Finite size scaling of current fluctuations in the totally asymmetric exclusion process

We study the fluctuations of the current J(t) of the totally asymmetric exclusion process with open boundaries. Using a density matrix renormalization group approach, we calculate the cumulant generating function of the current. This function can be interpreted as a free energy for an ensemble in which histories are weighted by exp(-sJ(t)). We show that in this ensemble the model has a first order space-time phase transition at s=0. We numerically determine the finite size scaling of the cumulant generating function near this phase transition, both in the non-equilibrium steady state and for large times.Comment: 18 pages, 11 figure

Leertechnologie in de lage landen

Op het terrein van onderwijs en ICT investeren onderwijsinstellingen, bedrijven, brancheorganisaties en overheden in het bewerkstelligen van leertechnologie-afspraken. Het doel van die gezamenlijke inspanning is om het onderwijs te kunnen verbeteren en efficiënter te maken. Gedeelde opvattingen, vastgelegd in specificaties en standaarden, maken uitwisseling van gegevens mogelijk tussen uiteenlopende systemen. Dat biedt grote kansen voor onderwijsvernieuwing. Basisgegevens hoeven slechts op één plek onderhouden te worden, maar zijn toch voor iedere instelling bruikbaar: eenmaal gemaakte lesmaterialen kunnen in verschillende leeromgevingen worden ingezet, studenten kunnen zich flexibel inschrijven voor cursussen aan verschillende instellingen terwijl hun studievoortgang zonder probleem wordt geregistreerd. Deze processen zijn essentiële voorwaarden voor een duurzame ontwikkeling van e-learning in de Lage Landen. Als samenwerkingsorganisatie voor het hoger onderwijs in Nederland neemt SURF deel aan de mars naar standaardisatie binnen de leertechnologie. De SURF SiX expertisegroep, een Special Interest Group van SURF, onderneemt activiteiten om realisatie en gebruik van leertechnologie-afspraken te bevorderen die voor het Nederlandse hoger onderwijs bruikbaar en nuttig zijn en die blijvende aansluiting van Nederland bij internationale e-learningontwikkelingen garanderen. Met dit boek geeft SURF SiX een brede groep onderwijsontwikkelaars en geïnformeerde eindgebruikers inzicht in de huidige Nederlandse situatie op het gebied van leertechnologie-afspraken. Daarnaast wil dit boek laten zien dat leertechnologiespecificaties en standaarden meerwaarde hebben.Stichting Sur

SU8 etch mask for patterning PDMS and its application to flexible fluidic microactuators.

Over the past few decades, polydimethylsiloxane (PDMS) has become the material of choice for a variety of microsystem applications, including microfluidics, imprint lithography, and soft microrobotics. For most of these applications, PDMS is processed by replication molding; however, new applications would greatly benefit from the ability to pattern PDMS films using lithography and etching. Metal hardmasks, in conjunction with reactive ion etching (RIE), have been reported as a method for patterning PDMS; however, this approach suffers from a high surface roughness because of metal redeposition and limited etch thickness due to poor etch selectivity. We found that a combination of LOR and SU8 photoresists enables the patterning of thick PDMS layers by RIE without redeposition problems. We demonstrate the ability to etch 1.5-μm pillars in PDMS with a selectivity of 3.4. Furthermore, we use this process to lithographically process flexible fluidic microactuators without any manual transfer or cutting step. The actuator achieves a bidirectional rotation of 50° at a pressure of 200 kPa. This process provides a unique opportunity to scale down these actuators as well as other PDMS-based devices.BG is a Doctoral Fellow of the Research Foundation—Flanders (F.W.O.), Belgium. MDV acknowledges support from the ERC starting grant HIENA (no. 337739)

Aging Is Accompanied by a Blunted Muscle Protein Synthetic Response to Protein Ingestion.

Published onlineJournal ArticleThis is the final version of the article. Available from Public Library of Science via the DOI in this record.PURPOSE: Progressive loss of skeletal muscle mass with aging (sarcopenia) forms a global health concern. It has been suggested that an impaired capacity to increase muscle protein synthesis rates in response to protein intake is a key contributor to sarcopenia. We assessed whether differences in post-absorptive and/or post-prandial muscle protein synthesis rates exist between large cohorts of healthy young and older men. PROCEDURES: We performed a cross-sectional, retrospective study comparing in vivo post-absorptive muscle protein synthesis rates determined with stable isotope methodologies between 34 healthy young (22±1 y) and 72 older (75±1 y) men, and post-prandial muscle protein synthesis rates between 35 healthy young (22±1 y) and 40 older (74±1 y) men. FINDINGS: Post-absorptive muscle protein synthesis rates did not differ significantly between the young and older group. Post-prandial muscle protein synthesis rates were 16% lower in the older subjects when compared with the young. Muscle protein synthesis rates were >3 fold more responsive to dietary protein ingestion in the young. Irrespective of age, there was a strong negative correlation between post-absorptive muscle protein synthesis rates and the increase in muscle protein synthesis rate following protein ingestion. CONCLUSIONS: Aging is associated with the development of muscle anabolic inflexibility which represents a key physiological mechanism underpinning sarcopenia

Thermodynamics of histories for the one-dimensional contact process

The dynamical activity K(t) of a stochastic process is the number of times it changes configuration up to time t. It was recently argued that (spin) glasses are at a first order dynamical transition where histories of low and high activity coexist. We study this transition in the one-dimensional contact process by weighting its histories by exp(sK(t)). We determine the phase diagram and the critical exponents of this model using a recently developed approach to the thermodynamics of histories that is based on the density matrix renormalisation group. We find that for every value of the infection rate, there is a phase transition at a critical value of s. Near the absorbing state phase transition of the contact process, the generating function of the activity shows a scaling behavior similar to that of the free energy in an equilibrium system near criticality.Comment: 16 pages, 7 figure

Hardware Sequencing of Inflatable Nonlinear Actuators for Autonomous Soft Robots

Soft robots are an interesting alternative for classic rigid robots in appli-cations requiring interaction with organisms or delicate objects. Elastic inflatable actuators are one of the preferred actuation mechanisms for soft robots since they are intrinsically safe and soft. However, these pneumatic actuators each require a dedicated pressure supply and valve to drive and control their actuation sequence. Because of the relatively large size of pres-sure supplies and valves compared to electrical leads and electronic control-lers, tethering pneumatic soft robots with multiple degrees of freedom is bulky and unpractical. Here, a new approach is described to embed hardware intelligence in soft robots where multiple actuators are attached to the same pressure supply, and their actuation sequence is programmed by the inter-action between nonlinear actuators and passive flow restrictions. How to model this hardware sequencing is discussed, and it is demonstrated on an 8-degree-of-freedom walking robot where each limb comprises two actua-tors with a sequence embedded in their hardware. The robot is able to carry pay loads of 800 g in addition to its own weight and is able to walk at travel speeds of 3 body lengths per minute, without the need for complex on-board valves or bulky tethers.ERC starting gran

Exact Current Statistics of the ASEP with Open Boundaries

Non-equilibrium systems are often characterized by the transport of some quantity at a macroscopic scale, such as, for instance, a current of particles through a wire. The Asymmetric Simple Exclusion Process (ASEP) is a paradigm for non-equilibrium transport that is amenable to exact analytical solution. In the present work, we determine the full statistics of the current in the finite size open ASEP for all values of the parameters. Our exact analytical results are checked against numerical calculations using DMRG techniques.Comment: 5 pages, references adde

Elastic Inflatable Actuators for Soft Robotic Applications

The 20th century’s robotic systems have been made out of stiff materials and much of the developments in the field have pursued ever more accurate and dynamic robots which thrive in industrial automation settings and will probably continue to do so for many decades to come. However, the 21st century’s robotic legacy may very well become that of soft robots. This emerging domain is characterized by continuous soft structures that simultaneously fulfil the role of robotic link and robotic actuator, where prime focus is on design and fabrication of the robotic hardware instead of software control to achieve a desired operation. These robots are anticipated to take a prominent role in delicate tasks where classic robots fail, such as in minimally invasive surgery, active prosthetics and automation tasks involving delicate irregular objects. Central to the development of these robots is the fabrication of soft actuators to generate movement. This paper reviews a particularly attractive type of soft actuators that are driven by pressurized fluids. These actuators have recently gained substantial traction on the one hand due to the technology push from better simulation tools and new manufacturing technologies including soft-lithography and additive manufacturing, and on the other hand by a market pull from the applications listed above. This paper provides an overview of the different advanced soft actuator configurations, their design, fabrication and applications.This research is supported by the Fund for Scientific Research-Flanders (FWO), and the European Research Council (ERC starting grant HIENA)