A geochemistry study has been done in four geothermal manifestations—Ie-Seu’um, Ie-Brôuk, Ie-Jue and the Van-Heutz crater—located in the north zone of Seulawah Agam mountain (Aceh Besar District, Indonesia). The study was performed through water and gas analysis. Water analysis were done for all geothermal manifestations, but gas analysis was only done for the Ie-Jue manifestation that has fumaroles. Cation and anion contents were analyzed by ion chromatography, ICP-OES, alkalimetry titrations, and spectrophotometry, meanwhile isotopes were measured by a Liquid Water Isotope Analyzer. The resulting data were used for fluid and gas geothermometry calculations, and plotted in a FT-CO2 Cross-Plot and a CH4-CO2-H2S triangle diagram to obtain reservoir temperatures. The data were also plotted by a Cl-HCO3-SO4 triangle and Piper diagram to obtain the water type and dominant chemical composition, a Na-K-Mg triangle diagram to obtain fluid equilibria, the isotope ratio in the stable isotope plot to obtain the origin of water, and a N2-He-Ar triangle diagram to establish the origin of fumaroles. The water analysis results showed that (1) Ie-Seu’um has an average reservoir temperature of 241.9 ± 0.3 °C, a chloride water type, a dominant Na-K-Cl chemical composition, a mature water fluid equilibrium, and water of meteoric origin; (2) Ie-Brôuk has an average reservoir temperature of 321.95 ± 13.4 °C, a bicarbonate water type, a dominant Na-Ca-HCO3chemical composition, an immature water fluid equilibrium, and water of meteoric origin; (3) Ie-Jue has an average reservoir temperature of 472.4 ± 91.4 °C, a sulphate water type, a dominant Ca-SO4 chemical composition, an immature water fluid equilibrium and water of meteoric origin; and (4) the Van-Heutz crater has an average reservoir temperature of 439.3 ± 95.3 °C, a sulphate water type, a dominant Ca-SO4 chemical composition, an immature water fluid equilibrium and water of magmatic origin. The results of our gas analysis showed that Ie-Jue has an average reservoir temperature of 258.85 °C, and water of meteoric origin. Based on the reservoir temperatures, the geothermal manifestation of the north zone of Seulawah Agam mountain is considered as a high-temperature geothermal system suitable for power plant development.

ABSTRAK Muhammad Yani (2014). Proses Berpikir Siswa Sekolah Menengah Pertama dalam Memecahkan Masalah Matematika Berdasarkan Langkah-langkah Polya Ditinjau dari Adversity Quotient. Matematika memiliki objek yang abstrak sehingga untuk memahaminya tidak cukup hanya dengan menghafal tetapi dibutuhkan adanya proses berpikir. Penelitian ini dilakukan untuk mendeskripsikan proses berpikir dan menganalisa kesulitan siswa dalam memecahkan masalah matematika berdasarkan langkah-langkah Polya ditinjau dari Adversity Quotient (AQ). Penelitian ini merupakan penelitian kualitatif deskriptif yang subjek penelitian adalah siswa kelas IX SMPN 1 Banda Aceh yang terdiri dari tiga siswa. Pemilihan subjek menggunakan teknik pemilihan sampel bertujuan ( purposive sampling) dan didasarkan pada tingkat AQ dan kelancaran komunikasi siswa. Pengumpulan data dilakukan dengan menggunakan metode wawancara berbasis tugas, kemudian dilakukan triangulasi untuk memeriksa keabsahan data. Data dianalisis dengan menggunakan konsep Miles dan Huberman: meliputi tahap reduksi data, penyajian data, dan penarikan kesimpulan. Hasil penelitian menunjukkan bahwa; (1) subjek climber melakukan proses berpikir secara asimilasi dalam memahami, menyusun rencana penyelesaian, dan memeriksa kembali penyelesaian masalah. Sementara itu, dalam melaksanakan rencana penyelesaian masalah proses berpikir yang dilakukan adalah asimilasi dan akomodasi. Kesulitan yang dialami subjek climber dalam memecahkan masalah matematika adalah kesulitan dalam memahami beberapa makna soal dari masalah yang diberikan, (2) subjek camper juga melakukan proses berpikir secara asimilasi dalam memahami, menyusun rencana penyelesaian, dan memeriksa kembali penyelesaian masalah. Namun, melakukan proses berpikir secara asimilasi dan akomodasi dalam melaksanakan rencana penyelesaian masalah. Kesulitan yang dialami subjek camper dalam memecahkan masalah matematika disebabkan lupa konsep, kesulitan memahami makna soal dari masalah yang diberikan dan terkadang juga kurang teliti ketika memecahkan masalah , dan (3) subjek quitter melakukan proses berpikir secara asimilasi dan akomodasi dalam memahami dan melaksanakan rencana penyelesaian masalah. Sementara itu, dalam menyusun rencana penyelesaian dan memeriksa kembali penyelesaian masalah dilakukan proses berpikir secara asimilasi. Kesulitan yang dialami subjek quitter dalam memecahkan masalah matematika disebabkan belum memahami dengan baik beberapa konsep dalam matematika, kesulitan memahami makna soal dari masalah yang diberikan dan kurang teliti ketika memecahkan masalah.

Abstrak: Penelitian kualitatif ini bertujuan untuk mendeskripsikan kemampuan representasi matematis siswa melalui pendekatan Pendidikan Matematika Realistik (PMR). Penelitian ini dilakukan di kelas VII-2 SMP Negeri 6 Banda Aceh yang melibatkan enam siswa. Kemampuan representasi siswa dianalisis dari hasil tes dan wawancara setelah penerapan PMR melalui tahap reduksi data, penyajian data, dan penarikan kesimpulan. Berdasarkan hasil tes, subjek penelitian dikategorikan menjadi siswa dengan kemampuan representasi matematika tinggi, sedang dan rendah. Keenam siswa tersebut diwawancara untuk mengonfirmasi hasil tes. Hasil penelitian menunjukan bahwa siswa yang berkemampuan tinggi dan sedang memenuhi ketiga indikator kemampuan representasi matematis yaitu menyajikan data atau informasi dari suatu masalah ke representasi tabel, menyelesaikan masalah yang melibatkan ekspresi matematis, serta menuliskan langkah-langkah penyelesaian masalah matematika dengan kata-kata. Siswa berkemampuan rendah memenuhi dua indikator kemampuan representasi matematis yaitu menyelesaikan masalah yang melibatkan ekspresi matematis dan menuliskan langkahlangkah penyelesaian masalah matematika dengan kata-kata. Kata kunci: Representasi Matematis; Kemampuan; Pendidikan Matematika RealistikAbstract: This qualitative reseach aims at describing students' representation ability through realistic mathematics education (RME). It is conducted in grade VII-2 SMP Negeri 6 Banda Aceh focusing on the six students. Students' representation ability is analyzed from the developed test and interview after applying RME through data reduction, data display and conclusion. Based on the result of the test, the subjects are categorized into students who have high, medium and

In order to increase the geothermal exploration, the magnetotelluric (MT) method has been used to study the subsurface of the Seulawah Agam volcano, Aceh Province, Indonesia. Similar to all resistivity methods that are based on measuring the electric field on the surface, the MT commonly contains a static shift problem, which is caused by the heterogeneities near the surface and the different topography of the volcano. The static effect can be expressed as a vertical shift from the apparent resistivity curve. In this study, the apparent resistivity data from the 1D inversion of the Transient Electromagnetic (TEM) method were used to correct the static shift problem in the MT data. Both methods were acquired in the same site at ten stations along with a 12 km distance profile that crosses the Seulawah Agam volcano. The north-south profile of the volcano area appeared to host a geothermal system. The 1D inversion in the TEM data shows a low resistivity layer that indicated a cap rock with a thickness up to 1000 m. The area below the cap rock is estimated to be a reservoir zone while the 2D inversion of MT shows that the deep conductor below 2000 m could be the heat source for the Seulawah Agam geothermal system.

Indonesia is a country with the largest geothermal reserves in the world, but exploration and utilization of geothermal energy are still low. As an effort in increasing exploration process, an integrated geophysical method to image the subsurface structure of the geothermal system has been done at Seulawah Agam Geothermal Field, Aceh Province, Indonesia. Very low frequency (VLF-R) method was used for shallow and magnetotellurics method for deep structures studies in the area. The magnetic method was used for a complementary of the electromagnetic methods. Magnetotelluric data were acquired at ten stations along a 30 km distance profile crossing the Seulawah Agam volcano in a north-south direction. The VLV-R and Magnetic stations were measured on the Ie Ju manifestation area only, located at the northern slope of the volcano. The magnetic and VLF-R methods have been able to investigate the local structure, while the regional structure of subsurface is described by the magnetotelluric method. 2D resistivity model of magnetotelluric data shows a conceptual model of the geothermal system based on resistivity variation. The model also reveals two local faults crossing the volcano in a northwest-southeast direction. Most of the geothermal manifestations in Seulawah Agam are controlled these faults. Application of VLF-R and magnetic methods on the Ie Ju manifestation area has shown clearly near surface structures of the area. The inverted models have strong agreement with a reduction to the pole of total magnetic field anomalies. Presence of the conductors in the resistivity models coincides with low total magnetic field anomalies. In addition, the total magnetic field anomalies map can be also used to locate the presence of geothermal manifestation with or without their appearance on the surface

A combination of geophysical methods has been applied in the earthquake-devastated area in late December of 2016 in Pidie Jaya Regency, Aceh Province, Indonesia. The methods are refraction seismic and Multichannel Analysis Surface Wave (MASW). This research aims to identify the types of near-surface lithologies through Poisson's ratio analysis. These velocity values were acquired through measurements in three sites among the devastated areas. The measurement of VP and VS values deploys the PASI 16S Seismograph with 24 channels. The geometry of seismic refraction lines was designed by placing 2-meter long geophone intervals, and nine total shot points were inserted, while in VS data measurement, the geophone intervals were the same set as the refraction seismic with differently laid out geometry of shot points and total. Both data were processed using ZondST2D for the 2D profile of VP and SeisImager for 2D section of VS. The result of the study indicated that all of the Poisson's ratio profiles show lithology consisting of clayey sand, clay and saturated clay with a value generally ranging from 0.22 to 0.46. The clay lithology is a prominent finding of this research. These interpretations more or less match other results even though some are in different research areas. This finding was proven by the damaged area affected by the earthquake in late 2016. Thus the result can be beneficial to designing and customizing building types according to lithological characteristics then mitigating from the forthcoming threat of the earthquake.

Magnetotellurics (MT) is an important geophysical method for exploring geothermal systems, with the Earth resistivity obtained from the MT method proving to be useful for the hydrothermal imaging changes of the system. In this research, we applied the MT method to map the geothermal system of the Seulawah Agam volcano in northern Sumatra, a site intended for the construction of a geothermal power plant with an estimated energy of 230 Mwe. Herein, 3D MT measurements were carried out, covering the entire area of the volcano and the various intersecting local faults from the Seulimeum segment in the NW–SE direction. Based on Occam 2D inversion, a conductive anomaly (<10 ohm·m) near the surface was identified in response to specific manifestation areas, including the Heutsz crater on the northern side and the Cempaga crater on the southern side. A further conductive anomaly was also found at a depth of 1 km, which was presumably due to a clay cap layer covering the fluid in the reservoir layer below the surface, where the manifestation areas are formed at various locations (where faults and fractures are found) owing to the fluid in the reservoir rising to the surface. The MT modeling also revealed that the reservoir layer in Seulawah Agam lies at a depth of 2 km with a higher resistivity of 40–150 ohm·m, which is the main target of geothermal energy exploration. At the same time, the heat source zone where magma is located was estimated to lie in two locations, namely, on the northern side centering on the Heutsz crater area and the southern side in the Cempaga crater area. A clear 3D structure obtained via Occam inversion was also used to visualize the hydrothermal flow in the Seulawah Agam volcano that originates from two heat source zones, where one structure that was consistent across all models is the conductive zone that reaches a depth of 5 km in the south in response to the regional faulting of the Seulimeum segment. Based on the MT research, we concluded that the volcano has the geothermal potential to be tapped into power plant energy in the future.

Triacetin, an alternative biodiesel additive, was prepared by esterification of glycerol with acetic acid in the presence of chemically activated natural zeolite. The esterification was carried out in a small reaction flask under microwave irradiation. The catalyst was characterized for its morphology by SEM and its chemical composition by X-ray Diffraction (XRD). The Scanning Electron Microscopy (SEM) micrograph indicates improved surface area of the zeolite, while the XRD analysis shows an increase in Si/Al ratio from natural zeolite to 6.042 and its crystallinity value of 12.23%. The Fourier Transform Infra Red (FTIR) analysis obtained showed that microwave-heated samples have an esters group spectrum of triacetin at 1702 cm-1. The conversion value of glycerol was more than 95% at molar ratio of the reactants 1:9 and catalyst loading of 3%. The selectivities for monoacetin, diacetin and triacetin were 80.1%, 15.4%, and 4.5% at 60 minutes, and 43.0%, 48.6%, and 8.3% at 90 minutes. It shows that the conversion took place in consecutive steps and the use of microwave allows the reaction proceeding at milder condition. Copyright © 2019 BCREC Group. All rights reserved