Judul: Karakteristik Biopelet Limbah Ampas Tebu dan Batang Singkong
Abstrak: Limbah ampas tebu (bagasse) dan batang singkong merupakan biomassa yang berpotensi menjadi alternatif bahan bakar terbarukan untuk memenuhi kebutuhan energi yang kian meningkat. Penelitian ini bertujuan untuk menganalisis karakteristik biopelet dan menentukan formulasi biopelet terbaik dari campuran limbah ampas tebu dan batang singkong. Pembuatan biopelet menggunakan pelletizer tipe rotary dies dengan perbandingan komposisi bahan baku yaitu A1 (100% serbuk batang singkong), A2 (100% limbah ampas tebu), A3 (20% limbah ampas tebu : 80% serbuk batang singkong), A4 (80% limbah ampas tebu : 20% serbuk batang singkong), A5 (50% limbah ampas tebu : 50% serbuk batang singkong), A6 (65% limbah ampas tebu : 35% serbuk batang singkong), A7 (35% limbah ampas tebu: 65% serbuk batang singkong). Penentuan biopelet terbaik berdasarkan pembobotan dengan tingkat kepentingan parameter dengan bobot tertinggi hingga terendah yaitu nilai kalor, kadar abu, kadar zat terbang, kerapatan, kadar air, dan laju pembakaran. Formulasi terbaik dari campuran kedua bahan baku berdasarkan SNI 8675-2018 didapatkan dari perlakuan A5 dengan rata-rata hasil uji kerapatan sebesar 0,60 g/cm³, kadar air 8,29%, kadar zat terbang 77,63%, kadar abu 4,10%, kadar karbon terikat 9,98%, nilai kalor 17,40 MJ/kg, keteguhan 96,55%, laju pembakaran 3,57 kg/jam, serta suhu pembakaran 761°C., Sugarcane bagasse and cassava stems are biomass waste which have potential as alternative renewable fuels by converting it into biopellets. This research aims to analyze the characteristics of biopellets made from a mixture of sugarcane bagasse and cassava stems waste, and determine the best formulation based on SNI no 8765-2018. A rotary dies type pelletizer has been used to produce the pellets. Pellets formulation was represented by the ratio of raw material composition, they were A1 (100% cassava stem powder), A2 (100% sugarcane bagasse waste), A3 (20% sugarcane bagasse waste : 80% cassava stem powder), A4 (80% bagasse waste : 20% cassava stem powder), A5 (50% sugarcane bagasse waste : 50% cassava stem powder), A6 (65% sugarcane bagasse waste : 35% cassava stem powder), A7 (35% sugarcane bagasse waste : 65 % cassava stem powder). Determination of the best biopellets is based on the scoring with the level of lightness of the parameters with the highest to lowest score is calorific value, ash content, volatile matter content, density, moisture content, and combustion rate. The best formulation obtained from A5 composition (50% bagasse and 50% cassava stem) with average density of 0,60 g/cm³, water content of 8,29%, volatile matter content of 77,63%, ash content of 4,10%, bound carbon content of 9,98%, calorific value 17,40 MJ/kg, durability 96,55%, and combustion rate 3,67 kg/hour, combustion temperature 761°C.
Keyword: biomassa, biopelet, bagasse, batang singkong, pelletizer

Judul: Utilization of Biodiesel Transesterification Waste as an  Additive to Improve the Quality of Biopellets
Abstrak: Energi alternatif yang potensial untuk dikembangkan salah satunya yaitu energi berbahan dasar limbah, seperti limbah biodiesel, sampah daun kering, dan kertas bekas dengan mengolahnya menjadi biopelet. Pengoptimalan pemanfaatan limbah biodiesel sebagai aditif merupakan upaya yang dapat dilakukan untuk meningkatkan mutu, terutama nilai kalor biopelet. Penelitian ini bertujuan membuat, melakukan pegujian mutu dan analisis karakteristik biopelet sebagai energi bahan bakar alternatif yang ramah lingkungan. Perbandingan formulasi bahan yang digunakan yaitu A1 sebagai kontrol (100% daun kering), A2 (70% daun kering : 20% limbah biodiesel : 10% kertas), A3 (65% daun kering : 25% limbah biodiesel : 10% kertas), A4 (60% daun kering : 30% limbah biodiesel : 10% kertas), A5 (55% daun kering : 35% limbah biodiesel : 10% kertas), dan A6 (50% daun kering : 40% limbah biodiesel : 10% kertas). Parameter nilai mutu biopelet mengacu pada SNI 8675:2018. Formulasi terbaik diperoleh pada perlakuan A6 dengan nilai kerapatan 0,7 g/cm3, kadar air 13,1%, ketahanan 97,6%, kadar zat terbang 58,3%, kadar abu 7,6%, karbon terikat 34,1%, nilai kalor 17,8 MJ/kg, laju pembakaran 1,42 kg/jam, dan rasio energi sebesar 3,577 yang menunjukkan energi hasil produk biopelet lebih tinggi dari keperluan energi untuk proses produksinya (energi listrik dan manusia). Penambahan limbah biodiesel hasil samping transesterifikasi berpengaruh positif dalam meningkatkan mutu biopelet, terutama pada nilai kalor, karbon terikat, kerapatan dan ketahanan., One of the potential alternative energies to be developed is waste-based energy, such as biodiesel waste, dry leaf waste, and used paper by processing them into biopellets. Optimizing the utilization of biodiesel waste as an additive is an effort that can be made to improve quality, especially the calorific value of biopellets. This study aims to manufacture, conduct quality testing and analyze the characteristics of biopellets as an alternative fuel energy that is environmentally friendly. Comparison of the formulation of the ingredients used, namely A1 as a control (100% dry leaves), A2 (70% dry leaves: 20% biodiesel waste: 10% paper), A3 (65% dry leaves: 25% biodiesel waste: 10% paper), A4 (60% dry leaves : 30% biodiesel waste : 10% paper), A5 (55% dry leaves : 35% biodiesel waste : 10% paper), and A6 (50% dry leaves : 40% biodiesel waste : 10% paper ). The parameters for the quality value of biopellets refer to SNI 8675:2018. The best formulation was obtained in A6 treatment with a density value of 0.7 g/cm3, moisture content 13.1%, durability 97.6%, volatile matter content 58.3%, ash content 7.6%, bound carbon 34.1%, calorific value 17.8 MJ/kg, combustion rate 1.42 kg/hour, and an energy ratio of 3.577 which indicates that the energy produced by the biopellet product is higher than the energy required for pelletizing process (electrical and human energy). The addition of biodiesel waste as a by-product of transesterification has a positive effect on improving the quality of biopellets, especially on calorific value, bound carbon, density and durability.
Keyword: biomassa, biopelet, daun kering, kertas bekas, limbah biodiesel

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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