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 $e^{+} e^{-}$ 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 $(92.4 \pm 0.4)$ with a $\pi^{\pm}$ fake rate of $(0.25 \pm 0.02)$ for the momentum range between 1.0 GeV/$c$ and 3.0 GeV/$c$ 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