Gadjah Mada University

About: Gadjah Mada University is a education organization based out in Yogyakarta, Indonesia. It is known for research contribution in the topics: Population & Adsorption. The organization has 17307 authors who have published 21389 publications receiving 116561 citations. The organization is also known as: University of Gajah Mada & Universitas Gadjah Mada.

Power System Stabilizer model based on Fuzzy-PSO for improving power system stability

Abstract: This paper proposed a Power System Stabilizer model based on Fuzzy-PSO for improving power system stability. Power System Stabilizer (PSS) is a device that can be used to enhance the damping of power system during low frequency oscillations. In multi-machine power systems, the PSS parameter tuning is a complex exercise due to the presence of several poorly damped modes of oscillation. The problem is further being complicated by continuous varied in power system operating conditions. In order to enhance the performance of PSS, the combination of fuzzy logic and particle swarm optimization (PSO) method is used in this study. Simulations were carried out using several fault tests at transmission line on a two-area multi-machine power system. In this work, Delta w PSS and Delta Pa PSS has been used for comparison with the fuzzy-PSO PSS. The result shows that power transfer response using the fuzzy-PSO PSS is more robust than Delta w PSS and Delta Pa PSS, especially for three phase faults and phase to ground faults.

Preparation and Characterization of Natural Hydroxyapatite: A Comparative Study of Bovine Bone Hydroxyapatite and Hydroxyapatite from Calcite

Abstract: The production of natural hydroxyapatite (HAp) specifically from cortical bovine bones and natural calcite was studied in this paper. Bovine hydroxyapatite (BHA) was produced from bovine bone in bulk form by de-fatting continued with calcination at 900°C. Natural calcite hydroxyapatite (CHA) was produced by hydrothermal method. It was confirmed from XRD, FTIR, and SEM results that HA have been successfully produced from natural sources like bulk bovine bone and natural calcite. The results also show that the crystallinity of BHA is higher than CHA, matching with the hardness test results of sintered BHA and CHA.

Estimating the codifference function of linear time series models with infinite variance

Abstract: We consider the codifference and the normalized codifference function as dependence measures for stationary processes. Based on the empirical characteristic function, we propose estimators of the codifference and the normalized codifference function. We show consistency of the proposed estimators, where the underlying model is the ARMA with symmetric α-stable innovations, 0 < α ≤ 2. In addition, we derive their limiting distribution. We present a simulation study showing the dependence of the estimator on certain design parameters. Finally, we provide an empirical example using some stocks from Indonesia Stock Exchange.