13,893 research outputs found
Orbital symmetry of a triplet pairing in a heavy Fermion superconductor UPt_3
The orbital symmetry of the superconducting order parameter in UPt_3 is
identified by evaluating the directionally dependent thermalconductivity and
ultrasound attenuation in the clean limit and compared with the existing data
for both basal plane and the c-axis of a hexagonal crystal. The resulting two
component orbital part expressed by (\lambda_x(k), \lambda_y(k)) is combined
with the previously determined triplet spin part, leading to clean limit and
compared with the existing data for both basal plane and the c-axis of a
hexagonal crystal. The resulting two component orbital part expressed by
(\lambda_x(k), \lambda_y(k)) is combined with the previously determined triplet
spin part, leading to the order parameter of either the non-unitary bipolar
state of the form: d(k) = b \lambda_x(k) + i j \lambda_y(k) or the unitary
planar state of the form: d(k) = b \lambda_x(k) + j \lambda_y(k) where b \perp
j = c, or a with the hexagonal unit vectors a, b and c. The d vector is
rotatable in the plane spanned by a and c perpendicular to b under weak applied
c-axis field because of the weak spin orbit coupling. Experiments are proposed
to distinguish between the equally possible these states.Comment: 8 pages, 8 eps figure
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
Impact of Protostellar Outflow on Star Formation: Effects of Initial Cloud Mass
Star formation efficiency controlled by the protostellar outflow in a single
cloud core is investigated by three-dimensional resistive MHD simulations.
Starting from the prestellar cloud core, the star formation process is
calculated until the end of the main accretion phase. In the calculations, the
mass of the prestellar cloud is parameterized. During the star formation, the
protostellar outflow is driven by the circumstellar disk. The outflow extends
also in the transverse direction until its width becomes comparable to the
initial cloud scale, and thus, the outflow has a wide opening angle of >40
degrees. As a result, the protostellar outflow sweeps up a large fraction of
the infalling material and ejects it into the interstellar space. The outflow
can eject at most over half of the host cloud mass, significantly decreasing
star formation efficiency. The outflow power is stronger in clouds with a
greater initial mass. Thus, the protostellar outflow effectively suppresses
star formation efficiency in a massive cloud. The outflow weakens significantly
and disappears in several free-fall timescales of the initial cloud after the
cloud begins to collapse. The natal prestellar core influences the lifetime and
size of the outflow. At the end of the main accretion phase, a massive
circumstellar disk comparable in mass to the protostar remains. Calculations
show that typically, ~30% of the initial cloud mass is converted into the
protostar and ~20% remains in the circumstellar disk, while ~40% is ejected
into the interstellar space by the protostellar outflow. Therefore, a single
cloud core typically has a star formation efficiency of 30-50%.Comment: 43 pages, 14 figures, Submitted to MNRAS. For high resolution figures
see http://jupiter.geo.kyushu-u.ac.jp/machida/arxiv/sfe.pd
Recurrent Planet Formation and Intermittent Protostellar Outflows Induced by Episodic Mass Accretion
The formation and evolution of a circumstellar disk in magnetized cloud cores
is investigated from prestellar core stage until sim 10^4 yr after protostar
formation. In the circumstellar disk, fragmentation first occurs due to
gravitational instability in a magnetically inactive region, and
substellar-mass objects appear. The substellar-mass objects lose their orbital
angular momenta by gravitational interaction with the massive circumstellar
disk and finally fall onto the protostar. After this fall, the circumstellar
disk increases its mass by mass accretion and again induces fragmentation. The
formation and falling of substellar-mass objects are repeated in the
circumstellar disk until the end of the main accretion phase. In this process,
the mass of fragments remain small, because the circumstellar disk loses its
mass by fragmentation and subsequent falling of fragments before it becomes
very massive. In addition, when fragments orbit near the protostar, they
disturb the inner disk region and promote mass accretion onto the protostar.
The orbital motion of substellar-mass objects clearly synchronizes with the
time variation of the accretion luminosity of the protostar. Moreover, as the
objects fall, the protostar shows a strong brightening for a short duration.
The intermittent protostellar outflows are also driven by the circumstellar
disk whose magnetic field lines are highly tangled owing to the orbital motion
of fragments. The time-variable protostellar luminosity and intermittent
outflows may be a clue for detecting planetary-mass objects in the
circumstellar disk.Comment: 48 pages, 16 figures, accepted for publication in Ap
Fixed field alternating gradient
The concept of a fixed field alternating gradient (FFAG) accelerator was
invented in the 1950s. Although many studies were carried out up to the late
1960s, there has been relatively little progress until recently, when it
received widespread attention as a type of accelerator suitable for very fast
acceleration and for generating high-power beams. In this paper, we describe
the principles and design procedure of a FFAG accelerator.Comment: presented at the CERN Accelerator School CAS 2011: High Power Hadron
Machines, Bilbao, 24 May - 2 June 201
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