The effect of a thin weak layer covering a basalt block on the impact cratering process     

Koji Dohi  Masahiko Arakawa  Chisato Okamoto  Sunao Hasegawa  Minami Yasui 《Icarus》2012,218(2):751-759

To clarify the effect of a surface regolith layer on the formation of craters in bedrock, we conducted impact-cratering experiments on two-layered targets composed of a basalt block covered with a mortar layer. A nylon projectile was impacted on the targets at velocities of 2 and 4 km s^?1, and we investigated the crater size formed on the basalt. The crater size decreased with increased mortar thickness and decreased projectile mass and impact velocity. The normalized crater volume, π_V, of all the data was successfully scaled by the following exponential equation with a reduction length λ₀: ${\pi }_{\text{V}}=b_0{\pi }_{\text{Y}}^{-b_1}\exp (-\lambda /{\lambda }_0)$, where λ is the normalized thickness T/L_p, T and L_p are the mortar thickness and the projectile length, respectively, b₀ and b₁ are fitted parameters obtained for a homogeneous basalt target, 10^?2.7±0.7 and ?1.4 ± 0.3, respectively, and λ₀ is obtained to be 0.38 ± 0.03. This empirical equation showing the effect of the mortar layer was physically explained by an improved non-dimensional scaling parameter, ${\pi }_{\text{Y}}^1$, defined by ${\pi }_{\text{Y}}^1=Y/({\rho }_{\text{t}}{u}_{\text{p}}^2)$, where u_p was the particle velocity of the mortar layer at the boundary between the mortar and the basalt. We performed the impact experiments to obtain the attenuation rate of the particle velocity in the mortar layer and derived the empirical equation of $\frac{u_{\text{p}}}{v_{\text{i}}}=0.50\exp \left(-\frac{\lambda }{1.03}\right)$, where v_i is the impact velocity of the projectile. We propose a simple model for the crater formation on the basalt block that the surface mortar layer with the impact velocity of u_p collides on the surface of the basalt block, and we confirmed that this model could reproduce our empirical equation showing the effect of the surface layer on the crater volume of basalt.  相似文献   

Restitution coefficients and sticking velocities of a chondrule analogue colliding on a porous silica layer at impact velocities between 0.1 and 80 m s−1     

Yo-ichiro Uchiyama  Masahiko Arakawa  Chisato Okamoto  Minami Yasui 《Icarus》2012,219(1):336-344

To study the accretional growth of rimmed chondrules and their agglomerates in the solar nebula, we measured the restitution coefficients, ε, and the sticking velocities to a porous silica layer, v_c, by impacting the silica layer with a glass ball at velocities from 0.1 to 80 m s^?1. We used a porous silica layer covering a basalt block with thicknesses ranging from 1/5 of the glass ball radius to equal to the glass ball radius as a rimmed chondrule analogue, and the porosity of the silica layer was set to be 70%, 80%, 85%, and 90%. Collisional experiments were conducted by means of the free fall method or by the use of a spring gun or a gas gun, allowing us to vary the impact velocity. We used a laser displacement meter to estimate the impact and rebound velocities as well as the acceleration during the collision at impact velocities below 1 m s^?1. As a result, the sticking velocity, v_c, of 90%- and 85%- porosity layers with a thickness equal to 1/2 of the glass ball diameter was 0.44 and 2.4 m s^?1, respectively. On the other hand, we found a distinct barrier to sticking for smaller-porosity layers: the silicate layer with a porosity smaller than 80% never exhibited sticking at any impact velocity below 1 m s^?1. Instead, we observed a rebound effect with restitution coefficients larger than 0.2. In the case of a silica layer with a porosity smaller than 80%, we observed the sub-sticking condition defined by ε < 0.1 at velocities extending from 5 m s^?1 to 70 m s^?1.  相似文献   

Petrogenesis of the Mesozoic intrusive complexes from the southern Taihang Orogen,North China Craton: elemental and Sr–Nd–Pb isotopic constraints     

B.?ChenEmail author  B.?M.?Jahn  Y.?Arakawa  M.?G.?Zhai 《Contributions to Mineralogy and Petrology》2004,148(4):489-501

A geochemical and isotopic study was carried out for three Mesozoic intrusive suites (the Xishu, Wuan and Hongshan suites) from the North China Craton (NCC) to understand their genesis and geodynamic implications. The Xishu and Wuan suites are gabbroic to monzonitic in composition. They share many common geochemical features like high Mg# and minor to positive Eu anomalies in REE patterns. Initial Nd–Sr isotopic compositions for Xishu suite are _Nd(135 Ma)=–12.3 to –16.9 and mostly I_Sr = 0.7056–0.7071; whereas those for Wuan suite are slightly different. Pb isotopic ratios for Xishu suite are (²⁰⁶Pb/²⁰⁴Pb)_i = 16.92–17.3, (²⁰⁷Pb/²⁰⁴Pb)_i=15.32–15.42, (²⁰⁸Pb/²⁰⁴Pb)_i=37.16–37.63, which are slightly higher than for Wuan suite. The Xishu–Wuan complexes are considered to originate from partial melting of an EM1-type mantle source, followed by significant contamination of lower crustal components. The Hongshan suite (mainly syenite and granite) shows distinctly higher _Nd(135 Ma) values (–8 to –11) and slightly higher Pb isotopic ratios than the Xishu–Wuan suites. It was formed via fractionation of a separate parental magma that also originated from the EM1-type mantle source, with incorporation of a small amount of lower crustal components. Partial melting of the mantle sources took place in a back-arc extensional regime that is related to the subduction of the paleo-Pacific slab beneath the NCC.  相似文献   

The ultraviolet spectra of thin evaporated films of carbonaceous chondrite     

T. Inagaki  S. Yabushita  K. Wada  E. T. Arakawa 《Astrophysics and Space Science》1993,206(1):111-117

Absorption spectra in the visible to the near ultraviolet were measured on the Belgica chondrite B-7904 in a form of thin solid film made by the vacuum evaporation. The spectra obtained exhibit a sharp peak at 226 nm and a broad bump around 280nm. These features were found arising from the meteorite component FeS (troilite). The peak at 226 nm shows a doublet structure with the band-width considerably narrower than the 217.5 nm feature in the interstellar extinction. The absorption spectra obtained previously with the pulverized chondrites suspended in a liquid were also found reproducible by the pulverized FeS.Sponsored by the Office of Health and Environmental Research, U.S. Department of Energy under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.  相似文献   

Two minima of the average rainfall at about the turn of the century and at about 1940 in the Far East     

H. Arakawa 《Theoretical and Applied Climatology》1956,7(3-4):406-412

Summary Secular changes as revealed by the readings of the river gauge at Hankow, China; rainfall records at Seoul since 1770 and annual totals of rainfall at six representative weather stations in Japan show two pronounced minima of the average rainfall at about the turn of this century and at about 1940. Thus this variation in rainfall was paralleled in the Far East, and it seems to have been of world-wide extent. Recent gradual increase of annual precipitation is really of great practical value for economical life in the Far East.

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Zusammenfassung Säkulare Schwankungen, die einerseits durch Ablesungen am Flußpegel in Hankau (China), andrerseits durch Regenmessungen in Söul (Korea) seit 1770 und durch Jahresniederschlagsmengen an sechs repräsentativen meteorologischen Stationen in Japan belegt sind, zeigen zwei ausgesprochene Minima der mittleren Regenmengen etwa um die letzte Jahrhundertwende und um 1940. Diese Niederschlagsschwankungen verliefen somit im ganzen Fernen Osten parallel, und sie scheinen sogar weltweite Ausdehnung gehabt zu haben. Die neuere allmähliche Zunahme der Jahresniederschläge besitzt eine große Bedeutung für das wirtschaftliche Leben im Fernen Osten.

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Résumé Les variations séculaires, établies d'une part à partir des résultats des lectures d'un limnimètre à Hankau (Chine), d'autre part des mesures pluviométriques à Séoul (Corée) depuis 1770 et des sommes annuelles des précipitations de six stations météorologiques représentatives du Japon, indiquent deux minima prononcés des quantités moyennes des précipitations, l'un se situant vers 1900, l'autre vers 1940. Cette variation des précipitations fut donc parallèle dans tout l'Extrême Orient et il semble même qu'elle s'étendit sur toute la terre. L'augmentation progressive récente des précipitations annuelles est d'une grande importance pour la vie économique en Extrême Orient.

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With 5 Figures  相似文献   

Über optische Erscheinungen während Eines Taifuns     

Dr. H. Arakawa 《Pure and Applied Geophysics》1955,32(1):225-226

Ohne Zusammenfassung  相似文献   

Sr–Nd isotopic and chemical characteristics of the silicic magma reservoir of the Aira pyroclastic eruption, southern Kyushu, Japan     

Yoji Arakawa  Mie Kurosawa  Kaori Takahashi  Yoji Kobayashi  Masashi Tsukui  Hiroshi Amakawa 《Journal of Volcanology and Geothermal Research》1998,80(3-4)

Sr and Nd isotope and geochemical investigations were performed on a remarkably homogeneous, high-silica rhyolite magma reservoir of the Aira pyroclastic eruption (22,000 years ago), southern Kyushu, Japan. The Aira caldera was formed by this eruption with four flow units (Osumi pumice fall, Tsumaya pryoclastic flow, Kamewarizaka breccia and Ito pyroclastic flow). Quite narrow chemical compositions (e.g., 74.0–76.5 wt% of SiO₂) and Sr and Nd isotopic values (⁸⁷Sr/⁸⁶Sr=0.70584–0.70599 and _Nd=−5.62 to −4.10) were detected for silicic pumices from the four units, with the exception of minor amounts of dark pumices in the units. The high Sr isotope ratios (0.7065–0.7076) for the dark pumices clearly suggest a different origin from the silicic pumices. Andesite to basalt lavas in pre-caldera (0.37–0.93 Ma) and post-caldera (historical) eruptions show lower ⁸⁷Sr/⁸⁶Sr (0.70465–0.70540) and higher _Nd (−1.03 to +0.96) values than those of the Aira silicic and dark pumices. Both andesites of pre- and post-caldera stages are very similar in major- and trace-element characteristics and isotope ratios, suggesting that the both andesites had a same source and experienced the same process of magma generation (magma mixing between basaltic and dacitic magmas). Elemental and isotopic signatures deny direct genetic relationships between the Aira pumices and pre- and post-caldera lavas. Relatively upper levels of crust (middle–upper crust) are assumed to have been involved for magma generation for the Aira silicic and dark pumices. The Aira silicic magma was derived by partial melting of a separate crust which had homogeneous chemistry and limited isotope compositions, while the magma for the Aira dark pumice was generated by AFC mixing process between the basement sedimentary rocks and basaltic parental magma, or by partial melting of crustal materials which underlay the basement sediments. The silicic magma did not occupy an upper part of a large magma body with strong compositional zonation, but formed an independent magma body within the crust. The input and mixing of the magma for dark pumices to the base of the Aira silicic magma reservoir might trigger the eruptions in the upper part of the magma body and could produce a slight Sr isotope gradient in the reservoir. An extremely high thermal structure within the crust, which was caused by the uprise and accumulation of the basaltic magma, is presumed to have formed the large volume of silicic magma of the Aira stage.  相似文献   

Intrinsic equations of motion in dynamical meteorology     

Dr. H. Arakawa 《Pure and Applied Geophysics》1951,20(1):50-55

Summary Tangential and normal equations of horizontal motion along and normal to the characteristic lines (for example: stream lines, isobars, isotherms, etc.) are derived in general form. Then the later section of this paper is devoted to applications to natural coordinates and the coordinates chosen to lie parallel and normal to the isobars.  相似文献   

F-2 Secondary devices of wave energy converters     

Chuichi Arakawa 《Ocean Engineering》1985,12(6):551

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Eruptive history of Sundoro volcano,Central Java,Indonesia since 34 ka     

Oktory Prambada  Yoji Arakawa  Kei Ikehata  Ryuta Furukawa  Akira Takada  Haryo Edi Wibowo  Mitsuhiro Nakagawa  M. Nugraha Kartadinata 《Bulletin of Volcanology》2016,78(11):81

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