Asymmetric mutation model in genetic algorithm

Genetic algorithms (GAs) are stochastic optimization techniques, and the theoretical study of the process of GA evolution is very important in the application of GA. Mutation is one of most important operators in GA, and Markov chain theory has attracted researchers’ attention for the study of mutation. By applying Markov chain to study symmetric mutation model in GA, we have obtained the relation between the mutation rate and the evolution of the first order schema. This paper theoretically analyzes the effects of mutation rates on GA with asymmetric mutation, and studies the evolution and stationary distribution of the first order schema. This study focuses on effects of asymmetry to the linkage of loci, and shows the degree of asymmetry in mutation has a large effect on the evolution of the first order schema.     

Preparation of SiC hollow particles by gas-phase reaction in the SiH4-CH4-H2 system

The formation of SiC hollow particles by gas-phase reaction in the silane-methane-hydrogen system was studied at temperatures from 1200 to 1400° C. Synthesized powders were analysed by means of the thermogravimetry, X-ray diffraction, transmission electron microscopy, infrared irradiation, etc. The powders synthesized at 1200 to 1300° C consisted ofβ-SiC and silicon phases, but they became almost hollowβ-SiC particles at 1400° C. The composition, particle size, and shell thickness of the synthesized particles were dependent on the reaction conditions. From lattice parameter measurements, a certain amount of excess silicon was verified to be incorporated into theβ-SiC lattice. On the other hand, excess carbon existed, for the most part, as an amorphous phase not forming solid solutions withβ-SiC. Transmission electron microscopy observations and infrared absorption measurements have shown that excess carbon is contained within the shells of hollow particles, while unreacted excess silicon exists as a crystalline phase mostly in the cores of the particles.     

Stacking Faults in β-SiC Formed during Carbothermal Reduction of SiO2

Factors affecting stacking fault formation during the synthetic fabrication of β-SiC were investigated in the present study. Two main reaction routes in the carbothermal reduction of SiO₂—solid–solid and solid-gas reactions—led to the formation of β-SiC, depending on the vapor pressure of the SiO gas. The β-SiC formed by the solid-gas (carbon-SiO gas) reaction showed a whisker morphology with a high stacking fault density (SFD), whereas that formed by the solid-solid (Si-carbon) reaction exhibited spherical particles with a low SFD. The average size of the synthesized particles decreased with decreasing reaction temperature and time, and their stacking fault content, measured by X-ray diffraction, was higher than the true value, possibly because of a size effect. The stacking fault density increased with increase in the heating rate because of an increased reaction rate.     

Hydrothermal synthesis of fibrous lead titanate powders

A fibrous lead titanate (PbTiO₃) powder with light-yellow colour has been prepared by hydrothermal synthesis. The influences of Pb/Ti ratio (0.3 to 1.0) in the mixture and reaction time on the formation of fibrous PbTiO₃ under hydrothermal conditions have been investigated. The preferable conditions for preparing fibrous perovskite-type PbTiO₃ from fibrous potassium titanate are that the Pb/Ti ratio is 1.0, reaction temperature 150 °C and time 72 h. The particles of fibrous powder of perovskite type are usually less than 2 m in diameter and more than 50 m in length. The fibrous morphology is essentially unchanged up to about 650 °C, but it disappeared after heating to 1000 °C.     

Development of a novel crossover of hybrid genetic algorithms for large-scale traveling salesman problems

This article proposes a novel crossover operator of hybrid genetic algorithms (HGAs) with a Lin-Kernighan (LK) heuristic for solving large-scale traveling salesman problems (TSPs). The proposed crossover, tentatively named sub-tour recombination crossover (SRX), collects many short sub-tours from both parents under some set of rules, and reconnects them to construct a new tour of the TSP. The method is evaluated from the viewpoint of tour quality and CPU time for ten well-known benchmarks, e.g., dj38, qa194, …, ch71009.tsp, in the TSP website of the Georgia Institute of Technology. We compare the SRX with three conventional crossover operators, a variant of the maximal preservative crossover operator (MPX3), a variant of the greedy sub-tour crossover operator (GSX2), and a variant of the edge recombination crossover operator (ERX6), and show that the SRX succeeded in finding a better solution and running faster than the conventional methods mentioned above.     

Thermoelectric Performance of Epitaxial Thin Films of Layered Cobalt Oxides Grown by Reactive Solid-Phase Epitaxy with Topotactic Ion-Exchange Methods

This article reviews high-quality epitaxial film growth of layered cobalt oxides by reactive solid-phase epitaxy (R-SPE) with topotactic ion-exchange methods. Epitaxial film of Na_0.8CoO₂ was grown on a (0001)-oriented α-Al₂O₃ substrate by R-SPE using CoO film as the starting material. The Na_0.8CoO₂ epitaxial films were converted into high-quality epitaxial films of Sr_0.32Na_0.21CoO₂ and [Ca₂CoO₃] _x CoO₂ by topotactic ion-exchange methods. The Sr_0.32Na_0.21CoO₂ film exhibited better stability against moisture than that of the Na_0.8CoO₂ film, while it retained the good thermoelectric properties of Na_0.8CoO₂. The [Ca₂CoO₃] _x CoO₂ film exhibited a high electrical conductivity of 2.95 × 10² S/cm and a large Seebeck coefficient of +125 μV/K at 300 K.     

Vapor-Phase Growth of Transparent Zinc Oxide Ceramics with c-Axis Orientation

Large transparent specimens of polycrystalline zinc oxide with c -axis orientation have been prepared by the vapor transport method. Optical transmittance is 80% to 90% at 800 nm. X-ray diffraction peaks from faces other than (001) are negligible.     

Inhibition mechanism of the anatase-rutile phase transformation by rare earth oxides

The effect of rare earth oxide additions on the anatase-rutile transformation in doped TiO₂ was investigated. Y₂O₃, La₂O₃, CeO₂, Nd₂O₃, Sm₂O₃, Gd₂O₃, Tb₄O₇, Ho₂O₃, Dy₂O₃, Tm₂O₃ and Yb₂O₃, were found to suppress the transformation. The transformation process occurs in three stages. In the first stage, rare earth metal ions dissolve into interstitial sites in anatase. The resulting decrease in oxygen vacancies caused by the solid solution suppresses the nucleation of the transformation. In the second stage, the activation energy of the transformation was found to be 124 ± 3 Kcal/mol and 138 ± 4 Kcal/mol for pure anatase and anatase with 1 mol% Dy₂O₃, respectively. The transformation mechanism of this stage is not necessarily affected by additives. The final stage is affected by the amount of rare earth oxide-titania compound phase.     

A detection method for intronic snoRNA genes using extended-weight-updating SOM with appearance probability of bases

Small nucleolar RNAs (snoRNAs) are known that they will participate with RNA modification. However, detail functions of snoRNAs have not been clear still yet. In order to make clear functions of snoRNA, finding more snoRNAs and studying their works in cells are required. In this paper, we propose a method to detect snoRNA genes using extended-weight-updating self-organizing map (eSOM). An input vector to eSOM consists of a feature vector and a target vector. Different from a conventional SOM, a winner node for an input vector is decided by the feature vector only, and all the weights around the winner node are updated to be close to the input vector. We employ bases appearance probabilities and complementary base pair ratio for a feature vector. A target vector is a flag which is 1.0 or 0.0 for a positive or a negative sample, respectively. Experimental results showed our method achieved 91 and 93 % detection ratio for boxC/D and boxH/ACA type snoRNA genes, respectively.     

Electrical conduction and effective mass of a hole in single-crystal NiO

The electrical conductivity and Seebeck coefficient of single-crystal NiO were measured at 1100 to 1400° C. The activation energies for conductivity and thermoelectric power were 84.1 and 76.5 kJ mol^–1, respectively, which was interpreted as showing band-like conduction occurring at high temperatures. Doubly ionized cation vacancies were believed to be the dominant point defects, and the impurity effect gave rise to a dependence of conductivity. The effective mass of a hole, m ^*, was calculated based on a band-conduction scheme using the literature value of the deviation from stoichiometry, , and the hole mobility . The value of m ^* was in the range 0.8 to 1.0m ₀, and slightly decreased with increasing temperature.