Hitoshi Matsubara

Carbonate precipitation through photoautotrophic microorganisms at the Giza cliff in Okinawa, Japan

Environmentally friendly options for restoring limestone using microorganisms have attracted recent attention. The governing principle of this technique is to use the metabolism of microorganisms to precipitate carbonate in the gaps of mineral particles; this process is known as microbial carbonate precipitation (MCP). Here, an outcrop associated with MCP under natural conditions at the Giza cliff in Okinawa, Japan was investigated. Colonies of photoautotrophic microorganisms containing chlorophyll were found inhabiting a layer of limestone 2–4xa0mm below the surface of the outcrop. These microorganisms survived and photosynthesised within the limestone under favorable conditions that include an effective photon flux density of 15–75xa0µmol/m2/s, and some fresh calcium carbonates (i.e., calcite) were precipitated around the cell walls and extracellular polymeric substances (EPS) of the microorganisms. Furthermore, the results of powder X-ray diffraction (XRD) suggest that the synthetic calcite within the limestone may improve the mechanical strength of the outcrop. These in situ and laboratory findings indicate that these microbial functions may be applicable to some weathered rock surfaces as a self-organizing surface protection and conservation technology.

Some Consideration on Derivative Approximation of Particle Methods

In this paper, the accuracy of the derivative approximation of the particle methods is discussed. Especially, we show that the issue of decreasing accuracy on a boundary area in the SPH method is due to the lack of the boundary integration. Through some numerical examples, the convergence of error norm of energy obtained by the SPH and the MPS methods is studied.