Suchergebnisse

As the threats from unmanned aerial vehicles (UAVs) increases gradually, to recognize and classify unknown UAVs have became more and more important in both civil and military security fields. Classification of signal modulation types is one of the basic techniques for specific UAV recognition. In this paper, to represent the hidden features involved in the transmitted signals from UAVs, we propose a two-dimensional squeezing transform (TDST) to characterize the UAV communication signals in a compressed time-frequency plane. The new time-frequency representation, TDST, retains the instantaneous characteristics of the UAV signal, and is with excellent data reduction and noise suppression capabilities. The TDST plane of different modulation types are then considered as input features, and we propose a convolutional neural network (CNN) based on deep-learning to recognize the UAV signals. We design an interception system and consider 10 types of UAV signals with random initial phase, bandwidth and frequency offset. Experimental results demonstrate the effectiveness and superiority of the proposed algorithm.

The file associated with this record is under embargo until 12 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above. ; As we know that more effective synthesis of diamond combined with physical and chemical properties of hydrogen termination in aqueous environment as well as device structure design can greatly facilitate the chemical and electrochemical applications of higher cost-performance diamond. For this purpose, the direct-current (DC) characteristics, surface reaction and reparation of a hydrogen-terminated DC arc jet plasma CVD polycrystalline diamond, which has a high cost-performance, were characterized by I-V experiments based on a FET-like structure device in multiple aqueous solutions. The variation trends of the I-V properties of device based on pH were similar in different aqueous solutions but could be affected by disparate ions (such as K + ions) or organic molecules (such as citric acid radicals or a benzene ring). Especially, owing to the founded replacement of hydrogen termination with hydroxyl (–OH), carboxyl radical (–COOH) or carbon-oxygen bond (–C–O–C–) in mixed solution, i.e., KHP + H 2 SO 4 (and +NaOH) solutions, the resistance of the device was remarkably increased from 13.57 kΩ to 95.78 kΩ. However, the raised resistance of surface reacted diamond (SRD) can be reduced prominently by repairing hydrogen termination through negative potential sweeps (NPS) at a low negative potential (−1 to −3 V) if the SRD was introduced as an electrode in a strong inorganic acid. What's more, the NPS repaired device, which subsequently stored for four weeks, was more sensitive than the original hydrogen plasma-treated diamond in aqueous solution environments. This repaired result was coming out of NPS re-formed C–H bonds with higher intensity. These findings will be the references of failure and reparation of diamond hydrogen termination in aqueous environment. ; This work was supported by the National Key Research and Development Program of China (No.2016YFE0133200 and 2018YFB0406500) and European Union's Horizon 2020 Research and Innovation Staff Exchange Scheme (No. 734578) and Nano-X experimental cooperation project (H008-2017). Special thanks to the national high-level university-sponsored graduate program of China Scholarship Council (CSC). ; Peer-reviewed ; Post-print

The file associated with this record is under embargo until 12 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above. ; The ultra-smooth surface and hydrophobic nitrogen-incorporated ultra-nano-crystalline diamond (N-UNCD) was directly synthesized by equilibrating the etching effect of OH radical and growth promotion of CN and CH in the 5% CH4 added H2 plasma environment with additional feeding of constant 0.16% O2 and from 0.3% to 3.3% N2 contents. The initially decreasing and then increasing trend of surface roughness, i.e., from as-grown appearance with pits to smooth and then to worm-like surface, was resulted from the offset and even suppressive effect on OH etched holes by the faster growth rate that under the help of more N2 promoted chemical groups of CH and CN. In addition, chemical composition, i.e., the large amount of sp2 phases (sp2/sp3 ratio up to 1.399) and H termination of N-UNCD surface (proportion was 75.54 ± 3.8%), played an another enhancing function for repelling water (contact angle from 81.3° to 93.8°) although the surface roughness decreased to smoothest of 1.36 nm in Root-Mean-Square (RMS) in the presence of N2 addition from 0.3% to 1%. However, continuing adding N2 to 3.3%, the formed surface (RMS 8.98 nm) with worm-like ultra-nano diamond crystallites together with higher H reconstructed sp2 contents (sp2/sp3 ratio rose to 1.478) further boosted the hydrophobicity, at which the contact angle was finally increased to 110.2°. Therefore, in C-H-O-N gas system, ultra-smooth and uniform N-UNCD surface with excellent hydrophobicity can be obtained by a one-step method without any post-treatment. ; This work was supported by the National Key Research and Development Program of China (No. 2016YFE0133200, 2018YFB0406500) and European Union's Horizon 2020 Research and Innovation Staff Exchange Scheme (No. 734578) and Nano-X experimental cooperation project (H008-2017). Special thanks to the national high-level university-sponsored graduate program of China Scholarship Council (CSC). ; Peer-reviewed ; Post-print

United Nations Secretary General Ban Ki-moon has invited world leaders to come to the Climate Summit on September 23, 2014 to deliver "bold pledges" to tackle climate change. This paper was prepared at the request of the Republic of Nauru, Chair of the Alliance of Small Island States, as part of their answer to that call.1 We believe the path to the global low-carbon transformation needed to tackle the climate crisis is within reach, but requires decisive political action from leaders around the world, now. This paper is unabashedly prescriptive on the need for action, but recognizes that there are multiple approaches and models from around the world that can be scaled up and adapted to national circumstances. Cost-effective technologies for a low-carbon economy are being implemented throughout the world, but at nowhere the scale and speed necessary. Emissions continue to rise. With every year of delay, human suffering, biodiversity loss, and the costs of mitigation and adaptation increase. We are running out of time.