Judul: Survei dan Karakterisasi Biologi Aphelenchoides besseyi di Sumatera Utara.
Abstrak: Indonesia merupakan negara agraris dengan konsumsi beras sebagai makanan pokok. Fluktuasi produksi padi berkaitan dengan faktor biotik berupa organisme pengganggu tanaman (OPT) yang turut membatasi potensi produksi padi. Salah satu OPT yang membatasi potensi produksi padi adalah nematoda Aphelenchoides besseyi. Penelitian ini bertujuan untuk mengetahui keberadaan Aphelenchoides besseyi dan menelaah Aphelenchoides besseyi yang ditemukan di Sumatera Utara secara morfologi dan morfometri. Manfaat yang diperoleh dari penelitian ini yaitu memberikan informasi keberadaan Aphelenchoides besseyi di Sumatera Utara sebagai langkah awal dalam menentukan strategi pengendalian. Sampel benih padi diperoleh dari kios pertanian dan hasil perbanyakan petani di Kabupaten Batu Bara pada Kecamatan Medang Deras, Talawi, dan Sei Balai; Kabupaten Deli Serdang pada Kecamatan Sunggal, Percut Sei Tuan, dan Pagar Merbau; Kabupaten Serdang Bedagai pada Kecamatan Sei Bamban, Dolok Masihul, dan Teluk Mengkudu; Kabupaten Simalungun pada Kecamatan Hutabayu Raja dan Pematang Bandar; serta Kabupaten Langkat pada Kecamatan Gebang, Securai Utara, dan Stabat. Sampel benih padi hasil perbanyakan petani diperoleh di Kabupaten Simalungun pada Kecamatan Siantar Marimbun. Ekstraksi benih padi dilakukan dengan merujuk pada standar ISTA yang telah dimodifikasi. Hasil ekstraksi benih digunakan untuk menghitung populasi Aphelenchoides besseyi dan menelaah Aphelenchoides besseyi secara morfologi dan morfometri. Identifikasi secara morfometri dilakukan pada Aphelenchoides besseyi betina untuk mengetahui keragaman nematoda yang didapatkan. Hasil penelitian menunjukkan bahwa Aphelenchoides besseyi ditemukan di Sumatera Utara. Gejala infeksi yang ditemukan adalah batang kerdil dan bercak putih pada ujung daun padi. Ciri morfologi Aphelenchoides besseyi yang ditemukan adalah star-shaped mucro pada ujung ekor nematoda betina dan posterior melengkung 180° dengan spikula seperti duri pada nematoda jantan.
Keyword: benih padi, morfologi, morfometri, nematoda

Judul: Nematoda Pucuk Putih Padi Aphelenchoides besseyi Christie di Sumatera Barat.
Abstrak: Aphelenchoides besseyi is an important pest that could reduce rice production. West Sumatera. This study aims to explore the presence of A. besseyi, to detect and identify seed-borne A. besseyi nematode in West Sumatera utilizing morphology and morphometric characters. Samples of rice seeds used are local varieties of rice and hybrid varieties from Agam District, Lima Puluh Kota District, and Solok District. Methods include nematode extraction from seeds, population counting, morphological and morphometric identification, and preparation of slide preparate. The results of this study showed that A. besseyi have infected Junjuang, Sokan, Kuriak, Pulau Sarundang, Sarundang Baru, Batang Pasaman, Pulau Bendang, Pulau Mundam, Bendang Baru, 42 C, Pulut Merah, CK, Mundam Pasaman, Damasraya, Koritiang, Ale-Ale, Hitam Putih, Sijunjung, Junjuang, Sokan, Marujang Bujang, Batang Piaman, Anak Daro, Cisokan, PB 42, and 42 C with number of nematode populations from 1.56-125.44 / 10 g of seed. The morphological characters of A. besseyi found were a vermiform body, slender, smooth body annulation, set off lips, a spear-like stylet with an enlarged knob at the base, a large and oval-shaped median bulb, clear esophageal ring, overlapping esophagus, vulva located at 60 -75% of the body, the posterior part of the body of the male nematode is curved up to 90 °, the spicules are rose thorns, and 2-3 star shaped mucros. Morphometric characteristics with total body length (L) 362.54-672.70 μm, stilet length (S) 9.80-14.01 μm, body diameter (D) 10.41-16.86 μm, tail length (T) 23.81-39.66 μm, vulva distance from anterior divided by total body length (V) 54.48-75.97%, L / D (A) 33.86-63.58 μm, L / distance of the esophageal base from the anterior (B) 5.18-9.97 μm, L / T (C) 9.84-26.04 μm.
Keyword: Aphelenchoides besseyi, morphology, morphometric, rice seed

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.
Keyword: