Generalized system function analysis of resonant behavior of electromagnetic open systems

1 Introduction A severe challenge for the electromagnetic compatibility (EMC) of a complex elec-tromagnetic system has been given with the increasingly complicated electromagnetic environment and dense electric devices. In particular, there are a lot of various antennas and scattering bodies on the large electromagnetic objects, such as airplane, ship, car, etc., and the interaction and mutual coupling between antennas and scatterers become more and more severe, which sometimes gives rise to …     

Memristive Artificial Synapses for Neuromorphic Computing

Neuromorphic computing simulates the operation of biological brain function for information processing and can potentially solve the bottleneck of the von Neumann architecture.This computing is realized based on memristive hardware neural networks in which synaptic devices that mimic biological synapses of the brain are the primary units.Mimicking synaptic functions with these devices is critical in neuromorphic systems.In the last decade,electrical and optical signals have been incorporated into the synaptic devices and promoted the simulation of various synaptic functions.In this review,these devices are discussed by categorizing them into electrically stimulated,optically stimulated,and photoelectric synergetic synaptic devices based on stimulation of electrical and optical signals.The working mechanisms of the devices are analyzed in detail.This is followed by a discussion of the progress in mimicking synaptic functions.In addition,existing application scenarios of various synaptic devices are outlined.Furthermore,the performances and future development of the synaptic devices that could be significant for building efficient neuromorphic systems are prospected.     

On the use of formal methods to model and verify neuronal archetypes

Having a formal model of neural networks can greatly help in understanding and verifying their properties, behavior, and response to external factors such as disease and medicine. In this paper, we adopt a formal model to represent neurons, some neuronal graphs, and their composition. Some specific neuronal graphs are known for having biologically relevant structures and behaviors and we call them archetypes. These archetypes are supposed to be the basis of typical instances of neuronal information processing. In this paper we study six fundamental archetypes (simple series, series with multiple outputs, parallel composition, negative loop, inhibition of a behavior, and contralateral inhibition), and we consider two ways to couple two archetypes: (i) connecting the output(s) of the first archetype to the input(s) of the second archetype and (ii) nesting the first archetype within the second one. We report and compare two key approaches to the formal modeling and verification of the proposed neuronal archetypes and some selected couplings. The first approach exploits the synchronous programming language Lustre to encode archetypes and their couplings, and to express properties concerning their dynamic behavior. These properties are verified thanks to the use of model checkers. The second approach relies on a theorem prover, the Coq Proof Assistant, to prove dynamic properties of neurons and archetypes.     

硫肥:新的机遇与挑战

列举了硫肥在中国、印度、阿根廷和巴西的应用。大量田间试验证明,SO^2-4或S^0微粒硫肥可显著提高农作物产量。比较了这两类硫肥的优缺点。SO^2-4为速效硫肥,易于被作物吸收,但容易发生淋溶损失。S^0须被微生物氧化成SO^2-4才能被作物吸收,由于这是一个渐进的过程,所以淋溶损失很小;此外S^0产品对后季作物具有良好的后效,这对双季耕作和一种或多种作物的轮作是很重要的。S^0转化成易于被植物吸收的SO^2-4形式受土壤和环境条件的影响。描述了S^0肥的一些新用途,如“种子膨胀”和病虫害的控制。植物养分硫具有良好的海外市场机遇,但高运费、高包装费用、产品在海运途中的破碎,可能使其缺乏可接受性。解决的方法是在有S^0资源的当地建立结构紧凑的模块式造粒装置。     

Silicon assistant carbothermal reduction for SiC powders

The silicon assistant method to increase the reaction yield of carbothermal reduction of silica at a lower temperature is reported. The effect of silicon on the carbothermal reduction process has been investigated in detail. Compared with traditional reduction, the introduction of silicon can change the reaction path and further increase the conversion of silicon carbide at a lower temperature. It is considered that the assistant reduction consists of three steps: vaporizing and melting of silicon, formation of silicon monoxide, and synthesis of silicon carbide. The morphology of the synthesized SiC powders through the silicon assistant method can be affected apparently by the experimental temperature.     

SiC/Si-W-Mo coating for protection of C/C composites at 1873 K

In order to prevent carbon/carbon composites from oxidation at 1873 K, an efficient oxidation protective SiC/Si-W-Mo coating was prepared by a two-step pack cementation technique. The microstructures and the phase composition of the as-received multi-coating were examined by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. It is seen that the compact multi-coating is composed of α-SiC, Si, and （WxMO1-x）Si2. Oxidation test shows that, after oxidation at 1873 K in air for 102 h and thermal cycling between 1873 K and room temperature for 10 times, the weight loss of the SiC/Si-W-Mo coated C/C composites is only 0.26%. The invalidation of the multi-coating is attributed to the formation of penetrable cracks in the coating. 2008 University of Science and Technology Beijing. All rights reserved.     

A Calculation Method of Rolling Characteristics of Canard Missile with Free-Spinning Tails

一种自旋尾翼鸭式导弹滚转特性的计算方法

刘平安,刘明远

（哈尔滨工程大学 航天与建筑工程学院,哈尔滨 150001）

创新点说明：

通过对固定尾翼的鸭式导弹进行数值模拟,提出一种新的方法计算同种型号的自旋尾翼鸭式导弹的滚转特性,计算结果表明该方法保证了准确性的同时,可以达到大幅度减小计算量的目的,具有实用价值。

研究目的：

在保证计算精度的同时,减小自旋尾翼鸭式导弹的滚转特性在传统的非定常计算模式下的计算工作量与工作时间。

研究方法：

对固定尾翼鸭式布局导弹的外部流场进行定常的数值模拟研究,根据各组件的滚转力矩特性,定量计算该型号鸭式导弹在自旋尾翼下的滚转特性,并将计算结果与风洞试验数据进行对比验证。

研究结果：

用此方法算得的该鸭式导弹在自旋尾翼下的滚转力矩系数与自旋尾翼鸭式导弹的风洞实验数据结果吻合较好。

结论：

用此方法计算自旋尾翼鸭式布局导弹的滚转特性,在保证了准确性的同时,可以达到大幅度减小计算量的目的,具有实用价值。

关键词：数值模拟;鸭式导弹;自旋尾翼;风洞实验;滚转特性

     

Three-Gorges Reservoir Area on the Yangtze River Faced with Risk of Induced Destructive Earthquakes

The Three-Gorge Water Conservancy Project on the Yangtze River started to impound water by locking gates on June１,２００３．A swarm of more than２０００small earthquakes suddenly occurred densely along the river section in Xinling Town north of Badong,Hubei Province,on June７．This caused grave concern in the following years,but,with the completion of the second- and third-phase engineering construction,the water level in the reservoir will rise up to１５６m and１７５m respectively,no matter whether it can induce larger and stronger earthquakes．After an analysis of the distribution of active faults in the eastern part of the reservoir area,their intersections and capability to generate earthquakes from a seismo-tectonic viewpoint,we consider that after the reservoir impounding,two potential focal zones existing in Badong and Zigui counties may generate M５.５earthquake,the seismic intensity of which may reachⅧ．It will induce landslide bodies in the reservoir area to be reactivated and slide．The evidence is the large-scale landslide occurring on the Shazhenxi Creek river in Zigui County on June１２,２００３．     

ANALYSIS OF TWO-PHASE FLOW PRESSURE BUILDUP DATA FROM A WELL IN AN INFINITE MULTIWELL RESERVOIR

NOMENCLATURE A1———drainage area of the tested well ( Well 1) At———total reservoir drainage area B———two-phase formation volume factor C———wellbore storage coefficient Cf———rock compressibility fator Co———oil compressibility fator Cw———water compressibility fator Ct———compressibility fator K———reservoir permeability m———slope of a semilog straight line m1———slope defined by Eq.(12) p-———average reservoir pressure-pD———di mensionless average drainag…     

AA7075高强铝合金热冲压流变行为本构模型对比研究

在热冲压过程中,AA7075高强铝合金板料经充分固溶后移入室温模具进行冲压成形并淬火。为表征AA7075铝合金在热冲压工艺中的变形行为,在温度200~480℃、应变速率0.01~10s-1范围内进行了高温拉伸试验。基于Arrhenius类型本构模型、Johnson-Cook模型以及Zerilli-Armstrong模型提出了多种修正本构模型,并应用实验所获流变曲线进行了拟合。提出的修正模型通过将模型参数表示为应变、应变速率及温度相关的多项式函数耦合了应变、应变速率及温度对流变应力的影响,并通过均方误差(MSE)以及相关系数R值对模型流变应力预测准确性进行了评价。结果表明,修正的Johnson-Cook模型能够更加准确的预测AA7075高温流变行为。