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: Karakterisasi Morfologi dan Morfometri Nematoda Aphelenchoides besseyi Christie pada Beberapa Varietas Padi.
Abstrak: Aphelenchoides besseyi merupakan nematoda parasit terbawa benih yang menyebabkan penyakit pucuk putih pada padi. Identifikasi A. besseyi secara morfologi dan morfometri pada beberapa varietas padi di Jawa Tengah dan Daerah Istimewa Yogyakarta (DIY) belum pernah dilaporkan, sehingga penelitian ini bertujuan untuk mengetahui keberadaan A. besseyi pada beberapa varietas padi di Jawa Tengah dan DIY serta menelaah karakter morfologi dan morfometrinya. Sampel benih diperoleh dari kios pertanian di Kecamatan Weru (Sukoharjo), Cawas (Klaten), Banguntapan (Bantul), Wonosari (Gunung Kidul), dan hasil perbanyakan petani di Cilacap Selatan (Cilacap). Metode yang dilakukan antara lain: pengambilan sampel benih, ekstraksi nematoda, penghitungan populasi, identifikasi morfologi dan morfometri. A. besseyi ditemukan berasosiasi dengan varietas Pandan wangi, Sintanur, Pepe, Inpari 33, Prima, dan Sembada 168 dengan populasi berkisar 1.4 sampai 27.2 ekor per 5 g benih padi. Ciri khas A. besseyi yang ditemukan bibir set off dengan stomatostilet, bulbus median berukuran besar dan berbentuk oval, star shaped mucro pada ujung ekor. Vulva pada nematoda betina terletak pada 60-75% panjang tubuh, dan spikula pada nematoda jantan berbentuk seperti duri mawar (rose thorn shaped spicule). Hasil pengukuran morfometri dengan karakteristik panjang tubuh (L) (0.55-0.84 μm), panjang stilet (S) (10.81- 12.92 mm), diameter tubuh maksimum (W) (14.09-22.87 mm), panjang ekor (T) (36.93 – 53.51 mm), panjang esofagus (ES) (58.17 – 86.51 mm). Persentase posisi dari katub esofagus dari anterior tubuh sampai setengah dari katub (bulb) dibagi dengan total panjang esofagus dari dasar kelenjar esofagus (MB) (100.11 – 146.52%). Persentase jarak vulva dari anterior dibagi dengan panjang tubuh (V) (55.35-85.67%), a (L/W) (29.58-52.04), b (L/MB) (8.12-14.97), dan c (L/T) (11.94- 19.92).
Keyword: benih, ekstraksi, identifikasi, kios, pengukuran

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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