Experimental and numerical study of laser-assisted machining of Ti6Al4V titanium alloy

Laser-assisted machining combines several experimental parameters such as cutting speed, feed rate, depth of cut, laser power and distance between tool rake face and the laser beam axis. The optimization of these parameters is necessary to ensure the efficiency of assistance and to increase productivity. This paper focuses on the understanding of the physical phenomena during laser-assisted machining, and on optimising this process. This contribution is based on an experimental and a numerical study. The experimentalpart highlights the effects of the laser power as well as the distance between the tool rake face and the axis of the laser beam. As for the numerical part, it was performed on the ABAQUS/Explicit software. The proposed model improves the understanding of the physical phenomena of chip formation and the cutting force reduction when machining with laser assistance. In addition, this model allows a better optimization of laser and cutting parameters.Numerical findings generally corroborate experimental results and can lead to some other information difficult to catch experimentally. The main contention in the paper is that the distance between the axis of the laser beam and the tool rake face is the most important parameter that controls the reduction of the cutting force. This cutting force reduction can exceed 50%

Wireless Power Transfer in Distributed Antenna Systems

This paper studies the performance of wireless power transfer in distributed antenna systems (DAS). In particular, the distributed remote radio heads (RRHs), which are conventionally distributed in the network to enhance the performance, are also used to increase the energy harvesting (EH) at the energy-constrained users. Based on this idea, the network area is divided into two zones, namely, A) EH zone and B) Interference zone. The users in the EH zones are guaranteed to harvest sufficient energy from the closed RRH, while the users in the interference zones harvest energy from the surrounding RRHs. A harvest-then-transmit protocol is adopted, where in the power transfer phase the multiple antennas RRHs broadcast energy signals to the users. In the information transmission phase, the users utilize the harvested energy to transmit their signals to the RRHs. In addition, zero-forcing is applied at the RRHs receivers, to mitigate the interference. The system spectral efficiency is evaluated in two different scenarios based on the channel state information (CSI), namely: 1) CSI is unknown at the RRHs; 2) CSI is perfectly known at the RRHs. In contrast to conventional EH-muliple input multiple output (MIMO) systems, performance analysis of EH DAS-MIMO is a challenging problem, because the channels are characterized by non-identical path-loss and EH effects which make the classical analytical methods nontractable. In light of this, new analytical expressions of the ergodic spectral efficiency are derived, and then Monte-Carlo simulations are provided to verify the accuracy of our analysis. The effects of main system parameters on the EH-DAS performance are investigated. The results show that there is an optimal value of the EH time for each users locations that maximizes the system performance. In addition, size of the EH-zone area depends on the required harvested power at the users which is dependent essentially on the target spectral efficiency

Classification of Southern Tunisian honeys based on their physicochemical and textural properties

This study investigated the physicochemical, rheological and textural properties of nine types of honey from different regions of southern Tunisia. Principal component and cluster analyses were used to classify the honeys into groups. The physicochemical results (water, proteins, total soluble solids, pH, free acidity, water activity, electrical conductivity, invertase activity, Hydroxymethylfurfural (HMF), vitamin C, lycopene and anthocyanins) were in accordance with those of the standards Established by the Codex Alimentarius. The invertase activity varied from 62.58 units/kg to 110.24 units/kg. The HMF values of the different types of honey ranged from 11.48 mg/kg in prickly pear honey to 25.56mg/kg in heather honey. Anthocyanin contents, lycopene and vitamin C contents ranged between 8.38 and 24.86 μg/L, 1.08 to 6.17 mg/kg and 30.71 to 129.38 mg/kg, respectively. The flow test confirmed the Newtonian behavior of all honeys, and their textural properties had very high extrusion forces varying from 113.50 g to 131.05 g. Cluster analysis (CA) and the biplot generated through PCA recognized four groups of honeys based on either the physicochemical parameters or textural attributes and only three groups based on color and sugar

Physical Layer Security With RF Energy Harvesting in AF Multi-Antenna Relaying Networks

In this paper, we analyze the secrecy capacity of a half-duplex energy harvesting (EH)-based multi-antenna amplify-and-forward relay network in the presence of a passive eavesdropper. During the first phase, while the source is in the transmission mode, the legitimate destination transmits an auxiliary artificial noise (AN) signal which has two distinct purposes: 1) to transfer power to the relay and 2) to improve system security. Since the AN is known at the legitimate destination, it is easily cancelled at the intended destination, which is not the case at the eavesdropper. In this respect, we derive new exact analytical expressions for the ergodic secrecy capacity for various well-known EH relaying protocols, namely, time switching relaying (TSR), power splitting relaying (PSR), and ideal relaying receiver (IRR). Monte Carlo simulations are also provided throughout our investigations to validate the analysis. The impacts of some important system parameters, such as EH time, power splitting ratio, relay location, AN power, EH efficiency, and the number of relay antennas, on the system performance are investigated. The results reveal that the PSR protocol generally outperforms the TSR approach in terms of the secrecy capacity

Performance analysis of secrecy capacity for two hop AF relay networks with zero forcing

© 2015 IEEE. In this paper, we analyze the secrecy capacity of a multiple-input multiple-out (MIMO) half duplex amplify-and-forward (AF) relay network in the presence of one passive eavesdropper. Zero forcing (ZF) processing is utilized at various locations to improve the capacity when the eavesdropper is equipped with a single antenna. The impact of the proposed ZF-based technique on the secrecy capacity is investigated for three different scenarios depending on where the ZF is applied, namely, 1) ZF at the relay and destination, 2) ZF at the source and relay, 3) ZF at the relay. For these configurations, analytical expressions for the ergodic-secrecy capacity are derived, and simulation results are provided throughout the paper to validate our analysis. Results reveal that reducing the number of source and/or destination antennas will enhance the ergodic-secrecy capacity and the significance of this enhancement is dependent on the particular scenario adopted. Furthermore, it will be shown that, in general, secrecy capacity improves with increasing the relay power

Morphological and Biological Characterization of Monosporascus cannonballus isolates, responsible of watermelon decline in Kairouan's area

Watermelon grown in Kairouan's region is infected by vine decline disease caused by M. cannonballus. In vitro tests showed that this pathogen produces perithecia with a diameter of 495 μm releasing ascospores with a diameter of 44 μm. The mycelium is very fine, rarely visible in the media KOMADA and TANAKA. The colony of different isolates on substrate culture such as Malt, MS and S, appears very dense. On PDA, the grayish brown color characteristic of this ascomycete was observed. The perithecia production in vitro test for this fungus requires relatively long period of incubation (45 days). The effect of culture media showed that the PDA, MS and Malt are the best for the mycelia development of M. cannonballus. The most favorable culture media for fructification arein descending order MS, S, PDA, Malt. M. cannonballus isolates tested in this study showed an optimum temperature of mycelial growth and reproduction of 30°C. MT15 andMT12 isolates originated from Chebika (Kairouan government) showed a significantmycelial growth at all temperatures of incubation. MT7 and MT14 isolates from the sameregion were the most fertile. The results of pH effect on M. cannonballus developmenthave revealed that the maximum mycelial growth occurred at pH 6 for most of isolates andfor the fructification occurred at pH 4 and pH 8. For the osmotic pression with the addition of NaCl and KCl, the optimal development for majority of isolates is registeredat -0.5 MPa and -2 MPa, with a minimum at -4MPa. The inhibition of the fructification of the M. cannonballus isolates occurred beyond -2MPa

Physicochemical and bioactive properties of six honey samples from various floral origins from Tunisia

The present study was undertaken to determine the physicochemical, biochemical, and antioxidant activities of Tunisian honey samples. All the extracted honey samples appeared to con- form to the European Legislation (EC Directive 2001/110) for all parameters. Mint honey, for instance, possesses significant pH value (p < 0.05), invertase activity, water, and protein contents. In addition, this study demonstrates that the color of the Tunisian honeys is highly variable and ranges from pale yellow to dark brown. The total phenolic, flavonoid and carotenoid contents sig- nificantly vary (p < 0.05). The highest values were found in mint honey, which has a very dark color. Correlations between the analyzed parameters are statistically significant (p < 0.05). The DPPH radical scavenging activity of rosemary honey was determined as lower (p < 0.05) than the other analyzed honey samples. Yet, the highest activity was detected in mint honey. The results suggest that Tunisian honeys could be beneficially used as a functional or nutraceutical substance as they prevent or moderate oxidative stress-related diseases

Screening of fungi implicated in the dieback of olive trees (Olea europea) in Chebika’s area

Several surveys were conducted during spring 2008 in Chebika’s area in Tunisia. Samples were collected from infected plants showed different types of symptoms and they have been the subject of mycological analysis. The morphological identification of fungal colonies isolated from roots, crown and stems of two olive varieties Koroneiki and Chemlali Sfax, revealed the presence of a fungi complex including Fusarium oxysporum, Fusarium solani, Rhizoctonia solani, Verticillium dahliae, Cladosporium fulvum, Alternaria solani, Alternaria tenuis, Bispora punctata. and Cylindrocarpon .sp; Although,those fungi Fusarium oxysporum, Fusarium solani, Rhizoctonia solani and Verticillium dahliae are ubiquitous and the predominant one. Pathogenicity results revealed that the fungi isolated from olive trees exhibited typical symptoms on Koroneiki variety incontrolled conditions

Prevalence of Child Labor among Elementary School Students from 5 th to 9 th Grade in Al Mukalla

Purpose To determined the prevalence of the child labor among male primary school students in Mukalla district in Yemen Methodology A cross-sectional study was designed to collect data from 5 th grade to 9 th grade primary school students in Mukalla city during the year 2015 2016 Results The study showed a high prevalence of child labor among school children in Mukalla city 54 2 where the common reason of child labor is that children have the interest to help their families 69 9 About 35 of students reported that they exposed to different kinds of abuse in their owner s place Child labor affects negatively on their school s achievements and about 20 7 of them thinking to leave school Educational level of parents did not indicate significant association with child labor p-value 0 11 Conclusion High prevalence of child labor may affect on their school achievements and being a predisposing factor to school drop-ou