Sticking in moderate velocity oblique impact: Application to planetology

The sticking behavior of metal—metal collisions in the velocity range ～50–650 m/sec—has been investigated experimentally. A map of sticking efficiency versus impact angle and impact velocity has been established for lead. The threshold sticking velocity for normal impact equals approximately 100 m/sec for lead, 140 m/sec for tin, and 500 m/sec for iron in the case of spherical projectiles of 8-mm diameter, and a semi-infinite target. The boundary between the plastic rebound area and the perfect sticking area is found to be a line of constant normal velocity. The case when projectile mass is equal to target. ass ($\text{?3}\text{g}$, lead) has been investigated as well. The experimental results have been extrapolated to higher temperature and then applied to iron, nickel, and magnesium silicate. Near the melting point ($\text{?1800°}\text{K}$), the sticking velocities were estimated as 250–350 m/sec for iron and nickel and about 40% higher for magnesium silicate. It was concluded that metals stick more easily than rocky materials because of their lower sticking velocity and much larger interval of temperature over which sticking is possible.     

Some instabilities in the 3/1 and 2/1 resonances

In a very simple way, it is possible to show the existence of small regions of instability, inside the observed 3/1 and 2/1 Kirkwood Gap, by using the classical Laplace-Lagrange secular theory.     

On the mass determination of collapsed objects in close binaries: Applications to black-holes and neutron stars

Observational information required for determination of the masses of collapsed objects in close binaries is examined. Assumptions commonly used to evaluate the masses or thier lower limits, in the absence of the required observational data, are critically discussed. A reliable determination of the mass of a collapsed object in X-ray emitting binaries is yet to be made. No definitive case has been made for or against the existence of a black-hole in CygX-1.     

Japanese Astrometry Satellite Mission for Infrared Exploration

JASMINE is the name of a Japanese infrared (K-band) scanning astrometric satellite. JASMINE (I and/or II-project) is planned to be launched between 2013 and 2017 and will measure parallaxes and proper motions with the precision of 10μas at K≃ 12 - 15 mag. JASMINE will observe a few hundred million stars belonging to the disk and the bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Furthermore, JASMINE will also obtain photometry of stars in K, J and H-bands. The main objective of JASMINE is to study the most fundamental structure and evolution of the disk and the bulge components of the Milky Way Galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Recovery of entire shocked samples in a range of pressure from ~100 GPa to Hugoniot elastic limit

We carried out laser shock experiments and wholly recovered shocked olivine and quartz samples. We investigated the petrographic features based on optical micrographs of sliced samples and found that each recovered sample comprises three regions, I (optically dark), II (opaque), and III (transparent). Scanning electron microscopy combined with electron backscattered diffraction shows that there are no crystal features in the region I; the materials in the region I have once melted. Moreover, numerical calculations performed with the iSALE shock physics code suggest that the boundary between regions II and III corresponds to Hugoniot elastic limit (HEL). Thus, we succeeded in the recovery of the entire shocked samples experienced over a wide range of pressures from HEL (~10 GPa) to melting pressure (~100 GPa) in a hierarchical order.     

Numerical modelling study on the flexural uplift of the Transantarctic Mountains

In this study, based on a 2-D thermomechanical finite element model, the uplift of the Transantarctic Mountains (TAM) is discussed in relation to the flexural uplift of a rheologically layered lithosphere, which is described by Vening-Meinesz's cantilever kinematics. The general model behaviour shows that the thickness of the crust and the geothermal gradient in the lithosphere are the principal factors in controlling the effective elastic thickness ( T _e). Although T _e is also significantly dependent on the magnitude of the uplift and the wet or dry rheological condition of rocks, these two factors do not have a dominant influence on the half-wavelength of the TAM. The model with a plausible crustal structure beneath Antarctica shows that the thermal structure beneath East Antarctica is the critical factor, controlling the half-wavelength of the TAM. If there is a significant radiogenic heat source in the Antarctic lithosphere, T _e beneath East Antarctica is estimated to be 50 km, at most, and the lithosphere has no potential to explain an exceptionally large-scale half-wavelength of the TAM. Even for the model without a heat source, if East Antarctica is significantly thermally influenced by West Antarctica, T _e is estimated to be about 60 km, and it is difficult to reproduce the half-wavelength of the TAM. Contrarily, when a radiogenic heat source is absent and the thermal structure beneath East Antarctica is not significantly affected by that beneath West Antarctica, the rheological structure beneath East Antarctica has the potential to reproduce the half-wavelength of the TAM ( T _e∼ 100 km). Thus, the presence of a radiogenic heat source in the crust and mantle and the thermal influence of West Antarctica on East Antarctica are crucial factors in the reproduction of the half-wavelength found in the TAM.     

Field experiments on remediation of coastal sediments using granulated coal ash

Field experiments were carried out to evaluate the effect of Granulated Coal Ash (GCA) on remediation of coastal sediments in terms of removing phosphates and hydrogen sulfide. Phosphate concentrations in the sediment were kept below 0.2 mg/l after the application of GCA, whereas those in the control sites increased up to 1.0 mg/l. The concentration of hydrogen sulfide in the sediment was maintained at almost zero in the experimental sites (GCA application sites) for over one year, whereas it ranged 0.1–2.4 mg S L⁻¹ in control sites. Meanwhile, individual number of benthos increased in the experimental sites by several orders of magnitude compared to the control sites. The major process involved in hydrogen sulfide removal by GCA was thought to be the increase in pH, which suppresses hydrogen sulfide formation. From our findings, we concluded that GCA is an effective material for remediating organically enriched coastal sediment.     

Effect of helix bending deflection on load settlement behaviour of screw pile

A screw pile has higher end bearing capacity than any other straight pipe piles due to its larger helix with respect to central shaft. However, larger helices are not frequently used as it will bend and may reduce the actual bearing capacity of the ground. In the present study, the effect of helix bending deflection on the load settlement behaviour and ultimate bearing capacity is investigated. To achieve the objectives, model scale pile load tests were conducted. The effect of helix bending on the load settlement behaviour at higher stress level was also investigated in this research. The helices with different helix-to-shaft-diameter ratios and thicknesses were used, so that clear difference of deformed and non-deformed screw piles in the load settlement behaviour can be observed. Dry Toyoura sand in dense state was used as a model ground. It is observed from test results that the helix bending deflection starts affecting the load settlement behaviour of the ground if it is more than the critical helix bending deflection. The ratio of critical helix bending deflection to outstand length decreases with increase in helix-to-shaft-diameter ratio, and its relationship is presented in this study. It is also observed that the Roark’s formula for flat circular plate having uniform load over a very small circular area with fixed outer edges showed good agreement with the measured helix bending deflection. In order to estimate the optimum helix thickness, the well-agreed equation is also modified with respect to critical helix bending deflection.

     

Expansion of the disturbing function for high eccentricity and large amplitude of libration

Following some ideas, developed by Woltjer (1928), Message (1989), Yokoyama (1988, 1989) and Duriez (1990) an expansion of the disturbing function is given for high values of the eccentricity and large amplitude of libration. The classical expansion can be obtained as a particular case of the present model. Several asteroids with high eccentricity and large amplitude of libration are tested and the results are much better than those obtained from the classical theory.