Large-scale structure of galaxies in the Ophiuchus region     

Takashi Hasegawa  †  Ken-ichi Wakamatsu  ‡  Matthew Malkan  ‡  Kazuhiro Sekiguchi  John W. Menzies  Quentin A. Parker  Jun Jugaku  Hiroshi Karoji  Sadanori Okamura 《Monthly notices of the Royal Astronomical Society》2000,316(2):326-344

The large-scale structure around the Ophiuchus cluster of galaxies in the vicinity of the Galactic Centre ( l =05, b =95, cz =8500 km s⁻¹) is investigated on the basis of a galaxy survey and spectroscopic observations made for a 12°×17° area. The galaxy survey was performed using six ESO/SERC Sky Survey Atlas films, and 4021 galaxies were detected in total. Recession velocities were newly obtained for 179 galaxies to make the total number of galaxies in the survey area with known velocities 219.
In the distribution of bright galaxies, we identified seven new clumps of galaxies. Comparing the surface number density of bright galaxies with the Galactic extinction, which is estimated from the 100‐μm flux density in the IRAS Sky Survey Atlas, we demonstrate that the seven clumps are not spurious as a result of the inhomogeneity of the Galactic extinction. Among the seven clumps, two are found to be clusters and four to be groups on the basis of the histogram of recession velocities and the number of member galaxies. The Ophiuchus cluster, two newly identified clusters, and four groups are all concentrated at 9000 km s⁻¹. Field galaxies are also distributed centred at 8500 km s⁻¹. Hence field galaxies occupy a common three-dimensional region with galaxies in the clusters and groups, and altogether they form a large-scale structure of supercluster size. As opposed to the overdensity in the supercluster region, the mean number density of galaxies in the velocity range 0–5000 km s⁻¹ is only 25 per cent of the mean number density of the Universe, comparable with the density of the well-known Böotes void. Hence this nearby three-dimensional region in Ophiuchus is a void of galaxies also.  相似文献   

Photosynthesis-irradiance relationship of phytoplankton and primary production in the vicinity of Kuroshio warm core ring in spring     

Ken Furuya  Osamu Hasegawa  Takashi Yoshikawa  Satoru Taguchi 《Journal of Oceanography》1998,54(5):545-552

The light-saturated maximum value (P ^B _max) and initial slope (α) of the photosynthesis-irradiance (P-E) curve were examined in a warm streamer, a cold streamer and a warm core ring off the Sanriku area in the subarctic western North Pacific Ocean during an ADEOS/OCTS Sanriku field campaign in early May 1997. BothP ^B _max and α were within the ranges of temperate populations. A regional difference was apparent inP ^B _max: populations in the warm streamer tended to show higher value ranging between 1.92 and 4.74 mgC (mgChla)⁻¹h⁻¹ than those in the cold streamer and the warm core ring (1.35–2.87 mgC (mgChla)⁻¹h⁻¹). A depth variation was also observed in α in both the warm streamer and the warm core ring: shallow populations tended to have lower α than deep populations. The depth variations in bothP ^B _max and α resulted in a lower light intensity of the light saturation in a deeper population than that of a shallower one. These depth-related variations in the P-E parameters were likely a manifestation of “shade-adaptation” of photosynthesis. Photoinhibition was not observed over in situ surface light intensity varying below ca 1600 μmol photon m⁻²s⁻¹. Water-column primary productivity was biooptically estimated to be 233 to 949 mgC m⁻²d⁻¹ using vertical distributions of the P-E parameters, chlorophylla, phytoplankton light absorption and underwater irradiance. Applicability of surface data sets for estimation of water-column productivity is discussed.  相似文献   

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia          下载免费PDF全文

Hitoshi Hasegawa  Hisao Ando  Noriko Hasebe  Niiden Ichinnorov  Tohru Ohta  Takashi Hasegawa  Masanobu Yamamoto  Gang Li  Bat‐Orshikh Erdenetsogt  Ulrich Heimhofer  Takayuki Murata  Hironori Shinya  G. Enerel  G. Oyunjargal  O. Munkhtsetseg  Noriyuki Suzuki  Tomohisa Irino  Koshi Yamamoto 《Island Arc》2018,27(3)

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.  相似文献   

A new approach for estimating seismic damage of buried water supply pipelines          下载免费PDF全文

H. Sakai  N. Pulido  K. Hasegawa  Y. Kuwata 《地震工程与结构动力学》2017,46(9):1531-1548

Conventional damage prediction methods for lifeline structures are primarily based on peak ground motion measurements. However, line structures such as lifelines suffer damage that is mainly induced by the strain of the ground and therefore are likely to be vulnerable to sharp spatial changes in the ground motion. In this study, we propose a measure for evaluating the damage incurred by underground water supply pipelines based on the spatial gradient of the peak ground velocity (PGV), in an attempt to quantify the effects of the geospatial variabilities in the ground motion on pipeline damage. We investigated the spatial distribution of the damage caused to water pipelines during the Niigata‐ken Chuetsu earthquake on October 10, 2004 (Japan Meteorological Agency magnitude (M_JMA) of 6.8) and the Kobe earthquake on January 17, 1995 (M_JMA7.3) and compared the surveyed damage with the PGV distribution as well as with the gradients of the PGV calculated around the damage areas. For the Kobe earthquake, we used the PGV distribution obtained by the strong‐motion simulation performed by Matsushima and Kawase 1 . In case of the Chuetsu earthquake, we estimated the ground motion using a broadband‐frequency‐based strong‐ground‐motion simulation method based on a multiasperity source model. In both cases, we calculated the gradients of the PGV along the geographical coordinates, with the amplitude of the PGV gradient vector being employed as the damage estimator. Our results show that the distribution of damage to underground water supply pipelines exhibits a greater correlation with the gradients of the PGV than with the PGV itself. Thus, the gradient of the PGV is a useful index for preparing initial‐screening hazard maps of underground facilities. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Upper ocean heat content and atmospheric anomaly fields in the off-equatorial North Pacific related to ENSO   总被引：2，自引：1，他引：1  

Takuya Hasegawa  Kimio Hanawa 《Journal of Oceanography》2007,63(4):561-572

We have investigated interannual-scale variations of oceanic and atmospheric anomaly fields, such as upper ocean heat content (OHC), sea surface temperature (SST), latent heat flux (LHF) through the sea surface, sea level pressure (SLP) and wind stress curl (WSC) in the tropical Pacific and their relationships to El Niño/Southern Oscillation (ENSO) events. The results reported here show that the OHC and SST anomalies are almost in phase and lead LHF anomalies in the western tropical Pacific (WTP) region, which are preferable to the generation of subsequent atmospheric anomalies in the WTP. We also describe linear relationships between the amplitudes of these variables in the WTP. In addition, the results show that the both WSC and LHF anomalies are in phase with the temporal trend of OHC anomalies in the WTP, and suggest a combined effect of the local WSC and LHF anomaly in the WTP and ENSO-related, off-equatorial, westward propagating OHC anomaly to generate a large OHC anomaly in the WTP. In contrast to the WTP, OHC and SST anomalies are not in phase to the east of the WTP. The results also indicate that OHC anomalies in the WTP have a potential effect on the generation of an equatorial OHC anomaly via both a reflection of waves at the western boundary and atmospheric variations, which force the enhancement of western equatorial OHC anomaly. Therefore, the WTP is a key region where ENSO events are significantly modulated, and OHC anomalies in the WTP play an important role in the subsequent ENSO event.  相似文献   

Causes of large-scale landslides in the Lesser Himalaya of central Nepal   总被引：1，自引：0，他引：1  

Shuichi Hasegawa  Ranjan Kumar Dahal  Minoru Yamanaka  Netra Prakash Bhandary  Ryuichi Yatabe  Hideki Inagaki 《Environmental Geology》2009,57(6):1423-1434

Geologically and tectonically active Himalayan Range is characterized by highly elevated mountains and deep river valleys. Because of steep mountain slopes, and dynamic geological conditions, large-scale landslides are very common in Lesser and Higher Himalayan zones of Nepal Himalaya. Slopes along the major highways of central Nepal namely Prithvi Highway, Narayangadh-Mugling Road and Tribhuvan Highway are considered in this study of large-scale landslides. Geologically, the highways in consideration pass through crushed and jointed Kathmandu Nappe affected by numerous faults and folds. The relict large-scale landslides have been contributing to debris flows and slides along the highways. Most of the slope failures are mainly bechanced in geological formations consisting phyllite, schist and gneiss. Laboratory test on the soil samples collected from the failure zones and field investigation suggested significant hydrothermal alteration in the area. The substantial hydrothermal alteration in the Lesser Himalaya during advancement of the Main Central Thrust (MCT) and thereby clay mineralization in sliding zones of large-scale landslide are the main causes of large-scale landslides in the highways of central Nepal. This research also suggests that large-scale landslides are the major cause of slope failure during monsoon in the Lesser Himalaya of Nepal. Similarly, hydrothermal alteration is also significant in failure zone of the large-scale landslides. For the sustainable road maintenance in Nepal, it is of utmost importance to study the nature of sliding zones of large-scale landslides along the highways and their role to cause debris flows and slides during monsoon period.  相似文献   

DEM-Based Analysis of Earthquake-Induced Shallow Landslide Susceptibility   总被引：3，自引：0，他引：3  

Shuichi Hasegawa  Ranjan Kumar Dahal  Toshiaki Nishimura  Atsuko Nonomura  Minoru Yamanaka 《Geotechnical and Geological Engineering》2009,27(3):419-430

  相似文献   

Mercury content in Atlantic sediments as a new indicator of the enlargement and reduction of Northern Hemisphere ice sheets          下载免费PDF全文

I. Kita  T. Yamashita  S. Chiyonobu  H. Hasegawa  T. Sato  Y. Kuwahara 《第四纪科学杂志》2016,31(3):167-177

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Installing single-propeller twin-rudder system with less asymmetric maneuvering motions     

Donghoon Kang  Vishwanath Nagarajan  Yoshiaki Gonno  Kazuhiko Hasegawa 《Ocean Engineering》2011,38(10):1184-1196

The inflow characteristics to each one of the rudders of single-propeller twin-rudder system are investigated. It is shown that this inflow is not parallel to ship's centerline. This may result in asymmetric maneuvering characteristic of the ship thereby reducing ship's maneuvering performance. For this purpose, a method of installing single-propeller twin-rudder system is proposed. This method is called “virtual zero rudder angle” arrangement. Here, each one of the twin-rudder is set at an angle corresponding to the inflow to the rudder. The improvement in ship's maneuvering characteristics with “virtual zero rudder angle” arrangement is investigated using experiments and numerical simulations for different ship types. It is shown that this arrangement may also improve ship's propulsion performance.  相似文献   

Millennial-scale oscillations of the westerly jet path during the last glacial period   总被引：1，自引：0，他引：1  

Kana Nagashima  Ryuji Tada  Atsushi Tani  Youbin Sun  Yuko Isozaki  Shin Toyoda  Hitoshi Hasegawa 《Journal of Asian Earth Sciences》2011,40(6):239-1220

It has been established that East Asian summer monsoon intensity varies with Dansgaard–Oeschger cycles, suggesting a connection between the climates of East Asia and the North Atlantic on a millennial timescale. However, the dynamics of such a connection are still unsolved. Here we demonstrate that temporal changes in the provenance of aeolian dust in Japan Sea sediments, which we interpret to reflect changes in the westerly jet path over East Asia, exhibit variations in harmony with Dansgaard–Oeschger cycles. The dominance of dust with a Mongolian Gobi provenance during stadials suggests a westerly jet axis located to the south of the Himalaya–Tibetan Plateau throughout most of the year, whereas the co-dominance of dust from both the Taklimakan Desert and the Mongolian Gobi during interstadials suggests that the westerly jet axis jumped to the north of the Tibetan Plateau at latest in summer. As the shift of the westerly jet axis to the north of the Tibetan Plateau is closely related to the onset of the East Asian summer monsoon, changes of the westerly jet path apparently critically affect the teleconnection between the climates of Asia and North Atlantic on a millennial timescale.  相似文献