ZnS:Mn nanocrystals thin film was fabricated at 300°C and 500°C via the spin coating method. Its sol-gel was spin coated for 20 s at 3000 rpm and 4000 rpm with metal tape being used to mold the shape of the thin film. A different combination of these parameters was used to investigate their influences on the fabrication of the film. Optical and structural characterizations have been performed. Optical characterization was analyzed using UV-visible spectroscopy and photoluminescence spectrophotometer while the structural and compositional analysis of films was measured via field emission scanning electron microscopy and energy dispersive X-ray. From UV-vis spectra, the wavelength of the ZnS:Mn was 250 nm and the band gap was within the range 4.43 eV–4.60 eV. In room temperature PL spectra, there were two emission peaks centered at 460 nm and 590 nm. Under higher annealing temperature and higher speed used in spin coating, an increase of 0.05 eV was observed. It was concluded that the spin coating process is able to synthesize high quality spherical ZnS:Mn nanocrystals. This conventional process can replace other high technology methods due to its synthesis cost.

No abstract

This paper focuses on the drying kinetics at different temperatures of air in the chamber (lab scale dryer). A theoretical drying model was suggested. A number of experiments were carried out to study the drying characteristics of the fresh pepper berries in a lab scale dryer at six different temperatures which ranged from 30o C to 55o C at 5oC interval. In accordance with the experiments and the proposed model of drying of pepper fruits, the main parameters that contribute to accelerate the process can be distinguished. The parameters include the temperature of drying, the air humidity of the fruits surrounding and velocity of saturated water vapour transfer between the fruits and the surrounding. From the experiments, it was noticed that the change in size over time depends on the drying temperature. The drying process was accompanied by a number of processes that may be taken into account in refining the theoretical model. Characteristic drying time, according to the developed model exponentially depends on temperature, is proportional to the volume of pepper fruit, and inversely proportional to the coefficient of mass transfer. Mass transfer coefficient can be changed by changing of the air flow surrounding the berries in the drying chamber. This will work effectively in case when the drying is limited by high humidity in the surrounding.

Impulse-momentum methods of analysis developed for rigid body impacts are applied in this paper to predict forces acting in a simplified spacecraft model during a touchdown impact. This paper presents both analytic and experimental effort for a complex, multi-body impacting system that include friction and deformable elements. Specifically, we analyze a vertically moving guided mass representing a landing spacecraft to which is attached a telescopic, energy-absorbing leg. The landing gear, which is used in our study, employs crushable material in the leg, strut, and foot plus surface friction to absorb the landing shock. The experimental setup consists of simplified landing system, and accelerometers for the dynamic measurement. Acceleration data collected via data acquisition system is converted to the crushing, normal and tangential velocities. The results showed good agreement between the analysis and experiment for the first phase of motion. The derivation of limiting condition equations for all possible alternatives for the second phase is incomplete. We conclude that the challenges of deriving and testing for all motion phase ending events make the impulse-momentum method inferior to straight-forward dynamic simulation as a design tool.