A potential biogenetic membrane constructed by hydrophilic carbonized rice husk for sustaining electricity generation from hydrovoltaic conversion

In recent years, the research on hydrovoltaic conversion has made rapid progress, showing potential prospect in the field of power generation. However, it still faces many issues, such as expensive, uncontrollable engineering, undetermined mechanism and difficulty in commercialization. To provide a low-cost, undemanding and practical strategy, the carbonized rice husk was first used to construct a biogenetic membrane device in this work, giving a sustaining hydrovoltaic voltage at ∼160 mV. Relevant studies that associated with mechanism and key factors for hydrovoltaic process were also implemented founded on different test conditions. It is proved that the fluids flow driven by evaporation and capillary effect is an essential prerequisite for hydrovoltaic conversion. The mechanism for generating electricity should be attributed to the streaming potential theory, which can provide an electric potential difference by selective transmission of ions owing to the Debye shielding effect. Based on this as-proposed theory, the controlling projects like improving pressure difference (ΔP) of fluid, ambient temperature and humidity, which generally enhance the hydrodynamic driving force and effective flowing area, logically demonstrate positive answers on hydrovoltaic performance. Moreover, in view of the super hydrophilicity of carbonized rice husk, this biogenetic membrane has demonstrated strong sensitivity on human breath monitoring with rapid response for every breath, which provides a potential way for the practical application of hydrovoltaic effect.     

Influence of geometry on thermal gradients and hotspot formation during flash sintering

Hotspot or preferential current path formation is a major problem halting the advance of flash sintering as an industry applicable densification method. In-situ infrared thermal imaging shows significant dependence of the surface temperature distribution on the sample geometry, causing significant changes in the onset parameters, the course of the flash event and sample quality. Current-ramped flash sintering is compared to conventional flash sintering experiments and reveals an effective reduction in temperature differences. The role of the setup design on the thermal losses and the gradients is highlighted.     

基于铝片取向的复合热控涂层吸收发射比调控

金属颗粒掺杂型复合涂层是重要的航天器热控材料,除了粒子材料、尺寸、体积分数、几何形貌、涂层厚度等常规调控手段,颗粒的取向也是影响涂层辐射特性的重要因素。颗粒取向可以通过改变工艺参数或使用定向剂控制,然而目前关于颗粒整体取向对涂层吸收发射比的影响规律尚不清晰,而且现有的采用二流法的研究中大多都将散射假定为各向同性。以热控涂层中常用的大尺寸铝片粒子掺杂型复合涂层为计算模型,采用考虑衍射的几何光学方法和考虑各向异性散射的二流法研究了铝片取向角对热控涂层吸收发射比的调控规律,同时考虑了铝片体积分数和涂层厚度等因素。结果表明：通过调节粒子取向可实现涂层吸收发射比在0.48～1.69范围内的调控。涂层平均吸收率和平均发射率在铝片取向角超过45°时明显增大。涂层吸收发射比在铝片取向角45°附近最小,并且随铝片体积分数的增大而减小。研究表明：通过控制粒子的整体取向可有效实现吸收发射比的调控,为热控涂层的设计和调控提供了新的思路。     

相对湿度和粒子形态对海盐气溶胶粒子散射特性的影响

根据海盐粒子在不同相对湿度条件下的不同形态,分别建立了低湿度（RH=0%）、中湿度（RH=50%）和高湿度（RH=95%）三种条件下海盐立方体和球形粒子模型。利用离散偶极子近似法（DDA）、Mie散射理论研究了相对湿度和粒子形态对海盐散射的特性影响,采用离散坐标法（DISORT）研究了相对湿度和粒子形态对海盐特性的影响。结果表明:相对湿度和粒子形态对海盐散射特性影响较大,不同相对湿度条件下,海盐气溶胶粒子由于相态不同,呈现出不同的特性。中湿度条件下,粒子形状因子对海盐散射辐射特性的影响更强。当光学厚度较小时,球形-立方体海盐气溶胶的双向反射分布函数（BRDF）相对差异超过15%,在研究海盐气溶胶散射辐射特性时,需同时考虑相对湿度和粒子形态的影响;当光学厚度较大时,相对差异不超过5%,一定精度范围内,可采用等效球方法进行模拟计算。研究结果对于大气气溶胶散射和辐射传输理论及应用研究具有重要的参考价值。     

固体火箭发动机喷焰复燃及其对红外辐射的影响

火箭发动机喷焰涉及复杂的流动、复燃和辐射效应,并对喷焰辐射的光学探测跟踪有着重要的影响。以固体火箭发动机为研究对象,建立喷焰化学反应复燃数值模拟方法和视线光辐射传输数值计算方法,对不同飞行条件下的喷焰流动、辐射特性进行计算分析,重点考察复燃效应对不同高度喷焰辐射特性的影响。研究结果表明:复燃效应引起喷焰温升可达到1 000 K,并使得喷焰谱带辐射强度有10倍以上的增强;对于不同谱带辐射强度会随高度先升后降,最大的高度在20~30 km,短波2.7 m波段有约17倍的辐射增强,中波4.3 m波段约有16倍增强,可见复燃引起辐射增强作用H2O分子的贡献大于CO2分子的贡献。研究结果可为进一步的理论研究和工程应用提供参考。     

基于黑体红外偏振特性的定量分析探索

通过基于微面元理论的偏振双向反射分布函数模型,推导分析了物体表面红外辐射偏振传输方程的Stokes表达式,得出物体表面红外线偏振度与表面反射率(发射率)、波长、探测角度以及波长、目标与背景辐射差异等参数的数学关系;针对环境因素对红外偏振度的影响,开展了不同材质以及标准黑体的中、长波红外偏振成像及红外高光谱偏振成像实验,结果表明:黑体表面的红外偏振度与波长不相关,进而提出以标准黑体红外偏振特性作为溯源基准进行红外偏振定量处理的方法.     

三种典型流动状态下的喷流红外辐射特性

计算了欠膨胀状态、设计状态和过膨胀状态三种典型流动状态下的轴对称收扩喷管在3~5 m波段的喷流红外辐射传输特性,并对三种状态的计算结果进行了分析比较。流场采用有限体积法和重整化群（RNG）k-湍流模型求解N-S方程得到,喷流的红外辐射强度采用有限体积法结合窄带模型求解吸收发射性介质辐射传输方程得到。计算结果显示:欠膨胀状态的喷流红外辐射强度最大,设计状态与过膨胀状态的喷流红外辐射依次降低,随天顶角的增大差距增大,这与喷流的流动特点有关,说明喷流流动特点的改变影响红外辐射的大小,通过控制喷流的流动可以控制喷流红外辐射强度。     

非均匀下垫面辐照环境对太空目标温度的影响

太空目标表面温度受地球下垫面辐射的影响,在对太空目标的计算中通常将下垫面作为均 匀的热辐射平衡体,而受地物类型及气象条件的影响,地球表面的反射率和热辐射值随地理位置和季 节变化,文中介绍了下垫面热流的计算方法,并根据所获得的地表温度数据以及地物类型信息,采用 不同的下垫面处理方式,初步分析了地球下垫面的不均匀性对太空目标表面温度的影响。     

一种提高光电跟踪设备捕获概率的搜索方法

大型光电跟踪设备跟踪测量精度高、惯量大、视场小,不具备大空域搜索目标能力,一般依靠雷达等设备提供的引导信息发现捕获目标,当目标引导误差超出光电设备视场后,光电跟踪设备难于发现目标。提出了一种在引导信息基础上的小空域快速螺旋搜索方法,通过系统建模仿真和外场试验验证,此方法适用于在目标引导信息误差超出视场情况下,快速搜索发现目标。在引导误差不超出两倍视场情况下,此方法可使捕获目标概率从20%左右提高到70%左右。此方法搜索过程中转台运动平稳,可根据不同光电设备系统性能、实际目标运动特征和引导误差灵活改变螺旋搜索参数,大大提高光电跟踪设备目标捕获概率,是大型光电跟踪设备小空域快速搜索发现目标的一种实用有效的方法,具有很高的通用性。     

The synthesis condition and characterization of thermally treated CeO2 and ZnOCeO2 composite fibers

Electrospinning derived nanostructured CeO₂ and ZnOCeO₂ composite fibers have been successfully fabricated, followed by a subsequent heat-treatment. X-ray line profile analysis is applied to the X-ray diffraction data collection for determination of microstructure parameters both area -and volume-averaged apparent crystallites size based on spherical crystallites with lognormal size distribution. The surface morphologies of the prepared samples were examined with scanning electron microscope (SEM). To gain insight into the optical properties of the fabricated nanofibers, the UV–vis diffuse reflectance absorption spectrums were measured. The correlation between the structural and optical properties is discussed.