River Water Pollution in Developed and Developing Countries: Judge and Assessment of Physicochemical Characteristics and Selected Dissolved Metal Concentration

To compare water quality in rivers of developed and developing countries, a study based on physicochemical parameters and dissolved metals levels was conducted. Water samples were collected from selected sites in Dhaka, Bangladesh; Hokkaido and Osaka, Japan; Erdenet, Mongolia and West Java, Indonesia. Analysis of least significant differences revealed that most water quality parameters were within comparable low levels in both developed and developing countries. The dissolved metals concentrations were found to be similar and below those of water standards except for manganese and cadmium at every sampling point, and lead in Erdenet, Mongolia. Some metals showed high enrichment factors in the rivers of Osaka, Japan and Erdenet, Mongolia, indicating accumulation possibility of metals in the river‐bed sediments. High concentrations of dissolved organic carbon, Escherichia coli and dissolved metals suggested greater water pollution in some rivers of developing countries than in the rivers of Japan. Principal component analysis showed strong correlations between “dissolved organic carbon and chemical oxygen demand” and “conductivity and total dissolved solids” at each sampling point, and E. coli, nitrate (NO), nitrite (NO), and pH levels were found to be higher in the rivers of Dhaka and Erdenet. In addition, there were high levels of Al and Zn in West Java, Pb in Erdenet, and Mn, Fe, and Cr in the rivers of Dhaka and Japan. Based on pressures and impacts, it is evident that dissolved metal, organic, and fecal pollution in the rivers of developing countries are in somewhat dreadful condition in comparison with the rivers of developed country.     

The temperature dependence of the crystal structure of berlinite, a quartz-type form of AlPO4

The temperature dependence of atomic positions, mean-square displacements and probability density functions in a synthetic specimen of berlinite was analyzed using X-ray single crystal data measured at fourteen values of temperature. The characteristic features and the temperature dependence of the structure of berlinite were found to be quite similar to those of quartz, in detail. With increasing temperature, the equilibrium position of an atom, if expressed in fractional coordinates, appears to move steadily toward its β-position along a straight line, and finally attain the β-phase positions after abrupt displacements in a narrow temperature range around 583?°C. The temperature dependence of the displacements of atoms from the corresponding high-symmetry β-positions, in α-berlinite, is well fitted with a classical Landau type expression of first-order phase transitions. The highly anisotropic mean square displacements, 〈u ²〉, of O atoms increase with increasing temperature, especially in a narrow range just below the α–β transition, in the directions nearly perpendicular to the librating Al-O-P bonds, attaining a local maximum of 0.115–0.117 Ų just above the transition point. With varying temperature, the principal axes for the O atoms change their directions smoothly toward those of the high temperature phase, while the axis with the largest 〈u ²〉 of the Al or P thermal ellipsoid remains in 〈100〉. These diffraction results are interpreted in terms of displacive structure transition involving both the ordered α- and β-forms. The Al–O and P–O bond distances are nearly constant around 1.73 and 1.53 Å, respectively, through the experimental range of temperature.     

Molecular dynamics study of structural changes in berlinite

Fractional coordinates and anisotropic temperature factors of atoms in berlinite, AlPO₄ with the quartz topology, were successfully simulated in a molecular dynamics simulation (MDS) at high temperatures. Time-dependent and time-averaged atomic order parameters were analyzed in detail with the aid of spectral densities calculated from trajectory data. These parameters show characteristic behavior of the order-disorder regime for a structure change, where atoms spend most of the time oscillating around the ₁-sites (or ₂-sites) in the low temperature α-phase, but oscillate over both sites in the higher temperature α-phase and the β-phase. In the spectral density functions calculated for atom order parameters, a nearly zero-frequency excitation, which is accompanied by the emergence of large-scale ₁ and ₂ clusters, appears at the Γ point of the Brillouin zone below the transition point T _o, and increases in intensity up to T _o. A low-lying optic branch along Γ-M, which is strongly temperature dependent in the small q-region, is another characteristic of the spectral density functions for the β phase. The spectrum at Γ continuously reduces its frequency from 0.6 THz at temperatures far above T _o to nearly 0 THz at temperatures approaching T _o from above. The dynamical behavior in β berlinite rapidly but continuously changes from that in less oscillatory clusters in the vicinity of T _o to that in the typical β phase at temperatures departing from T _o. Received: 10 August 1998 / Revised, accepted: 18 February 1999     

Molecular dynamics study and normal mode analysis of diffuse scattering in quartz

X-ray scattering intensities in quartz were investigated in molecular dynamics (MD) simulation at different temperatures with the aid of normal mode analyses. The MD-simulated structure produced diffuse streaks most remarkably along a hexagon joining symmetry-equivalent points of index 400 in the hk0 plane, extending in ± c ^*. In addition, most Bragg spots were found to be associated by radial diffuse scattering in the six a ^* directions. The normal mode analysis and calculations of first-order scattering intensities showed that the lowest-lying branch in G-M is of transversal acoustic characters, and is responsible for the diffuse scattering radiating from Bragg reflections in the a ^*-directions. The transversal acoustic characters of atomic displacements in these modes provide the scattering in phase at points on the fourth hexagon. Phonon dispersion relations of the MD crystal were examined in view of symmetry-adapted atomic displacement patterns, and a possibility was suggested for two curves in G-M, optic soft branch and transversal acoustic branch polarized in the z axis (the second-lowest branch), to exchange the eigenvectors in the middle range of q (0.2–0.3).     

Forced convection accompanying wind waves

Wind-wave tunnel experiments reveal, by use of techniques of the flow visualization, that wind waves are accompanied by the wind drift surface current with large velocity shear and with horizontal variation of velocity relative to the wave profile. The surface current converges from the crest to a little leeward face of the crest, making a downward flow there, even though the wave is not breaking. Namely, wind waves are accompanied by forced convections relative to the crests of the waves. Since the location of the convergence and the downward flow travels on the water surface as the crest of the wave propagates, the motion as a whole is characterized by turbulent structure as well as by the nature of water-surface waves. In this meaning, the term of real wind waves is proposed in contrast with ordinary water waves. The study of real wind waves will be essential in future development of the study of wind waves.