Reply to Comment on: "Are stress-free membranes really 'tensionless'?"

This is a reply to a comment on the paper arXiv:1204.2075 "Are stress-free membranes really tensionless ?" (EPL 95,28008 (2011))

Influence of clamp-widening on the quality factor of nanomechanical silicon nitride resonators

Nanomechanical resonators based on strained silicon nitride (Si$_3$N$_4$) have received a large amount of attention in fields such as sensing and quantum optomechanics due to their exceptionally high quality factors ($Q$s). Room-temperature $Q$s approaching 1 billion are now in reach by means of phononic crystals (soft-clamping) and strain engineering. Despite great progress in enhancing $Q$s, difficulties in fabrication of soft-clamped samples limits their implementation into actual devices. An alternative means of achieving ultra-high $Q$s was shown using trampoline resonators with engineered clamps, which serves to localize the stress to the center of the resonator, while minimizing stress at the clamping. The effectiveness of this approach has since come into question from recent studies employing string resonators with clamp-tapering. Here, we investigate this idea using nanomechanical string resonators with engineered clampings similar to those presented for trampolines. Importantly, the effect of orienting the strings diagonally or perpendicularly with respect to the silicon frame is investigated. It is found that increasing the clamp width for diagonal strings slightly increases the $Q$s of the fundamental out-of-plane mode at small radii, while perpendicular strings only deteriorate with increasing clamp width. Measured $Q$s agree well with finite element method simulations even for higher-order resonances. The small increase cannot account for previously reported $Q$s of trampoline resonators. Instead, we propose the effect to be intrinsic and related to surface and radiation losses.Comment: 7 pages, 4 figure

Final project report: EEC 2092/91 (ORGANIC) Revision

This report summarises the findings of the project that have been presented in a number of separate reports and publications. In the Chapters 2 to 5 the approach, results and conclusions of the project are summarised, following the structure of the different work packages. Chapter 2 summarises the work on ethical values of organic agriculture. Chapter 3 looks at the differences in the implementation of Regulation (EEC) 2092/91 across Europe and compares the European Regulation with international standards. Chapters 4 and 5 summarise the findings that relate to reducing the dependency on non-organic inputs in the case of feed and seed. The final Chapter 6 consolidates the recommendations of the whole project arising from the various different work packages in one place. Recommendations are aimed in particular at the second stage of the ongoing revision process of the European Regulation, the transfer of the detailed rules from the Annexes of the Regulation (EEC) 2092/91 that is expected to start after the completion of the project. Further recommendations for standard setting bodies, regulators and research recommendations are also presented. The overall objective of the project was to provide recommendations for the revision and further development of the Regulation (EEC) 2092/91 and other standards for organic agriculture, broken down into a number of specific objectives that resulted in 12 seperate reports. The basic ethical values and value differences of organic agriculture in Europe was identified through stakeholder consultation (D 2.1) and through literature as part of developing a procedure for balancing and integrating the basic values in developments of EU regulation (D 2.3). Organic standards from national and private organisations in Europe were compared with the EU regulation with help of database (www.organicrules.org) and differences were analysed to give recommendations on further harmonisation of the EU regulation (D 3.2). The knowledge on how to achieve 100 % organic rations in diets for livestock was expanded through a meta-analysis of literature and an overview of the current situation to characterise the availability of protein sources for 100% organic diets for pigs and poultry was produced (D 4.1 part 1 and 2). Criteria for use of organic inputs, evaluation criteria for Annex II C: Feed materials and Annex II D: Dietary supplements of Regulation (EEC) 2092/91 were developed (D. 4.2). A guide for operators was developed (D 4.3). The knowledge on how to reduce the use of non-organic seed and vegetative propagation materials was improved through reports on seed borne diseases in organic seed and propagation material (D 5.1), on the importance of quality characterising in organic seed and propagation material (D 5.2) and analysis of national derogation regimes (D 5.3). The project produced 12 reports, 7 scientific publications in peer-reviewed journals, and a project web-page at www.organic-revision.org where all reports and further documents are available. It organised 3 workshops with stakeholders and had ongoing communication with the Unit on Organic Farming in DG Agriculture responsible for the Organic Regulation. Members of the team produced in total more than 250 dissemination items

Steering the potential barriers: entropic to energetic

We propose a new mechanism to alter the nature of the potential barriers when a biased Brownian particle under goes a constrained motion in narrow, periodic channel. By changing the angle of the external bias, the nature of the potential barriers changes from purely entropic to energetic which in turn effects the diffusion process in the system. At an optimum angle of the bias, the nonlinear mobility exhibits a striking bell-shaped behavior. Moreover, the enhancement of the scaled effective diffusion coefficient can be efficiently controlled by the angle of the bias. This mechanism enables the proper design of channel structures for transport of molecules and small particles. The approximative analytical predictions have been verified by precise Brownian dynamic simulations.Comment: (6 pages, 7 figures) Submitted to PR

Evolution of Directed Triangle Motifs in the Google+ OSN

Motifs are a fundamental building block and distinguishing feature of networks. While characteristic motif distribution have been found in many networks, very little is known today about the evolution of network motifs. This paper studies the most important motifs in social networks, triangles, and how directed triangle motifs change over time. Our chosen subject is one of the largest Online Social Networks, Google+. Google+ has two distinguishing features that make it particularly interesting: (1) it is a directed network, which yields a rich set of triangle motifs, and (2) it is a young and fast evolving network, whose role in the OSN space is still not fully understood. For the purpose of this study, we crawled the network over a time period of six weeks, collecting several snapshots. We find that some triangle types display significant dynamics, e.g., for some specific initial types, up to 20% of the instances evolve to other types. Due to the fast growth of the OSN in the observed time period, many new triangles emerge. We also observe that many triangles evolve into less-connected motifs (with less edges), suggesting that growth also comes with pruning. We complement the topological study by also considering publicly available user profile data (mostly geographic locations). The corresponding results shed some light on the semantics of the triangle motifs. Indeed, we find that users in more symmetric triangle motifs live closer together, indicating more personal relationships. In contrast, asymmetric links in motifs often point to faraway users with a high in-degree (celebrities)

Surface anchoring on layers of grafted liquid-crystalline chain molecules: A computer simulation

By Monte Carlo simulations of a soft ellipsoid model for liquid crystals, we study whether a layer of grafted liquid-crystalline chain molecules can induce tilt in a nematic fluid. The chains are fairly short (four monomers) and made of the same particles as the solvent. They are attached to a substrate which favors parallel (planar) alignment. At low grafting densities, the substrate dominates and we observe planar alignment. On increasing the grafting density, we find a first order transition from planar to tilted alignment. Beyond the transition, the tilt angle with respect to the surface normal decreases continuously. The range of accessible anchoring angles is quite large.Comment: To appear in J. Chem. Phy

REDO RSVP: Efficient Signalling for Multimedia in the Internet

Alarming reports of performance and scalability problems associated with per-flow reservations, have led many to lose belief in RSVP and the Integrated Services Architecture that relies on it. Because we are convinced of the need for some form of resource reservation, to support multimedia communications in the Internet, we have set about trying to improve RSVP. By careful study of the protocol, we have identified areas for improvement, and propose REDO RSVP, a reduced overhead version that includes a fast establishment mechanism (FEM). In this paper we describe the rationale for REDO RSVP and present a detailed analysis of its features and operations. We also analyse REDO RSVP by means of simulations, and show that it offers improvements to the performance of RSVP

Asteroseismology of eclipsing binary stars using Kepler and the HERMES spectrograph

We introduce our PhD project in which we focus on pulsating stars in eclipsing binaries. The combination of high-precision Kepler photometry with high-resolution HERMES spectroscopy allows for detailed descriptions of our sample of target stars. We report here the detection of three false positives by radial velocity measurements.Comment: Proceedings paper, 2 pages, 2 figures, to appear in "Setting a New Standard in the Analysis of Binary Stars", Eds K. Pavlovski, A. Tkachenko, and G. Torres, EAS Publications Serie

Controlling diffusive transport in confined geometries

We analyze the diffusive transport of Brownian particles in narrow channels with periodically varying cross-section. The geometrical confinements lead to entropic barriers, the particle has to overcome in order to proceed in transport direction. The transport characteristics exhibit peculiar behaviors which are in contrast to what is observed for the transport in potentials with purely energetic barriers. By adjusting the geometric parameters of the channel one can effectively tune the transport and diffusion properties. A prominent example is the maximized enhancement of diffusion for particular channel parameters. The understanding of the role of channel-shape provides the possibility for a design of stylized channels wherein the quality of the transport can be efficiently optimized.Comment: accepted for publication in Acta Physica Polonica