Fast Measurement of Dielectric Conductivity for Space Application by Surface Potential Decay Method

Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the first few hours after irradiation and exponentially slowly for the remaining time. The measurement of dark conductivity with this method usually takes the slow part and needs a couple of days. Integrating the Fowler formula into the deep dielectric charging equations, we obtain a new expression for the fast decay part. The experimental data of different materials, dose rates and temperatures are fitted by the new expression. Both the dark conductivity and the radiation-induced conductivity are derived and compared with other methods. The result shows a good estimation of dark conductivity and radiation-induced conductivity in high-resistivity polymers, which enables a fast measurement of dielectric conductivity within about 600 rain after irradiation.

Phonon relaxation and heat conduction in one-dimensional Fermi Pasta Ulam β lattices by molecular dynamics simulations

The phonon relaxation and heat conduction in one-dimensional Fermi Pasta-Ulam （FPU） β lattices are studied by using molecular dynamics simulations. The phonon relaxation rate, which dominates the length dependence of the FPU β lattice, is first calculated from the energy autoeorrelation function for different modes at various temperatures through equilibrium molecular dynamics simulations. We find that the relaxation rate as a function of wave number k is proportional to k^1.688, which leads to a N^0.41 divergence of the thermal conductivity in the framework of Green-Kubo relation. This is also in good agreement with the data obtained by non-equilibrium molecular dynamics simulations which estimate the length dependence exponent of the thermal conductivity as 0.415. Our results confirm the N^2/5 divergence in one-dimensional FPU β lattices. The effects of the heat flux on the thermal conductivity are also studied by imposing different temperature differences on the two ends of the lattices. We find that the thermal conductivity is insensitive to the heat flux under our simulation conditions. It implies that the linear response theory is applicable towards the heat conduction in one-dimensional FPU β lattices.

Numerical Simulations of Nonlinear Interaction of Space Charge Waves in Microwave and Millimeter Wave Range in n-InN Films Using Negative Differential Conductivity

Numerical simulations of nonlinear interaction of space charge waves in microwave and millimeter wave range in n-InN films have been carried out. A micro- and millimeter-waves frequency conversion using the negative differential conductivity phenomenon is carried out when the harmonics of the input signal are generated. An increment in the amplification is observed in n-InN films at essentially at high-frequencies f < 450 GHz, when compared with n-GaAs films f < 44 GHz. This work provides a way to achieve a frequency conversion and amplification of micro- and millimeter-waves.

Effects of phonon bandgap on phonon-phonon scattering in ultrahigh thermal conductivityθ-phase TaN

Phonon bandgap typically has a significant effect on phonon-phonon scattering process.In this work,the effects of mass modified phonon bandgap inθ-phase Ta N are systemically investigated by the means of first-principles calculations with linearized Boltzmann transport equation.Through detailed calculations,we find that phonon bandgap has a significant effect on three-phonon process while exhibits a much weaker effect on four-phonon process.The reason for the ultrahigh thermal conductivity ofθ-phase Ta N is the long lifetime of phonons including both three-phonon and four-phonon processes,which originates from the weak phonon anharmonicity and large phonon bandgap-induced small phonon-phonon scattering phase space.This work advances the understanding of phonon bandgap effects on phonon transport.

非线性电导涂层对直流GIL绝缘子空间/表面电荷和沿面电场的调控研究

空间/表面电荷积聚是导致直流GIL绝缘子沿面闪络电压降低的潜在原因,涂敷非线性电导涂层是提升沿面绝缘性能的有效方法。本文建立了电场依赖性非线性电导涂层对绝缘子空间/表面电荷及沿面电场调控的数学模型,综合考虑了绝缘气体电流密度以及绝缘子固体电导率与电场强度的非线性关系,通过该模型研究了温度梯度分布下绝缘子内部电荷的分布规律,以及非线性电导涂层对绝缘子表面电荷积聚的影响机制。结果表明:非线性电导涂层对空间电荷消散有明显的促进作用,高压电极附近的同极性电荷主导了表面电荷分布;由于表面电荷分布和切向电场的改善,绝缘子的沿面闪络性能得到提高;在绝缘子与涂层界面之间会积聚正电荷,并从高压电极向地电极逐步递减。

相变储热技术在空气源热泵供暖中的应用研究现状

空气源热泵技术因具有节能、环保、高效等优点,在我国建筑供暖领域得到了广泛应用。文章分析了空气源热泵系统在供暖过程中存在的问题,介绍了利用相变储热技术优化空气源热泵运行性能的基本方式及原理。通过分析相变材料自身热物性以及相变储热单元在系统中的应用,从材料及系统两方面简述了相变储热技术在空气源热泵供暖中的研究现状及进展。最后,得出结论并针对相变储热技术在空气源热泵供暖中的应用难点,对未来发展进行了展望。

空间用高导热柔性石墨烯膜冷链性能研究

超柔性高导热冷链研究在空间载荷的红外焦平面制冷、活动性高效传热和均温热管理领域具有重要的工程价值和战略意义。提出一种新型石墨烯膜冷链构型,并对其开展热力协同设计和性能试验研究。系统地探究了冷链长度、搭接长度、端头立柱尺寸及数量等对导热带热传递的影响,同时验证了冷链长度、厚度和宽度分别对其振动传递的影响。研究结果表明:焊料填充对于冷链热导率的提升有着显著的影响。增加搭接长度、端头立柱数量和直径均能有效提高冷链热导率,而减小厚度、增加宽度和宽厚比均会增加冷链端部响应幅值。本文的研究结果可为兼具高柔性和高导热性的新一代冷链的选型与设计提供依据。

基于R-L分数阶定义的PCCM Boost变换器建模与分析

研究了基于R-L分数阶定义的电感电流伪连续PCCM(pseudo-continuous conduction mode)Boost变换器模型,并由此导出了变换器的状态平均模型,然后推导出升压比,直流静态工作点,电感电流波纹以及输出电压波纹的表达式。结果表明,与基于Caputo分数阶定义下的变换器模型相应表达式比较,R-L分数阶定义下的直流静态工作点和升压比不仅与占空比相关,而且还与电感和电容的阶数有关,输出电压波纹的表达式不仅与分数阶电感的阶数α有关,与分数阶电容的阶数β也相关。电感和电容的阶数对状态变量的直流分量和分数阶PCCM Boost的稳态特性有很大影响。最后,在MATLAB/SIMULINK中搭建了R-L分数阶PCCM Boost变换器数学模型和电路模型,仿真结果显示R-L分数阶PCCM Boost变换器模型的分析结果比其他PCCM Boost模型的分析结果更加稳定,误差更小。

芳纶针织面料透气透湿及隔热性能研究

通过棉、蚕丝混纺纱,竹炭纤维、丙纶混纺纱和芳纶纱的科学搭配,由龙星制版系统进行双面针织物结构数字化设计,利用艺术设计方法有效地在结构和空间中进行科学合理的分配和排列,制备了纬编间隔织物和罗纹空气层织物,探讨了芳纶协同高舒适性双面针织物的透气透湿、隔热等性能。结果表明:通过有效的数字化方法所设计的空气层组织中,芳纶与竹炭、丙纶混纺纱搭配织造的空气层织物透气性更好,纬编间隔组织中,芳纶与竹炭、丙纶混纺纱间隔织物比芳纶与蚕丝、棉混纺纱间隔织物的透气性好。蚕丝的透湿性比竹炭纤维更好,更适用于制作服装纤维材料。

多维非均质不可压缩热传导方程的适定性

利用调和分析方法和Lagrange方法研究多维非均质不可压缩热传导方程的Cauchy问题,在临界Besov空间中证明该系统在小初值条件下强解的整体适定性.

基于传导思维的人防工程专项规划编制方法

伴随着新时期国土空间规划体系的建立,新一轮人防工程专项规划编制需要与时俱进,不断提升其传导思维,以解决现行人防工程专项规划与城市规划衔接不够、内容传导不足等问题。本文首先阐述了国土空间专项规划横向、纵向以及内在三方面的传导需求,并基于以上需求,提出新一轮人防工程专项规划的编制框架及编制要点,结合A城市规划实践,从"加强现状问题识别传导规划目标、强化市域综合防护体系建设引导、突出城区人防工程体系逐级传导、构建防空区片管控要素传导机制、加强规划传导促进各类空间融合"五方面详细阐述了传导需求在具体城市人防工程专项规划中如何落实,期望为新时期人防工程专项规划的编制提供参考和借鉴。

国土空间规划传导体系与实施机制探讨

文章以新时代、新形势背景下,国土空间规划体系的建设工作为背景,以市县一级国土空间规划传导体系作为研究主体,尝试从组织架构的优化与保障机制与实施路径的落实两个方面探讨了新时代市县一级国土空间规划传导体系的构建思路与实施策略。县市一级国土空间规划的两种传达层级,一种是中心城市与新城共同规划,一种是常见的三个层级的规划模式,并对市县一级国土规划传导体系的实施机制提出了实施路径保障机制。

海洋空间的“领土化”构建与实践 ——以美国在南海地区的干涉行动为例

随着海洋与人类的联系越来越密切,控制人类海上活动的必要性,令海洋空间的“领土化”成为难以避免的趋势。主流话语开始从将海洋描述为无主之地,变成倾向于为扩大公共权力对海域控制的做法辩护,为海上力量投送和海域管控编织正当理由。由此,产生了一定的海洋空间“领土化”,国家从规范功能的角度逐渐控制海洋空间,将公共权力投射至领海和管辖水域外的海域。塑造符合自身利益需求的地区规范秩序,并在实践上强化地区军事力量投送,这两种海洋空间“领土化”扩张方式,鲜明地体现在美国在南海地区的干涉行动中。中国需在南海促进建设更有效的海洋治理体系,扩大行为规范塑造和海洋新秩序建设上的话语权,更好地维护国家海洋安全和发展利益。

可控源音频大地电磁测深法在地热水找矿勘查中的应用

贵州省荔波县处于扬子准地台黔南台陷贵定南北向构造变形区的有利空间部位,该变形区发育一系列高温地热水资源,具有集中开发绿色清洁能源的优势。针对该区域热源异常区普遍埋藏深的特征,采用可控源音频大地电磁测深法对深部热源场和导热构造等进行了预测。结果表明:①研究区地表无明显的地热异常显示,但根据地质条件等综合认为该区域具有寻找深部热水的条件;②通过可控源音频大地电磁测深验证了该区域深埋的3条断裂构造,其低阻体的空间分布及延伸特征与耕者倒转背斜吻合,下部F 2上盘与其接触部位、低阻碎屑岩层下部存在的宽缓次低阻带,为研究区主要储水储热有利部位,是进一步勘查的重点靶区;③储水有利部位为埋深2000~2800 m的次低阻带,同时钻孔还应充分考虑F_(2)、F_(5)断裂在深部的空间展布情况。

A Novel Magnetic Configuration for Space Radiation Active Shielding

Space radiation has been identified as the main health hazard to crews involved in manned Mars missions.Active shielding is more effective than passive shielding to the very energetic particles from cosmic rays.Particle motion in a magnetic field is studied based on the single-particle theory and Monte Carlo method.By comparing the shielding efficiency of different magnetic field configurations,a novel active magnetic shielding configuration with lower mass cost and power consumption is proposed for manned Mars missions.The new magnetic configuration can shield 92.8%of protons and 84.4%of alpha particles with E<4 GeV·n^(-1),when considering the passive shielding contribution of 10.0 g·cm^(-2) Al Shielding,the required magnetic stiffness can be reduced from 27 Tm to 16 Tm.The detailed analysis of mass cost and power consumption shows that active shielding will be a promising means to protect crews from space radiation exposure in manned Mars missions.

非线性电导聚合物材料研究进展

空间复杂辐射环境料可以保证正常情况(弱带电时)下的高绝缘性能,又能在高场强下以暂态高电导释放介质内部危险电下,高能带电粒子引起的航天器介质深层充放电效应是导致航天器故障的主要因素之一。研究表明,具有非线性I-U特性的复合材料可有效抑制航天器介质深层充放电。为此分析了非线性电导复合材料用于抑制航天器介质深层充放电的可行性,并从导电机理、改性方法、应用现状等方面阐述研究进展,并对非线性电导航天器介质的发展方向进行展望。分析结果表明:复合材料的非线性电导受多种电荷输运机制影响,非线性电导复合材料的制备工艺逐渐完善,并实现了从简单材料制备向仿真计算、空间环境地面模拟试验的突破。下一步的研究重点在于空间环境下的导电机理,材料制备和仿真计算、试验的协同性,仿真模型和多源模拟试验条件的优化。

Influence of Nonlocality on Amplification of Space Charge Waves in n-GaN Films

It is investigated theoretically the amplification of space charge waves (SCWs) due to the negative differential conduc-tivity (NDC) in n-GaN films of submicron thicknesses placed onto a semi-infinite substrate. The influence of the nonlo-cal dependence of the average electron velocity on the electron energy is considered. The simplest nonlocal model is used where the total electron concentration is taken into account. The relaxation momentum and energy frequencies have been calculated. The influence of the nonlocality on NDC results in the decrease of the absolute value of its real part and appearance of the imaginary part. The calculation of the diffusion coefficient leads to essential errors. The simulations of spatial increments of the amplification of SCWs demonstrate that the nonlocality is essential at the fre-quencies f ? 150 GHz, and the amplification is possible up till the frequencies f ? 400 ??? 500 GHz.

Advanced production decline analysis of tight gas wells with variable fracture conductivity

Considering the characteristics that the fracture conductivity formed by hydraulic fracturing varies across space and time, a new mathematical model was established for seepage flow in tight gas fractured vertical wells which takes into account the effects of dual variable conductivity and stress sensitivity. The Blasingame advanced production decline curves of the model were obtained using the finite element method with hybrid elements. On this basis, the effects of fracture space and time dual variable conductivity and stress sensitivity on Blasingame curve were analyzed. The study shows that the space variable conductivity mainly reduces decline curve value at the early stage; the time variable conductivity can result in drops of the production and the production integral curves, leading to a S-shaped curve; dual variable conductivity is the superposition of the effects given by the two variable conductivities; both time and space variable conductivities cannot delay the time with which the formation fluid flow reaches the quasi-steady state. The stress sensitivity reduces the curve value gradually rather than sharply, delaying the time the flow reaching the quasi-steady state. Ignoring the effects of variable conductivity and stress sensitivity will not affect the estimation on well controlled dynamic reserves. However, it can result in large errors in the interpretation of fractures and reservoir parameters. Conventional advanced production decline analyses of a tight gas fractured well in the Sulige gas field showed that the new model is more effective and reliable than the conventional model, and thus it can be widely applied in advanced production decline analysis of wells with the same characteristics in other gas fields.

Space Environment Simulator for Testing of Materials and Devices

Equipment has been designed and created for experimental simulation of space environment conditions of Geostationary orbit of the Earth. The following conditions are supported in the vacuum chamber having volume of 1.2 cubic meters: Vacuum 10-5 Torr. (1.3 × 10-3 Pa), electron beam with energy up to 8 MeV, temperatures from -150°C to +150°C and solar ultraviolet radiation. The peculiarity of this equipment is the possibility of analyzing complex simultaneous influence of mentioned above 4 factors on the sample and in-situ direct measurement of sample parameters under irradiation which provides almost real conditions. Silicon single crystals used in space environment were tested in the vacuum chamber and new results were received having scientific and applied interest. It was shown, particularly, that the electro-conductivity of silicon samples has higher value at in-situ condition than ex-situ after irradiation.

高电子迁移催化材料制备方法研究进展

通过提升材料的电子迁移率,可以提高材料的导电率,加速催化过程中氧化还原反应的进程,极大地提高催化活性。因此,高电子迁移催化材料的制备已经成为当前研究的热点。尽管诸多研究都认识到了催化材料电子迁移率提升对于催化性能的重要性,但是目前研究的系统性仍然不足,尤其是对固体表面催化领域电子迁移率如何影响材料催化性能的内在机理缺乏统一认识。亟待揭示电子迁移率与催化材料之间的构效关系,实现催化材料的可控制备。综述系统总结了高电子迁移催化材料的不同制备方法、化学物理机理、特性分析、面临的挑战,并对未来的发展方向进行了展望。重点阐述了材料的元素特性、导电特性和空间特性对高电子迁移催化材料制备的影响和限制。