Carbon Dots (C-Dots) was successfully prepared by simple heating method. The effect of additional elemental sulfur on the luminiscent performance of C-Dots was investigated. The preparation, chemical composition and optical properties such as absorbance and band gap energy are studied. The C-Dots were prepared with various mass sulfur 0.5-3.0 g and citric acid-urea was constant, i.e. 1.0 g and 4.0 g, respectively. This study used sulfur from natural deposit in Indonesia. The raw materials were prepared by mixing in pure water. The homogeneous solutions were heated at 225°C for 15 minutes under atmospheric pressure. The color emission of C-Dots is found in the visible light spectrum. The addition of sulfur in C-Dots phosphor caused the shifting of absorbance wavelength, i.e. 350-429 nm. By increasing mass of sulfur, the band gap energy of C-Dots decreased from 2.4 eV to 1.8 eV.

Rice winnowing is a process of separation of small and large rice grains by air flow practiced since the ancient human history especially in societies where rice is the main source of carbohydrate (in Asia, Africa, and Latin America). Indeed, this process contains rich of scientific rule but has never been documented by the old society. We report here experimental investigation of the rice winnowing and develop a physical model to explain the process of segregation of rice grains having different size or density. Flapping the tray in the winnowing process, generates a vortex centered at position around the tray free end. We demonstrated numerically that the effectiveness of segregation is strongly depended on the different in grain sizes (for grain from the same material), the initial position of the grain, and the angular velocity of the vortex generated by flapping the tray. We obtained a phase diagram describing different final conditions of winnowing process (either the small grains move towards the tray fee end or move toward the inner end of the tray, able or unable to leave the tray at the free end). The result can be useful to design a new method in separating grains based on size or density.

The present work focused on the effects of TiO2 in degrading organic wastewater. Technical TiO2 of anatase crystalline phase was used. TiO2 photocatalyst showed a powerful result in destroying organic effluent. Spray coating was conducted to immobilize the TiO2 particles onto the plastic buffer followed with heat-treatment process. As a result, 30 mL of 25 mg L−1 methylene blue (MB) used in the photocatalyst test was sucessfully degraded after 4 hours of irradiation. Repetitive use of the TiO2 films still has a great photodecomposition ability of removing 99% of the organic contaminant after 5 times use.

One activity that has been performed by human beings for a long time is washing clothes. Before the invention of the washing machine, clothes were washed by hand and then wrung before drying in the open air. When observed carefully, the wringing of cloth presents some interesting phenomena. However, there are no reports on the physical modelling of this very old activity. This paper reports a simple model to explain the discharge of water from clothes when squeezed. A simple tool was also designed to retrieve data to confirm the theory. We found that the theoretical predictions accurately explained the experimental results. The experiments were conducted on two types of cloth: towels and batik cloth. We also obtained a universal curve to which all the data converged.

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ABTRACTWe demonstrated the stability of tunnels made of granular matters is strongly dependent on the grain size, tunnel diameter, and water content in the granules. Larger tunnel radius, larger grain size, and too much water content tend to destabilize the tunnel. We also develop a model to describe such findings. We indentified a phase diagram of stability which greatly controlled by granular bond order. For granular bond order of larger than unity, we can alwaysmade a stable tunnel. However, for granular bond order of less than unity, we obtain a general expression for maximum tunnel thickness that can be made. To best of our knowledge, this is the first exploration regarding the granular tunnel stability.

An investigation of how coconut palm tree withstands gale force winds has been performed. When observed carefully, the motion of the stalks and leaves affected the wind resistance. The stalks and leaves move randomly when the wind blows continously. Although this is such an interesting phenomenon, there is still no report on the physical modelling. This paper proposes a simple mathematical model to analyze the phenomenon. A simple tool was also designed to retrieve data using Video Tracker. The experiments were conducted on several types of springs. The model showed that the theoretical prediction accurately explained the phenomenon.

Plastic trash in Indonesia has reached 64 million tons per year. Consequently, a solution is required to decrease synthetic plastic waste. A film based on nata de coco has been made as an alternative to biodegradable plastic material using materials consisting of nata de coco, chitosan, and 1% acetic acid. The nata de coco based film was made by varying the composition of chitosan. The variations of chitosan used were 0.1 gram, 0.2 gram, 0.3 gram, and 0.4 gram. The biodegradation test used the soil burial test method by immersing the sample in the soil and the mixed microbial batch method using effective microorganisms 4/EM4 with an estimated time of 15 days. The results of the soil burial test method showed a variation of 0.1 experienced a weight loss of 100%. Meanwhile, variations of 0.2, 0.3, and 0.4 experienced a weight loss of 60-75%. Meanwhile, the results of the mixed microbial batch method showed that the nata de coco-based film underwent biodegradation as indicated by the tearing of the surface of the nata de coco-based film. From these results, nata de coco-based films can be said to be biodegradable plastics.