Application of high temperature heat pipe in hypersonic vehicles thermal protection

In order to develop further the application of high temperature heat pipe in hypersonic vehicles thermal protection, the principles and characteristics of high temperature heat pipe used in hypersonic vehicles thermal protection were introduced. The methods of numerical simulation, theory analysis and experiment research were utilized to analyze the frozen start-up and steady state characteristic of the heat pipe as well as the machining improvement for fabricating irregularly shaped heat pipe which is suitable for leading edge of hypersonic vehicles. The results indicate that the frozen start-up time of heat pipe is long （10 min） and there exists large temperature difference along the heat pipe （47 ℃/cm）, but the heat pipe can reduce the temperature in stagnation area of hypersonic vehicles from 1 926 to 982 ℃ and work normally during 1 000-1 200℃. How to improve the maximum heat transfer capability and reduce the time needed for start-up from frozen state of the heat pipe by optimizing thermostructure such as designing of a novel wick with high performance is the key point in hypersonic vehicles thermal protection of heat pipe.

Analysis on the Transfer Characteristics of Rogowski-coil Current Transformer and Its Influence on Protective Relaying

This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.

Fibre Optic Protection System for Concrete Structures

The design concepts, modelling and implementation of various fibre optic sensor protection systems for development in concrete structures were investigated. Design concepts and on-site requirements for surface-mounted and embedded optical fibre sensor in concrete were addressed. Finite element （FE） modelling of selected sensor protection systems in strain-transfer efficiency from the structure to the sensing region was also studied. And experimental validation of specified sensor protection system was reported. Results obtained indicate that the protection system for the sensors performs adequately in concrete environment and there is very good correlation between results obtained by the protected fibre optic sensors and conventional electrical resistance strain gauges.

Positioning Temperature Sensors for Frost Protection in Northern Cranberry Production

Frost can cause serious economic losses in cranberry fields, particularly in northern regions. When the air temperature reaches a low critical threshold, sprinklers are operated to protect vines, to insure crop production and profitability. To avoid frost injury, proper positioning of temperature sensors is critical. A field experiment was designed and conducted to determine the optimal installation height of sensors above soil surface. Temperature data was used to investigate the spatial temperature gradient in the section of a cranberry field. A computer simulation of the temperature profile was performed to simulate the effect of wind velocity on the prediction of air temperature. For optimal use, sensors should be installed at the height of the canopy and several meters away from a dike. On nights with low wind velocities, the canopy air temperature was 2.7°C below that of 500 cm above the ground. The sensors should be put at least five m away from a dike to avoid the transfer of heat from the dike to the sensor. Also, multiple sensors should be installed because of the large variations in air temperature that were measured across the experiment. The simulated temperature indicated that wind velocity strongly influenced the temperature estimation;the effect of the wind on temperatures gradients was greater when the wind velocity was low (<2.3 m/s).

Comparison of Thermo-Structural Responses for Integrated Thermal Protection Panels with Different Corrugated Core Configurations

To explore new light-weight integrated thermal protection system panel configuration and gain good insight into the responses mechanism,heat transfer and structural field analysis for one single-layer and four double-layer corrugated core panels were performed. The obtained the temperature,buckling,stress and deflection responses were compared,and the deflection and stress distributions as well as thermal buckling mode at the time were discussed for the considered configurations when the temperature difference between the top and bottom face sheet was maximum. The results demonstrated that the non-orthogonal and hat-stiffened double-layer structures provide superior performance to resist thermal buckling deformation in comparison with other configurations. The useful information is provided for the forthcoming optimization in which thermal buckling is considered as critical design driver.

An Improved Transfer-Learning for Image-Based Species Classification of Protected Indonesians Birds

This research proposed an improved transfer-learning bird classification framework to achieve a more precise classification of Protected Indonesia Birds(PIB)which have been identified as the endangered bird species.The framework takes advantage of using the proposed sequence of Batch Normalization Dropout Fully-Connected(BNDFC)layers to enhance the baseline model of transfer learning.The main contribution of this work is the proposed sequence of BNDFC that can be applied to any Convolutional Neural Network(CNN)based model to improve the classification accuracy,especially for image-based species classification problems.The experiment results show that the proposed sequence of BNDFC layers outperform other combination of BNDFC.The addition of BNDFC can improve the model’s performance across ten different CNN-based models.On average,BNDFC can improve by approximately 19.88%in Accuracy,24.43%in F-measure,17.93%in G-mean,23.41%in Sensitivity,and 18.76%in Precision.Moreover,applying fine-tuning(FT)is able to enhance the accuracy by 0.85%with a smaller validation loss of 18.33%improvement.In addition,MobileNetV2 was observed to be the best baseline model with the lightest size of 35.9 MB and the highest accuracy of 88.07%in the validation set.

STEADY HEAT TRANSFER ANALYSIS AND PARAMETER OPTIMIZATION FOR MULTILAYER THERMAL INSULATIONS

The energy equilibrium equation and discrete ordinate methods are combined to establish the one-dimensional steady heat transfer mathematical model of multi-layer thermal insulations （MTIs） in metallic thermal protection systems. The inverse problem of heat transfer is solved by the genetic algorithm and data from the steady heat transfer experiment of fibrous thermal insulations. The density radiation attenuation coefficient, the albedo of fibrous thermal insulations and the surface emissivity of reflective screens are optimized. Finally, the one-dimensional steady heat transfer model of MTIs with optimized thermal physical parameters is verified by experimental data of the effective MTI conductivity.

Effect of Spacecraft Aerodynamics and Heat Shield Characteristics on Optimal Aeroassisted Transfer

A spacecraft designed to operate in a planetary atmosphere must have an adequate heat shield to withstand the high heat fluxes and heat loads that are generated by aerodynamic heating. Very often, the mass of the thermal protection system is a significant fraction of the total mass of the vehicle. In contrast, performing maneuvers in the atmosphere, that would be very costly in terms of propellant consumption if they were performed completely outside of the atmosphere in a classic way, is a very attractive prospective technique. The advantages and disadvantages in terms of total mass spared must be determined. The mission investigated involves an aeroassisted coplanar transfer from a high to a low Earth orbit. The approach uses a combination of three propulsive impulses in space together with an aerodynamic maneuver in the atmosphere. The heat shield adopted is fully ablative, given the expected high values of the entering heat flux. The convenience of the aeroassisted maneuver and the influence of the parameters involved are evaluated in comparison to a conventional Hohmann transfer. In particular, a parametric analysis is performed by varying the following characteristics of the vehicle: aerodynamic efficiency, mass-to-surface ratio, deorbit impulse, and initial altitude of the orbit. The influence of the thermal protection system is examined by assessing the impact of the type of ablative material employed, the thermal safety factor, and the allowable temperature for the adhesive layer on the substructure. The analysis is conducted with a highly representative thermal model by coupling the dynamic and thermal analyses and using a genetic optimizer. The optimization methodology and the thermal model are completely original. The results indicate the importance of choosing low-density ablative materials, of adopting a suitable thermal safety factor, and of choosing high-performance adhesives. The optimal trajectories obtained correspond to a zero second propulsive impulse.

Studies on transplantation of bone marrow stromal cells transferred by angiogenin gene in ischemic myocardium

Objective To evaluate the protective effect of bone marrow stromal cells (BMSCs) transferred by AD·ANG ex vivo on ischemic myocardium. Methods ELISA method was used to assay the expression and secretion of angiogenin (ANG) after Ad·ANG transfection of BMSCs ex vivo. Then BMSCs with Ad · ANG were transplanted into ischemic myocardium of isogenic Lewis rats. 4 weeks later, the parameters of hear function, such as EF and EDLV, were examined by echocardiography. Surival and differentiation of transplanted BMSCs and angiogenesis were appraised by histology and transmission electron electron micrography. Results ANG was found in both lysate and culture medium after transfection of BMSCs. A maximum expression of ANG was observed at 4-7 days after transfection and could still be assayed 15 days later. 4 weeks later after transplantation in the BMSCs with Ad· NAG, heart function improved better than the single BMSCs group (P【0.05), Ad·ANG group (P【0.01)and blank control group (P【0.01). Angiogenesis in

非法转让、倒卖土地使用权罪中“变相入罪”问题研究

非法转让、倒卖土地使用权罪在司法实践中存在着转让、倒卖行为的形式多样化,司法裁定不一,刑事违法性判断阙如,罪与非罪的判断受到政策影响等情况,推动了变相入罪在该罪中的司法适用。“变相”应当被定位为在刑法适用中运用实质思维对案件事实进行实质判断,以确定其是否符合构成要件的工具,它不应也无需应用于刑法解释中。非法转让、倒卖土地使用权罪的保护法益应当被具体化为市场资源利益,以发挥法益的解释论机能。对于司法实践中本罪的典型形态应当结合构成要件具体分析。

移动互联网背景下跨境数据转移的安全问题分析

随着移动互联网的快速发展和全球数据流动的日益频繁,跨境数据转移涉及的数据收集、存储、使用等环节面临着加密问题、终端安全问题、API安全问题等威胁。文中探讨了数据收集、存储、使用过程中的主要安全隐患,提出了设计跨境数据转移管理机制、建立跨境数据转移安全渠道等防护措施,旨在为相关从业人员提供指导建议,确保跨境数据流动的安全性和高效性,促进全球数字经济的发展。

矩形通道内超临界压力CO_(2)流动换热数值研究

针对高马赫数发动机热防护和机载设备长航程供电问题,基于超临界二氧化碳布雷顿循环提出了热防护与发电一体化系统。采用数值模拟方法探究了单侧受热矩形通道内超临界压力下CO_(2)的对流传热特性,并且分析了不同热流密度时入口温度、冷却流量和加热长度对冷却性能的影响。研究发现单侧受热矩形通道内SCO_(2)的流动换热存在周向不均匀性,增大冷却剂流量可以有效降低壁面温度。但对周向壁面温差影响较小并且温差随热流密度增大单调上升,由0.5 MW‧m^(-2)的最大温差75 K增加至2.0 MW‧m^(-2)的最大温差297 K。二次流在通道拐角处形成回流,局部扰流使传热增强。当流体温度高于拟临界温度时,定压比热容随入口温度的升高而减小,但是雷诺数的增大弥补了这一缺陷并使得换热能力增强。不同加热长度的冷却性能受传热特性影响,不发生传热恶化时,相同冷却流量条件下加热长度越大冷却后的壁面最高温度越高。但是当发生传热恶化时,不同加热长度冷却后的壁面最高温度分为相同和随加热长度增大两种情况。

氩气保护电渣重熔脱硫预测研究

在工业级氩气保护电渣重熔过程中,钢中脱除的硫在渣中积累,会影响脱硫反应效率,造成重熔锭中硫含量分布不均。目前,电渣脱硫研究主要是基于规格较小的实验级,与大规格的工业级电渣脱硫动力学条件差别明显,故相关研究成果在工业应用中存在局限性。因此,本研究建立了工业级电渣重熔过程脱硫反应模型,经3吨氩气保护电渣实验验证,模型计算结果与实验结果基本一致。研究结果表明,降低电极和渣中初始硫含量、增加渣量、提高硫容量、降低电极下降速度均有利于提高脱硫率。基于研究结果推导出模型简化公式,可直接近似求解重熔锭不同质量处的硫含量。

欧盟数据治理中的“一站式”监管:运行机制、实施困境及启示

《一般数据保护条例》的实施改变了欧盟数据治理法律碎片化的状态,欧盟国家数据保护机构以多种合作机制增强执法的统一性和权威性。“一站式”监管机制是保证欧盟成员国间共享权限的结构化合作方式,由领导型监管机构牵头开展数据跨境案件的执法,遵循闭门协商和客观标准两个原则,具有重要的执法管辖协调作用。但目前该机制的运行存在程序不透明及效率低下的问题,可能导致管辖竞择现象的出现,影响各成员数据保护机构的独立性。我国应当在司法层面积极回应欧盟的监管工具输出,通过数据合规部署全球数字经营战略,同时反思我国数据保护机构的设置与职权分配,借鉴“一站式”监管中的管辖协调机制,改革我国数据保护领域的“多头治理”模式,切实提高数据领域的执法水平。

高温环路热管设计方法研究与传热极限分析

高超声速飞行器在以高超声速飞行时尾喷管会面临严酷的燃烧热考验,结合高温热管导热性强和环路热管传热距离长等优势,高温环路热管可以作为尾喷管热防护的新方法.根据液态钠高导热系数及高表面张力的物性设计了一种新型蒸发器,提出了一套高温环路热管的设计流程.使用这套设计流程设计了一根高温环路热管,结合热管传热极限的计算方法,对钠热管进行仿真计算,分析了温度和结构对热管传热极限的影响.研究发现在高温环路热管的运行温区内,热管的传热性能随着温度升高一般由声速极限、毛细极限和沸腾极限依次决定.结合研究结论提出了热管结构优化方法,为热管设计提供了理论依据.

风速与风向对人体热交换影响的CFD仿真模拟

为了提升灾害环境中人体热损伤评估精度并保障应急救援人员的生命安全,首先将暖体假人进行三维激光扫描得到数值假人,并按照人体生理构造将其划分为20个区块,通过ICEM软件建立气候室,设置0°~180°的风向;然后通过FLUENT软件计算得到0.2~5.0 m/s风速时的人体显热换热量和辐射换热量,在此基础上求得对流换热量;最后将模拟结果与文献中数据进行对比验证,并分析不同风速与风向对人体热交换的影响。结果表明:提出的计算流体动力学(CFD)仿真模拟方法可有效模拟人体不同部位的换热量;风速的增加会促进人体与环境之间的热交换,当风速从0.2 m/s增加到5.0 m/s时,人体整体对流换热量从56 W/m^(2)增加到360 W/m^(2);人体表面局部部位之间对流换热量有明显的差异,其中四肢部位与环境之间的热交换受风速影响更为明显;风向对人体整体对流换热几乎没有影响,但躯干部位对流换热量受风向的影响较大;在非对称风向(45°、90°、135°)下,人体对流换热量呈现非对称式分布。本研究可为人员安全评估、极端环境下人体热反应建模、防护装备研发等提供基础数据。

基于不经意传输的密码方案设计与对比分析

随着数字化时代的发展,对数据安全和隐私保护的需求日益增加,基于不经意传输的密码方案作为一种重要的安全技术,保护数据安全和用户隐私方面发挥着重要作用。本文针对基于不经意传输的密码方案进行了设计与对比分析。首先,对数字产品交易、位置服务隐私保护和区块链数据保密查询等领域的应用需求进行了分析,在充分考虑其正确性、安全性和性能开销等方面的特点,计了满足相应安全和隐私保护要求的不经意传输方案;其次,对比分析了三种基于不经意传输的密码方案在安全性、功能、性能和实用性上的差异,为各个领域的实际应用提供了参考和指导;最后,总结了各方案的优缺点,并展望了自己未来基于不经意传输的密码方案的研究方向。

长尾喷管气凝胶隔热层结构设计

固体火箭发动机长尾喷管外围通常放置舵机等控制系统,为了满足控制系统的工作温度要求,设计了一种用于长尾喷管段的新型热防护复合结构。长尾段隔热层采用具有低热导率、低密度特点的二氧化硅气凝胶材料。首先建立了气凝胶材料热导率计算模型,并对高温环境气凝胶材料导热性能进行测试。随后结合气凝胶材料热导率计算,建立了长尾喷管的热防护复合结构模型,并对喷管热防护结构模型进行了瞬态传热分析和力学性能分析。结果表明,喷管热防护结构设计满足材料力学性能。在发动机工作20 s后气凝胶材料可以将喷管的长尾段外壳壁面温度控制在320 K以下。相较于传统的高硅氧酚醛隔热材料,气凝胶材料隔热效果表现更优,且可以有效减少喷管热防护结构的消极质量。

“精于算计”:社交媒体用户隐私保护脱离形成机制探讨

尽管数字时代用户的隐私风险与日俱增,但高昂的保护成本和诱人的让渡收益引发了用户隐私倦怠,进而导致隐私保护脱离。本研究基于多维发展理论,从信息管理维度和交互管理维度出发,构建社交媒体用户隐私保护脱离研究模型,通过线上问卷收集579个有效样本,运用SEM和fsQCA相结合的方法进行数据分析。研究发现,隐私倦怠是隐私保护脱离的正向影响因素,而隐私侵犯经历和隐私保护成本是引发隐私倦怠的正向前因变量,隐私设置可供性和隐私政策有效性对于隐私倦怠具有负向影响。隐私让渡收益则正向调节了隐私倦怠对隐私保护脱离的作用效果。与此同时,隐私保护脱离的前因构型共有5种,可划分为注重收益型和成本规避型2种模式,充分揭示了用户在隐私保护过程中“精于算计”的特征。

C/SiC复合材料的人工孔发汗冷却性能分析及优化研究

C/SiC复合材料在热防护领域中应用广泛,但受制备工艺、成本等方面的限制,具有低孔隙率、小孔径的特征,在发汗冷却过程中这些微小孔隙难以支撑足够的冷却剂供应量且易发生堵塞,限制了冷却的进行。针对此问题,本文研究通过增加人工孔来改善C/SiC复合材料发汗冷却性能的可行性。建立了人工孔表征单元结构及等效模型,获得了打孔后复合材料内冷却工质的流量比及等效渗透率的变化情况,探究了打孔方式与工质流量对复合材料等效体换热系数的影响规律,并拟合了打孔后复合材料等效体换热系数经验公式。结果表明:渗透特性方面,冷却工质的主要流量分布于人工孔中;对于渗透率为1×10^(-16) m^(2)的低渗透率材料,打孔后复合材料自身工艺孔中的流量占比小于0.1%,其中的工质流动可忽略;在换热特性方面,可通过调节打孔方式改善复合材料的换热性能,相同渗透率下调节打孔方式可使体换热系数提升154%。