Attack structural vulnerability of power grids: A hybrid approach based on complex networks

Power grids have been studied as a typical example of real-world complex networks. Different from previous methods, this paper proposes a hybrid approach for structural vulnerability analysis of power transmission networks, in which a DC power flow model with hidden failures is embedded into the traditional error and attack tolerance methodology to form a new scheme for power grids vulnerability assessment and modeling. The new approach embodies some important characteristics of power transmission networks. Furthermore, the simulation on the standard IEEE 118 bus system demonstrates that a critical region might exist and when the power grid operates in the region, it is vulnerable to both random and intentional attacks. Finally, a brief theoretical analysis is presented to explain the new phenomena.     

An eigen-based high-order expansion basis for structured spectral elements

We present an eigen-based high-order expansion basis for the spectral element approach with structured elements. The new basis exhibits a numerical efficiency significantly superior, in terms of the conditioning of coefficient matrices and the number of iterations to convergence for the conjugate gradient solver, to the commonly-used Jacobi polynomial-based expansion basis. This basis results in extremely sparse mass matrices, and it is very amenable to the diagonal preconditioning. Ample numerical experiments demonstrate that with the new basis and a simple diagonal preconditioner the number of conjugate gradient iterations to convergence has essentially no dependence or only a very weak dependence on the element order. The expansion bases are constructed by a tensor product of a set of special one-dimensional (1D) basis functions. The 1D interior modes are constructed such that the interior mass and stiffness matrices are simultaneously diagonal and have identical condition numbers. The 1D vertex modes are constructed to be orthogonal to all the interior modes. The performance of the new basis has been investigated and compared with other expansion bases.     

Annealing effect on the ultrafast dynamics of Ag nanoparticles embedded in soda-lime silicate glasses

Ag nanoparticles embedded in soda-lime silicate glasses were fabricated by the ion-exchange technique. Effects of thermal treatment on the optical nonlinearity and ultrafast dynamics of Ag nanoparticles were investigated by applying time-resolved optical Kerr effect and pump-probe techniques. The results indicate that thermal treatment is an efficient method to improve the nonlinear optical performance of this kind of material.     

Post‐Synthetic Polymerization of UiO‐66‐NH2 Nanoparticles and Polyurethane Oligomer toward Stand‐Alone Membranes for Dye Removal and Separation

Metal–organic frameworks (MOFs) are widely used as porous materials in the fields of adsorption and separation. However, their practical application is largely hindered by limitations to their processability. Herein, new UiO‐66‐Urea‐based flexible membranes with MOF loadings of 50 ( 1 ), 60 ( 2 ), and 70 wt % ( 3 ) were designed and prepared by post‐synthetic polymerization of UiO‐66‐NH₂ nanoparticles and a polyurethane oligomer under mild conditions. The adsorption behavior of membrane 3 towards four hydrophilic dyes, namely, eosin Y (EY), rhodamine B (RB), malachite green (MG), and methylene blue (MB), in aqueous solution was studied in detail. It exhibits strong adsorption of EY and RB but weak adsorption of MG and MB in aqueous solution. Owing to the selective adsorption of these hydrophilic dyes, membrane 3 can remove EY and RB from aqueous solution and completely separate EY/MB, RB/MG, and RB/MB mixtures in aqueous solution. In addition, the membrane is uniformly textured, easily handled, and can be reused for dye adsorption and separation.     

Bis‐tert‐Alcohol‐Functionalized Crown‐6‐Calix[4]arene: An Organic Promoter for Nucleophilic Fluorination

A bis‐tert‐alcohol‐functionalized crown‐6‐calix[4]arene (BACCA) was designed and prepared as a multifunctional organic promoter for nucleophilic fluorinations with CsF. By formation of a CsF/BACCA complex, BACCA could release a significantly active and selective fluoride source for S_N2 fluorination reactions. The origin of the promoting effects of BACCA was studied by quantum chemical methods. The role of BACCA was revealed to be separation of the metal fluoride to a large distance (>8 Å), thereby producing an essentially “free” F^?. The synergistic actions of the crown‐6‐calix[4]arene subunit (whose O atoms coordinate the counter‐cation Cs⁺) and the terminal tert‐alcohol OH groups (forming controlled hydrogen bonds with F^?) of BACCA led to tremendous efficiency in S_N2 fluorination of base‐sensitive substrates.