5,371 research outputs found
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
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
Correlations among superconductivity, structural instability, and band filling in Nb1-xB2 at the critical point x=0.2
We performed an extensive investigation on the correlations among
superconductivity, structural instability and band filling in Nb1-xB2
materials. Structural measurements reveal that a notable phase transformation
occurs at x=0.2, corresponding to the Fermi level (EF) in the pseudogap with
the minimum total density of states (DOS) as demonstrated by the
first-principles calculations. Superconductivity in Nb1-xB2 generally becomes
visible in the Nb-deficient materials with x=0.2. Electron energy-loss
spectroscopy (EELS) measurements on B K-edge directly demonstrated the presence
of a chemical shift arising from the structural transformation. Our
systematical experimental results in combination with theoretical analysis
suggest that the emergence of hole states in the sigma-bands plays an important
role for understanding the superconductivity and structural transition in
Nb1-xB2.Comment: 16 pages, 4 figure
Thermal Charm Production in Quark-Gluon Plasma at LHC
Charm production from the quark-gluon plasma created in the midrapidity of
central heavy ion collisions at the Large Hadron Collider (LHC) is studied in
the next-to-leading order in QCD. Using a schematic longitudinally
boost-invariant and transversally expanding fire-cylinder model, we find that
charm production could be appreciably enhanced at LHC as a result of the high
temperature that is expected to be reached in the produced quark-gluon plasma.
Sensitivities of our results to the number of charm quark pairs produced from
initial hard scattering, the initial thermalization time and temperature of the
quark-gluon plasma, and the charm quark mass are also studied.Comment: 8 pages, 9 figures; adding a figure and relevant discussion on the
sensitivity of our results to the number of charm quark pairs produced from
initial hard scattering. Version accepted for publication in PR
Evidence for s-wave pairing from measurement on lower critical field in
Magnetization measurements in the low field region have been carefully
performed on a well-shaped cylindrical and an ellipsoidal sample of
superconductor . Data from both samples show almost the same results.
The lower critical field and the London penetration depth
are thus derived. It is found that the result of normalized superfluid density
of can be well described by BCS
prediction with the expectation for an isotropic s-wave superconductivity.Comment: To appear in Phys. Rev.
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