A fast wavelet block Jacobi method

In this paper, we develop a fast block Jacobi method for linear systems based on discrete wavelet transform (DWT). Traditional wavelet-based methods for linear systems do not fully utilize the sparsity and the multi-level block structure of the transformed matrix after DWT. For the sake of numerical efficiency, we truncate the transformed matrix to be a sparse matrix by letting the small values be zero. To combine the advantages of the direct method and the iterative method, we solve the sub-systems appropriately based on the multi-level block structure of the transformed matrix after DWT. Numerical examples show that the proposed method is very numerically effective.     

Kinetic and thermodynamic modeling of Portland cement hydration at low temperatures

Portland cement have to hydrate in cold climates in some particular conditions. Therefore, a better understanding of cement hydration under low temperatures would benefit the cement-based composites application. In this study, Portland cement was, therefore, kinetically and thermodynamically simulated based on a simple kinetics model and minimization of Gibbs free energy. The results of an evaluation indicate that Portland cement hydration impact factors include the water–cement ratio (w/c), temperature, and specific surface area, with the latter being an especially remarkable factor. Therefore, increasing the specific surface area to an appropriate level may be a solution to speed the delayed hydration due to low temperatures. Meanwhile, the w/c ratio is believed to be controlled under cold climates with consideration of durability. The thermodynamic calculation results suggest that low-temperature influences can be divided into three levels: irrevocable effects (<0 °C), recoverable effects (0–10 °C), and insignificant effects (10–20 °C). Portland cement was additionally measured via X-ray diffraction, thermal gravity analysis, and low-temperature nitrogen adsorption test in a laboratory and comparisons were drawn that validate the simulation result.     

Surface modification by graphene oxide:An efficient strategy to improve the performance of activated carbon based supercapacitors

An efficient and cost-effective strategy to modificate the surface of active carbon (AC), form a 3D-conductive network, and therefore improve the electrochemical performance of AC based supercapacitor was developed.     

Localization of diffusion sources in complex networks with sparse observations

Locating sources in a large network is of paramount importance to reduce the spreading of disruptive behavior. Based on the backward diffusion-based method and integer programming, we propose an efficient approach to locate sources in complex networks with limited observers. The results on model networks and empirical networks demonstrate that, for a certain fraction of observers, the accuracy of our method for source localization will improve as the increase of network size. Besides, compared with the previous method (the maximum–minimum method), the performance of our method is much better with a small fraction of observers, especially in heterogeneous networks. Furthermore, our method is more robust against noise environments and strategies of choosing observers.     

Naphthodithiophene-based donor materials for solution processed organic solar cells

As an emerging donor building block, naphthodithiophene (NDT) is causing more concerns in the field of organic semiconductors. With the rigid and coplanar molecule structure, NDT will exhibit more application space relying on its own advantage for facilitating the charge carrier transport. In this review article, we have summarized the development progress on the NDT-based donor materials for solution processed organic solar cells. Discussions and comments on those representative NDT type materials about structure and property are also presented.     

Molecular dynamics simulations of displacement cascades in Fe-10%Cr systems

Molecular dynamics simulations of the displacement cascades in Fe-10%Cr systems are used to simulate the primary knocked-on atom events of the irradiation damage at temperatures 300,600,and 750 K with primary knockedon atom energies between 1 and 15 keV.The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade.During the cascade,all recoil Fe and Cr atoms combine with each other to form Fe-Cr or Fe-Fe interstitial dumbbells as well as interstitial clusters.The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature.A few large clusters consist of a large number of Fe interstitials with a few Cr atoms,the rest are Fe-Cr clusters with small and medium sizes.The interstitial dumbbells of Fe-Fe and Fe-Cr are in the 111 and 110 series directions,respectively.     

Preparation and Characterization of Chitosan-Blended Multiwalled Carbon Nanotubes

Composites comprised of chitosan (CS) and multiwalled carbon nanotubes (MWCNTs) were fabricated by milling and ultrasonication dispersion methods. Scanning electron microscopy images showed homogeneous dispersion of MWCNTs throughout the CS matrix for samples prepared by either ultrasonication or milling methods. Further, the crystallinity of the CS component was found to decrease with the addition of MWCNTs, although the decomposition temperature and the storage modulus (E′) of the samples were improved. The decomposition temperature for the composite prepared by milling was 7°C higher than that by the ultrasonication. Meanwhile, the E′ decreased relatively slowly with temperature in the dynamic mechanical analysis measurements. In addition, IR analysis implied an interaction between CS and MWCNTs, which likely originated from hydrogen bonds between the amino, hydroxyl, and carboxyl groups of the two components. Compared with the ultrasonication, milling was more effective to promote the formation of the hydrogen bonds between CS and the MWCNTs and thus enhance the thermal stability of CS.