Hasil Pencarian  ::  Simpan CSV :: Kembali

"Information about magnetic structure can not be obtained through X ray diffraction method. Therefore data from neutron diffraction are needed to find out substance magnetic structure. From that structure, we can get information about magnetic crystal structure and magnetic momentum or the structure of the spin. The research is aimed to find out magnetic structure at CaMnO3 dan LaMnO3 in powder. The preparation of CaMnO3 and LaMnO3 substance is made through powder method and stoikiometric calculation. Basic substance of CaMnO3 is CaCO3 and MnO2, while basic substance of LaMnO3 is La2O3 and MnO2. After the substances are mixed, time varied milling, temperature varied sintering and annealing are conducted. It is hoped that the substances will be united or form a new phase.The magnetic structure study of CaMnO3 and LaMnO3 at this research are explained by neutron powder diffraction. CaMnO3 is good analisis at crystal system on orthorhombic space group Pnma with lattice parameter at 12 k is a = 5.2692 Å, b = 7.4403 Å, c = 5.2596 Å. LaMnO3 is good analisis at crystal system on monoklinik space group P1121/a with lattice parameter at 12 K is a = 5.4726 Å, b = 7.7613 Å, c = 5.5324 Å. Magnetic parameter Mn atomic has charge ordered of CaMnO3 and LaMnO3 is Mn4+ ion and Mn3+ ion.Result at research with High Resolution Powder Diffractometer, HRPD to find, CaMnO3 has properties magnetic at Mn atomic with indeks miller hkl (011) angle θ 2 = 24.486 on 12 K. LaMnO3 has properties magnetic at Mn atomic with indeks miller hkl (200) and angle θ 2 = 38.966°. Magnetic structure Mn atomic at 4b(0,0, 2 1 ) simetri of CaMnO3 is four possible nonkolinear ferromagnetic, with value magnetic momen is m(Mn) = 1.73 B µ . Magnetic structure Mn atomic of LaMnO3 at 2c(0,0, 2 1 ) is two possible (antiferomagnetik and ferromagnetic) and 2d( 2 1 , 2 1 ,0) simetri is two possible antiferromagnetic, with value magnetic momen is m(Mn) = 2.23 B µ ."

"Friction Stir Welding FSW merupakan sebuah metode pengelasan ramah lingkungan yang telah diaplikasikan di banyak industri AA 5083 secara luas digunakan dalam berbagai aplikasi yang memanfaatkan kelebihan tahan korosi dengan kekuatan yang sangat baik setelah penyambungan AA 5083 disambungkan dalam proses FSW dengan mengorientasikan arah las sejajar dan tegak lurus rol pada beberapa variasi kecepatan pengelasan Analisis hasil pada zona las menunjukkan perbedaan sifat mekanik dan struktur mikro yang signifikan terhadap perubahan orientasi arah pengelasan dan pengerolan benda kerja.

---

Friction Stir Welding FSW is a eco friendly welding method that has been applicated in many industries AA 5083 are vastly used in various application to exploit the advantage of corrosive resistance with excellent strength after joining AA 5083 is joined by FSW process by orienting the weld direction parallel and perpendicular to the roll for some various of welding speed Analysis of results on the weld zone obtained exhibit differences in mechanical properties and micro structrure significantly on the change in orientation of the rolling and welding direction of the wokpiece."

"Magnet permanen berbasis Sm-Fe-N merupakan magnet kelas baru yang ditemukan pada tahun 1990. Sejak ditemukan fasa magnetik ini telah banyak studi lanjutan yang dilakukan terutama sekali untuk meningkatkan sifat magnetiknya. Dalam penelitian ini telah dilakukan analisis sifat magnetik dan struktur material magnet permanen berbasis Sm-Fe-N dengan komposisi nominal (SmxFe1oo-x)o.97N3, x = 6; 7,5; 9; 11,5 (at. %). Preparasi sampel dilakukan dengan teknik metalurgi serbuk menggunakan ball mill berenergi tinggi dan paduan nitrida didapatkan melalui reaksi gas-padatan. Kompaksi dilakukan dengan teknik kompaksi kejut. Hasil identifikasi fasa dengan difraksi sinar-x menunjukkan bahwa fasa mayoritas yang hadir adalah Sm2Fe17N3 dengan struktur Th2Zn17 (rhombohedral) dihitung sekitar 90 %. Disamping itu hadir pula fasa kedua yaitu a-Fe sebagai konsekuensi komposisi di luar stoikiometri. Khusus untuk komposisi pada x = 11,5 terdapat kehadiran fasa SmN sebesar 0,14 %. Hasil perhitungan konstanta kisi dengan metode Cohen memperlihatkan kesesuaian dengan nilai publikasi dan variasi komposisi magnet Sm-Fe-N tidak menyebabkan distorsi pada kisikisi kristal Sm2Fe17N3. Hasil analisis sifat magnetik diketahui terdapat peningkatan koersivitas dengan pertambahan kandungan Sm dalam' komposisi. Sedangkan harga remanen yang didapat melewati batas teoritis Stoner-Wohlfarth - 0,8 T. Namun secara umum remanen menurun dengan adanya peningkatan Sm. Demikian pula terjadi penurunan pada energi produk maksimum, (BH)n,. dengan bertambahnya kandungan Sm dalam komposisi.

---

Sm-Fe-N based permanent magnet belong to a new class of magnets were discovery in 1990. Since the discovery, a number of studies have been made to improve the magnetic properties. In this work, magnetic properties and materials structure of Sm-Fe-N based permanent magnets with (Sm)(Feio0.. )o,97N3 x = 6; 7,5; 9; 11,5 atomic persent composition have been analysed. Samples were prepared by powder metallurgy using high energy ball mills, then samples were nitrided using solid-gas reaction and subsequently compacted by shock compaction method.

Phase identification by XRD indicated that Sm2Fei7N3 is the majority magnetic phase with a volume fraction up to - 90 °I°. In addition, it was also identified an a-Fe as the second phase due to unstoichiometric composition of the magnet. Specially for x = 11,5 (at.%) also identified an SmN phase about 0,14 %. Lattice constants value of main phase that determined by Cohen's method is similar to that of published result. It is also shown that compositions of the magnets have no effect to lattice constants of main Sm2Fei7N3 phase.

The result of magnetic properties is increasing the coercivity with additional content of Sm composition. But the remanen value which is obtained more than Stoner-Wohlfarth theory - 0,8 T. In general, the remanen reduces by adding Sm. Also the maximum of product energy, (BH)max, is reduced by adding the content of Sm in the composition."

"The thesis examine about the influence of macroeconomy toward sectoral stock price index in Indonesia Stock Exchange period 2000 - 2008. The objective is to know how GDP, Bank Indonesia Certificate rate, REER, world crude oil price and Dow Jones index influence stock index fluctuation in stock sector and also the influence of each variable toward each stock sector index.Data was taken from panel data which contains from monthly data starting from 2000 up to 2008 for independent variable and stock sector price index as dependent variable. The author estimated independent variable as GDP, Bank Indonesia Certificate rate, REER, world crude oil price and Dow Jones index toward Stock Sector index price. The estimation used ordinary least squares method.Base on the estimation, most of variable accord with research hypothesis. However WTI or world crude oil price not in accordance with research hypothesis. It was presume by significant increase in agriculture and mining stock price index which caused by increasing in international commodity market. Meanwhile, increasing agriculture and mining commodity price caused by increasing in world crude oil price.The author recommendations are:1) As an alternative financial institution, government should force stock market by providing incentive which made the corporate move forward to be a member in stock market.2) Government should force agriculture sector since the significant increase in stock price index come from it. There after it will increase the contribution in agriculture sector toward GDP.

---

Penelitian ini tentang pengaruh makro ekonomi terhadap indeks harga saham sektoral di Bursa Efek Indonesia pada periode 2000-2008. Tujuan penelitian adalah mengetahui besarnya pengaruh PDB, tingkat suku bunga SBI, REER, harga minyak dunia dan indeks Dow Jones terhadap fluktuasi indeks saham sektoral dan besarnya pengaruh masing-masing variabel tersebut terhadap masing-masing indeks saham sektoral.Data yang dipergunakan data panel yang terdiri dari data bulanan tahun 2000 sampai dengan tahun 2008 untuk variabel independen dan indeks harga saham sektoral sebagai variabel dependen. Penulis mengestimasi variabel independen berupa PDB, tingkat suku bunga SBI, REER, harga minyak dunia dan indeks Dow Jones terhadap indeks harga saham sektoral. Estimasi mempergunakan methode OLS (ordinary least squares).Berdasarkan hasil estimasi, secara keseluruhan variabel yang diteliti telah sesuai dengan hipotesa penelitian. Hanya variabel WTI atau harga minyak dunia tidak sesuai dengan hipotesa penelitian. Hal ini diduga karena kenaikan indeks harga saham pertanian dan pertambangan yang sangat tinggi yang disebabkan oleh kenaikan harga komoditas di pasar international. Sementara tingginya harga komoditas pertanian dan pertambangan tersebut disebabkan oleh kenaikan harga minyak dunia.Penulis merekomendasikan agar:(1) Sebagai lembaga alternatif pembiayaan, pemerintah harus mendorong pasar modal dengan memberikan insentif bagi dunia usaha untuk menjadi emiten di pasar modal.(2) Pemerintah perlu mendorong sektor pertanian mengingat besarnya peningkatan indeks harga saham sektor pertanian. Sehingga akan meningkatkan kontribusi sektor pertanian terhadap PDB."

"Pada penelitian ini dilakukan studi sifat magnetik bahan magnet permanen melalui simulasi dan optimasi parameter model Jiles-Atherton (JA) dan model JAmodifikasi, yaitu model JA-gaussian dan model JA-extended. Simulasi dan optimasi parameter model dilakukan terhadap dua buah data histeresis magnet bahan BaFe12O19 dan SrFe12O19 yang diukur menggunakan permagraph. Algoritma genetika digunakan untuk optimasi parameter setiap model dan metode euler digunakan untuk mensimulasikan setiap model, yang keduanya diimplementasikan menggunakan program MATLAB.Hasil dari optimasi parameter dan simulasi model menunjukkan bahwa modifikasi yang dilakukan pada model JA-gaussian dan model JA-extended menghasilkan kecocokan yang lebih baik dari model JA dalam memodelkan kurva histeresis bahan BaFe12O19. Akan tetapi kedua model modifikasi ini tidak lebih baik dari model JA dalam memodelkan dan SrFe12O19. Hal tersebut disebabkan oleh sifat keanisotropian bahan SrFe12O19 yang tidak didefinisikan dalam model JA-modifikasi.

---

This research focused on a magnetic properties study of permanent magnet materials through simulation and parameters optimization of Jiles-Atherton (JA) model and modified-JA model that are gaussian JA model and extended JA model. Simulation and parameters model optimization conducted to BaFe12O19 and SrFe12O19 materials using their magnetic hysteresis data that measured by using permagraph. Genetic algorithm is utilized to optimize the parameters for each model and euler method is used to simulate the models and both of them are implemented by using MATLAB program.

The results of parameters optimization and model simulations show that the modification made by Gaussian JA model and extended JA-model produce a better match than the JA model in modeling of BaFe12O19 hysteresis curve. However, these modified JA-model are not better than JA model in modeling of SrFe12O19 hysteresis curve. This is due to the anisotropic properties that is shown by SrFe12O19 which can not defined in the modified-JA model."