Spark plasma sintering of double-walled carbon nanotubes

Bulk samples of double-walled carbon nanotubes are prepared for the first time. The best spark plasma sintering conditions are (1100 °C, 100 MPa). Raman spectroscopy and scanning electron microscopy show that the nanotubes are undamaged. The density is equal to 1.29 g cm⁻³ and the pores are all below 6 nm in diameter. The electrical conductivity is equal to 1650 S cm⁻¹. The transverse fracture strength is equal to 47 MPa.     

Electro-thermal measurements and finite element method simulations of a spark plasma sintering device

Current, voltage and temperature measurements were performed at different points of the system to identify the controlling parameters of the spark plasma sintering (SPS) process. The very low inductance effects despite the high intensity current circulating through the SPS column justifies the use of Joule heating to characterize the phenomenon. The measurements also enabled the improvement and validation of an earlier electro-thermal numerical model developed using the finite element method (FEM). It has been shown that the electrical resistivity and the thermal conductivity of each of the elements are crucial parameters for the simulations. These parameters strongly modify the current modeled, thereby affecting the temperature distribution throughout the SPS column.     

Nonparametric modeling of carbon prices

This paper constitutes the first exercise of nonparametric modeling applied to carbon markets. The framework of analysis is carefully detailed, and the empirical application unfolds in the case of BlueNext spot and ECX futures prices. The data is gathered in daily frequency from April 2005 to April 2010. First, we document the presence of strong nonlinearities in the conditional mean functions. Second, the conditional volatility functions reveal an asymmetric and heteroskedastic behavior which is dramatically different between carbon spot and futures logreturns. The results for spot prices are also robust to subsamples' decomposition. Third, we show in an out-of-sample forecasting exercise that nonparametric modeling allows reducing the prediction error by almost 15% compared to linear AR models. This latter result is confirmed by the Diebold–Mariano pairwise test statistic.     

Timed verification of the generic architecture of a memory circuit using parametric timed automata

Using a variant of Clariso-Cortadella’s parametric method for verifying asynchronous circuits, we analyse some crucial timing behaviors of the architecture of SPSMALL memory, a commercial product of STMicroelectronics. Using the model of parametric timed automata and model checker HYTECH, we formally derive a set of linear constraints that ensure the correctness of the response times of the memory. We are also able to infer the constraints characterizing the optimal setup timings of input signals. We have checked, for two different implementations of this architecture, that the values given by our model match remarkably with the values obtained by the designer through electrical simulation. Partially supported by project MEDEA+ Blueberries. A preliminary version appeared in the Proceedings of 4th International Conference on Formal Modelling and Analysis of Timed Systems (FORMATS’06), Sept. 2006.     

Platinum metals coatings by vacuum deposition processes

The technique of evaporation by electron bombardment was used to obtain thick coatings of Pd, Pt and Ir on substrates of Ni, mild steel, stainless steel, Ti, Ta, W and graphite. Vapor condensation was effected in three different ways: under vacuum, under a residual pressure of argon and by ion plating (polarization voltage V_c on the substrates 5 kV or less). The temperature range of the substrates was between 100 and 800°C. The coatings were examined for adherence to the substrate and for morphological characteristics. The results obtained allowed us to coat shaped substrates with the platinum metals for various applications.     

Observer-based monitoring of thermal runaway in microwaves food defrosting

Despite its energetic interest, the use of microwaves for the thawing or temperage of food products presents a major drawback called thermal runaway. This is mainly due to the important gap between the dielectric properties of water in solid and liquid phases. A monitoring approach of the temperatures inside a foodstuff during microwave defrosting is therefore proposed to, in a first step, detect the critical phenomena of thermal runaway, and, in further work, to control it. An observer allowing to estimate the internal temperatures from the temperature of the surface has been developed. An Extended Kalman Filter, because of its simplicity of design, has been chosen, but this choice is not exclusive. The heat transfer with phase change and microwave effects is represented by a nonlinear distributed parameters system, and the observer is based on a standard finite volume scheme. The approach is experimentally carried out and validated during the defrosting of a block of tylose.     

Characterisation of the dry salted process for the production of the msayer, a traditional lemon aromatising condiment

Msayer is a dry salted lemon used as an aromatising condiment in many North-African food recipes. This preparation is obtained by adding coarse salt (10 g/100 g fresh lemons) to fresh cut lemons in containers kept under dark conditions away from air for around a month and a half. A survey of 52 days showed low initial uptake of citric acid and sugars from the formed liquid phase. Nevertheless, there were still sugars detected even at the end of the survey attesting for the low microbial activity as also shown by carbon dioxide production and microbial viable counts. Indeed, the microbial counts showed a steady decrease reaching 2 log units at the 52nd day of curing. Moulds were detected only at the beginning but at low numbers. No viable counts of lactic acid bacteria were observed on MRS medium despite detection of lactic acid (8 g/l). In contrast, yeasts seem to dominate in the msayer preparation. They count for almost all the microbial population especially after the first week. Six of these acid and halotolerant yeast isolates were identified, by sequence analysis of the amplified 5.8S rRNA and the two internal transcribed spacer regions, as Candida parapsislosis (2 isolates) and unclassified Saccharomycetales (4 isolates).     

Development of a portable spectrofluorimeter for measuring the microbial spoilage of minced beef

The evaluation of meat spoilage is based on sensory and microbiological analyses. The disadvantages of sensory analyses are its reliance on highly trained panelists, a procedure which makes it costly and unattractive for routine analyses. Moreover, the classical microbiological analyses are lengthy, costly and destructive. In this study a portable fluorescence spectrometer was tested to quantify minced beef spoilage. This study was investigated on samples stored aerobically and under vacuum at 5 and 15 °C. Total viable counts (TVC), Pseudomonas, lactic acid bacteria, and yeast/molds counts were investigated with classical culture methods. Fluorescence spectra were recorded on the same samples using different excitation LEDs (280, 320, and 380 nm). PLS-R with leave-one-out cross validation was used to perform calibration and validation models. The PLS-R models presented good R2(CV) (0.50-0.99) and ratio of standard deviation (RPD(CV): 1.40-8.95) values after cross-validation. It could be concluded that portable spectrofluorimeters are promising devices to evaluate spoilage in minced beef.