The authors present simple equations to approximately evaluate elastic stress states in the vicinity of longwall face in flat coal seam. Required information is mining height, ratio of Young's modulus of coal seam to that of rock mass, horizontal component of initial rock stress and σ_vh, which is vertical stress at a distance of h ahead of face evaluated by DDM (displacement disontinuity method): h is half width of square element in DDM and is two to ten times greater than mining height.
The equations were derived by comparing solutions by using 2-dim DDM and that by using 2-dim, FEM (finite element method). In the DDM analysis, calculation is easily conducted. The stress states in the vicinity of the face, however, are not precisely calculated since the face is modeled by the crack tip. In the FEM analysis, displacements evaluated by using DDM are assigned on outer boundary and geometry of the face is precisely considered.
An application of the derived equations to stability analysis of longwall face is also shown.

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Uniaxial compression and creep tests were carried out under air-dried and water-saturated conditions. Sample rocks are Sanjome andesite and Tage tuff. The experimental results indicate that uniaxial compression strength follows the Weibull distribution for both sample rocks whether in air-dried condition or in water-saturated condition.
The logarithm of probability of survival in creep test was plotted against the failure life (P-t diagram). Curves opening upwards were obtained except for Sanjome andesite in water-saturated condition.
The failure process under constant load (creep test) is not differ from that under constant stress rate (uniaxial compression test), and the relation between fluctuation of strength and that of failure life was obtained. Through detailed examination, it was found that the experimental results conform fairly well to the theoretical estimation.

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At the Hijiori Hot Dry Rock test field in Yamagata prefecture, a three month circulation test (Exp. 9102) was conducted in 1991, using a injection well SKG-2, and three production wells HDR-1, HDR-2and HDR-3. During Exp. 9102, pressure, temperature and flow rate were periodically surveyed in the production wells with the PTS (Pressure, Temperature and Spinner) combination tool. Several flow paths were recognized from the PTS surveys and flow rate and temperature changes during Exp. 9102 were obtained.
To estimate the heat extraction area, which consisted of several flow paths in the Hijiori HDR reservoir, a model was developed for each flow path using both Finite Element Heat and Mass Transfer Code (FEHM) and Gringarten's model. Calculations were repeated, changing the heat extraction area, until the temperature of production well obtained the best match of Exp. 9102.
By matching the observed temperature in the producing zones, important features were observed. There were several flow paths in which the heat extraction area remained constant. Other flow paths, however, experienced an increase in heat extraction area. The main flow paths were produced in wells HDR-2 and HDR-3.
These paths had about the same length to heat transfer area ratio. During Exp.9102 very little heat transfer interaction between the fractures was observed.

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In this study, the change in gas permeability in the processes of coal fracture under triaxial compression has been investigated by applying the acoustic emission methods in order to clarify the effect of crack development on gas permeability. Actually, gas permeation rate decreased exponentially in the process of compaction. Gas permeation rate changed, however, from the decreasing tendency to the increasing in the process of pre-failure according to the change of the amplitudefrequency distribution of acoustic emissions, and increased rapidly in the process of post-failure. Moreover, the change in the opening rate of gas permeable cracks with the progress of coal fracture was considered on the basis of the relations between gas permeation rate and applied gas pressure. The opening or closing of permeable cracks converged to a steady state at low pore-pressure in response to an increase of cumulative acoustic events, and the gas permeability approached the Darcy law. From these results, it was proved that gas permeability of coal depended on the opening or closing of permeable cracks caused by irregularity of pore-pressure among cracks.

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In this study, the permeability tests of high gas pressure have been conducted in order to make clear the mechanism of irreversible change in gas permeability of coal. Practically, the opening behaviour of permeable cracks caused by action of pore-pressure on coal specimens under a constant hydrostatic pressure was monitored through the change in gas permeability and acoustic emission activity.
As these monitored results, the irreversible changes in the gas permeability and the opening rate of permeable cracks occurred according to the change of the amplitude-frequency distribution of acoustic emission as the effective pore-pressure became higher than the crack strength defined by the equation (4). After these irreversible changes, the relations between gas permeation rate and applied gas pressure changed to a straight line intersecting the origin and the opening of permeable cracks became invariable. From these opening behaviour of permeable cracks, it became clear that the irreversible change in gas permeability was caused by unstable crack propagation at a closing point of permeable cracks in which the permeative resistance acted selectively and effectively.

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Relaxation of rock after removal from in situ state consists of an elastic (instantaneous) component and an anelastic (time-dependent) component. Technique using anelastic strain recovery (ASR) have been aimed to determine the direction and magnitude of in situ principal stresses by measuring changes in geometry of recovered core with time immediately after retrieved from deep boreholes. Timedependent microcrack growth has been suggested as a possible mechanism for the strain recovery process, although it has been modeled by using viscoelastic theories. Time-dependent microcrack growth driven by the tensile residual stress as well as an instantaneous microcracking by the relaxation of the stresses was modeled by considering an homogeneous inclusion containing mocrocracks that grow due to subcritical crack growth. The inclusion having circular cross section was embedded in coaxial himogeneous matrix which was less stiffer than the inclusion. The model was able to predict the dependence of the time-strain curve of the inclusion on the initial stress level and agreed with the observed ASR data.

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The concentration and deposition of cobalt from ammoniacal alkaline solution was carried out by adding alcohol. Test solutions of cobalt were prepared with the reagent or a leach liquor obtained from cobalt crusts with the mixture of aqueous ammonium carbonate and ammonium sulfite solution. It was found that when propanol was added to an ammoniacal alkaline solution containing cobalt, the solution was separated into two phases of an aqueous phase containing propanol and a cobalt concentrated phase. The concentration rate of the cobalt varied with added amount of propanol. A addition ratio of propanol (PrOH/H₂0: O/A) of 5 enabled to obtain a cobalt concentration rate of 99% and to increase cobalt concentration to 5 times or more. To deposit the cobalt, methanol or ethanol was effective. A alcohol addition ratio (O/A) of 5, whether it was methanol or ethanol, enabled deposition rate to be 99% or more.

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A trend analysis mainly based on the multiple regression analysis, using some economic indexes including GNP, as the independent variables, was carried out on the electrolytic copper demand in Japan (hereafter called domestic copper demand) from 1969 to 1991. The analysis shows the following characteristics in the domestic copper demand trend.
(a) Overall, the domestic copper demand increased except the duration of the first oil-shock (1974), worldwide recession (1982) and the exchange rate in favor of the yen (1986), when the depressions are clearly recognizable.
(b) The growth rate of the domestic copper demand becomes slow with increasing GNP (gross national product).
(c) The domestic copper demand can be reliably explained by the multiple regression analysis using 4 economic indexes of GNP, PCF (public fixed capital formation), IPI (index of producer's final demand goods inventory to shipment ratio) and WPI (overall wholesale price indexes) as independent variables.
(d) In addition, it is thought that GNP, PCF and WPI indicate the whole trend of the domestic copper demand, and that IPI indicates turning point in the domestic copper demand.

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Iron nitride fine particles were prepared from magnetite particles by NH₃-H₂gas mixture. Two types of nitrogenizing processes were carried out. One is reduction with H₂gas followed by nitriding with NH3-H2 mixture (nitriding after reduction treatment), and other is continuous reaction with NH₃-H₂ mixture (reduction-nitridingtreatment). Starting materials were spherical magnetite particle (mean diameter, m. d.=0.35μm) and magnetite obtained by coprecipitation process (m. d.=100Å).
Iron nitrides prepared from the spherical magnetite wereγ'-Fe₄N andε-Fe_xN. Particle sizes were almost the same to that of the spherical magnetite and their surface were porous. In contrast, sintering among iron nitride particles were observed in the case of coprecipitated magnetite. In nitriding after reduction treatment, particle size of iron nitride depended on reduction temperature and it was bigger than the particle size from reductionnitriding treatment at the same temperature. These facts showed that sintering chiefly occurred during reduction process of magnetite.
Fe_2.9Al_0.1O₄coated with oleic acid which was obtained by coprecipitation process preserved sintering in both treatments. Therefore, adsorption of oleic acid and addition of Al for coprecipitated magnetite could control particle size of iron nitride. As compared with nitriding after reduction treduction treatment, the reductionnitriding treatment inhibits sintering. The smallest particle size of iron nitride in this study was 150Å. Saturation-magnetization of iron nitride was in the range between 106 and 174emu/g.Depletion of magnetization compared with bulk iron nitride component mainly depended on existence of Al in the particles.

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It is important to determine the particle size distribution of powder for mineral processing and other fine particle processing technologies. An improved sedimentation balance was developed for the analysis of particle size distribution of powder. Particle size distribution analysis of quartz powder (-22μm) was repeated 10 times using the apparatus. It was confirmed that there was good reproducibility of measurements by the results of a graphical analysis of measured sedimentation curves. A numerical calculation for the analysis of a measured sedimentation curve was developed. A starting point of the measurement and a maximum particle size of powder were determined by using a regression equationW=A+BT, whereWis weight of particle sedimented on the weighting pan, Tis time lapse of measurement, andAandBare coefficients of the equation. The measured sedimentation curve was approximated with regression equation y=a (1-e^-bx), where y is weight of particles sedimented on the weighting pan, xis time lapse of measurement, andaandbare coefficients determined at each part of the curve to be analyzed. The particle size distribution curves obtained by numerical calculation and graphical analysis were agreed with each other very well.

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