Judul: Kualitas Kayu Ampupu (Eucalyptus urophylla S. T.Blake) Berbagai Umur Tanam Sebagai Bahan Baku Pulp dan Kertas
Abstrak: Ampupu wood a fast growing species, has been a major raw material for pulp and paper production. Ampupu wood (Eucalyptus urophylla S. T. Blake) of 4, 5, 6, and 7 years old were determine the fiber dimension and chemical content of the wood. Pulp was then produced by Kraft pulping process. The operating conditions were active alkali of 17%, sulphidity of 30%, liquor/wood ratio of 4/1, maximum temperature of 1650C, and 3.5 hours total cooking time. The resulting pulp was then bleached by an ECF bleaching method following DEDD sequences. The result was determine fiber dimension and its derivative values, E. urophylla were classified into quality class of II for the raw material of pulp and paper. The age of wood influence chemical content but did not influence pulping yield and kappa number. It was found that the highest mechanical properties of pulp resulted from 6 years old E. urophylla. E. urophylla of 7 year old have stain on the sheets of pulp so it's poorly to used as raw material for pulp and paper
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Judul: Study on Site Quality of Industrial Plantation Forest of Eucalyptus urograndis hybrid as Raw Materials for Pulp Industry, in Sustainable Forest Management (Case Study in PT Toba Pulp Lestari, Simalungun, North Sumatera)
Abstrak: Eucalyptus urograndis (E. urophylla x E. grandis) is a hybrid resulting from cross mating between species E. urophylla S.T. Blake and species E. grandis W.Hill ex Maid and constitutes one of the fast growing species being used as pulp industry raw materials in Sector of Aek Nauli, PT Toba Pulp Lestari, North Sumatra. With the progressive decrease in length of cutting rotation, it is feared that there would be negative impacts on site quality which will ultimately influence productivity, if there is no proper management. The objective of this research was studying site quality of industrial plantation forests of E. urograndis hybrid. This research used survey method by collecting field data in first and second rotation (stand ages of 1, 2, 3, 4 and 5 years). Research results showed that up to age of 5 years, stand growth of E. urograndis hybrid at first rotation reached utilizable volume of 159.89 m3/ha, whereas at second rotation the volume acquired 142.49 m3, so there was volume decrease by 10.8 %. Rotation of maximum volume for first rotation occurred at age of 5.4 years with average volume increment of around 31.85 m3/ha/year, and that of second rotation occurred at age of 6 years with average volume increment of 28.80 m3/ha/ year. There was biomass decrease by 6.3 % for stems with diameter ≥ 5 cm between first and second rotation. There was decrease in site quality from first to second rotation as reflected by decrease in nutrient content in soil, up to depth of 40 cm by 24% for N, 16% for K, 6% for Ca and 16% for Mg. Nutrient elements P and Ca in soils had positive correlation with dominant height of E. urograndis hybrid. On the basis of results of leaf analysis, it could be shown that nutrient N was highly deficient, whereas nutrients Ca and Mg were categorized as deficient so they constituted the limiting factors for growth of E. urograndis hybrid which were planted in Inceptisol soils. Dynamics of nutrient balance with cutting rotation of 5 years was predicted to have negative balance, since the end of first rotation, up to rotation 5. At cutting rotation of 6 years, nutrient balance of N, K and Ca were positive, only at the end of rotation 1, whereas nutrient balances of P and Mg were still positive up to rotation 2. At cutting rotation of 7 years, nutrient balances of N, K and Ca had been negative since the end of rotation 1, except the nutrient balances of P and Mg which were still positive at the end of rotation 1. Quality of site with rotation of 5 years decreased more rapidly as compared with those with cutting rotation of 6 and 7 years. Fertilizer application and several silvicultural techniques are required for recovery of sites and nutrient balance. On the basis of maximum volume rotation, it could be suggested that the optimum rotation for hybrid of E. urograndis in Inceptisol soils is 6 years.
Keyword: Forest management, Forestry, North Sumatera

Judul: SEIRS Stochastic Model with Quarantine on the Spread of Covid-19 Disease
Abstrak: Penyakit Covid-19 merupakan penyakit yang disebabkan oleh virus yang bernama Severe Acute Respiratory Syndrome Coronavirus-2 (SARSCoV-2). Virus ini menyebar dari manusia ke manusia melalui droplet akibat batuk dan bersin. Virus juga dapat ditularkan dari orang tanpa gejala sehingga sulit mendeteksi penyebarannya. Upaya yang dapat dilakukan untuk menekan penyebarannya yaitu mematuhi protokol kesehatan dan melakukan karantina jika dinyatakan terinfeksi, baik isolasi mandiri ataupun dirawat di rumah sakit. Untuk memodelkan penyebaran penyakit Covid-19, dapat menggunakan model epidemik stokastik. Penelitian ini bertujuan untuk (1) membangun model SEIRS dengan karantina pada penyebaran penyakit Covid-19, (2) menentukan peluang transisi dan peluang wabah dengan menggunakan pendekatan CTMC, (3) melakukan simulasi untuk mengetahui pengaruh peningkatan laju transmisi tanpa karantina dan laju karantina pada sistem. Data yang digunakan untuk menentukan parameter model yaitu data harian Covid-19 DKI Jakarta mulai dari 25 Maret 2020 sampai 24 Maret 2021. Data tersebut terdiri dari data kasus Covid-19 masing-masing kelurahan di DKI Jakarta. Peluang transisi ditentukan dengan mengasumsikan terdapat enam peubah acak dan satu peubah yang nilainya dapat ditentukan secara pasti. Peubah acak tersebut meliputi banyaknya individu pada subpopulasi rentan, rentan yang dikarantina, terinfeksi tanpa gejala, terinfeksi tanpa gejala yang dikarantina (isolasi mandiri), terinfeksi dengan gejala, serta terinfeksi dengan gejala yang dikarantina (dirawat), sedangkan banyaknya individu sembuh dapat ditentukan secara pasti. Peluang wabah diperoleh melalui proses bercabang berganda. Pada proses bercabang berganda, peluang wabah bernilai 0 ketika nilai harapan banyaknya individu terinfeksi (m)≤ 1, dan lebih dari 0 ketika nilai harapan banyaknya individu terinfeksi (m) > 1. Simulasi pengaruh peningkatan laju karantina untuk individu terinfeksi dilakukan dengan 100 kali pengulangan untuk memperoleh sebaran peluang waktu bebas penyakitnya, selanjutnya dapat ditentukan rata-rata waktu bebas penyakitnya. Berdasarkan hasil simulasi, untuk nilai harapan banyaknya individu terinfeksi (m)≤1, didapatkan bilangan reproduksi dasar (R_0)<1. Ketika nilai m>1, peningkatan nilai m membuat peluang wabah semakin besar. Adapun nilai R_0,m, dan peluang wabah diperoleh secara analitik. Terdapat tiga skenario dalam simulasi numerik, yaitu pengaruh peningkatan laju transmisi dari individu rentan yang dipengaruhi individu tanpa gejala (β_1) dan dengan gejala (β_2), peningkatan laju karantina untuk individu dengan gejala (θ_3 ), dan peningkatan laju karantina untuk individu tanpa gejala (θ_2 ). Hasil simulasi pada skenario pertama menyatakan bahwa peningkatan β_1 dan β_2 dapat menaikkan R_0,m, dan waktu bebas penyakit. Sebaliknya, hasil simulasi pada skenario kedua menunjukkan bahwa peningkatan θ_3 dapat menurunkan nilai R_0, m, dan rata-rata waktu bebas penyakit. Sama halnya dengan hasil simulasi pada skenario ketiga menyatakan bahwa peningkatan θ_2 dapat menurunkan nilai R_0,m, serta rata-rata waktu bebas penyakit. Hasil simulasi skenario ketiga juga menunjukkan bahwa peningkatan θ_2 dengan ditetapkannya nilai θ_3, menyebabkan nilai R_0,m, dan rata-rata waktu bebas penyakit lebih kecil dibandingkan tanpa θ_3., Covid-19 disease is a disease caused by virus called Severe Acute Respiratory Syndrome Coronavirus-2 (SARSCoV-2). This virus spreads from person to person through droplets caused by coughing and sneezing. The virus can also be transmitted from asymptomatic individuals, making it difficult to detect its spread. Efforts that can be made to suppress the spread are complying with health protocols and quarantine if declared infected, either self-isolation or hospitalized. To model the spread of Covid-19 disease, we can
Keyword: continuous time Markov chain, Covid-19 disease, outbreak probability, quarantine