With the advance of the research on acoustic metamaterials, the limits of passive metamaterials have been observed, which prompts the studies concerning actively tunable metamaterials with adjustable characteristic frequency bands. In this work, we present a tunable acoustic metamaterial with doublenegativity composed of periodical membranes and side holes, in which the double-negativity pass band can be controlled by an external direct-current voltage. The tension and stiffness of the periodically arranged membranes are actively controlled by electromagnets producing additional stresses, and thus, the transmission and phase velocity of the metamaterial can be adjusted by the driving voltage of the electromagnets. It is demonstrated that a tiny direct-current voltage of 6V can arise a shift of double-negativity pass band by 40% bandwidth, which exhibits that it is an easily controlled and highly tunable acoustic metamaterial, and furthermore, the metamaterial marginally causes electromagnetic interference to the surroundings.Currently, acoustic metamaterials are extensively studied owing to unprecedented characteristics, which exhibit application potentials in various fields [1][2][3][4][5][6] . However, with the development of acoustic metamaterials, the limitations of passive metamaterials have been observed. First, the characteristic frequency bands related to extraordinary acoustic performance are restricted into narrow bands induced by resonance. In addition, since the unique characteristics of metamaterials are created by artificial structures, they cannot be freely changed once the metamaterials are fabricated. Therefore, tunable acoustic metamaterials with adjustable characteristic frequency bands are urgently required treading on the heels of their counterparts in electromagnetics and optics [7][8][9][10] . Different mechanisms were adopted to realize tunable metamaterials. First, tunable features arose from nonlinear effects in acoustic metamaterials, in which the constitutive parameters could be changed with the intensities of input acoustic fields, and they were considered to be self-modulation metamaterials [11][12][13] . On the other hand, actively tunable metamaterials, which could be controlled by an external source other than input acoustic fields, were presented. As an example, by mechanically changing the volumes of Helmholtz resonators in a metamaterial, the resonant frequency was adjusted, which could change the corresponding characteristic frequency bands 11,14 . A similar method on the analogy of the split-ring resonators in electromagnetic metamaterials was introduced into acoustic metamaterials, in which the resonant frequency of a split hollow sphere was tuned by filling water into the sphere to change the volume 15 . Similarly, the equivalent sound speed could be changed by filling a fluid into the intermediate gaps of a metamaterial 16 . Generally, an external electric signal is preferred as the control signal in tuning the performance of a metamaterial. Piezoelectric materials, which...

The Bi0.5Na0.5TiO3-xwt%BaTiO3 compound ceramics were prepared. The influence of different BaTiO3 content on structure was evaluated by scanning electron microscopy and X-ray diffraction analysis. The results show oriented is induced by plate-like BaTiO3 template. Signficant improvement of the piezoelectric (d33 = 112 pC/N) and dielectric properties ( max ≈ 5500) was observed. The improvement was attested to the apparent alignment of the BaTiO3 templates and grain oriented growth.

3D modeling of city has become a hot research topic in the field of GIS, it has very important significance in terms of urban construction, management and planning. Building model is an important sector of 3D city model, after analyzing the traditional algorithm of building modeling, a combined algorithm based on CSG and SketchUp is proposed in this paper. Using CSG model, the regular buildings are constructed firstly, then using SketchUp software, the irregular buildings are constructed. Finally, all building models are combined into a continuous building. The paper uses parts of the actual data to verify the feasibility of this modeling approach in the paper.

The Lower Yellow River is apt to deposit and migrate. The reach from Huayuankou to Jiahetan is the typical wandering reach, which has broad and shallow body, intertwined tributary and numerous shoals. The mainstream always swings, and the riverbed deforms rapidly. There exist lots of residential places, irrigation canals, roads, productive dikes and other controlling works within the embankments, which greatly limits the scope of flooding. When the peak discharge is very large, the flood is prone to resulting in productive dikes bursting, which will greatly endanger the lives of residents in flood plains. The 2-D water flow mathematical model which reflects flood routing in the reach from Huayuankou to Jiahetan has been developed based on MIKE 21 software in this paper. Through the numerical simulation of the “96.8” typical flood, the simulating results in the condition of present topography are agreement with the measured ones. It shows that this model is basically reasonable in the selection aspects of river terrain, boundary treatment, roughness and water flow parameters, and the model has a reference value.