Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges

With the rapid development of marine activities, there has been an increasing number of maritime mobile terminals, as well as a growing demand for high-speed and ultra-reliable maritime communications to keep them connected. Traditionally, the maritime Internet of Things (IoT) is enabled by maritime satellites. However, satellites are seriously restricted by their high latency and relatively low data rate. As an alternative, shore & island-based base stations (BSs) can be built to extend the coverage of terrestrial networks using fourth-generation (4G), fifth-generation (5G), and beyond 5G services. Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs. Despite of all these approaches, there are still open issues for an efficient maritime communication network (MCN). For example, due to the complicated electromagnetic propagation environment, the limited geometrically available BS sites, and rigorous service demands from mission-critical applications, conventional communication and networking theories and methods should be tailored for maritime scenarios. Towards this end, we provide a survey on the demand for maritime communications, the state-of-the-art MCNs, and key technologies for enhancing transmission efficiency, extending network coverage, and provisioning maritime-specific services. Future challenges in developing an environment-aware, service-driven, and integrated satellite-air-ground MCN to be smart enough to utilize external auxiliary information, e.g., sea state and atmosphere conditions, are also discussed

LASER IRRADIATION OF METAL NANOPARTICLE/POLYMER COMPOSITE MATERIALS FOR CHEMICAL AND PHYSICAL TRANSFORMATIONS

A metal nanoparticle supported on or dispersed in a polymer is irradiated with photons from a laser source to address the nanoparticles. The polymer is transmissive to the photons and addressed nanoparticles transform the energy of the photon to heat which is transferred to a material in the vicinity of the nanoparticle. The locally heated material undergoes a physical or chemical transformation upon heating. The transformed material can be a material in the proximity of the metal nanoparticle supported polymer or metal nanoparticle/polymer composite. In this manner thermally induced physical or chemical transformations can be carried out in very small volumes of material without significant heating to the bulk of the materia

Investigation on probing schemes in probe-based multicast admission control

Multicast is an efficient approach to save network bandwidth for multimedia streaming services. To provide Quality of Services (QoS) for the multimedia services while maintain the advantage of multicast in bandwidth efficiency, admission control for multicast sessions are expected. Probe-based multicast admission control (PBMAC) schemes are of a sort of scalable and simple admission control for multicast. Probing scheme is the essence of PBMAC. In this paper, after a detailed survey on three existing probing schemes, we evaluate these schemes using simulation and analysis approaches in two aspects: admission correctness and group scalability. Admission correctness of the schemes is compared by simulation investigation. Analytical models for group scalability are derived, and validated by simulation results. The evaluation results illustrate the advantages and weaknesses of each scheme, which are helpful for people to choose proper probing scheme for network

Research on bearing current damage description model of variable frequency motor

The bearing failure seriously affects the normal operation of the motor. In this paper, the early damage of bearing wear caused by the shaft current in the operating state of the variable frequency motor is proposed. From the perspective of the bearing capacitance storage capacitor charge, the method based on analyzing the relationship between pitting pit size and shaft current per unit area of bearing track surface is proposed, so that the model can directly judge whether the bearing is in an absolutely safe running state. In this paper, the description model between the size of the pitting pit per unit area of the bearing track surface and the mechanical and electrical parameters is derived based on the assumption that the charge required for the formation of pitting pits per unit area of the bearing track surface. It is shown that the shaft current can promote the bearing to produce pitting pit, which leads to the early damage of the bearing, and the size of the pitting pit is positively related to the shaft current. Matlab/Simulink simulation verifies the correctness of the description model