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31.
Local time variation of geomagnetic transfer functions 总被引:1,自引:0,他引:1
Masahiko Takeda 《Geophysical Journal International》1997,130(3):765-770
The local time (LT) variation of the geomagnetic transfer function at the 32-min period was examined for observatories distributed worldwide. Two distinct variation types (types 1 and 2) were found in the real part of A. Type 1 is conspicuous at lower latitudes and its seasonal variation is small, whereas type 2 is found at higher latitudes and has its maximum in summer. These two types of LT variation are seen globally and are conspicuous when solar activity is high. The amplitudes of both types of variation vary from 0.018 to 0.078, and are independent of the mean values at each observatory. These values are relatively small, but the amplitude of Chambon la Foret is larger than the mean value, which shows that Au changes its sign in local time. The amplitudes of type 1 and 2 variations decrease and increase with geomagnetic latitude, respectively. These features suggest that they are generated by some global external fields. The most probable cause is the Sq field, although the Dp field may contribute to type 1 variation. On the other hand, for the islands of the Pacific Ocean at low latitudes, such as Honolulu and Chichijima, the type 1 variation appears not in the real but in the imaginary part of A, which suggests that currents induced in the ocean also contribute to the local time variation. 相似文献
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Eriko Kamiya Shinji Izumiyama Masahiko Nishimura James G. Mitchell Kazuhiro Kogure 《Journal of Oceanography》2007,63(1):101-112
Flow cytometry (FCM) is now becoming a routine tool for the enumeration and optical characterization of bacteria in marine
environments. We investigated the effects of sample fixation and storage upon flow cytometric determination of marine bacteria.
Fixed and unfixed seawater samples were analyzed by FCM immediately aboard ship and/or later in the laboratory, and the appearances
of the fluorescence signals and bacterial counts of these samples were compared. Fixation and storage led to the formation
of multiple peaks in fluorescence histograms; this was also seen in 22 out of 36 samples frozen in liquid nitrogen. Fixation
did not, but storage did induce a decrease of bacterial counts: a rapid decrease during the first 3 days followed by a slower
decline. The decline of cell numbers in stored samples was expressed by a regression model. Our studies indicate that precaution
is necessary when interpreting the data from fixed and/or stored marine bacterial samples analyzed by FCM. The possibility
that the procedure of fixation and storage leads to the appearance of high DNA and low DNA bacterial groups should be considered. 相似文献
36.
Taku Sato Masato Kobayashi Takayuki Takebe Narisato Hirai Koichi Okuzawa Sayumi Sawaguchi Takahiro Matsubara Tomofumi Yamaguchi Rihito Shinoda Masahiko Koiso Kazuhisa Teruya 《Marine Ecology》2018,39(1)
Most behavioral studies on hermaphroditic fishes have focused on small‐sized species, which are tractable for research. Although many species of large hermaphroditic fishes are important fishery resources, their proximate mechanisms (visual, chemical and/or behavioral cues) in the social regulation of sex change have not been determined. Determination of these would inform resource management and aquaculture. In order to get closer to understanding the proximate mechanisms underlying the social regulation of female‐to‐male sex change in large hermaphroditic fishes, this study reports situations that induced female‐to‐male sex change in black‐spot tuskfish, Choerodon schoenleinii, a species of large protogynous fish, in massive laboratory tanks. The situations differed in the possibility of male‐to‐female tactile contact and in the group sex ratio, enabling us to infer plausible proximate mechanisms underlying sex change induction. Tactile contact between individuals is suspected to be closely related to the incidence of female‐to‐male sex change in C. schoenleinii. Visual and chemical cues alone may be insufficient to inhibit such sex changes. Male‐to‐female tactile contact may have an important influence on female‐to‐male sex change, i.e., inhibition of this sex change, in this species. The effect of sex ratio of a social group on the incidence of sex change may be due to the relative frequency and intensity of male tactile contact with each female, which may vary with the number of females. In the absence of a dominant male, tactile contact among females may affect the incidence of sex change, as well as determine which individuals change sex. 相似文献
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Study of the effect of water-soluble fractions of heavy-oil on coastal marine organisms using enclosed ecosystems,mesocosms 总被引:1,自引:0,他引:1
Ohwada K Nishimura M Wada M Nomura H Shibata A Okamoto K Toyoda K Yoshida A Takada H Yamada M 《Marine pollution bulletin》2003,47(1-6):78-84
Mesocosm facilities composed of 4 experimental and 2 reservoir tanks (1.5 m in diameter, 3.0 m in depth and 5 tons in capacity) made of FRP plastics, were constructed in the concrete fish rearing pond in the Fisheries Laboratory, The University of Tokyo. The water-soluble fraction of Rank A heavy residual oil was formed by mixing 500 g of the oil with 10 l of seawater, which was introduced to the 5000 l-capacity tanks. Experimental Run 4 was conducted from May 31 to June 7, 2000. Oil concentrations in the tanks were 4.5 microg/l called LOW, and 13.5 microg/l, called HIGH tank. Bacterial growth rates very quickly accelerated in the HIGH tank just after the loading of oil which corresponded with a high increase of bacterial cells in the same tank after 2 days. Later, bacterial numbers in HIGH tank rapidly decreased, corresponding with the rapid increase of heterotrophic nano-flagellates and virus numbers on the same day. Sediment traps were deployed at the bottom of the experimental tanks, and were periodically retrieved. These samples were observed both under light microscope and epi-fluorescent microscope with UV-excitation. It was observed that the main components of the vertical flux were amorphous suspended matter, mostly originating from dead phytoplankton and living diatoms. It was further observed from the pictures that vertical transport of oil emulsions were probably conducted after adsorption to amorphous suspended matter and living diatoms, and were settling in the sediment traps at the bottom of the tanks. This means that the main force which drives the soluble fraction of oil into bottom sediment would be vertical flux of such amorphous suspended particles and phytoplankton. Further incubation of the samples revealed that the oil emulsions were degraded by the activity of autochtonous bacteria in the sediment in aerobic condition. 相似文献
39.
Impact strength and cratering ejecta were studied for porous targets of pure ice and icy-silicate mixture in order to clarify the accumulation and destruction (shattering) condition of small icy bodies. The icy projectile impacted on the cylindrical targets with the porosity up to 55% at a velocity of 150 to 670 m/s at −10°C. The porosity dependence of the impact strength and that of the maximum ejecta velocity were measured in each type of these targets. As a result, the maximum ejecta velocity normalized by the impact velocity (Ve-max/Vi) is found to depend only on the porosity (φ), irrespective of the target type; a relationship is derived to be Ve-max/Vi=−2.17φ+1.29. The impact strength of pure ice increased with increased target porosity, but that of mixture target had an opposite trend; that is, the strength decreased with increased porosity. These porosity dependencies of the impact strength could be explained by the porosity dependence of the physical parameters such as impact pressure, pressure decay, and static strength. Finally, the accumulation of small icy bodies is discussed to show that the collisional events can be divided into three types by the porosity and the collision velocity according to our experimental results: mass loss, rubble pile formation, and regolith formation (compaction). 相似文献
40.
Hiroshi Satake Masahiko Ohashi Yoshimitsu Hayashi 《Pure and Applied Geophysics》1984,122(2-4):185-193
The concentration of H2 in soil gases has been measured weekly at five stations on the Atotsugawa and Ushikubi faults in northern central Main Island, Japan, since 1981 in search of possible relationship with earthquakes. The observed H2 concentration varies from lower than 1 ppm to 7.8% in time and place. When a large earthquake (M: 7.7, epicenter distance: 486 km) occurred on 26 May 1983, an outstanding discharge of H2 was observed at all five stations, preseismically at three of them, and coseismically at the other two. Simultaneous H2 emission was also observed at some stations in seven other occasions. These periods of unusual H2 discharge nearly coincided with occurrences of major earthquakes in Japan, but not of local minor earthquakes along the Atotsugawa fault. This fault, being a deep fracture zone, may be sensitive to large-scale crustal stress changes which incidentally cause the major earthquakes. Increased H2 may be produced by rock fracture caused by the increased stresses on the fault and by the earthquakes themselves. Local minor earthquakes along Atotsugawa fault with magnitude lower than 3 may be unable to cause sufficient rock fracture to produce significant H2. 相似文献