Nine requirements for the origin of Earth's life:Not at the hydrothermal vent,but in a nuclear geyser system     

Shigenori Maruyama  Ken Kurokawa  Toshikazu Ebisuzaki  Yusuke Sawaki  Konomi Suda  M.Santo 《地学前缘(英文版)》2019,10(4):1337-1357

The origin of life on Earth remains enigmatic with diverse models and debates.Here we discuss essential requirements for the first emergence of life on our planet and propose the following nine requirements:(1)an energy source(ionizing radiation and thermal energy);(2)a supply of nutrients(P.K.REE.etc.);(3)a supply of life-constituting major elements;(4)a high concentration of reduced gases such as CH_4,HCN and NH_3;(5)dry-wet cycles to create membranes and polymerize RNA;(6)a non-toxic aqueous environment;(7)Na-poor water;(8)highly diversified environments,and(9)cyclic conditions,such as dayto-night,hot-to-cold etc.Based on these nine requirements,we evaluate previously proposed locations for the origin of Earth's life,including:(1)Darwin's "warm little pond",leading to a "prebiotic soup" for life;(2)panspermia or Neo-panspermia(succession model of panspermia);(3)transportation from/through Mars;(4)a deepsea hydrothermal system;(5)an on-land subduct ion-zone hot spring,and(6)a geyser systems driven by a natural nuclear reactor.We conclude that location(6)is the most ideal candidate for the o rigin point for Earth's life because of its efficiency in continuously supplying both the energy and the necessary materials for life,thereby maintaining the essential "cradle" for its initial development.We also emphasize that falsifiable working hypothesis provides an important tool to evaluate one of the biggest mysteries of the universe-the origin of life.  相似文献   

Dynamic response of flexible rockfall barriers under different loading geometries   总被引：1，自引：1，他引：0  

Raymond C. H. Koo  Julian S. H. Kwan  Carlos Lam  Charles W. W. Ng  Jack Yiu  Clarence E. Choi  Axel K. L. Ng  Ken K. S. Ho  W. K. Pun 《Landslides》2017,14(3):905-916

Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing.  相似文献   

Assessing the additive risks of PSII herbicide exposure to the Great Barrier Reef     

Lewis SE  Schaffelke B  Shaw M  Bainbridge ZT  Rohde KW  Kennedy K  Davis AM  Masters BL  Devlin MJ  Mueller JF  Brodie JE 《Marine pollution bulletin》2012,65(4-9):280-291

Herbicide residues have been measured in the Great Barrier Reef lagoon at concentrations which have the potential to harm marine plant communities. Monitoring on the Great Barrier Reef lagoon following wet season discharge show that 80% of the time when herbicides are detected, more than one are present. These herbicides have been shown to act in an additive manner with regards to photosystem-II inhibition. In this study, the area of the Great Barrier Reef considered to be at risk from herbicides is compared when exposures are considered for each herbicide individually and also for herbicide mixtures. Two normalisation indices for herbicide mixtures were calculated based on current guidelines and PSII inhibition thresholds. The results show that the area of risk for most regions is greatly increased under the proposed additive PSII inhibition threshold and that the resilience of this important ecosystem could be reduced by exposure to these herbicides.  相似文献   

Toms River: A Story of Science and Salvation          下载免费PDF全文

Ken Hugo 《Ground water》2015,53(4):508-508

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Primary production and community respiration in a warm streamer associated with Kuroshio warm core ring in spring     

Mitsuyasu Waku  Ken Furuya 《Journal of Oceanography》1998,54(5):565-572

Daily rates of gross primary production, net community production and community respiration were determined in spring of 1997 at two stations in a warm streamer off Sanriku, Japan fromin vitro changes in dissolved oxygen. The phytoplankton community was composed of chlorophytes, cryptophytes and prymnesiophytes as determined by biomarker pigment analysis. Gross production, integrated from the surface to its 1% light level was 52.5 and 80.4 mmol O₂ m⁻²d⁻¹. The difference in gross production is ascribed to variations in photosynthetic activity of the population. Community respiration was 17.4 and 49.5 mmol O₂ m⁻²d⁻¹, and positive net community production was found within the euphotic zone. The contribution of autotrophic and heterotrophic respiration to community respiration was estimated on the basis of the observed respiration and the phytoplankton composition. Heterotrophic respiration was calculated to be highly variable and the observed difference in community respiration was due to heterotrophic respiration. Heterotrophic respiration was considered to play an important role in the rapid mineralization of organic materials.  相似文献   

The basement geology of Japan from A to Z     

Simon R. Wallis  Ken Yamaoka  Hiroshi Mori  Akira Ishiwatari  Kazuhiro Miyazaki  Hayato Ueda 《Island Arc》2020,29(1)

The Precambrian and lower Paleozoic units of the Japanese basement such as the Hida Oki and South Kitakami terranes have geological affinities with the eastern Asia continent and particularly strong correlation with units of the South China block. There are also indications from units such as the Hitachi metamorphics of the Abukuma terrane and blocks in the Maizuru terrane that some material may have been derived from the North China block. In addition to magmatism, the Japanese region has seen substantial growth due to tectonic accretion. The accreted units dominantly consist of mudstone and sandstone derived from the continental margin with lesser amounts of basaltic rocks associated with siliceous deep ocean sediments and local limestone. Two main phases of accretionary activity and related metamorphism are recorded in the Jurassic Mino–Tanba–Ashio, Chichibu, and North Kitakami terranes and in the Cretaceous to Neogene Shimanto and Sanbagawa terranes. Other accreted material includes ophiolitic sequences, e.g. the Yakuno ophiolite of the Maizuru terrane, the Oeyama ophiolite of the Sangun terrane, and the Hayachine–Miyamori ophiolite of the South Kitakami terrane, and limestone‐capped ocean plateaus such as the Akiyoshi terrane. The ophiolitic units are likely derived from arc and back‐arc basin settings. There has been no continental collision in Japan, meaning the oceanic subduction record is more complete than in convergent orogens seen in intracontinental settings making this a good place to study the geological record of accretion. Hokkaido lacks most of the Paleozoic history recognized in Honshu, Shikoku, Kyushu, and the Ryukyu Islands to the south and its geology reflects the Cenozoic development of two convergent domains with volcanic arcs, their approach, and eventual collision. The Hidaka terrane reveals a cross section through a volcanic arc and the main accretionary complex of the convergent system is represented by the Sorachi–Yezo terrane.  相似文献   

Wave plus current over a ripple-covered bed     

Jrgen Fredse  Ken H. Andersen  B. Mutlu Sumer 《Coastal Engineering》1999,38(4):594

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Improved numerical analysis for ultimate behavior of elastomeric seismic isolation bearings     

Ken Ishii  Masaru Kikuchi 《地震工程与结构动力学》2019,48(1):65-77

Elastomeric isolation bearings consist of multiple rubber layers with their top and bottom surfaces bonded to steel plates to restrict compressive deformation. Deformation constraints result in a variation of elastic modulus over the cross section of the rubber layers. In this paper, we describe a normalized compression modulus distribution on a circular rubber pad. The compressive and bending moduli of the rubber pad can be reproduced by applying the distribution to a series of axial springs. We also present a mechanical model for predicting the behavior of elastomeric seismic isolation bearings subject to large shear deformation and high compressive load. The mechanical model consists of a series of multiple shear springs at midheight and a series of axial springs at the top and bottom interfaces of the bearing. Simulation analyses of bearing tests were conducted to validate the proposed model. The analyses demonstrated that a model for circular lead-rubber bearings can successfully capture the influence of the axial load magnitude on the bearing shear behavior. The new model can simulate much more realistic behavior than prior models based on a uniform modulus assumption.  相似文献