Greenhouses bring us a continuous supply of agricultural products throughout the year. Therefore, their potential to improve upon Japan’s food self-sufficiency is greatly anticipated. Especially highly conditioned greenhouses, so-called plant factories, are expected to provide greater product availability for increasing food requirements. However the lighting and conditioning system for them now requires high costs and environmental stress by reason of using artificial energy. In addition, the sunlight system requires that a massive amount of expensive glasses be installed all around the sides of a greenhouse, which causes the structure to be relatively weak and monotonous in architectural design. To counteract the situation, studies on how to effectively use natural energy had to be conducted. We introduce here at first a study on efficient use of sunlight with reflectors on the internal side walls of a greenhouse. The effect was verified through a numerical simulation and some experiments. The illumination on the floor and the growth of the test plants were seen to greatly improve through the use of reflectors. For more efficient lighting, system with reflective blinds and outside reflectors was proposed. The results of these studies are helping us to realize the potential of employing less glass in greenhouses and the possibility of applying freer designs to their structures. We next introduce an investigation of a thermal conditioning system, whereby natural energy is converted into thermal preserver. In winter, the energy is stored during the daytime and then used for heating during the nighttime. Against the daytime heating in summer, thermal preservers are also applied, which are cooled during the winter. The applicability of this system was confirmed through experimental and theoretical studies. Finally, a new system for conditioned greenhouses is proposed, which uses natural energy more efficiently and offers more flexibility in the structural and the architectural designs.
Analysis of the pure mode I crack propagation (KII = 0) from tips of compressible joints in rock is improved by a minute computation of internal stresses in the joints, which takes a compressibility of joint and a dilatational overall sliding on joint surface into consideration. The Stress Compensation-Displacement Discontinuity Method (SC-DDM) is successfully applied to evaluate not only the internal stresses but also the stress intensity factors (KI, KII) at tips of propagating open cracks. It is firstly confirmed that the open crack propagates, describing a smooth curve, to the direction of the maximum compressive pressure applied at infinity. Subsequently the critical applied pressure to realize the critical state of KI = KIC is presented as a function of the crack elongation, and it is clarified, as a significant effect of interactive crack propagation, that the critical pressure has a maximum, and that the maximum critical pressure decreases with decreasing the joint spacing. Thus it is discussed that the quasi-brittle crack propagation in rock consists of a toughening process and a subsequent softening process, and that the maximum critical pressure appears at the transition from the toughening to the softening. Moreover, it is discussed the present improved method is a promising scheme available for the positive analysis of the critical pressure-crack elongation curve and the prediction of the strength characteristics of rock, including the delayed fracture, the effect of confining pressure and so on.
A macroscopic tension fracture of rock is analyzed as a result of the sub-critical crack growth in it, and a numerical procedure for the failure prediction is presented and discussed, basing upon the critical pressure-crack elongation curve (pc—a curve) for the pure mode I crack propagation (KII = 0, KI = KIC) in the homogenized joint model, which is accurately evaluated by means of the Stress Compensation-Displacement Discontinuity Method (SC-DDM). The crack elongation rate (da/dt) is formulated by the empirical equation of the form of da/dt ∝ KIn, where n: the sub-critical crack growth index. Computing the applied stress-crack elongation curves (p—a curves), the rate-dependent failure of rock in the tension test is concretely analyzed along with the time-dependent failure of rock in the creep test. The significant correlation between these experiments is discussed by comparing the non-linear stress-strain curves of the tension test to the non-linear time-strain curves of the creep test. It is clarified that the non-linearity is deeply associated with the sub-critical crack growth.
Calcium oxide (CaO)-based expansive cement, also known as “non-explosive demolition agents”, has been widely used to fracture massive rocks and concrete structures. When water is added to expansive cement, calcium oxide reacts with water, and changes into calcium hydroxide expanding 1.96 times larger in volume with generating heat. In previous researches, although expansive pressure due to the volume increase has been only focused, effect of thermal stress induced by the heat has not been carefully discussed. In this meaning, the fracture mechanism of calcium oxide-based expansive cement has not been clarified. To clarify the fracture mechanism, the authors made an experiment to fracture a mortar specimen of 300 mm cubic by setting a calcium oxide-based expansive cement in a 48 mm diameter hole bored in the center of the specimen. AE (acoustic emission) sources clustered on a middle part of the shortest line between the borehole wall and one of the lateral surfaces, just before macroscopic cracks generated. This suggests that macroscopic cracks originated between the borehole wall and the lateral surface rather than the vicinity of the hole. From the elastic theory, although the expansive pressure causes tensile stress in tangential direction of the hole, the stress is the maximum at the hole-wall and decrease in proportion to square of the distance from the hole. On the other hand, thermal stress due to heating of the hole is tensile away from a certain distance from the hole. Thus, it could be concluded that thermal stress has large effects in the fracture caused by the calcium oxide-based expansive cement, at least, in a rock or concrete block without preexisting crack.
The main drive of Hida Tunnel for Tokai-Hokuriku Highway was excavated by a world-largest-class TBM with the diameter of 12.84 m. The TBM have bored over 3.0 km of the tunnel through Nouhi Rhyolite, Granite Porphyry and Hida Gneiss. The uniaxial compressive strength of these rocks was found to be extremely high. Such high strength accompanied by high content of silicon dioxide resulted in significantly high wear rate of the disc cutters mounted on the TBM. In this study, cutter wear was carefully measured together with the operation conditions such as thrust force, penetration rate, cutter-head rotation rate and the rock properties such as uniaxial compressive strength, rock strength estimated from TBM cutting force, abrasivity obtained from turning operation test, chemical composition determined by X-ray analytical microscope. It was found that the extent of cutter wear largely depends on position of the disc cutter; cutter wear per unit rolling distance near the fringe of cutter head was extremely larger than that near the center of cutter head. A combination of rock strength estimated by TBM cutting force and length of wear flat in turning-operation test was found to be an excellent index to predict cutter wear rate.
A new hydrometallurgical process has been developed of silver recovery from chlorine leaching residue of anode slime in copper electro-refining, which includes the leaching of residue with aqueous Na2SO3 solution of pH=10.5 for 1h and at 25°C, followed by recovery of crude silver chloride at pH=1.0 with addition of 70% aqueous H2SO4 solution to the leaching solution and its purification with scrubbing by using various aqueous solutions of 6 kmol m-3 HCl and 30wt% H2O2, or 0.1 kmol m-3 EDTA at the temperatures ranging from 50 to 70°C. In this process, lead, selenium and tellurium are representative impurities in the crude silver chloride. Based on some chemical condition, it is speculated that the crude silver chloride contains mainly silver selenide and silver telluride as impurities. Scrubbing the silver chloride with HCl-H2O2 aqueous solution was effective to eliminate these impurities from the silver chloride. On the other hand, it is difficult to eliminate lead with the scrubbing, indicating that lead is incorporated in the silver chloride crystal. However, EDTA solution was effective for the elimination of lead to the level of less than 10 ppm.