| Judul | Abstract | Halaman |
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| Optimization of Laccase Production using White Rot Fungi and Agricultural Wastes in Solid-State Fermentation | Abstract. Laccase has been produced in a solid-state fermentation (SSF) process using white rot fungi and various lignocellulose-based substrates. The white rot fungi used were Marasmius sp., Trametes hirsuta, Trametes versicolor and Phanerochaete crysosporium. The solid substrates employed in this research were collected from agricultural waste, specifically empty fruit bunches (EFB), rice straw, corncobs and rice husks. The objective of this research was to determine the most promising fungus, the best solid substrate and the optimal conditions for the production of laccase. The results showed that Marasmius sp. on all solid substrates displayed a higher laccase activity than that of any other strain of white rot fungi. Marasmius sp. and a solid substrate of rice straw demonstrated the highest laccase activity of 1116.11 U/L on day 10. Three significant factors, i.e. pH, temperature and yeast extract concentration, were studied by the response surface method on laccase production using Marasmius sp. and rice straw. The optimized conditions were a pH, temperature and yeast extract concentration of 4.9, 31ºC and 0.36 g/L, respectively. The fermentation of Marasmius sp. in SSF on agricultural waste shows a great potential for the production of laccase. | 93-105 |
| Optimization of Vertical Well Placement for Oil Field Development Based on Basic Reservoir Rock Properties using a Genetic Algorithm | Comparing the quality of basic reservoir rock properties is a common practice to locate new infill or development wells for optimizing oil field development using reservoir simulation. The conventional technique employs a manual trial-and-error process to find new well locations, which proves to be time-consuming, especially for large fields. Concerning this practical matter, an alternative in the form of a robust technique is introduced in order to reduce time and effort in finding new well locations capable of producing the highest oil recovery. The objective of this research was to apply a genetic algorithm (GA) for determining well locations using reservoir simulation, in order to avoid the conventional manual trial-and-error method. This GA involved the basic rock properties, i.e. porosity, permeability, and oil saturation, of each grid block obtained from a reservoir simulation model, to which a newly generated fitness function was applied, formulated by translating common engineering practice in reservoir simulation into a mathematical equation and then into a computer program. The maximum fitness value indicates the best grid location for a new well. In order to validate the proposed GA method and evaluate the performance of the program, two fields with different production profile characteristics were used, fields X and Y. The proposed method proved to be a robust and accurate method to find the best new well locations for oil field development. The key to the success of the proposed GA method lies in the formulation of the objective functions. | 106-127 |
| A Buffer Stock Model to Ensure Price Stabilization and Availability of Seasonal Staple Foods under Free Trade Considerations | Price volatility and scarcity have become a great problem in the distribution system of seasonal staple foods produced by the agricultural industry. There is a salient supply disparity during the harvest and planting seasons. This condition could cause disadvantages to stakeholders such as producers, wholesalers, consumers, and government. This paper proposes a buffer stock model under free-trade considerations to substitute quantitative restrictions and tariffs with an indirect market intervention instrument. This instrument was developed using a buffer stock scheme in accordance with a warehouse receipt system (WRS) and a collateral management system. A public service institution for staple food buffer stock (BLUPP) is proposed as the wholesaler’s competitor, with as main responsibility to ensure price stabilization and availability of staple food. Multi-criteria decision-making is formulated as a single objective mixed integer non-linear programming (MINLP) model. The results shows that the proposed model can be applied to solve the distribution problem and can give more promising outcomes than its counterpart, direct market intervention. | 128-148 |
| A New Obstacle Avoidance Method for Service Robots in Indoor Environments | The objective of this paper is to propose an obstacle avoidance method for service robots in indoor environments using vision and ultrasonic sensors. For this research, the service robot was programmed to deliver a drinking cup from a specified starting point to the recognized customer. We have developed three main modules: one for face recognition, one for obstacle detection, and one for avoidance maneuvering. The obstacle avoidance system is based on an edg edetection method using information from the landmark and planned-path generation. Speed, direction and distance of the moving obstacle are measured using vision and distance sensors in order for the robot to make an avoidance maneuver. Algorithms for obstacle avoidance are proposed and a new geometric model is introduced for making good avoidance maneuvers. The main aim of this research is to provide a complete mechanism for obstacle avoidance by vision based service robots, where common obstacle avoidance methods, such as PVM, do not provide such a feature. We present the results of an experiment with a service robot in which the proposed method was implemented, after which its performance is evaluated. | 149-168 |
| Linear Parameter-Varying Versus Linear Time-Invariant Reduced-Order Controller Design for Turboprop Aircraft Dynamics | The applicability of parameter-varying reduced-order controllers to aircraft models is proposed. A generalization of the balanced singular perturbation method of the linear time-invariant (LTI) system was used to reduce the order of the linear parameter-varying (LPV) system. Based on the reducedorder model, a low-order LPV controller was designed using the H∞ synthesis technique. The performance of the reduced-order controller was examined by applying it to the lateral-directional control of a 20th-order aircraft model. Furthermore, the time responses of the closed-loop system with several reducedorder LPV controllers and a reduced-order LTI controller were compared. The simulation results show that an , 8th -order LPV controller can maintain stability and provide the same level of closed-loop system performance as a full-order LPV controller. This was not the case with the reduced-order LTI controller, which cannot maintain stability and performance for all allowable parameter trajectories. | 169-186 |
| Estimation of Slip Distribution of the 2007 Bengkulu Earthquake from GPS Observations Using the LeastSquares Inversion Method | Continuous Global Positioning System (GPS) observations showed significant crustal displacements as a result of the Bengkulu earthquake occurring on September 12, 2007. A maximum horizontal displacement of 2.11 m was observed at PRKB station, while the vertical component at BSAT station was lifted up with a maximum of 0.73 m, and the vertical component at LAIS station had subsided –0.97 m. Adding more constraints on the inversion for the Bengkulu earthquake slip distribution inferred from GPS observations can help solve the underdetermined least-squares inversion. Checkerboard tests were performed to help conduct the weighting for constraining the inversion. The inversion calculation yielded an optimal value for the slip distribution by giving the smoothing constraint a weight of 0.001 and the slip constraint a weight of = 0 at the edge of the earthquake rupture area. The maximum co-seismic slip of the optimal inversion calculation was 5.12 m at the lower area of PRKB station and BSAT station. The seismic moment calculated from the optimal slip distribution was 7.14 x 1021 Nm, which is equivalent to a magnitude of 8.5. | 187-206 |
