TLP bonding of Ti-6Al-4V and Mg-AZ31 alloys using pure Ni electro-deposited coats

Transient liquid phase (TLP) bonding of Mg-AZ31 and Ti-6Al-4V alloys was performed using pure thin Ni electro-deposited coat interlayer (12 μm). The effect of bonding temperature, time and pressure on microstructural developments and subsequent mechanical properties across joint interface was studied at a temperature range from 500 to 540 °C, bonding time from 1 to 60 min and bonding pressure from 0 to 0.8 MPa. The mechanisms of bond formation varied across the joint region, with solid-state diffusion dominant at the Ti-6Al-4V interface and eutectic diffusion at the Mg-AZ31 interface. Joint microstructure was examined by scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) was used to detect the formation of intermetallic phases at the fracture surface. The maximum joint shear strength of 61 MPa was obtained at a temperature of 520 °C, 20 min and at a bonding pressure of 0.2 MPa. This joint strength was three times the bond strength reported for joints made using adhesives and represents 50% of the Mg-AZ31 alloy shear strength.     

Boiling heat transfer on a high temperature silver sphere in nanofluid

To investigate boiling heat transfer characteristics of nanofluids, transient quenching experiments of a high temperature silver sphere in water-based nanofluids with Ag and TiO₂ nanoparticles were performed. A silver sphere with a diameter of 10 mm and an initial temperature of 700 °C was quenched in these nanofluids at a temperature of 90 °C. The results showed a considerable reduction in the quenching ability of nanofluids compared to that of pure water. The presence of nanoparticles in water caused the film boiling mode to vanish at lower temperatures depending on the mixture concentration. Calculated heat transfer rates in nanofluids were lower than those in pure water. In the quenching experiments with an unwashed heated sphere, the film boiling mode did not appear and the hot sphere quenched more rapidly through nucleate boiling. In this case the sphere surface was covered by a thin layer of nanoparticles. It was evident that nanoparticle deposition on the sphere surface prevented vapor film from forming around it and resulted in quick quenching of the hot sphere.     

Shaft misalignment effect on bearings dynamical behavior

The inherent problems of the rotating machine dysfunction are often caused by shaft misalignment. This defect generates some important loads and vibrations, and can lead to a premature failure of the bearing, the shaft, or the coupling. This work deals with the development of a theoretical model describing this phenomenon. This allows obtaining and analysing the vibration response as well as the reaction in bearings.     

Phenolic content and antioxidant activity of four date palm (Phoenix dactylifera L.) fruit varieties grown in Tunisia

Fruits of date palm ( Phoenix dactylifera L.) are consumed throughout the world and are a vital component of the diet in most Arabian countries. This study has been carried out to evaluate the total phenolic content and the antioxidant activity of four date palm fruit varieties grown in Tunisia. All measurements were made at the 'tamar' stage-the final stage of fruit ripeness. The date varieties were found to be rich in total phenolic ranging from 209.42 mg of equivalent gallic acid/100 g fresh weight in Kentichi to 447.73 mg equivalent gallic acid/100 g fresh weight in Allig. The date varieties studied were characterised by a high antioxidant activity ranging from 866.82 for the Deglet Nour to 1148.11 μmol Equivalent Trolox/100 g fresh weight for Khouet Kenta by the ABTS method. In fact, the DPPH method revealed that Allig having the lowest antioxidant activity (0.72) followed by Deglet Nour (1.53), Kentichi (1.68) and Khouet Kenta variety (1.96). This study suggest that Tunisian date palm fruit may serve as a good source of natural antioxidants and could potentially be considered as a functional food ingredient.     

Maghrebian dialect recognition based on support vector machines and neural network classifiers

This paper investigates the feed forward back propagation neural network (FFBPNN) and the support vector machine (SVM) for the classification of two Maghrebian dialects: Tunisian and Moroccan. The dialect used by the Moroccan speakers is called “La Darijja” and that of Tunisians is called “Darija”. An Automatic Speech Recognition System is implemented in order to identify ten Arabic digits (from zero to nine). The implementation of our present system consists of two phases: The features extraction using a variety of popular hybrid techniques and the classification phase using separately the FFBPNN and the SVM. The experimental results showed that the recognition rates with both approaches have reached 98.3 % with FFBPNN and 97.5 % with SVM.     

Hybrid Deep Neural Network-Based Text Representation Model to Improve Microblog Retrieval

Abstract

Retrieving relevant information from Twitter is always a challenging task given its vocabulary mismatch, sheer volume and noise. Representing the content of text tweets is a critical part of any microblog retrieval model. For this reason, deep neural networks can be used for learning good representations of text data and then conduct to a better matching. In this paper, we are interested in improving both representation and retrieval effectiveness in microblogs. For that, a Hybrid-Deep Neural-Network-based text representation model is proposed to extract effective features’ representations for clustering oriented microblog retrieval. HDNN combines recurrent neural network and feedforward neural network architectures. Specifically, using a bi-directional LSTM, we first generate a deep contextualized word representation which incorporates character n-grams form FasText. However, these contextual embedded existing in a high-dimensional space are not all important. Some of them are redundant, correlated and sometimes noisy making the learning models over-fitting, complex and less interpretable. To deal with these problems, we proposed a Hybrid-Regularized-Autoencoder-based method which combines autoencoder with Elastic Net regularization for an effective unsupervised feature selection and extraction. Our experimental results show that the performance of clustering and especially information retrieval in microblogs depend heavily on features’ representation.     

Natural Convection Heat Transfer in a Nanofluid Filled U-Shaped Enclosures: Numerical Investigations

In the present work, enhancement of convective heat transfer rate in three-dimensional U-shaped enclosures using nanofluids is numerically investigated. Two different types of nanoparticles, namely, Cu, and Al₂O₃, with pure water, are the considered single-phase nanofluids. Natural convection and geometric parameter effects on the averaged Nusselt numbers are investigated. Velocity vectors and isotherm fields for the Al₂O₃/H₂O nanofluid are presented at various Rayleigh numbers. The governing dimensionless equations are solved using the commercial finite-volume-based computational fluid dynamics code, FLUENT. Our results are consistent with previously published predictions. In particular, heat transfer enhancement is found to increase with increasing nanoparticles volume fractions, Rayleigh numbers, as well as cooled wall length extensions.     

A methanol – Tolerant carbon supported Pt–Sn cathode catalysts

Carbon supported Pt–Sn bimetallic electrocatalysts with a Pt:Sn 90:10 atomic ratio were prepared by impregnation method and then heat treated at 300 and 500 °C under Helium atmosphere. The purpose of this work is to investigate the effect of tin addition to platinum for methanol tolerant oxygen reduction reaction. In this sense, structure and morphological properties of supported bimetallic catalysts were correlated to the catalytic performance. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations confirm the formation of Pt–Sn bimetallic electrocatalysts with a Pt single-phase material alloy and revealed an increase in the average particle size after heat treatment. The electrocatalytic activities of these samples for the oxygen reduction reaction (ORR) were examined in acidic medium using both a rotating disk (RDE) and a rotating ring disk (RRDE) electrodes. Compared with the Pt/C, Pt–Sn/C bimetallic catalysts show superior electrocatalytic activity towards ORR with an approaching four electron pathway leading to water formation. The specific and mass activity for ORR follow the order of Pt–Sn/C-500 ≈ Pt–Sn/C-300 > Pt–Sn/C > Pt/C. Furthermore, it is found that among the three Pt–Sn samples, Pt–Sn/C-500 exhibits the highest methanol tolerance. These experimental observations indicate that the addition of Sn into Pt is favorable to maximize the ORR performances of platinum and further the heat treatment is beneficial to improve the methanol tolerance behavior. On this basis, the novel Pt–Sn catalysts can be considered as potential candidates to be used as cathodes in Direct Methanol Fuel Cells.     

Fatty acids distribution in different tissues of wild and reared Seriola dumerili

In this study, we compared the lipid and fatty acids content, between cultured and wild Seriola dumerili, in different edible portions. Results showed that cultured fish contained a higher level of lipids than wild fish. The fatty acids profiles revealed that, among all the split‐fish side, palmitic (C16:0) and oleic (C18:1n‐9) acid were the principal saturated and monounsaturated fatty acids, in cultured and wild S. dumerili. On the other hand, wild S. dumerili contained a higher level of saturated (38.12 ± 0.54% vs. 33.66 ± 0.15% in cultured fish), monounsaturated (33.13 ± 1.07% vs. 26.49 ± 0.17%), n‐3 polyunsaturated fatty acids (PUFA) (23.90 ± 1.02% vs. 19.77 ± 0.51%) particularly docosahexaenoic acid (DHA) (18.83 ± 0.48% vs. 11.77 ± 0.42%). However, the cultured fish showed a higher level of n‐6 PUFA due principally to the higher value of linoleic acid (C18:2n‐6). In fact, changes in fatty acids content between anatomical areas marked differences in the muscle quality of wild and cultured S. dumerili. According to this study, both groups of wild and farmed S. dumerili have nutritional benefits for human health. Cultured fish were characterised by higher hypocholesterolaemic and hypercholesterolaemic fatty acids ratio for all samples studied and a lower n‐3/n‐6 ratio due to the abundance of n‐3 PUFA particularly DHA in wild fish.     

Drilling Behavior of Flax/Poly(Lactic Acid) Bio-Composite Laminates: An Experimental Investigation

ABSTRACT

This paper aims to investigate the effects of machining parameters such as spindle speed, feed rate and drill diameter on machinability of flax/poly(lactic acid) bio-composites, to analyze the relations among cutting forces, drilling-induced damages and crack propagation of the drilled samples. In particular, a set of drilling experiments were conducted using different drilling conditions and a new low-cost measurement set-up was developed to measure the cutting force during the drilling operation. In addition, the analysis of variance (ANOVA) was applied to identify the significance of each individual cutting parameter. The experimental results indicate the relation between the thrust force and the machinability parameters of flax fiber reinforced bio-composite. The increase in spindle speed reduces thrust force and delamination size of the drilled holes, whereas an increase in feed and drill diameter leads to a considerable increase in both thrust force and delamination factor. The effect of spindle speed on peripheral damage was not significant for the drills tested, though the feed rate was found to play the key role on the delamination damage area. The best hole quality was achieved with the samples drilled at spindle speed and feed rate of 3000 rpm and 0.11 mm/rev, respectively.