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41.
We have elucidated the seasonal and spatial variation in the potential denitrifying activity in estuarine and coastal lagoonal
sediments in Lakes Shinji and Nakaumi, Japan. The denitrifying activity increased from summer through autumn and was positively
correlated with the temperature of the overlying water at all sites except one, where the bottom was always more reductive
than at the other sites and there was no NO3
− as a substrate for denitrification from spring to autumn. Moreover, the relationship between the denitrifying activity and
the distance from the sea showed different trends in estuarine and lagoonal sediments. These spatial differences indicate
that different factors regulate the denitrification in estuarine and lagoonal sediments. Denitrifying activity in estuarine
sediment was regulated by the discharge of freshwater containing NO3
− or organic matter, while in the lagoonal sediments the occurrence of nitrification via the intrusion of oxic seawater into
the reductive sediment appears to be a key requirement for the process of denitrification. Therefore, the denitrifying activity
in the lagoonal sediment appears to be greater near the sea. Water intrusion is one of the key factors controlling denitrification
in coastal marine ecosystems by affecting the supply of substrate available for denitrification. 相似文献
42.
43.
乐佩琦 《中国海洋湖沼学报》1995,(3)
Adult pharyngeal teeth in Mylopharyngodon piceus are molariform. Based on SEM observations ofthe developing teeth, this paper describes the morphological diversification of pharyngeal teeth in M.piceus. The larval and juvenile teeth are changed from conical to adult molariform teeth through sevenstages. Comparisons are made between each stage and corresponding types in some species of differentsubfamilies in Cyprinidae. It is considered that the ontogenetic resemblances of the pharyngeal teehbear relationship to the phylogeny of cyprinids. 相似文献
44.
R. Nakajima 《Astrophysics and Space Science》1985,116(2):285-297
In order to explain the variable H emission and the eclipse-like light variation of Ori E, we investigated the circumstellar gas trapped by the stellar magnetic field and corotating with the star. By considering the potential along the magnetic field line, we found that the gas concentrates to a potential minimum. The circumstellar gas forms either two condensations or a disk, depending on the inclination of the magnetic dipole to the stellar rotation axis. The geometrical thickness of the circumstellar disk, of about 0.2 stellar radii, and the distance from the center of the star to the inner edge of the disk, of about 3 stellar radii, were obtained. The H emission line profile at its maximum phase and the amplitude of light variation were calculated by assuming the isothermal gas in LTE with the maximum gas density which the magnetic field can hold. The model gives good agreement with observation in the low obliquity case, and also explains the phase correlation among the H emission maximum, the light minimum, and the magnetic extreme. The model, however, failed to explain the large IR excess in theM band. 相似文献
45.
Hiroyuki Usui Yasushi Asami 《International journal of geographical information science》2018,32(1):120-139
The size distribution of urban blocks is important for the characterisation of urban block patterns and is known to follow several parametric statistical distributions. However, it has not previously been analysed on the basis of a normative plane tessellation and in terms of urban block density and mean road width. In this article, we formulate the size distribution of Voronoi cells using the gamma distribution estimated by urban block density and mean road width. We found that (1) both log-normal and gamma distributions can be good candidates for the size distribution of urban blocks at the scale of a region that consists of regular urban blocks and that has a uniform road width; and (2) the size distribution of urban blocks depends on the balance between pattern and width improvement effects. Based on one study region in Tokyo, if the pattern improvement effect is more prominent than the width improvement effect, the mode of urban block sizes tends to be larger than if it is not. These findings are expected to provide scientific support for urban planning (e.g. land readjustment projects). 相似文献
46.
华南地区中生代Cu (Mo) W Sn矿床成矿作用与洋岭/转换断层俯冲 总被引:25,自引:1,他引:24
华南地区是我国重要的金属矿产资源产地,除了发育大量的钨锡钼铋和稀土等金属矿产外,还有铜金矿床分布。本文通过对华南地区29个典型CuMoWSn矿床的时空分布及其与之有关的花岗质岩体的侵位年龄分析,探讨了与不同成矿类型有关的花岗质岩石的地球化学特征。本文认为华南地区10个典型的与Cu有关的矿床主要发生在180~170Ma、160~150Ma以及105~90Ma三个时期,而10个钨矿床主要集中于170~130Ma;4个WSn矿床集中于170~130Ma和120~110Ma;而5个Sn矿床则发育于170~150Ma、130~110Ma以及100~90Ma三个时期。Cu矿床主要与同熔型花岗岩有关,而Mo、WSn既与同熔型花岗岩有关,又与改造型花岗岩有关。在岩石地球化学上,与Cu(Mo)WSn成矿作用有关的花岗质岩石也表现出不同的地球化学特点,如,从Cu(Mo)矿床到WSn矿床SiO2含量有逐渐增大、氧化性逐渐降低、还原性逐渐增加以及分异演化程度有逐渐增高的趋势。与Cu(Mo)Au矿床有关的花岗质岩石具有较低的SiO2(60.3%~68.1%),氧化性较高(Fe2O3/FeO=0.31~1.81),分异演化程度较低(Rb/Sr=0.05~3.3)的特点;与Cu(Pb)(Zn)矿床有关的花岗质岩石具有相对较高的SiO2(73.3%~75.2%),氧化性稍高(Fe2O3/FeO=0.68~1.74),分异程度稍低(Rb/Sr=10.8~57.8)的特点;而与Mo矿床有关的花岗质岩石具有较宽的SiO2(67.3%~76.2%)变化范围,氧化性稍低(Fe2O3/FeO=0.68~1.74),分异演化程度稍低(Rb/Sr=0.6~9.29);与W矿有关的花岗质岩石的SiO2含量为69.9%~80.1%,还原性稍低(Fe2O3/FeO=0.19~0.76),分异演化程度稍高(Rb/Sr=21.9~61.7);与WSn矿床有关的SiO2为74.8%~78.7%,还原性较低(Fe2O3/FeO=0.08~0.59),分异程度较高(Rb/Sr=10.8~139);与Sn矿床有关的花岗质岩石的SiO2为64.8%~76.9%,还原性高(Fe2O3/FeO=0.01~0.58),分异演化程度高(Rb/Sr=1~530)。在结合华南地区花岗岩类岩石的分布特征以及盆岭构造的特点,本文提出华南地区CuMoWSn矿床的成矿作用是不同时期大洋板块或者洋岭多阶段俯冲结果的新成因模型,即早侏罗世休眠的FarallonIzanagi洋岭俯冲导致早—中侏罗世Cu成矿作用;中—晚侏罗世活动的FarallonIzanagi洋岭和转换断层俯冲是中晚侏罗世Cu(Mo)(W)成矿作用以及多阶段WSn成矿作用的触发动力,而白垩纪Izanagi大洋板块俯冲则是白垩纪斑岩型CuWSn成矿作用的诱因。该模型的提出较好地解释了华南中生代大规模岩石圈拆沉—减薄—伸展的机制及其大规模成矿作用的动力。 相似文献
47.
The reversibility of the temperature effect on the chemical composition of interstitial waters of three deep-sea sediment samples was examined between 2 and 25°C for Cl, Na, K, Mg, Ca, Si, B, Mn and alkalinity. When the temperature of sediment samples was returned from 25°C to the initial value of 2°C, most chemical species gave nearly their initial concentrations. However, for alkalinity and in one case for magnesium, it took another three to four hours to reach their initial concentrations. 相似文献
48.
Peter G. Brewer Edward Peltzer Izuo Aya Peter Haugan Richard Bellerby Kenji Yamane Ryuji Kojima Peter Walz Yasuharu Nakajima 《Journal of Oceanography》2004,60(4):751-758
We have carried out a small-scale (∼20 l) CO2 sequestration experiment off northern California (684 m depth, ∼5°C, background ocean pH ∼7.7) designed as an initial investigation
of the effects of physical forcing of the fluid, and the problem of sensing the formation of a low pH plume. The buoyant CO2 was contained in a square frame 1.2 m high, exposing 0.21 m2 to ocean flow. Two pH electrodes attached to the frame recorded the signal; a second frame placed 1.9 m south of the CO2 pool was also equipped with two recording pH electrodes. An additional pH electrode was held in the ROV robotic arm to probe
the fluid interface. Local water velocities of up to 40 cm sec−1 were encountered, creating significant eddies within the CO2 box, and forcing wavelets at the fluid interface. This resulted in rapid CO2 dissolution, with all CO2 being depleted in a little more than 2 days. The pH record from the sensor closest (∼10 cm) to the CO2 showed many spikes of low pH water, the extreme value being ∼5.9. The sensor 1 m immediately below this showed no detectable
response. The electrodes placed 1.9 m distant from the source also recorded very small perturbations. The results provide
important clues for the design of future experiments for CO2 disposal and biogeochemical impact studies. These include the need for dealing with the slow CO2 hydration kinetics, better understanding of the fluid dynamics of the CO2-water interface, and non-point source release designs to provide more constant, controlled local CO2 enrichments within the experimental area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
49.
Naoto Ebuchi Yasushi Fukamachi Kay I. Ohshima Kunio Shirasawa Masao Ishikawa Toru Takatsuka Takaharu Daibo Masaaki Wakatsuchi 《Journal of Oceanography》2006,62(1):47-61
Three High Frequency (HF) ocean radar stations were installed around the Soya/La Perouse Strait in the Sea of Okhotsk in order
to monitor the Soya Warm Current (SWC). The frequency of the HF radar is 13.9 MHz, and the range and azimuth resolutions are
3 km and 5 deg., respectively. The radar covers a range of approximately 70 km from the coast. The surface current velocity
observed by the HF radars was compared with data from drifting buoys and shipboard Acoustic Doppler Current Profilers (ADCPs).
The current velocity derived from the HF radars shows good agreement with that observed using the drifting buoys. The root-mean-square
(rms) differences were found to be less than 20 cm s−1 for the zonal and meridional components in the buoy comparison. The observed current velocity was also found to exhibit reasonable
agreement with the shipboard ADCP data. It was shown that the HF radars clearly capture seasonal and short-term variations
of the SWC. The velocity of the Soya Warm Current reaches its maximum, approximately 1 m s−1, in summer and weakens in winter. The velocity core is located 20 to 30 km from the coast, and its width is approximately
40 km. The surface transport by the SWC shows a significant correlation with the sea level difference along the strait, as
derived from coastal tide gauge records at Wakkanai and Abashiri.
Deceased. 相似文献
50.
Fifteen day records of current velocity, water temperature and salinity were obtained at a coastal station in the Seto Inland Sea. It was observed that water movement was characterized by an exchange of two distinctive water masses east and west of the station. Cross-correlation analysis shows that, at the semi-diurnal period, the motion of these characteristic waters causes temperature and salinity variations. At frequencies higher than 2 cycles per day where power spectra of current velocity have a slope of ?5/3, coherence between current velocity and both water temperature and salinity decreases rapidly. 相似文献