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Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges. © T. Abu Hamed et al., published by EDP Sciences, 2018., European Cooperation in Science and Technology: MP1406, The authors are grateful for the financial support by the COST Action MP1406 “MultiscaleSolar.”

The IEEE 802.11ah Task Group is going to specify a global WLAN standard. However, .ah drafts still employs the carrier sense multiple access with collision avoidance (CSMA/CA) medium access protocol, which is an energy-consuming protocol and not suitable for networks where STAs are generally battery supplied. Besides, since .ah could support up to 6000 stations at most to be scheduled within one BSS, the introduced overhead and corresponding processing delay are non-trivial. In this paper, a power saving scheduling scheme is proposed which could greatly reduce the introduced overhead while successfully scheduling the uplink/downlink traffic of meters. Our model could also save the station’s battery with best efforts thus making our protocol specifically suitable for Smart-Grid networks where battery changing for stations is difficult. Numerical results show that our scheme outperforms the PSM (Power Saving Mechanism) and PSMP (Power Save Multi-Poll) protocols in terms of overheads, throughput and energy consumptions.

By using the Lyapunov second method, the robust control and robust optimal control for the gas tungsten arc welding dynamic process whose underlying continuous-time systems are subjected to structured uncertainties are discussed in time-domain. As results, some sufficient conditions of robust stability and the corresponding robust control laws are derived. All these results are designed by solving a class of linear matrix inequalities (LMIs) and a class of dynamic optimization problem with LMIs constraints respectively. An example adapted under some experimental conditions in the dynamic process of gas tungsten arc welding system in which the controlled variable is the backside width and controlling variable welding speed, is worked out to illustrate the proposed results. It is shown in the paper that the sampling period is the crucial design parameter

In a WLAN, when a great many nodes coexist, the network may readily be congested, thus causing packets dropping and network performance degradation. To solve this issue, a lot of schemes have been proposed. However, most of the previous works attempt to avoid the possible channel congestion by controlling the packets generation rate and/or transmitting power of nodes, while the effects of Clear Channel Assessment (CCA) threshold are not well examined. In our paper, a Joint CCA threshold and contending window control algorithm (JCCA) is proposed to avoid channel congestion or reduce the congestion probability of broadcasting in an IEEE 802.11e network. Both the network conditions and the priorities of messages are taken into account to improve the broadcasting performance in our paper. According to the simulation results, it can be concluded that our scheme can significantly increase the network throughput as well as packets delivery ratio and reduce the packet transmission delay compared to the IEEE 802.11e and Adaptive Carrier Sensing-Based MAC Designs (ACSBM) protocol.

Vehicular Ad Hoc Networks (VANETs) are going to be an important communication infrastructure in our moving life. The design of routing protocols in VANETs is a significant and necessary issue for supporting VANET-based applications. However, due to high mobility, frequent link disconnection, and uneven distribution of vehicles, it becomes quite challenging to establish a robust route for delivering packets. This paper presents a novel routing protocol called artificial spider-web based geographic routing protocol (ASGR) to address these problems by selecting the optimal route according to the information of the paths (e.g. connectivity, delay and number of hops) through the use of artificial spiders. By constructing the spider-web and path tree, ASGR can find a robust route to the destination taking the route connectivity, path delay and total number of hops into consideration. Simulation results show that our ASGR outperforms GyTAR and STAR in terms of packet delivery ratio (PDR) and end-to-end delay (E2ED) with the number of nodes and packets generation interval varying.

A novel type of aqueous fluorescent carbon dot (CD) was synthesized using citric acid as the only carbon source via an ammonium hydroxide modulated method, providing a blue color gamut. The amino group is considered to be the key factor in the high fluorescence of CDs and a model is established to investigate the mechanism of fluorescence. In addition, white light-emitting diodes (WLEDs) are fabricated by utilizing the prepared CDs and rare earth luminescent materials (SrSi2O2N2:Eu and Sr2Si5N8:Eu) as color conversion layers and UV-LED chips as the excitation light source. The WLEDs produce bright white light with attractive color rendering properties including a color rendering index of up to 95.1, a CIE coordinate of (0.33, 0.37), and a T c of 5447 K under a 100 mA driven current, indicating that the CDs are promising in the field of optoelectronic devices.

An adaptive method of helicopter track and balance is introduced to improve the search for the required blade adjustments. In this method, an interval model is used to represent the range of effect of blade adjustments on helicopter vibration, instead of exact values, to cope with the nonlinear and stochastic nature of aircraft vibration. The coefficients of the model are initially defined according to sensitivity coefficients between the blade adjustments and helicopter vibration, to include the ‘a priori’ knowledge of the process. The model coefficients are subsequently transformed into intervals and updated after each tuning iteration to improve the model’s estimation accuracy. The search for the required blade adjustments is performed according to this model by considering the vibration estimates of all of the flight regimes to provide a comprehensive solution for track and balance. The effectiveness of the proposed method is evaluated in simulation using a series of neural networks trained with actual vibration data. The results indicate that the proposed method improves performance according to several criteria representing various aspects of track and balance.

Improvement factor of bistatic radar suffers from the time and frequency synchronization, this is analyzed firstly in this paper. And then we design a field system which can fulfill the improvement factor measurement for bistatic radar.

A two-wheeled self-balancing robot with a fuzzy PD control method is described and analyzed as an example of a high-order, multiple-variable, nonlinear, strong-coupling, and unstable system. Based on a system structure model, a kinetic equation is constructed using Newtonian dynamics and mechanics. After a number of simulation experiments, we get the best Q, R, and state-feedback matrices. Then a fuzzy PD controller is designed for which the position and speed of the robot are inputs and for which the angle and angle rate of the robot are controlled by a PD controller. Finally, this paper describes a real-time control platform for the two-wheeled self-balancing robot that controls the robot effectively, after some parameter debugging. The result indicates that the fuzzy PD control algorithm can successfully achieve self-balanced control of the two-wheeled robot and prevent the robot from falling.

An angular resolving method of two closely spaced jammers for passive monopulse seeker is presented in this paper. In the case of two narrowband noise frequency modulation (FM) jammers within main beam, an analysis of average angle of arrival (AOA) shows that the average AOA does not point to the centroid, but the stronger jammer. So the stronger jammer can be resolved in angle by using average angle of arrival-the big signal method. In the case of multipath, the real jammer can also be resolved by using the big signal method. The method is verified with the results of computer simulation.

In this paper, a rear-end collision control model is proposed using the fuzzy logic control scheme for the autonomous or cruising vehicles in Intelligent Transportation Systems (ITSs). Through detailed analysis of the car-following cases, our controller is established on some reasonable control rules. In addition, to refine the initialized fuzzy rules considering characteristics of the rear-end collisions, the genetic algorithm is introduced to reduce the computational complexity while maintaining accuracy. Numerical results indicate that our Genetic algorithm-optimized Fuzzy Logic Controller (GFLC) outperforms the traditional fuzzy logic controller in terms of better safety guarantee and higher traffic efficiency.

A method of helicopter track and balance is introduced that uses a forward-model to search for the appropriate blade modifications. This method uses an interval model to represent the ranges of effects of blade modifications on helicopter vibration, instead of exact values, in order to cope with the stochastic nature of aircraft vibration. The coefficients of the interval model are initially defined according to sensitivity coefficients between the blade modifications and helicopter vibration, but they are subsequently updated after each tuning iteration to improve the model’s estimation accuracy. The effectiveness of the proposed method is demonstrated through a simulation model that represents experimental vibration measurements of Black Hawk helicopters.Copyright © 2002 by ASME