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A great number of efficient methods to improve the performance of the networks have been proposed in physical-layer security for wireless communications. So far, the security and privacy in wireless communications is optimized based on a fixed assumption about the trustworthiness or trust degrees (TD) of certain wireless nodes. The nodes are often classified into different types such as eavesdroppers, untrusted relays, and trusted cooperative nodes. Wireless nodes in different networks do not completely trust each other when cooperating or relaying information for each other. Optimizing the network based on trust degrees plays an important role in improving the security and privacy for the modern wireless network. We proposed a novel algorithm to find the route with the smallest total transmission time from the source to the destination and still guarantee that the accumulated TD is larger than a trust degree threshold. Simulation results are presented to analyze the affects of the transmit SNR, node density, and TD threshold on different network performance elements.

Graphene has been enjoyed significant recent attention due to its potential applications in electronic and optoelectronic devices. Graphene is usually prepared via Hummers' method or modified Hummers' methods. These methods are the most suitable for the large-scale production of single graphene at low cost. But their main drawbacks are the use of strong oxidizing agents which make graphene films separating into small sheets and this extremely decrease the electrical conductivity of graphene. Herein, we report an inexpensive, fast and facile method for preparation of a double layer structured transparent, flexible hybrid electrode from silver nanowires (Ag NWs) with chemically converted graphene (CCG) coating on arbitrary substrate. These films dramatically decreases the resistance of graphene films and exhibited high optical transmittance (82.4 %) and low sheet resistance (18 Ω/ sq), which is comparable to ITO transparent electrode. The ratio of direct conductivity to optical conductivity DC/OP = 104 of this electrode is very close to that displayed by commercially available ITO. Especially, the whole fabrication process is carried out at low temperature. The graphene films are spin coated directly on the substrate without transferring therefore eliminating troubles that are brought from the transfer method.

Gas sensing is one of the most promising applications for reduced graphene oxide (rGO). High surface-to-volume ratio in conjunction with remaining reactive oxygen functional groups translates into sensitivity to molecular on the rGO surface. The response of the rGO based devices can be further improved by functionalizing its surface with metal nano-materials. In this paper, we report the ammonia (NH3) sensing behavior of rGO based sensors functionalized with nano-structured metal: silver (Ag) or platinum (Pt) or gold (Au) in air at room temperature and atmospheric pressure. The gas response is detected by the monitoring changes in electrical resistance of the rGO/metal hybrids due to NH3 gas adsorption. Compared to bare rGO, significantly improved NH3 sensitivity is observed with the addition of nano-structured metals. These materials are applied to play the small bridges role connecting many graphene islands together to improve electrical conduction of hybrids while maintaining the inherent advantage of rGO for NH3 gas sensitivity.