Judul: Pembentukan Portofolio Optimal Model Mean-Variance Markowitz dan Analisis Value at Risk pada Indeks IDX30 di Bursa Efek Indonesia
Abstrak: Investor perlu melakukan diversifikasi terhadap portofolio investasinya guna meminimumkan risiko tanpa mengurangi imbal hasil yang diharapkan. Penelitian ini bertujuan untuk membentuk portofolio optimal menggunakan model mean-variance Markowitz serta menghitung besarnya potensi kerugian yang mungkin terjadi menggunakan Value at Risk. Value at Risk dihitung menggunakan pendekatan Varian-Kovarian dengan parameter standar deviasinya diduga menggunakan metode EWMA. Data yang digunakan dalam penelitian ini adalah saham-saham yang tergabung dalam Indeks IDX30 selama empat periode. Hasil penelitian ini menunjukkan komposisi portofolio optimal terdiri atas BBCA 71.9696%, PGAS 14.6881%, dan SMGR 13.3421%. Portofolio optimal ini memberikan imbal hasil yang diharapkan sebesar 0.1141% per hari dan varian sebesar 0.0164% per hari. Berdasarkan portofolio optimal yang diperoleh, potensi kerugian yang mungkin terjadi sebesar Rp 2,331,939.95 untuk satu hari periode investasi dengan nilai awal investasi sebesar Rp 100,000,000.00 dan tingkat kepercayaan sebesar 95%.
Keyword: EWMA, mean-variance, value at risk, variance-covariance

Judul: Comparative Analysis of Optimal Portfolio Using Markowitz Model and Single Index Model Based on Value at Risk (VaR)
Abstrak: Investasi merupakan salah satu variabel penentu dan berpengaruh positif terhadap pertumbuhan ekonomi (PDB). Berinvestasi pada saham dengan kapitalisasi pasar besar akan meningkatkan pertumbuhan IHSG. IDX80 merupakan indeks yang terdiri dari 80 saham yang memiliki likuiditas tinggi, kapitalisasi pasar besar, dan fundamental perusahaan yang baik. Penelitian ini bertujuan untuk mencari kombinasi saham yang memenuhi kriteria dalam pembentukan portofolio optimal berdasarkan model Markowitz dan Single Index Model serta mencari kinerja portofolio optimal terbaik menggunakan Value at Risk. Penelitian ini menggunakan data harga saham bulanan, IHSG, dan suku bunga acuan BI7DRR periode Februari 2019–Februari 2022. Hasil penelitian menunjukan bahwa terdapat 17 kombinasi saham yang membentuk portofolio optimal Single Index Model dengan expected return sebesar 0,01882 dan nilai varian sebesar 0,002582 perbulan. Sedangkan portofolio optimal yang terbentuk dengan model Markowitz menghasilkan enam kombinasi saham, expected return dan varian masing-masing sebesar 0,002243 dan 0,003866 per bulan. Berdasarkan hasil perbandingan menggunakan Value at Risk, portofolio optimal menggunakan metode Single Index Model lebih baik dibandingkan dengan model Markowitz karena memiliki expected return tertinggi, varian terbaik, kemungkinan kerugian terendah, dan kinerja portofolio terbaik., Investment is one of the determining variables and has a positive effect on economic growth (GDP). Investing in stocks with large market capitalization will increase JKSE growth. IDX80 is an index consisting of 80 stocks that have high liquidity, large market capitalization, and good company fundamentals. This study aims to find a combination of stocks that meet the criteria in forming an optimal portfolio based on the Markowitz model and the Single Index Model also to find the best portfolio performance using Value at Risk. This study uses reports of monthly stock price, JKSE, and interest rates BI7DRR period February 2019– February 2022. The results show there are 17 stocks combination form the optimal portfolio of the Single Index Model with an expected return of 0,01882 and a variance value of 0,002582 per month. While the optimal portfolio formed by the Markowitz model produces six stocks combination, the expected return and variance are 0,002243 and 0,003866 per month, respectively. Based on comparison using Value at Risk, the optimal portfolio by the Single Index Model is better than the Markowitz model because it has the highest expected return, the best risk, the lowest possible loss, and the best portfolio performance.
Keyword: Single Index Model, Value at Risk (VaR), IDX80 Index, Optimal Portofolio, Markowitz Model

Judul: Synthesis of Apatite - Chitosan Composite Using Duck Eggshell and Chitosan with Temperature and pH Control
Abstrak: Composite of apatite-chitosan was prepared by using chitosan as polymer matrix. Calcium phosphate was prepared from CaO and (NH4)2HPO4, which the ratio Ca : P had to be 1.67. Chitosan is produced by deacetilase from biopolymer chitin. Duck eggshell (95% CaCO3) as starting material was converted to be calcium oxide (CaO) through calcinations with temperature 1000oC for 5 hours. In-situ and ex-situ methods were prepared from apatite and chitosan (dissolved with acetate acid 2%). Calcium phosphate prepared for bone implantation, but it is too fragile and brittle to be implant into the body. So addition of chitosan can decrease crystalinity and increase mechanic characteristic (tougher). Composite apatite-chitosan was resulted by fast precipitation. Fast precipitation was held in a breaker glass with nitrogen atmosphere, under controlled temperature at 37oC and pH 7, in order to increase amount of hydroxyapatite. Precipitation with CaO which was dropped by (NH4)2HPO4. Hydroxyapatite and chitosan were appearing at samples with in-situ and ex-situ methods which indicating by peak matching of XRD (closed lattice parameter, crystal size), overlapping at FTIR spectra and supporting by SEM picture (homogenous and agglomerated particle). However, it still needs further research to examine biocompatibility osteoconductive degree of sample by in-vivo and in-vitro test.
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