EXAFS Study on Local Structure of Iron Crystal by the Use of Asymmetrical Monochromator and PSPC

The EXAFS spectroscopy equipment constructed from an asymmetrical cut flat monochromator and PSPC is applied to the structural determination of pure α-iron which has small difference (0.038nm) in the first and second nearest neighbour distance. The efficiency of the curve fitting method for the two shell model of known structure material (α-iron) is discussed, in addition to describing the details of the experimental procedure of our new type of spectrometer and of the EXAFS data analysis

Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains

The plateau-non-plateau transition in the antiferromagnetic-(ferromagnetic)$_{n}$ polymerized $S=1/2$ XXZ chains under the magnetic field is investigated. The universality class of this transition belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points are determined by level spectroscopy analysis of the numerical diagonalization data for $4 \leq p \leq 13$ where $p(\equiv n+1)$ is the size of a unit cell. It is found that the critical strength of ferromagnetic coupling decreases with $p$ for small $p$ but increases for larger enough $p$. It is also found that the plateau for large $p$ is wide enough for moderate values of exchange coupling so that it should be easily observed experimentally. This is in contrast to the plateaus for $p = 3$ chains which are narrow for a wide range of exchange coupling even away from the critical point

Computing automorphic forms on Shimura curves over fields with arbitrary class number

We extend methods of Greenberg and the author to compute in the cohomology of a Shimura curve defined over a totally real field with arbitrary class number. Via the Jacquet-Langlands correspondence, we thereby compute systems of Hecke eigenvalues associated to Hilbert modular forms of arbitrary level over a totally real field of odd degree. We conclude with two examples which illustrate the effectiveness of our algorithms.Comment: 15 pages; final submission to ANTS I

The antiferromagnetic order in an F-AF random alternating quantum spin chain : (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3

A possibility of the uniform antiferromagnetic order is pointed out in an S=1/2 ferromagnetic (F) - antiferromagnetic (AF) random alternating Heisenberg quantum spin chain compound: (CH_3)_2 CHNH_3 Cu(Cl_x Br_{1-x})_3. The system possesses the bond alternation of strong random bonds that take +/- 2J and weak uniform AF bonds of -J. In the pure concentration limits, the model reduces to the AF-AF alternation chain at x=0 and to the F-AF alternation chain at x=1. The nonequilibrium relaxation of large-scale quantum Monte Carlo simulations exhibits critical behaviors of the uniform AF order in the intermediate concentration region, which explains the experimental observation of the magnetic phase transition. The present results suggest that the uniform AF order may survive even in the presence of the randomly located ferromagnetic bonds.Comment: 4 pages, 3 figure

Pengembangan Modul Tata Bahasa Indonesia Berbasis E-learning Untuk Mahasiswa Bipa Tingkat Pemula

Pada mahasiswa BIPA sangat jarang ditemukan bahan ajar yang dapat menunjang pembelajaraan. Begitu pula tidak terjangkaunya kelas pembelajaran disebabkan oleh permasalahan jarak. Sehingga modul berbasis e-learning merupakan jawaban dari permasalahan jarak pada pembelajaran. Penelitian ini bertujuan untuk mengembangkan modul tata bahasa Indonesia untuk BIPA tingkat pemula yang dirinci menjadi pendeskripsian pengembangan modul dan pendeskripsian kualitas modul yang didasarkan pada produk dan pengguna. Penelitian ini merupakan penelitian pengembangan dan produk yang dikembangkan berupa modul tata bahasa Indonesia berbasis e-learning untuk mahaasiswa BIPA tingkat pemula. Model pengembangan ini menggunakan model Four D Model (define, design, develop, disseminate) yang dikembangan oleh Thiagarajan, namun penelitian ini hanya sampai tahap pengembangan saja. Hasil penelitian ini adalah pengembangan modul tata bahasa untuk BIPA tingkat pemula. Penulisan dan penyusunan modul ini berdasarkan pada kurikulum BPKLN (Biro Perencanaan Kerjasama Luar Negeri) dan saran dari validator. Penilaian presentase pada penelitian ini mengadaptasi interval presentase Ratumanan (2011:34). Hasil rekapitulasi rata-rata kualitas modul uji I pada skor 3,5, uji II pada skor 4,2, dan rata-rata 3,9. Dapat dikatakan kualitas modul Baik. Respon dosen pada modul pada skor rata-rata 4,2 yang dapat dikatakan Baik. Aktivitas dan respon mahasiswa uji coba I pada skor 4,3, uji coba II pada skor 4,8, dan rata-rata 4,5 dalam hal ini aktivitas/respon mahasiswa dapat dikatakan sangat baik. Hasil belajar uji coba I dan uji coba II pada rumus t (test) pada skor 4,5 dan dapat dikatakan signifikan. Dari uraian diatas, dapat disimpulkan bahwa modul tata bahasa Indonesia tersebut layak digunakan Kata Kunci: modul, tata bahasa, e-learning

Effects of Single-site Anisotropy on Mixed Diamond Chains with Spins 1 and 1/2

Effects of single-site anisotropy on mixed diamond chains with spins 1 and 1/2 are investigated in the ground states and at finite temperatures. There are phases where the ground state is a spin cluster solid, i.e., an array of uncorrelated spin-1 clusters separated by singlet dimers. The ground state is nonmagnetic for the easy-plane anisotropy, while it is paramagnetic for the easy-axis anisotropy. Also, there are the N\'eel, Haldane, and large-$D$ phases, where the ground state is a single spin cluster of infinite size and the system is equivalent to the spin-1 Heisenberg chain with alternating anisotropy. The longitudinal and transverse susceptibilities and entropy are calculated at finite temperatures in the spin-cluster-solid phases. Their low-temperature behaviors are sensitive to anisotropy.Comment: 8 pages, 4 figure

Magnetization Plateaus in One Dimensional Sˇ=1/2\v{S}=1/2 Heisenberg Model with Dimerization and Quadrumerization

The one dimensional $S=1/2$ Heisenberg model with dimerization ($1-j$) and quadrumerization ($\delta$) in the magnetic field is studied by means of the numerical exact diagonalization of finite size systems and the conformal field theory. It is found that the magnetization plateau at half of the saturation value exists for $\delta \neq 0$. For $\delta = 0$, this model is described by the conformal field theory with central charge $c=1$ at this value of magnetization. The critical exponent $\nu$ which characterizes the $\delta$-dependence of the width of the plateau is calculated using the level spectroscopy method. The $j$-dependence of the critical exponent $\nu$ is found to be non-monotonic and discontinuous at $j = 0$. The effective theory of the magnetization plateau is also presented for various limiting cases.Comment: 5 pages, 9 figure

Quasiperiodic Hubbard chains

Low energy properties of half-filled Fibonacci Hubbard models are studied by weak coupling renormalization group and density matrix renormalization group method. In the case of diagonal modulation, weak Coulomb repulsion is irrelevant and the system behaves as a free Fibonacci chain, while for strong Coulomb repulsion, the charge sector is a Mott insulator and the spin sector behaves as a uniform Heisenberg antiferromagnetic chain. The off-diagonal modulation always drives the charge sector to a Mott insulator and the spin sector to a Fibonacci antiferromagnetic Heisenberg chain.Comment: 4 pages, 4 figures; Final version to appear in Phys. Rev. Let

Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets

It is conjectured that the Haldane phase of the S=1 antiferromagnetic Heisenberg chain and the $S=1/2$ ferromagnetic-antiferromagnetic alternating Heisenberg chain is stable against any strength of randomness, because of imposed breakdown of translational symmetry. This conjecture is confirmed by the density matrix renormalization group calculation of the string order parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and main text. Final accepted versio

Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain

The low temperature magnetization process of the ferromagnetic-antiferromagnetic Heisenberg chain is studied using the interacting boson approximation. In the low field regime and near the saturation field, the spin wave excitations are approximated by the $\delta$ function boson gas for which the Bethe ansatz solution is available. The finite temperature properties are calculated by solving the integral equation numerically. The comparison is made with Monte Carlo calculation and the limit of the applicability of the present approximation is discussed.Comment: 4 pages, 7 figure