Characterization of ozone sensors based on WO3 reactively sputtered films: influence of O2 concentration in the sputtering gas, and working temperature

We report on electrical responses of tungsten oxide thin film ozone sensors based on a tungsten trioxide (WO₃)/tin oxide (SiO₂)/Si structure with interdigitated Pt electrodes. The influence of O₂ concentration in the sputtering gas and working temperature of the sensor are investigated. Sensitivity to ozone increases with O₂ content in the sputtering gas. It reaches its highest value for sensors fabricated with 50% O₂. For these sensors, the best ozone sensitivity and shortest response and recovery times are obtained at a working temperature of 523 K. Ozone sensitivity is compared to other ozone sensors.     

Rapid homogeneous esterification of cellulose extracted from Posidonia induced by microwave irradiation

In this article, we report on the synthesis of cellulose esters by the reaction of cellulose and some cyclic anhydrides, such as succinic, maleic, and phthalic anhydrides. For this, an esterification method was finalized. Indeed, cellulose extracted from Posidonia biomass was first solubilized in the solvent system lithium chloride (LiCl)/N,N‐dimethylacetamide and then esterified by cyclic anhydride in the presence of catalysts such as N,N‐dimethyl‐4‐aminopyridine, tripropylamine, tributylamine, and calcium carbonate. This method was fast and reproducible with the LiCl system as a solvent and with an efficient activation by controlled microwave power. In this way, the reaction time was reduced from several hours to just a few minutes. The reaction products were characterized by IR and solid‐state cross‐polarization/magic angle spinning ¹³C‐NMR spectroscopy. The degree of substitution (DS) and the grafted ester group content of the different products were obtained by alkali saponification followed by titration of the excess alkali. Two activation methods were compared, and the results show that the application of classical heating gave less successful results than those obtained by microwave activation. Indeed, with microwave activation, a higher DS (2.25) was obtained after 10 min. However, with classical heating, a value of DS equal to 1.2 was obtained after 12 h. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental study on carboxymethylation of cellulose extracted from Posidonia oceanica

The production of carboxymethylcellulose (CMC) from bleached cellulose pulps obtained from Posidonia oceanica was explored. The optimal reaction conditions were studied for the carboxymethylation of cellulose in organic liquids. The carboxymethylation reaction was carried out with NaOH and monochloroacetic acid (MAC) as the reagent. Different alcohols were compared in terms of the degree of substitution (DS). The highest DS was obtained with n‐butanol. For this alcohol, the effects of the temperature, alkali concentration, and MAC concentration were studied. The reaction was also carried out in three consecutive steps. The resulting CMC had a DS of about 2.75. The functionalization of cellulose was checked using FTIR spectroscopy and ¹³C‐NMR. The X‐ray analysis showed that the crystalline structure of cellulose decreased when the DS increased and the structure was totally amorphous in high DS material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1808–1816, 2006     

On the performance of the base-stock inventory system under a compound Erlang demand distribution

In this paper, we propose a new method for determining the optimal base-stock level in a single echelon inventory system where the demand is a compound Erlang process and the lead-time is constant. The demand inter-arrival follows an Erlang distribution and the demand size follows a Gamma distribution. The stock is controlled according to a continuous review base-stock policy where unfilled demands are backordered. The optimal base-stock level is derived based on a minimization of the total expected inventory cost. A numerical investigation is conducted to analyze the performance of the inventory system with respect to the different system parameters and also to show the outperformance of the approach that is based on the compound Erlang demand assumption as compared to the classical Newsboy approach. This work allows insights to be gained on stock control related issues for both slow and fast moving stock keeping units.     

Temperature compensated CMOS ring VCO for MEMS gas sensor

This paper presents a CMOS voltage controlled ring oscillator with temperature compensation circuit suitable for low-cost and low-power gas sensor. To operate at low frequency, a control voltage generated by a CMOS bandgap reference is described and the measurement results of the fabricated chips are presented. The output voltage of the reference is set by resistive subdivision. In order to achieve small area and low power consumption, n-well resistors are used. This design features a reference voltage of 1 V. The chip is fabricated in AMS 0.35 μm CMOS process with an area of 0.032 mm². Operating at 1.25 V, the output frequency is within 200 ± l0 kHz over the temperature range of ?25 to 80 °C with a power consumption of 810 μW.     

Identification of Constitutive Parameters using Hybrid ANN multi-objective optimization procedure

This paper deals with the identification of material parameters for an elastoplastic behaviour model with isotropic hardening using several experimental tests at the same time. But, these tests are generally inhomogeneous and finite element simulations are necessary for their analysis. Therefore an inverse analysis is carried out and the identification problem is converted into a multi-objective optimization where prohibitive computing time is required. We propose in this work a hybrid approach where Artificial Neural Networks (ANN) are trained by finite element results. Then, the multi objective procedure calls the ANN function in place of the finite element code. The proposed approach is exemplified on the identification of non-associative Hill’48 criterion and Voce parameters model of the Stainless Steel AISI 304.     

In situ studies of bovine serum albumin adsorption onto functionalized polystyrene latices monitored with a quartz crystal microbalance technique

The adsorbability of bovine serum albumin (BSA) onto poly(styrene‐co‐itaconic acid) (PS–IA), poly(styrene‐co‐hydroxyethyl methacrylate) (PS–HEMA), poly(styrene‐co‐acrylic acid) (PS–AA), and poly(styrene‐co‐methacrylic acid) (PS–MAA) latices were investigated with a quartz crystal microbalance. The amount adsorbed onto the functionalized latices, except for PS–MAA, was greater than that adsorbed onto polystyrene (PS) latex. To explain this result, two kinds of interaction forces were considered, hydrogen bonding and hydrophobic interactions, whereas electrostatic interaction was assumed to be small. When comparing the two extremes of hydrophobic interaction and hydrogen bonding, the latter was stronger. The corrected adsorption mass suggested that the BSA molecules were adsorbed onto the PS–MAA latex in a side‐on mode. However, in the case of the PS, PS–IA, PS–HEMA, and PS–AA latices, the BSA molecules were probably adsorbed in multiple layers. The presence of the BSA in the latex particle surface was verified by attenuated total reflectance/Fourier transform infrared spectroscopy and atomic force microscopy. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42055.     

The evolution of a-GaAs1−xNx/c-GaAs interface states as a function of Ar-NH3 plasma

This work concerns investigations on electrical properties of amorphous GaAs_1−xN_x thin films grown on GaAs substrates. Film deposition was carried out by RF sputtering of a GaAs target by adding a nitrogen carrier gas (NH₃) to an Ar plasma. Chemical etching of substrates followed by different plasma treatments (like reverse bias and/or NH₃ glow discharge) prior to film deposition have been studied. The effects of substrate and growth temperature and of total pressure in the reactor have been analysed. Electrical characteristics (C–V and C–V(T)) have enabled us to put in evidence the evolution of interface states of the a-GaAs_1−xN_x/c-GaAs junctions. The amorphous GaAs_1−xN_x thin films are potentially interesting to be considered for GaAs-based MIS structures, due to their relatively high resistivity values, or as passivating layers on GaAs devices.     

Microstructure and electrical properties of RuO2-CeO2 composite thin films

RuO₂-CeO₂ composite thin films are deposited on various Si substrates by a radiofrequency magnetron sputtering technique. Compacted polycrystalline pellets of the nanostructured CeO₂-RuO₂ composite system are used as standard samples for comparative electrical analyses. All films and composite samples are analyzed by X-ray diffraction and transmission electron microscopy. Electrical measurements of radiofrequency sputtering of thin films are performed as a function of the RuO₂ fraction and of the temperature (between 25 and 400 °C). A nonlinear variation in the electrical conductivity of the RuO₂-CeO₂ composite thin films as a function of the RuO₂ volume fraction (Φ) is observed and discussed. It is interpreted in terms of a power law (in (Φ − Φc)^m ), where m and Φc are parameters characteristic of the distribution of the conducting phase in a composite medium.