LoRaWAN is a promising LPWAN technology for IoT connectivity. It offers long-range and wide-area communication at low-power, low cost and low data rate. LoRaWAN performance has been evaluated according to many features such as coverage, scalability, physical layer parameters, communication reliability and latency. Existing studies assume that the LoRaWAN end-devices are already connected to the LoRa NetServer. Therefore, the performance of LoRaWAN activation procedure has not been well investigated. In this work, we study the performance of LoRaWAN during the Over-The-Air activation procedure. This process enables a large number of end-devices to join the network before being able to exchange any kind of packets. Thus, we analyze the average activation delay and the average energy consumption for an end-device in a large scale LoRaWAN. To achieve this goal, we first implement the Over-The-Air activation procedure in ns-3, especially in the ’lorawan’ module and conduct extensive simulations. Then, we elaborate a mathematical model using Markov-chain to evaluate both the delay and the energy consumption analytically. Our study shows that in a LoRaWAN cell composed of 1000 end-devices, the average activation delay for an end-device is about 35 minutes and this activation requires an average of three join-packet transmissions and an average energy consumption of 0.0887J.
The effect of microscopic pores on the behavior of a ductile material during deformation are experimentally and numerically investigated taking into account the history of loading. The object of the investigation is a polyester-resin-based composite material with inclusions of glass beads. During moulding of these constituents, pores are left in the material because of the resin viscosity. The experimental technique used for the characterization of the effect of pores is a tensile test. Constitutive equations of poroelastoplasticity have been developed according to the micromechanical consideration. The material model developed by Gurson is extended to this composite material. Numerical results have been obtained and compared with the experimental ones. 相似文献
Chronic forms of Q fever (endocarditis) are rare, but are responsible for severe and desperately recurrent infections, resulting in multiple valve replacements with a reserved prognosis. The authors report the case of a 35-year-old patient with a known history of rheumatic fever, who developed blood culture negative infectious endocarditis on a mitral bioprosthesis. The diagnosis of Q fever was based on serological arguments. Despite long-term antibiotic therapy, serology remained strongly positive and was associated with repeated mitral valve disinsertion. The patient died immediately after the fourth operation in a context of haemodynamic failure. This clinical case emphasizes the importance of performing Q fever serology in any case of culture negative endocarditis and the therapeutic difficulties encountered in chronic recurrent endocarditis. 相似文献
This study is concerned by the determination of the toxicity of an Olea europaea L.aqueous leaf extract after repeated administrations. Female and male rats were given 37.5, 75, 150, 300, 600 and 1200 mg/Kg/24h of the extract for 60 days. The results show that the drug studied induces an increase of weight growth, an hypotension, an hypoglycaemia and an hypouricaemia in treated animals. 相似文献