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Abstrak :
Pengolahan data magnetik menghasilkan nilai magentik total yang telah dikoreksi oleh koreksi IGRF, Variasi Harian dan Koreksi Drift. Hasil pengolahan data kemudian diplot menjadi kontur anomali magnetik pada software SURFER 9.0. Dari kontur inilah kemudian didapatkan indikasi anomali magnetik pada data pengukuran. Anomali inilah yang nantinya akan dijadikan patokan untuk membuat permodelan. Permodelan menggunakan data magnetik bertujuan untuk mengidentifikasikan anomali magnetik yang terdapat pada data pengukuran. Anomali magnetik biasanya dipengaruhi oleh hot rock yang berada pada bawah permukaan. Pada penelitian ini, data magnetik yang digunakan adalah data pengukuran magnetik di daerah Arjuna-Welirang. Daerah prospek geothermal Arjuna-Welirang terletak di wilayah Kabupaten Malang, Kabupaten Mojokerto, Pasuruan, dan Kota Batu. Daerah prospek ini berada di lingkungan geologi yang didominasi oleh batuan vulkanik berumur kuarter. ......Magnetic data processing give a magnetic total value that has been corrected by the correction IGRF, Diurnal Variety and Drift Correction. Then the data processing?s results are plotted into the contours of the magnetic anomalies in the software Surfer 9.0. This contour is then obtained an indication of magnetic anomalies on the measurement data. This is an anomaly that will be used as a benchmark for modeling. Modeling using magnetic data aims to identify magnetic anomalies are present in the measurement data. Magnetic anomalies are usually influenced by the hot rock that is on the bottom surface. In this study, which used magnetic data is the data of magnetic measurements in the Arjuna-Welirang. Geothermal prospect area Arjuna-Welirang located in Malang regency, regency Mojokerto, Pasuruan, and Batu. This prospect area is located in the geological environment which is dominated by old volcanic rocks quarter.

Abstrak :
A magnetic Fe3O4@ZnO nanocomposite (NC) was successfully synthesized by a wet milling method using a high energy milling (HEM) machine. The magnetic Fe3O4@ZnO NC was characterized by an X-ray Diffractometer (XRD), scanning and transmission electron microscopes (SEM and TEM), and a vibrating sample magnetometer (VSM). X-ray diffraction results show that Fe3O4@ZnO NC consisted of ZnO and Fe3O4 phases. The microstructure analysis indicated that Fe3O4@ZnO NC presented a ZnO shell wrapped around the surface of a magnetic Fe3O4 surface. The average diameter of the aggregated Fe3O4 nanoparticle (NP) is 20 nm, while that of Fe3O4@ZnO NCs is nearly 30 nm. The Fe3O4 NP and Fe3O4@ZnO NC show typical superparamagnetic behavior with low coercivity. The saturation magnetization (Ms) of Fe3O4 NP was measured at about 66.26emu.g-1 and then declined to 34.79emu.g-1 after being encapsulated with a ZnO shell. The photoactivities of the Fe3O4@ZnO NC under UV irradiation were quantified by the degradation of a methylene blue (MB) dye solution. The result reveals that the photodegradation efficiency of Fe3O4@ZnO NC is favorable at pH neutral (pH = 7) reaching 100%. By increasing the MB dye concentration from 10 ppm to 40 ppm, the photodegradation efficiency decreases from 100% to 52%. The Fe3O4@ZnO NC can be easily collected by an external magnet. The magnetic Fe3O4@ZnO NC could be extended to various potential applications, such as purification processes, catalysis, separation, and photodegradation.

Abstrak :
Series of Ti2+-Mn4+ ions substituted BaFe12-2xTixMnxO19 samples with x = 0.0–0.8 have been studied to find out the effect of ion substitution on their microstructure, magnetic, and microwave absorption characteristics. The materials were synthesized through the mechanical alloying process. X-ray diffraction pattern for all sintered samples confirmed that the materials are single phase materials with BaFe12O19 structure. Referring to the results, it is shown that all samples that are subject to ultrasonic irradiation treatment characterized by a crystallite size distribution with the width get slimmer and mean crystallite size get smaller as the substitution level increased from x = 0 to x = 0.8. A sample of latter composition has fine crystals between 10–200 nm with the mean size of 42 nm. The effect of ionic substitution also affected the magnetic properties in which coercivity decreased proportionally with an increase of x value. The saturation magnetization increased to 0.41 T at x = 0.4, and then decreased for higher x values. Hence, the increase occurred only in samples with low-level substitutions of Ti2+-Mn4+ ions. Microwave absorption characterization clearly shows that the reflection loss (RL) value of Ti2+-Mn4+ substituted BaFe12-2xTixMnxO19 samples was enhanced from 2.5 dB in a doped free sample (x = 0) to 22 dB (~92% absorption) in a sample with x = 0.6 in the frequency range 8–12 GHz.

Abstrak :
Pulau Jawa berada di dekat zona subduksi Lempeng Eurasia dan Indo-Australia, yang menyebabkan terbentuknya patahan-patahan di daratan. Salah satu daerah yang terdampak adalah Kabupaten Sumedang, Jawa Barat. Prediksi gempabumi penting untuk meminimalisir kerusakan. Analisis aktivitas anomali geomagnetik Ultra-low Frequency (ULF) sebelum gempabumi dilakukan di sekitar stasiun geomagnetik TJS Sumedang menggunakan metode Polarization Ratio Analysis (PRA). Metode ini membandingkan nilai medan magnetik komponen vertikal terhadap horizontal (SZ/SG) berbasis Fast Fourier Transform (FFT) untuk mendeteksi anomali geomagnetik ULF (0.01 Hz - 0.04 Hz). Frekuensi ini dipilih karena mudah merambat ke permukaan, memungkinkan deteksi anomali yang jelas. Tiga gempabumi tahun 2020-2021 dengan magnitudo (M) ≥ 5 dan jarak episenter (R) ≤ 150 km (10 Maret 2020, M5; 25 Oktober 2020, M5.4; dan 27 April 2021, M5) dianalisis. Data geomagnetik malam hari komponen X, Y, dan Z dipilih untuk mengurangi noise. Hasil menunjukkan frekuensi 0.01 Hz - 0.04 Hz optimal mendeteksi prekursor gempa pada 27 April 2021. Anomali geomagnetik ULF tidak berkaitan dengan badai geomagnetik, dibuktikan dengan nilai indeks Dst (Disturbance storm time) yang tidak melebihi ambang batas. ......Java Island is adjacent to the subduction zone of the Eurasian and Indo-Australian Plates, causing the formation of several faults on land. From the formation of faults that can be caused by earthquakes, there are areas that are affected, one of which is Sumedang Regency, West Java. Earthquake prediction efforts are very important to minimize the damage that will occur. Ultra-low Frequency (ULF) geomagnetic anomaly activity was analyzed before the earthquake around the TJS Sumedang geomagnetic station using the Polarization Ratio Analysis (PRA) method, which compares the magnetic field value of the vertical component to the horizontal component (SZ/SG) based on Fast Fourier Transform (FFT), which is used to convert data from the time domain into the frequency domain to see ULF scale geomagnetic anomaly activity from 0.01 Hz - 0.04 Hz because this frequency wave easily propagates to the surface, allowing clear anomaly detection. Three earthquakes in 2020-2021 taken at magnitude (M) ≥ 5 and earthquake epicenter (R) ≤ 150 km (EQ1 with M5 on March 10, 2020, EQ2 with M5.4 on October 25, 2020, and EQ3 with M5 on April 27, 2021) in the vicinity of the TJS Sumedang geomagnetic station were selected because the larger the M and the closer the R of the earthquake can strengthen the geomagnetic anomaly readings. Nighttime geomagnetic data of X, Y, and Z components were selected to reduce noise or human activity. The results showed that the frequency of 0.01 Hz - 0.04 Hz was optimal for detecting possible precursors of the M5 earthquake on April 27, 2021 (EQ1), and the ULF geomagnetic anomaly in this study was not related to geomagnetic storms, which was obtained from the Dst (Disturbance storm time) index value which did not exceed the threshold line.

Abstrak :
This paper reports on the magnetic properties and electromagnetic characterization of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8). The La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8) materials were prepared using a mechanical alloying method. All the materials were made of analytical grade precursors of BaCO3, Fe2O3, MnCO3, TiO2, and La2O3, which were blended and mechanically milled in a planetary ball mill for 10h. The milled powders were compacted and subsequently sintered at 1000°C for 5h. All the sintered samples showed a fully crystalline structure, as confirmed using an X-ray diffractometer. It is shown that all samples consisted of LaMnO3 based as the major phase with the highest mass fraction up to 99% found in samples with x < 0.3. The mass fraction of main phase in doped samples decreased in samples with x > 0.3. The hysteresis loop derived from magnetic properties measurement confirmed the present of hard magnetic BaFe12O19 phase in all La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8) samples. The results of the electromagnetic wave absorption indicated that there were three absorption peaks of ~9 dB, ~8 dB, and ~23.5 dB, respectively, at respective frequencies of 9.9 GHz, 12.0 GHz, and 14.1 GHz. After calculations of reflection loss formula, the electromagnetic wave absorption was found to reach 95% at the highest peak frequency of 14.1 GHz with a sample thickness of around 1.5 mm. Thus, this study successfully synthesized a single phase of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1–0.8) for the electromagnetic waves absorber material application.