10,604 research outputs found
Winds from accretion disks driven by the radiation and magnetocentrifugal force
We study the 2-D, time-dependent hydrodynamics of radiation-driven winds from
luminous accretion disks threaded by a strong, large-scale, ordered magnetic
field. The radiation force is due to spectral lines and is calculated using a
generalized multidimensional formulation of the Sobolev approximation. The
effects of the magnetic field are approximated by adding a force that emulates
a magnetocentrifugal force. Our approach allows us to calculate disk winds when
the magnetic field controls the flow geometry, forces the flow to corotate with
the disk, or both. In particular, we calculate models where the lines of the
poloidal component of the field are straight and inclined to the disk at a
fixed angle. Our numerical calculations show that flows which corotate with the
disk have a larger mass loss rate than their counterparts which conserve
specific angular momentum. The difference in the mass loss rate between these
two types of winds can be several orders of magnitude for low disk luminosities
but vanishes for high disk luminosities. Winds which corotate with the disk
have much higher velocities than angular momentum conserving winds. Fixing the
wind geometry stabilizes winds which are unsteady when the geometry is derived
self-consistently. The inclination angle between the poloidal velocity and the
normal to the disk midplane is important. Non-zero inclination angles allow the
magnetocentrifugal force to increase the mass loss rate for low luminosities,
and increase the wind velocity for all luminosities. Our calculations also show
that the radiation force can launch winds from magnetized disks. The line force
can be essential in producing MHD winds from disks where the thermal energy is
too low to launch winds or where the field lines make an angle of < 30^o with
respect to the normal to the disk.Comment: LaTeX, 11 pages, 6 color postscript or PJEG files, to appear in Ap
Experimental observation of the crystallization of a paired holon state
A new excitation is observed at 201 meV in the doped-hole ladder cuprate
SrCuO, using ultraviolet resonance Raman scattering with
incident light at 3.7 eV polarized along the direction of the rungs. The
excitation is found to be of charge nature, with a temperature independent
excitation energy, and can be understood via an intra-ladder pair-breaking
process. The intensity tracks closely the order parameter of the charge density
wave in the ladder (CDW), but persists above the CDW transition
temperature (), indicating a strong local pairing above .
The 201 meV excitation vanishes in LaCaCuO,
and LaCaCuO which are samples with no holes in the
ladders. Our results suggest that the doped holes in the ladder are composite
bosons consisting of paired holons that order below .Comment: Accepted for publication in Physical Review Letters (4 figures
Observation of huge thermal spin currents in magnetic multilayers
Thermal spin pumping constitutes a novel mechanism for generation of spin
currents; however their weak intensity constitutes a major roadblock for its
usefulness. We report a phenomenon that produces a huge spin current in the
central region of a multilayer system, resulting in a giant spin Seebeck effect
in a structure formed by repetition of ferromagnet/metal bilayers. The result
is a consequence of the interconversion of magnon and electron spin currents at
the multiple interfaces. This work opens the possibility to design thin film
heterostructures that may boost the application of thermal spin currents in
spintronics
Flow profiling of a surface acoustic wave nanopump
The flow profile in a capillary gap and the pumping efficiency of an acoustic
micropump employing Surface Acoustic Waves is investigated both experimentally
and theoretically. Such ultrasonic surface waves on a piezoelectric substrate
strongly couple to a thin liquid layer and generate an internal streaming
within the fluid. Such acoustic streaming can be used for controlled agitation
during, e.g., microarray hybridization. We use fluorescence correlation
spectroscopy and fluorescence microscopy as complementary tools to investigate
the resulting flow profile. The velocity was found to depend on the applied
power somewhat weaker than linearly and to decrease fast with the distance from
the ultrasound generator on the chip.Comment: 12 pages 20 figure
Cohomogeneity one manifolds and selfmaps of nontrivial degree
We construct natural selfmaps of compact cohomgeneity one manifolds with
finite Weyl group and compute their degrees and Lefschetz numbers. On manifolds
with simple cohomology rings this yields in certain cases relations between the
order of the Weyl group and the Euler characteristic of a principal orbit. We
apply our construction to the compact Lie group SU(3) where we extend identity
and transposition to an infinite family of selfmaps of every odd degree. The
compositions of these selfmaps with the power maps realize all possible degrees
of selfmaps of SU(3).Comment: v2, v3: minor improvement
Turbulent Origin of the Galactic-Center Magnetic Field: Nonthermal Radio Filaments
A great deal of study has been carried out over the last twenty years on the
origin of the magnetic activity in the Galactic center. One of the most popular
hypotheses assumes milli-Gauss magnetic field with poloidal geometry, pervading
the inner few hundred parsecs of the Galactic-center region. However, there is
a growing observational evidence for the large-scale distribution of a much
weaker field of B \lesssim 10 micro G in this region. Here, we propose that the
Galactic-center magnetic field originates from turbulent activity that is known
to be extreme in the central hundred parsecs. In this picture the spatial
distribution of the magnetic field energy is highly intermittent, and the
regions of strong field have filamentary structures. We propose that the
observed nonthermal radio filaments appear in (or, possibly, may be identified
with) such strongly magnetized regions. At the same time, the large-scale
diffuse magnetic field is weak. Both results of our model can explain the
magnetic field measurements of the the Galactic-center region. In addition, we
discuss the role of ionized outflow from stellar clusters in producing the long
magnetized filaments perpendicular to the Galactic plane.Comment: 11 pages, accepted to ApJ Letter
An Experimental Study on Relationship Between Intellectual Concentration and Personal Mental Characteristics
1st International Conference on Human Systems Engineering and Design (IHSED2018): Future Trends and Applications, October 25-27, 2018, CHU-Université de Reims Champagne-Ardenne, France.As a proposal of new diagnosis for mental diseases, this study focused on the relationship between intellectual concentration and personal mental characteristics. It is expected that the measurement of concentration characteristics may help the diagnosis of the mental disorders because the mental characteristics such as psychiatric disease, developmental disorder and behavioral feature are supposed to be closely related to their mental activity such as concentration. When analyzing the relationship, the characteristics of concentration are expressed as 36 feature values by analyzing answering time distribution of cognitive task, and the values of concentration were compressed to 5 main factors by principal component analysis. Then the combination of the factors and one of 36 parameters of mental characteristics were given to a decision tree analysis tool
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