3,320 research outputs found
Protostellar Jet and Outflow in the Collapsing Cloud Core
We investigate the driving mechanism of outflows and jets in star formation
process using resistive MHD nested grid simulations. We found two distinct
flows in the collapsing cloud core: Low-velocity outflows (sim 5 km/s) with a
wide opening angle, driven from the first adiabatic core, and high-velocity
jets (sim 50 km/s) with good collimation, driven from the protostar.
High-velocity jets are enclosed by low-velocity outflow. The difference in the
degree of collimation between the two flows is caused by the strength of the
magnetic field and configuration of the magnetic field lines. The magnetic
field around an adiabatic core is strong and has an hourglass configuration.
Therefore, the low-velocity outflow from the adiabatic core are driven mainly
by the magnetocentrifugal mechanism and guided by the hourglass-like field
lines. In contrast, the magnetic field around the protostar is weak and has a
straight configuration owing to Ohmic dissipation in the high-density gas
region. Therefore, high-velocity jet from the protostar are driven mainly by
the magnetic pressure gradient force and guided by straight field lines.
Differing depth of the gravitational potential between the adiabatic core and
the protostar cause the difference of the flow speed. Low-velocity outflows
correspond to the observed molecular outflows, while high-velocity jets
correspond to the observed optical jets. We suggest that the protostellar
outflow and the jet are driven by different cores (the first adiabatic core and
protostar), rather than that the outflow being entrained by the jet.Comment: To appear in the proceedings of the "Protostellar Jets in Context"
conference held on the island of Rhodes, Greece (7-12 July 2008
Direct Imaging of Spatially Modulated Superfluid Phases in Atomic Fermion Systems
It is proposed that the spatially modulated superfluid phase, or the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state could be observed in resonant
Fermion atomic condensates which are realized recently. We examine optimal
experimental setups to achieve it by solving Bogoliubov-de Gennes equation both
for idealized one-dimensional and realistic three-dimensional cases. The
spontaneous modulation of this superfluid is shown to be directly imaged as the
density profiles either by optical absorption or by Stern-Gerlach experiments.Comment: 4 pages, 3 figure
Theory for Photon-Assisted Macroscopic Quantum Tunneling in a Stack of Intrinsic Josephson Junctions
We propose a theory for photon-assisted macroscopic quantum tunneling (MQT)
in a stack of capacitively-coupled intrinsic Josephson junctions in which the
longitudinal Josephson plasma, i.e., longitudinal collective phase oscillation
modes, is excited. The scheme of energy-level quantization in the collective
oscillatory states is clarified in the -junction system. When the MQT occurs
from the single-plasmon states excited by microwave irradiation in the
multi-photon process to the uniform voltage state, our theory predicts that the
escape rate is proportional to . This result is consistent with the recent
observation in Bi-2212 intrinsic Josephson junctions.Comment: 5 pages, 2 figure
Knight shift detection using gate-induced decoupling of the hyperfine interaction in quantum Hall edge channels
A method for the observation of the Knight shift in nanometer-scale region in
semiconductors is developed using resistively detected nuclear magnetic
resonance (RDNMR) technique in quantum Hall edge channels. Using a gate-induced
decoupling of the hyperfine interaction between electron and nuclear spins, we
obtain the RDNMR spectra with or without the electron-nuclear spin coupling. By
a comparison of these two spectra, the values of the Knight shift can be given
for the nuclear spins polarized dynamically in the region between the relevant
edge channels in a single two-dimensional electron system, indicating that this
method has a very high sensitivity compared to a conventional NMR technique.Comment: 4 pages, 4 figures, to appear in Applied Physics Letter
Vortex state in double transition superconductors
Novel vortex phase and nature of double transition field are investigated by
two-component Ginzburg-Landau theory in a situation where fourfold-twofold
symmetric superconducting double transition occurs. The deformation from 60
degree triangular vortex lattice and a possibility of the vortex sheet
structure are discussed. In the presence of the gradient coupling, the
transition changes to a crossover at finite fields. These characters are
important to identify the multiple superconducting phase in PrOs_4_Sb_12.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Voltage-biased I-V characteristics in the multi-Josephson junction model of high T superconductor
By use of the multi-Josephson junction model, we investigate voltage-biased
I-V characteristics. Differently from the case of the single junction, I-V
characteristics show a complicated behavior due to inter-layer couplings among
superconducting phase differences mediated by the charging effect. We show that
there exist three characteristic regions, which are identified by jumps and
cusps in the I-V curve. In the low voltage region, the total current is
periodic with trigonometric functional increases and rapid drops. Then a kind
of chaotic region is followed. Above certain voltage, the total current behaves
with a simple harmonic oscillation and the I-V characteristics form a
multi-branch structure as in the current-biased case. The above behavior is the
result of the inter-layer coupling, and may be used to confirm the inter-layer
coupling mechanism of the formation of hysteresis branches.Comment: 12 pages, Latex, 4 figure
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