Non-linear Frequency Transduction of Nano-mechanical Brownian Motion

We report on experiments addressing the non-linear interaction between a nano-mechanical mode and position fluctuations. The Duffing non-linearity transduces the Brownian motion of the mode, and of other non-linearly coupled ones, into frequency noise. This mechanism, ubiquitous to all weakly-nonlinear resonators thermalized to a bath, results in a phase diffusion process altering the motion: two limit behaviors appear, analogous to motional narrowing and inhomogeneous broadening in NMR. Their crossover is found to depend non-trivially on the ratio of the frequency noise correlation time to its magnitude. Our measurements obtained over an unprecedented range covering the two limits match the theory of Y. Zhang and M. I. Dykman, Phys. Rev. B 92, 165419 (2015), with no free parameters. We finally discuss the fundamental bound on frequency resolution set by this mechanism, which is not marginal for bottom-up nanostructures.Comment: Article plus Supplementary Materia

A clinical and molecular project on gonadoblastoma needs international collaboration

<p>No abstract available.</p

Classical decoherence in a nanomechanical resonator

SI not providedInternational audienceDecoherence is an essential mechanism that defines the boundary between classical and quantum behaviours, while imposing technological bounds for quantum devices. Little is known about quantum coherence of mechanical systems, as opposed to electromagnetic degrees of freedom. But decoherence can also be thought of in a purely classical context, as the loss of phase coherence in the classical phase space. Indeed the bridge between quantum and classical physics is under intense investigation, using classical nanomechanical analogues of quantum phenomena. In the present work, by separating pure dephasing from dissipation, we quantitatively model the classical decoherence of a mechanical resonator: through the experimental control of frequency fluctuations, we engineer artificial dephasing. We report on the methods available to define pure dephasing in these systems, which are prerequisite in the understanding of decoherence processes in mechanical devices, both classical and quantum

On the link between mechanics and thermal properties: mechanothermics

We report on the theoretical derivation of macroscopic thermal properties (specific heat, thermal conductivity) of an electrically insulating rod connected to two reservoirs, from the linear superposition of its mechanical mode Brownian motions. The calculation is performed for a weak thermal gradient, in the classical limit (high temperature). The development is kept basic as far as geometry and experimental conditions are concerned, enabling an almost fully analytic treatment. In the modeling, each of the modes is subject to a specific Langevin force, which enables to produce the required temperature profile along the rod. The theory is predictive: the temperature gradient (and therefore energy transport) is linked to motion amplitude cross-correlations between nearby mechanical modes. This arises because energy transport is actually mediated by mixing between the modal waves, and not by the modes themselves. This result can be tested on experiments, and shall extend the concepts underlying equipartition and fluctuation-dissipation theorems. The theory links intimately the macroscopic size of the clamping region where the mixing occurs to the microscopic lengthscale of the problem at hand: the phonon mean-free-path. We believe that our work should impact the domain of thermal transport in nanostructures, with future developments of the theory toward the quantum regime

Measuring frequency fluctuations in nonlinear nanomechanical resonators

Advances in nanomechanics within recent years have demonstrated an always expanding range of devices, from top-down structures to appealing bottom-up MoS$_2$ and graphene membranes, used for both sensing and component-oriented applications. One of the main concerns in all of these devices is frequency noise, which ultimately limits their applicability. This issue has attracted a lot of attention recently, and the origin of this noise remains elusive up to date. In this Letter we present a very simple technique to measure frequency noise in nonlinear mechanical devices, based on the presence of bistability. It is illustrated on silicon-nitride high-stress doubly-clamped beams, in a cryogenic environment. We report on the same $T/f$ dependence of the frequency noise power spectra as reported in the literature. But we also find unexpected {\it damping fluctuations}, amplified in the vicinity of the bifurcation points; this effect is clearly distinct from already reported nonlinear dephasing, and poses a fundamental limit on the measurement of bifurcation frequencies. The technique is further applied to the measurement of frequency noise as a function of mode number, within the same device. The relative frequency noise for the fundamental flexure $\delta f/f_0$ lies in the range $0.5 - 0.01~$ppm (consistent with literature for cryogenic MHz devices), and decreases with mode number in the range studied. The technique can be applied to {\it any types} of nano-mechanical structures, enabling progresses towards the understanding of intrinsic sources of noise in these devices.Comment: Published 7 may 201

Nanomechanical damping via electron-assisted relaxation of two-level systems

We report on measurements of dissipation and frequency noise at millikelvin temperatures of nanomechanical devices covered with aluminum. A clear excess damping is observed after switching the metallic layer from superconducting to the normal state with a magnetic field. Beyond the standard model of internal tunneling systems coupled to the phonon bath, here we consider the relaxation to the conduction electrons together with the nature of the mechanical dispersion laws for stressed/unstressed devices. With these key ingredients, a model describing the relaxation of two-level systems inside the structure due to interactions with electrons and phonons with well separated timescales captures the data. In addition, we measure an excess 1/f-type frequency noise in the normal state, which further emphasizes the impact of conduction electrons

Identifying innovation in higher education elearning strategies

There are many case studies of individual Higher Education Institutions (HEIs) devising distinctive eLearning strategies, reported by the HEI itself, journalists, or research observatories. An extraordinarily wide range of university-level eLearning programmes are rapidly becoming available from large numbers of HEIs across Europe, and there are strong attempts being made to identify and disseminate case studies of innovative eLearning practices (e.g. MENON, 2006). However, the vital research goal of obtaining more systematic evidence across countries in relation to HEIs' innovations in eLearning strategies represents a particular challenge for collectors of case studies, especially given the diverse processes in different countries for measuring pedagogical value and cost-effectiveness. By contrast, there are typically several reports a year of large-scale attempts to survey HEIs in relation to eLearning, sponsored, for example, by EU programmes or industry groups. Yet the factors that determine educational effectiveness are not, so far, well understood; and consequently it can be difficult to develop reliable quantitative survey items that simultaneously enable valid and insightful comparisons between essentially qualitative eLearning strategies. Moreover, such quantitative evidence is not collected systematically by the typical HEI; when collected, such evidence is commercially sensitive; and it is not easy for researchers to obtain independently of the HEI. So, claims are made, for example, that European universities plan to 'expand their use of eLearning' (BBC News, 2005), but it is not at all clear what measures of expansion are appropriate, and what kinds of strategies are associated with such expansion. The two-year research study described here attempted a mixed-method approach to the problem of identifying examples of innovation in relation to the eLearning strategies developed by HEIs. Where possible the study estimated the impact of the implemented eLearning programmes, but the emphasis was on illuminating a range of innovative eLearning strategy cases, rather than necessarily determining best practice. Two key research questions asked by the study are: 1. How can innovation in Higher Education eLearning strategies be identified? 2. What factors are critical to the success of these strategies? This research did not set out to obtain, directly, insight into why eLearning has not been more widely adopted by HEIs, why various eLearning projects have failed, why some eLearning projects have achieved less success than anticipated, or why some eLearning projects have achieved success more slowly than anticipated. However, by researching innovation, the challenges faced by the innovators, and how strategies needed to change over time, it is anticipated that the findings from this study might indirectly illuminate these crucial questions. It is not possible within the space available here to do more than outline the methodology and highlight a few key findings: fuller reports are available on the project website www.spi.pt/innounilearning

The Sine-Gordon Solitons as a N-Body Problem

We consider the N-soliton solutions in the sine-Gordon model as a N-body problem. This leads to a relativistic generalization of the Calogero model first introduced by Ruijsenaars. We show that the fundamental Poisson bracket of the Lax matrix is quadratic, and the $r$-matrix is a dynamical one. This is in contrast to the Calogero model where the fundamental Poisson bracket of the Lax matrix is linear.Comment: 10 pages LATEX SPhT-93-072; LPTHE-93-4

Thermodynamics of Gambling Demons

The stochastic nature of games at the casino allows lucky players to make profit by means of gambling. Like games of chance and stocks, small physical systems are subject to fluctuations, thus their energy and entropy become stochastic, following an unpredictable evolution. In this context, information about the evolution of a thermodynamic system can be used by Maxwell's demons to extract work using feedback control. This is not always the case, a challenging task is then to develop efficient thermodynamic protocols achieving work extraction in situations where feedback control cannot be realized, in the same spirit as it is done on a daily basis in casinos and financial markets. Here we study fluctuations of the work done on small thermodynamic systems during a nonequilibrium process that can be stopped at a random time. To this aim we introduce a gambling demon. We show that by stopping the process following a customary gambling strategy it is possible to defy the standard second law of thermodynamics in such a way that the average work done on the system can be below the corresponding free energy change. We derive this result and fluctuation relations for the work done in stochastic classical and quantum non-stationary Markovian processes at stopping times driven by deterministic nonequilibrium protocols, and experimentally test our results in a single-electron box. Our work paves the way towards the design of efficient energy extraction protocols at the nanoscale inspired by investment and gaming strategies.Comment: 8 pages (including methods), 3 figures. v2: some typos correcte

The fostering of innovative eLearning strategies in European higher education

Although there are strong attempts being made by various European observatories and European Commission programmes to identify and disseminate innovative eLearning practices (MENON, 2006), the factors that determine educational effectiveness are, as yet, not well understood. In particular, while an extraordinarily wide range of university-level eLearning programmes are rapidly becoming available from large numbers of Higher Education Institutions (HEIs) across Europe, the sharing of good practice requires detailed accounts of successful innovative eLearning strategies. There are many relevant checklists and sets of principles described in EU websites (e.g. elearningeurope.info, 2006) and in the academic literature (e.g. Conole et al, 2004), but it is often only through thoroughly appreciating what others have done that such abstract guidance come alive. However, it can still be difficult for HEIs to learn from others. While there are many media reports of innovation, these typically have to omit the level of detail that would enable optimal understanding by those HEIs wishing to apply such innovations in their own contexts. Meanwhile, case studies presented at conferences and in the academic literature can provide the necessary level of detail, but it can be difficult to collate such case studies into a form that facilitates consistent descriptions across the diversity of European HEIs. By identifying the various eLearning programmes applied by HEIs in a number of EU member states and conducting a detailed assessment of a sample of eLearning strategies found to be effective supporters of higher education requirements, the EC-funded InnoUniLearning project is disseminating a range of eLearning strategy case studies. Where possible this project is estimating the potential impact of the implemented eLearning programmes, but more importantly it will identify and detail the strategies applied by leading institutions and well-known success stories, as well as those institutions that have applied new and innovative eLearning programmes. It is hoped that the dissemination of these case studies will be of assistance to HEIs across Europe in implementing eLearning strategies that meet their own particular curricular and cohort requirements. The study is concentrating on illuminating a range of successful eLearning strategy cases, rather than necessarily determining best practice, which could be argued an impossible task at the moment because of a lack of learner feedback. Nevertheless, most, if not all, organisations that have implemented eLearning have gone through a period of adjustment in order to obtain an eLearning programme that is cost-efficient and effective; so capturing something of the challenges overcome by the HEIs leading this field should assist the wider EU higher education community. This paper describes background and the methodological approach of the two-year study and some preliminary results, which will be elaborated in the conference presentation