The accumulation of rice husks (RH), oil palm empty fruit bunch (OPEFB), and plastic waste (PW) can reduce the fertility of the soil. The objective of this study was to compare the quality of the low density particle boards using that waste. Experimental design was used by testing the quality of particle boards with a substitution of 50 % by weight of the total mixes for each waste (RH and OPEFB) and 50% of PW with 3 replications. The results revealed that the quality of the low density particle boards based on water content, density, and modulus of rupture (MOR) tests meet the requirements of SNI 03-2105-2006, whereas the modulus of elasticity (MOE), thickness swelling, water absorption, and the tension perpendicular to surface tests do not comply to the requirements. This preliminary study revealed that the quality of particle boards using OPEFB was better than the particle boards using RH for building materials such as ceilings.

The accumulation of coconut fibre (CF), oil palm empty fruit bunch (OPEFB), and rice husks (RH) every year can reduce the fertility of soil and water absorption, and causes water acidification. Waste utilization as a filler material of concrete blocks was discussed in this research. Experimental design was used by comparing the quality of concrete blocks based on 36 specimens with varied compositions of waste (1%, 2%, 3%, and 4% by dry weight of total sand) and 3 specimens (0%) as control specimens with 3 replications for each composition. The quality of paving blocks was determined based on the testing of water absorption, porosity, compressive strength, and density. The results revealed that the quality of concrete blocks with the composition of CF (1% and 2%), OPEFB (1% and 2%), and RH (1%) meet the requirements of SNI 03-0691-1996 criteria in category B for parking paver and the maximum composition of each waste materials (3% and 4%) still comply SNI 15-2094-2000 in class 100 and 150 for the block walls. Statistical analysis revealed that the best treatments for compressive strength was RH (1%) and for water absorption it was RH (2%) and CF (4%).

The increasing population at Teluk Pemedas and Sanipah coastal areas of Kutai Kartanegara Regency, East Kalimantan Province, has led to coastal degradation. The problem was mainly caused by conversion of mangrove into aquaculture, agriculture, plantation industrial, and residential areas. This research was a study case, used descriptive analysis to describe the local fishermen activity using belat traditional device to catch fish. The results revealed that there were many fishermen still did not know the benefits of mangrove for economy growth, ecological, ecotourism etc. This condition affects to the decline of the mangrove function. Fisherman who used belat often move from one location to another location in order to find places that have many catches. The belat which are placed in good environment mangrove areas produces lots of catches that greatly benefit the fisherman, therefore mangrove ecosystem must be well preserved for the sustainability of fishermen’s efforts to earn a living.

Characteristic of sand at Sambera village based on crystallography using X-ray diffraction and X-ray fluorescence methods was discussed in this article. This research aims to determine the concentration of quartz based on two specimens obtained from two different places at Sambera village. The metal test on quartz sand with XRD method (X-Ray 0.15406 nm) revealed that the scatter angle at 2θ are 26.7321⁰ and 26.7313⁰ with crystal width of each location are 1.81085 nm and 1.03421 nm. While the XRF test revealed that the concentration of quartz are 79.1 % and 79.5 %. The Aluminium concentration are 14.9 % and 15.2 % respectively. The result revealed that the sand of Sambera village has potential to be used as quartz material and aluminum.

Mangrove forest in the coastal area in the Suli subdistrict is one of the sources of livelihood for the local people. The objective of this research is to analyze the public perception of the coastal community towards mangrove forests. The analysis was carried out using a questionnaire-multilevel scale with the level of assessment that refers to the Likert scale. The questionnaires, which were disseminated to 100 respondents, contained questions about the public perception in the coastal mangrove area. The questions were divided into 5 part questions, namely: 4 questions for the public perception towards ecological functions, 7 questions for community participation, 5 questions for economic benefit, 5 questions for social and culture, and 5 questions for government regulation. The results revealed that the average of public perception towards the ecological functions of mangrove was good, with a value of 4.11 (in category 4). The public perception towards public participation was also good, with a value of 3.69 (in category 4). Moreover, the public perception about the economic benefits of mangrove was quite good, with a value of 3.37 (in category 3). The social and culture was quite good, with a value of 3.32 (in category 3). Finally, the public perception towards government regulation (law enforcement) was good, with a value of 3.57 (in category 4). Based on the results, the average value was 3.61, which means that mangroves management is good (in category 4) based on the perceptions of a coastal community in the Suli Subdistrict. The level of education does not affect the perception of the importance of mangrove management. This was caused by the existence of local wisdom, which considers that mangroves are the nails of the earth that can prevent coastal abrasion. This local wisdom is maintained up to now, where the local community formed a group of mangrove lovers that aims to plant and conserve mangroves.

The equation of the minimum time trajectory (the brachistochrone) does not contain the gravity acceleration explicitly. The proof of the gravitational field effect on the trajectory is revealed by solving functional for the uniform gravitational field and nonuniform gravitational field for the central gravity in this article. The Findings revealed that the effect of constant gravity acceleration is inversely proportional on the arc length of the cycloid, except at g = 0 m/s², which means that the trajectory could not be formed without gravity acceleration at a location where a particle are not affected by the gravitational field, whereas in nonuniform gravitational field, the particle's trajectory is not a cycloid and lies in two quadrant. The curve in first quadrant is a mirror image of the curve in fourth quadrant and vice versa. The difference trajectory between uniform and nonuniform gravitational cases is the proof of the existence of the gravitational field effect.