3+1 formulation of non-ideal hydrodynamics

The equations governing dissipative relativistic hydrodynamics are formulated within the 3+1 approach for arbitrary spacetimes. Dissipation is accounted for by applying the theory of extended causal thermodynamics (Israel-Stewart theory). This description eliminates the causality violating infinite signal speeds present in the conventional Navier-Stokes equation. As an example we treat the astrophysically relevant case of stationary and axisymmetric spacetimes, including the Kerr metric. The equations take a simpler form whenever the inertia due to the dissipative contributions can be neglected.Comment: 24 pages, LateX, uses mn.sty and AMS fonts, no figures, accepted for publication in the MNRAS, also available via http://www.lsw.uni-heidelberg.de/~jpeitz/Personal.htm

Viscous accretion discs around rotating black holes

The stationary hydrodynamic equations for transonic viscous accretion discs in Kerr geometry are derived. The consistent formulation is given for the viscous angular momentum transport and the boundary conditions on the horizon of a central black hole. An expression for the thickness of the disc is obtained from the vertical Euler equation for general accretion flows with vanishing vertical velocity. Different solution topologies are identified, characterized by a sonic transition close to or far from the marginally stable orbit. A numerical method is presented that allows to integrate the structure equations of transonic accretion flows. Global polytropic solutions for the disc structure are calculated, covering each topology and a wide range of physical conditions. These solutions generally possess a sub-Keplerian angular momentum distribution and have maximum temperatures in the range $10^{11}-10^{12}$ K. Accretion discs around rotating black holes are hotter and deposit less angular momentum on the central object than accretion discs around Schwarzschild black holes.Comment: 15 pages LateX, requires mn.sty, accepted for publication in the MNRAS, figures available at http://www.lsw.uni-heidelberg.de/~jpeitz/PV

Pressure-driven Instabilities in Cylindrical Geometry: A New General Criterion

A new criterion for pressure-driven interchange instabilities in cylindrical geometry is derived, based on an alternate use of the Energy Principle. This criterion is inequivalent to Suydam's criterion and does not contain the magnetic shear. In fact, it is shown that Suydam's criterion relates to the instability of the slow magnetosonic branch, while the present criterion relates to the Alfv\'enic one, which is the most dangerous of the two. These findings explain why pressure-driven modes nearly always exist even if Suydam's criterion is satisfied by a large margin.Comment: 4 pages. Submitted to Phys. Rev. Let

Plasma physics in clusters of galaxies

Clusters of galaxies are the largest self-gravitating structures in the universe. Each cluster is filled with a large-scale plasma atmosphere, in which primordial matter is mixed with matter that has been processed inside stars. This is a wonderful plasma physics laboratory. Our diagnostics are the data we obtain from X-ray and radio telescopes. The thermal plasma is a strong X-ray source; from this we determine its density and temperature. Radio data reveal a relativistic component in the plasma, and first measurements of the intracluster magnetic field have now been made. Energization of the particles and the field must be related to the cosmological evolution of the cluster. The situation is made even richer by the few galaxies in each cluster which host radio jets. In these galaxies, electrodynamics near a massive black hole in the core of the galaxy lead to a collimated plasma beam which propagates from the nucleus out to supergalactic scales. These jets interact with the cluster plasma to form the structures known as radio galaxies. The interaction disturbs and energizes the cluster plasma. This complicates the story but also helps us understand both the radio jets and the cluster plasma.Comment: 12 pages, 6 figures, 3 in color. Invited review, to appear in Physics of Plasmas, May 2003. After publication it can be found at http://ojps.aip.org/po

Dynamics and Structure of Three-Dimensional Trans-Alfvenic Jets. II. The Effect of Density and Winds

Two three-dimensional magnetohydrodynamical simulations of strongly magnetized conical jets, one with a poloidal and one with a helical magnetic field, have been performed. In the poloidal simulation a significant sheath (wind) of magnetized moving material developed and partially stabilized the jet to helical twisting. The fundamental pinch mode was not similarly affected and emission knots developed in the poloidal simulation. Thus, astrophysical jets surrounded by outflowing winds could develop knotty structures along a straight jet triggered by pinching. Where helical twisting dominated the dynamics, magnetic field orientation along the line-of-sight could be organized by the toroidal flow field accompanying helical twisting. On astrophysical jets such structure could lead to a reversal of the direction of Faraday rotation in adjacent zones along a jet. Theoretical analysis showed that the different dynamical behavior of the two simulations could be entirely understood as a result of dependence on the velocity shear between jet and wind which must exceed a surface Alfven speed before the jet becomes unstable to helical and higher order modes of jet distortion.Comment: 25 pages, 15 figures, in press Astrophysical Journal (September

Two-dimensional vortex behavior in highly underdoped YBa_2Cu_3O_{6+x} observed by scanning Hall probe microscopy

We report scanning Hall probe microscopy of highly underdoped superconducting YBa_2Cu_3O_{6+x} with T_c ranging from 5 to 15 K which showed distinct flux bundles with less than one superconducting flux quantum (Phi_0) through the sample surface. The sub-Phi_0 features occurred more frequently for lower T_c, were more mobile than conventional vortices, and occurred more readily when the sample was cooled with an in-plane field component. We show that these features are consistent with kinked stacks of pancake vortices.Comment: 11 pages, 8 figures, accepted for publication in Physical Review

On the Dynamics and Structure of Three-Dimensional Trans-Alfvenic Jets

Three-dimensional magnetohydrodynamical simulations of strongly magnetized ``light'' conical jets have been performed. An investigation of the transition from sub-Alfv\'enic to super-Alfv\'enic flow has been made for nearly poloidal and for helical magnetic fields. The jets are stable to asymmetric modes of jet distortion provided they are sub-Alfv\'enic over most of their interior but destabilize rapidly when they become on average super-Alfv\'enic. The jets are precessed at the origin and the resulting small amplitude azimuthal motion is communicated down the jet to the Alfv\'en point where it couples to a slowly moving and rapidly growing helical twist. Significant jet rotation can contribute to destabilization via increase in the velocity shear between the jet and the external medium. Destabilization is accompanied by significant mass entrainment and the jets slow down significantly as denser external material is entrained. Synchrotron intensity images satisfactorily reveal large scale helical structures but have trouble distinguishing a large amplitude elliptical jet distortion that appears as an apparent pinching in an intensity image. Smaller scale jet distortions are not clearly revealed in intensity images, largely as a result of the relatively small total pressure variations that accompany destabilization and growing distortions. Fractional polarization is high as a result of the strong ordered magnetic fields except where the intensity image suggests cancellation of polarization vectors by integration through twisted structures.Comment: 27 pages, 11 figures, AASTeX, to appear in Oct 20 issue of ApJ, postscript versions of Figures 5 and 6 are available at this URL http://crux.astr.ua.edu/~rosen/tralf/hr.htm

PENGEMBANGAN PROGRAM PENGAJARAN BAHASA INDONESIA SEBAGAI BAHASA ASING PADA JURUSAN PENDIDIKAN BAHASA DAN SASTRA INDONESIA, FAKULTAS BAHASA DAN SENI UNIVERSITAS NEGERI YOGYAKARTA

Tujuan jangka panjang dari penelitian ini adalah melakukan pengembangan desain instruksional bagi a) Paket Program PBIPA bagi calon guru Bahasa Indonesia sebagai Bahasa Asing dan b) Paket Program Pengajaran BIPA dan membina jejaring dengan rekanan dalam dan luar negeri yang berminat terhadap pengembangan pengajaran bahasa dan budaya Indonesia. Target khusus yang akan dicapai dikaitkan dengan Kurikulum FBS UNY 2002, bahwa (1) Paket Program PBIPA merupakan paket pilihan yang berdiri sendiri dan kelulusannya diberikan sertifikat terpisah dari transkrip program S1 dan akan dibuka untuk mahasiswa Jurusan Bahasa Indonesia atau non-bahasa Indonesia. Karenanya, perlu dilakukan studi: i) desain instruksional dan beberapa aspeknya, ii) sosialisasi paket pada mahasiswa dan rekanan yang memerlukan lulusan program Paket Pengajaran PBIA, dan iii) melakukan penelitian perbaikan pengajaran untuk semua mata kuliah dalam Paket Pengajaran PBIA; (2) Paket Pengajaran BIPA akan ditekankan pada: i) penyusunan kurikulum bagi program in country 3 atau 6 bulan, pengajaran BIPA bagi keperluan khusus (Indonesian for Specific Purposes), dan penyusunan modul pembelajaran; ii) pembentukan jejaring dan kerjasama dengan universitas di luar negeri yang berminat terhadap pembelajaran bahasa dan budaya Indonesia, dan iii) membina kolaborasi dengan rekanan yang dimungkinkan terlibat dalam pelaksanaan Paket Pengajaran BIPA. Metode yang dipakai disesuaikan dengan tujuan pengembangan, antara lain: survei, observasional, dan berbagai metode yang dipakai dalam research-based teaching. Hasil penelitian ialah sebagai berikut. Dalam rancangan kurikulum 2007, program PBIPA diintegralkan dengan jumlah 144 sks. Hal ini berbeda dengan rancangan semula, yaitu memisahkan program PBIPA dari jumlah 144 sks. Pengintegralan ini sejalan dengan salah satu program I-MHERE, yaitu perintisan Jurusan PBSI menjadi program studi yang bertaraf internasional. Salah satunya ialah dengan memasuk-kan program PBIPA dalam kurikulum 2007 sebagai bagian yang integral dari jumlah 144 sks. Oleh karena hal tersebut, program ini untuk sementara waktu belum dapat dibuka untuk jurusan non PBSI. Silabus telah direvisi berdasarkan angket dan wawancara yang ditujukan kepada pihak-pihak (dosen) yang terlibat BIPA. Berdasarkan silabus yang telah direvisi ini dibuat tujuh modul yang akan diujicobakan pada tahap selanjutnya. Sosialisasi program PBIPA telah dilakukan secara nonformal kepada mahasiswa. Sosialisasi program ini secara formal baru akan dilakukan setelah kurikulum 2007 selesai dibuat. FBS, 2007 (PEND. BHS & SASTRA INDONESIA