Dynamical interpretation of the very hot region appearing at the top of the loop     

Kzunari Shibata  Yutaka Uchida  Takashi Sakurai 《Solar physics》1983,86(1-2):345-351

In order to explain the appearance of a hard X-ray source at the top of a loop, we present a model in which the dynamical effects of the dark filament mass infallng along the loop in association with the “disparition brusque” plays an important role. The crash of the infalling mass produces high temperature regions in the low corona above the two footpoints of the loop, and the up-going shocks, created in the crash and strengthened in propagating upwards along the steep density gradient in the tail of the infalling mass, produce a very high temperature (10⁸ K) region upon colliding with each other near the top of the loop. Successive occurrence of this process in successively higher loops in magnetic arcade may account for the sources of gradual hard X-ray bursts appearing at the top of the loop-like structure.  相似文献   

Evidence for anomalous body-wave radiation between 0.3 and 0.7 Hz from the 1985 September 19 Michoacan, Mexico earthquake     

S. K. Singh  A. Mori  E. Mena  F. Krüger  R. Kind 《Geophysical Journal International》1990,101(1):37-48

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Excess heating of corona and chromosphere above magnetic regions by non-linear Alfvén waves     

Yutaka Uchida  Osamu Kaburaki 《Solar physics》1974,35(2):451-466

Excess heating of the active region solar atmosphere is interpreted by the decay of MHD slow-mode waves produced in the corona through the non-linear coupling of Alfvén waves supplied from subphotospheric layers. It is stressed that the Alfvén-mode waves may be very efficiently generated directly in the convection layer under the photosphere in magnetic regions, and that such magnetic regions, at the same time, provide the ‘transparent windows’ for Alfvén waves in regard to the Joule and frictional dissipations in the photospheric and subphotospheric layers. Though the Alfvén waves suffer considerable reflection in the chromosphere and in the transition layer, a certain fraction of this large flux is propagated out to the corona, and a large velocity amplitude exceeding the local Alfvén velocity is attained during the propagation along the magnetic tubes of force into a region of lower density and weaker magnetic field. The otherwise divergence-free velocity field in Alfvén waves gets involved in such a case with a compressional component (slow-mode waves) which again is of considerable velocity amplitude relative to the local acoustic velocity when estimated by using the formulation for non-linear coupling between MHD wave modes derived by Kaburaki and Uchida (1971). Therefore, the compressional waves thus produced through the non-linear coupling of Alvén waves will eventually be thermalized to provide a heat source. The introduction of this non-linear coupling process and the subsequent thermalization of thus produced slow-mode waves may provide means of converting the otherwise dissipation-free Alfvén mode energy into heat in the corona. The liberated heat will readily be redistributed by conduction along the magnetic lines of force, with higher density as a consequence of increased scale height, and thus the loop-like structure of the coronal condensations (or probably also the thread-like feature of the general corona) may be explained in a natural fashion.  相似文献   

Star formation induced by supersonic turbulence in interstellar molecular cloud     

Yutaka Sabano  Makoto Tosa 《Astrophysics and Space Science》1985,115(1):85-98

We studied fragmentation process of the interstellar molecular cloud which is predominated by supersonic turbulence with special regard to collisions of turbulent gas elements and formation of a shock-compressed layer by receding shock waves. The propagation of the shock waves and the evolution of the compressed layer are followed by one-dimensional gas dynamical simulation until self-gravity becomes significant, taking account of the effects of thermal properties of the molecular gas and magnetic fields. It is shown that the efficient cooling by CO molecules and its sensitive dependence on gas density make the shock-compressed layer so cold and dense that the layer becomes gravitationally unstable and breaks into fragments even if the gas elements are gravitationally stable prior to the collision. The mass of the unstable fragment is estimated to be about two solar masses or less, irrespective of the presence of the magnetic field. The stars formed by collisions of supersonic turbulent gas elements accelerate the surrounding gas in T Tauri stage and replenish the turbulent energy to maintain the mechanical equilibrium of the molecular cloud.  相似文献   

High-pressure phase behaviors of ZnTiO3: ilmenite–perovskite transition,decomposition of perovskite into constituent oxides,and perovskite–lithium niobate transition     

M. Akaogi  K. Abe  H. Yusa  H. Kojitani  D. Mori  Y. Inaguma 《Physics and Chemistry of Minerals》2015,42(6):421-429

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Regional projection of future extreme wave heights around Korean Peninsula   总被引：1，自引：0，他引：1  

Dae-Ung Lim  Kyung-Duck Suh  Nobuhito Mori 《Ocean Science Journal》2013,48(4):439-453

In this study, future changes in regional extreme wave heights around the Korean Peninsula are projected by using the results of an atmosphere general circulation model and a third-generation wave model. The direct use of the model output at each grid point is not appropriate even though high resolution of 20 km is used for the models. Therefore, the model output is grouped into six regions around the Korean Peninsula. The grouping approach is reasonable in assessing climate change effects with alleviated model uncertainty. The extreme wave heights are simulated for two climate periods of 1979–2003 (present climate) and 2075–2099 (future climate). The model results are validated by comparing the simulated wave heights for the present climate with observed and hindcasted wave data. The extreme wave heights for the future climate are then projected for different seasons and in different regions. The 50-year return wave height in summer is projected to increase in most regions, especially in the high-latitude Yellow Sea and the East Sea, while the wave height in winter is projected to decrease in all the regions, especially in the East Sea.  相似文献   

Failure process of masonry buildings during earthquake and associated casualty risk evaluation   总被引：1，自引：0，他引：1  

Aiko Furukawa  Yutaka Ohta 《Natural Hazards》2009,49(1):25-51

Collapse of masonry structures during an earthquake is analyzed using the three-dimensional distinct element method (3D-DEM) code developed by the first author. The DEM is a numerical analysis technique, in which positions of elements are calculated by solving equations of motion step by step. Both individual and group behavior can be simulated. The structure is modeled as an assembly of distinct elements connected by virtual springs and dashpots, where elements come into contact. First, the validity of the developed 3D-DEM code is confirmed by comparing analytical results with static experimental results of masonry walls. Second, failure process of masonry buildings due to earthquake is investigated using DEM. Effects of reinforcing methods are also examined. Finally, injury to human bodies in the collapsing masonry buildings is also calculated. Assuming that occupants lie down on the floor, two types of casualty criteria are introduced and assessed.  相似文献   

Balloon-Borne Hard X-Ray Spectrometer Using CdTe Detectors     

K. Kobayashi  S. Tsuneta  T. Tamura  K. Kumagai  Y. Katsukawa  M. Kubo  Y. Sakamoto  N. Kohara  T. Yamagami  Y. Saito  K. Mori 《Solar physics》2008,250(2):431-441

Spectroscopic observation of solar flares in the hard X-ray energy range, particularly the 20 ∼ 100 keV region, is an invaluable tool for investigating the flare mechanism. This paper describes the design and performance of a balloon-borne hard X-ray spectrometer using CdTe detectors developed for solar flare observation. The instrument is a small balloon payload (gondola weight 70 kg) with sixteen 10×10×0.5 mm CdTe detectors, designed for a 1-day flight at 41 km altitude. It observes in an energy range of 20−120 keV and has an energy resolution of 3 keV at 60 keV. The second flight on 24 May 2002 succeeded in observing a class M1.1 flare.  相似文献   

Disaster prevention,disaster preparedness and local community resilience within the context of disaster risk management in Cameroon     

Aka  Festus Tongwa  Buh  Gaston Wung  Fantong  Wilson Yatoh  Issa  Zouh  Isabella Tem  Djomou  Serges Laurent Bopda  Ghogomu  Richard Tanwi  Gibson  Terry  Marmol del  Mary-Ann  Sigha  Luc Nkamdjou  Ohba  Takeshi  Kusakabe  Minoru  Yoshida  Yutaka  Tanyileke  Gregory  Nnange  Joseph Metuk  Hell  Joseph Victor 《Natural Hazards》2017,87(1):57-81

This paper presents a simulation of three components of near-field ground shaking recorded during the main shock at three stations of the September 16, 1978, Tabas (M _w = 7.4), Iran, earthquake, close to the causative fault. A hybrid method composed of a discrete wavenumber method developed by Bouchon (Bouchon in Bull Seismol Soc Am 71:959–971, 1981; Cotton and Coutant in Geophys J Int 128:676–688, 1997) and a stochastic finite-fault modeling based on a dynamic corner frequency proposed by Motazedian and Atkinson (Bull Seismol Soc Am 95:995–1010, 2005), modified by Assatourians and Atkinson (Bull Seismol Soc Am 97:935–1949, 2007), is used for generating the seismograms at low (0.1–1.0 Hz) and high frequencies (1.0–20.0 Hz), respectively. The results are validated by comparing the simulated peak acceleration, peak velocity, peak displacement, Arias intensity, the integral of velocity squared, Fourier spectrum and acceleration response spectrum on a frequency-by-frequency basis, the shape of the normalized integrals of acceleration and velocity squared, and the cross-correlation with the observed time-series data. Each characteristic is compared on a scale from 0 to 10, with 10 being perfect agreement. Also, the results are validated by comparing the simulated ground motions with the modified Mercalli intensity observations reported by reconnaissance teams and showed reasonable agreement. The results of the present study imply that the damage distribution pattern of the 1978 Tabas earthquake can be explained by the source directivity effect.  相似文献   

Chemical monitoring of volcanic gas using remote FT-IR spectroscopy at several active volcanoes in Japan     

Kenji Notsu  Toshiya Mori 《Applied Geochemistry》2010

Chemical compositions of volcanic gases of several Japanese active volcanoes have been monitored from distant safe places since the beginning of the 1990s using an FT-IR spectral radiometer. For absorption measurements, an infrared light source behind volcanic gas emissions is necessary in a volcanic environment. In the early observations, infrared radiation from hot lava domes (Unzen volcano) and hot ground heated by high-temperature fumaroles (Usu, Aso, and Satsuma-Iwojima volcanoes) were used as infrared light sources. However, these sources were not available in many cases. This remote FT-IR method became more commonly applied to chemical monitoring of volcanic gases emitted from the summit or slopes of active volcanoes using scattered solar infrared light as infrared light sources (Sakurajima, Miyakejima, and Asama volcanoes). To date, eight species have been measured using this method: SO₂, HCl, HF, CO, CO₂, COS, SiF₄, and H₂O. The observations indicate that volcanic gases for each volcano have different chemical composition on a SO₂–HCl–HF ternary diagram in spite of similar tectonic settings, suggesting that vapor/melt volume ratios during volcanic gas formation differ among volcanoes. During more than 15 years of monitoring, chemical changes in volcanic gases attributable to ascent of magma were observed only at Asama, where HCl/SO₂ and HF/HCl ratios in the eruptive period were higher than those in non-eruptive period because of scrubbing of more soluble components in surface hydrothermal systems in the non-eruptive stage or solubility-controlled fractionation processes. Results show that these parameters are the most prospective ones among the various parameters measured using the remote FT-IR method to monitor volcanic activities.  相似文献