Simulasi Waveguide Sederhana Menggunakan Metode Galerkin dalam Matlab

Tulisan ini, merupakan sebuah tutorial bagaimana mengimplementasikan metode Galerkin untuk menyelesaikan persamaan Helmholtz. Persamaan ini, misalnya digunakan untuk memodelkan persamaan gelombang skalar. Misalnya untuk memperoleh informasi perilaku waveguide, persamaan Helmholtz perlu diselesaikan secara numerik, mengingat bentuk geometrik bahan penyusun menyebabkan solusi analitik sulit didapat. Persamaan gelombang skalar untuk waveguide isotropik homogen digunakan untuk memperkenalkan FEM. Untuk lebih sederhananya, digunakan elemen segitiga orde pertama. Makalah ini menunjukkan bagaimana pengetahuan tentang metode elemen hingga (FEM) dapat dipelajari dalam waktu singkat dengan menggunakan MATLAB. Hal ini menunjukkan bagaimana pengetahuan yang diperoleh dapat diperluas untuk masalah elektromagnetik lainnya

X-ray Scattering Study of the spin-Peierls transition and soft phonon behavior in TiOCl

We have studied the S=1/2 quasi-one-dimensional antiferromagnet TiOCl using single crystal x-ray diffraction and inelastic x-ray scattering techniques. The Ti ions form staggered spin chains which dimerize below Tc1 = 66 K and have an incommensurate lattice distortion between Tc1 and Tc2 = 92 K. Based on our measurements of the intensities, wave vectors, and harmonics of the incommensurate superlattice peaks, we construct a model for the incommensurate modulation. The results are in good agreement with a soliton lattice model, though some quantitative discrepancies exist near Tc2. The behavior of the phonons has been studied using inelastic x-ray scattering with ~2 meV energy resolution. For the first time, a zone boundary phonon which softens at the spin-Peierls temperature Tsp has been observed. Our results show reasonably good quantitative agreement with the Cross-Fisher theory for the phonon dynamics at wave vectors near the zone boundary and temperatures near Tsp. However, not all aspects of the data can be described, such as the strong overdamping of the soft mode above Tsp. Overall, our results show that TiOCl is a good realization of a spin-Peierls system, where the phonon softening allows us to identify the transition temperature as Tsp=Tc2=92 KComment: 14 pages, 14 figure

Observation of a continuous phase transition in a shape-memory alloy

Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and pressure-dependent electrical transport measurements have been made on single crystals of AuZn and Au_{0.52}Zn_{0.48} above and below their martensitic transition temperatures (T_M=64K and 45K, respectively). In each composition, elastic neutron scattering detects new commensurate Bragg peaks (modulation) appearing at Q = (1.33,0.67,0) at temperatures corresponding to each sample's T_M. Although the new Bragg peaks appear in a discontinuous manner in the Au_{0.52}Zn_{0.48} sample, they appear in a continuous manner in AuZn. Surprising us, the temperature dependence of the AuZn Bragg peak intensity and the specific-heat jump near the transition temperature are in favorable accord with a mean-field approximation. A Landau-theory-based fit to the pressure dependence of the transition temperature suggests the presence of a critical endpoint in the AuZn phase diagram located at T_M*=2.7K and p*=3.1GPa, with a quantum saturation temperature \theta_s=48.3 +/- 3.7K.Comment: 6 figure

SIMULASI WAVEGUIDE SEDERHANA MENGGUNAKAN METODE GALERKIN DALAM MATLAB

Tulisan ini, merupakan sebuah tutorial bagaimana mengimplementasikan metode Galerkin untuk menyelesaikan persamaan Helmholtz. Persamaan ini, misalnya digunakan untuk memodelkan persamaan gelombang skalar. Misalnya untuk memperoleh informasi perilaku waveguide, persamaan Helmholtz perlu diselesaikan secara numerik, mengingat bentuk geometrik bahan penyusun menyebabkan solusi analitik sulit didapat. Persamaan gelombang skalar untuk waveguide isotropik homogen digunakan untuk memperkenalkan FEM. Untuk lebih sederhananya, digunakan elemen segitiga orde pertama. Makalah ini menunjukkan bagaimana pengetahuan tentang metode elemen hingga (FEM) dapat dipelajari dalam waktu singkat dengan menggunakan MATLAB. Hal ini menunjukkan bagaimana pengetahuan yang diperoleh dapat diperluas untuk masalah elektromagnetik lainnya

Cluster Dynamical Mean-field calculations for TiOCl

Based on a combination of cluster dynamical mean field theory (DMFT) and density functional calculations, we calculated the angle-integrated spectral density in the layered $s=1/2$ quantum magnet TiOCl. The agreement with recent photoemission and oxygen K-edge X-ray absorption spectroscopy experiments is found to be good. Th e improvement achieved with this calculation with respect to previous single-site DMFT calculations is an indication of the correlated nature and low-dimensionality of TiOCl.Comment: 9 pages, 3 figures, improved version as publishe

Six-reflection meV-monochromator for synchrotron radiation

A design is presented for a cryogenically stabilized monochromator for 10–40 keV synchrotron radiation that uses six crystal reflections to achieve a meV-bandpass with high efficiency

Explaining varieties of corruption in the Afghan justice sector

© 2015 Taylor & Francis. Judicial reform in Afghanistan is seriously undermined by systemic corruption that has resulted in low legitimacy of the state and weak rule of law. This article reviews the main shortcomings in the Afghan justice system with reference to 70 interviews conducted in Kabul. Building on legal pluralism and a political economic approach, the shortcomings and causes and consequences of corruption in the Afghan justice sector are highlighted. These range from low pay, resulting in bribery; criminal and political intrusion into the judiciary; non-adherence to meritocracy, with poorly educated judges and prosecutors; and low funding in the judicial sector resulting in weak case tracking and human rights abuses in the countryside. This is followed by sociological approaches: understanding corruption from a non-Western approach and emphasis on religion, morality and ethics in order to curb it