Impact of flood events on macrobenthic community structure on an intertidal flat developing in the Ohta River Estuary

We investigated the effects of river floods on the macrobenthic community of the intertidal flat in the Ohta River Estuary, Japan, from 2005 to 2010. Sediment erosion by flood events ranged from about 2–3 cm to 12 cm, and the salinity dropped to 0‰ even during low-intensity flood events. Cluster analysis of the macrobenthic population showed that the community structure was controlled by the physical disturbance, decreased salinity, or both. The opportunistic polychaete Capitella sp. was the most dominant species in all clusters, and populations of the long-lived polychaete Ceratonereis erythraeensis increased in years with stable flow and almost disappeared in years with intense flooding. The bivalve Musculista senhousia was also an important opportunistic species that formed mats in summer of the stable years and influenced the structure of the macrobenthic community. Our results demonstrate the substantial effects of flood events on the macrobenthic community structure.     

Geophysical techniques to aquifer locating and monitoring for industrial zones in North Hanoi, Vietnam

Geophysical methods were applied for hydrogeological targets in many countries including Vietnam. This paper presents results of using complex geophysical techniques as well as 2D electrical resistivity imaging (ERI), vertical electrical sounding (VES), very low frequency (VLF), and seismic refraction for geological structure investigation for locating the aquifers and assessing the hydrogeological conditions for groundwater potential in industrial zones of North Hanoi, Vietnam. The locations of two aquifers are determined by their depth and thickness on the basis of resistivity and seismic velocity values which were proved by stratifications of three boreholes to 40–60 m of depth on the study area. There are connections from surface water to shallow aquifer by hydraulic windows, as follows from VLF data. The deeper aquifer can be considered as a potential groundwater supply, but the water level is descending in time, as shown by hydrological monitoring. However, with careful use and by reducing sources of pollution, groundwater can continue to be an important natural resource for future.     

Building damage characteristics based on surveyed data and fragility curves of the 2011 Great East Japan tsunami

A large amount of buildings was damaged or destroyed by the 2011 Great East Japan tsunami. Numerous field surveys were conducted in order to collect the tsunami inundation extents and building damage data in the affected areas. Therefore, this event provides us with one of the most complete data set among tsunami events in history. In this study, fragility functions are derived using data provided by the Ministry of Land, Infrastructure and Transportation of Japan, with more than 250,000 structures surveyed. The set of data has details on damage level, structural material, number of stories per building and location (town). This information is crucial to the understanding of the causes of building damage, as differences in structural characteristics and building location can be taken into account in the damage probability analysis. Using least squares regression, different sets of fragility curves are derived to demonstrate the influence of structural material, number of stories and coastal topography on building damage levels. The results show a better resistant performance of reinforced concrete and steel buildings over wood or masonry buildings. Also, buildings taller than two stories were confirmed to be much stronger than the buildings of one or two stories. The damage characteristic due to the coastal topography based on limited number of data in town locations is also shortly discussed here. At the same tsunami inundation depth, buildings along the Sanriku ria coast were much greater damaged than buildings from the plain coast in Sendai. The difference in damage states can be explained by the faster flow velocities in the ria coast at the same inundation depth. These findings are key to support better future building damage assessments, land use management and disaster planning.     

The modified Lagrangian equations of general-relativistic hydrodynamics for a nonideal fluid

The general-relativistic equations of hydrodynamics for a nonideal fluid are derived in the modified Lagrangian form. Together with the zeroth and first moment equations of radiative transfer derived by Morita and Kaneko (1986), the equations provide a complete set of the modified Lagrangian equations of radiation hydrodynamics. The equations of hydrodynamics are specialized for a thermally conducting, Newtonian viscous fluid in the modified Lagrangian form, which are the generalization of the specialrelativistic equations of hydrodynamics derived by Greenberg (1975).     

Estimation of chlorophyll concentration from the specific fluorescence at 685nm in the upward irradiance just below the sea surface

An algorithm for estimating the chlorophyll concentration from the fluorescence intensity at 685nm in upward irradiance observed just below the sea surface is presented and discussed. The observed chlorophyll concentration is closely related to the ratio of the fluoresced quanta to the total incident quanta (downward plus upward quanta) in the spectral range between 350nm and 600nm. The correlation between them, however, is not good and the rate of increase of the ratio decreases as the chlorophyll concentration increases. This is due to the fact that the number of fluoresced quanta varies with attenuation of the incident light by various materials in the sea.A better correlation is obtained between the ratio of the fluoresced quanta to the upward quanta at wavelengths around 480nm. This is explained by the fact that dividing by the upward quanta at the appropriate wavelength compensates for apparent variation of fluorescence intensity with attenuation by the sea water. In this method, upward quanta at the four wavelengths of 480nm, 640nm, 685nm and 740nm are necessary for estimation of chlorophyll concentration. The quanta at 640nm and 740nm are used for interpolating the quanta at 685nm in the absence of fluorescence.It is also shown that the correlation of the observed chlorophyll concentration with the ratio of upward quanta at the wavelengths of 685nm and 480nm is also good. Use of this ratio is recommended for remote sensing of chlorophyll concentration since the number of spectral channels required by the remote multispectral imager can be minimized.     

Analysis of ocean color spectra (II)

A method for evaluating the radiance due to sky light reflected by the sea surface and radiance emerging from the sea is described. The calculation is made as a function of the sun altitude, sky condition and sea state for varying optical properties of sea water. As a result of the contribution of reflected sky light, the shape of the spectral distribution for radiance just below the surface is considerably distorted above the surface, especially when chlorophyll concentrations are high. Special attention is paid to the ratio of radiance emerging from the sea to total upwelling radiance at the wavelength of 670 nrn. The variation in the ratio with wind-speed is small and the ratio decreases with increase in the atomospheric turbidity factor.     

Analysis of ocean color spectra (I)

By using the two-flow optical model, the variation in the irradiance reflectance of the ocean just below the surface has been calculated for varying water optical properties, for the interpretation of remotely-sensed ocean color data. The input variables used in our model are the concentration of phytoplankton (chlorophyll-a), the absorption coeffiicient of yellow substance, the particle scattering coefficient, the ratio of the back-scattering coefficient to the total scattering coefficient of particles, and the ratio of the absorption to scattering coefficients for particles.The irradiance reflectance increases monotonically with the ratio of the back-scattering coefficient to the total scattering coefficient. Spectral changes occur in the irradiance reflectance for increases in chlorophyll-a concentration and yellow substance as well as the ratio of the absorption to scattering coefficients.Because slightly different mathematical expressions have been derived by other investigators using the two-flow model, an evaluation of the resulting calculation differences is presented and discussed.     

Parametric excitation induced by solar pressure torque on the roll-yaw attitude motion of a gravity-gradient stabilized spacecraft

The parametric excitation of a gravity gradient stabilized spacecraft induced by the periodic solar pressure torque is discussed. The solar pressure torque in the linearized equations of motion appears as linear terms with periodic coefficients. The attitude stability is analyzed numerically through the calculation of the Floquet multiplier. The perturbation method is also applied to identify the instability condition analytically. It is made clear that the periodic solar pressure torque can destabilize the coupled roll and yaw attitude motion of the spacecraft. It is also shown that the conditions of parametric resonance are included in the gravity gradient stability condition. Nonlinear simulations are also carried out to verify the effect of the parametric resonance. The numerical simulation using actual parameters shows that the spacecraft inevitably experiences a large amplitude attitude motion due to the periodic solar pressure torque even if the gravity gradient stability condition is satisfied.