6,527 research outputs found
Bi-Directional Energy Cascades and the Origin of Kinetic Alfv\'enic and Whistler Turbulence in the Solar Wind
The observed sub-proton scale turbulence spectrum in the solar wind raises
the question of how that turbulence originates. Observations of keV energetic
electrons during solar quite-time suggest them as possible source of free
energy to drive the turbulence. Using particle-in-cell simulations, we explore
how free energy in energetic electrons, released by an electron two-stream
instability drives Weibel-like electromagnetic waves that excite wave-wave
interactions. Consequently, both kinetic Alfv\'enic and whistler waves are
excited that evolve through inverse and forward magnetic energy cascades.Comment: 12 pages, 5 figures, Submitted to Physical Review Letter
Momentum anisotropies in the quark coalescence model
Based on the quark coalescence model, we derive relations among the momentum
anisotropies of mesons and baryons in relativistic heavy ion collisions from a
given, but arbitrary azimuthal distribution for the partons. Besides the
familiar even Fourier coefficients such as the elliptic flow, we also pay
attention to odd Fourier coefficients such as the directed flow, which has been
observed at finite rapidity even at RHIC energies.Comment: 5 page
Electron Holes and Heating in the Reconnection Dissipation Region
Using particle-in-cell simulations and kinetic theory, we explore the
current-driven turbulence and associated electron heating in the dissipation
region during 3D magnetic reconnection with a guide field. At late time the
turbulence is dominated by the Buneman and lower hybrid instabilities. Both
produce electron holes that co-exist but have very different propagation
speeds. The associated scattering of electrons by the holes enhances electron
heating in the dissipation region.Comment: 14 pages, 5 figures, submitted to GR
Nonlinear Development of Streaming Instabilities In Strongly Magnetized Plasmas
The nonlinear development of streaming instabilities in the current layers
formed during magnetic reconnection with a guide field is explored. Theory and
3-D particle-in-cell simulations reveal two distinct phases. First, the
parallel Buneman instability grows and traps low velocity electrons. The
remaining electrons then drive two forms of turbulence: the parallel
electron-electron two-stream instability and the nearly-perpendicular lower
hybrid instability. The high velocity electrons resonate with the turbulence
and transfer momentum to the ions and low velocity electrons.Comment: Accepted by PR
Shunt Active Power Filter – SIMULINK simulation and DSP-based hardware realization
2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Functional dynamics of the folded ankyrin repeats of I kappa B alpha revealed by nuclear magnetic resonance.
Inhibition of nuclear factor kappaB (NF-kappaB) is mainly accomplished by IkappaB alpha, which consists of a signal response sequence at the N-terminus, a six-ankyrin repeat domain (ARD) that binds NF-kappaB, and a C-terminal PEST sequence. Previous studies with the ARD revealed that the fifth and sixth repeats are only partially folded in the absence of NF-kappaB. Here we report NMR studies of a truncated version of IkappaB alpha, containing only the first four ankyrin repeats, IkappaB alpha(67-206). This four-repeat segment is well-structured in the free state, enabling full resonance assignments to be made. H-D exchange, backbone dynamics, and residual dipolar coupling (RDC) experiments reveal regions of flexibility. In addition, regions consistent with the presence of micro- to millisecond motions occur periodically throughout the repeat structure. Comparison of the RDCs with the crystal structure gave only moderate agreement, but an ensemble of structures generated by accelerated molecular dynamics gave much better agreement with the measured RDCs. The regions showing flexibility correspond to those implicated in entropic compensation for the loss of flexibility in ankyrin repeats 5 and 6 upon binding to NF-kappaB. The regions showing micro- to millisecond motions in the free protein are the ends of the beta-hairpins that directly interact with NF-kappaB in the complex
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