between these two regimes.publishe

Experiences in aligning WHO SMART guidelines to classification and terminology standards

Objectives Digital adaptation kits (DAKs) distill WHO guidelines for digital use by representing them as workflows, data dictionaries and decision support tables. This paper aims to highlight key lessons learnt in coding data elements of the antenatal care (ANC) and family planning DAKs to standardised classifications and terminologies (CATs).Methods We encoded data elements within the ANC and family planning DAKs to standardised CATs from the WHO CATs and other freely available CATs.Results The coding process demonstrated approaches to refine the data dictionaries and enhance alignment between data elements and CATs.Discussion Applying CATs to WHO clinical and public health guidelines can ensure that recommendations are operationalised in a digital system with appropriate consistency and clarity. This requires a multidisciplinary team and careful review to achieve conceptual equivalence between data elements and standardised terminologies.Conclusion The systematic translation of guidelines into digital systems provides an opportunity for leveraging CATs; however, this approach needs further exploration into its implementation in country contexts and transition into machine-readable components