Judul: Masalah Kontrol Optimum Hama Secara Hayati
Abstrak: Pests are species that can attack crops and interfere farming activity. Effort to reduce the effect of pests is necessary. It can be accomplished either by chemical control through insecticides or by biological control using natural enemy intervention. In this work, pest control effort is formulated by a mathematical model, i.e., an optimal pest control problem. The primary objective of this work is to determine control strategies which maintain the density of the pest population in the equilibrium level below economic losses. Two-step control strategy is proposed by using the combination of chemical and biological controls; in the first step to speed-up pest reduction, and solely by using the biological control in the second step to maintain the admissible level. The control strategy is then applied to a predator-prey model which involves Anticarsia gemmatalis as a pest to soybean and Geocoris sp. as a natural enemy. It shows that the admissible level of 20 pest/m2 can be attained and maintained subsequently.
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Judul: Strategi Optimal Pengendalian Serangga Hama Nonvektor Menggunakan Intervensi Green Insecticide dan Mating Disruption
Abstrak: Dalam karya ilmiah ini, dipelajari sebuah model siklus reproduksi serangga yang memperhitungkan empat kompartemen yang merepresentasikan larva, serangga betina yang belum dibuahi, serangga betina yang sudah dibuahi, dan serangga jantan. Kompartemen densitas tanaman ditambahkan untuk menjelaskan interaksi serangga nonvektor dan tanaman. Untuk mengendalikan populasi serangga hama, digunakan pendekatan kontrol optimum. Diberikan dua metode pengendalian hama, yaitu intervensi green insecticides dan mating disruption. Tujuan dari pemberian kontrol adalah untuk meminimalkan populasi total serangga hama dan memaksimalkan densitas tanaman. Untuk menyelesaikan masalah ini, digunakan prinsip maksimum Pontryagin. Dalam mendapatkan solusi numerik dari kedua sistem persamaan diferensial dan mendapatkan fungsi kontrol yang optimal, digunakan metode Runge-Kutta orde 4 dan forward-backward sweep method.
Keyword: kontrol optimum, green insecticide, mating disruption, prinsip maksimum Pontryagin, solusi numerik

Judul: Characterizations of low alloy steel sae 4422  plated with chromic acid (Cro3)
Abstrak: Characterizations of low alloy steel SAE 4422 plated with chromic acid (CrOrO3) was use Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), RD),Energy Dispersive Analysis of X-Ray (EDAX), Hardness Test and Roughness Test. Microstructures analysis exhibits cracks and grain boundaries microcracks as a characteristics of chrome metal found at plating metal. Perlite and Ferrite as grains of steel found at base metal with grain boundaries around it. Phase analysis of plating metal appropriate to chrome metal with lattice constant (a) is 2.559 Å and phase analysis of base metal appropriate to iron ferrite with lattice constant (a) is 3.318 Å. Both plating and base metal have cubic system. Chemical analysis of plating metal at surface section exhibits that cracks area have highest value of carbon element compare with grains and grains boundaries area. While chemical analysis of base metal at cross section exhibits that perlite have highest value of carbon element compare with ferrite and grain boundaries. The hardness value of plating metal at surface section and cross section are 753 and 637 VHN. While, the hardness value of base metal and interface area at cross section are 205 and 373 VHN. The roughness value at measurement points of chrome surface for as received sample are 0.445 μm. Observation used Optical Microscopy and Scanning Electron Microscopy exhibits surface irregularities combine to form surface texture of plating metal at surface section.
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