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Asymptotic Computation of Invariant Manifolds of large Finite Element structures with Geometric Nonlinearities
No full textInternational audienceIn this contribution we present a method to directly compute asymptotic expansion of invariant manifolds of large finite element models from physical coordinates and their reduced order dynamics on the manifold. We show the accuracy of the reduction method on selected models, exhibiting large rotations and internal resonances. The results obtained with the reduction compared to full-order harmonic balance simulations show that the proposed methodology can reproduce extremely accurately the dynamics of the original systems with a very low computational cost
Remarkable Challenges of High-Performance Language Virtual Machines
No full textLanguage Virtual Machines (VMs) are pervasive in every laptop, server, and smartphone, as is the case with Java or Javascript. They allow application portability between different platforms and better usage of resources. They are used in critical applications such as stock exchange, banking, insurance, and health [25]. Virtual machines are an important asset in companies because they allow the efficient execution of high-level programming languages. Nowadays, they even attract investments from large non-system companies, e.g., Netflix 1 , Meta 2 , Shopify 3 and Amazon 4. VMs achieve high-performance thanks to aggressive optimization techniques that observe and adapt the execution dynamically, either by doing just-in-time compilation [5] or by adapting the memory management strategies at runtime [90, 91]. For all these reasons Virtual Machines are highly-complex engineering pieces, often handcrafted by experts, that mix state-of-the-art compilation techniques with complex memory management that collaborate with the underlying operating systems and hardware. However, besides some well-known techniques that are published in research venues, most knowledge and technology around virtual machines are highly concentrated in large companies such as Microsoft, Google, and Oracle, making Virtual Machine construction difficult, and experiments difficult to reproduce and replicate. Language VMs present many multidisciplinary scientific challenges that appear at the intersection of fields such as hardware, system software, compiler, and software language engineering. This document aims to give a brief overview of the current challenges the VM community faces. To keep this document short, we selected remarkable challenges in managed execution, managed memory, performance evaluation, software engineering and security
Smart Specialization Strategy and regional resilience: conceptual ambivalences and empirical linkages
No full textInternational audienceSmart specialization strategy should evolve according to the capacity of the actors of the region, first, to generate resilience and, second, to transform the specialization of the region in a smart way. We propose here a method for understanding this transformation of regional specialization over time for qualifying the nature of the associated resilience. To reach our goal, we use the framework of the econimic dominance theory applied on dataset of regional technological knowledge exchange in the European technology market (EPO patent citation data) for the period 1991-2015
When IoT Data Meets Streaming in the Fog
No full textInternational audienceIoT and video streaming are the main driving applications for digital data generation today. The traditional way of storing and processing data in the Cloud cannot satisfy many latency critical applications. This is why Fog computing emerged as a continuum infrastructure from the Cloud to end-user devices. Misplacing data in such an infrastructure results in high latency, and consequently increases the penalty for Internet Service Providers (ISPs) incurred by violating the service level agreement (SLA). In past studies, two issues have been investigated separately: the IoT data placement and the streaming cache placement. However, both placements rely on the same Fog distributed storage system. In this paper, we address those issues in a unique model with the aim to minimize the penalty for ISPs incurred by the SLA violation and maximize storage resources usage. We subdivided each Fog node storage space into a storage part and a cache part. First, our model consists in placing IoT data in the storage part of Fog nodes, and then placing streaming data in the cache part of these nodes. The novelty of our model is the flexibility it offers for managing the cache volume, which can, adaptively, spill on the free part dedicated to IoT data. Experiments show that using our model makes it possible to reduce the streaming data penalty of the ISP’s SLA violation by more than 47% on average
Introduction to the Special Issue on Memory and Storage Systems for Embedded and IoT Applications: Part 2
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Effects of Atmospheric Turbulence on Optical Wireless Communication in NEOM Smart City
No full textInternational audienceThe foundation of any smart city requires an innovative and robust communication infrastructure. Many research communities envision free-space optical communication (FSO) as a promising backbone technology for the services and applications provided by such cities. However, the channel through which the FSO signal travels is the atmosphere. Therefore, the FSO performance is limited by the local weather conditions. The variation in meteorological variables leads to variations of the refractive index along the transmission path. These index inhomogeneities (i.e., atmospheric turbulence) can significantly degrade the performance of FSO systems. Thus, a practical implementation of the FSO link must carefully consider the atmospheric turbulence effect. This paper aims to investigate the feasibility of FSO communication for NEOM, a promising smart city in Saudi Arabia. We study the effect of weather conditions on FSO links using the micrometeorology model, taking into account actual weather data. The FSO performance in winter and summer was compared in terms of the bit error rate, signal-to-noise ratio (SNR), link availability, and transmission distance. The study shows that the atmospheric turbulence strength is moderate and strong in winter and summer, respectively. The temperature has the biggest impact on the FSO system when compared to the other meteorological elements included in this study. Furthermore, at transmission distances less than 300 m, atmospheric turbulence does not significantly affect the FSO for the operating wavelength of 1550 nm. Furthermore, it has been shown that at transmission distances greater than 300 m, the SNR in summer is more than 18% higher than in winter. The findings of this research enable understanding of the effect of turbulence caused by NEOM weather on the FSO link, thus assisting engineers in establishing a reliable FSO backbone link by adjusting the relevant parameters
A low-cost GNSS buoy for water vapour monitoring over the Oceans
No full textInternational audience<p>In recent years, the significant growth of positioning applications has come with the development of low-cost dual frequency Global Navigation Satellite Systems (GNSS) receivers. The accuracy of these receivers in terms of positioning has been proved. Various studies have also highlighted the ability of these receivers to precisely monitor the atmospheric water vapour. The low cost of such receivers enables large deployment, thus presenting an advantage for many geoscience applications.</p><p>In this context, we have developed a hydrographic buoy prototype, equipped with low-cost GNSS receiver and antenna. This buoy was first aimed to be used for the monitoring in delayed time of offshore tides and currents, by a precise point positioning analysis of the GNSS raw data. In addition, the ability of this low-cost GNSS buoy for the water vapour monitoring was also investigated through the assessment of Zenith Tropospheric Delay (ZTD) estimates from the post-processing of the raw data. The comparisons with ZTD estimates from a nearby ground-based GNSS geodetic antenna and the ECMWF fifth ReAnalysis (ERA5), provide pretty good results with RMS differences lower than 10 mm.&#160;</p><p>These conclusive results highlight the opportunities for the use of such low-cost systems for meteorology and climatology applications over the Oceans.</p>
Successive Convexification for Optimal Control with Signal Temporal Logic Specifications
No full textInternational audienceAs the scope and complexity of modern cyber-physical systems increase, newer and more challenging mission requirements will be imposed on the optimal control of the underlying unmanned systems. This paper proposes a solution to handle complex temporal requirements formalized in Signal Temporal Logic (STL) specifications within the Successive Convexification (SCvx) algorithmic framework. This SCvx-STL solution method consists of four steps: 1) Express the STL specifications using their robust semantics as state constraints. 2) Introduce new auxiliary state variables to transform these state constraints as system dynamics, by exploiting the recursively defined structure of robust STL semantics. 3) Smooth the resulting system dynamics with polynomial smooth min-and maxfunctions. 4) Convexify and solve the resulting optimal control problem with the SCvx algorithm, which enjoys guaranteed convergence and polynomial time subproblem solving capability. Our approach retains the expressiveness of encoding mission requirements with STL semantics, while avoiding the usage of combinatorial optimization techniques such as Mixed-integer programming. Numerical results are shown to demonstrate its effectiveness
Understanding the damage mechanisms in 3D layer-to-layer woven composites from thermal and acoustic measurements
No full textInternational audienceThis article deals with an interlock woven composite and aims at providing a better understanding of the dissipative mechanisms activated under cyclic loadings and describing the damage scenario characteristic of heat build-up experiments. Since the ultimate objective of heat build-up experiment analyses is usually fatigue life predictions that are based on constitutive modelling, the correct interpretation of experimental results is essential. Three different loading protocols are proposed. The instrumentation of these experiments includes infrared thermometry and acoustic emission monitoring. The results show that the coupling of these two techniques provides useful information in order to identify the most important dissipation sources: viscoelasticity, damage and friction. Furthermore, by analysing different loading sequences, it is possible to elaborate the dissipation evolution scenario as well as the damage evolution scenario occurring during heat build-up experiments