综采工作面可靠性分析

应用可靠性理论对综采工作面进行分析,进而找到影响可靠性的因素,提出改善系统可靠性的意见,从而达到提高矿井的产量,增加经济效益的目的。该文从人-机系统可靠性、环境系统可靠性、综采工艺系统可靠性、供电系统可靠性、支架-围岩系统可靠性等方面对综采工作面的可靠性分析做了综述。     

Carbon Nanotube‐Encapsulated Noble Metal Nanoparticle Hybrid as a Cathode Material for Li‐Oxygen Batteries

Although Li‐oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end‐opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT‐encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li₂O₂ nanocrystals on CNT surfaces instead of localized distribution of Li₂O₂ aggregation, thus providing efficient charge transfer for the decomposition of Li₂O₂.     

Multiple layer design for mass data transmission against channel congestion in IoT

Internet of Things (IoT) is well studied from many aspects; however, data transmission in a large‐scale constructed IoT network is still an open topic. In this paper, the problems of channel congestion caused by mass data transmission are discussed respectively from different perspectives. Then, a multiple layer solution is proposed, pointing to each layer including data processing architecture, data dimension reduction, data abandon protocol, and spectrum sharing. In the architecture layer, a combined scheme with cloud computing and sea computing is introduced. Context awareness and granular computing is exploited to implement the data dimension reduction. And cognitive protocol is involved with type of service, which drops certain data to guarantee the entire network connectivity. Then, a principal–agent theory based two‐step game model is proposed with the consideration of cooperation and price coefficient, which affect the secondary user's choice and primary user's profit. Some incomplete information is assumed as random variables so that certainty equivalent is introduced in the model. A simple scenario shows how the data dimension reduction works and how simulations for data abandon protocol and spectrum sharing test the two parts, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

TD—LTE系统Reed—Muller译码的仿真及FPGA实现

主要基于FPGA实现TD—LTE系统中的Reed—Muller译码,包括Reed—Muller译码的介绍、方案的构成、FPGA实现流程、以及实现结果分析。并在Virtex-6芯片上,进行了仿真、综合、板级验证。实现结果表明,该Reed—Muller译码算法应用到TD—LTE射频一致性测试仪表中具有良好的高效性和可靠性。     

食物安全与我国农业资源环境

本文谈及了我国食物资源与环境的总体情况,并对食物生产潜力和供需情况进行了分析,提出了食物资源可持续利用和发展的对策建议.     

Chemotaxis of Beneficial Rhizobacteria to Root Exudates: The First Step towards Root–Microbe Rhizosphere Interactions

Chemotaxis, the ability of motile bacteria to direct their movement in gradients of attractants and repellents, plays an important role during the rhizosphere colonization by rhizobacteria. The rhizosphere is a unique niche for plant–microbe interactions. Root exudates are highly complex mixtures of chemoeffectors composed of hundreds of different compounds. Chemotaxis towards root exudates initiates rhizobacteria recruitment and the establishment of bacteria–root interactions. Over the last years, important progress has been made in the identification of root exudate components that play key roles in the colonization process, as well as in the identification of the cognate chemoreceptors. In the first part of this review, we summarized the roles of representative chemoeffectors that induce chemotaxis in typical rhizobacteria and discussed the structure and function of rhizobacterial chemoreceptors. In the second part we reviewed findings on how rhizobacterial chemotaxis and other root–microbe interactions promote the establishment of beneficial rhizobacteria-plant interactions leading to plant growth promotion and protection of plant health. In the last part we identified the existing gaps in the knowledge and discussed future research efforts that are necessary to close them.     

Research on the performances of VPEG macromonomer grafted different functional groups to prepare polycarboxylate superplasticizers

The advent of novel polyether macromonomer has garnered significant attention within the industrial domain. In this study, a range of polycarboxylate superplasticizers (PCEs) was produced via free radical polymerization, employing a new polyether monomer, 4-hydroxybutyl vinyl polyethylene glycol ether (VPEG). This monomer served as the predominant component and was grafted with various functional monomers on its main chain. The molecular configuration of the resultant PCEs was discerned through Fourier infrared spectroscopy and gel permeation chromatography, while the surface tension underwent assessment via a surface tension meter. Both the initial and subsequent fluidity of cement paste and mortar were leveraged to ascertain the dispersion and retention efficacy of the synthetic PCEs. The ramifications of diverse functional group grafts of the new polyether monomer on the cement hydration procedure and strength attributes were elucidated via setting time, hydration heat assays of cement paste, SEM analysis, and compressive strength evaluations of mortar. Observations reveal that the carboxylic acid group significantly reduces surface tension, whereas the sulfonic acid group's effect remains minimal. The incorporation of both the amide and sulfonic acid groups marginally impacts the preliminary dispersion efficacy of PCEs but notably affects dispersion retention. Furthermore, these functional groups facilitate cement hydration, expedite the primary setting time of the cement paste, and bolster the initial compressive strength of the mortar. Specifically, the grafted of sodium methacrylsulfonate (SMAS) yields the most noticeable results. Finally, the working mechanism of PCEs with varying molecular structures has been explained in light both theoretical and experimental results. This research offers valuable insights for subsequent investigations into the fabrication of polycarboxylate superplasticizers using the VPEG macromonomer.     

Opal photonic crystal double-network hydrogel for visual detection through structural color and fluorescent responsiveness

Photonic crystal hydrogels are widely used in the field of visual detection, based on the response of the structural color to external stimulus, such as pH, temperature, near-infrared light, and so on. Here, we develop an opal photonic crystal hydrogel by combining polystyrene (PS) photonic crystals with a fluorescent double-network hydrogel and focus on both its visual detection function and mechanical property. The opal hydrogel is composed of nanocomposite hydrogel as the first network and ionic crosslinked hydrogel as the second network. The introduction of PS photonic crystals and terbium ions endows the opal hydrogel distinctive structural colors and fluorescence, respectively. Because of volume changes, the structural color of the opal hydrogel selectively responses to metal ions and organic solvents. Attributing to the ion exchange interaction, the opal hydrogel exhibits fluorescent responses to various metal ions. Combining the responsiveness of structural color and fluorescence, a visual dual-detection mode is set up, with better detection sensitivity and selectivity. Moreover, the characteristics of nanocomposite and double-network crosslinking ensure the opal hydrogel enough mechanical properties to undergo cycle visual detection. Consequently, the fabricated opal hydrogel is promising for use in visual detection to multiple substances in single- or dual-detection mode.     

白骛鸭常压杀菌保鲜技术的研究

为获得软包装白鹜鸭在常压杀菌工艺下的最佳品质,采用微波脱水与预杀菌处理技术并结合使用乳酸链球菌素(Msin),对产品品质及保鲜防腐的应用效果进行了研究.结果表明,在微波脱水6.5 min后,加入净鸭质量0.02%的乳酸链球菌素和0.08%的柠檬酸,真空包装后采用常压杀菌,使白鸭产品的保鲜防腐效果达到预期目的,且产品的品质、口感和风味均达到最佳.     

The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd2−xYxFe17−yGay intermetallic compounds

The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd_2−xY_xFe_17−yGa_y compounds with x = 0, 0.5, 1.0, 1.5 and y = 0, 1, 2, 3 have been investigated using X-ray and neutron powder diffractions. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th₂Zn₁₇-type structure with only small amounts of alpha iron. It is found that the addition of Ga atoms lessens the decreasing rates of the a-axis and unit cell volume V on the Y content but almost does not affect the decreasing rates of the c-axis. However, the substitution of Y has a positive effect on the increasing rates of the a-axis and unit cell volume V on the Ga content but has a very slight effect on the increasing rate of the c-axis. The c/a ratio of Nd_2−xY_xFe_17−yGa_y as a function of Ga content exhibits a different increase for different Y content owe to the combined effects of Y and Ga on the crystallographic structure. The substitution of Y is found to have little effect on the site occupancy of Ga in Nd_2−xY_xFe_17−yGa_y. The combined effects of Y and Ga on the bond lengths and ASBL of Nd_2−xY_xFe_17−yGa_y indicate that more bonds detrimental to ferromagnetic exchange can be modulated into the desirable ferromagnetic exchange distance range through suitable combined substitution, which provides a valuable way to improve the magnetic properties of rare earth-transition intermetallic compounds.