360 research outputs found
Formulating Mass-Loss Rates for Sun-like Stars: A Hybrid Model Approach
We observe an enhanced stellar wind mass-loss rate from low-mass stars
exhibiting higher X-ray flux. This trend, however, does not align with the Sun,
where no evident correlation between X-ray flux and mass-loss rate is present.
To reconcile these observations, we propose a hybrid model for the stellar wind
from solar-type stars, incorporating both Alfv\'en wave dynamics and flux
emergence-driven interchange reconnection, an increasingly studied concept
guided by the latest heliospheric observations. For establishing a mass-loss
rate scaling law, we perform a series of magnetohydrodynamic simulations across
varied magnetic activities. Through a parameter survey concerning the surface
(unsigned) magnetic flux () and the open-to-surface magnetic
flux ratio (), we derive a
scaling law of the mass-loss rate given by , where , , and . By comparing cases with
and without flux emergence, we find that the increase in the mass-loss rate
with the surface magnetic flux can be attributed to the influence of flux
emergence. Our scaling law demonstrates an agreement with solar wind
observations spanning 40 years, exhibiting superior performance when compared
to X-ray-based estimations. Our findings suggest that flux emergence may play a
significant role in the stellar winds of low-mass stars, particularly those
originating from magnetically active stars.Comment: Accepted for publication in The Astrophysical Journa
Geometric flux formula for the gravitational Wilson loop
Finding diffeomorphism-invariant observables to characterize the properties
of gravity and spacetime at the Planck scale is essential for making progress
in quantum gravity. The holonomy and Wilson loop of the Levi-Civita connection
are potentially interesting ingredients in the construction of quantum
curvature observables. Motivated by recent developments in nonperturbative
quantum gravity, we establish new relations in three and four dimensions
between the holonomy of a finite loop and certain curvature integrals over the
surface spanned by the loop. They are much simpler than a gravitational version
of the nonabelian Stokes' theorem, but require the presence of totally geodesic
surfaces in the manifold, which follows from the existence of suitable Killing
vectors. We show that the relations are invariant under smooth surface
deformations, due to the presence of a conserved geometric flux.Comment: 36 pages, 5 figures; minor text changes, clarifying the role of
diffeomorphism invariance; agrees with published versio
Photoinduced charge separation in Q1D heterojunction materials: Evidence for electron-hole pair separation in mixed-halide solids
Resonance Raman experiments on doped and photoexcited single crystals of
mixed-halide complexes (=Pt; =Cl,Br) clearly indicate charge
separation: electron polarons preferentially locate on PtBr segments while hole
polarons are trapped within PtCl segments. This polaron selectivity,
potentially very useful for device applications, is demonstrated theoretically
using a discrete, 3/4-filled, two-band, tight-binding, extended Peierls-Hubbard
model. Strong hybridization of the PtCl and PtBr electronic bands is the
driving force for separation.Comment: n LaTeX, figures available by mail from JTG ([email protected]
Competing Ground States of the New Class of Halogen-Bridged Metal Complexes
Based on a symmetry argument, we study the ground-state properties of
halogen-bridged binuclear metal chain complexes. We systematically derive
commensurate density-wave solutions from a relevant two-band Peierls-Hubbard
model and numerically draw the the ground-state phase diagram as a function of
electron-electron correlations, electron-phonon interactions, and doping
concentration within the Hartree-Fock approximation. The competition between
two types of charge-density-wave states, which has recently been reported
experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp
Quantum and Thermal Phase Transitions of Halogen-Bridged Binuclear Transition-Metal Complexes
Aiming to settle the controversial observations for halogen-bridged binuclear
transition-metal (MMX) complexes, finite-temperature Hartree-Fock calculations
are performed for a relevant two-band Peierls-Hubbard model. Thermal, as well
as quantum, phase transitions are investigated with particular emphasis on the
competition between electron itinerancy, electron-phonon interaction and
electron-electron correlation. Recently observed distinct thermal behaviors of
two typical MMX compounds Pt_2(CH_3CS_2)_4I and
(NH_4)_4[Pt_2(P_2O_5H_2)_4I]2H_2O are supported and further tuning of their
electronic states is predicted.Comment: 5 pages, 3 figures embedded, to be published in J. Phys. Soc. Jpn.
Vol.70, No.5 (2001
Holographic Dark Energy Like in Gravity
We investigate the corresponding relation between gravity and
holographic dark energy. We introduce a kind of energy density from
which has role of the same as holographic dark energy.
We obtain the differential equation that specify the evolution of the
introduced energy density parameter based on varying gravitational constant. We
find out a relation for the equation of state parameter to low redshifts which
containing varying correction.Comment: 10 page
Quasiperiodic functions theory and the superlattice potentials for a two-dimensional electron gas
We consider Novikov problem of the classification of level curves of
quasiperiodic functions on the plane and its connection with the conductivity
of two-dimensional electron gas in the presence of both orthogonal magnetic
field and the superlattice potentials of special type. We show that the
modulation techniques used in the recent papers on the 2D heterostructures
permit to obtain the general quasiperiodic potentials for 2D electron gas and
consider the asymptotic limit of conductivity when . Using the
theory of quasiperiodic functions we introduce here the topological
characteristics of such potentials observable in the conductivity. The
corresponding characteristics are the direct analog of the "topological
numbers" introduced previously in the conductivity of normal metals.Comment: Revtex, 16 pages, 12 figure
Temporal Evolution of Spatially-Resolved Individual Star Spots on a Planet-Hosting Solar-type Star: Kepler 17
Star spot evolution is visible evidence of the emergence/decay of the
magnetic field on stellar surface, and it is therefore important for the
understanding of the underlying stellar dynamo and consequential stellar
flares. In this paper, we report the temporal evolution of individual star spot
area on the hot-Jupiter-hosting active solar-type star Kepler 17 whose transits
occur every 1.5 days. The spot longitude and area evolution are estimated (1)
from the stellar rotational modulations of Kepler data and (2) from the
brightness enhancements during the exoplanet transits caused by existence of
large star spots. As a result of the comparison, number of spots, spot
locations, and the temporal evolution derived from the rotational modulations
is largely different from those of in-transit spots. We confirm that although
only two light curve minima appear per rotation, there are clearly many spots
present on the star. We find that the observed differential intensity changes
are sometimes consistent with the spot pattern detected by transits, but they
sometimes do not match with each other. Although the temporal evolution derived
from the rotational modulation differs from those of in-transit spots to a
certain degree, the emergence/decay rates of in-transit spots are within an
order of magnitude of those derived for sunspots as well as our previous
research based only on rotational modulations. This supports a hypothesis that
the emergence/decay of sunspots and extremely-large star spots on solar-type
stars occur through the same underlying processes.Comment: 37 pages, 12 figures, 1 table. Accepted for publication in The
Astrophysical Journa
Soliton excitations in halogen-bridged mixed-valence binuclear metal complexes
Motivated by recent stimulative observations in halogen (X)-bridged binuclear
transition-metal (M) complexes, which are referred to as MMX chains, we study
solitons in a one-dimensional three-quarter-filled charge-density-wave system
with both intrasite and intersite electron-lattice couplings. Two distinct
ground states of MMX chains are reproduced and the soliton excitations on them
are compared. In the weak-coupling region, all the solitons are degenerate to
each other and are uniquely scaled by the band gap, whereas in the
strong-coupling region, they behave differently deviating from the scenario in
the continuum limit. The soliton masses are calculated and compared with those
for conventional mononuclear MX chains.Comment: 9 pages, 10 figures embedded, to be published in J. Phys. Soc. Jpn.
71, No. 1 (2002
Solar Intranetwork Magnetic Elements: bipolar flux appearance
The current study aims to quantify characteristic features of bipolar flux
appearance of solar intranetwork (IN) magnetic elements. To attack such a
problem, we use the Narrow-band Filter Imager (NFI) magnetograms from the Solar
Optical Telescope (SOT) on board \emph{Hinode}; these data are from quiet and
an enhanced network areas. Cluster emergence of mixed polarities and IN
ephemeral regions (ERs) are the most conspicuous forms of bipolar flux
appearance within the network. Each of the clusters is characterized by a few
well-developed ERs that are partially or fully co-aligned in magnetic axis
orientation. On average, the sampled IN ERs have total maximum unsigned flux of
several 10^{17} Mx, separation of 3-4 arcsec, and a lifetime of 10-15 minutes.
The smallest IN ERs have a maximum unsigned flux of several 10^{16} Mx,
separations less than 1 arcsec, and lifetimes as short as 5 minutes. Most IN
ERs exhibit a rotation of their magnetic axis of more than 10 degrees during
flux emergence. Peculiar flux appearance, e.g., bipole shrinkage followed by
growth or the reverse, is not unusual. A few examples show repeated
shrinkage-growth or growth-shrinkage, like magnetic floats in the dynamic
photosphere. The observed bipolar behavior seems to carry rich information on
magneto-convection in the sub-photospheric layer.Comment: 26 pages, 14 figure
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