Relationship between daily variation of cosmogenic nuclide Be-7 concentration in atmosphere and solar activities

Daily Be-7 concentrations in air at the height of 15 m are continuously observed at 38°15.2′N, 140°20.9′E, between 2000 and 2001. The average concentration and the relative standard deviation were 4.0 mBq/m³ and 50% in 2000–2001, respectively. The Be-7 concentrations increased 2.5% with the decrease in the sunspot numbers by 6.7% for the term of two years. From the power spectral analysis, the periodicity of 26 days is shown for the daily Be-7 concentrations. The folding analysis indicates that the time variation of the Be-7 concentration is similar to that of the ground-based neutron counting rate, and the phase delay for the minimum portion of Be-7 concentration was roughly 8 days to the maximum sunspot number. These results indicate that the Be-7 concentrations in the air at ground level have 26 day periodicity as a component of time variations and the time variation is caused by the solar modulation of galactic cosmic rays, which corresponds to the variation of the sunspot number due to the rotation of the sun.     

The Sun as an inconstant star

It has been thought for a long time that the luminosity of the Sun has remained constant since the Sun evolved into the Main Sequence stage almost 4.5 billion yr ago. However, many of recent data obtained from the isotopic analyses in the tree rings, meteoritic and lunar samples have shown that the luminosity and the activity of the Sun must have been varied for such long years. It seems that the one of the most important discoveries on the variability of the Sun is that of the Maunder Minimum (1645–1715), during which the solar activity had been extremely weak so that no sunspot had been observed for almost seventy years. Furthermore, this minimum was almost coincident with the severest period of the Little Ice Age having covered the Earth from the early 14th to the middle 19th centuries. These results suggest a possible connection between the long-term variation of the Earth's climate and that of the solar activity.The Sun shines as emitting continuously the nuclear energy as light quanta. As well known, this energy is almost constantly being released from the thermonuclear reactions taking place in the central core of the Sun. Whenever the efficiency of these reactions changes due to some mechanisms to occur inside the Sun, the light emissivity from the Sun, namely, the Sun's luminosity, would change accordingly. Thus some change in the physical processes inside the Sun may always induce various kinds of variability as related to the rearrangement of the internal structure of the Sun. As a result of this kind of change, the Earth's climatic condition also seems to be critically influenced in association with the variation of the Sun's luminosity. Since it seems that the mean level of the solar activity for a long time, say, 100 yr, is dependent on the long-term change in the physical processes inside the Sun as related to the variation of the solar luminosity, the Earth's climatic condition may be necessarily changeable as dependent on the long-term variation of the solar activity. Some evidence is here shown by reviewing the historical records on the climatic change.A brief account is finally given on the possible origin of the inconstancy in the solar luminosity and activity.     

Capability for ozone high-precision retrieval on JEM/SMILES observation

We estimate the capability of ozone (O₃) retrieval with the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) instrument attached to the Exposed Facility of the Japanese Experiment Module (JEM) on the International Space Station (ISS). SMILES carries a 4-K mechanical refrigerator to cool superconducting devices in space. Since SMILES has high sensitivity thanks to the superconducting receiver, it is expected that SMILES has ability to retrieve O₃ profiles more precisely than the previous millimeter–submillimeter limb measurements from satellites.     

Motion Analysis of Trunk Using Simplified Human Model in Sagittal Plane

The mass of very small vehicles is often comparable to that of their drivers,and thus there is a greater degree of coupling between the vehicle and the driver,compared with a case for traditional vehicles.When developing small vehicles,it is necessary to give ample consideration to the dynamics of the person who ride them.Here,a model of a human body riding a small personal vehicle was constructed to investigate the dynamics of the person inside such a vehicle.Moreover,an experiment on posture maintenance by acceleration of direction of travel was conducted and the parameters for posture control were identified using agenetic algorithm.Results shows that body behavior could be successfully simulated using the proposed model,and the control parameters were effective in determining the posture maintenance characteristics of the vehicle occupant.     

Effect of liquid bridge form on oscillatory thermocapillary convection under 1 g and μg conditions

This study analyses the effect of temperature difference between hot and cool disk (ΔT), and non-dimensional liquid bridge volume (V/V_o) on the transition process from steady thermocapillary convection to periodic or chaotic thermocapillary convection in a liquid bridge modeled after the floating zone method under normal gravity and microgravity conditions. From normal gravity and drop shaft experiments, the difference of the regime of the steady state and the oscillatory state was clarified on the ΔT−V/V_o plane under 1 g and μg conditions. A gap or stability region was observed in the specific V/V_o range under 1 g conditions. In the gap or stable region, after the gravity changed from 1 g to μg conditions, the temperature signals showed oscillation. From these results, the critical temperature difference under the μg conditions appeared to be smaller than that under the 1 g conditions. Temperature signals were defined as 6 different types of states. The various temperature oscillatory state regimes were obtained on a ΔT−V/V_o plane under 1 g and μg conditions. Under μg conditions, in these experimental conditions, all temperature oscillatory states exhibited only the Periodic state.     

Studies on the imaging characteristics of Yohkoh Soft X-ray Telescope: Optical aberration and scattering

In order to better understand the characteristics of Yohkoh Soft X-ray Telescope (SXT) mirror, we have analyzed the in-flight overexposed image (the starburst image) obtained during the solar flare observation. It has been revealed from our study that the intensity distribution inside the shadows shown in the scattering difference image contains little of the scattered component of the PSF and matches almost correctly the extension of the PSF core profile. Also it is found that the scattering wing of the SXT PSF is connected smoothly to the PSF core within the distance of about 100–200 arcsec from the peak. With numerical simulations we have shown that an increase in energy affects not only the level of scattering wing, but also both the shape and the absolute level of the PSF core. The results have revealed, however, that the energy dependence for the SXT PSF cannot be easily estimated with the data obtained from one filter alone, which implies that the data analysis using multiple filters will enable us to determine the absolute amount of scattered component as well as the energy dependence of the SXT PSF. Details on the analysis of starburst image and the results from numerical simulations will be introduced and discussed thoroughly.     

Future of Venus Research and Exploration

Despite the tremendous progress that has been made since the publication of the Venus II book in 1997, many fundamental questions remain concerning Venus’ history, evolution and current geologic and atmospheric processes. The international science community has taken several approaches to prioritizing these questions, either through formal processes like the Planetary Decadal Survey in the United States and the Cosmic Vision in Europe, or informally through science definition teams utilized by Japan, Russia, and India. These questions are left to future investigators to address through a broad range of research approaches that include Earth-based observations, laboratory and modeling studies that are based on existing data, and new space flight missions. Many of the highest priority questions for Venus can be answered with new measurements acquired by orbiting or in situ missions that use current technologies, and several plausible implementation concepts have been studied and proposed for flight. However, observations needed to address some science questions pose substantial technological challenges, for example, long term survival on the surface of Venus and missions that require surface or controlled aerial mobility. Missions enabled by investments in these technologies will open the door to completely new ways of exploring Venus to provide unique insights into Venus’s past and the processes at work today.     

The origin of cosmic rays as viewed from their source composition

Based on the fact that the chemical composition of cosmic rays in their sources is similar to that of the interstellar clouds or grains which are relatively rich in refractory and siderophile elements as compared to the chemical composition of the solar atmosphere, it is shown that cosmic ray source matter can be identified as the dusts or grains observed in the envelope of red supergiants or the matter originally ejected from supernova explosions and that it must have passed through a state as reaching to 1000K or less in temperature.     

Experimental study of impact-cratering damage on brittle cylindrical column model as a fundamental component of space architecture

The cylindrical column of brittle material processed from soil and rock is a fundamental component of architectures on the surface of solid bodies in the solar system. One of the most hazardous events for the structure is damaging by hypervelocity impacts by meteoroids and debris. In such a background, cylindrical columns made of plaster of Paris and glass-bead-sintered ceramic were impacted by spherical projectiles of nylon, glass, and steel at velocity of about 1–4.5 km/s. Measured crater radii, depth, and excavated mass expressed by a function of the cylinder radius are similar irrespective of the target material, if those parameters are normalized by appropriate parameters of the crater produced on the flat-surface target. The empirical scaling relations of the normalized crater radii and depth are provided. Using them, crater dimensions and excavated mass of crater on cylindrical surface of any radius can be predicted from the existing knowledge of those for flat surface. Recommendation for the minimum diameter of a cylinder so as to resist against a given impact is provided.     

High-cadence Hα imaging of solar flares

The Hα observation is a powerful tool to study the high-energy aspect of solar flares. Spiky brightenings of flare kernels at the Hα center reflect the rapid fluctuation in particle acceleration; linear polarization of Hα emission might be evidence of accelerated protons; red-shifts of the Hα line are caused by the chromospheric evaporation. To study the spiky brightenings of flare kernels with high-cadence imaging at the Hα center, a high-speed Hα camera for the Solar Flare Telescope at Mitaka, NAOJ, had been developed and it started the regular observation in 2001 July. However, the polarimetry and the Dopplermetry are also important and they are required to be carried out in parallel with the high-cadence imaging at the Hα center. Then, we upgraded the original high-speed Hα camera to a new Hα camera system for the multi-aspect Hα observations, which performs all of the high-cadence imaging, the linear polarization measurements, and the off-band imaging for velocity measurements. The new system started the observation in 2002 July. In this paper, the multi-aspect Hα imaging system is described and sample Hα images are presented.