X-ray Photoelectron Spectroscopy Study on the Process of Apatite Formation on a Sodium Silicate Glass in Simulated Body Fluid

The process of apatite formation on the surface of Na₂O–SiO₂ glass in a body environment was investigated, mainly by X-ray photoelectron spectroscopy, as a function of soaking time in a simulated body fluid (SBF). The glass was found to release Na⁺ ions via exchange with H₃O⁺ ions in the SBF to form Si—OH groups on its surface. These Si—OH groups induced apatite formation indirectly, by forming calcium silicate and amorphous calcium phosphate. The formation of the calcium silicate and amorphous calcium phosphate is attributed to electrostatic interactions between the Si—OH groups on the glass surface and the calcium and phosphate ions in the SBF.     

Mechanical,setting, and biological properties of bone cements containing micron-sized titania particles

In this study, polymethylmethacrylate-based composite cements containing 40–55.6 wt% micron-sized titania (titanium oxide) particles were developed, and their mechanical, setting, and biological properties evaluated. Three types of composite cement containing 40, 50, and 55.6 wt% silanized titania were designated ST2-40c, ST2-50c, and ST2-56c, respectively. In animal experiments, ST2-50c and ST2-56c were implanted into rat tibiae and solidified in situ. An affinity index was used to evaluate osteoconductivity. Compressive and bending strength of ST2-56c was 147.7 ± 3.2 and 69.3 ± 7.4; those of the other cements exceeded 100 MPa and 50 MPa, respectively. The affinity indices of ST2-56c were 42.1 ± 12.9 at six weeks and 53.4 ± 16.6 at 12 weeks, and were significantly higher than for ST2-50c and a commercial PMMA bone cement within 12 weeks. Our data indicate that bone cement containing micron-sized titania particles can be applied to prosthesis fixation as well as vertebroplasty, and ST2-56c is a good candidate cement.     

Utilization of the Perfluoroarene-Arene Interaction for Stabilization of Liquid Crystal Phases

Utilization of the perfluoroarene-arene interaction for stabilization of liquid crystal phases is reviewed. This interaction is strong (3.7–5.6 kcal/mol), but it is difficult to generate stable liquid crystal phases by using it. From the examples in this review, it is strongly suggested that flatness of the mesogenic units is important for obtaining stable liquid crystal phases. Introduction of a perfluorinated benzene ring to a rodlike molecule is effective in generating local biaxiality in the nematic and smectic A phases. Furthermore, the absence of an odd-even effect and the presence of a “trans-gauche-gauche” effect in the liquid crystal phases of monoalkylated rodlike molecules possessing a pentafluorophenyl group are explained by suppression of the molecular spin movements.     

Formation of a bioactive calcium titanate layer on gum metal by chemical treatment

The so-called gum metal with the composition Ti–36Nb–2Ta–3Zr–0.3O is free from cytotoxic elements and exhibits a low elastic modulus as well as high mechanical strength. In the present study, it was shown that this alloy exhibited a high capacity for apatite formation in a simulated body fluid when subjected to 1 M NaOH treatment, 100 mM CaCl₂ treatment, heat treatment at 700°C, and then hot water treatment. The high apatite formation was attributed to the CaTi₂O₅ which was precipitated on its surface, and found to be maintained even in a humid environment over a long period. The treated surface exhibited high scratch resistance, which is likely to be useful in clinical applications. The surface treatment had little effect on the unique mechanical properties described above. These results show that gum metal subjected to the present surface treatments exhibits a high potential for bone-bonding, which will be useful in orthopedic and dental implants.     

Interactive self-reflection and its architecture based on cellular automata

This paper proposes a novel concept ofinteractive self-reflection (ISR), and claims its importance and necessity for implementingautonomy. Concretely, ISR includes three elements that (a) precisely recognize the current situation by determining the boundary between self and others, (b) appropriately detect or produce the required information according to a sense of values, and (c) autonomously generate both the goal and the evaluation criteria. To address these issues on ISR, we implement an ISR architecture based on cellular automata, and investigate its adaptation ability as one aspect of autonomy. Through intensive simulations, we reveal the following implications: (1) the ISR architecture provides a high level of adaptability that cannot be obtained by either adaptation to the environment or adaptation from the environment; (2) the adaptability of the architecture is supported by appropriate interaction control between adaptation to the environment and adaptation from the environment. This work was presented in part at the Fifth International Symposium on Artificial Life and Robotics, Oita, Japan, January 26–28, 2000     

Agent architecture based on an interactive self-reflection classifier system

This paper extends the learning classifier system (LCS) to introduce a mechanism for recognizing a current situation by determining a boundary between self and others, and investigates its capability through interaction with an agent. Intensive simulations for adapting to an interacting agent have revealed the following implications: (1) the proposed architecture adapts to an interacting agent more quickly and appropriately than the conventional LCS, and (2) our architecture keeps its adaptation to an interacting agent even when the agent changes its internal models before our architecture acquires it completely. This work was presented in part at the Fifth International Symposium on Artificial Life and Robotics, Oita, Japan, January 26–28, 2000     

Controlling selection areas of useful infeasible solutions for directed mating in evolutionary constrained multi-objective optimization

As an evolutionary approach to solve constrained multi-objective optimization problems (CMOPs), recently an algorithm using the two-stage non-dominated sorting and the directed mating (TNSDM) was proposed. In TNSDM, the directed mating utilizes infeasible solutions dominating feasible solutions in the objective space to generate offspring. The directed mating significantly contributes to the search performance improvement in evolutionary constrained multi-objective optimization. However, the conventional directed mating has two problems. First, since the conventional directed mating selects a pair of parents based on the conventional Pareto dominance, two parents having different search directions may be mated. Second, the directed mating cannot be performed in some cases especially when the population has few useful infeasible solutions. In this case, the conventional mating using only feasible solutions is performed instead. Thus, the effectiveness of the directed mating cannot always be achieved depending on the number of useful infeasible solutions. To overcome these problems and further enhance the effect of the directed mating in TNSDM, in this work we propose a method to control the selection area of useful infeasible solutions by controlling dominance area of solutions (CDAS). We verify the effectiveness of the proposed method in TNSDM, and compare its search performance with the conventional CNSGA-II on discrete m-objective k-knapsack problems and continuous mCDTLZ problems. The experimental results show that the search performance of TNSDM is further improved by controlling the selection area of useful infeasible solutions in the directed mating.     

Nongovernance rather than governance in a multiagent economicsociety

This paper explores how to achieve goals at the macro level without controlling self-interested economic agents at the micro level and investigates the effectiveness of our claim suggesting that we make use of properties arising from interaction among economic agents to address the above issue. Intensive experiments on a complex domain problem have found the following implications: (1) as an institution design, it is important not to control economic agents at the micro level, but to promote them to self-activate in order to achieve goals at the macro level and (2) as a role of an administrative party like a government, it is important to have a clear view to determine which results are good because the timing for finding such results depends on the environmental situation and there is no guarantee that these results will converge. Other implications are summarized as follows: (1) it is important to remove evaluation level intervention to find good results, while it is important to introduce this intervention to reduce costs and (2) behavior intervention does not contribute to finding good results nor reducing costs     

Apatite-forming ability of Ti–15Zr–4Nb–4Ta alloy induced by calcium solution treatment

Ti–15Zr–4Nb–4Ta alloy free from cytotoxic elements shows high mechanical strength and high corrosion resistance. However, simple NaOH and heat treatments cannot induce its ability to form apatite in the body environment. In the present study, this alloy was found to exhibit high apatite-forming ability when it was treated with NaOH and CaCl₂ solutions, and then subjected to heat and hot water treatments to form calcium titanate, rutile, and anatase on its surface. Its high apatite-forming ability was maintained even in 95% relative humidity at 80°C after 1 week. The surface layer of the treated alloy had scratch resistance high enough for handling hard surgical devices. Thus, the treated alloy is believed to be useful for orthopedic and dental implants.     

Learning model for adaptive behaviors as an organized group of swarm robots

This paper describes a novel organizational learning model for multiple adaptive robots. In this model, robots acquire their own appropriate functions through local interactions among their neighbors, and get out of deadlock situations without explicit control mechanisms or communication methods. Robots also complete given tasks by forming an organizational structure, and improve their organizational performance. We focus on the emergent processes of collective behaviors in multiple robots, and discuss how to control these behaviors with only local evaluation functions, rather than with a centralized control system. Intensive simulations of truss construction by multiple robots gave the following experimental results: (1) robots in our model acquire their own appropriate functions and get out of deadlock situations without explicit control mechanisms or communication methods; (2) robots form an organizational structure which completes given tasks in fewer steps than are needed with a centralized control mechanism. This work was presented, in part, at the Second International Symposium on Artificial Life and Robotics, Oita, Japan, February 18–20, 1997