Predicting the trajectories of surrounding vehicles is an essential task in autonomous driving, especially in a highway setting, where minor deviations in motion can cause serious road accidents. The ...future trajectory prediction is often not only based on historical trajectories but also on a representation of the interaction between neighbouring vehicles. Current state-of-the-art methods have extensively utilized RNNs, CNNs and GNNs to model this interaction and predict future trajectories, relying on a very popular dataset known as NGSIM, which, however, has been criticized for being noisy and prone to overfitting issues. Moreover, transformers, which gained popularity from their benchmark performance in various NLP tasks, have hardly been explored in this problem, presumably due to the accumulative errors in their autoregressive decoding nature of time-series forecasting. Therefore, we propose MALS-Net, a Multi-Head Attention-based LSTM Sequence-to-Sequence model that makes use of the transformer's mechanism without suffering from accumulative errors by utilizing an attention-based LSTM encoder-decoder architecture. The proposed model was then evaluated in BLVD, a more practical dataset without the overfitting issue of NGSIM. Compared to other relevant approaches, our model exhibits state-of-the-art performance for both short and long-term prediction.
Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low ...photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2–8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn4+ as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.
High‐entropy alloys (HEAs) in which interesting physical, chemical, and structural properties are being continuously revealed have recently attracted extensive attention. Body‐centered cubic (bcc) ...HEAs, particularly those based on refractory elements are promising for high‐temperature application but generally fail by early cracking with limited plasticity at room temperature, which limits their malleability and widespread uses. Here, the “metastability‐engineering” strategy is exploited in brittle bcc HEAs via tailoring the stability of the constituent phases, and transformation‐induced ductility and work‐hardening capability are successfully achieved. This not only sheds new insights on the development of HEAs with excellent combination of strength and ductility, but also has great implications on overcoming the long‐standing strength–ductility tradeoff of metallic materials in general.
The “metastability‐engineering” strategy is exploited in brittle body‐centered cubic high‐entropy alloys (HEAs) via tailoring the thermal and mechanical stability of the constituent phases, and consequently, transformation‐induced ductility and work hardening capability are successfully achieved. This not only has important implications for developing high‐performance HEAs, but also sheds light on overcoming the long‐standing strength–ductility tradeoff of metallic materials in general.
With the increase of population and the fast growth of private vehicle ownership in urban areas, many roads have become more congested than ever before. The road traffic information plays a crucial ...role in traffic management. The currently available traffic information collection systems mainly rely on static road-side units, which passively record the traffic information. This article considers an alternative option, i.e., the usage of unmanned aerial vehicles (UAVs) for aerial surveillance, which is more efficient than the conventional ground-based strategies. We focus on deploying a UAV network to monitor the traffic on a road. We propose a decentralized navigation scheme that enables the UAV network to detect blockage and then gather to the blocked area to have better views of the ground vehicles. This scheme only requires the UAVs to share some light measurement information and positions, and it can be implemented in real time.
In recent years, unmanned aerial vehicles (UAVs) have gained popularity due to their flexibility, mobility, and accessibility in various fields, including search and rescue (SAR) operations. The use ...of UAVs in SAR can greatly enhance the task success rates in reaching inaccessible or dangerous areas, performing challenging operations, and providing real-time monitoring and modeling of the situation. This article aims to help readers understand the latest progress and trends in this field by synthesizing and organizing papers related to UAV search and rescue. An introduction to the various types and components of UAVs and their importance in SAR operations is settled first. Additionally, we present a comprehensive review of sensor integrations in UAVs for SAR operations, highlighting their roles in target perception, localization, and identification. Furthermore, we elaborate on the various applications of UAVs in SAR, including on-site monitoring and modeling, perception and localization of targets, and SAR operations such as task assignment, path planning, and collision avoidance. We compare different approaches and methodologies used in different studies, assess the strengths and weaknesses of various approaches, and provide insights on addressing the research questions relating to specific UAV operations in SAR. Overall, this article presents a comprehensive overview of the significant role of UAVs in SAR operations. It emphasizes the vital contributions of drones in enhancing mission success rates, augmenting situational awareness, and facilitating efficient and effective SAR activities. Additionally, the article discusses potential avenues for enhancing the performance of UAVs in SAR.
We report a facile nonaqueous emulsion synthesis of colloidal halide perovskite quantum dots by controlled addition of a demulsifier into an emulsion of precursors. The size of resulting CH3NH3PbBr3 ...quantum dots can be tuned from 2 to 8 nm by varying the amount of demulsifier. Moreover, this emulsion synthesis also allows the purification of these quantum dots by precipitation from the colloidal solution and obtains solid-state powder which can be redissolved for thin film coating and device fabrication. The photoluminescence quantum yields of the quantum dots is generally in the range of 80–92%, and can be well-preserved after purification (∼80%). Green light-emitting diodes fabricated comprising a spin-cast layer of the colloidal CH3NH3PbBr3 quantum dots exhibited maximum current efficiency of 4.5 cd/A, power efficiency of 3.5 lm/W, and external quantum efficiency of 1.1%. This provides an alternative route toward high efficient solution-processed perovskite-based light-emitting diodes. In addition, the emulsion synthesis is versatile and can be extended for the fabrication of inorganic halide perovskite colloidal CsPbBr3 nanocrystals.
The Internet of Flying Robots (IoFR) has received much attention in recent years thanks to the mobility and flexibility of flying robots. Although a lot of research has been done, there is a lack of ...a comprehensive survey on this topic. This paper analyzes several typical problems in designing IoFR for real applications, including wireless communication support, monitoring targets of interest, serving a wireless sensor network, and collaborating with ground robots. In particular, an overview of the existing publications on the coverage problem, connectivity of flying robots, energy capacity limitation, target searching, path planning, flying robot navigation with collision avoidance, etc., is presented. Beyond the discussion of these available approaches, some shortcomings of them are indicated and some promising future research directions are pointed out.
This study provides an observer-based robust preview tracking controller for Lipschitz non-linear systems. Firstly, the non-linear system dynamics is studied and the non-linear observer is designed. ...By introducing the Lyapunov function, the observer gain matrix is obtained through linear matrix inequalities (LMIs). To obtain an effective tracking control law, an augment error system which consists of difference of estimation error, tracking error, difference of estimated status and reference preview information is constructed. The sufficient solutions for observer-based robust preview controller are analysed using the LMI approach. Two numerical examples are provided to show the flexibility and effectiveness of the proposed robust preview tracking controller.
The paper focuses on surveillance and monitoring using aerial drones. The aim is to estimate the minimal number of drones necessary to monitor a given area of a very uneven terrain. The proposed ...problem may be viewed as a drone version of the 3D Art Gallery Problem. A computationally simple algorithm to calculate an upper estimate of the minimal number of drones together with their locations is developed. Computer simulations are conducted to demonstrate the effectiveness of the proposed method.
We consider the problem of navigating a military aircraft in a threat environment to its final destination while minimizing the maximum threat level and the length of the aircraft path. The proposed ...method to construct optimal low-risk aircraft paths involves a simple geometric procedure and is very computationally efficient. The effectiveness of the developed algorithm is illustrated by a number of examples and comparisons with a fuzzy logic based algorithm.
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