Journal of Mathematical and Fundamental Sciences
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Pelarutan Besi Selektif pada Korosi Baja Karbon dalam Larutan Buffer Asetat, Natrium Bikarbonat - CO2 Jenuh
Get PDF This work has investigate conditions which allow pitting corrosion of carbon steel in acetate buffered test solutions of pH 3.82, 4.12, 5.12 and 6.12, 0.2 M NaOAc and standard brine solutions, all of which contains 100 mg/L sodium bicarbonate and saturated with CO2. Corrosion rates is determined by corrosion wheel and corrosion bubble tests, while surface morphology is observed by electron microscopy (SEM) and metallographic optical microscopy, whereas surface deterioration as well as corroded lattice structure of the steel is monitored through measurements by X-ray Diffraction (XRD) patterns. The X-ray Diffraction Patterns of corroded carbon steel in any of the above test solutions exhibit a decrease in relative intensity of 110 and 200 lattice planes and an increase in the 211 lattice plane. The extent of decrease of the diffracted X-ray intensities increases with the increase in the percentage of corroded carbon steel coupon weight loss. This might reflect a selective dissolution of iron atoms situated in both lattice planes. It is suspected that this observation is due to the fact that 211 lattice plane has the smallest percentage of atomic occupancy among the three, thus it might have the greatest chance to be inserted with carbon atoms which in turn gives a protective effect toward iron atoms against further dissolution. Although, the corrosion process starts from the surface phase, this experiment reveals that X-ray diffraction pattern of the three lattice planes could be employed as some sort of carbon steel corrosion indicator. Consequently, corrosion inhibitor performance could be deduced from its ability to maintain diffraction pattern of the initial carbon steel specimen
Analisa Gempa dalam C050296F untuk Penyelidikan Kecepatan Gelombang S di Bawah Plato Ontong-Jawa
Get PDFSeismogram gempa bumi dalam C050296F telah dianalisa pada berbagai stasiun di sekitarnya, yaitu HNR, MSVF, CTAO dan SNZO untuk menyelidiki struktur kecepatan gelombang S di bawah Plato Ontong-Jawa (POJ) di Equator Pasifik Barat. Seismogram sintetik dihitung dengan metoda GEMINI, yang input awalnya adalah model bumi PREMAN, solusi CMT gempa dan koordinat stasiun observasi. Fase-fase gelombang S, Love dan Rayleigh, dan gelombang dalam ScS, ScS2 dan fase-fase dalam yang dipantulkan oleh permukaan bumi digunakan dalam penelitian ini. Perbandingan seismogram antara seismogram terukur dan sintetiknya menunjukkan diskrepansi yang berbeda-beda untuk beragam arah azimuth dari hiposenter. Di daerah POJ ke tenggara anomali bernilai negatif, sama dengan hasil riset seismologi sebelumnya di daerah yang sama. Ke arah stasiun MSVF daerah POJ memiliki anomali positif, berbeda dengan hasil riset seismologi sebelumnya. Anomali terjadi tidak hanya di mantel atas, tetapi juga pada lapisan-lapisan di bawahnya hingga CMB
Sistem Kontrol Hibrida Sinyal Rujukan Berbasis Logika Fuzzy untuk Peningkatan Kinerja Transien Pengontrol PID
Get PDFMakalah ini membahas suatu metoda kontrol yang disebut kontrol sinyal rujukan (set-point) dengan pengambilan keputusan menggunakan logika fuzzy. Metoda ini dirancang untuk mengurangi keterbatasan sistem kontrol umpan balik yang harus mempunyai penguatan pengontrol tinggi untuk menghasilkan kinerja transien yang cepat. Metoda kontrol sinyal rujukan dapat memperbaiki kinerja transien dengan tanpa mempengaruhi karakteristik dinamik sistem kontrol lup tertutupnya. Pada makalah ini, pengontrol umpan balik yang digunakan adalah pengontrol PID dan kontrol sinyal rujukan menggunakan pengambilan keputusan dengan sistem fuzzy berdasarkan sinyal kesalahan. Kinerja metoda kontrol sinyal rujukan dengan sistem logika fuzzy dan sistem kontrol umpan balik dengan pengontrol PID diperlihatkan oleh beberapa hasil simulasi pada model umum sistem berorde satu dan dua dengan waktu mati
The Influence of Silane Gas Flow Rate on Optoelectronic Properties of µc-Si:H Prepared by HWC-VHF-PECVD Technique
Get PDFHydrogenated microcrystalline silicon (µc-Si:H) thin films have been deposited using 10% silane (SiH4) in H2 dilution by Hot Wire Cell Very High Frequency Plasma Enhanced Chemical Vapor Deposition (HWC-VHF-PECVD) technique. The resulted thin film characteristics were systematically studied as a function of the deposition parameter. The previous structural studies showed that the structural phase transition from amorphous to microcrystalline thin film was obtained using the filament temperature of 800 °C. In this study, the optoelectronic properties of µc-Si:H thin films were investigated as a function of the silane gas flow rate from 40 sccm to 80 sccm. The highest deposition rate of 3.6 A/sec and the lower optical bandgap of 1.4 eV were obtained using 80 sccm and 60 sccm of the silane gas flow rate, respectively. The film showed the photosensitivity of 3 x 107, which is quite high above the minimal value of 103 for solar cell application
Detecting Rice Phenology in Paddy Fields with Complex Cropping Pattern Using Time Series MODIS Data
Get PDFMonitoring paddy rice phenology and cropping schedules over wide areas is essential for many applications. Remote sensing provides a viable means to meet the requirement of improved regional-scale data set of paddy rice fields, such as phenological stages. A number of methods have been developed for detecting seasonal vegetation changes by using satellite images. Development of such methods to paddy fields with complex cropping pattern is still challenging. In this study, we developed a method for remotely determining phenological stages of paddy rice that uses time series of two vegetation indices (EVI and LSWI) obtained from MODIS data. We ran the algorithm to determine the planting date, heading date, and harvesting date of paddy rice in 5 districts of West Java Province, using the 8-day composite MODIS Surface Reflectance products (500-m spatial resolution) in 2004. Estimated harvesting dates were then used to calculate paddy rice harvested area. We validated the performance of the method against statistical data in 13 subdistricts. The root mean square errors of the estimated paddy rice harvested area against the statistical data were: 851 Ha for monthly data, 1227 Ha for quarterly data, and 2433 Ha for yearly data. Subdistrict-level comparisons of paddy rice harvested area between the MODIS estimation and statistical data showed moderate correlation, with coefficient of determination (r2) 0.6, 0.7, and 0.6 for monthly, quarterly and yearly data, respectively. The results of this study indicated that the MODIS-based paddy rice phenological detection algorithm could potentially be applied at large spatial scales to monitor paddy rice agriculture on a timely and frequent basis
Doping Calcia and Yttria into Zirconia Obtained from by Product of Tin Concentrator to Improve its Ionic Conductivity
Get PDFZirconia has been prepared from Zircon concentrate by caustic fusion methods. Zircon is a by product from tin ore concentration plant at Bangka island of Indonesia. Yttria Stabilized-Zirconia (YSZ) was prepared by introducing the 8 % mol yttrium oxide into zirconia and sintered at 1500 "žaC for 5 hours. In order to obtain constant oxygen vacancy of 8 % mol in Zirconia, an appropriate amount of Yttria and Calcia were introduced into Zirconia and the mixtures were heated at 1350 oC for 5 hours. Elemental composition was determined by SEM/EDX and XRF and lattice parameters were determined using X-ray diffraction method. Ionic conductivity was measured by complex impedance spectroscopy. The results show that doping of Yttria into Zirconia (YSZ) and Calcia-Yttria into Zirconia (CYZ) allows phase transformation of Zirconia from tetragonal with space group P42/nmc into cubic Fm3m and enhance the ionic conductivity. However, the prepared materials are porous and have not met the requirement for the electrolyte material yet
Mechanism of Action of Coumarin against Candida albicans by SEM/TEM Analysis
Get PDFThe aim of this study was to identify the antifungal activity of coumarin isolated from Ageratum conyzoides L. leaves and to observe its influence on Candida albicans cells by scanning electron microscope (SEM) and transmission electron microscope (TEM). Antifungal activity testing with the disk diffusion method showed coumarin was active toward pathogenic fungus Candida albicans with an MIC value of coumarin of 125 ïg mL-1. The results show that this compound damaged the cell by pores formation on the cell wall. Death of cells occurred due to leakage and necrosis of cytoplasmic content
A Note Concerning Hamilton Cycles in Some Classes of Grid Graphs
Get PDFA graph G is called hamiltonian if it contains a Hamilton cycle, i.e. a cycle containing all vertices. Deciding whether a given graph has a Hamilton cycle is an NP-complete problem. But, it is a polynomial problem within some special graph classes. In this paper we consider three classes of grid graphs, namely rectangular grid graph, eta grid graph and omega grid graph. Our main result characterizes which of these graphs are hamiltonian
Polychromatic Source Excitable and Enhanced Green Photoluminescence of ZnO Nanoparticles Dispersed in High Molecular Weight Polymer Matrix
Get PDFComposite of zinc oxide (ZnO) nanoparticles in polyethylene glycol (PEG) has been produced by mixing the as prepared ZnO colloid with a solution of PEG in ethanol. ZnO colloid was produced by hydrolizing zinc acetate in ethanol solution. The produced composite exhibits a wide band excitation spectra compared to ZnO colloid to allow the excitation using a wide range excitation wavelength for producing high green luminescence intensity. Since ZnO nanoparticles were trapped in a matrix of polymer (solid phase) no further growing as well as agglomeration process took place (as observed in ZnO colloid) so that the shape and positions of excitation and luminescence spectra were time independent. Heating the prepared composite results an increase in the luminescence intensity due the increase in the ZnO nanoparticles concentration in the heated composites
Variasi Nilai Gradien Hidrolik dan Pengaruhnya terhadap Perubahan Nilai Tahanan Jenis pada Sistem Akifer Bersudut Berdasarkan Pendekatan Model Fisik
Get PDFThe core of this research is simulation on a physical model of inclined confined aquifer in laboratory scale. The model dimensions is 79.50 cm long, 78.00 cm wide, and 10.00 cm tall. The aquifer is simulated as single confined aquifer with thickness of 8 cm. The aquifer material is composed of coarse sand with good gradation and has uniformity coefficient of 7.105. The measurements consist of elevation head (z), pressure head (hp), total head (h), and resistivity with Schlumberger configuration. The confined aquifer layer is set up to be horizontal. Then, in order to get the hydraulic gradient and dip layer variations, the position of the model box is inclined with varied degree of: 00, 100, 200, and 270. To get the most representative result, the resistivity is measured with line spread parallel to strike and perpendicular to strike.The analysis shows that the increase of the hydraulic gradient (i) have the tendency to cause the decrease of true resistivity values (Ï). Based on the line spread direction and R2 values, there are 2 representatives equations as follows: 1). With line spread parallel to strike:4,88ln()64,60Ï=−+i;R2=0,95. 2). With line spread perpendicular to strike without correction on AB/2 and K value:Ï=;R3,80ln()58,20−+i2=0,99