Multihour engineering and traffic routing optimization in hierarchical telephone networks

Classical hierarchical routing in telephone networks is extended to a wider class called out-of-chain routing in such a way that some useful properties of hierarchical routing are retained. This new routing pattern offers more potential paths than the fixed hierarchical one and can be introduced as a dynamic routing where the fixed alternate sequences change at some predetermined instants during the day. The effect of this new routing pattern on the network performances is examined. The main topic of this paper is to present heuristic methods used to optimise such routings in large networks. We show on artificial networks that the throughput of a given network can be significantly improved by suitable routing choices. We demonstrate that the integration of routing changes within a multihour dimensioning process is possible but the lack of realistic data does not permit at this time to quantify the value of routing optimization on real networks.     

A computational skin model: fold and wrinkle formation

This paper presents a computational model for studying the mechanical properties of skin with aging. In particular, attention is given to the folding capacity of skin, which may be manifested as wrinkles. The simulation provides visual results demonstrating the form and density of folds under the various conditions. This can help in the consideration of proper measures for a cosmetic product for the skin.     

Picosecond photodiffraction in semiconductor multiquantum wells and microcavities

We study the transient gratings photogenerated in the picosecond regime in three families of structures, namely : - structures of thickness in the order of one micron, including quantum wells (GaAs/GaAlAs, CdTe/ CdZnTe). A transmission modulation due to the electric field has been observed. We show that, in accordance with our calculations, this modulation is screened faster than 10 ps at a fluence of a few µJ/cm2. - A structure including GalnAs/GalnAsP MQWS in a cavity. This structure shows a top diffraction efficiency of 2.5 × 10-² at 1.55 µm for an energy of excitation in the order of 100 µJ/cm2. The diffraction efficiency exhibits several oscillations due to Fabry-Pårot effects. By introducing cavity effects in our model, we show that the diffraction efficiency is amplified by more than a factor 2 with respect to the no-cavity case. Calculations show that the diffraction efficiency may reach 6 × 10-² around 1.625 µm, for a front mirror reflectivity of 90 %. - Structures including bulk GaAs microcavities. The risetime is lower or in the order of 1 ps while the diffraction efficiency attains 1 %, with an average power of 4 mW (i.e. an energy of 2 µJ/cm²/pulse), compatible with a commutation of packets at 80 MHz.     

Ultrathin PECVD epitaxial Si solar cells on glass via low‐temperature transfer process

Fabrication of high‐quality ultrathin monocrystalline silicon layers and their transfer to low‐cost substrates are key steps for flexible electronics and photovoltaics. In this work, we demonstrate a low‐temperature and low‐cost process for ultrathin silicon solar cells. By using standard plasma‐enhanced chemical vapor deposition (PECVD), we grow high‐quality epitaxial silicon layers (epi‐PECVD) from SiH₄/H₂ gas mixtures at 175 °C. Using secondary ion mass spectrometry and transmission electron microscopy, we show that the porosity of the epi‐PECVD/crystalline silicon interface can be tuned by controlling the hydrogen accumulation there. Moreover, we demonstrate that 13–14% porosity is a threshold above which the interface becomes fragile and can easily be cleaved. Taking advantage of the H‐rich interface fragility, we demonstrate the transfer of large areas (∽10 cm²) ultrathin epi‐PECVD layers (0.5–5.5 µm) onto glass substrates by anodic bonding and moderate annealing (275–350 °C). The structural properties of transferred layers are assessed, and the first PECVD epitaxial silicon solar cells transferred on glass are characterized. Copyright © 2016 John Wiley & Sons, Ltd.     

Brillouin distributed time-domain sensing in optical fibers: state of the art and perspectives

Optical fiber sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements. The fiber is used as sensing element, and a value for temperature and/or strain can be obtained from any point along the fiber. After explaining the principle and presenting the standard implementation, the latest developments in this class of sensors will be introduced, such as the possibility to measure with a spatial resolution of 10 cm and below while preserving the full accuracy on the determination of temperature and strain.     

An end‐to‐end alternative to TCP PEPs: Initial Spreading,a TCP fast start‐up mechanism

While Transmission Control Protocol (TCP) Performance Enhancing Proxy (PEP) solutions have long been undisputed to solve the inherent satellite problems, the improvement of the regular end‐to‐end TCP congestion avoidance algorithms and the recent emphasis on the PEPs drawbacks have opened the question of the PEPs sustainability. Nevertheless, with a vast majority of Internet connections shorter than ten segments, TCP PEPs continue to be required to counter the poor efficiency of the end‐to‐end TCP start‐up mechanisms. To reduce the PEPs dependency, designing a new fast start‐up TCP mechanism is therefore a major concern. But, while enlarging the Initial Window (IW) up to ten segments is, without any doubt, the fastest solution to deal with a short‐lived connection in an uncongested network, numerous researchers are concerned about the impact of the large initial burst on an already congested network. Based on traffic observations and real experiments, Initial Spreading has been designed to remove those concerns whatever the load and type of networks. It offers performance similar to a large IW in uncongested network and outperforms existing end‐to‐end solutions in congested networks. In this paper, we show that Initial Spreading, taking care of the satellite specificities, is an efficient end‐to‐end alternative to the TCP PEPs. Copyright © 2015 John Wiley & Sons, Ltd.     

Municipalities as a Driver for Wireless Broadband Access

Municipalities can form a driving force behind the deployment of new telecom infrastructure. While a telecom operator focuses on direct (financial) profits, a municipality is mainly interested in the social benefits for its inhabitants. In this paper, we evaluate a wireless municipality network from both a technical and an economic point of view. WiFi and WiMAX are considered as the most suited technologies for this purpose. A detailed techno-economic study has been performed including forecasting of the user adoption, dimensioning of the wireless network and modelling the related costs and revenues. The trade-off between installing a high number of relatively cheap WiFi access points, and a smaller number of more expensive WiMAX base stations for delivering full coverage is investigated in several scenarios.

Efficient computer analysis of ideal switched-capacitor circuits using matrix compaction techniques

In this paper we describe how three simple observations can be used in order to obtain an efficient algorithm for the computer analysis of ideal switched-capacitor circuits. the resulting algorithm is linear in the number of phases. the first observation uses the structure of the r-domain MNA-matrix to come up with a new LU-decomposition scheme which is gradual per timeslot. the second observation allows a great reduction in size of the z-domain MNA-matrix by a matrix compaction algorithm which also operates gradually per timeslot and which can be interleaved with the first gradual LU-decomposition process. This leads to a small matrix which can then be used for a time- and direct frequency-domain analysis. Third, the computations of transfer functions, aliasing functions and sensitivities can be optimized by applying appropriate excitations and making appropriate combinations of the terms in the expressions. These algorithms have been implemented in the SC-analysis program DIANA.SC. the usefulness and efficiency of the program is then illustrated with some examples.     

Effect of Thermomechanical Fatigue on Precipitation Microstructure in Two Precipitation-Hardened Cast Aluminum Alloys

Thermal loading induces modifications of the precipitation microstructure of Al–Si–Cu–Mg alloys. This study focuses on the effect of deformation on precipitation microstructure during thermomechanical loadings. Several specimens were thermomechanically cycled while others were exposed to the same thermal cycles without any mechanical loading. The nature and morphological characteristics of the precipitation microstructure of the thermomechanically cycled specimens are compared to those of the thermally aged ones, using transmission electron microscopy (TEM), in order to assess the effect of deformation on the precipitation microstructure and especially on the kinetics of precipitate growth. The absence of any significant effect of superimposed straining during thermal cycling is discussed. Implications for the prevision of yield strength degradation during service operation are briefly presented.