Selection effects on the size and frequency distribution of cosmic gamma-ray bursts     

Yamagami  Takamasa  Nishimura  Jun 《Astrophysics and Space Science》1986,121(2):241-253

We investigate selection effects on the size and frequency relation (logN-logS curve) of cosmic gamma-ray bursts. After analyzing the published data, we find an indication that an effect is caused by the different time profiles of the bursts. The effect is important for small bursts and causes significant changes in the logN-logS curve. in order to avoid this selection effect, we mention that it is essential to use the logN-logP relation of the logN-logS relation, as already suggested by other authors. Here,P is the peak flux of the burst, which is free from bias due to the difference in time profiles. After an analysis of the published data, we find a distribution nearP ^–3/2 in the range above a peak flux of 40 counts/0.25 s.We also show that the relation between the logN-logP curve and the observed celestial distribution for the bursts can easily be explained by our general arguments on a disk-like spatial distribution of burst sources in the Galaxy.  相似文献   

Infrared detector for mid-infrared astronomy     

Tetsuo Nishimura 《Astrophysics and Space Science》1989,160(1-2):325-332

Recent developments of infrared detectors and arrays for mid-infrared astronomical observations are discussed with an emphasis on technical issues in designing and fabricating photometers and cameras. The discussion includes a small-scale silicon bolometer array being tested at the Steward Observatory.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.  相似文献   

Evaluation of strength of heterogeneity in the lithosphere from peak amplitude analyses of teleseismic short-period vector P waves     

Mungiya Kubanza  Takeshi Nishimura  Haruo Sato 《Geophysical Journal International》2007,171(1):390-398

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New automated maritime telephone system     

Komura  M. Yoneoka  Y. Nishimura  S. Tsujioku  N. 《Oceanic Engineering, IEEE Journal of》1977,2(3):263-266

As one of the most valuable services in telecommunication service, NTT has developed a new automated maritime telephone system for public use. Calls between ship and land subscribers, or between one ship and another can be connected automatically by subscribers' dialing in the nationwide system. The new system adopts a lot of technical features such as automatic location registration, new signaling methods, etc. An outline of system performance and function is described herein.  相似文献   

Time variations of hard X-rays from Sco X-1     

M. Matsuoka  M. Fujii  S. Miyamoto  J. Nishimura  M. Oda  Y. Ogawara  S. Hayakawa  I. Kasahara  F. Makino  Y. Tanaka  P. C. Agrawal  B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):472-490

Simultaneous hard X-ray and optical observations of Sco X-1 were carried out on 1971 May 1 at Hyderabad, India, when Sco X-1 was optically bright. The X-ray intensity observed by balloon-borne counter telescopes increased in coincidence with optical enhancements, while the plasma temperature derived by fitting the X-ray spectrum in the energy range 20–40 keV to the thermal bremsstrahlung spectrum did not appreciably change over the whole period of observation.  相似文献   

Determination of the role of entrapped air in water flow in a closed soil pipe using a laboratory experiment          下载免费PDF全文

Takuhei Yamasaki  Hiromi Imoto  Shoichiro Hamamoto  Taku Nishimura 《水文研究》2017,31(21):3740-3749

Soil pipes, continuous macropores parallel to the soil surface, are an important factor in hillslope hydrological processes. However, the water flow dynamics in soil pipes, especially closed soil pipes, are not well understood. In this study, the water and air dynamics within closed soil pipes have been investigated in a bench‐scale laboratory experiment by using a soil box with an artificial acrylic soil pipe. In order to grasp the state of water and air within the soil pipe, we directly measured the existing soil pipe flow and air pressure in the soil pipe. The laboratory experiment showed that air in the soil pipe had an important role in the water flow in the closed soil pipe. When air entrapment occurred in the soil pipe before the soil matrix around the soil pipe was saturated with water, water intrusion in the soil pipe was prevented by air entrapped in the pipe, which inhibited the soil pipe flow. This air entrapment in the soil pipe was controlled by the soil water and air flow. Moreover, after the soil pipe flow started, the soil pipe was not filled completely with water even when the soil pipe was completely submerged under the groundwater table. The entrapped air in the soil pipe prevented further water intrusion in the soil pipe.  相似文献   

Seismicity and magma supply rate of the 1998 failed eruption at Iwate volcano,Japan     

Takeshi Nishimura  Sadato Ueki 《Bulletin of Volcanology》2011,73(2):133-142

Iwate volcano, Japan, showed significant volcanic activity including earthquake swarms and volcano inflation from the beginning of 1998. A large earthquake of magnitude 6.1 hit the south-west of the volcano on September 3. Although a 1 km² fumarole field formed, blighting plants on the ridge in the western part of the volcano in the spring of 1999, no magmatic eruptions occurred. We reconcile the spatio-temporal distributions of volcanic pressure sources determined by previously reported studies in which GPS, strain and tilt data from dense geodetic station networks are analyzed (Miura et al. Earth Planet Space 52:1003–1008, 2000; Sato and Hamaguchi J Volcanol Geotherm Res 155:244–262, 2006). We calculate the magma supply rates from their results and compare them with the occurrence rates of volcanic earthquakes. The results show that the magma supply rates are almost constant or even decrease with time while the earthquake occurrence rate increases with time. This contrast in their temporal changes is interpreted to result from stress accumulation in the volcanic edifice caused by constant magma supply without effusion of magma to the surface. We further show that data showing slight acceleration in strain can be best explained by magma ascent at a constant velocity, and that there is no evidence for increased magma buoyancy resulting from gas bubble growth. This consideration supports the interpretation that the magma stayed at 2 km depth and horizontally migrated. These findings relating magma supply rate and seismicity to magma ascent process are clues to understanding why no magmatic eruption occurred at Iwate volcano in 1998.  相似文献   

Impact of vertical mixing induced by small vertical scale structures above and within the equatorial thermocline on the tropical Pacific in a CGCM     

Wataru Sasaki  Kelvin J. Richards  Jing-Jia Luo 《Climate Dynamics》2013,41(2):443-453

Oceanic vertical mixing is known to influence the state of the equatorial ocean which affects the climate system, including the amplitude of El Niño/Southern Oscillation (ENSO). Recent measurements of ocean currents at high vertical resolution capture numerous small vertical scale structures (SVSs) within and above the equatorial thermocline that contribute significantly to vertical mixing but which are not sufficiently resolved by coarse resolution ocean models. We investigate the impact of the vertical mixing induced by the SVSs on the mean state and interannual variability in the tropical Pacific by using a coupled general circulation model. The vertical mixing induced by the SVSs is represented as an elevated vertical diffusivity from the surface down to the 20 °C isotherm depth, a proxy for the depth of the thermocline. We investigate different forms for the elevated mixing. It is found that the SVS-induced mixing strongly affect the mean state of the ocean leading to a warming of sea surface temperature (SST) and associated deepening and sharpening of the thermocline in the eastern equatorial Pacific. We find that the SST warming induced by the elevated mixing is further strengthened through the Bjerknes feedback and SST-shortwave flux feedback. We also find a reduction in the number of large amplitude ENSO events and in certain cases an increase in the skewness of ENSO.  相似文献   

The infrared variability of a dust model for Seyfert galaxies     

Noboru Kaneko  Kiyotaka Toyama  Masaki Nishimura 《Astrophysics and Space Science》1972,18(1):121-127

Assuming a dust model of Reeset al. (1969), we study the time dependence of the infrared emission from grains which absorb variable ultraviolet radiation. A time scale for the variability is shown to be fairly small compared with the light travel-time across the infrared emitting region, of which size depends on the wavelength strongly. Comparison of calculated infrared light curves with observations of NGC 4151 leads to the conclusion that the variability at 2.2 is consistent with interpretation by the infrared emission on the basis of thermal process.  相似文献   

Characterization of forests and deforestation in Cambodia using ALOS/PALSAR observation     

Ram Avtar  Haruo Sawada  Wataru Takeuchi  Gulab Singh 《国际地球制图》2013,28(2):119-137

In this study, we have demonstrated the capability of full polarimetric ALOS/Phased Array L-band Synthetic Aperture Radar data for the characterization of the forests and deforestation in Cambodia, to support climate change mitigation policies of Reducing Emission from Deforestation and Forest Degradation (REDD). We have observed mean backscattering coefficient (σ°), entropy (H), alpha angle (α), anisotropy (A), pedestal height (PH), Radar Vegetation Index (RVI) and Freeman–Durden three-component decomposition parameters. The observations show that the forest types and deforested area are showing variable polarimetric and backscattering properties because of the structural difference. Evergreen forest is characterized by a high value of σ° HV (?12.96 dB) as compared with the deforested area (σ° HV=?22.2 dB). The value of polarimetric parameters such as entropy (0.93), RVI (0.91), PH (0.41) and Freeman–Durden volume scattering (0.43) is high for evergreen forest, whereas deforested area is characterized by the low values of entropy (0.36) and RVI (0.17). Based on these parameters, it is found that σ° HV, entropy, RVI and PH provide best results among other parameters.  相似文献