No abstract

Fluorine (F) and chlorine (Cl) substitution in organic semiconductors has been found to be effective for enhancing the performance of organic photovoltaics. However, the effect of these substitutions on charge transport properties of organic semiconductors remains elusive. A series of naphthalene diamide (NDI)‐based copolymers: N2200, the corresponding fluorinated N2200 (F‐N2200), and chlorinated N2200 (Cl‐N2200) are employed to fabricate field‐effect transistors. Gate‐dependent and temperature‐dependent mobility are measured and analyzed to reveal the intrinsic electronic properties of the polymers. It is found that F substitution decreases energetic disorder of the semiconductor while Cl substitution increases it. These findings are further supported by density functional theory calculations and characterizations on the performance of doped devices based on the three polymers. Overall, the influence of fluorination and chlorination on charge transport in those NDI‐based polymers is identified and clarified, which is important for justifying the wide employment of fluorination and chlorination strategies in organic electronics.

This paper presents an offline word-recognition system based on structural information in the unconstrained written word. Oriented features in the word are extracted with the Gabor filters. We estimate the Gabor filter parameters from the grayscale images. A two-dimensional fuzzy word classification system is developed where the spatial location and shape of the membership functions are derived from the training words. The system achieves an average recognition rate of 74% for the word being correctly classified in the top position and an average of 96% for the word being correctly classified within the top five positions.

A class of three-dimensional acoustic cloak for underwater operation is designed by using a multi-area coordinate transformation method. To overcome the difficulty of achieving materials with the ideal parameters of the cloak in nature, layered metamaterials consisting of mercury and water are designed based on effective medium theory. The acoustic properties of the layered metamaterials can be characterized by the anisotropic densities and isotropic modulus, which can satisfy the material requirements of the cloak shell. This design has many advantages over previous designs of acoustic cloak, including a large cloaking area, omnidirectional invisibility, broad working frequency and easier design methodology. Our transformation strategy and method of metamaterials design offer a cost-effective way and efficient technique for fabricating a large-scale cloak. Excellent invisibility is achieved by using simulations based on the finite element method. The good cloaking performances have demonstrated great potential in the promotion of the practical applications of a large-scale acoustic cloak, especially for lowfrequency sound manipulation underwater.

Narrow bandwidth and specific incident angle are the main drawbacks in real-life applications for the existed carpet cloaking based on the acoustic metasurface (AM). Here, we tackle to get over the problems by proposing a reprogrammable AM. The unit cell is composed of water sink and filling nozzle. By incorporating an external water pumping system into each individual unit cell, the reflected phase can be readily regulated. Since the pumping process is reversible, the AM is reprogrammable under the control of the water pumping system in the frequency range of 3430–6860[Formula: see text]Hz. Both the acoustic cloaking and disguising are designed based on the proposed AM. The double security for the target object can be ensured to avoid being detected by combining the two designs. Simulated results with the finite element method indicate that the acoustic cloaking and disguising can work in the broad bandwidth of 66.7% of the central frequency with full-range incident angles from [Formula: see text] to [Formula: see text]. Our design shows promise for applications in realizing the practical skin cloaking and disguising one step closer.