Studies on the electrosynthesis of organic compounds: II. Reducibility of some Schiff's bases on lead and copper cathodes

The electrochemical reducibility of some Schiff's bases was studied on copper and lead cathodes. The effects of different substituents and the nature of the cathode material on the reduction efficiency of these compounds were investigated. The products of reduction were found to catalyse the reduction process itself leading to an increase of reducibility (reduction efficiency) with time.     

Influence of measurement accuracy on the application of the 1991 NIOSH equation

A relatively neglected topic in manual materials handling (MMH) research is the impact of the accuracy of task parameter measurements on the application of various assessment methods. A laboratory experiment was conducted to investigate the accuracy of NIOSH equation parameter measurements made by eight subjects following a 4-h training session. Five individual tasks were measured; two were single tasks and three were part of a multiple-component simulated palletizing operation. Significant differences between reference parameter measurements and average measurements made by subjects were found. The sensitivity analysis showed that frequency and horizontal location are the most important parameters. These parameters also tended to have the highest measurement errors. Recommendations for increasing the effectiveness of training programs for NIOSH equation users based on the results of the study are presented.     

Synthesis of nanocrystalline NiAl by mechanical alloying

The nanocrystalline NiAl intermetallic compound was synthesized by mechanical alloying of the elemental powders. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometery, scanning electron microscopy and microhardness measurements. The mechanical alloying resulted in the gradual formation of nanocrystalline NiAl with a grain size of 20 nm. It was found that NiAl phase develops by continuous diffusive reaction at Ni/Al layers interfaces. The NiAl compound exhibited high microhardness value of about 1035 Hv.     

Nanoscale Grain Growth Behaviour of CoAl Intermetallic Synthesized by Mechanical Alloying

Grain growth behaviour of the nanocrystalline CoAl intermetallic compound synthesized by mechanical alloying has been studied by isothermal annealing at different temperatures and durations. X-ray diffraction method was employed to investigate structural evolutions during mechanical alloying and annealing processes. The disordered CoAl phase with the grain size of about 6 nm was formed via a gradual reaction during mechanical alloying. The results of isothermal annealing showed that the grain growth behaviour can be explained by the parabolic grain growth law. The grains were at nanometric scale after isothermal annealing up to 0·7 T _m. The grain growth exponent remained constant above 873 K indicating that grain growth mechanism does not change at high temperatures. The calculated activation energy indicated that the grain growth mechanism in the disordered CoAl phase at high temperatures was diffusing Co and Al atoms in two separate sublattices. Furthermore, an equation has been suggested to describe the grain growth kinetics of nanocrystalline CoAl under isothermal annealing at temperatures above 873 K (T/T _m ≥ 0·5).     

Development of NiFe-CNT and Ni3Fe-CNT nanocomposites by mechanical alloying

NiFe-CNT and Ni₃Fe-CNT nanocomposites were fabricated by high energy mechanical alloying method. X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and optical microscopy were employed for evolution of phase composition, morphology and microstructure of the powder particles. Ball milled powders were heat treated at 500 °C for 1 h to release the milling induced stresses. Bulk samples were prepared by sintering of cold pressed (300 MPa) samples at 1040 °C for 1 h. XRD patterns of powders, as-milled and after annealing at 500 °C did not show any peak related to CNTs or excess phases due to the interaction between CNTs and matrix. SEM micrographs showed that the addition of CNTs caused a reduction of powder particles size. The hardness value of as-milled NiFe and Ni₃Fe powders reach to 660 and 720 HV, respectively. According to optical microscopy evaluations, the amount and size of the porosities of the composites bulk samples decreased in comparison with matrix ones.     

Complexity reduction of equalization/pre-emphasis using set membership filtering for NG LR-PON

Coherent receivers, with advanced and low-complexity digital signal processing (DSP), have the advantage of increasing the loss/power budget of next generation-long-reach passive optical networks (NG-LRPONs). This reduces the network capital expenditures by eliminating or reducing the number of amplifiers to be installed between the optical line terminal (OLT) and the optical network units (ONUs). In this paper, we investigate the complexity and convergence speed of two adaptive equalization and/or pre-emphasis strategies for mitigating chromatic and polarization mode dispersions (CD and PMD) in NG-LRPON. We first identify two potential deployment strategies of equalization and/or pre-emphasis. The first equally splits the signal processing in the OLT and ONU; however, the second concentrates most of DSP in the OLT trying to reduce the cost and alleviate the complexity of ONUs. Our investigation shows that the second strategy achieves 50 % faster convergence rate in terms of number of symbols for 16QAM/5 Gbaud. Moreover, we apply the enhanced set membership filtering (SMF) technique, recently introduced for next generation wireless communications, to our LR-PON in order to reduce the update rate of equalizers’ taps, hence reduce the calculation complexity of the OLT and ONUs. Our results show that by employing SMF technique a substantial reduction in the number of mathematical operations needed to attain convergence is achieved. Simulation results reveal that our proposed SMF can reduce the equalizers’ update rate, hence calculation complexity, by 55 % for 16QAM and 75 % for QPSK with marginal degradation of the BER.     

Mechanochemical behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al–Fe powder mixtures to produce Fe<Subscript>3</Subscript>Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powder

Mechanical treatment of Fe₂O₃, Al and Fe powder mixtures was carried out in a high energy ball mill to synthesize Fe₃Al–Al₂O₃ intermetallic matrix nanocomposite. Different compositions including 3Fe + Al, Fe₂O₃ + 2Al, 3Fe₂O₃ + 8Al and Fe₂O₃ + 3Al+Fe were chosen in this study. Phase development and structural changes occurring during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during MA, Fe₂O₃, Al, and Fe react to give a nanocrystalline Fe₃Al intermetallic compound matrix. The presence of pure Fe in initial powder mixture changed the modality of mechanochemical process from sudden to gradual reaction. The Fe₃Al–Al₂O₃ compound had a finer microstructure and particles size compared to the Fe₃Al compound.     

Effect of defects on electrical properties of 4H-SiC Schottky diodes

Most of power electronic circuits use power semiconductor switching devices which ideally present infinite resistance when off, zero resistance when on, and switch instantaneously between those two states. Switches and rectifiers are key components in power electronic systems, which cover a wide range of applications, from power transmission to control electronics and power supplies.

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has properties that allow devices with high power voltage rating and high operating temperatures. The technology overcomes some crystal growth obstacles, by using the hydrogen in the fabrication of 4H-SiC wafers.

The presence of structural defects on 4H-SiC wafers was shown by different techniques such as optical microscopy and scanning electron microscopy. The presence of different SiC polytypes inclusions was found by Raman spectroscopy. Schottky diodes were realized on investigated wafers in order to obtain information about the correlation between those defects and electrical properties of the devices. The diodes with voltage breakdown as 600 V and ideality factor as 1.05 were obtained and characterized after packaging.