Modified smectitic Tunisian clays used in the formulation of high performance lubricating greases

Two smectitic Tunisian clays were organically modified by exchange reaction with dioctadecyl dimethylammonium chloride (DODMA) and hexadecyl benzyl dimethylammonium chloride (HBDMA). The resulting organoclays were used in the formulation of lubricating greases. The results of the performance tests applied to the obtained greases showed that their physicochemical and mechanical characteristics are in conformity with the extreme-pressure (EP) greases specifications. The obtained greases present good EP properties with only 0.5% EP additives. The smectitic clays used could constitute a raw material in the formulation of high performance lubricating greases.     

Thermo-optic designs for electromagnetic-field probes formicrowaves and millimeter waves

The development of an electromagnetic-field probe for microwave and millimeter-wave frequencies is reported. The probe uses an optically sensed thermometer to measure the heating of a resistive element in an electromagnetic field. The response is calculated for several different configurations of the resistive element, and two optimal designs are chosen. Measurements on experimental probes of these designs are presented. One of the designs displays a flat frequency response above 30 GHz and a sensitivity of 38 V/m. Improvements in the design are identified that should significantly increase the sensitivity and improve the low-frequency response     

Eco-friendly process for soft drink industries wastewater reuse as growth medium for Saccharomyces cerevisiae production

Soft drink industries suffer inadequate handling of their product losses generally considered as wastes. Those products contribute to the wastewater organic load augmentation and cause fastidious environmental impact. In this study, an industrial scale bioconversion process based on multistage fermentation was proposed to treat and reuse soft drink factories’ high-loaded effluents for valuable components production. An upstream segregation of non-consumed beverage was performed to reduce the organic load of the soft drink wastewater. Beverage characterization revealed an important sugar content. Such an organic compound is undoubtedly responsible of the high organic load of soft drink wastewater. Thus, the bioconversion of the sugar content of soft drink waste to single-cell proteins was proposed as a solution to reduce wastewater polluting load. Soft drink wastewater including rejected and returned products was tested to be used as a substrate for yeast biomass production using a commercial yeast strain of Saccharomyces cerevisiae. The effect of nutrient supplementation and the initial sugar concentration effect in culture media on the biomass production were investigated using batch and fed-batch process. Results indicated that supplementation is necessary for successful fermentation. Juices and nectars gave better sugar-biomass conversion yields (0.38–0.45 g g⁻¹). Depletion of the sugar contained in the soft drinks exceeded 96 % for all fermented media. Fed-batch culture revealed a biomass concentration improvement reaching 9.16 g L⁻¹ compared to batch biomass concentration resulting from batch cultures (5.2 g L⁻¹). The proposed process was shown to enable beverage industries to reduce water pollution generation through an on-site segregation procedure and a storage system to valorize product losses as source medium for single-cell protein production.

     

Non-linear dynamic system identification: A multi-model approach

We are concerned with models which are able to describe multiple-input multiple-output (MIMO) non-linear dynamic systems. These models are represented in the form of rules and are known as Tagaki-Sugeno models. An identification algorithm for these models based on input and output data is presented. Parameter estimation is based on the calculation of model sensitivity functions with respect to their parameters. Some aspects of structure identification are also tackled, i.e. determination of local model orders and number of rules.     

Cooperative Association/Re-association Approaches to Optimize Energy Consumption for Real-Time IEEE 802.15.4/ZigBee Wireless Sensor Networks

The major challenge of real-time Wireless Sensor Networks stills the optimization of both constraints: energy consumption, to get long network lifetime and the communication delay, to meet real-time requirements. In the context of IEEE 802.15.4/ZigBee networks, the association procedure has a direct effect on building paths optimizing those constraints. In this paper, we are interested on the definition of an ideal approach of load balancing to fairly distribute energy consumption among nodes in IEEE 802.15.4/ZigBee WSNs. This approach leads to conserve energy of each node in order to extend the network lifetime. To be closer to this ideal, we propose new dynamic association/re-association approaches allowing path alternation relative to association criteria and their threshold parameters. The implementation of those approaches in NS2 simulator highlights the efficiency of cooperative and dynamic association criteria particularly the one based on the sum of the inverses of remaining energy. Indeed, this approach gives better results with regard to energy distribution according to ideal approach which leads to a longer lifetime. It also performs lower latency for real time communication.     

Changes in Fatty Acid, Tocopherol and Xanthophyll Contents During the Development of Tunisian-Grown Pecan Nuts

Among oil compounds, fatty acids, tocopherols and xanthophylls (lutein and zeaxanthin) are of special interest due to their nutritional properties. The identification and quantification of these compounds in pecan nuts (Carya illinoinensis) could therefore be very useful to produce functional foods rich in compounds of this type. This paper reports studies on their accumulation and the effect of ripening on the content of these high value-added compounds. The total lipid content increased during the ripening. Saturated and polyunsaturated fatty acids decreased significantly, whereas, monounsaturated fatty acids increased during the ripening of pecan nut fruit. Maximum levels of total tocopherol (279.53 mg/kg oil) and xanthophyll (6.18 mg/kg oil) were detected at 20th weeks after the flowering date. These amounts decreased gradually as ripening advances. The early stages of pecan ripening seem to have nutritional and pharmaceutical interests. These results may be useful for evaluating the pecan nut quality and determining the optimal period when the pecans accumulated the maximum of these nutritional and healthy compounds.     

Simple analytical solution and efficiency improvement of polysilicon emitter solar cells

A simple analytical model has been developed to simulate the performance of solar cells with polysilicon contact on the front surface. The polysilicon layer with a columnar grain structure is modeled by an effective recombination velocity using a two-dimensional transport equation. A one-dimensional transport equation in the single-crystal emitter is solved, taking into account bulk recombination and non-uniformly doped emitter. Then, simple analytical expressions for the emitter reverse saturation current and light-generated current densities are obtained. The collection of the light-generated carriers in polysilicon layer has been discussed and an analytical solution of the light-generated current is derived. The results show that the polysilicon layer can result in a decrease in emitter reverse saturation current density and an increase in solar cell photovoltaic parameters. In fact, the emitter region should not be treated as a ‘dead layer’ because thin polysilicon layer front surface contact gives an improvement of about 60 mV for the open-circuit voltage, 3.6 mA/cm² for the photocurrent, and 3.9% for the cell efficiency.     

Unsaponified and unsaponifiable determinations as applied to incompletely saponified soaps

Unsaponified and unsaponifiable determinations were made on toilet bar soap, potash vegetable oil paste soap, yellow laundry soap and hardwater cocoa bar soap according to the method of (1) the American Oil Chemists’ Society, and (2) the Society of Public Analysts (British). The results obtained by the two methods were comparable for toilet bar soap, potash vegetable oil paste soap and yellow laundry soap. The unsaponifiable matter in hardwater cocoa bar soap, however, appeared considerably lower when determined by the A. O. C. S. method than when determined by the S. P. A. method. Extraction of unsaponified matter in the former method is by petroleum ether; in the latter method by ethyl ether. In order to determine whether the difference in results could be traced to the difference in solvents, extraction with petroleum ether in the A. O. C. S. method was followed by extraction with ethyl ether. The weight of unsaponified matter (50 gram sample) was increased thereby from 0.791 g. to 1.423 g. The saponification value of the ethyl ether extract under the A. O. C. S. method tended to show that practically all of the additional material extracted with ethyl ether was made up of mono and diglycerides with the mono predominating.