Rate-dependent strength of porous ice–silica mixtures and its implications for the shape of small to middle-sized icy satellites     

Minami Yasui  Masahiko Arakawa 《Icarus》2010,210(2):956-967

Porosity is one of the most important physical properties in the rheology of small icy satellites composed of ice–silicate mixtures. Deformation experiments involving ice and 1 μm silica bead mixtures were conducted to clarify the effect of porosity on the flow law of ice–silica mixtures. Mixtures with silica mass contents of 0, 30, and 50 wt.% were used for the experiments, and the porosity was changed from 0% to 25% in each mixture. The temperature ranged from −10 to −20 °C, and the strain rate was changed from 1.2 × 10⁻⁶ to 4.2 × 10⁻⁴ s⁻¹. As a result, it was found that the ice–silica mixtures deformed plastically, and that the relationship between the maximum stress, σ_max, on the stress–strain curve and the applied strain rate, , could be described by the following flow law: . The mixture became softer as the porosity or silica mass content increased, and the stress exponent n and activation energy Q were independent of porosity, depending only on the silica mass content. Furthermore, the parameter A₀ could be written as A₀ = B(1 − ?)^−α, where ? is the porosity. The constants B and α also depended only on the silica mass content, and they increased with the increase in this content. The Maxwell relaxation time was calculated in order to estimate the conditions for topographic relaxation of icy satellites, and it was found that topographic relaxation occurred at temperatures higher than 160 K in the case of icy satellites with mean radii of 200 km.  相似文献   

Experimental study on the collisional disruption of porous gypsum spheres     

Chisato Okamoto  Masahiko Arakawa 《Meteoritics & planetary science》2009,44(12):1947-1954

Abstract— In order to study the catastrophic disruption of porous bodies such as asteroids and planetesimals, we conducted several impact experiments using porous gypsum spheres (porosity: 50%). We investigated the fragment mass and velocity of disrupted gypsum spheres over a wide range of specific energies from 3 times 10³ J/kg to 5 times 10⁴ J/kg. We compared the largest fragment mass (m₁/M_t) and the antipodal velocity (V_a) of gypsum with those of non‐porous materials such as basalt and ice. The results showed that the impact strength of gypsum was notably higher than that of the non‐porous bodies; however, the fragment velocity of gypsum was slower than that of the non‐porous bodies. This was because the micro‐pores dispersed in the gypsum spheres caused a rapid attenuation of shock pressure in them. From these results, we expect that the collisional disruption of porous bodies could be significantly different from that of non‐porous bodies.  相似文献   

Petrographic and Geochemical Constraints on the Provenance of Sanidine‐Bearing Temper in Ceramic Potsherds,Four Corners Region,Southwest USA     

David A. Gonzales  Fumi Arakawa  Alan Koenig 《Geoarchaeology》2015,30(1):59-73

Previous researchers proposed that trachybasalt temper with “poikilitic” sanidine, found in pottery from the Mesa Verde region of the American Southwest, was procured along the eastern Chuska Mountains. This served as one line of evidence that Chaco Canyon was a regional trade center linked to the Chuska Mountains in the ninth to thirteenth centuries. Recent geologic studies, however, revealed other potential sources for the trachybasalt temper. A comparison of petrographic features and geochemical signatures of poikilitic sanidine in rock samples and potsherds shows no definitive correlation of temper materials and a specific geologic source. Several outcrops of trachybasalt are identified as less viable prospects, but the results do not support the idea that the sanidine‐rich temper was exclusively gathered in the Chuska Mountains. This conclusion opens up the possibility that raw materials were gathered from local sources that were more accessible, reducing the dependence on a regional trade center.  相似文献   

Cratering of icy targets by different impactors: Laboratory experiments and implications for cratering in the Solar System     

M.J. Burchell  J. Leliwa-Kopystyński  M. Arakawa 《Icarus》2005,179(1):274-288

Studies of impacts (impactor velocity about 5 km s⁻¹) on icy targets were performed. The prime goal was to study the response of solid CO₂ targets to impacts and to find the differences between the results of impacts on CO₂ targets with those on H₂O ice targets. The crater dimensions in CO₂ ice were found to scale with impact energy, with little dependence on projectile density (which ranged from nylon to copper, i.e., 1150-8930 kg m⁻³). At equal temperatures, craters in CO₂ ice were the same diameter as those in water ice, but were shallower and smaller in volume. In addition, the shape of the radial profiles of the craters was found to depend strongly on the type of ice and to change with impact energy. The impact speed of the data is comparable to that for impacts on many types of icy bodies in the outer Solar System (e.g., the satellites of the giant planets, the cometary nuclei and the Kuiper Belt objects), but the size and thus energy of the impactors is lower. Scaling with impact energy is demonstrated for the impacts on CO₂ ice. The issue of impact disruption (rather than cratering) is discussed by analogy with that on water ice. Expressions for the critical energy density for the onset of disruption rather than cratering are established for water ice as a function of porosity and silicate content. Although the critical energy density for disruption of CO₂ ice is not established, it is argued that the critical energy to disrupt a CO₂ ice body will be greater than that for a (non-porous) water ice body of the similar mass.  相似文献   

Foreword     

Yoji Kondo  Jürgen Rahe 《Astrophysics and Space Science》1987,130(1-2):1-2

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Measurements of the log-irradiance distribution of a laser wave propagated through the turbulent atmosphere     

Yoji Furuhama  Madoka Fukushima 《Boundary-Layer Meteorology》1973,4(1-4):433-447

Log-irradiance fluctuations of He-Ne laser light were simultaneously measured at three different points in the receiving plane. The cumulative probability distributions of log-irradiance show excellent agreement with the Rice-Nakagami distribution in the region of weak fluctuations. The irradiance distributions strongly depend upon the locations of the observing points with respect to the center of the beam, as expected from recent theory.  相似文献   

Oscillations and pulsations in the sun and stars (invited review)     

Yoji Osaki  Hiromoto Shibahashi 《Astrophysics and Space Science》1986,118(1-2):195-207

The discovery of the solar global oscillations, and their identification to many radial and nonradial eigenmodes of the Sun, have opened a new important field of research called solar seismology, in which we may probe the internal structure of the Sun by using its oscillations. In recent years, pulsations and oscillation-related phenomena have also been discovered in many stars which were hitherto regarded as non-pulsating stars. They include white dwards (ZZ Ceti-stars), Ap-stars, early-type stars with slow and rapid rotation (53 Per and Oph-stars, respectively). Developments in high spectral and high time-resolution observations will be expected to reveal variability in many other stars as well, in near future.In this review, the general properties of stellar eigenmode oscillations are first discussed. Recent observational and theoretical developments in the solar seismology and on pulsations and oscillations of newly discovered variable stars will then be reviewed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

Fundamental analysis of deep sea mooring line in static equilibrium     

Yoji Ogawa 《Applied Ocean Research》1984,6(3):140-147

The integrated equations of deep sea mooring lines in static equilibrium under consideration of gravity force and line elongation are obtained. The most useful forms of the equations for designing deep sea mooring system are those in which horizontal displacement and horizontal and vertical components of tension are obtained as functions of line length, water depth, critical tension and unit weight of line.When the dynamic simulation of a buoy system is carried out, line tensions acting on the buoy should be represented as a linear function of displacement. Therefore the linearisation method is introduced by use of linearisation coefficient matrix. Translation formulae for the matrix from two to three dimensions is also presented.The influence of line elongation on the horizontal component of tension in a taut mooring condition is important, therefore the elongation of stretched deep sea mooring line must be considered carefully. Also, the scaling law under consideration of line elongation in static equilibrium, which is necessary in estimation from a small sized experiment, is discussed.  相似文献   

Ultraviolet photometry from the orbiting astronomical observatory XXII. Ultraviolet light variation ofβ Lyrae     

Yoji Kondo  George E. McCluskey  Joel A. Eaton 《Astrophysics and Space Science》1976,41(1):121-137

Six-color ultraviolet light curves of the complex eclipsing binary system Lyr were obtained with the OAO-2 Wisconsin Experiment Package. The filters had a typical width at half maximum of 150 to 200 Å and centered at 1430, 1550, 1910, 2460, 2980 and 3320 Å. The most striking characteristics of the ultraviolet light curves are that the secondary minimum deepens at shorter wavelengths. This indicates that we arenot observing the eclipse effect of two stars having roughly a Planckian distribution of energy. In combination with the high resolution far ultraviolet spectra of Lyr recently obtained withCopernicus (OAO-3) Princeton Telescope Spectrometer, it is concluded that the far ultraviolet light curves are dominated by emission from the high temperature gas surrounding the binary system. The ultraviolet observations with OAO-2 andCopernicus are consistent with a model in which the enigmatic secondary component involves a gravitationally collapsed object, i.e., a black hole; however, alternative models are also admissible.  相似文献   

Rossby-Haurwitz's equation for the conservation of vertical vorticity component in the baroclinic atmosphere     

Dr. H. Arakawa 《Pure and Applied Geophysics》1950,18(1):158-159

Summary It is shown that the conservation equation of potential vorticity in the barotropic atmosphere holds good, even in the baroclinic atmosphere, if it is permissible to introduce the isentropic and mass-conservation approximations.  相似文献