1.3-µm BH laser performance at microwave frequencies

We have studied the performance of In1-xGaxAsyP1-yburied heterostructure (BH) 1.3-μm lasers in the microwave range. This study consisted of small-signal, large-signal, and digital pseudo-random word evaluation of these lasers. The small-signal study pointed out the impact of the oxide stripe capacitance on the laser response at microwave frequencies. The large-signal study uncovered basic laser non-linearities that affect the temporal response, spectral broadening, and wavelength chirp. Finally, digital pseudo-random word tests performed at 1.7 Gbit/s indicated that in spite of these inherent laser nonlinearities, the 1.3-μm BH lasers performed well enough to be considered as promising sources for gigabit optical communication systems.     

The effects of heat treatment temperatures on photocatalytic activity of cobalt ferrite nanoparticles synthesised by microwave-assisted combustion method

In this study, the effects on the photocatalytic activities of particles after heat treatment has been applied to cobalt ferrite nanoparticles produced by microwave-assisted combustion method were observed. The heat treatment applied to the samples was produced with only the microwave effect, at temperatures ranging from 300 to 1000°C. Thermogravimetric analysis was performed on the precursor sample in air atmosphere. During this analysis, the gases released up to 1200°C were identified with a Fourier-transform infrared (FTIR) spectrometer integrated into a thermogravimetric analysis system. Then, the cobalt ferrite nanoparticles produced with heat treatments applied at various temperatures were used as a photocatalyst to remove the dyestuff content in synthetic wastewaters prepared by using Astrazon Red GTL textile dye by photocatalytic oxidation, and their photocatalytic activities were compared. In these experiments, the operational parameters for photocatalysis processes were applied as 400 rpm for stirring speed, 50 mg/L for initial contaminant concentration, 0.5 g/L for catalyst dosage, 25°C for temperature, and 4400 μW/cm² for light intensity. As a result of the experiments, it was observed that the crystal structure of the cobalt ferrite nanoparticles produced with the increase of the applied heat treatment temperature improved significantly. The obtained data show a strong relationship between the structural properties of materials and their photocatalytic activities. In addition, it was determined that the dyestuff in the solution was completely degraded in the experiments, and it was determined that all processes were compatible with the pseudo-first-order kinetic model.     

Enhancing magnetic levitation and guidance force and weight efficiency of high-temperature superconducting maglev systems by using sliced bulk YBCO

We aimed to enhance the magnetic force efficiency of Maglev systems without increasing total weight. For this aim, we divided YBCO bulks into three slices horizontally to utilize the YBCO-permanent magnetic guideway (PMG) interaction surface as much as possible. We used whole YBCO above PMGs with different magnetic pole directions (PMG-A and PMG-B) in two lying positions of transversal and longitudinal and investigated levitation and guidance force performances. It is determined that levitation and guidance forces by using YBCO in transversal lying mode are bigger compared to the longitudinal mode. For sliced YBCO, the maximum levitation force increased by 69% and 78%, while the guidance force enhancements are determined as 212% and 91%, compared to the whole YBCO above PMG-A and PMG-B, respectively. The levitation and guidance force density with respect to the total mass of unit a set of slices YBCO increased by 92% and 106%, respectively, compared to the whole YBCO above PMG-B in transversal mode. Since the higher levitation force and the lower total weight of the onboard unit are important parameters in point of the energy efficiency in Maglev and other levitation applications, the result of this study supplies useful data for the engineers and industrial partners.