To improve the effectiveness of limited spectral resources, an adaptive orthogonal frequency division multiplexing integrated radar and communications waveform design method is proposed. First, the ...conditional mutual information (MI) between the random target impulse response and the received signal, and the data information rate (DIR) of frequency selective fading channel are formulated. Then, with the constraint on the total power, the optimization problem, which simultaneously considers the conditional MI for radar and DIR for communications, is devised, and the analytic solution is derived. With low transmit power, the designed integrated waveform outperforms the fixed waveform (i.e., equal power allocation). Finally, several simulated experiments are provided to verify the effectiveness of the designed waveform.
Abstract
The development of mechanochemistry substantially expands the traditional synthetic realm at the molecular level. Here, we extend the concept of mechanochemistry from atomic/molecular solids ...to the nanoparticle solids, and show how the macroscopic grinding is being capable of generating chirality in self-assembled nanorod (NR) assemblies. Specifically, the weak van der Waals interaction is dominated in self-assembled NR assemblies when their surface is coated with aliphatic chains, which can be overwhelmed by a press-and-rotate mechanic force macroscopically. The chiral sign of the NR assemblies can be well-controlled by the rotating directions, where the clockwise and counter-clockwise rotation leads to the positive and negative Cotton effect in circular dichroism and circularly polarized luminescence spectra, respectively. Importantly, we show that the present approach can be applied to NRs of diverse inorganic materials, including CdSe, CdSe/CdS, and TiO
2
. Equally important, the as-prepared chiral NR assemblies could be served as porous yet robust chiral substrates, which enable to host other molecular materials and induce the chirality transfer from substrate to the molecular system.
As an important tropospheric trace gas and precursor of photochemical smog, the accumulation of NO2 will cause serious air pollution. China, as the largest developing country in the world, has ...experienced a large amount of NO2 emissions in recent decades due to the rapid economic growth. Compared with the traditional air pollution monitoring technology, the rapid development of the remote sensing monitoring method of atmospheric satellite has gradually become the critical technical means of global atmospheric environmental monitoring. To reveal the NO2 pollution situation in China, based on the latest NO2 products from Sentinel-5P TROPOMI, the spatial–temporal characteristics and impact factors of troposphere NO2 column concentration of mainland China in the past year (February 2018 to January 2019) were analyzed on two administrative levels for the first time. Results show that the monthly fluctuation of tropospheric NO2 column concentration has obvious characteristics of “high in winter and low in summer”, while the spatial distribution forms a “high in East and low in west” pattern, bounded by Hu Line. The comparison of Coefficient of Variation (CV) and spatial autocorrelation models at two kinds of administrative scales indicates that although the spatial heterogeneity of NO2 column concentration is less affected by the observed scale, there is a “delayed effect” of about one month in the process of NO2 column concentration fluctuation. Besides, the impact factors analysis based on Spatial Lag Model (SLM) and Geographic Weighted Regression (GWR) reveals that there is a positive correlation between nighttime light intensity, the secondary and tertiary industries proportion and NO2 column concentration. Furthermore, for regions with serious NO2 pollution in North China Plain, the whole society electricity consumption and vehicle ownership also play a positive role in increasing the NO2 column concentration. This study will enlighten the government and policy makers to formulate policies tailored to local conditions, to more effectively implement NO2 emission reduction and air pollution prevention.
While silver nanoparticles are widely used to endow materials with antibacterial activity, silver nanowires (AgNWs) have not attracted much attention. Herein, the composites of bacterial cellulose ...(BC) and AgNWs were prepared through a novel step-by-step in situ biosynthesis which retains the three-dimensional network of BC. The results of water vapor permeability, water uptake rate, and water retention rate showed that the BC/AgNW wound dressings could absorb wound skin exudates and maintain moisture environments. Furthermore, the BC/AgNW dressings were robust and stretchable. More importantly, the BC/AgNW dressings exhibited sustained release of Ag+. The results from animal tests indicated that the BC/AgNW dressing with 38.4 wt% AgNWs exhibited higher expression levels of cytokeratin-10 and integrin-β4, greater proliferation of keratinocytes and formation of epithelial tissues and greatly improved skin regeneration over the bare BC. We propose that the integrated nanofibrous structure and the excellent and sustained antibacterial activity of AgNWs are responsible for the excellent in vivo wound healing ability and biocompatibility. These results suggest that the BC/AgNW composites have promising application as wound dressings.
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•Silver nanowires (AgNWs) and bacterial cellulose (BC) were integrated to obtain an advanced wound dressing.•The BC/AgNW dressing exhibited sustained release of silver ions.•The BC/AgNW dressing is robust, stretchable, antibacterial, and biocompatible.•The BC/AgNW dressing showed improved in vivo skin regeneration over bare BC.
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•A novel layer-by-layer in situ culture (LBLC) method was developed.•Bacterial cellulose/graphene/polyaniline nanocomposites were made by LBLC and polymerization.•The as-prepared ...nanocomposites are mechanically strong and highly flexible.•The as-prepared nanocomposites show excellent gravimetric capacitance and cycling stability.
Rational structure, mechanical robustness, high conductivity, and favorable flexibility are important requirements for superior electrodes, which should not only possess high capacitance but also have freestanding structure without collector to improve the overall performance of supercapacitors. Herein, we demonstrate the fabrication of three-dimensional (3D) porous graphene-containing nanocomposites with highly dispersed graphene (GE) nanosheets in a 3D matrix of bacterial cellulose (BC) by a novel layer-by-layer in situ culture (LBLC) method. The BC/GE nanocomposites are then deposited with polyaniline (PANI), leading to the formation of BC/GE/PANI nanocomposites. Mechanical tests demonstrate excellent robustness and flexibility of the as-prepared BC/GE/PANI nanocomposites, which are used as electrodes directly without any nickel foam or stainless steel wire. The BC/GE/PANI electrode with an optimal GE content has a specific capacitance of 645 F g−1 at a current density of 1 A g−1, which is 2.5 times higher than that of BC/PANI and superior to most previously reported PANI-based electrodes. In addition, the symmetric supercapacitor assembled with BC/GE/PANI demonstrates a high energy density of 14.2 Wh kg−1 at a power density of 200 W kg−1. The excellent electrochemical performance of this BC/GE/PANI electrode is due to its unique 3D porous structure with the uniform distribution of GE nanosheets in the BC matrix and even PANI on BC nanofibers and GE nanosheets, which makes it very promising for diverse flexible energy storage devices. The methodology presented in this work can be extended to the preparation of other BC-based nanocomposite electrodes.
In the airborne or spaceborne radar applications, prolonging the coherent integration time is one of the effective methods to improve the radar detection ability of a weak maneuvering target, whereas ...the coherent integration performance may degrade due to the complex range migration (RM) and Doppler frequency migration (DFM) effects. In this paper, detection and motion parameter estimation for a weak maneuvering target with the third-order RM and DFM are considered. Firstly, Keystone transform is applied to compensate the linear range walk. Then, the matched filtering processing is performed in the range-frequency and azimuth-time domain to eliminate the residual coupling effects between range and azimuth. Finally, a well-focused image of a moving target is obtained, and three motion parameters, i.e., velocity, acceleration, and acceleration rate, are effectively estimated. In addition, as for a fast-moving target with Doppler ambiguity, two cases, i.e., target azimuth spectrum within a pulse repetition frequency (PRF) and spanning over neighboring PRF bands, are analyzed. Compared with the generalized Radon Fourier transform (GRFT), the proposed method can acquire a close integration performance but with lower computational complexity since the parameter searching dimension is reduced. Simulated processing results are provided to validate the effectiveness of the proposed method.
Building energy systems, i.e. heating, ventilation, and air-conditioning (HVAC) systems, are essential for modern buildings. They provide a comfortable and healthy indoor environment. Design quality ...has significant impact on HVAC system efficiency. The typical building energy system design process involving several procedures is repetitive and time-consuming. It is often limited by the engineer's experience, capabilities, and time constraints; thus, the design in most cases barely satisfies building codes. In recent decades, computational intelligence (CI) has achieved substantial improvements in various fields. This paper presents a comprehensive review of using CI for HVAC system optimization design. Firstly, this paper analyzes seven procedures which constitute a typical HAVC system design process and finds that optimization problems encountered during design process can be divided into three categories: model estimation, decision making and uncertainty analysis. Then a brief introduction of CI techniques used to solve HVAC design optimization problems and detailed literature review of application examples are given. Though the design problem varies with each other, this paper outlines a typical workflow which is able to solve most HVAC optimization design problems. At last, a framework of an integrated HVAC automation and optimization design tool is proposed. The framework is developed based on building information modeling (BIM) and extracted typical design optimization workflow. It is able to connect various design stages by implementing structured information transfer between them and ultimately improve design efficiency and quality.
•Three types of optimization problems are defined and corresponding solving methods are presented.•Detailed literature review of CI application in each procedure of HVAC design process is presented.•A typical workflow to solve HVAC design optimization problems is extracted.•Framework of an integrated HVAC automation and optimization design tool based on BIM and typical design optimization workflow is proposed.
A novel facile and scalable strategy is developed to prepare freestanding carbon nanofiber/graphene nanosheet composites using a scalable membrane–liquid interface culture method followed by ...carbonization. The carbon nanofibers (CNFs) and graphene nanosheets (GNs) are uniformly dispersed in a three‐dimensional (3D) conductive architecture. Robust mechanical properties are demonstrated with fine flexibility, good structure stability, and high specific surface area. As supercapacitor electrodes, the 3D nanocomposite delivers good electrochemical performance with a high capacitance of 215 F g−1 at 1 A g−1 and extraordinary cycling stability with no capacitance degradation after 5000 cycles, which are among the best carbon electrodes in supercapacitors. The energy density is as high as 20 Wh kg−1 at a power density of 900 W kg−1, superior to other CNF‐based electrode materials. The superb electrochemical performance of the 3D nanocomposite electrode is ascribed to the unique structure: 3D conductive network, uniform dispersion of carbon nanofibers and graphene nanosheets, robust mechanical property, and large specific surface area. The combination of facile fabrication method, good performance, and robust mechanical property makes the 3D nanocomposites very promising as a new type of superior supercapacitor electrodes.
Large‐area freestanding carbon nanofiber/graphene nanosheet composite electrodes are prepared using a facile and scalable membrane–liquid interface biological culture method and demonstrate a high reversible capacity and extraordinary cycling stability with no capacitance degradation after 5000 cycles. The energy density is as high as 20 Wh kg−1 at a power density of 900 W kg−1.
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