Structurally preserved Zamites bayeri Kvaček from the Coniacian Kashima Formation (Yezo Group) of Hokkaido,Japan     

Toshihiro Yamada 《Cretaceous Research》2009,30(5):1301-1306

A permineralized frond from the Coniacian Kashima Formation (Yezo Group) of Hokkaido, Japan, is identified as Zamites bayeri based on leaf shape, transverse orientation of stomata, papillate epidermal surface, and hollow subsurface bodies formed only on the abaxial epidermis. The specimen has an articulation at the base of the leaflet from which the leaflet was detached by means of an abscission zone. This finding suggests that Z. bayeri has compound leaves that are functionally equivalent to a twig bearing simple leaves. This functional conversion is often found in extant compound-leaved ferns or cycads growing in infertile conditions; thus Z. bayeri might have lived in a similar habitat. Leaflet articulation is also found in other Zamites species including the type species of the genus, whereas it is unknown in other bennettitalean foliar morphogenera. The rachis of the specimen has a columnar vascular bundle, which is common in bennettitalean foliage.  相似文献   

Apparent downward CO2 flux observed with open-path eddy covariance over a non-vegetated surface     

K. Ono  A. Miyata  T. Yamada 《Theoretical and Applied Climatology》2008,92(3-4):195-208

Summary The open-path eddy covariance (EC) method often shows unlikely downward CO₂ fluxes in late winter and early spring over drained paddy fields with few active plants. To understand why, we carried out intensive measurements in a bare paddy field from 9 to 11 April 2003, simultaneously using open- and closed-path EC methods; aerodynamic and dynamic closed-chamber methods were also used. During this period, the open-path EC method showed downward daytime CO₂ fluxes ranging from 0 to −5.9 μmol m⁻² s⁻¹, even after application of the WPL correction (density correction) and ordinary quality control tests. Because the closed-path EC and aerodynamic methods showed upward CO₂ fluxes, the downward CO₂ fluxes observed with open-path EC appear not to represent true CO₂ transport. Diurnal variations in the downward daytime CO₂ fluxes appeared to be correlated with increases in solar radiation during the day, and also with increases in sensible heat flux in weak winds but not under strongly windy conditions. The daytime 10-Hz time series data of vertical wind and CO₂ mixing ratio demonstrated that updrafts were CO₂ depleted in the open-path system, whereas the same updrafts were CO₂ enriched in the closed-path system. Careful examination of the discrepancies between the open- and the closed-path EC measurements revealed that the amplitudes of the 10-Hz temperature signals from the sonic anemometer and the resultant sensible heat fluxes were too small to compensate for the discrepancies observed during the daytime. The open-path EC method with the conventional application of the WPL correction is not necessarily appropriate for measuring small magnitudes of CO₂ flux (≤5 μmol m⁻² s⁻¹) under such surface and atmospheric conditions that the magnitude of the WPL correction is as great as that of the uncorrected CO₂ flux itself. Author’s addresses: Keisuke Ono, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan; Akira Miyata, Tomoyasu Yamada, National Institute for Agro-Environmental Sciences, Tsukuba, Japan  相似文献   

The Crab Nebula's dynamical age as measured from its northern filamentary jet     

G. C. Rudie  R. A. Fesen  T. Yamada 《Monthly notices of the Royal Astronomical Society》2008,384(3):1200-1206

We present a deep [O  iii ]λλ4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2-m Subaru telescope. Using this image and an image taken with the Kitt Peak National Observatory (KPNO) 4-m in 1988, we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar's rapidly expanding synchrotron nebula. The jet's apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 ± 24 CE, a date much closer to the appearance of the historic 1054 CE guest star than the 1120–1140 CE dates estimated in previous studies using filaments located within the remnant's main nebula. Our proper motion measurements suggest the jet likely formed during the 1054 supernova explosion and represents the remnant's highest velocity knots possibly associated with a suspected N–S bipolar outflow from the supernova explosion.  相似文献   

Gas hydrate saturation at Site C0002, IODP Expeditions 314 and 315, in the Kumano Basin,Nankai trough     

Ayumu Miyakawa  Saneatsu Saito  Yasuhiro Yamada  Hitoshi Tomaru  Masataka Kinoshita  Takeshi Tsuji 《Island Arc》2014,23(2):142-156

The degree of gas hydrate saturation at Integrated Ocean Drilling Program (IODP) Site C0002 in the Kumano Basin, Nankai Trough, was estimated from logging‐while‐drilling logs and core samples obtained during IODP Expeditions 314 and 315. Sediment porosity data necessary for the calculation of saturation were obtained from both core samples and density logs. Two forms of the Archie equation (‘quick‐look’ and ‘standard’) were used to calculate gas hydrate saturation from two types of electrical resistivity log data (ring resistivity and bit resistivity), and a three‐phase Biot‐type equation was used to calculate gas hydrate saturation from P‐wave velocity log data. The gas hydrate saturation baseline calculated from both resistivity logs ranges from 0% to 35%, and that calculated from the P‐wave velocity log ranges from 0% to 30%. High levels of gas hydrate saturation (>60%) are present as spikes in the ring resistivity log and correspond to the presence of gas hydrate concentrations within sandy layers. At several depths, saturation values obtained from P‐wave velocity data are lower than those obtained from bit resistivity data; this discrepancy is related to the presence of free gas at these depths. Previous research has suggested that gas from deep levels in the Kumano Basin has migrated up‐dip towards the southern and seaward edge of the basin near Site C0002. The high saturation values and presence of free gas at site C0002 suggest that a large gas flux is flowing to the southern and seaward edge of the basin from a deeper and/or more landward part of the Kumano Basin, with the southern edge of the Kumano Basin (the location of site C0002) being the main area of fluid accumulation.  相似文献   

A Note on Seasonal Variation in Radiolarian Abundance     

Richard Arthur Reyment  Isao Motoyama  Miyuki Ota  Yuichiro Tanaka 《Natural Resources Research》2008,17(3):187-195

A statistical analysis of two consecutive sequences of observations on radiolarian abundances in the western North Pacific, by methods appropriate to data on the simplex (i.e., compositional data), show that although the overall graphical presentations of the frequencies appear similar, there are substantial differences in the earlier part of each of the series. The results of the multivariate analyses are used for identifying those species that contribute most to the analysis. A brief guide to the mathematical properties of compositional data is given.  相似文献   

In situ Measurements of Tide Gauge Response and Corrections of Tsunami Waveforms from the Niigataken Chuetsu-oki Earthquake in 2007     

Yuichi Namegaya  Yuichiro Tanioka  Kuniaki Abe  Kenji Satake  Kenji Hirata  Masami Okada  Aditya R. Gusman 《Pure and Applied Geophysics》2009,166(1-2):97-116

Linear and nonlinear responses of ten well-type tide gauge stations on the Japan Sea coast of central Japan were estimated by in situ measurements. We poured water into the well or drained water from the well by using a pump to make an artificial water level difference between the outer sea and the well, then measured the recovery of water level in the well. At three tide gauge stations, Awashima, Iwafune, and Himekawa, the sea-level change of the outer sea is transmitted to the tide well instantaneously. However, at seven tide gauge stations, Nezugaseki, Ryotsu, Ogi, Teradomari, Banjin, Kujiranami, and Naoetsu, the sea-level change of the outer sea is not always transmitted to the tide well instantaneously. At these stations, the recorded tsunami waveforms are not assured to follow the actual tsunami waveforms. Tsunami waveforms from the Niigataken Chuetsu-oki Earthquake in 2007 recorded at these stations were corrected by using the measured tide gauge responses. The corrected amplitudes of the first and second waves were larger than the uncorrected ones, and the corrected peaks are a few minutes earlier than the uncorrected ones at Banjin, Kujiranami, and Ogi. At Banjin, the correction was significant; the corrected amplitudes of the first and second upward motion are +103 cm and +114 cm, respectively, while the uncorrected amplitudes were +96 cm and +88 cm. At other tide gauge stations, the differences between the uncorrected and corrected tsunami waveforms were insignificant.  相似文献   

Seismic velocity structure around the Hyuganada region, Southwest Japan, derived from seismic tomography using land and OBS data and its implications for interplate coupling and vertical crustal uplift   总被引：3，自引：0，他引：3  

M. Tahara  K. Uehira  H. Shimizu  M. Nakada  T. Yamada  K. Mochizuki  M. Shinohara  M. Nishino  R. Hino  H. Yakiwara  H. Miyamachi  K. Umakoshi  M. Goda  N. Matsuwo  T. Kanazawa 《Physics of the Earth and Planetary Interiors》2008,167(1-2):19-33

The Hyuganada region, a forearc region of Southwest Japan, is characterized by several interesting geological and geophysical features, i.e., significant aseismic crustal uplift of 120 m during the past 120 thousand years at the Miyazaki Plain, negative free-air gravity anomalies with the maximum magnitude of −130 mgal, and relatively less cohesive interplate coupling compared with that for off the Shikoku and Kii Peninsula. In order to examine the causes of these observations, we determined a detailed three-dimensional seismic velocity structure based on the seismic data observed by ocean bottom seismometers (OBS) and land stations. P- and S-wave tomographic velocity structures clearly indicate the subducting slab and also the zones of high Poisson's ratio at 25–35 km depth along the coastline of the northeastern part of the Hyuganada. The region with high Poisson's ratio may correspond to the serpentinized mantle wedge as suggested for other mantle wedges, and appears to be coincident with the zone for observed aseismic slips such as the slow-slip and after-slip events. Also, the detection may be related to a relatively weak interplate coupling in the Hyuganada region. The tomographic structures also indicate low velocity zones with a horizontal scale comparable to the Kyushu-Palau Ridge in and around the subducting slab. If we assume that the low velocity zones correspond to the subducted Kyushu-Palau Ridge, then the predicted gravity anomaly due to the density contrast between the low velocity zones and the surrounding region can explain about 60% of the gravity anomaly in the Hyuganada region. The buoyancy is probably an important factor for the crustal uplift observed in the Miyazaki Plain, the steep bending of the subducting slab and the normal fault-type earthquakes around the Hyuganada region.  相似文献   

The linear stability of the post-Newtonian triangular equilibrium in the three-body problem     

Kei Yamada  Takuya Tsuchiya 《Celestial Mechanics and Dynamical Astronomy》2017,129(4):487-507

Continuing a work initiated in an earlier publication (Yamada et al. in Phys Rev D 91:124016, 2015), we reexamine the linear stability of the triangular solution in the relativistic three-body problem for general masses by the standard linear algebraic analysis. In this paper, we start with the Einstein–Infeld–Hoffmann form of equations of motion for N-body systems in the uniformly rotating frame. As an extension of the previous work, we consider general perturbations to the equilibrium, i.e., we take account of perturbations orthogonal to the orbital plane, as well as perturbations lying on it. It is found that the orthogonal perturbations depend on each other by the first post-Newtonian (1PN) three-body interactions, though these are independent of the lying ones likewise the Newtonian case. We also show that the orthogonal perturbations do not affect the condition of stability. This is because these do not grow with time, but always precess with two frequency modes, namely, the same with the orbital frequency and the slightly different one due to the 1PN effect. The condition of stability, which is identical to that obtained by the previous work (Yamada et al. 2015) and is valid for the general perturbations, is obtained from the lying perturbations.  相似文献   

Distribution of sea cucumbers in relation to sediment characteristics in coral reef lagoons and adjacent waters around Ishigaki Island,southern Japan     

Iwao Tanita  Hideaki Yamada 《Marine Ecology》2019,40(5)

To elucidate which environmental factors affect lagoonal‐scale sea cucumber distributions in Ishigaki Island, Okinawa, Japan, intertidal and subtidal areas of three coral reef lagoons were classified into several ground divisions by bottom characteristics, and sea cucumber densities therein were compared with the composition of sediment cover, grain size and organic content, and coverage of macroalgae, seagrass, and massive corals. Holothuria atra, Holothuria leucospilota, Stichopus chloronotus, and Synapta maculata had highest densities in the nearshore areas but were rare in reef flats, probably because of wave disturbance and low areal cover of sand sediment as potential feeding environments. No relationship was observed between sea cucumber densities and sediment organic content or grain size. Thus, even if these sea cucumbers have selectivity for habitats with a high sediment organic content, the effect of such selectivity on the distribution seems to be limited to relatively small areas. The sea cucumber distributions can be classified by bottom sediment/biota composition into bedrock (H. leucospilota), sand (H. atra), and lagoonal types (St. chloronotus and Sy. maculata). These habitat selections were possibly related to various aspects of sea cucumber ecology such as refuge from predators or turbulence, or settlement and nursery place, which have implications for importance of the complexity of lagoonal‐scale topography and sediment/biota conditions for the coexistence of various holothurian species.  相似文献   

Rapid subsidence of the Kikai Seamount inferred from drowned Pleistocene coral limestone: Implication for subduction of the Amami Plateau,northern Philippine Sea     

Tsutomu Nakazawa  Akira Nishimura  Yasufumi Iryu  Tsutomu Yamada  Hiroshi Shibasaki  Satoshi Shiokawa 《Marine Geology》2008,247(1-2):35-45

Carbonate rock cores drilled on the Kikai Seamount, northern Philippine Sea are examined for better understanding of tectonic history of the northern Philippine Sea. The Kikai Seamount, the summit of which is at 1960 m water depth, is an isolated high on the northwestern part of the Amami Plateau formed by subduction-related arc volcanism, and is situated close to the axis of the Ryukyu Trench in front of the Ryukyu Arc, SW Japan. The seamount is capped with shallow-water carbonates such as coral rudstone. Detailed examinations of lithology, larger foraminiferal assemblages, and Sr isotope composition reveal that the core material comprises Miocene carbonates unconformably overlain by Early Pleistocene carbonates. It indicates rapid subsidence of the Kikai Seamount since the Early Pleistocene. The most probable cause of rapid subsidence is collision and subduction of the Amami Plateau laden with the Kikai Seamount. The rapid subsidence may have started when the western corner of the plateau reached the Ryukyu Trench and began subduction beneath the Ryukyu Arc. The onset of the subsidence is likely to be controlled by a motion change in the Philippine Sea Plate. The latest change in subduction direction from north to northwestward into northwestward to west has been believed to have occurred at 1-2 Ma during latest Pliocene to Early Pleistocene time. The change of direction resulted in the shift from oblique into right-angle subduction of the plate beneath the Ryukyu Arc and also the onset of the collision and subduction of the Amami Plateau.  相似文献