Backyard spectroscopy and photometry of Titan, Uranus and Neptune     

Ralph D Lorenz  Jessica M DooleyJ.Doug West  Mitsugu Fujii 《Planetary and Space Science》2003,51(2):113-125

We present and discuss observations of Titan (photometry and spectroscopy) and Uranus and Neptune (spectroscopy only) obtained using off-the-shelf equipment, affordable and available to many amateur astronomers and small colleges. Spectral observations compare well with published results from front-line observatories, and some evidence of seasonal change is evident in both spectra and narrowband photometry. Scattered Saturn light presents a significant problem for Titan observations, in particular, for slitless spectroscopy, and our attempts to reproduce Titan's lightcurve have so far been unsuccessful.  相似文献   

Varying Fine-Structure Constant and the Cosmological Constant Problem     

Yasunori Fujii 《Astrophysics and Space Science》2003,283(4):559-564

We start with a brief account of the latest analysis of the Oklo phenomenon providing the still most stringent constraint on time variability of the fine-structure constant α. Comparing this with the recent result from the measurement of distant QSO's appears to indicate a non-uniform time-dependence, which we argue to be related to another recent finding of the accelerating universe. This view is implemented in terms of the scalar-tensor theory, applied specifically to the small but nonzero cosmological constant. Our detailed calculation shows that these two phenomena can be understood in terms of a common origin, a particular behavior of the scalar field, dilaton. We also sketch how this theoretical approach makes it appropriate to revisit non-Newtonian gravity featuring small violation of Weak Equivalence Principle at medium distances. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Magnetic-Tower Jet Solution for Launching Astrophysical Jets     

Yoshiaki Kato 《Astrophysics and Space Science》2007,307(1-3):11-15

In spite of the large number of global three-dimensional (3-D) magnetohydrodynamic (MHD) simulations of accretion disks and astrophysical jets, which have been developed since 2000, the launching mechanisms of jets is somewhat controversial. Previous studies of jets have concentrated on the effect of the large-scale magnetic fields permeating accretion disks. However, the existence of such global magnetic fields is not evident in various astrophysical objects, and their origin is not well understood. Thus, we study the effect of small-scale magnetic fields confined within the accretion disk. We review our recent findings on the formation of jets in dynamo-active accretion disks by using 3-D MHD simulations. In our simulations, we found the emergence of accumulated azimuthal magnetic fields from the inner region of the disk (the so-called magnetic tower) and also the formation of a jet accelerated by the magnetic pressure of the tower. Our results indicate that the magnetic tower jet is one of the most promising mechanisms for launching jets from the magnetized accretion disk in various astrophysical objects. We will discuss the formation of cosmic jets in the context of the magnetic tower model.  相似文献   

High-resolution beamforming by the Wigner-Ville distribution method     

Imai  R. Hashimoto  Y. Kikuchi  K. Fujii  S. 《Oceanic Engineering, IEEE Journal of》2000,25(1):105-110

The Wigner-Ville distribution (WVD) function was originally proposed by Wigner in quantum mechanics and Ville applied it for signal analysis. This method has made it possible to represent a signal's power density spectrum in the time-frequency domain as a natural extension of the Fourier transform method (FTM). Recently, it has attracted great interest for its validity to analyze time-varying signals accomplished by the development of high-speed digital signal processing, and it is used for analyzing nonstationary signals. Conventionally, a sonar beamformer is constructed using delay lines, but the development of the high-speed processor has made it possible to apply the FTM for sonar beamforming. However, the bearing resolution of the beamformer is not enough for discriminating small underwater objects on the sea bottom by this method. To solve this problem, we aim to apply the WVD method, which can represent finer structure of signals as a natural extension of the FTM, for sonar beamforming to obtain sharper beam patterns than those of the beamforming method by FTM. Simulation results by computational calculations to clarify the resolution by the WVD method, which is presented in this paper, becomes approximately twice as high as by conventional FTM. The results of an experiment at sea also show the performance of this method  相似文献   

Incessant excitation of the Earth's free oscillations: global comparison of superconducting gravimeter records     

Kazunari Nawa  Naoki Suda  Yoshio Fukao  Tadahiro Sato  Yoshiaki Tamura  Kazuo Shibuya  Herbert McQueen  Heikki Virtanen  Jussi Kriinen 《Physics of the Earth and Planetary Interiors》2000,120(4):289-297

Records of superconducting gravimeters (SGs) at Canberra (Australia), Esashi (Japan), Metsähovi (Finland) and Syowa Stations (Antarctica) were analyzed to search for further evidence of background free oscillations of the Earth. Spectrograms for 1-year period and averaged power spectra for seismically quiet periods were obtained for each of the stations. Anomalous features of the oscillations observed at Syowa Station, such as an apparent seasonal variation and a high intensity at frequencies between 3 and 4 mHz, were absent at the other SG stations. Among the SG stations used in this study, the background free oscillations were detected most consistently and distinctly at Canberra, where the noise level was comparable to that at the IDA quietest station, while that at Syowa Station was close to the critical limit for detecting the oscillations. The background free oscillations provide a good reference to evaluate the noise level in the milliHertz band.  相似文献   

Zircon U–Pb sensitive high mass-resolution ion microprobe dating of granitoids in the Ryoke metamorphic belt, Kinki District, Southwest Japan     

Teruo Watanabe  Trevor Ireland  Yoshiaki Tainosho and  Yutaka Nakai 《Island Arc》2000,9(1):55-63

Abstract Zircon U–Pb sensitive high mass-resolution ion microprobe dating was carried out on three types of granitic rock (gneissose biotite granodiorite, biotite granite and two-mica granite) from the Cretaceous Ryoke belt of the Kinki district, Southwest Japan. The results give the ages of granitic magmatism in the Shigi-san area of between 87 and 78 Ma and suggest extensive melting of the Cretaceous Ryoke granitic crust to form the two-mica granite, probably at ca 80 Ma. Discrimination into older and younger granites based on development of gneissosity does not appear to represent the sequence of magma generation, although there is some scope in the interpretation of the zircon U–Pb data that would allow all three granites to form at 83 Ma. Compilation of chemical Th-U-total Pb isochron dating method ages, whole rock Rb–Sr isotope ages and U–Pb isotope ages indicates that most Ryoke plutonism occurred from ca 70 Ma to ca 100 Ma. Younger (85 Ma–70 Ma) plutonism with the formation of two-mica granite occurred only in the eastern sector of the Ryoke belt, including the Kinki District.  相似文献   

A fluorescent approach to the identification of grout injected into fissures and pore spaces   总被引：6，自引：0，他引：6  

Youqing Chen  Takashi Nishiyama  Michinao Terada  Yoshiaki Iwamoto 《Engineering Geology》2000,56(3-4):395-401

A new fluorescent approach was developed to visualize grouting processes. The evaluation of the effect of grouting is carried out by methods based mainly on physical measurements such as permeability and porosity characteristics. However, these estimates do not necessarily correlate with practical grouting data. In this paper, the distributions of various grout mixtures containing fluorescent substances were clearly visualized under ultraviolet light, using a borehole television system or a microscope. Since this approach enabled direct observation of grout distribution, it is considered that this approach is useful for analysis of grouting mechanisms, designing grout curtains, etc.  相似文献   

The effect of the contorted 'nose' of a subducting slab on the stress field in the continental lithosphere at an arc-arc junction     

Toshizo Minamino  Naoyuki Fujii 《Geophysical Journal International》1981,67(1):145-158

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Tsunami Source of the 2010 Mentawai, Indonesia Earthquake Inferred from Tsunami Field Survey and Waveform Modeling     

Kenji Satake  Yuichi Nishimura  Purna Sulastya Putra  Aditya Riadi Gusman  Haris Sunendar  Yushiro Fujii  Yuichiro Tanioka  Hamzah Latief  Eko Yulianto 《Pure and Applied Geophysics》2013,170(9-10):1567-1582

The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 10²¹ Nm, which corresponded to M_w 7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.  相似文献   

Heat as a tracer to estimate dissolved organic carbon flux from a restored wetland   总被引：1，自引：0，他引：1  

Burow KR  Constantz J  Fujii R 《Ground water》2005,43(4):545-556

Heat was used as a natural tracer to characterize shallow ground water flow beneath a complex wetland system. Hydrogeologic data were combined with measured vertical temperature profiles to constrain a series of two-dimensional, transient simulations of ground water flow and heat transport using the model code SUTRA (Voss 1990). The measured seasonal temperature signal reached depths of 2.7 m beneath the pond. Hydraulic conductivity was varied in each of the layers in the model in a systematic manual calibration of the two-dimensional model to obtain the best fit to the measured temperature and hydraulic head. Results of a series of representative best-fit simulations represent a range in hydraulic conductivity values that had the best agreement between simulated and observed temperatures and that resulted in simulated pond seepage values within 1 order of magnitude of pond seepage estimated from the water budget. Resulting estimates of ground water discharge to an adjacent agricultural drainage ditch were used to estimate potential dissolved organic carbon (DOC) loads resulting from the restored wetland. Estimated DOC loads ranged from 45 to 1340 g C/(m2 year), which is higher than estimated DOC loads from surface water. In spite of the complexity in characterizing ground water flow in peat soils, using heat as a tracer provided a constrained estimate of subsurface flow from the pond to the agricultural drainage ditch.  相似文献