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: Vegetation and Environmental Characteristics in Land Ecosystems Results from Revegetation on Post-Coal Mining Lands PT. Pesona Khatulistiwa Nusantara
Abstrak: Pertambangan batu bara mengakibatkan hilangnya vegetasi yang berada di atas permukaan tanah, mengubah struktur, dan tekstur tanah. Kegiatan revegetasi dilakukan untuk memulihkan kembali kondisi lingkungan. Penelitian ini bertujuan untuk menganalisis karakteristik vegetasi dan lingkungan pada areal revegetasi lahan pascatambang batu bara. Metode penelitian menggunakan analisis vegetasi dan analisis biofisik lingkungan (edafis dan klimatis). Hasil penelitian menunjukkan bahwa hutan alam (ekosistem referensi) memiliki jenis vegetasi yang lebih banyak. Lahan revegetasi yang diamati hanya didominasi oleh satu jenis saja, yaitu sengon laut (Falcataria moluccana), sehingga nilai indeks keanekaragaman jenis, indeks kekayaan jenis, dan indeks kemerataan jenis hutan alam lebih tinggi daripada lahan revegetasi. Nilai indeks kesamaan tergolong tinggi hanya ditemukan pada lokasi lahan revegetasi umur 10 tahun dan 2 tahun pada tingkat pancang dan tiang. Lahan revegetasi umur 10 tahun memiliki total biomassa dan simpanan karbon lebih tinggi dibandingkan lahan revegetasi umur 2 tahun. Karakteristik kesuburan tanah lahan revegetasi umur 2 tahun memiliki nilai rendah daripada kedua lokasi lainnya, karena memiliki pH masam, C-organik sangat rendah, kapasitas tukar kation (KTK) rendah, dan kejenuhan basa (KB) yang sedang., Coal mining results in the loss of aboveground vegetation, changing the structure and texture of the soil. Revegetation activities are carried out to restore environmental conditions. This study aims to analyze the characteristics of vegetation and the environment in the revegetation area of post-coal mining land. The research method used vegetation analysis and biophysical analysis of the environment (edaphic and climatic). The results showed that natural forest (reference ecosystem) has more vegetation types. The revegetated land is only dominated by sengon laut (Falcataria moluccana), so the value of the species diversity index, species richness, and species evenness of natural forest is higher than the revegetated land. High similarity index values were only found in the second location of revegetated land at the sapling and pole levels. The 10-year-old revegetated land had higher total biomass and carbon storage than the 2-year-old revegetated land. Soil fertility characteristics of 2-year-old revegetated land have low values than the two locations, because they have acidic pH, very low C-organic, low cation exchange capacity (CEC), and medium base saturation.
Keyword: coal, post-mining, revegetation, soil, vegetation

Judul: Construction of Strongly Optimal Binary Linear Code with Minimum Distance 9 and 11
Abstrak: A binary linear code of length n over q F is a subspace of n q F . A code has three parameters that attached to it, namely length, dimension, and minimum distance. A code with length n, dimension k and minimum distance d is often called [n, k, d ]-code. Usually, when two parameters are given, then we want to find a code that has the best value for the last parameter. Based on Gilbert- Varshamov bound, if a [n, k, d ]-code exists and can not be expanded, we call it a strongly optimal code. In this paper, we construct strongly optimal code with minimum distance 9 and 11. In constructing the code, we created a theorem and algorithm based on Gilbert-Varshamov bound before we implement the algorithm to MAPLE programming language. Because of computational limitations, the program can only construct up to k = 10 for d = 9 and k = 12 for d = 11.
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