In this paper, the estimation of groundwater residence time and geomorphological changing processes are discussed by focusing on isotopes of noble gases and radionuclides with a long half-life as an environmental tracer. Noble gases and radionuclides are produced in the atmospheric air and terrestrial rocks by spallation and various muon reactions during cosmic rays irradiation. Groundwater dating and geomorphological changing are estimated from changes in the number of atoms of cosmogenic and terrigenic nuclides in groundwater and terrestrial rock. The main tools of groundwater dating are combination of the dissolved helium and tritium (half-life T_1/2= 12.3 y) for younger groundwater less than 60 years of residence time, and of the dissolved helium and ³⁶Cl (T_1/2= 3.01 ×10⁵ y) for older groundwater over million years. On the other hand, the main tools on the geomorphological changes are the estimation of exposure time using cosmogenic radionuclides (¹⁰Be (half-life T_1/2= 1.6×10⁶ y), ¹⁴C (T_1/2= 5730 y), ²⁶Al (T_1/2= 7.16×10⁵ y) and ³⁶Cl) and cosmogenic stable noble gases (³He and ²¹Ne) produced in rock.

抄録全体を表示

Phase diagrams and thermodynamical data play key roles in the field of materials science and engineering. They give us information on phase stabilities and process conditions, which are a sort of guide maps for materials design. Therefore, huge thermodynamical data have been accumulated by many researchers so far, which are listed in several databases, such as NIST-JANAF Thermochemical Tables and Thermochemical Data of Pure Substance (Barin). However, the coverage of the available data is still limited due to a great number of compounds on the earth. On the other hand, rapid development of computational power enables us to evaluate many physical properties from first principles in recent years. They include thermodynamical properties at finite temperatures, e.g., specific heats, enthalpies, entropies, and free energies, though first-principles calculations, i.e., electronic structure calculations, have been considered to be able to evaluate only total energies at absolute zero. In this article, I would detail a first-principles approach to thermodynamical properties which readers here are familiar with. The key is the technique to evaluate“ vibrational free energies”, which mainly determine the temperature dependences of thermodynamical properties of solid phases. In general, the harmonic and quasiharmonic approximations are employed to analyze the lattice vibrations, and they are reasonable in most solid phases. In the case of gas phases, rotational and translational free energies should be taken into account in addition to the vibrational free energies. I would be happy if you could find the great potential of“ first-principles thermodynamics” in this article.

抄録全体を表示

In this study, friction tests were conducted on simulating casing in the sand under high confining pressure in order to clarify frictional properties of the casing compose production well and formation which are prepared for methane hydrate development. Three types of simulated casing (maximum roughness Rz=2.7, 14.7, 30.0) and Toyoura sand (mean particle size D₅₀=200μm), No.8 silica sand (D₅₀=90μm) were used for the specimens. Simulating casing was produced based on the surface roughness of actual casing. During the friction tests, effective confining pressure was increased step by step from 0.2 MPa to 3.0 MPa and frictional strength was measured in each step. As the results, relation curve between friction and casing displacement changes from hardening behavior to softening behavior as effective confining pressure increases. In addition, effective secant friction angle decreases with effective confining pressure increase for high roughness specimen instead of increase with effective confining pressure increase for low roughness specimen. Friction between casing and sand under high confining pressure is dependent on effective confining pressure and the ratio of mean particle size of sand surface to surface roughness of casing. Finally, an estimated formula for frictional strength using effective confining pressure, mean particle size and surface roughness was proposed which can express experimental results well.

抄録全体を表示

Jig performance is influenced by water pulsation causing fluidization of feed particles in the separation chamber.The authors studied monitoring of the fluidization with pressure and level sensors in column tests and jig separation experiments using two plastics (PVC and PE).The minimum fluidization flow velocity in the column tests was determined from the pressure loss vs. apparent flow velocity diagram. In the jig experiments, the expansion of particle bed in the separation chamber was monitored, and the minimum displacement for particle fluidization was determined from the pressure loss vs. displacement diagram. The velocity of rising water in the jig at the minimum displacement was slightly larger than the minimum fluidization flow velocity. Good separation results were obtained at displacements near the minimum displacement inducing fluidization of the particles.A method to determine the optimum water pulsation parameter was developed, here the jig experiments were conducted with increasing displacement in a step-by-step manner at different frequencies of water pulsation, and the minimum displacement for the fluidization can be established from the measured pressure and water level data.Jig separation of a fine coal – quartz mixture demonstrated the applicability of the developed method.

抄録全体を表示