Possible associations of daytime fireballs and minor planets     

Ichiro Hasegawa 《Earth, Moon, and Planets》1995,71(3):311-316

Chinese and Japanese historical records of daytime fireballs, and world-wide daytime meteorite falls in the catalogue have been investigated. Among them, there are 253 and 104 records of great daytime fireballs in China and in Japan respectively, and 506 meteorite falls in the daytime are recorded in the Catalogue of Meteorites (1985).The same trends of seasonal and daily variations in the flux of daytime fireballs are clearly seen in both Chinese and Japanese records, and then the distributions of the daytime fireballs seem to suggest the association with meteorites and near-earth minor planets rather than with comets.Possible relations with minor planets, such as (1566) Icarus, (3671) Dionysius, (4450) Pan, (4486) Mithra and others are suggested.  相似文献   

Historical variation in the meteor flux as found in Chinese and Japanese chronicles     

Ichiro Hasegawa 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):129-142

Numbers of meteors recorded in Chinese and Japanese histories are counted. Two distinct maxima in Chinese records are found in the 11th and 15th centuries, and the latter is also recorded in Japan. Of those records, numbers of bright meteors with sound and great fireballs that appeared in the daytime are also investigated.Correlations between the meteor numbers and the apparitions of naked-eye comet likely to be found, and seasonal variations in the meteor flux recorded during nineteen centuries show two maxima in July–August and October–November, the latter may be related to the Taurid complex.  相似文献   

Frictional discharge at fault asperities: Origin of fractal seismo-electromagnetic radiation   总被引：1，自引：0，他引：1  

Jun Muto  Hiroyuki Nagahama  Takashi Miura  Ichiro Arakawa 《Tectonophysics》2007,431(1-4):113

To investigate the relation between the rock friction and the fractal electromagnetic radiation before the main-shock of earthquakes, we conducted a friction experiment simulating the motion of an asperity on a fault plane, and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals. This indicates that frictional discharges (plasma generations) could occur locally at microscopic asperities on fault surfaces. From concepts on the fractal size-distribution and temporal evolution of fault asperities, the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation (Benioff electromagnetic radiation) prior to earthquakes.  相似文献   

Additional flux arising from unresolved scales in eddying ocean models     

Mikitoshi Hirabara  Hiroshi Ishizaki  Goro Yamanaka  Hiroyuki Tsujino  Ichiro Ishikawa 《Journal of Oceanography》2010,66(5):633-647

An analysis is presented of snapshot data (eastward and northward velocity components: u and v; tracer such as potential temperature: τ) from an eddy-resolving (Rgrid: 1/12°) ocean model experiment, in order to explore a method for improving eddy-permitting model performance. Horizontal 3 × 3 R-grid averages give the eddy-permitting grid (P-grid: 1/4°) variables: 〈u〉, 〈v〉, and 〈τ〉, where 〈〉 denotes the spatial P-grid scale average. The difference between the horizontal tracer flux across the boundary face of a P-grid and that across the corresponding faces of R-grids is estimated as F_2E. It is found that the correlations among the gradients of u, v, and τ give a good approximation F_2C to the estimated flux F_2E. The approximated flux is a function of these gradients and the grid size. A method is presented for implementing the F_2C for density to an eddying ocean model as an additional advection. Practical experiments were conducted with a realistic configuration. It is shown that the zonal mean isotherms in the Kuroshio extension region are more flattened in the run using the proposed method than in another run using the conventional horizontal biharmonic operator, suggesting that the additional flux correction leads to an enhancement of sub-basin scale mixing.  相似文献   

Variable gain feedback control technique of active mass damper and its application to hybrid structural control     

Ichiro Nagashima  Yuzo Shinozaki 《地震工程与结构动力学》1997,26(8):815-838

A systematic design procedure and an algorithm are devised for variable gain feedback (VGF) control of buildings with active mass damper (AMD) systems. The limit of the stroke length of the auxiliary mass, which is considered to be one of the most important physical constraints for application of AMD systems to actual structures, is studied. A set of variable feedback gains is designed as a function of a single variable that indicates a trade-off between the reduction of the building response and the amplitude of the auxiliary mass stroke, and this variable is on-line controlled to keep the amplitude of the auxiliary mass stroke constant, and within its limits. A design method of static output feedback controller for modal control of buildings with non-classical damping is also presented. Next, an efficient control method for hybrid structural control is developed, with combined use of the VGF control and the static output feedback control. It is shown through numerical examples that the proposed control method effectively adapts the control performance according to the variation in the intensity level of the external excitations in such a manner that the amplitude of the auxiliary mass stroke is kept within its limits and the control power is restrained as well. The application range of the AMD systems is thereby improved significantly. © 1997 John Wiley & Sons, Ltd.  相似文献   

Two-dimensional asymmetric vortex merger: merger dynamics and critical merger distance     

Ichiro Yasuda  Glenn R. Flierl 《Dynamics of Atmospheres and Oceans》1997,26(3):159-181

Two-dimensional asymmetric merger of two like-signed vorticity monopoles with different sizes and vorticities is examined by combining simplified analytical models and contour dynamics experiments. The model results can capture the key dynamics and hence allow the prediction of the critical merger distance in a number of the situations. The models ignore deformation of one of the two vortices, replacing it with a point vortex, and employ a corotating frame of reference with a rotation rate estimated by point vortices. Thus, the two vortex problem becomes two separate problems of a single vortex in a background shear flow. Vortex merger is found to happen when the vortex cannot resist the background shear flow. Vortex merger and merging processes depend on the centroid distance d, the circulation ratio, (q_i and r_i are the vorticity and radius, respectively) and initial conditions. In the lowest order, the background flow is approximated by a uniform shear field, and the behavior of an elliptical vortex can be described by the Kida (1981) equation supplemented with one describing the time evolution of the centroid distance. This model reveals that merger takes place because the natural rotation of an elliptical vortex is overcome by the background uniform shear flow; the ellipse inversely rotates and is drawn out by the background straining field. The vortex deformation in a background flow field induces an inward flow at the position of the other vortex; as a result, the centroid distance decreases and two vortices merge. The critical merger distance from this model agrees quite well with the results from contour dynamics experiments for two vortices. Inclusion of higher order non-uniform shear in the background flow extends the critical merger distance, which gives almost perfect estimates for the experiment. In the non-uniform shear flow, partial merger occurs, where the vortex sheds off a filament, but the remaining part of the vortex resumes its natural rotation.  相似文献