Judul: Tutupan Lahan, Cadangan Karbon, dan Potensi Nilai Ekonomi Agroforestri Kayu Putih-Sereh Wangi di Lahan Pascatambang PT Berau Coal
Abstrak: Agroforestri kayu putih-sereh wangi telah digunakan untuk mereklamasi lahan bekas tambang. Sistem agroforestri ini memberikan keuntungan ekologi, ekonomi, dan sosial. Tujuan dari penelitian ini adalah mengukur tutupan lahan, cadangan karbon, dan potensi nilai ekonomi kombinasi agroforestri kayu putih-sereh wangi di PT Berau Coal. Metode penelitian terdiri dari pengumpulan data, pembuatan petak ukur penelitian dengan ukuran 25 m x 40 m, mengukur pohon dengan parameter persentase tumbuh, diameter batang, diameter tajuk, luas tajuk, tutupan tajuk. Selanjutnya, penelitian ini mengukur sereh wangi dengan parameter persen tumbuh, diameter rumpun, luas rumpun, tutupan rumpun, dan kerapatan tutupan. Penelitian juga menghitung biomassa pohon, cadangan karbon, dan potensi nilai ekonomi. Hasil penelitian mengungkapkan tutupan tajuk pohon di Blok IPDK Binungan terdiri dari pohon kayu putih, waru, dan akasia dengan persentase tutupan tajuk paling tinggi sebesar 112,7%. Biomassa dan cadangan karbon tertinggi terdapat pada jenis akasia secara berturut- turut sebesar 25,4 ton/ha dan 11,9 ton/ha. Potensi nilai ekonomi tertinggi yang diperoleh dari kayu putih dengan jumlah kayu putih sebanyak 430 pohon/ha sebesar Rp 1.290.000/ha. Potensi nilai ekonomi tertinggi yang diperoleh dari sereh wangi dengan jumlah rumpun sebanyak 3.920 rumpun/ha sebesar Rp 6.480.270/ha., Eucalyptus-lemongrass agroforestry has been used to reclaim ex-mining land. This agroforestry system provides ecological, economic and social benefits. The aim of this research is to measure land cover, carbon stocks, and the potential economic value of the eucalyptus-lemongrass agroforestry combination at PT Berau Coal. The research method consists of collecting data, making research measuring plots measuring 25 m x 40 m, measuring trees using the parameters of growth percentage, trunk diameter, crown diameter, crown area, crown cover. Furthermore, this research measured citronella with the parameters of percent growth, clump diameter, clump area, clump cover and cover density. The research also calculated tree biomass, carbon stocks and potential economic value. The research results revealed that tree canopy cover in the Binungan IPDK Block consisted of eucalyptus, hibiscus and acacia trees with the highest percentage of canopy cover at 112,7%. The highest biomass and carbon reserves were found in the acacia species at 25,4 tonnes/ha and 11,9 tonnes/ha respectively. The highest potential economic value is obtained from eucalyptus with a total of 430 eucalyptus trees/ha amounting to Rp 1.290.000/ha. The highest potential economic value obtained from citronella with a total of 3.920 clumps/ha is Rp 6.480.270/ha.
Keyword: citronella, reclamation, mining, Eucalyptus

Judul: Performa Sereh Wangi (Cymbopogon nardus L) Dalam Memperbaiki Fisik Tanah dan Konservasi Tanah Pada Lahan Pasca Tambang Batubara
Abstrak: Mining activities had positive and negative impacts on the environment. Erosion is one of the negative impacts that must be managed. The quality of this ex-mining land must be improved through reclamation activities which are expected to slowly return the soil to its original state. Evaluation of several physical characteristics of PT Berau Coal's post-mining land, to analyze erosion predictions from post-mining land as well as from the results of citronella revegetation and its opportunities in the essential oil business that will be carried out by PT Berau Coal as an effort to create sustainable development by selecting valuable crops. economical and ecological. Soil sampling at the Binungan Site in locations where cover crops and citronella are planted. the objectives of this study are 1) To evaluate the physical and chemical properties of the soil in the post-mining area of PT. Berau Coal, 2) Analyzing the estimated erosion in the post-mining area of PT. Berau Coal and 3) Analyzing the cost of revenue from the citronella revegetation business in the post-mining area of PT. Berau Coal. The analytical methods used are analysis of erosion prediction using USLE, analysis of physical and chemical properties of soil using laboratory analysis and cost-of-income analysis. The results showed that the physical properties of the soil at the study site were dominated by the clay fraction between 23.58-46.72%, followed by the sand fraction 10.20-48.73% and the dust fraction between 13-66.22%. The N content in the soil is classified as low to very low, the value is 0.09-0.13%. The value of bulk density is 1.27 gr/cm3-1.76 gr/cm3, the level of soil permeability is classified as slow to rather fast, and the porosity is categorized as poor to good. The magnitude of the erosion prediction that occurred at the study site using the USLE method which was planted with covercrop at a slope of 10% (Pit D2 CC D) had the lowest erosion value of 18.13 tons/ha/yr, while the highest was at the study site planted with citronella grass at 30% slope (Pit H4 SW L) of 268.91 tons/ha/year. The results of the calculation of the cost analysis of citronella oil business obtained a profit of Rp. 69,627,951 yr/ha.
Keyword: Sereh wangi, erosi, usle, lahan pasca tambang

Judul: Dynamical System of Hepatitis B in Three Groups with Vaccination
Abstrak: The aim of this study is to modify the hepatitis B transmission model in three age groups involving vaccination from the model conducted by Zhoe and Zhang.The method used is to analyze the stability of the fixed point and its basic reproduction number (R_0). Performed stability analysis and numerical simulation to see population dynamics. Next, a sensitivity analysis of the parameters was carried out to see its effect on R_0. From the analysis obtained two fixed points, namely non-endemic and endemic fixed points. Non-endemic fixed points are locally asymptotically stable if R_0 <1 Meanwhile, the endemic fixed point is locally asymptotically stable if R_0 > 1. Hepatitis vaccination affects the number of susceptible population, because the more successful the vaccination, the smaller the number of susceptible populations so that the smaller the population will be infected.
Keyword: Dynamic, Hepatitis B, Vaccine, Mathematical model