Judul: The use of materials having low adhesion and friction coefficient on soil as landside of moldboard plow to reduce tillage draft
Abstrak: Farm machinery has an important role in agricultural activities, especially in tillage. One of the tillage indicators is draft, which has relation with tillage quality and energy consumption. One of the factors affected pulling draft was the friction between the tool and the soil. Friction resistamce had two variables that were adhesion and friction coefficiemt. Almost tillage tools have friction with the soil, one of them is moldboard plow. Moldboard plow was the oldest tillage tool, but it is still used by the farmers, since at produces good work and it has a simple and a unique design.
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Judul: Draft force and energy reduction of soil tillage by Selfexcited Vibration method
Abstrak: Soil compaction potentially inhibits plant growth and reduces crop productivity. To loosen the compact soil, however high draft force and energy consumption are needed. The cause of which is due to soil cohesion, adhesion and friction between soil and tillage tool. It’s well known that vibratory-tillage could reduce that soil cohesion, adhesion and friction between soil and tillage tools so that the draft force and energy consumption required is reduced. In this research, soil tillage by self-excited vibration (SEV) method has been conducted. The objective of this research was to obtain vibratory-system of self-excited vibration vibratory-tillage (SEVVT) so that the vibration of the tillage tool will reduce draft force and energy consumption during tillage operation. The research was divided into three steps, i.e.: analytical study, equipment design and experiment study. In the analytical study, the vibration of SEVVT was simulated as a vibration with single degree of freedom system (SDOF) and two degrees of freedom system (TDOF). The vibration of tillage tool was exerted by natural excitation of the varying cutting force. The elasticity of the elastic spring or the inertia of the tillage tool was optimized such that the tillage tool vibrates violently around its resonant frequency. Draft force reductions about 22-47 % were observed. In the second step, the equipment was designed methodologically using VDI2221, with focus on the conceptual design. The embodiment design was then conducted to exemplify that the conceptual design was simple, easy to understand, and economically realizable. In the last step, soil tillage was conducted in a soil bin with the dimension of 1.2 m long, 0.3 m wide and 0.4 m depth. Clay loam soil was conditioned in soil bin into two layer namely hardpan and top soil. The tillage tool was connected to a fixed structure using a new model of semi-elliptical spring. The tillage speeds used were 0.158, 0.212 and 0.265 m/s. Five treatments were tested, i.e.: Non vibratory-system (NST), SDOF with rear spring orientation (RST), SDOF with front spring orientation (FST), TDOF system (TST) and low energy vibratory-system (VST). In the RST orientation, the draft force raised the elevation of the tillage tool tip, and the draft force caused the tillage tool tip elevation decrease in the FST orientation. Compared to NST, the average draft force in the FST orientation showed an increase of up to 46-96 %, whereas a draft force reduction were found in the RST and in the TST treatment. In the VST treatment, a small unbalance mass of 0.24 and 0.35 kg was rotated 530 and 1150 rpm respectively and causing tillage tool vibrate with low amplitude. Compared to NST, draft force reduction about 7.3-38.3 % and energy reduction about 4.8- 14.4% were found.
Keyword: Low energy vibratory-system, Tillage tool, Agricultural machine

Judul: Reproduksi Ikan "Shirogisu" Sillago japonica (Temminck dan Schlegel) di Perairan Teluk Omura, Nagasaki, Jepang
Abstrak: Ikan S. japonica pertama kali matang gonad pada ukuran kelas panjang 185 - 198 mm dan frekuensi terbesar pada ikan jantan pada selang kelas rata-rata 220 mm (100 %) dan ikan betina pada selang kelas rata-rata 234 mm (100 %). Melalui histologi gonad ikan betina, pada TKG II terdapat sel oogonia dimana sel telur belum matang (perinucleolus) yaitu inti sel mulai membesar dan membran sel yang tebal. Pada TKG III, sel telur berkembang menjadi oocyte primer dan kemudian menjadi oocyte sekunder dimana sel telur telah matang (ripe eggs), butiran kuning telur telah terbentuk dan membran sel mulai menipis. Pada TKG IV, sel telur berkembang menjadi ootid, dimana terjadinya penyatuan butiran kuning telur yang menuju salah satu kutub anima (Fusion of yolk globule) dan terdapat membran sel yang menipis pada sel telur yang matang (Oolema of ripe eggs). Pada TKG V, sel telur berkembang menjadi ovum yang akan dikeluarkan pada saat pemijahan, mulai berkurangnya ootid dan terdapat folikel yang kosong. Sedangkan pada testes ikan jantan, TKG I ditunjukkan adanya sel spermatogonia yang berada di dalam kantung tubulus seminifer. Pada TKG I1 sel berkembang menjadi sel spermatogonia. Pada TKG III sel spermatogonia berkembang menjadi spermatocytes primer dimana terjadi pembelahan sel secara miosis (pembelahan pertama) dan kemudian berkembang menjadi spermatocytes sekunder dimana terjadi pembelahan sel yang kedua. Pada TKG IV sel spermatocytes berkembang menjadi sel spermatid, dan pada TKG V sel spermatid herkembang menjadi spermatozoa yang akan dikeluarkan pada saat pemijahan.
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