The role of boron in phosphorescence persistence of rare-earth co-activated alkalai aluminates

Rare-earth co-doped (Eu, Dy) SrAl4O7 (SA2ED) phosphor powders were synthesized by using a modified Pechini process. It has been noted that the addition of boron has two impacts on these phosphors—the persistence duration is extended, and the processing of phase pure powders is facilitated. Thus the objective of this thesis work is to investigate the effect of boron on SA2ED phosphors. Varying amounts of boron were incorporated into the SA2 lattice to investigate the effects on crystal structure and optical properties. X-ray diffraction spectra showed that boron addition enhances the phase purity of the powder at a calcination temperature of 1000 °C, whereas the formation of a new S4A7 phase was induced when a calcination temperature of 1100 °C was used. The afterglow duration was extended to longer than 5 hours when boron was present in 5-30 mol%. To elucidate the enhanced optical properties, interband trap characteristics were studied by thermoluminescence and photoluminescence. Moreover, to understand the structure-property relationship via investigating the electronic structure of the boron inside the crystal, ELNES studies were performed. With ELNES fingerprinting and quantitative analysis of the ELNES data, information on local bonding of boron and its effects on the crystal lattice were investigated

REAL-TIME WATER QUALITY MONITORING OF AN ARTIFICIAL LAKE USING A PORTABLE, AFFORDABLE, SIMPLE, ARDUINO-BASED OPEN SOURCE SENSOR

Water quality assessment is vital to identify existing problems and any changes that emerge in water sources over a period of time. Conventional water quality monitoring systems remain to be limited to on-site sample collection and further analysis in environmental laboratories. The progress in Arduino-based low-cost and open-source hardware has paved the way for the development of low-cost, portable, and on-site measuring platforms. In this work, we have assembled an Arduino-based open-source water testing platform out of commercially available sensors and controllers. The water testing system was powered by a 9 V battery and had the capability of measuring water turbidity, acidity, and temperature on-site in real-time. The calibration and validation studies were carried out to assess the measurement capabilities of turbidity and pH sensors in the lab using calibration samples and UV-Vis-NIR absorption spectroscopy. The water quality platform was tested in an artificial lake that is located at Sabanci University Campus (Istanbul, Turkey), which serves as a reservoir for treated wastewaters and rainwater. Untreated wastewater samples were collected from the wastewater treatment station of the university for comparison. The measurements performed on several locations along the coast of the artificial lake were also validated in the laboratory. The water testing platform showed significant potential for miniaturization and portability of such analytical platforms for on-site environmental monitoring

Numerical modeling of anode-bleeding PEM fuel cells:Effects of operating conditions and flow field design

Operating the PEM fuel cell in the dead-ended anode mode reduces the overall cost and complexity of the system but causes a voltage loss and carbon corrosion in the cathode catalyst layer due to hydrogen starvation in the anode. Whereas allowing an ultra-low flowrate at the anode outlet offers a very high utilization of hydrogen and achieves a stable voltage transient. Here, a time-dependent pseudo-three-dimensional, two-phase, and non-isothermal model is developed to study the optimum bleeding rate, which maximizes the hydrogen utilization, achieves a stable cell voltage and avoids carbon corrosion, which is commonly observed when the bleed rate is set to zero, i.e. the dead-ended mode. The model is validated against the experimental data by comparing the polarization curves and cell voltage transients during the dead-ended anode operation of small experimental cells with serpentine and straight anode flow channels. Moreover, the effects of operating conditions on cell performance during the anode bleeding operation mode are investigated. Results demonstrate that the hydrogen utilization exceeds 99% in the anode-bleeding mode without hydrogen starvation, and the cell performance improves significantly for higher anode pressure, lower cell temperature, and lower relative humidity at the cathode inlet. Lastly, it is found that serpentine channels in the anode improve the uniformity of the distribution of hydrogen compared to straight and interdigitated channels in the anode-bleeding mode while the cathode flow field consists of serpentine channels

Real-time water quality monitoring of an artificial lake using a portable, affordable, simple, arduino-based open source sensor

Water quality assessment is vital to identify existing problems and any changes that emerge in water sources over a period of time. Conventional water quality monitoring systems remain to be limited to on-site sample collection and further analysis in environmental laboratories. The progress in Arduino-based low-cost and open-source hardware has paved the way for the development of low-cost, portable, and on-site measuring platforms. In this work, we have assembled an Arduino-based open-source water testing platform out of commercially available sensors and controllers. The water testing system was powered by a 9 V battery and had the capability of measuring water turbidity, acidity, and temperature on-site in real-time. The calibration and validation studies were carried out to assess the measurement capabilities of turbidity and pH sensors in the lab using calibration samples and UV-Vis-NIR absorption spectroscopy. The water quality platform was tested in an artificial lake that is located at Sabanci University Campus (Istanbul, Turkey), which serves as a reservoir for treated wastewaters and rainwater. Untreated wastewater samples were collected from the wastewater treatment station of the university for comparison. The measurements performed on several locations along the coast of the artificial lake were also validated in the laboratory. The water testing platform showed significant potential for miniaturization and portability of such analytical platforms for on-site environmental monitoring