The definition of the ecliptic

The ecliptic as a mean orbital plane of the Sun in Le Verrier's theory is a mean orbital plane determined from the secular parts of the longitude of the ascending node and the inclination of the Sun with respect to a reference plane. On the other hand, the ecliptic in Newcomb's theory is so chosen that the latitude with respect to his ecliptic does not have cosg nor sing whereg is the mean anomaly of the Sun. The two definitions are really different in spite of their apparent similarity. Standish (1981) defined the ecliptic from a kinematical point of view, and it is shown that the ecliptic defined by Standish (in the rotating sense) does coincide with the ecliptic defined by Newcomb.     

Comment on ‘Poisson Equations of Rotational Motion for a Rigid Triaxial Body with Application to a Tumbling Artificial Satellite’ by Liu and Fitzpatrick

Liu and Fitzpatrick (1975) discussed the secular and long-periodic behavior of a dynamical system by using improper time-averaged equations. The correct time-averaged equations are given in this note.     

Undrained dynamic-loading ring-shear apparatus and its application to landslide dynamics

Landslides are gravitational mass movements of rock, debris or earth. Some move very slowly, thus conforming to the field of statics, but some move rapidly. Study of the initiation and motion of rapid landslides needs to develop Landslide Dynamics involving dynamic loading and dynamic generation/dissipation of excess pore-water pressure. New developments in science can be facilitated by new technological advances. This study aimed to develop a new apparatus that can geotechnically simulate the formation of the shear zone and the following long and rapid shear displacement that occurs in high-velocity landslides. Professor K. Sassa and his colleagues at DPRI (Disaster Prevention Research Institute), Kyoto University, have worked to develop an undrained dynamic-loading ring-shear apparatus for this purpose. A series of different types of apparatus (DPRI-3, 4, 5, 6, 7) have been developed from 1992 to the present. This paper describes the development of this apparatus and its application to the study of earthquake-induced landslides and the latest landslide-triggered debris flow in Japan. Also, tests of the latest version (DPRI-7) with a transparent shear box for direct observation of the shear zone during a rapid shearing are described.     

Seismic diagnosis of railway substructures by using secondary acoustic emission

One difficult task for the seismic diagnosis of existing structures is how to nondestructively evaluate the damage degree of invisible substructures, such as embedded foundations. To diagnose substructures efficiently, a method for nondestructive inspection is developed by applying acoustic emission (AE) technique. As a newly proposed method, characteristics of secondary AE induced by train operations were investigated, and experiments using model piles and in-situ AE monitoring of in-service railway bridges conducted under railroad traffic, from which it was demonstrated that the proposed method is practicable enough to detect invisible defects in structures. A new index, known as RTRI (ratio of Repeated Train load at the onset of AE activity to Relative maximum load for Inspection period) is proposed for structural damage qualification based on the results of in-situ AE monitoring.     

Location and parameters of a microwave millisecond spike event

A typical microwave millisecond spike event on November 2, 1997 was observed by the radio spectrograph of National Astronomical Observatories (NAOs) at 2.6–3.8 GHz with high time and frequency resolution. This event was also recorded by Nobeyama Radio Polarimeters (NoRP) at 1–35 GHz and Radio Heliograph (NoRH) at 17 GHz. The source at 17 GHz is located in one foot-point of a small bright coronal loop of YOHKOH SXT and SOHO EIT images with strong photospheric magnetic field in SOHO MDI magnetograph. It is assumed that the electron cyclotron maser instability and gyro-resonance absorption dominate, respectively, the rising and decay phase of the spike event. For different harmonic number of gyro-frequency or magnetic field strength, a fitting program with free plasma parameters is used to minimize the difference between the observational and theoretical values of the exponential growth and decay rates for a given spike. The plasma parameters at third harmonic number are more comparable to their typical values in solar corona. Hence, it is able to provide a diagnosis for the source parameters (magnetic field, density, and temperature), the properties of radiations (wave vector and propagation angle), and the properties of non-thermal electrons (density, pitch angle, and energy). The results are also comparable with the diagnosis of the gyro-synchrotron radiation model, the frequency drift rates and a dipole magnetic field model, as well as the YOHKOH SXT and SOHO MDI data. This study is supported by the NFSC project nos. 10333030 and 10273025, and “973” program with no. G2000078403.     

Candidate precursors: pulse-like geoelectric signals possibly related to recent seismic activity in Japan

Telemetric network observations of pulse-like geoelectric charge signals using a vertical dipole buried under the ground were undertaken at various observation sites over a wide area in Japan from April 1996. From continuous records of the signals during the six months following that, we attempted to select anomalous signals, possibly related to seismic electric activity. Special attention was paid to the elimination of noise resulting from industrial and meteorological electric activity, comparison with other electromagnetic signals in the VLF band and the relation between the precursor period and the distance from the eventual main shock that occurred in Japan. Four candidate precursor electric signals, which were not contaminated by industrial and meteorological electric activity, were then selected, of which the second appeared before the Akita-ken Nairiku-nanbu earthquake swarm, for which the maximum M = 5.9 occurred on 1996 August 11, and the third and fourth before the Chiba-ken Toho-oki earthquake, M = 6.6, on 1996 September 11. A tentative qualitative model explaining why the candidate precursory signal is related to stress building up before an earthquake is presented in terms of the electrification of gases released from fracturing rocks immediately prior to the main shock.     

Use of an optical oxygen sensor to measure dissolved oxygen in seawater

The use of an optical oxygen sensor to measure dissolved oxygen in seawater was investigated. The sensor is based on the dynamic quenching of an oxygen-sensitive fluorochrome embedded in the tip. Dissolved oxygen in seawater samples collected from eight stations at depths ranging from 3000 to 6000 m was analyzed both with the optical sensor and by the Winkler titration method. The two sets of data did not differ significantly. The stability and simplicity of the method and the good agreement of the results with those of the titration method indicate that the sensor would be useful for fieldwork.     

Simulation of Formation and Spreading of Salinity Minimum Associated with NPIW Using a High-Resolution Model

A series of numerical experiments were conducted with a high-resolution (eddy-permitting) North Pacific model to simulate the formation and spreading of the salinity minimum associated with the North Pacific Intermediate Water (NPIW). It was found that two factors are required to simulate a realistic configuration of the salinity minimum: a realistic wind stress field and small-scale disturbances. The NCEP reanalyzed wind stress data lead to better results than the Hellerman and Rosenstein wind stress data, due to the closer location of the simulated Oyashio and Kuroshio at the western boundary. Small-scale disturbances formed by relaxing computational diffusivity included in the advection scheme promote the large-scale isopycnal mixing between the Oyashio and Kuroshio waters, simulating a realistic configuration of the salinity minimum. A detailed analysis of the Oyashio water transport was carried out on the final three-year data of the experiment with reduced computational diffusivity. Simulated transport of the Kuroshio Extension in the intermediate layer is generally smaller than the observed value, while those of the Oyashio and the flow at the subarctic front are comparable to the observed levels. In the Oyashio-Kuroshio interfrontal zone the zonally integrated southward transport of the Oyashio water (140–155°E) is borne by the eddy activity, though the time-mean flow reveals the existence of a coastal Oyashio intrusion. In the eastern part (155°E–180°) the zonally integrated transport of the Oyashio water indicates a southward peak at the southern edge of the Kuroshio Extension, which corresponds to the branching of the recirculating flow from the Kuroshio Extension. This revised version was published online in July 2006 with corrections to the Cover Date.