Judul: Comparison of ARIMA and Fuzzy Time Series Methods in Forecasting West Texas Intermediate Crude Oil Prices
Abstrak: Minyak dunia merupakan komoditas penting dan bernilai tinggi di pasar internasional. Salah satu jenis minyak mentah dunia adalah West Texas Intermediate (WTI) yang memiliki kandungan sulfur 0,24% dan gravity 39,6 derajat. Patokan harga minyak WTI digunakan oleh Amerika Serikat dan sangat mempengaruhi pasar global. Amerika Serikat menyumbang 36,3% pasar modal global sehingga menjadikan harga WTI sebagai standar internasional. Di pasar global, minyak mentah sangat aktif diperdagangkan dengan volatilitas tahunan 25% sehingga menyebabkan fluktuasi harga yang sulit diprediksi dan berdampak pada perekonomian dunia, terutama negara berkembang seperti Indonesia. Kenaikan harga minyak yang signifikan dan ketidakpastian ekonomi global mempengaruhi semua sektor masyarakat. Peramalan harga minyak yang akurat penting untuk pengambilan keputusan para pemangku kepentingan. Peramalan menggunakan data historis melibatkan metode seperti Autoregressive Integrated Moving Average (ARIMA) dan fuzzy time series (FTS). Penelitian ini membandingkan metode ARIMA dan fuzzy time series Stevenson Porter untuk peramalan harga minyak WTI dan dievaluasi berdasarkan nilai MAPE terkecil. Kedua metode berfungsi sangat baik dalam peramalan, dengan ARIMA menunjukkan kestabilan dalam membaca pola data yang lebih baik dan MAPE senilai 1,45% sedangkan nilai MAPE untuk FTS Stevenson Porter senilai 2,13%. Hal ini menunjukkan akurasi peramalan yang sangat baik dari kedua metode., World oil is an important and highly valuable commodity in the international market. One type of crude oil is West Texas Intermediate (WTI), which has a sulfur content of 0,24% and a gravity of 39,6 degrees. The price benchmark for WTI oil is used by the United States and significantly influences the global market. The United States accounts for 36,3% of the global capital market, making WTI prices an international standard. In the global market, crude oil is actively traded with an annual volatility of 25%, causing price fluctuations that are difficult to predict and impacting the global economy, especially developing countries like Indonesia. Significant increases in oil prices and global economic uncertainty affect all sectors of society. Accurate oil price forecasting is important for stakeholders' decision-making. Forecasting using historical data involves methods such as Autoregressive Integrated Moving Average (ARIMA) and fuzzy time series (FTS). This study compares the ARIMA and fuzzy Time Series Stevenson Porter methods for forecasting WTI oil prices and evaluates them based on the smallest MAPE value. Both methods perform very well in forecasting, with ARIMA showing better stability in reading data patterns and a MAPE of 1,45%, while the MAPE for FTS Stevenson Porter is 2,13%. This indicates a very good forecasting accuracy for both methods.
Keyword: ARIMA, peramalan, fuzzy time series, MAPE, minyak mentah

Judul: Penerapan Metode Generalized AutoRegressive Conditional Heteroskedasticity untuk Peramalan Harga Minyak Mentah Dunia.
Abstrak: Minyak mentah merupakan salah satu komoditas yang sangat dibutuhkan di berbagai bidang. Harga minyak mentah dunia yang terus mengalami fluktuasi tentunya mengambil pengaruh yang besar terhadap perekonomian negara. Data harga minyak mentah yang dikumpulkan bersifat time series atau proses pengumpulannya dilakukan dari waktu ke waktu dengan periode bulanan. Oleh karena itu, diperlukan suatu sistem yang dapat membuat peramalan harga minyak mentah dunia kedepannya yang diharapkan dapat menjadi bahan pertimbangan pemerintah untuk pengambilan keputusan. Salah satu metode yang dapat digunakan untuk meramalkan harga minyak mentah dunia adalah ARIMA (Auto-Regressive Integrated Moving Average) dan model GARCH (Generalized Auto-Regressive Conditional Heteroskedasticity). Pemodelan yang dilakukan terbukti bahwa data harga minyak mentah dunia periode Januari tahun 2002 hingga Juni 2022 memiliki efek heteroskedastisitas yang tidak dapat diatasi jika hanya menggunakan model ARIMA. Hasil dari pengolahan data diperoleh bahwa model ARIMA (0,1,2) yang dilanjutkan model ARCH (2) merupakan model terbaik dengan nilai MAPE sebesar 5,32%. Nilai akurasi yang diperoleh tergolong sangat baik untuk peramalan harga minyak mentah dunia., Crude oil is one of the commodities that are needed in various fields. World crude oil prices that continue to fluctuate, of course, have a big influence on the country's economy. Crude oil price data collected is time series or the collection process is carried out from time to time with monthly periods. Therefore, we need a system that can forecast future world crude oil prices which are expected to be taken into consideration by the government for decision making. One method that can be used to predict world crude oil prices is ARIMA (Auto-Regressive Integrated Moving Average) and GARCH (Generalized Auto-Regressive Conditional Heteroskedasticity) model. After modeling, it is proven that the world crude oil price data for the period January 2002 to June 2022 has a heteroscedasticity effect that cannot be overcome if only using the ARIMA model. The results of data processing show that the ARIMA (0,1,2) followed by the ARCH model(2) is the best model with a MAPE value of 5,32%. The accuracy values obtained are classifield as very good for forecasting world crude oil prices.
Keyword: ARIMA, ARCH, GARCH, harga minyak mentah, peramalan

Judul: Hybrid solar cells of ZnO nanoparticles/chlorophyll was modified metal ions (Zn2+ and Cu2+ )
Abstrak: Zinc Oxide (ZnO) is a n-type semiconductor with a wide the energy band (Band Gap) is 3.37 eV at room temperature and 3.34 eV at low temperature with a large exiton binding energy is 60 meV. ZnO has been synthesized by hydrothermal method, resulting in a decrease in particle size over the duration of the hydrothermal changes. Crystallographic structure of ZnO were characterized using XRD, has shown the characteristic pattern of a hexagonal wurtzite structure, the crystallite size increases to changes in particle size. Changes in particle size has also led to a change in the absorption peak of ZnO as has been demonstrated posted under test using the optical properties of UV-Vis spectrophotometer. Changes of this uptake has also led to changes in the energy band gap, which increases its band gap energy of the particle size. In electronic applications, especially in solar cells. Chlorophyll is considered less effective, because of their very nature are easily degraded as a result of several reactions which are acid, lighting and temperature. The results of the stability test using a halogen lamp 34 W/m2 for 5 hours, that the substitution of chlorophyll with metal ions Zn2+ and Cu2+ has been shown to form more stable than natural chlorophyll. The characterization of the optical properties, the combination of ZnO / chlorophyll in the form of hybrid films has led to a shift in the absorption region of ZnO becomes more widely from the UV to Visible. ZnO/chlorophyll has absorption range of 350-515 nm, ZnO / Zn-feofitin 332-401 nm and 332-632 nm for Cu-feofitin. The combination of ZnO/chlorophyll and CuSCN as a solid electrolite in hybrid solar cell, a modified chlorophyll with metal ions Zn2+ and Cu2+ has been shown to form a more stable I-V curve. It is characterized by its fill factor value greater than natural chlorophyll. Nevertheless, solar cells with natural chlorophyll has been able to produce higher efficiency values of chlorophyll were substituted.
Keyword: Hydrothermal, ZnO/Chlorophyll modified, Hybrid Solar Cell