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991.
Minoru Gamo Masato Shinoda Takahisa Maeda 《International journal of remote sensing》2013,34(19):6701-6722
It is preferable to prepare internally consistent maps of arid regions on a global scale in order to understand the present conditions of arid regions, especially deserts and soil degradation areas. We attempted to delimit arid regions at a global scale by combining climate data, i.e. aridity index (AI), and vegetation data, i.e. vegetation index. The annual AI was estimated by the ratio of mean annual precipitation to mean annual potential evapotranspiration, using the Thornthwaite method. The long-term mean of yearly maximum normalized difference vegetation index (NDVIymx) was used as an indicator of the vegetation condition. Arid regions of the world were classified into four categories, namely A, severe deserts, where both aridity and vegetation indices are very small; G, semi-arid regions, where the vegetation index is proportionally related to the AI; I, irrigated areas and oases, where the vegetation is relatively abundant despite severe dryness; and S, soil degradation areas, where the vegetation is poor despite relatively humid conditions. The Sahel from Niger to Chad, the Sahel in Darfur, and the Ordos Plateau in China are within Category S. The standard deviation of NDVIymx is very small/large in severe deserts/semi-arid areas, respectively. Thus, the Sahara desert was clearly distinguished from the Sahel; the latter belongs to Category G and drought occurs frequently here. In Category S zones, the standard deviation of NDVIymx is relatively small compared with that within the Category G zone because the return rainfall does not seem to promptly restore productivity. Category S was divided into three subdivisions according to the degree of degradation, expressed by the ratio of the AI to vegetation index. Category G was also divided into four classes, according to degree of vegetation (or aridity). The distribution of Category S is comparable to the soil degradation areas mapped by Global Assessment of Human-Induced Soil Degradation (GLASOD) data. True deserts, where the standard deviation of NDVIymx is very small, were selected from the ‘severe desert’ group. Desert areas were classified as true deserts, severe deserts, grassland deserts (Category G), and soil degradation deserts (Category S). 相似文献
992.
The lattice Boltzmann method (LBM) has been widely used for the simulations of the incompressible Navier–Stokes (NS) equations. The finite difference Boltzmann method (FDBM) in which the discrete-velocity Boltzmann equation is solved instead of the lattice Boltzmann equation has also been applied as an alternative method for simulating the incompressible flows. The particle velocities of the FDBM can be selected independently from the lattice configuration. In this paper, taking account of this advantage, we present the discrete velocity Boltzmann equation that has a minimum set of the particle velocities with the lattice Bharnagar–Gross–Krook (BGK) model for the three-dimensional incompressible NS equations. To recover incompressible NS equations, tensors of the particle velocities have to be isotropic up to the fifth rank. Thus, we propose to apply the icosahedral vectors that have 13 degrees of freedom to the particle velocity distributions. Validity of the proposed model (D3Q13BGK) is confirmed by numerical simulations of the shear-wave decay problem and the Taylor–Green vortex problem. With respect to numerical accuracy, computational efficiency and numerical stability, we compare the proposed model with the conventional lattice BGK models (D3Q15, D3Q19 and D3Q27) and the multiple-relaxation-time (MRT) model (D3Q13MRT) that has the same degrees of freedom as our proposal. The comparisons show that the compressibility error of the proposed model is approximately double that of the conventional lattice BGK models, but the computational efficiency of the proposed model is superior to that of the others. The linear stability of the proposed model is also superior to that of the lattice BGK models. However, in non-linear simulations, the proposed model tends to be less stable than the others. 相似文献
993.
994.
Engineers and researchers are paying more attention to reinforcement learning (RL) as a key technique for realizing computational intelligence such as adaptive and autonomous decentralized systems. In general, it is not easy to put RL into practical use. In prior research our approach mainly dealt with the problem of designing state and action spaces and we have proposed an adaptive co-construction method of state and action spaces. However, it is more difficult to design state and action spaces in dynamic environments than in static ones. Therefore, it is even more effective to use an adaptive co-construction method of state and action spaces in dynamic environments. In this paper, our approach mainly deals with a problem of adaptation in dynamic environments. First, we classify tasks of dynamic environments and propose a detection method of environmental changes to adapt to dynamic environments. Next, we conducted computational experiments using a so-called “path planning problem” with a slowly changing environment where the aging of the system is assumed. The performances of a conventional RL method and the proposed detection method were confirmed. 相似文献
995.
Effect of Polyelectrolyte Dispersants on the Preparation of Silica-Coated Zinc Oxide Particles in Aqueous Media 总被引:3,自引:0,他引:3
Hongzhi Wang Hiroyuki Nakamura Ken Yao Masato Uehara Satoshi Nishimura Hideaki Maeda Eiichi Abe 《Journal of the American Ceramic Society》2002,85(8):1937-1940
Sodium silicate was utilized to obtain a SiO2 coating on ZnO particles to prevent a photocatalytic reaction between ZnO and phenol. During the coating process, pH control is important to avoid dissolution of the ZnO as well as to obtain a good dispersion. Two kinds of polyelectrolyte dispersants were used to control the surface charge of the ZnO particles in aqueous media. As a result, poly(ethylenimine) (PEI) shifted the isoelectric point of ZnO from pH 9 to pH 10, whereas poly(ammonium acrylate) (PAA) made the surface charge of ZnO negative between pH 6 and pH 11. The change in the ZnO surface charge produced by adding polyelectrolyte dispersants makes it possible to obtain uniform silica–coated ZnO particle in aqueous media. UV–irradiation experiments showed that PEI, which can make the surface charge opposite to that of SiO2 , is more effective in obtaining a thick silica coating on ZnO. 相似文献
996.
997.
The mechanism of extraction of nickel from an aqueous ammonia-ammonium nitrate mixture by an n-hexane solution of Versatic 10 was investigated from the viewpoint of extraction equilibrium and extraction kinetics. From the equilibrium study, it was found that nickel is extracted according to the following two extraction reactions which are in accordance with the loading ratio of nickel to Versatic 10: in the range of lower loading ratio, and in the range of higher loading ratio. The equilibrium constants for each reaction were also determined. From the study of extraction kinetics, the extraction rate was found to be proportional to the total concentrations of nickel and Versatic 10 and inversely proportional to that of hydrogen ion. A reaction mechanism is proposed in order to give a reasonable explanation for the observed concentration dependence of each of the reactant species. 相似文献
998.
Plastic GRIN rod and fiber lenses have been fabricated by photocopolymerization of a ternary monomer system, methyl methacrylate-N-vinyl carbazole-vinyl acetate. We now propose the general mechanism for forming radial GRIN in the ternary monomer system using computer simulation. The relationship between the preparation condition and the optical characteristics was clarified. The region having quadratic-index distribution and the numerical aperture were remarkably improved by the ternary monomer system. 相似文献
999.
The gel rod, partially polymerized CR-39 [diethylene glycol-bis-(allyl carbonate)], is placed in the atmosphere of trifluoroethyl methacrylate (3FMA) vapor, followed by heat-treatment to yield the GRIN rod. Examining the relationship between the preparation conditions and the optical properties of the GRIN rod, the plastic GRIN rods with a quadratic-index distribution up to their periphery and with higher than 0.36 N.A. were fabricated. 相似文献
1000.
The hyperfine-enhanced nuclear moment in TmPO4 was studied by SQUID NMR. A resonance frequency
x
/2 = 274 MHz per tesla was obtained, leading to an enhancement factor of 77.9. The temperature dependence of the spin-lattice relaxation time T
1 of 169Tm nuclear spin in TmPO4 was measured at liquid helium temperatures. The temperature dependence of T
1 can be understood in terms of nuclear Orbach and direct processes. 相似文献