Energy Efficient Ant Colony Algorithms for Data Aggregation in Wireless Sensor Networks

In this paper, a family of ant colony algorithms called DAACA for data aggregation has been presented which contains three phases: the initialization, packet transmission and operations on pheromones. After initialization, each node estimates the remaining energy and the amount of pheromones to compute the probabilities used for dynamically selecting the next hop. After certain rounds of transmissions, the pheromones adjustment is performed periodically, which combines the advantages of both global and local pheromones adjustment for evaporating or depositing pheromones. Four different pheromones adjustment strategies are designed to achieve the global optimal network lifetime, namely Basic-DAACA, ES-DAACA, MM-DAACA and ACS-DAACA. Compared with some other data aggregation algorithms, DAACA shows higher superiority on average degree of nodes, energy efficiency, prolonging the network lifetime, computation complexity and success ratio of one hop transmission. At last we analyze the characteristic of DAACA in the aspects of robustness, fault tolerance and scalability.Comment: To appear in Journal of Computer and System Science

Positive solutions of a derivative dependent second-order problem subject to Stieltjes integral boundary conditions

In this paper, we investigate the derivative dependent second-order problem subject to Stieltjes integral boundary conditions \begin{equation*} \begin{cases}-u''(t)=f(t,u(t),u'(t)),\quad t\in[0,1],\\ au(0)-bu'(0)=\alpha[u],\ cu(1)+du'(1)=\beta[u],\end{cases} \end{equation*} where $f$: $[0,1]\times \mathbb{R}^{+}\times \mathbb{R}\rightarrow \mathbb{R}^{+}$ is continuous, $\alpha[u]$ and $\beta[u]$ are linear functionals involving Stieltjes integrals. Some inequality conditions on nonlinearity $f$ and the spectral radius condition of linear operator are presented that guarantee the existence of positive solutions to the problem by the theory of fixed point index. Not only is the general case considered but a large range of coefficients can be chosen to weaken the conditions in previous work for some special cases. The conditions allow that $f(t,x_{1},x_{2})$ has superlinear or sublinear growth in $x_{1}, x_{2}$. Two examples are provided to illustrate the theorems under multi-point and integral boundary conditions with sign-changing coefficients

Controlling vacancies in chalcogenides as energy harvesting materials

Recent years witnessed fruitful results on tailoring properties and application performance, especially in the field of clean energy storage and harvesting materials. Defects, especially elemental vacancies, exist universally and are inevitable in materials. Due to the difficulties to precisely map vacancy distributions and concentrations, their influence on properties is often underestimated. Moreover, in comparison with other strategies, vacancy engineering does not need to introduce impurities. Thus, the problem of lattice distortions, second phase formation, which is often detrimental to material performance, can be avoided this way. Thus, the study of the effect of vacancies is important not only in terms of fundamental scientific research, but also to limit global warming. In this thesis, we studied the influence of elemental vacancies on the magnetism, electrical transport, and band structures in several metal chalcogenides. By creating vacancies in the investigated materials, one can tailor the metal-insulator transitions, electronic structures, and introduction of magnetism to non-magnetic materials. With these strategies in mind, we can design and synthesize advanced functional materials as active electrode materials of lithium or sodium ion batteries, catalysts for water splitting and hydrogen evolution, as well as for next generation thermoelectric devices

Child population, economic development and regional inequality of education resources in China

There is great inequality of educational resources between different provinces in China due to unbalanced economic development. Despite continued redistribution of financial resources by the central government in favor of poorer provinces, educational inequality remains. In this paper, we argue that focusing on educational resources is far from sufficient. Poorer provinces do not only suffer from a lower level of educational resources, but they also have more children to educate, i.e. a greater need for education. Combining and analyzing the data in the Sixth National Population Census of China and the official statistics on education spending and resources, we found that provincial-level variations in the child population and the child dependency ratio have made access to educational resources even more unequal given the unequal financial capacity at the provincial level. Poorer provinces face a higher child dependency ratio and have lower economic development, and these two factors jointly lead to limited educational resources. Apart from a much higher level of redistribution in favor of less developed provinces, encouraging more balanced distribution of teachers and more broadly promoting economic equality are essential to reduce inequality in educational resources in China