A system of astronomical constants in the relativistic framework

The relation between the units and readings of time and space coordinates of terrestrial and barycentric reference frames is discussed from the viewpoint of general relativity. Attention is paid to the unit of space coordinates since the International Astronomical Union (IAU) regulates only the unit of time in the above two frames. Two definitions of unit of length are examined and their effects on the numerical expression of coordinate transformation, equations of planetary motions, and those for light propagation time are discussed. A clear conflict is found between the IAU (1976) recommendation on the definition of the time-scales in different frames of reference and the statement that all constants in the IAU (1976) new system of astronomical constants are defined in terms of the Internationsl System of units (SI units). One of the above two definitions is proposed to resolve this conflict by the least alteration to current procedures for analysing the recent astrometric observations such as the radar/laser rangings, the range and range-rate, and the very long baseline interferometric observations. Also, an interpretation of numerical values in the IAU (1976) new system of astronomical constants is presented. It is stressed that the definition proposed in this paper requires that a formula slightly different from that in current use be employed in the numerical transformation of readings of coordinates between the terrestrial and barycentric reference frames.     

Exsolved garnet-bearing pyroxene megacrysts from some South African kimberlites

Clinopyroxene and orthopyroxene megacrysts containing garnet lamellae up to 1.2 mm thick as an exsolved phase are found rarely in kimberlites from Frank Smith and Bellsbank. Chemically the clinopyroxenes are characteristically subcalcic, being within the range of 100 Ca/Ca + Mg + Fe = 27 to 36, and the orthopyroxenes are characterized by high Al₂O₃ and Cr₂O₃. Immediately after crystallization during very slow cooling, clinopyroxene and orthopyroxene exsolve wide-spaced orthopyroxene and clinopyroxene phases parallel to (100) of the host phases, respectively, then both host and exsolved phases exsolve garnet lamellae. Topotactic relations between pyroxenes and garnet are determined by X-ray for the first time. Partitioning of major and minor elements among the coexisting clinopyroxene, orthopyroxene and garnet in pyroxene megacrysts is the same as that of the granular-type garnet peridotite xenoliths in Lesotho and South African kimberlies. Mineralogy and chemistry indicate that subcalcic clinopyroxene and orthopyroxene megacrysts contain respectively about 10 and 3 mole % of the garnet molecule in solid solution.     

A new technique for non‐destructive field measurement of rock‐surface strength: an application of the Equotip hardness tester to weathering studies

Tafone‐like depressions have developed on the Aoshima sandstone blocks used for a masonry bridge pier in the coastal spray zone. A thin layer of partial granular disintegration was found on the surface in depressions. To evaluate quantitatively the strength of the thin weathered layer, the hardness was measured at the surface of the sandstone blocks using both an Equotip hardness tester and an L‐type Schmidt hammer. Comparison of the two testing results indicates that the Equotip hardness value is more sensitive in evaluating the strength of a thin layer of weathered surface rock than the Schmidt hardness value. By applying two methods, i.e. both the repeated impact method and the single impact method, the Equotip tester can evaluate the strengths of fresh internal and weathered surficial portions of rocks having a thin weathering layer. Comparison of the two strengths enables evaluation of strength reduction due to weathering. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface lowering rates of uplifted limestone terraces estimated from the height of pedestals on a subtropical island of Japan

In Kikai‐jima, south‐western Japan, many pedestal rocks have developed on the surface of Holocene raised coral‐reef terraces with known dates of emergence. Pedestals are formed just under boulders, which are considered to have been transported by tsunami and settled on a reef flat before emergence. On the assumption that boulders protect the underlying limestone terrace from rainfall solution, the rate of surface lowering of these limestone terraces was evaluated from the height of pedestals and the period of their formation. The result showed that the mean lowering rate over 6000 years is 205 mm/ky. Copyright © 2007 John Wiley & Sons, Ltd.     

Growth of twinned magnetic crystals in talc and talc-magnesite rock at Torika,Nagasaki Prefecture,Japan

Spinel-type twins of magnetite in a talc rock and a talk-magnesite rock at Torika, Nagasaki Prefecture, Japan have been studied by means of optical microscopy, differential interference microscopy, microprobe analysis and size distribution analysis. The growth processes are discussed in detail. The number of magnetite twins in the talc-magnesite rock is larger than in the talc rock, and the percentage of the frequency number increases rapidly with increase in grain size. It is suggested that magnetite crystals in the talc-magnesite rock have grown by rapid crystallization in the earlier stage and by a layer-growth mechanism in the later stage in the carbonation-dehydration reaction that occurred within the rock. As large number of twin nuclei formed by rapid crystallization in the earlier stage of magnetite formation. As the dehydration reaction proceeded, the number of twin nuclei gradually decreased with the lowering of supersaturation by addition of some water. Magnetite crystals in the talc rock formed after talc crystallization by silicification and dehydration reactions in the process of steatitization. The twin nuclei here must have formed with difficulty, governed by the distribution of talc which crystallized before the magnetite and at relatively low supersaturation.     

Chromian spinels in lherzolite inclusions from Itinome-gata,Japan

Spinel, which constitutes from 0.7% to 3% of lherzolite inclusions, occurs as primary anhedral grains (chrome-rich variety) and as a secondary phase as breakdown products of garnet (alumina-rich variety). Although individual primary spinel grains are chemically homogeneous, spinels are characterized by a wide range of Cr/Al ratios and a relatively narrow range of Mg/Fe″ ratios, even in a single lherzolite sample. The chemical variations of spinels are considered to have the following origin: When garnet lherzolite enters the stability field of the spinel peridotite facies as a consequence of slow upward transport, both orthopyroxenes and clinopyroxenes are recrystallized with loss of jadeite and some Tschermak's component to reach equilibrium. A part of the Tschermak's component reacts with olivine to form pyroxene and spinel. This secondary spinel component is alloted to the primary chromian spinel. However, these reactions did not always reach equilibrium with the major constituent minerals in the lherzolites.     

Sanidine—olivine—diopside Association in a Metasomatized Garnet Lherzolite Xenolith from Southeastern China

A garnet lherzolite xenolith hosted in olivine nephelinite from Xilong,Zhejiang Province ,southeastern China, shows clear evidence of modal metasomatism involving a special sanidine-olivine-diopside(SOD) association which was produced by replacement of primary orthopyroxene.The fluid responsible for the measomatism was a silica-undersaturated vapour,rich in K,Ba,Sr and Ti.It is suggested that the SOD assemblage is the product of metasomatism of a depleted lherzolite precursor,and formed in the upper mantle prior to entrainment and eruption.     

Raman spectroscopy and heat capacity measurement of calcium ferrite type MgAl2O4 and CaAl2O4

Raman spectroscopy of calcium ferrite type MgAl₂O₄ and CaAl₂O₄ and heat capacity measurement of CaAl₂O₄ calcium ferrite were performed. The heat-capacity of CaAl₂O₄ calcium ferrite measured by a differential scanning calorimeter (DSC) was represented as C_P(T)=190.6–1.116 × 10⁷T^–2 + 1.491 × 10⁹T^–3 above 250 K (T in K). The obtained Raman spectra were applied to lattice dynamics calculation of heat capacity using the Kieffer model. The calculated heat capacity for CaAl₂O₄ calcium ferrite showed good agreement with that by the DSC measurement. A Kieffer model calculation for MgAl₂O₄ calcium ferrite similar to that for CaAl₂O₄ calcium ferrite was made to estimate the heat capacity of the former. The heat capacity of MgAl₂O₄ calcium ferrite was represented as C_P(T)=223.4–1352T ^–0.5 – 4.181 × 10⁶T ^–2 + 4.300 × 10⁸T ^–3 above 250 K. The calculation also gave approximated vibrational entropies at 298 K of calcium ferrite type MgAl₂O₄ and CaAl₂O₄ as 97.6 and 114.9 J mol^–1 K^–1, respectively.     

Geostatistical Evaluation of the Mechanical Properties of Rock Mass for TBM Tunnelling by Seismic Reflection Method

Summary. The evaluation of the rock mass mechanical properties by the seismic reflection method and TBM driving is proposed for TBM tunnelling. The relationship between the reflection number derived from the three-dimensional seismic reflection method and the rock strength index (RSI) derived from TBM driving data is examined, and the methodology of conversion from the reflection number to the RSI is proposed. Furthermore a geostatistical prediction methodology to provide a three-dimensional geotechnical profile ahead of the tunnel face is proposed. The performance of this prediction method is verified by actual field data.     

Simulation of an Inertial Acoustic Navigation System With Range Aiding for an Autonomous Underwater Vehicle

This paper presents an integrated navigation system for underwater vehicles to improve the performance of a conventional inertial acoustic navigation system by introducing range measurement. The integrated navigation system is based on a strapdown inertial navigation system (SDINS) accompanying range sensor, Doppler velocity log (DVL), magnetic compass, and depth sensor. Two measurement models of the range sensor are derived and augmented to the inertial acoustic navigation system, respectively. A multirate extended Kalman filter (EKF) is adopted to propagate the error covariance with the inertial sensors, where the filter updates the measurement errors and the error covariance and corrects the system states when the external measurements are available. This paper demonstrates the improvement on the robustness and convergence of the integrated navigation system with range aiding (RA). This paper used experimental data obtained from a rotating arm test with a fish model to simulate the navigational performance. Strong points of the navigation system are the elimination of initial position errors and the robustness on the dropout of acoustic signals. The convergence speed and conditions of the initial error removal are examined with Monte Carlo simulation. In addition, numerical simulations are conducted with the six-degrees-of-freedom (6-DOF) equations of motion of an autonomous underwater vehicle (AUV) in a boustrophedon survey mode to illustrate the effectiveness of the integrated navigation system.