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

Body Mass Index–Mortality Relationship in Severe Hypoglycemic Patients With Type 2 Diabetes

AbstractBackgroundHypoglycemia is associated with a higher risk of death. This study analyzed various body mass index (BMI) categories and mortalities of severe hypoglycemic patients with type 2 diabetes mellitus (DM) in a hospital emergency department.MethodsThe study included 566 adults with type 2 diabetes who were admitted to 1 medical center in Taiwan between 2008 and 2009 with a diagnosis of severe hypoglycemia. Mortality data, demographics, clinical characteristics and the Charlson’s Comorbidity Index were obtained from the electronic medical records. Patients were stratified into 4 study groups as determined by the National institute of Health (NiH) and World Health organization classification for BMi, and the demographics were compared using the analysis of variance and χ2 test. Kaplan-Meier’s analysis and the Cox proportional-hazards regression model were used for mortality, and adjusted hazard ratios were adjusted for each BMi category among participants.ResultsAfter controlling for other possible confounding variables, BMI <18.5 kg/m2 was independently associated with low survival rates in the Cox regression analysis of the entire cohort of type 2 DM patients who encountered a hypoglycemic event. Compared to patients with normal BMI, the mortality risk was higher (adjusted hazard ratios = 4.9; 95% confidence interval [CI] = 2.4-9.9) in underweight patients. Infection-related causes of death were observed in 101 cases (69.2%) and were the leading cause of death.ConclusionsAn independent association was observed between BMI less than 18.5 kg/m2 and mortality among type 2 DM patient with severe hypoglycemic episode. Deaths were predominantly infection related

High-performance InSe Transistors with Ohmic Contact Enabled by Nonrectifying-barrier-type Indium Electrodes

The electrical contact to two-dimensional (2D)-semiconductor materials are decisive to the electronic performance of 2D-semiconductor field-effect devices (FEDs). The presence of a Schottky barrier often leads to a large contact resistance, which seriously limits the channel conductance and carrier mobility measured in a two-terminal geometry. In contrast, ohmic contact is desirable and can be achieved by the presence of a nonrectifying or tunneling barrier. Here, we demonstrate that an nonrectifying barrier can be realized by contacting indium (In), a low work function metal, with layered InSe because of a favorable band alignment at the In-InSe interface. The nonrectifying barrier is manifested by ohmic contact behavior at T=2 K and a low barrier height, {\Phi}$_B$=50 meV. This ohmic contact enables demonstration of an ON-current as large as 410 {\mu}A/{\mu}m, which is among the highest values achieved in FEDs based on layered semiconductors. A high electron mobility of 3,700 and 1,000 cm$^2$/Vs is achieved with the two-terminal In-InSe FEDs at T=2 K and room temperature, respectively, which can be attributed to enhanced quality of both conduction channel and the contacts. The improvement in the contact quality is further proven by an X-ray photoelectron spectroscopy study, which suggests that a reduction effect occurs at the In-InSe interface. The demonstration of high-performance In-InSe FEDs indicates a viable interface engineering method for next-generation, 2D-semiconductor-based electronics

A Three-dimensional Adaptive Strategy with Uniform Background Grid in Element-free Galerkin Method for Extremely Large Deformation Problems

A novel three-dimensional adaptive element-free Galerkin method (EFGM) based on a uniform background grid is proposed to cope with the problems with extremely large deformation. On the basis of this uniform background grid, an interior adaptive strategy through an error estimation within the analysis domain is developed. By this interior adaptive scheme, additional adaptive nodes are inserted in those regions where the solution accuracy needs to be improved. As opposed to the fixed uniform background grid, these inserted nodes can move along with deformation to describe the particular local deformation of the structure. In addition, a triangular surface technique is adopted to depict the geometry of the three-dimensional structure and a new surface adaptive strategy on the surface of the structure is also proposed. The complicated geometry of the three-dimensional structure can be thus analyzed precisely even under extremely large deformation. Besides, the contact regions of the structure can be determined accurately when the contact behavior occurs. Therefore, the present EFGM adaptive strategy not only retains the advantage of the uniform background grid for solving the extremely deformed problems, but also enhances the solution accuracy in the interior and surface of the structure