Judul: Peramalan Nilai Tukar Rupiah Terhadap Dolar Singapura Menggunakan Regresi Linear Sederhana Dan Model ARIMA
Abstrak: Nilai tukar adalah kurs mata uang satu negara yang dinyatakan dalam mata uang negara lain. Tujuan penelitian ini adalah meramalkan nilai tukar rupiah terhadap dolar Singapura dengan menggunakan metode regresi linear sederhana dan model Autoregressive Integrated Moving Average (ARIMA), serta membandingkan keakuratan hasil ramalan kedua metode dengan melihat ukuran kesalahan menggunakan Mean Absolute Percentage Error (MAPE). Metode regresi linear adalah pendekatan yang memodelkan hubungan antara dua variabel, yaitu variabel independen dan variabel dependen. Model ARIMA merupakan sebuah metode peramalan data deret waktu yang menggunakan sifat dan karakteristik dari data historis untuk meramalkan data deret waktu selanjutnya. Kedua metode ini menggunakan data harian nilai tukar rupiah terhadap dolar Singapura selama satu tahun untuk meramalkan satu bulan yang akan datang. Model ARIMA memberikan hasil ramalan yang lebih akurat daripada metode regresi linear sederhana.
Keyword: ARIMA, nilai tukar, peramalan, regresi linear sederhana

Judul: Peramalan Nilai Tukar Rupiah Terhadap Dolar Amerika dengan Pendekatan Analisis Regresi dan ARIMA
Abstrak: Nilai tukar merupakan harga mata uang satu negara yang dinyatakan dalam mata uang negara lain. Nilai tukar berfluktuatif sehingga perlu dilakukan peramalan agar dapat membantu pelaku ekonomi dalam membuat keputusan yang tepat. Fluktuasi nilai tukar dipengaruhi oleh faktor-faktor makroekonomi, seperti inflasi dan jumlah uang beredar. Pengaruh faktor-faktor makroekonomi terhadap nilai tukar dapat dimodelkan dengan regresi linear berganda. Parameter model regresi diestimasi menggunakan metode Ordinary Least Square (OLS). Pada model regresi linear berganda terdapat asumsi-asumsi klasik yang harus dipenuhi. Apabila terjadi korelasi antara residual ke-t dengan residual ke-(t-1), dikatakan residual model mengalami autokorelasi. Dalam karya ilmiah ini, digunakan metode Cochrane-Orcutt untuk mengatasi pelanggaran asumsi tidak adanya autokorelasi pada residual model. Selain faktor makroekonomi, fluktuasi nilai tukar juga dipengaruhi oleh nilai tukar pada periode sebelumnya. Pada karya ilmiah ini dilakukan peramalan nilai tukar rupiah terhadap dolar AS menggunakan metode regresi linear dan ARIMA. Setelah itu, akan dilakukan perbandingan hasil ramalan menggunakan Mean Absolute Percentage Error (MAPE). Hasil peramalan menunjukkan bahwa metode regresi linear memiliki tingkat keakuratan yang lebih baik dibandingkan dengan model ARIMA karena memiliki nilai MAPE yang lebih kecil., Exchange rate is the price of one country’s currency which is expressed in other country’s currency. The exchange rate is volatile so it is necessary to forecast in order to assist economic actors in making the right decisions. Exchange rate fluctuations are influenced by macroeconomic factors such as inflation and money supply. The effect of macroeconomic factors on the exchange rate can be estimated using multiple linear regression. The regression parameters are estimated using the Ordinary Least Square (OLS) method. There are classical assumptions that must be satisfied in multiple linear regression. If there is correlation between the (t)-th residual and the (t-1)-th residual then the residual model has autocorrelation. In this study, the Cochrane-Orcutt method is used to overcome the violation of assumption that there is no autocorrelation in the residual model. The exchange rate fluctuations are also influenced by exchange rate in previous period. In this study, the exchange rate is forecasted using linear regression and ARIMA. Then, their accuracy are compared by evaluating Mean Absolute Percentage Error (MAPE). The forecasting results showed that linear regression has a better accuracy rate than ARIMA model because it has a smaller MAPE value.
Keyword: ARIMA, Cochrane-Orcutt, exchange rate, linear regression

Judul: Heterologous Expression Of Endo-Β-Xylanase From Bacillus Pumilus Strain Bcrs-01 In Escherichia Coli.
Abstrak: Xylanases are glycoside hydrolase family 11 which depolymerise xylan in the plant cell wall, the most excessive form of hemicellulose. Endo-β-xylanases (EC 3.2.1.8) are most important to breakdown β-1,4-glicoside bond of xylan to produce disaccaride xyloolygosaccaride (XOs) and xylose (monomer). Bovine rumen fluids have potential to obtain endo-β-xylanase produced of bacteria. The objectives of this study were to obtain xylanase producing bacteria and to express xynA gene encoding endo-β-xylanase from bacterium in Escherichia coli. Twenty nine isolate bacteria have been succesfully isolated from bovine rumen fluid in agar medium containing birchwood xylan. Isolate BCRS-01 bacterium was previously screened for the high production of xylanase. Based on 16S rRNA gene sequence analysis, BCRS-01 showed high similarity (99%) to Bacillus pumilus (accession number NR043241). The crude xylanase had optimal activity at 55oC, pH 7.0. Furthermore, the crude xylanase exhibited broad pH stability from 4.0 to 10.0 and remained more than 60% and 40% of its activity after incubation at pH 4.0 until 10.0, respectively for 60 min. It also showed a stability at temperature 25-50oC since it retained 80% and 50% of its activity when incubated at 50oC or 30 and 60 min, respectively. The xylanase activity was strongly inhibited by Ca2+ and Cu2+ at concentration 10 mM, and as little as 1 mM for Mn2+. Therefore, this xylanase has potentially used as additive feeds in animal feed industry. The DNA sequence xynA gene encoded endo-β-xylanase was amplified and cloned into the expression vector pET-15by under the control of T7 promoter. The recombinant protein had succesfully expressed in Escherichia coli BL21 (DE3) pLysS. A protein recombinant of approximately, 26.7 kDa was observed on the SDS-PAGE analysis. Crude extract of recombinant endo-β-xylanase demonstrated activity of enzyme at 56 U mL-1 using birchwood xylan as a substrate at 55oC for 10 min.
Keyword: Bacillus pumilus, bovine rumen fluid, endo-β-xylanase, heterologous expression.