35 research outputs found
Pengendali Motor Induksi 1 Fasa Dengan Metode PWM Sinusoida Berbasis Mikrokontroler 68HC11
Pada pengendalian motor induksi yang dilakukan secara konvensional tidak diperoleh
pengaturan yang kontinyu dan linier, sehingga perlu dilakukan penelitian tentang pengendalian
motor induksi dengan teknik inverter. Penelitian ini bertujuan melakukan pengembangan dan
evaluasi unjuk kerja pengendalian motor induksi satu fasa dengan metode PWM sunusoida
berbasis mikrokontroler. Pengendalian menggunakan rangkaian jembatan inverter jenis PWMVSI
(DC-Link inverter) dengan teknik modulasi PWM menggunakan mikrokontroler 68HC11E9,
dan diharapkan dapat menggerakkan motor induksi pada kecepatan yang berbeda-beda. Pada
penelitian ini digunakan motor induksi satu fasa Z-406, 220 Volt, 50-60 Hz, 125W. Penelitian
dimulai dengan pembuatan perangkat keras berupa inverter menggunakan MOSFET sebagai
komponen pensaklaran dan diteruskan dengan menyusun rangkaian penggerak inverter satu
fasa. Pola sinyal PWM sinusoida dibentuk dengan teknik perhitungan lima modulasi PWM yang
berbeda. Dari pola gelombang tersebut dibuat program pembangkit pulsa PWM satu fasa dan
perangkat pendukungnya. Selanjutnya dilakukan pengamatan bentuk gelombang PWM
keluaran MCU, tegangan, arus keluaran inverter dan mengukur kecepatan putar motor untuk
lima indeks modulasi, yaitu (1), (0,81), (0,59), (0,37), dan (0,15). Hasil penelitian menunjukkan
bahwa pengaturan kecepatan putar motor induksi untuk frekuensi tetap 50 Hz dengan 5 indeks
modulasi berbeda dengan metode PWM sinusoida berbasis mikrokontroler dapat
menghasilkan putaran motor yang bervariasi
Short-and long term niche segregation and individual specialization of brown trout ( Salmo trutta ) in species poor Faroese lakes
Trophic niche divergence is considered to be a major process by which species coexistence is facilitated. When studying niche segregation in lake ecosystems, we tend to view the niche on a one-dimensional pelagic-littoral axis. In reality, however, the niche use may be more complex and individual fidelity to a niche may be variable both between and within populations. In order to study this complexity, relative simple systems with few species are needed. In this paper, we study how competitor presence affects the resource use of brown trout (Salmo trutta) in 11 species-poor Faroese lakes by comparing relative abundance, stable isotope ratios and diet in multiple habitats. In the presence of three-spined sticklebacks (Gasterosteus aculeatus), a higher proportion of the trout population was found in the pelagic habitat, and trout in general relied on a more pelagic diet base as compared to trout living in allopatry or in sympatry with Arctic charr (Salvelinus alpinus). Diet analyses revealed, however, that niche-segregation may be more complex than described on a one-dimensional pelagic-littoral axis. Trout from both littoral and offshore benthic habitats had in the presence of sticklebacks a less benthic diet as compared to trout living in allopatry or in sympatry with charr. Furthermore, we found individual habitat specialization between littoral/benthic and pelagic trout in deep lakes. Hence, our findings indicate that for trout populations interspecific competition can drive shifts in both habitat and niche use, but at the same time they illustrate the complexity of the ecological niche in freshwater ecosystem
Fish but not macroinvertebrates promote trophic cascading effects in high density submersed plant experimental lake food webs in two contrasting climate regions
Predators play a key role in the functioning of shallow lakes. Differences between the response of temperate and subtropical systems to fish predation have been proposed, but experimental evidence is scarce. To elucidate cascading effects produced by predators in contrasting climatic zones, we conducted a mesocosm experiment in three pairs of lakes in Uruguay and Denmark. We used two typical planktivorous-omnivorous fish species (Jenynsia multidentata + Cnesterodon decemmaculatus and Gasterosteus aculeatus + Perca fluviatilis) and one littoral omnivorous-predatory macroinvertebrate (Palaemonetes argentinus and Gammarus lacustris), alone and combined, in numbers resembling natural densities. Fish predation on zooplankton increased phytoplankton biomass in both climate zones, whereas the effects of predatory macroinvertebrates on zooplankton and phytoplankton were not significant in either climate zone. Macroinvertebrates (that freely colonized the sampling devices) were diminished by fish in both climate areas; however, periphyton biomass
did not vary among treatments. Our experiments demonstrated that fish affected the structure of both planktonic and littoral herbivorous communities in both climate regions, with a visible positive cascading effect on phytoplankton biomass, but no effects on periphyton. Altogether, fish impacts appeared to be a strong driver of turbid water conditions in shallow lakes regardless of climatic zone by indirectly contributing to increasing phytoplankton biomass
Water chemistry of lakes in Zackenbergdalen between 1997-2003, East Greenland
The ecology of arctic lakes is strongly influenced by climate-generated variations in snow coverage and by the duration of the ice-free period, which, in turn, affect the physical and chemical conditions of the lakes (Wrona et al., 2005, http://www.acia.uaf.edu/PDFs/ACIA_Science_Chapters_Final/ACIA_Ch08_Final.pdf). Most arctic lakes are characterised by a long period (8-10 months) of ice-cover, cold water and low algal biomass. The water temperature and nutrient concentrations, and most probably the nutrient input from the catchments, are closely related to the duration of snow- and ice-cover in the lakes. In years when the ice-out is late, - that is, in late July, - phytoplankton photosynthesis is limited by the lack of light and nutrients. Less food is then available to the next link in the food chain, such as copepods and daphnids, with implication on their growth rates