Judul: The Resistance of Citrus Rootstock Japansche Citroen to In Vitro Drought Stress Condition
Abstrak: Varietas batang bawah jeruk diharapkan dapat beradaptasi dengan baik dalam berbagai kondisi cekaman lingkungan. Seleksi in vitro menggunakan polietilen glikol (PEG) dapat digunakan untuk memperoleh individu yang toleran terhadap kekeringan. Penelitian ini bertujuan untuk mempelajari pengaruh penggunaan PEG sebagai agen penyeleksi terhadap pertumbuhan jeruk varietas Japansche Citroen pada kondisi cekaman kekeringan secara in vitro. Penelitian dilaksanakan di Laboratorium Kultur Jaringan 1, Departemen Agronomi dan Hortikultura, Institut Pertanian Bogor, Bogor. Penelitian dimulai pada bulan Desember 2019 hingga Februari 2021. Penelitian ini menggunakan metode rancangan kelompok lengkap teracak faktor tunggal yaitu konsentrasi PEG dengan empat taraf: 0 %, 5 %, 10 %, dan 15 %. Hasil pengamatan menunjukkan bahwa jumlah daun, jumlah akar, dan tinggi tanaman batang bawah jeruk menurun sebagai respon terhadap penambahan 5–15 % PEG pada media in vitro. PEG tidak berpengaruh nyata terhadap persentase kontaminasi, persentase hidup eksplan, dan panjang akar., Citrus rootstock varieties are expected to be well adapted in various environment stress condition. In vitro selection using polyethylene glycol (PEG) can be used to obtain drought stress tolerant individual. The objective of the experiment was to study the effect of using PEG as selector agent to the growth of citrus Japansche Citroen variety on in vitro drought stress condition. The experiment was conducted at Tissue Culture 1 Laboratory, Department of Agronomy and Horticulture, IPB University, Bogor. The experiment was started on December 2019 until February 2021. The experiment used randomized complete block design with one factor, PEG concentration which had four levels: 0 %, 5 %, 10 %, and 15 %. The result of observation showed that number of leaves, number of roots, and plant height of citrus rootstock decreased in response to the addition of 5–15 % PEG to in vitro media. PEG did not affect the contamination persentage, survival persentage, and length of root significantly.
Keyword: phytotoxic, growth, polyethylene glycol

Judul: Seleksi Kekeringan pada Beberapa Varietas Batang Bawah Jeruk secara In vitro
Abstrak: Drought stress could be simulated by decreasing the water potensial media through polyethylene glycol (PEG) addition. The objective of this experiment was to explain the effect of drought stress to some citrus rootstocks growth under in vitro conditions. The experiment used a factorial completely randomized design (CRD). The first factor was PEG addition which consist of four level: 0 g l-1 PEG is equivalent to 0% (0 bar), 20 g l-1 PEG is equivalent to 2% (-0.12 bar), 40 g l-1 PEG is equivalent to 4% (-0.32 bar), 60 PEG g l-1 is equivalent to 6% (-0.59 bar). The second factor was citrus rootstock varieties, which consist of Rough Lemon, Kunci-10, and Nipis. The result showed that all of the parameters decreased with the increasing of osmotic stress by PEG. Three varieties showed same response toward PEG addition on the last week of observation. Kunci-10 and Nipis have more stability under drought stress simulation rather than Rough Lemon.
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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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