New Insights into Dissipation in the Electron Layer During Magnetic Reconnection

Detailed comparisons are reported between laboratory observations of electron-scale dissipation layers near a reconnecting X-line and direct two-dimensional full-particle simulations. Many experimental features of the electron layers, such as insensitivity to the ion mass, are reproduced by the simulations; the layer thickness, however, is about 3-5 times larger than the predictions. Consequently, the leading candidate 2D mechanism based on collisionless electron nongyrotropic pressure is insufficient to explain the observed reconnection rates. These results suggest that, in addition to the residual collisions, 3D effects play an important role in electron-scale dissipation during fast reconnection.Comment: 17 pages, 4 figure

Experimental study of ion heating and acceleration during magnetic reconnection

Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada , Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma outflow is sub-Alfvenic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that ions are heated largely via nonclassical mechanisms. The T-i rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations show that nonclassical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process

An Obliquely Propagating Electromagnetic Drift Instability in the Lower Hybrid Frequency Range

By employing a local two-fluid theory, we investigate an obliquely propagating electromagnetic instability in the lower hybrid frequency range driven by cross-field current or relative drifts between electrons and ions. The theory self-consistently takes into account local cross-field current and accompanying pressure gradients. It is found that the instability is caused by reactive coupling between the backward propagating whistler (fast) waves in the moving electron frame and the forward propagating sound (slow) waves in the ion frame when the relative drifts are large. The unstable waves we consider propagate obliquely to the unperturbed magnetic field and have mixed polarization with significant electromagnetic components. A physical picture of the instability emerges in the limit of large wavenumber characteristic of the local approximation. The primary positive feedback mechanism is based on reinforcement of initial electron density perturbations by compression of electron fluid via induced Lorentz force. The resultant waves are qualitatively consistent with the measured electromagnetic fluctuations in reconnecting current sheet in a laboratory plasma

Modeling of magnetic island formation in magnetic reconnection experiment

Formation of a magnetic island found in the Magnetic Reconnection Experiment (MRX) [M. Yamada, H. Ji, S. Hsu, et al., Phys. Plasmas 4, 1936 (1997)] is investigated by a magnetohydrodynamic (MHD) relaxation theory and a numerical simulation. In the cohelicity injection with a mean toroidal field, the growing process of the island into a spheromak-type configuration is explained by quasistatic transition of the force-free and minimum energy state to a state with larger normalized helicity. It also turns out that no magnetic island would be generated in the counterhelicity case. The MHD simulation with inhomogeneous electric resistivity agrees with experimental results, which clearly shows formation and growth of the magnetic island in a diffusion region where the reconnection takes place

Activation of channel activity of the NMDA receptor-PSD-95 complex by guanylate kinase-associated protein (GKAP)

AbstractThe channel-associated protein PSD-95 functionally modulates NMDA receptor channels, interacting with the channels via PDZ domain of PSD-95. PSD-95 also interacts with guanylate kinase-associated protein (GKAP) through the guanylate kinase-like domain of PSD-95. Here we report that GKAP markedly potentiates the channel activity of the receptor-PSD-95 complex. However, GKAP had no effect on basic properties of the channels nor on PSD-95-induced changes in channel properties. Thus, GKAP affects the channel activity of the NMDA receptor via PSD-95 quantitatively, which may make signal transmission more efficient at postsynaptic sites

Three-loop anomalous dimension of the heavy-light quark current in HQET

The anomalous dimension of the heavy-light quark current in HQET is calculated with three-loop accuracy, as well as the renormalized heavy-quark propagator. The NNL perturbative correction to f_B/f_D is obtained.Comment: 16 pages, 7 eps figures. Typos in the discussion of fB/fD corrected. Paper is also available at http://www-ttp.physik.uni-karlsruhe.de/Preprints/ Results and REDUCE programs are available at http://www-ttp.physik.uni-karlsruhe.de/Progdata/ttp03/ttp03-10