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INDONESIA
Makara Journal of Technology
Published by Universitas Indonesia
ISSN : -     EISSN : -     DOI : -
Core Subject : Science,
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Articles 8 Documents
Search results for , issue " Vol 12, No 2 (2008)" : 8 Documents clear
The Decompositioning of Volatile-Matter of Tanjung Enim Coal by using Thermogravimetry Analyzer (TGA) Nukman, Nukman
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.145

Abstract

Coal is a nature material which a kind of energy source. The decompotition of coal could analyze by heat treated using thermogravimetry analyzer. The decomposition of the volatile matter for three kinds of Tanjung Enim coal could be known. The value of activation energy that be found diference, then for Semi Anthracite, Bitumonius and Sub Bituminous Coal, the initial temperatures are 60.8 oC, 70.7 oC, 97.8oC, and the last temperatures are 893.8 oC, 832 oC, 584.6oC.
Physical Characteristics and Utilization oft the Karst Beaches in Kabupaten Gunungkidul Damayanti, Astrid; Ayuningtyas, Ranum
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.150

Abstract

Karsts beaches at Gunungkidul Regency (Baron, Kukup, Sepanjang, Drini, Krakal, Ngandong, and Sundak), located in south of Daerah Istimewa Yogyakarta Province, have economic potential. Even they have similarity in geological condition (genesis and morphological processes), but they have different physical characteristics. Based on result of observation environment on morphological conditions and spatial analysis method, we found the proper utilization of the beaches.
Hydrogen Absorption in Weldments of Overlaid Claded Pressure Vessel Rusli, Ronnie
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.146

Abstract

Cracks was found in type 347 stainless steel internal attachment welds of a reactor for a high temperature, and highpressure hydrogen service. One of the possible causes of cracking is low cycle fatigue cracking induced by repetition ofthermal stress to embrittled weld metal. Type 347 weld metal loses its ductility by presence of sigma phase andhydrogen.
Spectral Response Surfaces and the Ringing Response of Offshore Structures Suastika, I Ketut
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.151

Abstract

A method, called spectral response surface method, is proposed for the study of the ringing phenomenon of offshore structures. Newman’s results for diffraction force on a column were reformulated in terms of the frequency components of the ocean surface and their Hilbert transforms. Using a first-order reliability method together with a dynamic model for the structural response, it is straightforward to calculate the ocean surface history most likely to generate an extreme ringing response and the ringing response history.
Phase Unwrapping InSAR Image Using Local Energy Minimization Approach Adi, Kusworo; Mengko, Tati; Suksmono, Andriyan; Gunawan, Hendra
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.147

Abstract

Reconstruction process of phase data from its cover is called Phase Unwrapping (PU). Ideally, without any noise phrase, singularity, and aliasing problems, the phase information can be unwrapped easily. However, in fact, the phase data actually always get noise disturbance and discontinuity. The PU process becomes more complicated and needs a better PU algorithm to addressthe problems properly. In this research, the local PU algorithm is developed using minimization of close related firstorder pixels energy approach. In this method, the energy difference between four close related pixels is counted, followed by getting the probability value to obtain its total multiple ranges. Based on the research using synthesis ring image and InSAR with coherence 0.8, the Peak Signal to Noise Ratio (PNSR) range will be 30.5373 dB in 20 itteration.
Two Element Microstrip Antenna Array with Defected Ground Structure Zulkifli, Fitri; Rahardjo, Eko; Asvial, Muhamad; Hartanto, Djoko
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.148

Abstract

This paper presents a two element microstrip antenna array using trapezium shape defected ground structure (DGS). The DGS is inserted in the ground plane between two elements of antenna array. Insertion of the DGS is intended to suppress the mutual coupling effect produced by antenna array. Simulation and measurement results were taken and compared between antenna array with and without DGS. Measurement results show that the antenna with DGS compared to antenna without DGS can suppress mutual coupling effect to 7.9 dB, improve the return loss to 33.29% from -30.188 dB to -40.24 dB and axial ratio bandwidth enhancement to 10 MHz. This bandwidth enhancement is achieved from frequency 2.63 GHz – 2.67 GHz for antenna without DGS and from frequency 2.63 GHz – 2.68 GHz for antenna with DGS. In addition, the DGS antenna also improved the antenna gain to 0.6 dB. The results show that the implementation of the trapezium DGS can improve the radiation properties of the antenna without DGS.
Isolation of Methyl Laurate from Coconut Oil as Raw Material for Fatty Alcohol Sulfate Arbianti, Rita; Utami, Tania Surya; Nugroho, Astri
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.144

Abstract

Methyl laurate is a raw or base material for many industries, including surfactant industries. In this research, coconut oil (VCO) is transesterified with methanol to produce methyl ester, using NaOH as the catalyst. Methyl laurate is then separated by method based on the difference in melting point. This research focuses at determining the effects of some variables in transesterification on the concentration of produced methyl laurate. The variables are temperature (40 oC, 50 oC, 60 oC, 80 oC), time of transesterification reaction (0,5 hour, 1 hour, 1,5 hours, 2 hours, 3 hours), and the percent weight of the catalyst NaOH (0,5 %, 1 %, 1,5 %, 2 %, 3 %). Research showed the concentration of methyl laurate increased, following the increased temperature, time, and percent weight of catalysts. Optimal conditions were acquired at reaction temperature of 60oC, reaction time of 2 hours, and percent weight of the catalyst NaOH of 2 %. Laurate acid conversionto methyl laurate that yielded from optimal conditions, after the separation based on melting point, was 55,61 %.
Neutron Irradiation on SS316 Material for Radioactive Endovascular Stent Production Awaludin, Rohadi; Abidin, Abidin; Sriyono, Sriyono
Makara Journal of Technology Vol 12, No 2 (2008)
Publisher : Directorate of Research and Community Services, Universitas Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.7454/mst.v12i2.149

Abstract

It was reported that restenosis could be prevented by radioactive endovascular stent. SS316 material of endovascular stent has been irradiated at pneumatic rabbit system of G.A. Siwabessy reactor for 5 minutes for producing radioactive stent by neutron activation. After 10 days of decay, the irradiated SS316 was measured by gamma spectrometer. The radioisotopes of 51Cr, 59Fe and 60Co were detected in the irradiated SS316 with radioactivity of 5990, 107 and 109 Bq/mg respectively. The Calculation results showed that radioisotopes of 51Cr, 59Fe and 55Fe were produced by neutron activation. The radioactivity of 51Cr, 59Fe and 55Fe were 6051, 70 and 110 Bq/mg respectively. In the irradiated materials, the 55Fe was not detected because the radioisotope emitted radiation with very low energy (5.9 keV). It isconsidered that radioisotope of 60Co was produced from cobalt impurity in the SS316.

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