Measuring the variability in supply chains with the peakedness

This paper introduces a novel way to measure the variability of order flows in supply chains, the peakedness. The peakedness can be used to measure the variability assuming the order flow is a general point pro- cess. We show basic properties of the peakedness, and demonstrate its computation from real-time continuous demand processes, and cumulative demand collected at fixed time intervals as well. We also show that the peakedness can be used to characterize demand, forecast, and inventory variables, to effectively manage the variability. Our results hold for both single stage and multistage inventory systems, and can further be extended to a tree-structured supply chain with a single supplier and multiple retailers. Furthermore, the peakedness can be applied to study traditional inventory problems such as quantifying bullwhip effects and determining safety stock levels. Finally, a numerical study based on real life Belgian supermarket data verifies the effectiveness of the peakedness for measuring the order flow variability, as well as estimating the bullwhip effects.variability, peakedness, supply chain

Breaking of non-Newtonian character in flows through a porous medium

International audienceFrom NMR measurements we show that the velocity field of a yield stress fluid flowing through a disordered well-connected porous medium is very close to that for a Newtonian fluid. In particular, it is shown that no arrested regions exist even at very low velocities, for which the solid regime is expected to be dominant. This suggests that these results obtained for strongly nonlinear fluid can be extrapolated to any nonlinear fluid. We deduce a generalized form of Darcy's law for such materials and provide insight into the physical origin of the coefficients involved in this expression, which are shown to be moments of the second invariant of the strain rate tensor

Approximating multiple class queueing models with loss models

Multiple class queueing models arise in situations where some flexibility is sought through pooling of demands for different services. Earlier research has shown that most of the benefits of flexibility can be obtained with only a small proportion of cross-trained operators. Predicting the performance of a system with different types of demands and operator pools with different skills is very difficult. We present an approximation method that is based on equivalent loss systems. We successively develop approximations for the waiting probability, The average waiting time and the service level. Our approximations are validated using a series of simulations. Along the way we present some interesting insights into some similarities between queueing systems and equivalent loss systems that have to our knowledge never been reported in the literature.

Slider : un Raisonneur Incrémental Évolutif

National audienceThe main drawbacks of current reasoning methods over ontologies are they struggle to provide scalability for large datasets. The batch processing reasoners who provide the best scalability so far are unable to infer knowledge from evolving data. We contribute to solving these problems by introducing Slider, an efficient incremental reasoner. Slider exhibits a performance improvement by more than a 70% compared to the OWLIM-SE reasoner. Slider is conceived to handle expanding data from streams with a growing background knowledge base. It natively supports ρdf and RDFS, and its architecture allows to extend it to more complex fragments with a minimal effort.Les solutions existantes pour le raisonnement incrémental souffrent principalement de leur incapacité à prendre en charge des ontologies complexes et ne sont pas conçues pour gérer de grandes quantités de connaissances. Dans cet article, nous présentons Slider (Chevalier et al. (2015)), un raisonneur incrémental évolutif par chaînage avant, permettant de raisonner sur des flux de données sémantiques

Finely tunable 1.55 µm emitting VeCSELs for embedded and compact optical and microwave systems

International audienceCompact wavelength-tunable laser sources are important for the development of optical based system units which can be used for numerous applications, ranging from optical communications, optical sensors, and even microwave photonics and high resolution spectroscopy. In most cases, large mode-hop-free wavelength tuning is of high interests to increase system performances and versatilities. In the metrology area, a small but very accurate wavelength tuning is required to fulfill system requirements. Thanks to their long cavity, VeCSELs offer the opportunity to get small laser wavelength linewidth, and shot noise limited behavior (class-A lasers). In this work we summarize the objectives and the preliminary results of the ANR Astrid HYPOCAMP project (HYbrid Polarisation controlled and mOnolithic tunable vertical Cavity surface emitting lAsers, for eMbedded and comPact optical and microwave systems), which is lead by FOTON in partnership with IPR (Rennes), CNRS-LAAS (Toulouse), CNRS-LPN (Marcoussis) and Telecom Bretagne. The project aims to develop a compact, reliable and low cost monolithic and versatile technology for the realization of tunable V(e)CSEL lasers, emitting in the 1.55 µm range (InP-based technology). In Fig.1 the optically-pumped external-cavity version of the device is presented

VCSEL Based on InAs Quantum-Dashes With a Lasing Operation Over a 117-nm Wavelength Span

International audienceWe report an InP based vertical cavity surface emitting laser (VCSEL) achieving a lasing operation between 1529 and 1646 nm. This optically-pumped VCSEL includes a wide-gain bandwidth active region based on InAs quantum dashes and wideband dielectric Bragg mirrors. Based on a wedge microcavity design, we obtain a spatial dependence of the resonant wavelength along the wafer, enabling thus to monitor the gain material bandwidth. We demonstrate a 117 nm continuous wavelength variation of the VCSEL emission, a consequence of the important and wide gain afforded by the use of optimized quantum dashes

Thermal conductivity of InAs quantum dot stacks using AlAs strain compensating layers on InP substrate

International audienceThe growth and thermal conductivity of InAs quantum dot (QD) stacks embedded in GaInAs matrix with AlAs compensating layers deposited on (1 1 3)B InP substrate are presented. The effect of the strain compensating AlAs layer is demonstrated through Atomic Force Microscopy (AFM) and X-ray diffraction structural analysis. The thermal conductivity (2.7 W/m K at 300 K) measured by the 3ω method reveals to be clearly reduced in comparison with a bulk InGaAs layer (5 W/m K). In addition, the thermal conductivity measurements of S doped InP substrates and the SiN insulating layer used in the 3ω method in the 20-200 °C range are also presented. An empirical law is proposed for the S doped InP substrate, which slightly differs from previously presented results

Joint analysis of human and bovine serological data: new insight on the risk and mechanisms of transmission of Rift Valley fever in Madagascar. [260]

Purpose: In 2008-09, an outbreak of Rift Valley fever (RVF) virus occurred in Madagascar. Spatial heterogeneity in seroprevalence (SP) and case occurrence frequencies suggested that some areas are more favorable to RVF circulation. The objectives of our study were to identify environmental factors in favor to human and cattle infections; test the relevance of using local cattle infection as human infection predictor and give a new insight on the respective role of direct and vectorial transmission both in human and cattle. Methods: We used 2 independent cattle and human serological datasets originating from two national surveys (2009 and 2011-13). Multiple Factor Analysis (MFA) was used to characterize environments of the whole island in terms of climate and landscape. The datasets were analyzed independently using a generalized linear mixed model (GLMM) with the individual serological status- human or cattle- as the binomial response. Explicative variables were age and MFA factors for cattle model (M1) and age, gender, MFA factors and contact with ruminants and their product for human model (M2). Then human and cattle data were analyzed jointly by GLMM with the human individual status as binomial response. In addition to the previous explicative variables cattle SP predicted by M1 was used. Models accuracies were tested using ROC curve method. Results: Four MFA factors were selected. Age and factor4 - humid (irrigation, lake, marshland) environment - had a positive effect on SP of cattle and human living in rural areas (p<0.001 and p<0.01) while factor1- warm, dry and herbaceous environment- had a negative effect (p<0.05). Humans consuming raw milk were at risk. Predicted cattle SP were associated with human SP (p<0.05). Conclusions: Our results support an endemic transmission of RVF in rural area with humid landscape settings in both human and cattle populations suggesting the predominance of vectorial transmission for both populations. Local cattle infection seems to be a good predictor of human infection. Relevance: This joint analysis allowed deciphering transmission mechanisms and should help health and veterinary authorities to assess risk of RVF and optimize surveillance network. (Texte intégral

Design of InGaAs/InP 1.55μm vertical cavity surface emitting lasers

International audienceThe design of an electrically pumped InGaAs quantum well based vertical cavity surface emitting laser (VCSEL) on InP substrate is presented. Such optically pumped VCSELs have already been demonstrated. To design electrically pumped VCSEL, three simulations steps are needed: optical simulation gives access to the electric field repartition, to design the active zone and the Bragg mirrors. Thermal simulation is helpful to design metallic contacts while the energy band diagram is obtained by electrical simulation to design the buried tunnel junction useful for carrier injection. All these simulations are compared to experiment