Multimode VCSEL model for wide frequency-range RIN simulation

In this paper, we present an equivalent circuit model for oxide-confined AlGaAs/GaAs VCSEL with the noise contribution adapted to optomicrowave links applications. This model is derived from the multimode rate equations. In order to understand the modal competition process, we restrain our description to a two-modes rate equations system affected by the spectral hole-burning. The relative intensity noise (RIN) measurements which were achieved on a prober in Faraday cage confirm the low frequency enhancement described by the model. We validate our model for a wide frequency-range [1 MHz–10 GHz] and high bias level up to six times the threshold current

Minimizing makespan in flowshop with time lags

We consider the problem of minimizing the makespan in a flowshop involving maximal and minimal time lags. Time lag constraints generalize the classical precedence constraints between operations. We assume that such constraints are only defined between operations of the same job. We propose a solution method and present several extensions.Comment: 2 pages. Also available at http://hal.inria.fr/inria-0000014

Adaptive low-rank approximation and denoised Monte-Carlo approach for high-dimensional Lindblad equations

We present a twofold contribution to the numerical simulation of Lindblad equations. First, an adaptive numerical approach to approximate Lindblad equations using low-rank dynamics is described: a deterministic low-rank approximation of the density operator is computed, and its rank is adjusted dynamically, using an on-the-fly estimator of the error committed when reducing the dimension. On the other hand, when the intrinsic dimension of the Lindblad equation is too high to allow for such a deterministic approximation, we combine classical ensemble averages of quantum Monte Carlo trajectories and a denoising technique. Specifically, a variance reduction method based upon the consideration of a low-rank dynamics as a control variate is developed. Numerical tests for quantum collapse and revivals show the efficiency of each approach, along with the complementarity of the two approaches.Comment: 5 pages, 3 figures, Submitte

Noise and signal modeling of various VCSEL structures

Current evolution in Datacoms and Gigabit Ethernet have made 850nm Vertical Cavity Surface Emitting Lasers(VCSEL) the most important and promising emitter. Numerous different structures have been growth, to obtain bestcurrent confinement and then to control the emitted light modal behavior. We have developed a small signal equivalent electrical model of VCSEL including Bragg reflectors, active area, chip connection and noise behavior. Easy tointegrate with classical software for circuit studies, this model which is widely adaptable for different structures takesinto account the complete electrical environment of the chip. An experimental validation for RF modulation up to 10GHz has been realized on oxide confined VCSEL, demonstrating that the model could be used to get realistic valuesfor the VCSEL intrinsic parameters.Including Langevin noise sources into the rate equations and using the same electrical analogy, noise current andvoltage sources can be added to the model. It allows good prediction for the RIN function shape up to 10GHz formonomodal emitter

Regulation of tomato fruit ripening

Fruit ripening is a sophisticatedly orchestrated developmental process, unique to plants, that results in major physiological and metabolic changes, ultimately leading to fruit decay and seed dispersal. Because of their strong impact on fruit nutritional and sensory qualities, the ripeningassociated changes have been a matter of sustained investigation aiming at unravelling the molecular and genetic basis of fruit ripening. Tomato rapidly emerged as the model of choice for fleshy fruit research and a wealth of genetic resources and genomics tools have been developed, providing new entries into the regulatory mechanisms involved in the triggering and coordination of the ripening process. Some of the key components participating in the control of tomato fruit ripening have been uncovered, but our knowledge of the network of signalling pathways engaged in this complex developmental process remains fragmentary. This review highlights the main advances and emphasizes issues still to be addressed using the rapidly developing ‘omics’ approaches

Optimal Sensors Placement to Enhance Damage Detection in Composite Plates

This paper examines an important challenge in ultrasonic structural health monitoring (SHM), which is the problem of the optimal placement of sensors in order to accurately detect and localize damages. The goal of this study is to enhance damage detection through an optimal sensor placement (OSP) algorithm. The problem is formulated as a global optimization problem, where the objective function to be maximized is evaluated by a ray tracing approach, which approximately models Lamb waves propagation. A genetic algorithm (GA) is then used to solve this optimization problem. Simulations and experiments were conducted to validate the proposed method on a carbon epoxy composite plate. Results show the effectiveness and the advantages of the proposed method as a tool for OSP with reasonable computation time.Projet AIRCELLE (EPICE/CORALIE

Spark plasma sintering as a reactive sintering tool for the preparation of surface-tailored Fe–FeAl2O4–Al2O3 nanocomposites

Al1.86Fe0.14O3 powders were partially or totally reduced in H2. The fully reduced Fe–Al2O3 nanocomposite powder was sintered by spark plasma sintering (SPS) without any reaction taking place. For the other powders, the SPS induced the formation of FeAl2O4 and sometimes Fe. The most severe reducing conditions were found at the surface of the materials, producing nanocomposites with a surface layer composition and microstructure different to those of the core. This in situ formed composite layer confers a higher hardness and fracture strength

Spark plasma sintering of alumina: Study of parameters, formal sintering analysis and hypotheses on the mechanism(s) involved in densification and grain growth

The spark plasma sintering (SPS) of an undoped commercial α-Al2O3 powder (0.14 μm) was investigated. The SPS parameters such as the dwell temperature, applied external pressure, temperature of pressure application, dwell time and pulse pattern were varied. A sintering path (relative density vs. grain size) showing two regimes has been brought to the fore: densification without grain growth occurring at the lower temperatures and grain growth without much further densification taking place at the higher temperatures, with a threshold between 1100 and 1200 °C. In addition, a formal sintering analysis was performed in order to identify the mechanism(s) involved in densification and grain growth

Mechanical and tribological properties of Fe/Cr-FeAl2O4-Al2O3 nano/micro hybrid composites prepared by Spark Plasma Sintering

Fe/Cr–Al2O3 nanocomposite powders are prepared by H2 selective reduction of oxide solid solutions. These powders, an alumina powder and a starting oxide powder, are sintered by spark plasma sintering. The microstructure of the resulting materials is studied. The composites show a lower microhardness and higher fracture strength than unreinforced alumina. The friction coefficient against an alumina ball is lower, revealing the role of the intergranular metal particles, whereas FeAl2O4 grains formed during SPS are beneficial for higher cycle numbers