The first confirmed Perseid lunar impact flash     

Masahisa Yanagisawa  Kouji Ohnishi  Hiroshi Masuda  Miyoshi Ida  Masayuki Ishida 《Icarus》2006,182(2):489-495

The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18^h28^m27^s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are 48±1° N and 72±2° E, and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have been 12 g based on a nominal model with conversion efficiency from kinetic to optical energy of 2×¹⁰⁻³. Extrapolation of a power law size-frequency distribution fitting the sub-centimeter Perseid meteoric particles to large meteoroids suggests that several flashes should have been observed at this optical efficiency. The detection of only one flash may indicate that the optical efficiency for Perseid lunar impact is much lower, or that the slope of the size distribution differs between large meteoroids and typical sub-centimeter meteoric particles.  相似文献   

The absence of apparent correlations between iras and optical spectral features of late-type stars     

M. Othman  K. Ishida  S. Okamura  S. Nishimura 《Astrophysics and Space Science》1988,148(2):191-198

The spectral signatures of circumstellar dust shells (CS) of late-type stars cannot be tied in a simple manner to their optical spectral features. The spectral indices of featureless low-resolution spectrometer (LRS) spectra of K and early-M (M0-M5) stars are consistent with that of the Rayleigh-Jeans law and those of late-M (M6 and later) stars tend to have lower values showing CS radiation. There is no correlation observed between the optical sub-type and the 10 m emission strength for M stars. The absence of a simple relationship is also evident for C stars where the temperature and abundance indices show no correlation with the 11 m emission strength. The sample is confined to the IRC stars identified with accurate spectra observed by the LRS of IRAS. The IRC stars are the whole sky survey done with the 2 m band, where late-type stars are bright and interstellar extinction is one-tenth of the visual colour band.  相似文献   

The spectroscopic study of astrometric binaries     

Goro Ishida 《Astrophysics and Space Science》1985,110(1):161-162

The spectroscopic observations of several astrometric binaries, obtained by the author during the past 20 years, are described. Main emphasis is placed on the determination of orbital elements of visual binaries, and the detection of unseen companions.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).  相似文献   

Effect of Injected Water on Hydraulic Fracturing Deduced from Acoustic Emission Monitoring     

T. Ishida  Q. Chen  Y. Mizuta 《Pure and Applied Geophysics》1997,150(3-4):627-646

—In order to investigate the effects of injected water in hydraulic fracturing, experiments were conducted on cubic granite specimens, comparing fracturings induced by conventional water injection with those induced by pressurization of a urethane sleeve, thereby realizing "hydraulic fracturing" without the use of fracturing fluid. In both experiments, a shear type mechanism was found to be dominant in fault plane solutions of AE events. However, in the case of water injection, cracks extended rapidly with large drops in hole water pressure and bursts of AE, whereas in pressurization by the urethane sleeve, cracks extended stepwise with no such large drops in hole pressure and no bursts of AE. The difference in crack extension in the two experiments can be analyzed by comparing relations between crack length and stress intensity factor of mode I at a crack tip. The observation and analysis indicate that existence of fracturing fluid like water helps initiated cracks to extend rapidly and widely in hydraulic fracturing in actual HDR fields. Received September 12, 1996, accepted January 24, 1997  相似文献   

The effect of artificial viscosity on a hydrodynamic model of Cepheids     

Takeuti  Ishida  & Tanaka 《Monthly notices of the Royal Astronomical Society》1998,294(2):224-228

The effect of artificial viscosity on a hydrodynamic simulation of stellar radial pulsation is examined for the purpose of studying the dependence of the modal coupling on the sharpness of the shock front. The model used in our study is a 2.5-d first-overtone pulsator in the Cepheid instability strip. By increasing the parameters in the von Neumann–Richtmyer formula of artificial viscosity, we obtained a low growth rate together with a small pulsation amplitude. The time-scale related to pulsation mode-switching is also increased.  相似文献   

Cation disordering in heat-treated anthophyllites through oxidation and dehydrogenation     

K. Ishida 《Physics and Chemistry of Minerals》1998,25(2):160-167

Oxidation and dehydrogenation processes for heat-treated anthophyllites were investigated using Mössbauer and infrared spectroscopy. At temperatures from 350°C to about 650°C, Fe²⁺ at the M1 and M3 sites oxidizes, yielding Fe³⁺ + one electron. A proton from the (OH)^– is liberated and combines with this electron to form a hydrogen atom; and some Fe²⁺ ions at the M2 and M4 sites exchange with Mg at the M1 and M3 sites and then are oxidized in a similar way; at higher temperature, OH remaining in the (MgMgMg/Fe³⁺)-(OH)-configuration are dehydrogenated by decomposition of the amphibole to orthopyroxene and quartz. During oxidation and dehydrogenation of anthophyllite, there is disordering of Mg and Fe at the M1, M2, M3 and M4 sites in all samples studied. When all Fe²⁺ is oxidized, the site occupancies of at the M4 and M1, M2, M3 sites become identical, indicating that Mg and Fe³⁺ are completely disordered at these sites.  相似文献   

Interaction Between Wind and Snow Surface     

Shun’ichi Kobayashi  Tamotu Ishida 《Boundary-Layer Meteorology》1979,16(3):35-47

The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew at a speed of more than 7 m s⁻¹ after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence and snow-wave formation interact with each other.  相似文献   

Interaction between wind and snow surface     

Shun'ichi Kobayashi  Tamotu Ishida 《Boundary-Layer Meteorology》1979,16(1):35-47

The horizontal and vertical wind velocity fluctuations were measured using two sonic anemometers at a height of 135 cm above a snow surface under a transverse snow wave-forming condition. A snow-wave was formed when the wind at a height of 1 m blew at a speed of more than 7 m s^–1 after an approximate accumulation of from 10 to 20 cm of new snow on a snowfield. For example, when a snow-wave had a wavelength of 10 m and a wave height of 15 to 20 cm, the measured horizontal and vertical velocity components showed that they had a frequency peak of 0.7 Hz in coherence and co-spectrum corresponding to this wavelength. The results suggest that wind turbulence and snow-wave formation interact with each other.  相似文献   

Effects of regional temperature,wind speed and soil wetness on spatial structure of surface air temperature     

S. Kawashima  T. Ishida 《Theoretical and Applied Climatology》1992,46(2-3):153-161

Summary Climate parameters are usually collected on some grid or pattern that is supposed to represent the unobserved neighborhood. Spatial dependence is a measure of the extent to which observed data represent the unobserved neighborhood. Geostatistical analyses provide procedures for measuring spatial dependence. In this study, semivariograms were estimated from hourly observations of screen-height air temperature obtained from a dense meteorological observation network. The range and spatial component normalized by the sill were estimated from the semivariogram in order to obtain information on the spatial structure of the air temperature. Zones of spatial correlation were delineated, using the range of the semivariogram. Scales of spatial correlation depended on the regional mean air temperature and regional wetness at the ground. The range or spatial scale for data collected in winter was larger than those in summer. The range under wet conditions was larger than under dry conditions. Effects of regional wind speed on range were different, depending on the regional mean air temperature. The normalized spatial component was used as an index for measuring continuities on the interpolation surface. The normalized spatial component generally increased as the range increased.With 5 Figures  相似文献   

Sedimentary records of reduction in resting egg production of <Emphasis Type="Italic">Daphnia galeata</Emphasis> in Lake Biwa during the 20th century: a possible effect of winter warming     

Narumi K. Tsugeki  Seiji Ishida  Jotaro Urabe 《Journal of Paleolimnology》2009,42(2):155-165

To clarify long-term variations in the resting egg production of Daphnia galeata in Lake Biwa during the 20th century, we examined an abundance of plankton remains and ephippia in a 26-cm sediment core with a time resolution of approximately 2–6 years. Historical changes shown by these plankton remains indicated that the Daphnia population has not produced resting eggs since the 1980s, but it has remained the most abundant zooplankton species in the lake. Plankton monitoring data collected from 1966 to 2000 revealed that the overwintering individuals (January–March) of D. galeata plankters showed a significant increasing trend in recent years, such increase being negatively correlated with ephippial abundance in the sediment samples. Further analyses showed that the dominant phytoplankton in winter has changed from large inedible diatoms to edible flagellated algae, probably due to changes in vertical mixing regimes resulting from winter warming. These changes that occurred in the last several decades suggest that global warming has improved winter food conditions and thus enabled the Daphnia plankton to maintain its population without producing resting eggs in Lake Biwa.  相似文献