Nowadays Vehicular Ad-Hoc Networks (VANETs) are very popular and significantly used, due to their unique abilities to improve road safety. As a consequence, the security of these networks is of great importance and it has become one of the central topics in scientific and research fields such as information exchange. Sybil attack is one of the challenges for Ad-Hoc networks security. In this paper, a cross-layer approach and fuzzy logic method are used to detect the Sybil attacks. The proposed fuzzy logic method has four inputs form different OSI layers: entry time to the network, a number of neighbors, buffer size and signal to noise ratio. These inputs are imported to several membership functions of the fuzzy logic methods and the simulation results indicate that the proposed solution provides a robust technique in Sybil attack detection.
Abstract:Cooperative communication techniques have recently enabled wireless technologies to overcome their challenges. The main objective of these techniques is to improve resource allocation. In this paper, we propose a new protocol in medium access control (MAC) of the IEEE 802.11 standard. In our new protocol, which is called Fair Cooperative MAC (FC-MAC), every relay node participates in cooperation proportionally to its provided cooperation gain. This technique improves network resource allocation by exploiting the potential capacity of all relay candidates. Simulation results demonstrate that the FC-MAC protocol presents better performance in terms of throughput, fairness, and network lifetime.
BackgroundCardiac dysfunction is a serious complication of cirrhosis which is usually asymptomatic. We investigated the clinical and electrocardiographic (ECG)‐related factors among patients with cirrhosis and our aim was to find any associations between ECG changes and the etiology of cirrhosis, as well as Child‐Pugh score.HypothesisWe hypothesized that some ECG‐related factors, particularly prolonged QT interval, are more common in patients with cirrhosis. Also, these factors are associated with the severity of cirrhosis, measured by the Child‐Pugh score.MethodsFrom April 2019 to December 2022, we reviewed admitted patients to Namazi and Abu‐Ali Sina hospitals, Shiraz, Iran. Patients with confirmed diagnosis of cirrhosis and without concurrent disorders affecting the cardiovascular system were selected. Clinical and ECG‐related data were then extracted for participants, and Child‐Pugh score was calculated.ResultsA total of 425 patients were included; the median age was 36 years, and 245 patients (57.6%) were men. Cryptogenic and primary sclerosing cholangitis were the most common etiologies. Prolonged QT followed by early transitional zone were the most common ECG changes (24.7% and 19.8%, respectively), which were significantly associated with the etiology of cirrhosis and Child‐Pugh class.ConclusionsProlonged QT interval and presence of early transitional zone in patients with cirrhosis may indicate cardiac dysfunction, necessitating further evaluations.
In modern microwave telecommunication systems, especially in low phase noise oscillators, there is a need for resonators with low insertion losses and high Q-factor. More specifically, it is of high interest to design resonators with high group delay. In this paper, three novel dual-band complementary split-ring resonators (CSRRs) featuring high group delay etched on the waveguide surface by using substrate integrated waveguides are investigated and proposed. They are designed for a frequency range of 4.5–5.5 GHz. Group delay rates for the first, second, and third resonators were approximated as much as 23 ns, 293 ns, and 90 ns, respectively. We also proposed a new practical method to develop a wide tuning range SIW CSRR cavity resonator with a small tuning voltage in the second resonator, which leads to about 19% and 1% of tuning frequency band in the first and second bands, respectively. Finally, some of their applications in the design of filter, diplexer, and low phase noise oscillator will be investigated.
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