Hydroxyapatite, Ca₁₀ (PO4) ₆ (OH) ₂ (HAp) is a main constituent of teeth and bones, and one of “Lattice Ion Ion-exchangers”, discovered by T. Suzuki. Two structure modified HAp were successfully synthesized and they have been found to have better ion-exchange characteristics for Zn²⁺and Cd²⁺ions than those of normal HAp. The one included CO₃^2-ions (CAp) and the other included SiO₄^4-ions (SiAp) in HAp structure. The reason why the ion-exchange characteristics were improved, was considered to be due to the loosened crystal structure by the substitution of CO₃^2-and SiO₄^4-ions for PO₄^3-ions of HAp and thus activated Ca²⁺ions in HAp.
The SiAp was found to be chaneged gradually to HAp in water and many OH^-ions were released as shown in the following reaction.
3Ca₁₀ (PO₄) ₄ (SiO₄) ₂+18H₂O 2Ca₁₀ (PO₄) ₆ (OH) 2+10Ca²⁺+6H₃SiO₄^-+140H^-
Since Escherichia coli (E. coli) is known to be disinfected in high pH environment, the SiAp was investigated as a disinfectant. The SiAp exhibited a rapid and effective bactericidal activity in water. Generally, HAp has high affinity to bacteria such asE.coli, so it can't be thought that HAp shows some bactericidal activity. Thus, this bactericidal activity was considered to be caused by a synergistic effect of both the OH^-ons in water diffused from the surface of the SiAp and the direct contact ofE.colicells with concentrated OH^-layers formed on the surface of suspended SiAp particles.

View full abstract

Though in-situ stress state is one of the key factors for development of hot dry rock (HDR), a reliable method to estimate the stress state has not been established. The depth and the high temperature prevent us to apply a conventional method of in-situ stress measurement, such as a strain relief method or a hydraulic fracturing method. We have tried to estimate the stress state of an actual HDR reservoir, located in Yamagata prefecture, using DSCA (Differential Strain Curve Analysis). DSCA is one of new methods of stress measurement, based on a laboratory work for an oriented core. We compared the results of DSCA to phenomena reflecting in-situ stress state of the reservoir and results obtained by other stress measuring methods applied in that field. Through the comparison, we found that the DSCA results of principal stress directions generally matched with a stress state that controlled the direction of the actual HDR reservoir.

View full abstract

In the previous study, authors discussed the decrease of strength with specimen size or number of elements of FEM mesh. In this study, time-dependent behaviour in consideration of specimen size is examined by computer simulation. A non-linear constitutive equation proposed by the authors is implemented in FEM program and the simulation is carried out with special attention to inhomogeneity of rock as in the previous study.
First, loading-rate dependency of compressive strength, which is well known by many laboratory works, is discussed. Through computer simulation, it is found that loading-rate dependency decreases with specimen size, especially when strength varies from place to place and specimen is highly inhomogeneous. However, under confining pressure, loading-rate dependency decreases at only small amount with specimen size.
Secondly, creep test is simulated. It is found that primary creep where creep strain-rate decreases with elapsed time becomes gradually apparent with extent of inhomogeneity of specimen model. On the other hand, regardless of homogeneity, creep strain-rate in tertiary creep increases inversely proportional to residual life. Also, it is found that life time in creep test as well as strength in compression test decreases with specimen size.

View full abstract

Methods to evaluate minimum principal strain of cylindrical rock specimen at peak load were experimentally investigated under uniaxial compression and Brazilian tests.
It was clarified that a chain-type circumferential extensometer is the best to measure it in uniaxial compression test, and that paper-base strain gauge, whose effective length is short enough, attached to a specimen with a rubber-type adhesive is the best to do in Brazilian test.
A method to record load and strains on a hard disc, which can make a small data file with a sufficient rapid sampling frequency around peak load, was also shown.

View full abstract

In the first part of this study, strains under hydrostatic pressure in an elastic and isotropic body containing a number of penny-shaped microcracks were theoretically investigated to clarify the physical meaning of the parameters used in Differential Strain Curve Analysis (DSCA) and then, a new parameter was proposed to reduce the effects of anisotropy in the intrinsic linear compressibility on the evaluation of crack density.
In the second part of this study, the effects of loading methods were experimentally investigated first and the results in the third loading cycle were proposed to be used to evaluate microcracks in rock. Then the parameters characterizing microcracks were determined for some rocks by DSCA. The results showed that better reproducibility was obtained by the new parameter, (Δβ/βl) _I, and that microcracks in a soft and porous sedimentary rock can be evaluated by DSCA if the maximum pressure is chosen so that the pressure does not cause new microfracturing in the rock.

View full abstract

In this study, in order to make the rock cutting mechanism of disc cutters clear, and to find a simple experimental method for examining cutting performance of disc cutters, penetration experiments of disc cutters were carried out with 7 kinds of rock. The main results obtained from the present study are:
(1) Beforechipping, the penetrating resistance FT is proportional to penetrating depth P as:
FT=KTP_3/2.
The coefficient KT is proportional to uniaxial compressive strength of rocks.
(2) Penetrating resistance when chipping occurs depends on fracture toughness of rock.
(3) Comparing with the result of the first report, it was shown that the cutting experiment of disc cutters can be replaced by penetration experiment for examining the cutting performance of disc cutters.

View full abstract

Acoustic wave is characterized by some elements such as frequency, attenuation, travel time and so on. When acoustic wave propagates through the water in which bubbles exist, these characteristics are influenced by various bubbles conditionsuch as volumetric ratio, elastic modulus, number density and so on. The geometric conditions of bubbles such as size, position, and number density are the factors of that affect the acoustic wave characteristics. Therefore conversely analyzing these characteristic of acoustic wave, it is possible to estimate the geometric condition of bubbles.
The subject of this study is to estimate such geometric condition of bubbles underwater target area, using distribution characteristic of travel time of acoustic wave that propagate through the water in which bubbles exist. In this paper, an attention was paid to the distribution characteristic of raypath ratio of acoustic wave, that propagate through the water in which bubbles exist, in order to make clear the relationship between the bubbles condition and the characteristic of raypath ratio by numerical simulation using discrete element model.
Consequently, the followings become clear.
1) Acoustic wave that propagate through the water in which bubbles exist is influenced bynot only volumetric ratio of bubbles but also geometric condition such as size, position, and number density in a target area.
2) Probability density of minimum raypath ratio is related to the geometric condition such as size, position and number density in a target area quantitatively.
3) In case of this two dimensional discrete model, it is possible to estimate not only volumetric ratio ofbubbles but also geometric condition such as size, position, and number density in a target area by measurement of distribution characteristic of travel time ofacoustic wave.

View full abstract

This paper is concerned with numerical simulations of flow fields around a deformable gas bubble rising through an incompressible viscous fluid in a pipe. In the present analysis, an orthogonal boundary-fitted coordinate system proposed by Ryskin and Leal was applied for the grid generation around a deformable gas bubble. The simulations were performed using the MAC-type solution method to solve afinite differencing approximation of the Navier-Stokes equations governing an incompressible viscous fluid flow. It is assumed that the boundary geometry and flow fields are both axisymmetric and steady owing to the fact that the Reynolds number used here is comparatively low.(Re≤60).
The steady solutions obtained by the mathematical model have been compared with the previous experimental data for the bubble shape and the drag coefficient. It has been shown that a fairly good agreement is obtained between them. It has been clarified by the numerical results that the drag coefficient of the bubble strongly depends upon the ratio of the pipe radius to the bubble radius, but there is no effect of the ratio on the drag coefficient when the ratio exceeds five on condition that Re=20.

View full abstract

This paper is concerned with constructing the numerical model for steady gas-liquid-solid threephase mixture flow in a lifting pipe. Air lift pumps are regardedas one of the convenient means of lifting slurries and solid particles such as manganese nodules from the deep-sea bed of about 5, 000m to the sea surface.
Here, the case is treated where the three-phase fluid is the slurry consisting of very small air bubble phase and solid particle phase mixed in water phase. The equations governing the gas-liquid-solid threephase slurry flow are formed by three continuity equations, only one momentum equation, a gas equation of state andan equation for three-phase volume fractions. These six equations are cooperatedinto the only one equation to find the change in the gas-phase volume fraction according to the vertical position. Thereby, the remaining flow parameters can quantitatively be determined in the present model.
Again, some numerical experiments are performed using this model. When the gas-phase volume fraction is given at the deep-sea bed, the corresponding solid-phase volume fraction can be determined between the upper and lower limits. It is shown that the solid-phase volume fraction near the lower limits leads to increasing the lifting efficiency of the solid-phase. Furthermore, it is demonstrated that there is a limiting curve to predict the maximum solid-phase mass flux against the solid-phase volume fraction at the deep sea bed.

View full abstract

Crushing experiments using a Jaw Crusher and cylindrical mortar samples were performed to analyse crushing load and sample stress. The crushing load was derivedby assuming the log motion of the crusher's movable jaw as the lever crank mechanism.
The solution of Boussinesq was applied to calculate the stress of specimen by piling up the stress caused on one point loading and compared with the result of finite element method (FEM). The values by Boussinesq's solution were similar to those by FEM.
In the case of load more than one point, half-splitting of a cylindrical sample just like radial compression splitting was occured. Itcorresponded to the calculation result that a sum of individual influence coefficients (I (ζ)) on the major axis of the sample was constant. The destructioncoefficient (Kp) obtained experimentaly agreed with that by Boussinesq's solution.

View full abstract