Wireless propagation channel modeling for optimized Handoff algorithms in wireless LANs

In this paper, we present a time-series analysis technique which covers the basic concepts and mechanisms driving the wireless propagation channel. We also use a generated series for simulation study of Handoff performance showing the impact of multipath phenomena. Moreover, the extraction of the average signal has been used to reduce significantly the number of unnecessary Handoffs.The wireless propagation channel modeling is based on the linear model concept of the received power from the access point (AP). This concept has a crucial role in modeling new decentralized Handoff based on the ratio of expected and current signal slopes already provided by the linear model. Hence, a fuzzy-based solution is developed and a comparison with the analytical solution results is established. Until recently, Handoff mechanisms are implemented entirely in software, which increasingly becoming infeasible. Therefore, this work attempt to follow the top-down co-design approach providing hardware prototype which leads to reduce the power consumption and support high processing speed.     

The Chemical Properties and Volatile Compounds of Virgin Olive Oil from Oueslati Variety: Influence of Maturity Stages in Olives

The aim of the present work was to investigate the influence of fruit ripening on oil quality and volatile compounds in an attempt to establish an optimum harvesting time for Oueslati olives, the minor olive variety cultivated in Tunisia. Our results showed that many analytical parameters, i.e., peroxide value, UV absorbance at 232–270 nm, chlorophyll pigments, carotenoids and oleic acid contents decreased during ripening, whilst linolenic acid increased. Free acidity remained practically stable with a very slight rise at the highest maturity index. The volatile compounds emitted by the Oueslati olive oil were characterized and quantified by HS‐SPME‐GC‐EIMS. Twenty‐three volatile compounds were identified, mainly aldehydes, sesquiterpenes and esters. The results show variations in the volatile fractions and quality parameters of Oueslati extra virgin olive oil obtained at different olive‐ripening stages. Fifteen sesquiterpenes were identified for the first time in this cultivar, mainly hydrocarbon derivatives, but also oxygenated ones. On the basis of the quality parameters and volatile fractions studied, the best stage of Oueslati olive fruits for oil processing seems to be at ripeness index about 3.0. Indeed, these results suggested the possibility of using sesquiterpenes for olive authenticity and traceability and demonstrated that the volatile fractions can be used as indicators of the degree of ripening of the olives used to obtain the corresponding virgin olive oils.     

Evaluation of different supplementary nutrients for enhanced biohydrogen production by Enterobacter aerogenes NRRL B 407 using waste derived crude glycerol

Crude glycerol (CG) has several advantages over a range of conventional substrates used for biohydrogen production by Enterobacter aerogenes NRRL B 407. Meanwhile, high process cost due to requirement of expensive supplementary media component is a concern. Therefore, different less expensive (or wastes) materials have been evaluated as supplementary nutrient for H₂ production by CG (meat processing and restaurant waste based biodiesel derived) bioconversion. Among the materials selected, slaughterhouse liquid waste (SL), brewery waste biomass (BWB) and urea was found to improve the production by 18.81 ± 3.56, 27.30 ± 3.54 and 38.57 ± 3.66%, respectively. Further, in the case of urea (10 mg/L), cumulative production as high as 116.41 ± 3.72 mmol H₂/L media has been achieved; which is comparable to other reports available on CG bioconversion. Thus, present study demonstrates successful replacement of large amount (∼5–6 g/L) of expensive nutrients/buffering agents by negligible amount (∼10 mg/L) of different waste materials, without compromising the cumulative H₂ yield. Further, the strain used in the present study was found to grow at an acidic pH as low as 3.3, indicating its prospective application for dark fermentative H₂ production.     

The influence of the heat extraction mode on the performance and stability of a mini solar pond

The performance and stability of a 0.64 m² mini solar pond were experimentally and numerically studied. The experimental results showed that the daily average temperatures of the mini pond increased quickly to reach 54 °C in the lower convective zone after only 20 days. A 1 D numerical model to predict the temperature and the salinity in the mini pond was developed. The results obtained from the numerical calculation were compared with our experimental results and good agreement was found. Therefore a new method of heat extraction from the non convective zone was numerically investigated in order to enhance the mini pond performance. Using this new method of heat extraction, the numerical results showed that the mini pond efficiency could be considerably improved. However, the method was found to reduce the stability of the lower interface.     

The compositional quality and volatile compounds of samples from the blend of monovarietal olive oils cultivated in Tunisia

Chemlali olive oil has been blended with oils obtained from Oueslati and Chetoui varieties to improve the quality of the former one. Parameters such as acidity, acids compositions, phenol content, oxidative stability and volatile compounds were characterised for various blends Chemlali × Oueslati and Chemlali × Chetoui. The accumulation of volatiles originating from the lipoxygenase pathway in the monovarietal oils was different and closely dependent on the genetic store of each variety. The concentrations appeared to proportionally vary according to the relative proportion of each monovarietal oil in the mixtures. The blending process improved fatty acids by increasing the oleic acid content and decreasing the palmitic and linoleic acids levels of Chemlali oil. At 40% blending, oleic acid increased from 54% to 62%, while palmitic acid decreased from 18.59% to 16% when Oueslati and Chetoui olive oil was used.     

Influence of olive storage period on volatile compounds and oil quality of two Tunisian cultivars of Olea europea,Chemlali and Chetoui

Olives (Olea europaea cv. Chemlali and Chetoui) used for oil production were stored, in plastic containers, at 5 °C for four different periods (0–3 weeks) before oil extraction. After storage, the oils were extracted from the fruits, and the acidity, peroxide value, coefficients of specific extinction at 232 and 270 nm, stability, pigments, total phenols, fatty acids, and volatile compounds were determined. The results showed that storage of fruits produced losses in the olive oil quality. During storage, a marked decrease in total phenols content was observed. The cultivar richer in phenols (862.16 mg kg^?1 in Chétoui) had a lower loss (25%). On the contrary, in Chemlali olive oil, the starting value of 728.52 mg kg^?1 decreased to 469.25 mg kg^?1, with a loss of 35%. Chétoui and Chemlali olive oils presented the highest oxidative stability before storage (58.76 and 47.05 h, respectively), while the lowest values were recorded using olives stored for 3 weeks (54.46 and 43.43 h, respectively). The changes in the volatile bouquet were determined using headspace solid phase microextraction (HS‐SPME). Thirty compounds were characterised by GC–FID and GC–MS. Compounds belonging mainly to alcohols, esters, aldehydes, ketones and hydrocarbons chemical classes characterised the volatile profiles.     

A robust CBIR framework in between bags of visual words and phrases models for specific image datasets

One objective of the Content Based Image Retrieval research field is to propose new methodologies and tools to manage the increasing number of images available. Linked to a specific context of small expert datasets without prior knowledge, our research work focuses on improving the discriminative power of the image representation while keeping the same efficiency for retrieval. Based on the well-known bag of visual words model, we propose three different methodologies inspired by the visual phrase model effectiveness and a compression technique which ensures the same effectiveness for retrieval than the BoVW model. Our experimental results study the performance of our proposals on different well known benchmark datasets and show its good performance compared to other recent approaches.