Judul: Comparison of Indonesia's Export Value Forecasting Using Chen's Fuzzy Time Series Method with Huarng Model
Abstrak: Ekspor merupakan kegiatan menjual hasil produksi dalam negeri ke luar negeri. Nilai ekspor sering kali tidak stabil, sehingga dibutuhkan suatu metode peramalan untuk mengetahui pertumbuhan nilai ekspor pada masa yang akan datang. Fuzzy time series merupakan salah satu metode peramalan yang menggunakan fuzzy logic sebagai landasannya. Pada penelitian ini digunakan 72 training data dan 12 testing data dengan metode peramalan fuzzy time series dengan dua model berbeda, yaitu model Chen dan model Huarng (heuristic). Hasil yang diperoleh ialah model Huarng memiliki hasil peramalan lebih baik daripada model Chen, hal tersebut ditunjukkan dengan nilai Mean Absolute Percentage Error (MAPE) model Huarng lebih kecil daripada model Chen., Export is the activity of selling domestic products abroad. Export value is often unstable, so a forecasting method is needed to determine the growth of export value in the future. Fuzzy time series is a forecasting method that uses fuzzy logic as its foundation. In this study, 72 training and 12 testing data were used with fuzzy time series forecasting methods with two different models, namely the Chen and the Huarng model (heuristic). The result obtained is that the Huarng model has better forecasting results than the Chen model, which is indicated by the Mean Absolute Percentage Error (MAPE) value of the Huarng model being smaller than the Chen model.
Keyword: Chen Model, Export Value, Forecasting, Fuzzy Time Series, Huarng Model

Judul: Comparative Analysis of ARIMA and Fuzzy Time Series Methods for Stock Price Forecasting in the Energy Sector (Case Study: PT XYZ)
Abstrak: Peramalan merupakan hal penting untuk dapat memaksimalkan keuntungan dengan memprediksi di masa mendatang. Metode peramalan terus dikembangkan hingga dibagi menjadi metode konvensional dan soft-computing yang bertujuan untuk mendapatkan galat terkecil. Penelitian ini bertujuan untuk membandingkan kinerja prediksi metode ARIMA dan Fuzzy Time Series menggunakan model Saxena-Easo. Data yang digunakan adalah data harian dari PT XYZ sejak 1 Januari 2022 hingga 31 Desember 2022. Evaluasi kinerja model dilakukan dengan membandingkan nilai Mean Absolute Percentage Error (MAPE) untuk menentukan model yang lebih unggul. Hasilnya, baik model ARIMA(0,1,1) maupun Fuzzy Time Series merupakan model yang baik. MAPE yang dihasilkan oleh model ARIMA(0,1,1) sebesar 4,78% sementara Fuzzy Time Series dengan model Saxena-Easo sebesar 1,72%. Secara visual model ARIMA(0,1,1) menghasilkan peramalan garis lurus yang terus meningkat, sementara metode Fuzzy Time Series dengan model Saxena-Easo cenderung mengikuti pola data aktual. Sehingga didapatkan kesimpulan bahwa metode Fuzzy Time Series dengan model Saxena-Easo memiliki kinerja yang lebih baik daripada model ARIMA dalam meramal data non-linear., Forecasting is crucial for maximizing profits by predicting future prices. Forecasting methods have evolved, braching into conventional and soft-computing techniques aimed at minimizing prediction errors. The objective is to compare the predictive performance of ARIMA and Fuzzy Time Series models using the Saxena-Easo framework. Daily data from PT XYZ spanning from January 1, 2022, to December 31, 2022, is employed in this study. Model performance is assessed by comparing the Mean Absolute Percentage Error (MAPE) values to determine the superior model. Both the ARIMA(0,1,1) and Fuzzy Time Series models demonstrate strong predictive capabilities. ARIMA(0,1,1) yields a MAPE of 4.78%, while Fuzzy Time Series with the Saxena-Easo model achieves an even lower MAPE of 1.72%. Visually, ARIMA(0,1,1) generates a steadily increasing linear forecast, whereas the Fuzzy Time Series method with the Saxena-Easo model closely tracks the actual data pattern. Consequently, it can be concluded that the Fuzzy Time Series method with the Saxena-Easo model outperforms the ARIMA model in forecasting non-linear data.
Keyword: ARIMA, forecasting, fuzzy time series, saxena-easo model

Judul: Application of phycocyanin from microalgae Spirulina platensis as light harvesting in anatase TiO2 nanoparticle solar cell.
Abstrak: The dye sensitized solar cell (DSSC) has been assemblied used hybrid titanium oxide (TiO2) film/phycocyanin. The TiO2 film was synthesized by sol gel method with titanium chlorida (TiCl4) as precursor by hydrolysis used sulfuric acid (H2SO4). Furthermore, it calcinated for 2,5 hours in variation of annealing temperature (400oC, 600oC, 800oC, dan 1000oC). In XRD patterns exhibited which annealing temperature at 400oC to 800oC were anatase phase all. When annealed at temperature 1000oC, it caused phase transformation from anatase to rutile. The crystals size according to XRD patterns were 13,75 nm, 20,79 nm, 25,25 nm, 48,88 nm and particle size from SEM images were 43,06 nm, 44,91 nm dan 64,99 nm, 80,40 nm, respectively. The crystals and particle size increased with annealing temperature. The film thickness influenced material absorption. The optical measurement of TiO2 film and TiO2/phycocyanin hybrid film used UV-Vis spectrophotometer. Additional phycocyanin caused peak width of absorbed region from ultraviolet to visible region. The band gap energy of TiO2 can be calculated using the cut off wavelength obtained from the absorbance spectrum of a nanoparticles TiO2 films. Based on intersection between linear and energy (hv) axis. In this study just limited for anatase phase. It was caused anatase band gap is wider than rutile phase. That’s meaningful for solar cell application such as dye sensitized solar cell (DSSC). The absorption coefficient average at difference annealing temperature such as at 400oC, 600oC, 800oC were 8,1600x102, 1,7535x103 and 4,0154x102, where α < 104 include to direct transition. Band gap energy 400oC, 600oC, 800oC were 3,79 eV, 3,59 eV, and 3,35 eV, respectively. Based on this result, exhibition that band gap energy of TiO2 semiconductor film decreased with increasing annealing temperature. Spirulina platensis was cultivated in technical modification (Hastuti) with aeration under light intensity about 3000 lux. The cell density (stationer phase) for eighth day which OD value was more than 0,5. It means, the culture can be harvested. In 80 liters Spirulina platensis culture have been produced biomass dry about 10,46 gram and extracted phycocyanin in dry powders was 5,50 gram. The phycocyanin absorption spectrum at the wavelength of 619,36 nm (visible region) which had relaxation energy was 2,945 eV. The emission peak at the wavelength of 708,55 nm with relaxation energy about 2,793 eV. The Stokes shift based on difference energy absorption and emission calculated about 0,152 eV. Both of this showed phycocyanin can absorbed and radiated the sun light which received. This choice characteristic pigment was a good one related to sensitizer in solar cell application. Integration between light harvesting protein and TiO2 semiconductor surface had important role in improving of output as solar cell materials. The presence of carboxylate group (-COOH) made pigment be more efficient was due to anchored to the surface of TiO2 ampoter. The phycocyanin pigment had carboxylate group which reacted with TiO2 surface formed ester. The carboxylate group increased of dye electronics couple from excited state (p anti bonding orbital) to semiconductor acceptor state (TiO2 conduction band). The samples which made based on annealing temperature variation formed be solar cell respectively. Furthermore, cells be assembled for
Keyword: anatase, dye sensitized solar cell, efficiency, gap energy, phycocyanin