Judul: Fuzzy Time Series Markov Chain and Its Application in Jakarta  Islamic Index (JKII) Stock Price Prediction
Abstrak: Saham atau stock merupakan instrumen investasi yang populer dan banyak dipilih oleh para investor karena mampu memberikan tingkat keuntungan yang menarik. Pergerakan harga penutupan saham yang flukluatif membuat para investor sulit untuk mengikuti naik atau turunnya harga saham. Oleh sebab itu dibutuhkan suatu model matematis untuk meramalkan harga saham. Salah satu metode yang dapat digunakan untuk peramalan harga saham adalah metode fuzzy time series Markov chain. Penelitian ini menggunakan data harga penutupan saham Jakarta Islamic Index (JKII) dari Januari 2016 sampai Maret 2022. Penelitian ini menggunakan 7 himpunan, dan hasil yang didapatkan yaitu ramalan harga penutupan saham Jakarta Islamic Index (JKII) untuk bulan April 2022 sebesar 580.5576 dengan tingkat penyimpangan sebesar 2.2996%., Stocks are popular investment instruments and are widely chosen by investors because they are able to provide attractive profit levels. The fluctuating movement of closing stock prices makes it is difficult for investors to follow rising or falling stock prices. Therefore it is needed a mathematical model to forecast stock prices. One method that can be used to forecast stock price is the fuzzy time series Markov chain method. This study uses Jakarta Islamic Index (JKII) closing price data from January 2016 to March 2022. This study uses 7 sets, and the results obtained are the Jakarta Islamic Index (JKII) closing stock price forecast for April 2022 of 580.5576 with a level deviation of 2.2996%.
Keyword: fuzzy time series Markov chain, forecasting, stock price

Judul: Peramalan Harga Indeks Saham Menggunakan Model ARMA-GARCH.
Abstrak: perlunya suatu metode dalam sebuah perencanaan investasi saham, guna memprediksi kondisi di masa yang akan datang. Peramalan merupakan penghitungan objektif yang bertujuan untuk memanfaatkan data masa lalu dalam menentukan suatu kejadian di masa mendatang. Saham yang digunakan dalam penelitian ini adalah indeks harga saham Jakarta Islamic Index (JII) periode 30 Juli 2013 hingga 29 April 2016. Penelitian ini bertujuan untuk memodelkan harga indeks saham JII dan meramalkan harga indeks saham JII untuk beberapa periode mendatang. Model yang dapat digunakan dalam memodelkan harga saham di antaranya adalah Autoregressive (AR), Moving Average (MA) dan Autoregressive Moving Average (ARMA). Model tersebut dapat digunakan pada data dengan salah satu asumsi stasioneritas terhadap varian (homoskedastisitas). Oleh karena itu, diperlukan suatu model tambahan yang dapat memodelkan data dengan kondisi heteroskedastisitas, yaitu model Generalized Autoregressive Conditional Heteroscedastisity (GARCH). Model yang diperoleh dalam penelitian ini adalah ARMA(2,1)-GARCH(1,1) dengan data peramalan yang telah mendekati data aktual.
Keyword: JII, ARMA, heteroskedastisitas, GARCH, peramalan

Judul: Growth, Concentration Chlorophyll-a, and Structure of Macroalgae Gracilaria edulis in the Culture Media Containing Copper
Abstrak: The physiological responses (specific growth rate, concentration of chlorophyll-a, morphological and anatomical structure of the vegetative cells) of the marine macroalga Gracilaria edulis at the different concentrations of copper (0.01 as control, 0.04, 0.06 and 0,5 ppm) delivered continuously for 28 days under controlled laboratory conditions were investigated. Result showed that the degree of copper toxicity depends on both factor the concentration and exposure time. Copper concentration and day of exposure decreased significantly the specific growth rate (SGR) of the Gracilaria edulis but only 0,5 ppm Cu decreased the chlorophyll-a content when compared to control. Of the various physiological end points measured, growth proved to be the most sensitive response than chlorophyll-a with reductions in specific growth rate (SGR). The reason for this could be related to a greater sensitivity of the enzymes involved in growth than those related to chlorophyll-a or a greater energy needs to maintain cellular integrity and metabolic processes under sublethal Cu stress. In all cases, the main effect on vegetative cells were structure changes in cortex and subcortex cells, compared to control, macroalgae exposed to copper showed depigmentation and blending in the lateral branches, heavy staining of the cell wall and severe damage of cell membrane, while the mucilage and the cell walls was densely fibrillar, thick and heavily stained, the cortex cell was clearly vacuolated, the presence of endophytic on the cell wall and endophytic spores in the mucilage. The presence vacuoles should be related to a metal immobilization mechanism, minimizing the Cu toxicity for cells. The epiphytic bacteria can act as a biofilter diminishing the availability of Cu for macroalgae accumulation.
Keyword: