Judul: Peramalan Harga Saham PT Garuda Indonesia Saat Covid-19   dengan Menggunakan Model ARIMA
Abstrak: Avlation is one of the industries that has an impact on the restriction system to prevent the spread of the Covid-19 virus. Therefore, investors find it difficult to assume whether making an investment at the time of restriction will bring future profits or losses. To overcome this, forecasting is needed. One method that is often used is the ARIMA model. The data used is the daily stock price of PT Garuda Indonesia from January 1, 2020 to April 26, 2021. The most suitable model is ARIMA(2,1,2) with a MAPE around 4.3%. After forecasting for the next 10 periods, the MAPE is obtained at around 0.78%, this means that the error rate is quite low., Penerbangan merupakan salah satu industri yang berdampak pada saat sistem pembatasan untuk mencegah penyebaran virus Covid-19. Oleh karena itu, investor merasa kesulitan untuk mengasumsikan apakah melakukan investasi pada saat pembatasan akan mendatangkan keuntungan atau kerugian di masa yang akan datang. Untuk mengatasi hal tersebut perlu dilakukan peramalan. Salah satu metode yang sering digunakan adalah Model ARIMA. Data yang digunakan adalah data saham harian PT Garuda Indonesia dari 1 Januari 2020 sampai dengan 26 April 2021. Model yang paling sesuai adalah ARIMA(2,1,2) dengan MAPE sebesar 4.3%. Setelah dilakukan peralaman untuk 10 periode yang akan datang diperoleh MAPE sebesar 0.78%, artinya tingkat kesalahan yang dihasilkan cukup rendah.
Keyword: ARIMA, Covid-19, forecasting, avlation.

Judul: Comparison of Symmetric and Asymmetric GARCH Model in Forecasting Jakarta Composite Index 2018-2023
Abstrak: Metode peramalan deret waktu yang sering digunakan adalah metode ARIMA. Metode ARIMA yang menyertakan deret waktu lain sebagai peubah eksogen disebut metode ARIMAX. Metode ARIMAX mengasumsikan ragam sisaan homogen tetapi data dengan volatilitas yang tinggi dapat menyebabkan pelanggaran asumsi tersebut. Metode yang dapat digunakan adalah metode ARCH/GARCH tetapi metode ARCH/GARCH kurang baik dalam memodelkan volatilitas asimetris pada data. Metode lain yang dapat digunakan adalah metode GARCH asimetris seperti TGARCH. Tujuan dari penelitian ini adalah untuk membandingkan akurasi peramalan model simetris ARCH/GARCH dan asimetris TGARCH dalam peramalan data IHSG mingguan periode 1 Januari 2018 sampai 24 April 2023 dengan melibatkan pengaruh COVID-19 sebagai peubah kovariat serta menerapkan beberapa skenario validasi model pada data latih dan data uji. Berdasarkan model terbaik yang terpilih, dilakukan peramalan pada periode 1 Mei 2023 sampai 3 Juli 2023. Data yang digunakan dalam penelitian ini adalah data pembukaan IHSG mingguan periode 1 Januari 2018 sampai 24 April 2023 dengan peubah kovariat berupa periode COVID-19. Model terbaik yang dihasilkan adalah model ARIMAX(3,1,3)-TGARCH(1,2) dengan pengaruh peubah COVID-19 yang signifikan dan rata rata nilai MAPE dari empat skenario data sebesar 3,158%. Peramalan dilakukan dengan hasil peramalan yang cenderung stabil dan selang kepercayaan yang cenderung melebar di setiap periode waktunya., The time series forecasting method that often used is the ARIMA method. The ARIMA method which includes other time series as exogenous variables is called the ARIMAX method. The ARIMAX method assumes a homogeneous residual variance but data with high volatility can cause violations of this assumption. The method that can be used is the ARCH/GARCH method but the ARCH/GARCH method is not good at modeling asymmetric volatility in data. Another method that can be used is an asymmetric GARCH method such as TGARCH. The purpose of this study is to compare the accuracy of the symmetric ARCH/GARCH and asymmetric TGARCH models in forecasting weekly JCI data for the period January 1 2018 to April 24 2023 by involving the influence of COVID-19 as a covariate variable and applying several validation scenario models to training and testing data. Based on the best selected model, forecasting was carried out for the period May 1 2023 to July 3 2023. The data used in this study is weekly JCI opening data for the period January 1 2018 to April 24 2023 with the covariate variable being the COVID-19 period. The best model produced is the ARIMAX(3,1,3)-TGARCH(1,2) model with a significant influence of COVID-19 variables and an average MAPE value of the four data scenarios of 3,158%. Forecasting is done with forecasting results that tend to be stable and confidence intervals that tend to widen in each time period.
Keyword: ARCH, ARIMAX, GARCH, stock prices, TGARCH

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