Nusantara RW, Aspan A, Alhaddad AM, Suryadi UE, Makhrawie, Fitria I, Fakhrudin J, Rezekikasari. 2018. Peat soil quality index and its determinants as influenced by land use changes in Kubu Raya District, West Kalimantan, Indonesia. Biodiversitas 19: 535-540. Tropical peatland is continuously damaged in large area in Indonesia, caused by deep and wide drains which change the ecosystem. This research was conducted to evaluate the soil quality index (SQI) based on peatland use. The research was conducted in Kubu Raya District, West Kalimantan Province, in secondary peat forest, shrubland, oil palm plantation and corn field. The variables observed in this research were subsidence, water-table level, depth of peat, bulk density, water content, porosity, organic carbon, total nitrogen, total potassium, cation exchange capacity, base saturation, ash content, available phosphorus, and exchangeable calcium, magnesium, sodium, C/N ratio and soil acidity. The results showed that SQI in secondary peat forest, shrubland, corn field and palm oil plantation were 0.40, 0.37, 0.37 and 0.37 respectively. The stepwise regression analyses showed that the variables influencing SQI were the depth of peat, water-table level, and ash content. Secondary forest had the highest level (0.74) for the depth of peat with 509 cm depth while the other sites had average level (0.41-0.43) with 108.4 cm-115.5 cm mean depth. SQI of peatland increased with the increasing depth of peat and ash content. The differences showed that land use change of peatland, from forest to plantation area would decrease its SQI.
The mathematical modelling and dynamics optimization of cholera disease spread are discussed. The proposed SEIQR (Susceptible-Educated-Infected-Quarantined-Recovered) type model takes into account the bacterial concentration of the cholera spread dynamics. Three controls are considered to minimize the spread of cholera which are the treatment of quarantined populations and intervention efforts as a strategy in preventing the spread of disease through improved sanitation and education. Furthermore, the dynamics optimization problem is solved using the Pontryagin Minimum Principle method. The purpose is to decrease the populations of infected human populations and bacterial populations while minimizing the costs incurred for sanitation, educational and quarantine improvement. Numerical results are presented to show that the three controls can effectifely minimize the spread of cholera.
Sudarmono. 2018. Decreased populations of Scutellaria discolor and Plectranthus galeatus (Lamiaceae) on Mount Gede, West Java, Indonesian and its surrounding. Biodiversitas 19: 1866-1870. Scutellaria discolor Colebr. and Plectranthus galeatus Vahl. are herbs belonging to mint family (Lamiaceae) which have the potential to be used for medicinal purposes. However, their population is gradually declining. The population of the two species are now only found in the mountains or highlands or the edges of the forests that are still protected, i.e. Mount Gede and Telaga Warna protected forest. This research aimed to know the condition of parent and seedling population of Scutellaria discolor Colebr and Plectranthus galeatus Vahl. on Mount Gede and Telaga Warna vicinities, West Java Province, Indonesia. The research method used was parallel transect lines. Association of the existing plants in the vicinity of the area were also observed. In Mount Gede at altitudes about 1200 m above sea level there are 203 seedlings and 167 parents of S. discolor species, while there are 69 seedlings and 11 parents of P. galeatus. This is higher than the populations of 1100 m altitude, i.e. there are 76 seedlings and 45 parents of S. discolor and 12 seedlings and 9 parents of P galeatus. In Telaga Warna, S. discolor exist only at altitudes about 1500 m asl., i.e.. 47 seedlings and 52 parents. While for P. galeatus, there are 37 seedlings and 31 parents at altitudes about 1500 m. At altitude below 1400 m, there are 18 seedlings and 8 parents, this is very rare. Populations of S. discolor and P. galeatus in Mount Gede at an altitude between 1100-1300 m asl is a balance between the seedlings and its parent population which is the same for seedling populations of S. discolor in Telaga Warna at an altitude of 1400-1500 m asl, but for P. galeatus seedling number decreases from an altitude of 1400 to 1500 m asl.
Saidy AR, Mariana ZT, Adji FA, Nusantara RW, Fitria I, Syahrinudin. 2018. Carbon mineralization dynamics of tropicalpeats in relation to peat characteristics. Biodiversitas 19: 1413-1421. Understanding the dynamics of carbon mineralization of peats inthe tropical areas is of essential significance in controlling carbon dioxide (CO2) gas emission rates. An incubation study of tropicalpeats sampled from 3 different sites of the Barito Basin on the Borneo Island, Indonesia (uncultivated, used for paddy cultivation for 5years and 5-10 years) was carried out to investigate a relationship between CO2 production and peat characteristics. Results of studyrevealed that land use change from uncultivated peats to paddy fields resulted in significant changes in the chemical structure of peatorganic carbon. Carbohydrate contents of the peat decreased significantly as a consequence of the conversion of natural peats to paddyfields. However, the paddy peats contained higher lignin than uncultivated peats. Changes in the chemical structure of the tropical peatsresulted in changes in carbon mineralization. Carbon mineralization of uncultivated peats ranged from 29255310 mg CO2-C kg-1 peat,while carbon mineralization of 10652678 mg CO2-C kg-1 C peat was observed for paddy peats. Moreover, carbon mineralization dataobtained from the experiment fitted properly to a two-pool C mineralization model. The developed carbon mineralization model showedthat slowly and rapidly decomposable pools have a close relation with rubbed fiber and carbohydrate content data. Thus, results of thisstudy suggested that carbon mineralization of peats could be estimated appropriately using rubbed fiber and carbohydrate content data.
Geometric Brownian Motion is a mathematical model that can be used in stock price forecasting. This research aimed to predict the stock prices during the outbreak of coronavirus in Indonesia. There are four important steps of this research, such as calculating the return of the stocks, analyzing the normality test of stock price return, forecasting the stock price by using Geometric Brownian Motion, and calculating the errors of the forecasting. Based on the research, the MAPE for three forecasted stock prices is mostly around 10%.
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