Three dimensional particle-in-cell simulation of particle acceleration by circularly polarised inertial Alfven waves in a transversely inhomogeneous plasma

The process of particle acceleration by left-hand, circularly polarised inertial Alfven waves (IAW) in a transversely inhomogeneous plasma is studied using 3D particle-in-cell simulation. A cylindrical tube with, transverse to the background magnetic field, inhomogeneity scale of the order of ion inertial length is considered on which IAWs with frequency $0.3 \omega_{ci}$ are launched that are allowed to develop three wavelength. As a result time-varying parallel electric fields are generated in the density gradient regions which accelerate electrons in the parallel to magnetic field direction. Driven perpendicular electric field of IAWs also heats ions in the transverse direction. Such numerical setup is relevant for solar flaring loops and earth auroral zone. This first, 3D, fully-kinetic simulation demonstrates electron acceleration efficiency in the density inhomogeneity regions, along the magnetic field, of the order of 45% and ion heating, in the transverse to the magnetic field direction, of 75%. The latter is a factor of two times higher than the previous 2.5D analogous study and is in accordance with solar flare particle acceleration observations. We find that the generated parallel electric field is localised in the density inhomogeneity region and rotates in the same direction and with the same angular frequency as the initially launched IAW. Our numerical simulations seem also to suggest that the "knee" often found in the solar flare electron spectra can alternatively be interpreted as the Landau damping (Cerenkov resonance effect) of IAWs due to the wave-particle interactions.Comment: Physics of Plasmas, in-press, September 2012 issue, final accepted versio

A Semicoarsening Multigrid Algorithm for SIMD Machines

A semicoarsening multigrid algorithm suitable for use on single instruction multiple data (SIMD) architectures has been implemented on the CM-2. The method performs well for strongly anisotropic problems and for problems with coefficients jumping by orders of magnitude across internal interfaces. The parallel efficiency of this method is analyzed, and its actual performance is compared with its performance on some other machines, both parallel and nonparallel

PENGARUH PENERAPAN MEDIA AUDIO VISUAL TERHADAP PENGUASAAN KETERAMPILAN DASAR PASSING, DRIBBLING DAN SHOOTING DALAM PEMBELAJARAN FUTSAL DI SEKOLAH.

Penelitian ini dilatar belakangi oleh keadaan yang ada, yaitu keterbatasan guru, siswa, lingkungan sekolah, yang kurang memadai, metode pembelajaran yang kurang bervariasi, media yang dipergunakan kurang baik dalam proses pembelajaran. Berdasarkan latar belakang di atas, maka yang menjadi masalah dalam penelitian ini adalah apakah berpengaruh secara signifikan pengunaan media audio visual terhadap hasil belajar Passing, Dribbling dan Shooting dalam pembelajaran futsal. Pada penelitian ini bertujuan untuk mengetahui apakah berpengaruh secara signifikan secara statistik pengunaan media audio visual terhadap hasil belajar Passing, Dribbling dan Shooting dalam pembelajaran futsal. Eksperimen adalah metode yang digunakan dalam penelitian ini. Populasi dalam penelitian ini adalah siswa Pribadi Bilingual Boarding School Bandung. Sedangkan sampel yang dipakai adalah siswa kelas VII yang mengikuti esktrakulikuler futsal sebanyak 20 orang. Dalam penelitian ini menggunakan “pre test and post test control group design” sebagai desain penelitian. Alat ukur tes yang digunakan berupa tes Passing, Dribbling dan Shooting pada permainan futsal menurut Nurhasan. Berdasarkan hasil analisis pengujian signifikansi, peningkatan hasil belajar mengunakan media audio visual menunjukan perbedaan yang nyata dibandingkan dengan pembelajaran tanpa mengunakan media audio visual terhadap hasil belajar keterampilan Passing, Dribbling dan Shooting futsal. dari analisis di atas, maka dapat disimpulkan bahwa pengunaan media audio visual memberikan pengaruh signifikan secara statistik terhadap hasil belajar keterampilan, passing, dribbling, dan shooting dalam pembelajaran futsal di Sekolah;--

The Language Attitude of Border Peoples Insular Riau, West Kalimantan, East Kalimantan, North Sulawesi, and the Eastern Sunda Islands

This research aims at describing (1) the language use of border area societies (Insular Riau, West Kalimantan, East Kalimantan, North Sulawesi, and the Eastern Sunda Islands) in terms of local language (BD), Indonesian (BI), and foreign language (BA) in the domains of family, society, and occupation, (2) language activity of border area societies relating to news observation, language attention, and language constraints in mass media, (3) language attitude of border area societies towards BD, BI, and BA. The findings are as follows. First, within the family and society at large, BD is more frequently used than BI and BA. This shows that BD functions in non-formal situations. In the professional field, however, BI is more frequently used than BD. Second, people in border provinces widely observe mass media, whether printed or electronic. They also often pay attention to the language the mass media uses. Third, border societies have a positive attitude towards BD as is shown (agree/totally agree) by the answers to eight questions relating to BD. The language attitude of border societies towards BI is positive based on the answers (agree/totally agree) to seven questions concerning BI. This also means that BI is prestigious for border people, especially in formal communication. The language attitude of border societies towards BA is mixed. In as far as it is negative it implies a positive evaluation of BD and BI because people appreciate them as part of their local and national identities

Surfatron and stochastic acceleration of electrons in astrophysical plasmas

Electron acceleration by large amplitude electrostatic waves in astrophysical plasmas is studied using particle-in-cell (PIC) simulations. The waves are excited initially at the electron plasma frequency $\omega_{\rm pe}$ by a Buneman instability driven by ion beams: the parameters of the ion beams are appropriate for high Mach number astrophysical shocks, such as those associated with supernova remnants (SNRs). If $\omega_{\rm pe}$ is much higher than the electron cyclotron frequency $\Omega_{\rm e}$, the linear phase of the instability does not depend on the magnitude of the magnetic field. However, the subsequent time evolution of particles and waves depends on both $\omega_{\rm pe}/\Omega_{\rm e}$ and the size of the simulation box $L$. If $L$ is equal to one wavelength, $\lambda_0$, of the Buneman-unstable mode, electrons trapped by the waves undergo acceleration via the surfatron mechanism across the wave front. This occurs most efficiently when $\omega_{\rm pe}/\Omega_{\rm e} \simeq 100$: in this case electrons are accelerated to speeds of up $c/2$ where $c$ is the speed of light. In a simulation with $L=4\lambda_0$ and $\omega_{\rm pe}/\Omega_{\rm e} = 100$, it is found that sideband instabilities give rise to a broad spectrum of wavenumbers, with a power law tail. Some stochastic electron acceleration is observed in this case, but not the surfatron process. Direct integration of the electron equations of motion, using parameters approximating to those of the wave modes observed in the simulations, suggests that the surfatron is compatible with the presence of a broad wave spectrum if $\omega_{\rm pe}/\Omega_{\rm e}> 100$. It is concluded that a combination of stochastic and surfatron acceleration could provide an efficient generator of mildly relativistic electrons at SNR shocks

X-ray diffraction from shock-loaded polycrystals

X-ray diffraction was demonstrated from shock-compressed polycrystalline metal on nanosecond time scales. Laser ablation was used to induce shock waves in polycrystalline foils of Be, 25 to 125 microns thick. A second laser pulse was used to generate a plasma x-ray source by irradiation of a Ti foil. The x-ray source was collimated to produce a beam of controllable diameter, and the beam was directed at the Be sample. X-rays were diffracted from the sample, and detected using films and x-ray streak cameras. The diffraction angle was observed to change with shock pressure. The diffraction angles were consistent with the uniaxial (elastic) and isotropic (plastic) compressions expected for the loading conditions used. Polycrystalline diffraction will be used to measure the response of the crystal lattice to high shock pressures and through phase changes