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Yoshikazu Hasegawa Yojiro Taketani Hajime Taru Osamu Sakamoto Makoto Manabe 《Island Arc》1994,3(4):513-521
Abstract Upon studying the well preserved skulls referred to Paleoparadoxia tabatai from Japan, the short and low skull of the Yanagawa specimen requires an explanation. Six cranial and dental characters lead us to suggest that the Yanagawa individual is a female while the Izumi, Ohnohara, and Itsukaichi skulls are male. The important characters in the Yanagawa skull are its shortness and shallow depth, less pronounced sagittal and nuchal crests, smaller zygoma, and the small dentition with especially poorly erupted canines, most of which are indicative of weak masticatory musculature. 相似文献
154.
Tomoko Kyuka Satomi Yamaguchi Yusuke Inoue Kattia Rubi Arnez Ferrel Hideto Kon Yasuyuki Shimizu 《地球表面变化过程与地形》2021,46(7):1225-1237
Previous studies have demonstrated that riparian vegetation leads to channel transformation from a multi-bar to a single-thread channel planform. However, it still remains unclear how the presence of pioneer and mature vegetation affects the morphodynamics of single-thread meandering rivers. In this study, we therefore investigated the effects of vegetation strength on the morphodynamic evolution of an experimental meandering channel. Three physical laboratory experiments were conducted using alfalfa sprouts in different life stages – no vegetation, immature vegetation, and mature vegetation – to simulate different floodplain vegetation strengths. Our results demonstrate that vegetation plays a key role in mediating bank erosion and point-bar accretion, and that this is reflected in both the evolution of the channel bed as well as the sediment flux. The presence of mature vegetation maintained a deep, single-thread channel by reducing bank erosion, thereby limiting both channel widening and sediment storage capacity. Conversely, an unvegetated floodplain led to channel widening and high sediment storage capacity. Channel evolution in the unvegetated scenario showed that the active sediment supply from outer bank erosion led to slightly delayed point-bar accretion on the inner banks due to helical flow, deflecting the surface flow toward the outer banks and causing further erosion. In contrast, in the immature vegetation scenario, the outer banks were also initially eroded, but point-bar accretion did not clearly progress. This led to a greater width-to-depth ratio, resulting in a transition from a single- to a multi-thread channel with minor flow paths on the floodplain. The experimental results suggest that the eco-morphodynamic effects of young (low-strength) and mature (high-strength) vegetation are different. Notably, low-strength, early-stage vegetation increases channel complexity by accelerating both channel widening and branching, and therefore might promote the coexistence of multi-bars and pioneer vegetation. 相似文献
155.
Kattia Rubi Arnez Ferrel Jonathan Mark Nelson Yasuyuki Shimizu Tomoko Kyuka 《地球表面变化过程与地形》2021,46(4):715-727
Field observations on small rivers of the Amazon basin are less common due to their remote location and difficult accessibility. Here we show, through remote sensing analysis and field works, the planform evolution and riverbed topography of a small river located in the upper foreland Amazon basin, the Ichilo River. By tracking planform changes over 30 years, we identified the factors that control meander migration rates in the Ichilo River: cutoffs, climate and human interventions. The data suggest that neck cutoffs are the main controls in the Ichilo River, with an annual density of 0.022 cutoffs/km. In addition, climate controls have been identified in the form of high-precipitation events that may have promoted cutoffs, an increase in meander migration rate and channel widening. The width distribution of the Ichilo River is well represented by general extreme value and inverse Gaussian distributions. The spatiotemporal variability of meandering migration rates in the Ichilo River is analysed in two locations where neck cutoffs are expected. Analysing the distance across the neck in these two points, we predict the occurrence of a new cutoff. The combined methodology of bathymetric surveys and structure from motion photogrammetry shows us the Ichilo riverbed topography and banks at high resolution, where two scour holes were identified. Finally, we discuss the impact of planform changes of the Ichilo River on communities that are established along its riverbanks. 相似文献
156.
Tomoko Sato Hiroto Takada Takehiko Yagi Hirotada Gotou Taku Okada Daisuke Wakabayashi Nobumasa Funamori 《Physics and Chemistry of Minerals》2013,40(1):3-10
We have investigated the high-pressure behavior of cristobalite in helium by powder X-ray diffraction. Cristobalite transformed to a new phase at about 8 GPa. This phase is supposed to have a molar volume of about 30 % larger than cristobalite, suggesting the dissolution of helium atoms in its interstitial voids. On further compression, the new phase transformed to a different phase which showed an X-ray diffraction pattern similar to cristobalite X-I at about 21 GPa. On the other hand, when the new phase was decompressed, it transformed to another new phase at about 7 GPa, which is also supposed to have a molar volume of about 25 % larger than cristobalite. On further decompression, the second new phase transformed to cristobalite II at about 2 GPa. In contrast to cristobalite, quartz did not show anomalous behavior in helium. The behavior of cristobalite in helium was also consistent with that in other mediums up to about 8 GPa, where the volume of cristobalite became close to that of quartz. These results suggest that dissolution of helium may be controlled not only by the density (amount of voids) but also by the network structure of SiO4 tetrahedra (topology of voids). 相似文献
157.
Abstract Very large scale mapping (1/250) was experimented on the basis of FMC camera, high resolution film and total station surveying. The future attractive combination of precision photogrammetry and personal computer assisted terrestrial surveying was investigated from the point of view of accuracy, time effectiveness and total procedures control. 相似文献
158.
Takahito Kazama Hideaki Hayakawa Toshihiro Higashi Shingo Ohsono Shunsuke Iwanami Tomoko Hanyu Harumi Ohta Koichiro Doi Yuichi Aoyama Yoichi Fukuda Jun Nishijima Kazuo Shibuya 《Polar Science》2013,7(3-4):260-277
Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2 ± 0.7 μgal (1 [μgal] = 1 × 10?8 [m/s2]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1 mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection. 相似文献
159.
Tomoko Nakagawa 《Solar physics》1993,147(1):169-197
Planar magnetic structure (PMS) is an interplanetary magnetic structure in which magnetic field vectors are all parallel to a plane but highly variable in both magnitude and direction in that plane. This magnetic structure corresponds to re-entrant loops of magnetic field lines in the photosphere that emanate into interplanetary space. To find information on the generation site, occurrence properties of PMSs are investigated by using the interplanetary magnetic field data obtained by Sakigake and ISEE-3 spacecraft. No significant correlation is found between PMS occurrence and the solar wind velocity gradient which would suggest interplanetary formation of PMSs. No significant correlation is found between the PMS events and flares or filaments, either. Instead, a half of the PMSs were projected to the vicinity of the sector boundary in the source surface magnetic field, although there are exceptions when PMS appeared in the center of a sector. The PMS planes were not parallel to the current sheet at the sector boundary. Sometimes PMSs were observed recurrently at the same heliospheric longitude in successive rotations of the Sun, suggesting persistence of the source of PMS on the Sun. The orientation of the PMS planes were not conserved in the recurrent PMSs. 相似文献
160.