989 research outputs found
Improvement of solar cycle prediction: Plateau of solar axial dipole moment
Aims. We report the small temporal variation of the axial dipole moment near
the solar minimum and its application to the solar cycle prediction by the
surface flux transport (SFT) model. Methods. We measure the axial dipole moment
using the photospheric synoptic magnetogram observed by the Wilcox Solar
Observatory (WSO), the ESA/NASA Solar and Heliospheric Observatory Michelson
Doppler Imager (MDI), and the NASA Solar Dynamics Observatory Helioseismic and
Magnetic Imager (HMI). We also use the surface flux transport model for the
interpretation and prediction of the observed axial dipole moment. Results. We
find that the observed axial dipole moment becomes approximately constant
during the period of several years before each cycle minimum, which we call the
axial dipole moment plateau. The cross-equatorial magnetic flux transport is
found to be small during the period, although the significant number of
sunspots are still emerging. The results indicates that the newly emerged
magnetic flux does not contributes to the build up of the axial dipole moment
near the end of each cycle. This is confirmed by showing that the time
variation of the observed axial dipole moment agrees well with that predicted
by the SFT model without introducing new emergence of magnetic flux. These
results allows us to predict the axial dipole moment in Cycle 24/25 minimum
using the SFT model without introducing new flux emergence. The predicted axial
dipole moment of Cycle 24/25 minimum is 60--80 percent of Cycle 23/24 minimum,
which suggests the amplitude of Cycle 25 even weaker than the current Cycle 24.
Conclusions. The plateau of the solar axial dipole moment is an important
feature for the longer prediction of the solar cycle based on the SFT model.Comment: 5 pages, 3 figures, accepted for publication in A&A Lette
Acute Geometric Changes of the Mitral Annulus after Coronary Occlusion: A Real-Time 3D Echocardiographic Study
We performed real-time 3D echocardiography in sixteen sheep to compare acute geometric changes in the mitral annulus after left anterior descending coronary artery (LAD, n=8) ligation and those after left circumflex coronary artery (LCX, n=8) ligation. The mitral regurgitation (MR) was quantified by regurgitant volume (RV) using the proximal isovelocity surface area method. The mitral annulus was reconstructed through the hinge points of the annulus traced on 9 rotational apical planes (angle increment=20°). Mitral annular area (MAA) and the ratio of antero-posterior (AP) to commissure-commissure (CC) dimension of the annulus were calculated. Non-planar angle (NPA) representing non-planarity of the annulus was measured. After LCX occlusion, there were significant increases of the MAA during both early and late systole (p<0.01) with significant MR (RV: 30±14 mL), while there was neither a significant increase of MAA, nor a significant MR (RV: 4±5 mL) after LAD occlusion. AP/CC ratio (p<0.01) and NPA (p<0.01) also significantly increased after LCX occlusion during both early and late systole. The mitral annulus was significantly enlarged in the antero-posterior direction with significant decrease of non-planarity compared to LAD occlusion immediately after LCX occlusion
Lectures on the Asymptotic Expansion of a Hermitian Matrix Integral
In these lectures three different methods of computing the asymptotic
expansion of a Hermitian matrix integral is presented. The first one is a
combinatorial method using Feynman diagrams. This leads us to the generating
function of the reciprocal of the order of the automorphism group of a tiling
of a Riemann surface. The second method is based on the classical analysis of
orthogonal polynomials. A rigorous asymptotic method is established, and a
special case of the matrix integral is computed in terms of the Riemann
-function. The third method is derived from a formula for the
-function solution to the KP equations. This method leads us to a new
class of solutions of the KP equations that are
\emph{transcendental}, in the sense that they cannot be obtained by the
celebrated Krichever construction and its generalizations based on algebraic
geometry of vector bundles on Riemann surfaces. In each case a mathematically
rigorous way of dealing with asymptotic series in an infinite number of
variables is established
Polar Field Reversal Observations with Hinode
We have been monitoring yearly variation in the Sun's polar magnetic fields
with the Solar Optical Telescope aboard {\it Hinode} to record their evolution
and expected reversal near the solar maximum. All magnetic patches in the
magnetic flux maps are automatically identified to obtain the number density
and magnetic flux density as a function of th total magnetic flux per patch.
The detected magnetic flux per patch ranges over four orders of magnitude
( -- Mx). The higher end of the magnetic flux in the polar
regions is about one order of magnitude larger than that of the quiet Sun, and
nearly that of pores. Almost all large patches ( Mx) have the
same polarity, while smaller patches have a fair balance of both polarities.
The polarity of the polar region as a whole is consequently determined only by
the large magnetic concentrations. A clear decrease in the net flux of the
polar region is detected in the slow rising phase of the current solar cycle.
The decrease is more rapid in the north polar region than in the south. The
decrease in the net flux is caused by a decrease in the number and size of the
large flux concentrations as well as the appearance of patches with opposite
polarity at lower latitudes. In contrast, we do not see temporal change in the
magnetic flux associated with the smaller patches ( Mx) and that of
the horizontal magnetic fields during the years 2008--2012.Comment: 21 pages, 7 figures. Accepted for publication in Ap
- …