6,489 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
Electron Identification in Belle
We report on electron identification methods and their performance in the
Belle experiment at the KEK-B asymmetric B-Factory storage ring.
Electrons are selected using a likelihood approach that takes information from
the electromagnetic calorimeter, the central drift chamber, and the silica
aerogel Cherenkov counters as input. We achieve an electron identification
efficiency of with a fake rate of for the momentum range between 1.0 GeV/ and 3.0 GeV/ in
laboratory frame.Comment: 20 page
The monitoring system for the aerogel Cherenkov counter of the BELLE detector
We report on a design and performances of a monitoring system developed for
the aerogel Cherenkov counters (ACC) of the BELLE detector. The system consists
of blue LEDs, a diffuser box, and optical distributors which distribute the LED
light to the ACC modules. The employed LED (NSPB series) has been observed to
have high reliability on the long term stability and the temprature dependence.
The diffuser box is employed to reduce the intrinsic non-uniformity of the LED
light intensity. The overall performances of the present monitoring system on
uniformity and intensity of the light output have been found to satisfy all the
requirements for the monitoring.Comment: 24 pages, LaTeX, 13 eps figures, to be published in Nucl. Instrum.
and Meth. A. Postscript file (4.5 MB) is available at
http://www-hep.phys.saga-u.ac.jp/~murakami/paper/xxx_accmon.p
Semi-conservative reduced speed of sound technique for low Mach number flows with large density variations
The reduced speed of sound technique (RSST) has been used for efficient
simulation of low Mach number flows in solar and stellar convection zones. The
basic RSST equations are hyperbolic, and are suitable for parallel computation
by domain decomposition. The application of RSST is limited to cases where
density perturbations are much smaller than the background density. In
addition, non-conservative variables are required to be evolved using this
method, which is not suitable in cases where discontinuities like shock waves
co-exist in a single numerical domain. In this study, we suggest a new
semi-conservative formulation of the RSST that can be applied to low Mach
number flows with large density variations. We derive the wave speed of the
original and newly suggested methods to clarify that these methods can reduce
the speed of sound without affecting the entropy wave. The equations are
implemented using the finite volume method. Several numerical tests are carried
out to verify the suggested methods. The analysis and numerical results show
that the original RSST is not applicable when mass density variations are
large. In contrast, the newly suggested methods are found to be efficient in
such cases. We also suggest variants of the RSST that conserve momentum in the
machine precision. The newly suggested variants are formulated as
semi-conservative equations, which reduce to the conservative form of the Euler
equations when the speed of sound is not reduced. This property is advantageous
when both high and low Mach number regions are included in the numerical
domain. The newly suggested forms of RSST can be applied to a wider range of
low Mach number flows.Comment: 12 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
Anomalous dip observed in intensity autocorrelation function as an inherent nature of single-photon emitters
We report the observation of an anomalous antibunching dip in intensity
autocorrelation function with photon correlation measurements on a
single-photon emitter (SPE). We show that the anomalous dip observed is a
manifestation of quantum nature of SPEs. Taking population dynamics in a
quantum two-level system into account correctly, we redefine intensity
autocorrelation function. This is of primary importance for precisely
evaluating the lowest-level probability of multiphoton generation in SPEs
toward realizing versatile pure SPEs for quantum information and communication.Comment: 10 pages including 3 figire
Different mechanics of snap-trapping in the two closely related carnivorous plants Dionaea muscipula and Aldrovanda vesiculosa
The carnivorous aquatic Waterwheel Plant (Aldrovanda vesiculosa L.) and the
closely related terrestrial Venus Flytrap (Dionaea muscipula SOL. EX J. ELLIS)
both feature elaborate snap-traps, which shut after reception of an external
mechanical stimulus by prey animals. Traditionally, Aldrovanda is considered as
a miniature, aquatic Dionaea, an assumption which was already established by
Charles Darwin. However, videos of snapping traps from both species suggest
completely different closure mechanisms. Indeed, the well-described snapping
mechanism in Dionaea comprises abrupt curvature inversion of the two trap
lobes, while the closing movement in Aldrovanda involves deformation of the
trap midrib but not of the lobes, which do not change curvature. In this paper,
we present the first detailed mechanical models for these plants, which are
based on the theory of thin solid membranes and explain this difference by
showing that the fast snapping of Aldrovanda is due to kinematic amplification
of the bending deformation of the midrib, while that of Dionaea unambiguously
relies on the buckling instability that affects the two lobes.Comment: accepted in Physical Review
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