Judul: Dinamika Model Mangsa-Pemangsa pada Populasi Ikan yang Berperilaku Berkelompok
Abstrak: Salah satu bentuk interaksi antar ikan adalah hubungan mangsa dan pemangsa. Organisme yang memakan organisme lainnya disebut sebagai pemangsa, sedangkan organisme yang dimakan oleh organisme lainnya disebut sebagai mangsa. Model mangsa-pemangsa yang ditinjau dalam penelitian ini dikembangkan dari model Lotka-Volterra pada populasi ikan yang berperilaku berkelompok. Model sistem persamaan diferensial yang diperoleh berbentuk tak linear dengan tiga titik tetap. Kestabilan dari ketiga titik tetap tersebut dipengaruhi oleh upaya pemanenan ikan. Titik tetap karena tidak adanya pemangsa selalu tidak stabil, sedangkan titik tetap yang lainnya stabil asimtotik lokal. Hasil lain dari penelitian ini menunjukan bahwa semakin kecil upaya pemanenan ikan yang dilakukan mengakibatkan perubahan kestabilan dari stabil ke tidak stabil sehingga terjadi bifurkasi Hopf.
Keyword: mangsa-pemangsa, upaya pemanenan, bifurkasi Hopf

Judul: Bifurkasi hopf model mangsa-pemangsa dengan waktu tunda
Abstrak: dalam karya ilmiah ini dipelajari akibat dari waktu tunda dan tingkat pemanenan konstan pada dinamika model mangsa-pemangsa lotka-volterra. dalam model ini, waktu tunda diberikan pada interaksi antar mangsa dari persamaan mangsa. selanjutnya mangsa dan pemangsa akan dipanen dengan tingkat pemanenan yang konstan. dalam model ini terdapat satu, dua, atau tiga titik tetap. ketika terdapat dua titik tetap positif, satu diantaranya stabil. perubahan parameter waktu tunda dari kecil menjadi besar dari batas waktu tunda kritis menyebabkan perubahan kestabilan titik tetap stabil menjadi tidak stabil, disertai adanya kemunculan limit cycle. kemunculan limit cycle tersebut menandakan bahwa model mangsa pemangsa dengan tingkat pemanenan dan waktu tunda terjadi bifurkasi hopf.
Keyword: mangsa-pemangsa, limit cycle, waktu tunda, tingkat pemanenan konstan, bifurkasi hopf

Judul: Enhancement of photon absorbtion on BaxSr1-xTiO3 thin films semiconductor using photonic crystals.
Abstrak: In this research, has been conducted BaxSr1-xTiO3 (BST) thin films manufacturing for mole fraction x = 0.25, 0.35, 0.45, and 0.55; and concentration of 1 molar using chemical solution depositon (CSD) method. The materials, which are used in this research, are barium acetate [Ba(CH3COO)2, 99%], strontium acetate [Sr(CH3COO)2, 99%], titanium isopropoxide [Ti(C12O4H28), 97.999%], gallium trioxide [Ga2O3], 2-methoxyethanol [H3COOCH2CH2OH, 99%] and 1 x 1 cm of transparent conductive oxide (TCO) glass as substrate. Two BST thin films are made that for BST thin films which are doped by 10% galium (BGST) as p-type layer and pure BST solution as n-type. BST solution is made by reacting barium acetate [Ba(CH3COO)2, 99%], strontium acetate [Sr(CH3COO)2, 99%] and titanium isopropoxide [Ti(C12O4H28)] into 2-methoxyethanol solvent [H3COOCH2CH2OH, 99%] in accordance with mass gram for each x value. While, BGST solution is made in the same way as BST solution, plus adding gallium at 10% of the mass of BST. Once all materials are reacted, then vibrated using ultrasonic for 90 minutes, and followed by coating BGST / BST on the TCO substrate. Once the layer is formed, then annealed for 15 hours at temperature of 500 °C with increasing rate of 1.67 oC/minute. Characterizations of BST thin films with or without photonic crystals include the absorbance and transmittance in the visible light spectrum, as well as the electrical photoconductivity characterizations. From BST thin films without photonic crystals indicate that our thin films have light absorption area on almost the entire range of the visible light spectrum even to the infrared range with absorption value over than 67.6%, in addition, it can be seen that the maximum absorbance of BST thin films for all mole fractions lie in blue to green light spectrum region, 457 nm ≤ λ ≤ 570 nm and the minimum in yellow to red light spectrum region, 570 nm ≤ λ ≤ 678 nm. The largest absorbance is found at x = 0.25 with average absorbance value of 92.04% and maximum and minimum absorbance peaks at wavelength of 500.89 and 657.72 nm, respectively. At x = 0.35, average absorbance value decreased to 83.55% with maximum and minimum peaks at 505.73 and 613.68 nm, respectively. Then increased to 91.16% at x = 0.45 with maximum and minimum peaks at 506.04 and 618.56 nm, respectively. At x = 0.55, average absorbance value decreased to 80.12% with maximum and minimum peaks at 507.85 and 608.79 nm, respectively. Moreover, it can be seen that the addition of barium mole fraction leads to wider maximum absorbance or minimum transmittance peaks and narrower minimum absorbance or maximum transmittance peaks in the same range of the green and blue & red light spectrums, respectively. BST thin films with photonic crystals show increasing in absorption for all x values in the range of 3.04 into 13.33%. At x = 0.25, average absorbance percentage increased 3.96% from 92.4 into 95.68%, for x = 0.35 average percentage increased 7.07% into 89.45 from 83.55%. Furthermore, average absorbance of BST thin films at x = 0.45 increased 3.04% from 91.16 into 93.93% and x = 0.55 has
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