N-Heterocyclic phosphenium triflates (NHP-OTf) 1 serve as efficient catalysts for the regio- and chemoselective hydroboration of pyridines under ambient condition with good functional group ...tolerance. Mechanistic studies indicate that a boronium salt, (Py)2·BpinOTf 4, is generated concomitant with NHP-H 5 via hydride abstraction from HBpin by 1 in the initial reaction step. Hydride reduction of the activated pyridine in (Py)2·BpinOTf 4 by NHP-H 5 affords the 1,4-hydroboration product selectively. Thus, the phosphenium species act as a hydrogen transfer reagent in the catalytic cycle.
Air-stable Rh complexes ligated by strongly σ-donating cyclic (amino)(alkyl)carbenes (CAACs) show unique catalytic activity for the selective hydrogenation of aromatic ketones and phenols by ...reducing the aryl groups. The use of CAAC ligands is essential for achieving high selectivity and conversion. This method is characterized by its good compatibility with unsaturated ketones, esters, carboxylic acids, amides, and amino acids and is scalable without detriment to its efficiency.
An efficient aminocyanation by the direct addition of aryl cyanamides to arynes is described, enabling incorporation of highly useful amino and cyano groups synchronously via cleavage of inert N–CN ...bonds, affording synthetically useful 1,2-bifunctional aminobenzonitriles. The postsynthetic functionalization of the aminocyanation products allows diverse formation of synthetically important derivatives such as drug molecule Ponstan and fused heterocycles.
The dynamic uncertain environment and complex tasks determine that the unmanned aerial vehicle (UAV) system is bound to develop towards clustering, autonomy，and intelligence. In this paper, we ...present a comprehensive survey of UAV swarm intelligence from the hierarchical framework perspective. Firstly, we review the basics and advances of UAV swarm intelligent technology. Then we look inside to investigate the research work by classifying UAV swarm intelligence research into five layers, i.e., decision-making layer, path planning layer, control layer, communication layer, and application layer. Furthermore, the relationship between each level is explicitly illustrated, and the research trends of each layer are given. Finally, limitations and possible technology trends of swarm intelligence are also covered to enable further research interests. Through this in-depth literature review, we intend to provide novel insights into the latest technologies in UAV swarm intelligence.
Communication networks, whether they are wired or wireless, have traditionally been assumed to be connected at least most of the time. However, emerging applications such as emergency response, ...special operations, smart environments, VANETs, etc. coupled with node heterogeneity and volatile links (e.g. due to wireless propagation phenomena and node mobility) will likely change the typical conditions under which networks operate. In fact, in such scenarios, networks may be mostly disconnected, i.e., most of the time, end-to-end paths connecting every node pair do not exist. To cope with frequent, long-lived disconnections,
opportunistic routing
techniques have been proposed in which, at every hop, a node decides whether it should forward or store-and-carry a message. Despite a growing number of such proposals, there still exists little consensus on the most suitable routing algorithm(s) in this context. One of the reasons is the large diversity of emerging wireless applications and networks exhibiting such “episodic” connectivity. These networks often have very different characteristics and requirements, making it very difficult, if not impossible, to design a routing solution that fits all. In this paper, we first break up existing routing strategies into a small number of common and tunable
routing modules
(e.g. message replication, coding, etc.), and then show how and when a given
routing module
should be used, depending on the set of
network characteristics
exhibited by the wireless application. We further attempt to create a taxonomy for intermittently connected networks. We try to identify generic
network characteristics
that are relevant to the routing process (e.g., network density, node heterogeneity, mobility patterns) and dissect different “challenged” wireless networks or applications based on these characteristics. Our goal is to identify a set of useful
design guidelines
that will enable one to choose an appropriate routing protocol for the application or network in hand. Finally, to demonstrate the utility of our approach, we take up some case studies of challenged wireless networks, and validate some of our routing design principles using simulations.
The Internet of Things (IoT) is empowering various sectors and aspects of daily life. Green IoT systems typically involve Low-Power and Lossy Networks (LLNs) with resource-constrained nodes. ...Lightweight routing protocols, such as the Routing Protocol for Low-Power and Lossy Networks (RPL), are increasingly being applied for efficient communication in LLNs. However, RPL is susceptible to various attacks, such as the black hole attack, which compromises network security. The existing black hole attack detection methods in Green IoT rely on static thresholds and unreliable metrics to compute trust scores. This results in increasing false positive rates, especially in resource-constrained IoT environments. To overcome these limitations, we propose a delta-threshold-based trust model called the Optimized Reporting Module (ORM) to mitigate black hole attacks in Green IoT systems. The proposed scheme comprises both direct trust and indirect trust and utilizes a forgetting curve. Direct trust is derived from performance metrics, including honesty, dishonesty, energy, and unselfishness. Indirect trust requires the use of similarity. The forgetting curve provides a mechanism to consider the most significant and recent feedback from direct and indirect trust. To assess the efficacy of the proposed scheme, we compare it with the well-known trust-based attack detection scheme. Simulation results demonstrate that the proposed scheme has a higher detection rate and low false positive alarms compared to the existing scheme, confirming the applicability of the proposed scheme in green IoT systems.
We developed a photoacoustic imaging system that has real-time imaging capability with optical resolution. The imaging system is capable of scanning at 20 Hz over a 9 mm range and up to 40 Hz over a ...1 mm scanning range. A focused laser beam provides a lateral resolution of 3.4 μm as measured in an optically nonscattering medium. Flows of micrometer-sized carbon particles or whole blood in a silicone tube and individual red blood cells (RBCs) in mouse ear capillaries were also imaged in real time, demonstrating the capability to image highly dynamic processes in vivo at a micrometer-scale resolution.
The rise of biomimetic unmanned aerial vehicle (UAV) cluster has brought new challenges for radar target tracking and identification. Different cluster flight modes will have different impacts on ...radar data processing and cluster target identification. For analyzing the influence mechanism of the cluster on radar tracking and identification, this paper models the flight process of UAV cluster based on three kinds of species: geese, wolves and bees, which respectively simulated the large-scale transport, close-in rounding attack and robust information communication of UAV cluster. Secondly, it discusses the influence mechanism of different cluster modes on several algorithms of tracking: track initiation, data association and tracking filter. Finally, combined with the characteristics of three biological movements, it designs the identification methods of cluster event pattern based on clustering in detail, and gives the judgment rules. The simulation results show that there is the suitable combination of rada
An elliptical Hough transform (EHT) algorithm is proposed in the framework of track-before-detect (TBD) for joint detection and tracking of weak exoatmospheric targets. The new approach exploits the ...fact that when restricted to a two-body problem, the exoatmospheric target often follows an elliptical orbit, and thus the Hough transform integrated with orbital geometry information would have better detection performance. The relationship between the original radar measurements in data space and the elliptical parameters in parameter space is explicitly derived with multiple steps of coordinate transformation. It is found that the data points mapping into the parameter space essentially represent a quartic curve. An EHT-based algorithm is then designed, and orbit planarity is also taken into account to reduce the effect of noise accumulation. The influences of primary and secondary thresholds and the signal-to-noise ratio (SNR) on the detection performance are compared by simulations. Additionally, a real radar tracking dataset from a scientific satellite on 28 May 2017 is used to investigate the efficiency of the method. By adding some imaginary clutter to the raw orbit, the results indicate that it is very effective in detecting the real satellite trajectory in a low signal-to-noise ratio (SNR) environment. The advantage of the new method lies in it can not only simultaneously detect and track weak exoatmospheric targets but also can predict the trajectory by using these available detected parameters.
Content-Centric Networking (CCN) is a novel architecture that is shifting host-centric communication to a content-centric infrastructure. In recent years, in-network caching in CCNs has received ...significant attention from research community. To improve the cache hit ratio, most of the existing schemes store the content at maximum number of routers along the downloading path of content from source. While this helps in increased cache hits and reduction in delay and server load, the unnecessary caching significantly increases the network cost, bandwidth utilization, and storage consumption. To address the limitations in existing schemes, we propose an optimization based in-network caching policy, named as opt-Cache, which makes more efficient use of available cache resources, in order to reduce overall network utilization with reduced latency. Unlike existing schemes that mostly focus on a single factor to improve the cache performance, we intend to optimize the caching process by simultaneously considering various factors, e.g., content popularity, bandwidth, and latency, under a given set of constraints, e.g., available cache space, content availability, and careful eviction of existing contents in the cache. Our scheme determines optimized set of content to be cached at each node towards the edge based on content popularity and content distance from the content source. The contents that have less frequent requests have their popularity decreased with time. The optimal placement of contents across the CCN routers allows the overall reduction in bandwidth and latency. The proposed scheme is compared with the existing schemes and depicts better performance in terms of bandwidth consumption and latency while using less network resources.
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