Judul: Kajian Efek Lockdown dalam Penyebaran Penyakit Menular Covid-19: Analisa Model Matematika SIQ
Abstrak: COVID-19 dapat menyebar dengan cepat melalui kontak langsung dengan penderita COVID-19. Perpindahan penduduk dari wilayah yang telah banyak memiliki kasus COVID-19pun menjadi salah satu penyebab penyakit ini menyebar begitu cepat, maka pembatasan suatu wilayah atau yang biasa disebut dengan lockdown diperlukan untuk dapat menanggulangi penyebaran COVID-19 ini. Model SIQ digunakan untuk mempelajari penyebaran COVID-19. Diperoleh dua titik tetap ketika lockdown diterapkan, yaitu titik tetap bebas penyakit dan titik tetap endemik. Saat titik tetap bebas penyakit, maka penyakit dapat punah. Sedangkan saat titik tetap endemik, berdasarkan simulasi numerik penerapan lockdown berpengaruh untuk menekan peningkatan populasi individu terinfeksi. Pertumbuhan populasi individu terinfeksi saat lockdown juga sangat kecil jika dibandingkan dengan tanpa pemberlakuan lockdown., COVID-19 can spread quickly through direct contact with people with COVID-19. The movement of the people from the areas that already have a lot of COVID-19 cases is also one of the causes of this disease spreading so fast, so the restriction of an area or commonly called a lockdown is needed to be able to cope with the spread of COVID-19. The SIQ model is used to study the spread of COVID-19. Two fixed points are obtained when the lockdown has been implemented, namely the disease-free fixed point and the endemic fixed point. In the disease-free fixed point, the disease can become extinct. Meanwhile, in the endemic fixed point, based on numerical simulations, the implementation of the lockdown is intended to result lower of the level of infected individuals. In fact, the growth of the population of infected individuals when the lockdown is applied is very small, compared to simulation of no lockdown applied.
Keyword: COVID-19, lockdown, mathematical model, SIQ

Judul: Dinamika Penyebaran Penyakit COVID-19 dengan Intervensi Kebijakan “Tinggal di Rumah” Berupa Model SHEIQRD
Abstrak: Mewabahnya penyakit COVID-19 mendorong diterapkannya kebijakan “tinggal di rumah” dan karantina di beberapa negara untuk membatasi penyebaran penyakit. Efek dari kebijakan tersebut dapat dianalisis menggunakan model SHEIQRD yang berupa sistem persamaan diferensial tak linear. Pada penelitian ini ditentukan bilangan reproduksi dasar (ℛ0) dan dilakukan analisis sensitivitasnya. Ketika ℛ0<1 penyakit akan hilang dari populasi, sedangkan ketika ℛ0>1 penyakit akan menjadi endemik. Analisis sensitivitas menunjukkan bahwa pengetatan kebijakan “tinggal di rumah” dan karantina dapat menurunkan ℛ0. Hal ini dikonfirmasi pada hasil simulasi numerik yang dilakukan. Simulasi numerik model SHEIQRD dilakukan menggunakan metode Runge-Kutta orde empat dan Runge-Kutta Fehlberg yang dilakukan pada software Octave. Kedua metode tersebut menghasilkan solusi yang sangat mirip, namun metode Runge-Kutta Fehlberg jauh lebih efisien karena membutuhkan runtime 19 kali lebih singkat dibandingkan metode Runge-Kutta orde empat., COVID-19 disease outbreak has led to the implementation of "stay at home" and quarantine policies in several countries to limit the spread of the disease. Effects of the policies can be analyzed using SHEIQRD model that takes a non-linear differential equation system form. In this study, the basic reproduction number (ℛ0) is acquired and its sensitivity analysis performed. When ℛ0<1 the population will free from disease, while when ℛ0>1 the disease will become endemic. Sensitivity analysis shows that a stricter controls of “stay at home” and quarantine policies can lower ℛ0. This is confirmed by the result of the numerical simulations that performed. Numerical simulation of the SHEIQRD model is performed using the fourth-order Runge-Kutta and Runge-Kutta Fehlberg method on Octave software. Both methods give very similar solutions, but the Runge-Kutta Fehlberg method is much more efficient because it needs 19 times less runtime than the fourth-order Runge-Kutta method.
Keyword: COVID-19, fourth-order Runge-Kutta, Runge-Kutta Fehlberg, SHEIQRD, stay at home

Judul: Metil Ester Gondorukem sebagai Kandidat Bahan Bakar Nabati
Abstrak: The objective of this research is to produce ester of rosin distillate using methanol and H2SO4 (pa) as a catalyst. The result showed an optimum yield of methyl ester was 88.5% at an operating condition of 1.2 mL catalyst in 1.5 hours. The infrared spectra showed that carboxyl groups was replaced by C=O ester group, proofing that the rosin distillate was esterified. Furthermore, the gas chromatography-mass spectrometer spectra showed that the resin acids consists of ester derivates of abietic acid, sandaracopimaric acid, dehidroabietic acid, isopimaric acid, palustric acid. Based on SNI 04 -7182-2006, the kinematic viscosity at 40ºC (4.2 mm2/s), cloud point (-18ºC), total sulfur (67 ppm), acid number (0.1 mg-KOH/g), iodine number (12.8%), and total alkyl ester (99.8%), the methyl ester of pine rosin would be feasible to be used as a biodiesel material. The flash point was considered too low for biodiesel, but would be suitable f or biogasoline.
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