Judul: Dinamika Sistem Mangsa-Pemangsa Fitoplankton-Zooplankton dengan Mangsa Fitoplankton yang Terinfeksi Virus
Abstrak: Dalam tulisan ini dipelajari model populasi fitoplankton sebagai mangsa yang terinfeksi virus dan zooplankton sebagai pemangsa dengan menggunakan respon fungsional dari Holling II. Model tersebut dianalisis sehingga diperoleh enam titik tetap. Berdasarkan nilai eigen dari hasil pelinearan tiga titik tetap pertama diperoleh empat kasus kestabilan yang berbeda. Dinamika model digambarkan dengan bantuan software Matematica 5.2. Secara keseluruhan dari setiap kasus yang diamati, kestabilan populasi fitoplankton terinfeksi bergantung pada penyebaran virus dan angka kematian dari fitoplankton yang terinfeksi. Jika laju penyebaran virus lebih besar dari angka kematian fitoplankton yang terinfeksi, maka populasi fitoplankton yang terinfeksi virus dapat bertahan hidup. Jika laju penyebaran virus lebih kecil dari angka kematian fitoplankton yang terinfeksi, populasi fitoplankton yang terinfeksi akan menuju kepunahan
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Judul: Pengaruh Infeksi Virus pada Phytoplankton dan Racun yang Dihasilkan Phytoplankton dalam Model Interaksi Phytoplankton-Zooplankton
Abstrak: Interaction of phytoplankton and zooplankton can be considered as a prey-predator interaction, where phytoplankton as prey and zooplankton as predator. This interaction is modeled into mathematical equations that was investigated by Gakkhar & Negi (2005). This model studied the effect of viral infection on phytoplanktons and the toxin produced by phytoplankton. In this model, phytoplanktons are divided into two groups, suspectible phytoplankton and infected phytoplankton. Hopf bifurcation describes the stability changes of population. The Hopf bifurcation occurs when the rate of viral infection and the toxin quantity produced by phytoplakton were changed. Both phytoplankton and zooplankton populations stable when the infection rate and toxin quantity are low. If the viral infection rate and toxin quantity increase then phytoplankton and zooplankton populations became unstable. If the viral infection rate and the toxin quantity relatively high then the zooplankton population would lead to extinction
Keyword: zooplankton, phytoplankton, toxin, viral infection, Hopf bifurcation

Judul: Characterization of The Chemical Constituents and Antioxidant Capacity of Green and Oolong Teas (Camellia sinensis) Manufactured in Thailand
Abstrak: Tea in Thailand most manufactured in northern area, especially Chiang Rai, Chiang Mai, Nan, and Mai Hang Son province. The aim of this study was to determine and compare the chemical compositions and antioxidant capacity of 4 important Thai tea products. A total of 13 of green teas of 2 major cultivars, assamicaand cv. oolong no.12 (chin hsuan oolong) and 26 of oolong tea of 2 major varieties, cv. oolong no. 12 and cv. oolong no. 17 (chin shin oolong) were collected from 18 factories in Chiang Rai province in 2011. The total polyphenol content was determined according to International Organization for Standardization (ISO 14502-1). For antioxidant capacity, DPPH radical scavenging activitiy assay and ferric reducing antioxidant power assay were determined. The catechins content and caffeine content were determined using HPLC by ISO method (ISO-14502-2). Results showed that about 95% of the 39 tea samples manufactured in Thailand had moisture content below 7%, 5% of tea samples being above 7%. The total polyphenol content in green tea was found to vary from 11.86 to 21.19%GAE, while in oolong tea was found in a range of10.22 to 17.57%GAE. The caffeine content in green tea samples were in a range of 1.69 to 3.7%, while in oolong tea samples were in a range of 1.61 to 3.26%. The catechin content in green tea samples were in a range of 8.31-14.08%, while in oolong tea samples were in a range of 6.81-12.46%. The antioxidant capacity in green tea samples was 164.01 mmole TE/100 g dry basis, while in oolong tea samples was about 132.73mmole TE/100 g dry basis. This study provided useful information for the tea industry in Thailand and other countries in processing and selecting a good-quality tea.
Keyword: Antioxidant capacity, Camellia sinensis, Green tea, Oolong tea, Thailand