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Pd-based alloy coating on optical fiber is widely employed for hydrogen concentration sensing. However, it is difficult to distinguish the Pd-based alloy expansion from hydrogen adsorption or thermal effect. In this article, a novel fiber-optic hydrogen sensor based on $\pi $ -shifted fiber Bragg grating (FBG) with locally coated Pd/Ta alloy layer, which enables an in situ temperature compensation, is proposed and experimentally demonstrated. The hydrogen sensitivity difference between the extremely narrow peak of $\pi $ -shifted FBG and the sidelobe wavelength is employed to realize the hydrogen concentration detection with temperature compensation. Theoretical simulation and experiment show that the hydrogen sensitivity of the structure can be enhanced by optimizing the partially coating length. When the alloy length is 2 mm for a 10-mm grating, the wavelength shifts of central and sidelobe 19.2 pm and 6.0 pm are achieved, respectively, at 1% hydrogen concentration. Maximum hydrogen sensitivity after temperature compensation of 13.2 pm is obtained. The proposed local-compensated method based on partially coating on $\pi $ -shifted FBG is particularly potential for oxygen-free environments with high requirement on hydrogen accuracy. [ABSTRACT FROM AUTHOR]

With the rapid development of urbanization, the problem of urban traffic congestion has become increasingly prominent. Dynamic route guidance promises to improve the capacity of urban traffic management and mitigate traffic congestion in big cities. In the design of simulation-based experiments for most dynamic route guidance methods, the simulation data is generally estimated from a specific traffic scenario in the real-world. However, highly dynamic traffic in the city implies that traffic scenarios in real systems are diverse. Therefore, if a route guidance method cannot adjust its strategy according to the spatial and temporal characteristics of different traffic scenarios, then it cannot guarantee optimal results under all traffic scenarios. Thus, ideal dynamic route guidance methods should have a highly adaptive learning ability under diverse traffic scenarios so as to have extensive improvement capabilities for different traffic scenarios. In this study, an A* trajectory rejection method based on multi-agent reinforcement learning (A*R2) is proposed; the method integrates both system and user perspectives to mitigate traffic congestion and reduce travel time (TT) and travel distance (TD). First, owing to its adaptive learning ability, the A*R2 can comprehensively analyze the traffic conditions for different traffic scenarios and intelligently evaluate the road congestion index from a system perspective. Then, the A*R2 determines the routes for all vehicles from user perspective according to the road network congestion index. An extensive set of simulation experiments reveal that, under various traffic scenarios, the A*R2 can rely on its adaptive learning ability to achieve better traffic efficiency. Moreover, even in cases where many drivers are not fully compliant with the route guidance, the traffic efficiency can still be improved significantly by A*R2. [ABSTRACT FROM AUTHOR]

We propose and demonstrate Mach-Zehnder interferometer (MZI), which is the refractive index (RI) insensitive and temperature highly sensitive based on etched multi-core fiber (MCF) structure. The MCF and Fiber Bragg Grating (FBG) are used as hybrid sensing elements. The fabrication of the interferometer is provided a new taper-like structure by etching the MCF to further expose the side cores to the surroundings. The interferometer has produced a sensitivity of 103.2pm/°C within the ambient temperature up-to 70°C. Moreover, the superior temperature sensitivity is 89.19pm/°C, 66.64pm/°C, 56.42pm/°C in the range of 24°C to 130°C, and RI-insensitive in the range of 1.34 to 1.38, for different waists of etched seven-core fiber interferometers (E7CFIs) $\sim ~84.70\mu \text{m}$ , $93.10\mu \text{m}$ , $108.67\mu \text{m}$ , respectively. Compared with the conventional FBGs, the sensitivity of the interferometer is significantly improved by 8 times. E7CFI’s novel and advantageous features can easily be distinguished other devices. Besides, the proposed sensing architecture is compact, easy to fabricate, highly sensitive, easy to reproduce, and makes it an inexpensive fiber optic device. [ABSTRACT FROM AUTHOR]

NDN has been widely regarded as a promising representation and implementation of information- centric networking (ICN) and serves as a potential candidate for the future Internet architecture. However, the security of NDN is threatened by a significant safety hazard known as an IFA, which is an evolution of DoS and distributed DoS attacks on IP-based networks. The IFA attackers can create numerous malicious interest packets into a named data network to quickly exhaust the bandwidth of communication channels and cache capacity of NDN routers, thereby seriously affecting the routers' ability to receive and forward packets for normal users. Accurate detection of the IFAs is the most critical issue in the design of a countermeasure. To the best of our knowledge, the existing IFA countermeasures still have limitations in terms of detection accuracy, especially for rapidly volatile attacks. This article proposes a TC to detect the distributions of normal and malicious interest packets in the NDN routers to further identify the IFA. The trace back method is used to prevent further attempts. The simulation results show the efficiency of the TC for mitigating the IFAs and its advantages over other typical IFA countermeasures. [ABSTRACT FROM AUTHOR]

Wireless on-demand data broadcasting (ODDB) has become the preferred method of disseminating data to a large number of mobile users. The rapid boom in client requests has resulted in an urgent demand for improved ODDB system capacity (number of service users), especially in client-intensive and request-frequent environments. There are two bottlenecks in ODDB systems: the base station access capacity and the server concurrency capability. However, existing algorithms do not consider these bottlenecks, leading to deficient performance in ODDB system capacity and broadcast efficiency. In this paper, a three-layer ODDB system architecture and a request pre-processing method (RPPM) are proposed. The innovations of this study are twofold: (1) The three-layer ODDB system architecture enhances the base station access capacity by introducing a virtual node layer to share the high load of the base station. (2) Based on the proposed architecture, the RPPM handles request merger and priority evaluation to reduce server concurrency and improve broadcast efficiency. The results of experiments and analyses reveal that the proposed method can significantly enhance the ODDB system capacity and obtain outstanding broadcast efficiency. [ABSTRACT FROM AUTHOR]

An improved glucose-sensitive membrane (GSM) was prepared by immobilizing glucose oxidases (GODs) onto silica mesocellular foams and trapping them in a polyacrylamide gel. This gel was then coated on a gold/glass sheet to realize surface plasmon resonance (SPR) sensors. A series of sensing experiments was conducted to obtain the optimized parameters with the improved GSM. The experimental results showed that the improved SPR glucose sensor has a sensitivity of 0.0135 degree/(mg/dL) and a linear range of 0–160 mg/dL. This linear range is twice that obtained with the GSM by immobilizing GODs on SiO2 nanoparticles. [ABSTRACT FROM PUBLISHER]

The detection of early corrosion is a key issue to mitigate the damage induced by metal corrosion. This paper presents a corrosion sensor for steel based on an iron film-coated optical fiber polarizer. The polarizer is fabricated by sputtering a Fe-C film on a side-polished single mode fiber. The new fabricated polarizer shows highly birefringence, indicated by the difference of the transmission between the TE and TM modes, as well as the extinction ratio (ER). A series of simulations has been performed based on two models. The influences of the parameters of the sensor fabrication, the surrounding media, and film composition on the ER ratio and leakage are studied by the simulations. The accelerated corrosion experiments by immersing the polarizer into NaCl solution show that the polarizers become weakly birefringent after exposure. The results show that the ER and measured optical power decrease gradually during the corrosion process. The proposed polarizer can be used for monitoring the early stage of steel corrosion by building the relationship between the corrosion status and the polarization characteristics. [ABSTRACT FROM PUBLISHER]

Recently, social networks have witnessed a massive surge in popularity. A key issue in social network research is network evolution analysis, which assumes that all the autonomous nodes in a social network follow uniform evolution mechanisms. However, different nodes in a social network should have different evolution mechanisms to generate different edges. This is proposed as the underlying idea to ensure the nodes’ evolution diversity in this paper. Our approach involves identifying the micro-level node evolution that generates different edges by introducing the existing link prediction methods from the perspectives of nodes. We also propose the edge generation coefficient to evaluate the extent to which an edge's generation can be explained by a link prediction method. To quantify the nodes’ evolution diversity, we define the diverse evolution distance. Furthermore, a diverse node adaption algorithm is proposed to indirectly analyze the evolution of the entire network based on the nodes’ evolution diversity. Extensive experiments on disparate real-world networks demonstrate that the introduction of the nodes’ evolution diversity is important and beneficial for analyzing the network evolution. The diverse node adaption algorithm outperforms other state-of-the-art link prediction algorithms in terms of both accuracy and universality. The greater the nodes’ evolution diversity, the more obvious its advantages. [ABSTRACT FROM PUBLISHER]

A variable-on-time (VOT) control scheme for a critical conduction mode (CRM) integrated buck–flyback power factor correction (PFC) converter with high power factor (PF) and low total harmonic distortion (THD) is proposed in this paper. By utilizing the input and output voltage to modulate the on-time of both buck and flyback switches, the input current harmonics can be eliminated and high PF will be obtained. The operating principles of both the conventional constant-on-time (COT) control and VOT control for the CRM buck–flyback PFC converter are analyzed. A 100-W prototype has been built and tested in the lab. The experimental results demonstrate that the THD and PF of the converter with VOT control are greatly improved compared to those with COT control. [ABSTRACT FROM AUTHOR]

A three-phase single-switch discontinuous conduction mode (DCM) boost power factor correction (PFC) converter features zero-current turn on for the switch, no reverse recovery in the diode, a constant-switching-frequency operation, a simple control, and a low cost, which are suitable for low-to-medium-power and cost-sensitive applications. Due to the DCM, the energy transfer does not cover the whole switching cycle, the rms and peak values of the inductor current are large, and those of the switch and the diode are also large. This increases not only the current stress of the power components but also the conduction and switching turn-off losses, which lower the efficiency of the converter. An optimum utilization control of switching cycles is proposed in this paper to increase the critical boost inductance. The rms and peak current values of the main power components are reduced, and the conduction and switching turn-off losses are therefore decreased, leading to higher efficiency. The proposed method also slightly achieves an output voltage ripple reduction, and the input current harmonics comply with the standard of the International Electrotechnical Commission 61000-3-2 Class A. [ABSTRACT FROM AUTHOR]

In order to solve the neutral-point voltage unbalancing problem for three-level inverters, this paper proposes a method to balance the neutral-point voltage for three-level inverters with variable modulation wave offset sinusoidal pulse-width modulation (SPWM) control. Based on the mathematical expressions of neutral-point voltage unbalancing, the factors are studied, which affect the fluctuation of neutral-point voltage. Theoretically the mathematical expressions of the neutral-point voltage with the proposed method are derived, and the mathematical relationship between the fluctuation of neutral-point voltage and the adjusting offset of modulation wave is studied. This proposed method realizes controlling the neutral-point voltage balance by dynamically calculating the offset superimposed to the modulation wave based on SPWM (DCOSPWM). This DCOSPWM method is very simple, which has good steady-state performance and is easy for digital implementation. The simulation results verify the correctness of the theoretical analysis in this paper, and the feasibility and effectiveness of this method is verified by the experiments in the experimental platform of neutral point clamped three-level inverters based on digital signal processor (DSP)-complex programmable logic device (CPLD). [ABSTRACT FROM AUTHOR]

As electrolytic capacitor is apt to fail in power circuits, it is very important to identify its electrical parameters, mainly the equivalent series resistance (ESR) and capacitance (C). A noninvasive online identification method of capacitor's ESR and C for continuous-conduction-mode (CCM) buck converter is proposed in this paper. Based on the ac component of capacitor voltage, the calculation model is founded. By sampling the pulse width modulation signal and output voltage, the method needs no current sensor and is effective for the CCM buck converter operating at different conditions. Implementation of the identification system is presented. The tests are carried out for different aged capacitors and ambient temperatures. The experimental results validate the effectiveness of the method. [ABSTRACT FROM AUTHOR]

The discontinuous current mode boost power factor (PF) correction converter features a zero-current turn-on for the switch, no reverse recovery in diode, and constant frequency operations. However, when the duty cycle is constant in a line cycle, the input current contains rich third harmonic which has a phase difference of π with respect to the fundamental component. The harmonic results in not only a lower PF but also larger peak and RMS current values of the main power components, which lead to a higher conduction and switching turn-off loss. In this paper, a variable duty cycle control scheme is proposed to make the input current contain only third harmonic which is in phase with fundamental component, while remaining the same PF at a certain input voltage as that of constant duty cycle control. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. The efficiency is improved as the critical inductance increases and the peak and RMS current values consequently decrease. The proposed method also achieves an output voltage ripple or the output storage capacitance reduction. The experimental results from a prototype of 120 W are given to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]