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Takenaka K 《The Journal of geography》1996,105(1):31-52
"In this study, the internal migration in Spain from 1962 to 1993 is analyzed from the viewpoint of migration flows, with special emphasis on the spatial scale and direction of migration as well as the migration fields.... The evolution of the spatial scale and direction of migration shows a radical change in the middle 1970s: migrations from 1962 to 1975 (first period) were unidirectional movements at great distance (interprovincial and interregional), whereas those from 1976 to 1993 (second period) are characterized by the weight of intraprovincial movements and the bidirectionality of interprovincial movements. Through the two periods, the major sector in which migrants are employed has shifted from the industry to the service sector." (EXCERPT) 相似文献
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Norimichi Takenaka Tohru Daimon Akihiro Ueda Keiichi Sato Masaru Kitano Hiroshi Bandow Yasuaki Maeda 《Journal of Atmospheric Chemistry》1998,29(2):135-150
Nitrite oxidation in the tropospheric aqueous phase by freezing was evaluated by freezing a field sample. Nitrite oxidation by dissolved oxygen in the freezing process is much faster than by other oxidation processes, such as reactions with ozone, hydrogen peroxide or dissolved oxygen in an aqueous solution at pHs 3 to –6. At pH 4.5 and 25°C, the lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidation by ozone (6×10-10 mol dm-3), ca. 10 hr in oxidation by H2O2 (2×10-4 mol dm-3), and 7.5 hr (Fischer and Warneck, 1996) in photodissociation at midday in summer. Under the same conditions at a temperature below 0°C, the lifetime of nitrite in the freezing process is estimated as ca. 2 sec when the droplets are frozen within a second. The reaction by freezing is affected by the presence of salts, such as NaCl or KCl, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrite oxidation proceeds below pH 6, and the conversion ratio of nitrate from nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an ultrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sample) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of other ions. From the present study, it seems that the freezing process plays an important role in the nitrite sink process in the tropospheric aqueous phase. 相似文献
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Ammonia (NH3) is the most abundant alkaline gas in the atmosphere and plays a key role in atmospheric chemistry. Reliable and high-time-resolution data for gaseous ammonia are necessary to understand the sources and sinks of ammonia gas in ambient air. In the present study, a sensitive and continuous instrument for measuring gaseous ammonia was developed. Ammonia gas in ambient air was collected in an aqueous solution using a counter-current flow tube (CCFT) sampler. Then, ammonium formed in the aqueous solution was detected by the indophenol method. Based on a CCFT length of 50 cm and air flow rate of 1 L/min, the collection efficiency exceeded 98.5 % at an ammonia mixing ratio of up to 120 ppbv. The detection limit of this method was 0.062 ppbv. Interferences from several gases were investigated, and the results showed that the present method was not affected by NOx, O3, SO2, HONO, methylamine, formaldehyde, hydrogen sulfide or a mixture of these gases. The most important result was that only gaseous ammonia was detected in the present method without any interference from the particulate ammonium in ambient air. Comparisons with data based on the dry denuder method indicated that the present method showed good agreement with the denuder method. 相似文献
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We delineate shallow structures of the Mozumi–Sukenobu fault, central Japan, using fault zone waves generated by near-surface explosions and detected by a seismometer array. Two explosive sources, S1 and S2, were placed at a distance of about 2 km from the array, and the other two, S3 and S4, were at a distance of about 4 km. Fault zone head waves and fault zone trapped waves following direct P wave arrivals were clearly identified in the seismograms recorded by a linear seismometer array deployed across the fault in a research tunnel at a depth of 300 m. Synthetic waveforms generated by a 3-D finite-difference (3-D FD) method were compared with observed fault zone waves up to 25 Hz. The best fitting model indicates a 200-m-wide low-velocity zone extending at least to shot site S1 located 2 km east of the seismic array with a 20% decrease in the P wave velocity relative to the wall rock. The width of the low-velocity zone is consistent with the fault zone defined by direct geological observation in the research tunnel. However, the low-velocity zone should disappear just to the east of the site S1 to explain the observed fault zone waves for shot S3 and S4 located 4 km east of the seismometer array. Yet the observation and the simulation show notable trapped wave excitation even though shots S3 and S4 are outside the fault zone. These results indicate that (1) the effective waveguide for seismic waves along the fault does not exist east of source site S1 although the surface traces of the fault are observed in this region, and (2) considerable trapped waves can be excited by sources well outside the fault zone. These results highlight the along-strike variability in fault zone structure. 相似文献
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A scheme to treat the singularity in global seismic wavefield simulation using pseudospectral method with staggered grids 
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下载免费PDF全文 The pseudospectral method has been applied to the simulation of seismic wave propagation in 2-D global Earth model. When a whole Earth model is considered, the center of the Earth is included in the model and then singularity arises at the center of the Earth where <i<r</i<=0 since the 1/<i<r</i< term appears in the wave equations. In this paper, we extended the global seismic wavefield simulation algorithm for regular grid mesh to staggered grid configuration and developed a scheme to solve the numerical problems associated with the above singularity for a 2-D global Earth model defined on staggered grid using pseudospectral method. This scheme uses a coordinate transformation at the center of the model, in which the field variables at the center are calculated in Cartesian coordinates from the values on the grids around the center. It allows wave propagation through the center and hence the wavefield at the center can be stably calculated. Validity and accuracy of the scheme was tested by compared with the discrete wavenumber method. This scheme could also be suitable for other numerical methods or models parameterized in cylindrical or spherical coordinates when singularity arises at the center of the model. 相似文献
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