Judul: Identifying the Severity of Basal Stem  Rot Disease in Oil Palm (Elaeis guineensis Jacq.) Plantation Using Sentinel-2
Abstrak: Kelapa sawit merupakan sektor perkebunan yang paling diunggulkan di Indonesia. Pemantauan perkebunan skala besar membutuhkan kekhususan dalam pengumpulan data dan analisisnya. Pengamatan cakupan perkebunan telah lama dilakukan dengan menggunakan data penginderaan jauh. Dengan berbagai masalah yang kompleks di perkebunan kelapa sawit, fokus riset umumnya berada dalam ranah perkiraan nutrisi daun dan untuk mengidentifikasi dampak penyakit tanaman. Fokus riset terakhir ini perlu menjadi perhatian, terutama pada penyakit busuk pangkal batang (BPB) yang disebabkan oleh cendawan Ganoderma boninense. Data multispektral Sentinel-2 yang tersedia secara bebas dimanfaatkan dalam penelitian ini. Identifikasi gejala awal dampak BPB dianalisis dengan menggunakan pendekatan pemelajaran mesin yang populer, yaitu random forest (RF). Data lapangan sebagai referensi dikumpulkan di Kebun Kelapa Sawit Cikasungka, Kabupaten Bogor. Dengan menggunakan model RF yang disetel (tuned), akurasi keseluruhan sebesar 82% diperoleh dengan lima target berbeda, yaitu empat tingkat keparahan dan pohon sehat. Penelitian ini juga menyimpulkan bahwa data tambahan seperti indeks vegetasi mampu membedakan tingkat keparahan penyakit meskipun tidak responsif. Penelitian ini menunjukkan bahwa model RF yang disetel sangat bermanfaat untuk membangun model pemelajaran mesin yang tepat dan adaptif., Oil palm remains the most prominent plantation sector in Indonesia. Monitoring large scale plantations requires specificity in datasets and approaches. Observing the extent of plantations has long been conducted using remotely-sensed data. With the complex issues in oil palm plantations, focus has also been made in investigating the utility of earth-observing satellites to estimate foliar nutrients and to identify the impact of plant diseases. The latter has been one of research interests, especially the basal stem rot (BSR) caused by Ganoderma boninense. This research proposed a freely-available, multispectral data of Sentinel-2, taking its advantage of frequent observation period. Preliminary identification of BSR impacts was examined by using a popular machine learning approach, i.e. random forests (RF). Ground data as the reference were collected in Cikasungka plantation, Bogor Regency. Using tuned RF model, overall accuracy was about 82% with five distinctive targets, i.e. four severity levels and the normal trees. Additional data, such as the vegetation index, were able to distinguish the severity of the disease, although they were irresponsive. This research suggests that tuned random forest model could be invaluable for constructing a proper machine learning model that adaptive to data feeds.
Keyword: busuk pangkal batang, kelapa sawit, random forest, Sentinel-2, basal stem rot, oil palm

Judul: Distribution and Factors Affecting the Development of  Basal Stem Rot Disease (Ganoderma boninense) in Oil Palm (Elaeis guinensis Jacq.) in Indonesia
Abstrak: Indonesia merupakan negara penghasil kelapa sawit terbesar di dunia. Perkebunan kelapa sawit di Indonesia saat ini semakin berkembang seiring dengan meningkatnya kebutuhan industri. Namun, dalam proses budi daya tanaman terdapat kendala seperti munculnya hama dan penyakit tanaman. Penyakit busuk pangkal batang yang disebabkan oleh cendawan Ganoderma boninense merupakan penyakit yang paling merusak pada perkebunan kelapa sawit di Indonesia. Kajian pustaka ini bertujuan mempelajari perkembangan penyebaran penyakit busuk pangkal batang pada tanaman kelapa sawit di Indonesia. Metode kajian pustaka dilakukan dengan pengumpulan data sekunder, pengolahan data, dan analisis. Sumber data diperoleh dari publikasi ilmiah seperti laporan tahunan Direktorat Jenderal Perkebunan, Kementerian Pertanian RI, data online BMKG, jurnal penelitian, tesis, skripsi dan kajian-kajian ilmiah. Hasil studi Pustaka menunjukkan bahwa penyakit busuk pangkal batang (G. boninense) telah menyebar di 13 provinsi dan telah menjadi penyakit endemik yang sulit dikendalikan. Insidensi penyakit paling tinggi terdapat di Sumatera Utara, Riau, Aceh, dan Sulawesi Barat. Intensitas penyakit cenderung meningkat pada kebun peremajaan. Penyakit ini berpotensi menyebar ke seluruh provinsi sentra kelapa sawit di Indonesia dan menimbulkan kerugian yang lebih besar., Indonesia is the largest palm oil producing country in the world. Oil palm plantations in Indonesia are currently growing in line with the increasing needs of the industry. However, in the process of plant cultivation there are obstacles such as the emergence of pests and plant diseases. Basal stem rot disease caused by the fungus Ganoderma boninense is the most destructive disease in oil palm plantations in Indonesia. This literature review aims to study the development of the spread of basal stem rot disease in oil palm plantations in Indonesia. The literature review method is carried out by collecting secondary data, data processing, and analysis. Sources of data are obtained from scientific publications such as the annual report of the Directorate General of Plantations, the Indonesian Ministry of Agriculture, BMKG, research journals, theses, and scientific studies. The results of the study show that basal stem rot disease (G. boninense) has spread in 13 provinces and has become an endemic disease that is difficult to control. The highest incidence of disease is found in North Sumatra, Riau, Aceh, and West Sulawesi. Disease intensity tends to increase in replanting plantations. This disease has the potential to spread to all oil palm center provinces in Indonesia and cause greater losses.
Keyword: BSR, disease incidence, impact, potential

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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