Judul: Komunitas Staphylinidae (Coleoptera) di Kebun Ubi Jalar
Abstrak: Staphylinidae is a member of order Coleoptera (beetle). This family characterized by elongated slender body, large abdominal section and tapered end of the abdomen, and very short elitra. Most of staphylinids role as predators, saprofag, polifag, and as bioindicators of soil fertility. This research aimed to study the community of staphylinids in the sweet potato fields at Bogor. Observations and collections of beetle were done by using road sampling method. Samples collected were preserved in the ethanol 70% for identification purposes. Environmental factors, i.e. air temperature, humidity, and light intensity were measured during observations of beetles. Result showed that the community of staphylinids found in the sweet potato fields were Paederus fuscipes (subfamili Paederinae), Medon sp. (subfamili Paederinae), and Stenus sp. (subfamili Steninae). The dominant staphylinid species in the sweet potato was P. fuscipes
Keyword: Community, Coleoptera, staphylinid, sweet potato fields.

Judul: Keanekaragaman dan Kelimpahan Spesies Staphylinid (Coleoptera) di Habitat Persawahan Sekitar Bogor
Abstrak: Staphylinid beetles (order Coleoptera) are characterized by elongated and slender body shape, short elytra that covered some segments of the abdomen, and body usually shiny black, brown, or yellow-brown. In the paddy field ecosystem, these beetles are known as predator. This research aimed to measure the diversity and abundance of staphylinid beetles in the paddy field at some areas in Bogor. The research also studied the hemolymph structure of Paederus fuscipes. Collections of beetle were done by using road sampling method in some paddy fields. Observations of hemolymph structure were done by making a blood smear. Staphylinid beetles found in six paddy fields in Bogor were Paederus fuscipes (subfamily Paederinae), Stenus sp. (subfamily Steninae), Hypostenus arachnoides (subfamily Steninae), and Astenus lombokianus (subfamily Paederinae). Diversity of staphylinid species in paddy fields is low. The most dominant species staphylinid at the paddy fields was P. fuscipes. Hemocytes type found in the hemolymph of P. fuscipes beetles were prohemocyte, plasmatocyte, adipohemocyte, and cystocyte.
Keyword: Bogor Agricultural University (IPB), staphylinid., paddy fields, hemocyte, diversity, Dominance

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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