Design and implementation of a smart dual axis sun tracker based on astronomical equations

This paper presents a new design algorithm for stand-alone solar tracking system based on ATMEL Microcontroller. The proposed idea of the design is based on astronomical equations to determine the position of the sun in the sky at any time of the day to calculate the tilt angle and polar angle for the two axis tracking purposes. The system is capable of tracking the sun properly at any position on the earth because of the general nature of the algorithm used in the design. At the same time the system reliability, cost effectiveness, precision and flexibility are taken into consideration

STUDI POTENSIAL KOROSI BETON BUSA BERTULANG DENGAN POZZOLAN SEBAGAI BAHAN PENGISI MENGGUNAKAN METODE HALF-CELL POTENTIAL MAPPING

Penelitian ini bertujuan untuk mempelajari pengaruh tebal selimut beton terhadap potensial korosi pada beton busa pozzolan bertulang dan membandingkan risiko korosi beton busa pozzolan dengan beton normal konvensional. Spesimen berbentuk balok dengan panjang 50 cm, lebar 8 cm dan tinggi 8 cm sebanyak 3 buah dengan variasi tebal selimut beton yaitu 2 cm, 3 cm, dan 4 cm. Spesimen mendapatkan perlakuan wet-dry cycle dalam media larutan NaCl 3,5 % untuk mempercepat proses terjadinya korosi. Untuk mencari letak tulangan di dalam beton digunakan Profometer 3 dan untuk mengukur nilai potensial pada permukaan beton digunakan Half-Cell Potential Meter. Potensial korosi dianalisis berdasarkan kriteria dalam ASTM C876. Hasil pengukuran potensial korosi pada beton busa pozzolan bertulang SG 1,2 dengan tebal selimut 2 cm setelah 8 minggu dan 10 minggu wet-dry cycle menunjukkan nilai rata-rata sebesar -221 mV dan -250 mV. Pada tebal selimut 3 cm sebesar -220 mV dan -246 mV. Sedangkan untuk tebal tebal selimut 4 cm sebesar -219 mV dan -243 mV. Sementara untuk tebal selimut 5 cm sebesar -214 mV dan -236 mV. Kemudian, nilai potensial korosi beton busa pozzolan SG 1,4 dengan tebal selimut 2 cm menunjukkan nilai rata-rata -268 mV dan -285 mV, pada tebal selimut 3 cm sebesar -247 mV dan -255 mV. Untuk tebal selimut 4 cm nilai potensial korosi sebesar -226 mV dan -247 mV, dan untuk tebal selimut 5 cm sebesar -213 mV dan -213 mV. Perbadingan antara beton busa pozzolan bertulang dengan beton normal konvensional setelah 10 minggu wet-dry cycle menunjukkan nilai rata-rata sebesar -250 mV dan -348 mV. Melalui hasil pengukuran tersebut dapat disimpulkan bahwa ketebalan selimut beton belum memberikan pengaruh yang berarti terhadap nilai potensial korosi dalam masa 10 minggu wet dry cycle. Kemudian, terlihat bahwa risiko korosi beton busa pozzolan cenderung lebih rendah dibandingkan beton normal konvensional. Oleh karena itu, perlu adanya penelitian lebih lanjut dengan menambah waktu wet-dry cycle guna melihat pengaruh tebal selimut terhadap potensial korosi

Desıgn of a control and data acquısıtıon system for a multı-mode solar trackıng farm

This paper presents a combination network design for a solar tracking farm consisting of n-solar tracking systems. Serial communication protocol has been adopted for this network with developed strategy to make the farm expandable for possible future extension. The master control unit is responsible for managing all the trackers of the sun location in multi-tracking mode, diagnosis all the trackers for any faults and give complete information about the produced power by each of the solar tracking system. This network protocols is designed to deal with the error control, congestion control and flow control for data transmission in the network

Unconventional aspects of electronic transport in delafossite oxides

The electronic transport properties of the delafossite oxides ABO$_2$ are usually understood in terms of two well separated entities, namely, the triangular A$^+$ and (BO$_2$)$^-$ layers. Here we review several cases among this extensive family of materials where the transport depends on the interlayer coupling and displays unconventional properties. We review the doped thermoelectrics based on CuRhO$_2$ and CuCrO$_2$, which show a high-temperature recovery of Fermi-liquid transport exponents, as well as the highly anisotropic metals PdCoO$_2$, PtCoO$_2$ and PdCrO$_2$ where the sheer simplicity of the Fermi surface leads to unconventional transport. We present some of the theoretical tools that have been used to investigate these transport properties and review what can and cannot be learned from the extensive set of electronic structure calculations that have been performed.Comment: 35 pages, 19 figure

Intrinsic effects of substitution and intercalation on thermal transport in two-dimensional TiS2_2 single crystals

The promising thermoelectric material TiS$_2$ can be easily chemically doped and intercalated. We present here studies of single crystals that are intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the intrinsic impact of these dopants on the thermal transport in the absence of grain boundary scattering. We show that Ta doping has the greatest impact on the thermal scattering rate per ion added, leading to a five-fold reduction in the lattice thermal conductivity as compared to stoichiometric single crystals.Comment: 5 pages, 2 figure

Effects of cage culture on dissolved inorganic nutrient and surface sediment composition in Sulaman Bay Lagoon, Sabah, Malaysia

The major nutrient inputs into Sulaman Bay lagoon are wastes from a nearby village together with particulate organic matter and surface sediment as runoff from mangrove area, as well as from aquaculture activities. The main objective of this study was to determine the dissolved inorganic nutrients (DIN) of water and nutrients of surface sediment in Sulaman Bay lagoon. The data could be was used in developing management strategies for the sustainable aquaculture activity in lagoon ecosystem. Water sample and surface sediment were collected from six stations: five located inside the lagoon and one station at a point that connected the lagoon with South China Sea. The parameters determined included ammonium-nitrogen (mg/L), nitrate (mg/L) and phosphate (mg/L) in water, and particle size, total nitrogen (mg/g), total phosphorus (mg/g), total organic carbon (%) and total inorganic carbon (%) as carbonate equivalent in sediment samples. The highest concentrations of 0.072 mg/L nitrate, 0.121 mg/L of ammonium-nitrogen and 0.058 mg/L of phosphate were obtained from the sea opening point, station nearby village with mollusk culture and village waste drainage areas respectively. Sediment in the Sulaman Bay lagoon was mainly in the form of silt, sand and gravel. The values of total nitrogen and total phosphorus (mg/100g of sediment) were observed to be higher than the values obtained in all stations located inside lagoon. No significant (p>0.05) differences was observed in the total nitrogen of sediment among the stations located inside the lagoon. The highest total organic carbon (TOC) of 22.5% was observed in stations near to the village and cage culture area. The highest value of TOC from the aforesaid stations were significantly different (P 0.05) from the TIC values at other stations. However, the concentration of organic carbon, total nitrogen and total phosphorus in the sediment was higher not only due to commercial cage culture, but also from other human induced activities such as discharge waste from the village, and leafy material with surface sediment as runoff from nearby mangrove vegetation

Designing driving and control circuits of four-phase variable reluctance stepper motor using fuzzy logic control

Precise positioning and repeatability of movement for stepper motors require designing a robust control system. To achieve that, an analytical model of a four-phase variable reluctance stepper motor is presented. A proposed open-loop driving circuit is designed to control the motion of a variable reluctance stepper motor. The driving circuit has an ability to drive the motor into two-step angles, i.e. a full step (15◦) and a half step (7.5◦). The direction of movement can be either into clockwise or counterclockwise direction. The operation of the variable reluctance stepper motor in an open-loop control circuit has demonstrated disadvantages of an oscillation and a relatively high settling time. Therefore, a closed-loop control circuit has been introduced using fuzzy logic control to overcome the oscillation problem and to obtain on a precise positioning within a reasonable settling time. The fuzzy logic control is used to improve and enhance the behaviour of the step position response based on oscillatory response and hence to reduce the overshoot significantly. The comparisons between the open- and closed-loop circuits are presented to demonstrate the disparity between both control circuits. The simulation results of the open-loop and the closed-loop circuits show that the time responses have been improved using different loads conditions. The simulation experiments are conducted and investigated using MATLAB–SIMULINK software package

Local structures of polar wurtzites Zn_{1-x}Mg_{x}O studied by Raman and {67}Zn/{25}Mg NMR spectroscopies and by total neutron scattering

Local compositions and structures of Zn_{1-x}Mg_{x}O alloys have been investigated by Raman and solid-state {67}Zn/{25}Mg nuclear magnetic resonance (NMR) spectroscopies, and by neutron pair-distribution-function (PDF) analyses. The E2(low) and E2(high) Raman modes of Zn_{1-x}Mg_{x}O display Gaussian- and Lorentzian-type profiles, respectively. At higher Mg substitutions, both modes become broader, while their peak positions shift in opposite directions. The evolution of Raman spectra from Zn_{1-x}Mg_{x}O solid solutions are discussed in terms of lattice deformation associated with the distinct coordination preferences of Zn and Mg. Solid-state magic-angle-spinning (MAS) NMR studies suggest that the local electronic environments of {67}Zn in ZnO are only weakly modified by the 15% substitution of Mg for Zn. {25}Mg MAS spectra of Zn_{0.85}Mg_{0.15}O show an unusual upfield shift, demonstrating the prominent shielding ability of Zn in the nearby oxidic coordination sphere. Neutron PDF analyses of Zn_{0.875}Mg_{0.125}O using a 2x2x1 supercell corresponding to Zn_{7}MgO_{8} suggest that the mean local geometry of MgO_{4} fragments concurs with previous density functional theory (DFT)-based structural relaxations of hexagonal wurtzite MgO. MgO_{4} tetrahedra are markedly compressed along their c-axes and are smaller in volume than ZnO_{4} units by ~6%. Mg atoms in Zn_{1-x}Mg_{x}O have a shorter bond to the $c$-axial oxygen atom than to the three lateral oxygen atoms, which is distinct from the coordination of Zn. The precise structure, both local and average, of Zn_{0.875}Mg_{0.125}O obtained from time-of-flight total neutron scattering supports the view that Mg-substitution in ZnO results in increased total spontaneous polarization.Comment: 12 pages, 14 figures, 2 table