Base Pressure Control with Semi-Circular Ribs at Critical Mach Number

When better fuel-air mixing in the combustion chamber or a reduction in base drag are required in vehicles,rockets,and aeroplanes,the base pressure control is activated.Controlling the base pressure and drag is necessary in both scenarios.In this work,semi-circular ribs with varying diameters(2,4,and 6 mm)positioned at six distinct positions(0.5D,1D,1.5D,2D,3D,and 4D)inside a square duct with a side of 15 mm are proposed as an efficient way to apply the passive control technique.In-depth research is done on optimising rib size for various rib sites.According to this study,the base pressure rises as rib height increases.Furthermore,the optimal location for the semi-circular ribs with a diameter of 2 mm is at 0.5D.The 1D location appears to be optimal for the 4 mm size as well.For the 6 mm size,however,the 4D position fills this function.

Numerical Analysis of Cavity-Based Control of Base Pressure Variations at Supersonic Mach Numbers

In the present study,the base pressure variations induced by the presence of a cavity,known to have a strong influence of the behaviour of supersonic projectiles,are investigated through numerical solution of the balance equations for mass,momentum,and energy.An area ratio of four is considered and numerical simulations are carried out at Mach M=1.2,1.4,1.6,and 1.8 assuming no cavity or cavity locations 0.5D,1D,1.5D,and 2D.The inlet pressure of the nozzle is considered as a flow variable.The Taguchi method is also used,and the considered cases are then analyzed using a full factorial experimental design.The results show that the cavity is effective in increasing the base pressure for the conditions examined.For other nozzle pressure ratios,cavities do not lead to passive control due the change in the reattachment length.The distribution of wall pressure reveals that,in general,a cavity used to implement passive control of the base pressure does not adversely influence the flow pattern in the domain.

Post-processing Free Quantum Random Number Generator Based on Avalanche Photodiode Array

Quantum random number generators adopting single negligible dead time of avalanche photodiodes （APDs） photon detection have been restricted due to the non- We propose a new approach based on an APD array to improve the generation rate of random numbers significantly. This method compares the detectors＇ responses to consecutive optical pulses and generates the random sequence. We implement a demonstration experiment to show its simplicity, compactness and scalability. The generated numbers are proved to be unbiased, post-processing free, ready to use, and their randomness is verified by using the national institute of standard technology statistical test suite. The random bit generation efficiency is as high as 32.8% and the potential generation rate adopting the 32× 32 APD array is up to tens of Gbits/s.

A moment-based criterion for determining the number of components in a normal mixture model

Determining the number of components is a crucial issue in a mixture model. A moment-based criterion is considered to estimate the number of components arising from a normal mixture model. This criterion is derived from an omnibus statistic involving the skewness and kurtosis of each component. The proposed criterion additionally provides a measurement for the model fit in an absolute sense. The performances of our criterion are satisfactory compared with other classical criteria through Monte-Carlo experiments.

Biased Random Number Generator Based on Bell's Theorem

We propose a biased random number generation protocol whose randomness is based on the violation of the Clauser Home inequality. Non-maximally entangled state is used to maximize the Bell violation. Due to the rotational asymmetry of the quantum state, the ratio of Os to ls varies with the measurement bases. The experimental partners can then use their measurement outcomes to generate the biased random bit string. The bias of their bit string can be adjusted by altering their choices of measurement bases. When this protocol is implemented in a device-independent way, we show that the bias of the bit string can still be ensured under the collective attack.

Efficient Single Event Upset-Tolerant FIR Filter Design Based on Residue Number for OBP Satellite Communication Systems

Cosmic radiation has several effects on the On-Board Processing(OBP)platform in satellite communications systems,and Single Event Upsets(SEUs)are one of its most important effects.In order to protect the Finite Impulse Response(FIR)filters against SEU,this paper proposes a novel Residue Number(RN)-based method.The proposed method applies the transpose form of the FIR filter to avoid the fault missing caused by SEU on shift registers.It also adjusts the input intelligently to avoid the fault missing caused by SEU on the filter coefficients.After all the fault missing events are avoided,the modulus can be minimised to achieve the minimum overhead.Theoretical analysis and simulation results show that the noise introduced by the input adjustment is negligible.Fault injection shows that the fault missing rate of the proposed method is zero.Finally,FPGA implementation shows that the overhead of the proposed method is approximately 75% of Triple Modular Redundancy,and is only 1%-2% higher than that of the traditional RN-based design.

A Number of Major Natural Gas Production Bases Establishedby CNOOC

ItisreportedthatabundantnaturalgasresourcesexistinChina'soffshoreareasandCNOOChasalreadyestablishedanumberofmajoroffshorenaturalgasproductionbasesinSouthChinaSea,BobalSeaandEastChinaSea.Thecombinedannualproductionreaches4billioncubicmeters.Accordingt...

Development of Maintenance Management Strategy Based on Reliability Centered Maintenance for Marginal Oilfield Production Facilities

The present work adopted Reliability Centered Maintenance (RCM) methodology to evaluate marginal oilfield Early Production Facility (EPF) system to properly understand its functional failures and to develop an efficient maintenance strategy for the system. The outcome of the RCM conducted for a typical EPF within the Niger Delta zone of Nigeria provides an indication of equipment whose failure can significantly affect operations at the production facility. These include the steam generation unit and the wellhead choke assembly, using a risk-based failure Criticality Analysis. Failure Mode and Effect Analysis (FMEA) was conducted for the identified critical equipment on a component basis. Each component of the equipment was analyzed to identify the failure modes, causes and the effect of the failure. The outcome of the FMEA analysis aided the development of a robust maintenance management strategy, which is based on an optimized mix of corrective, preventive and condition-based monitoring maintenance for the marginal oilfield EPF.

基于实数化的均匀圆阵矩阵重构方法

为了减小低快拍数和低信噪比下采样协方差矩阵误差,并降低其运算复杂度,提出了一种基于实数化的均匀圆阵采样协方差矩阵重构方法。针对均匀圆阵的特点,通过组建特殊的基向量,构成特殊的重构矩阵。通过将采样协方差矩阵实数化,进一步降低了重构矩阵的复杂度。考虑到多通道不一致性对重构矩阵的影响,引入0位校正算法,提高了重构方法的稳健性。最后应用重构后的协方差矩阵进行子空间类波达方向估计(direction of arrival,DOA)。实验仿真证明,该特殊重构矩阵在实数化下与原矩阵重构能力相同;当快拍数为100、信噪比为0 dB时,双信源分辨力较重构前由74%提高到95%以上;理论重构运算复杂度降低到原来的53.99%。

悬挂式单轨交通车辆基地站场设计关键技术研究

[目的]悬挂式单轨交通车辆基地的总平面布局形式直接影响列车作业及工程造价。道岔选型对车辆基地站场总平面布局影响较大,运用库单线列位数的选择也将直接影响道岔数量及段场规模,因此需对悬挂式单轨交通车辆基地站场设计的关键技术进行深入研究。[方法]依托武汉光谷生态大走廊悬挂式单轨交通工程的龙泉山车辆段,阐述了该车辆段的总平面布局形式及创新点,分析了该车辆段道岔选型及场坪标高的制定方法,建立了理想条件下车辆段运用库单线列位数模型。[结果及结论]悬挂式单轨交通车辆基地总平面布置宜采用贯通式洗车方案,将洗车库放在出入线上;咽喉设计时,需同时考虑桥墩布置的美观性;需联合道岔厂家加快对三开道岔及五开道岔的研发,并合理选用不同道岔组合以更进一步节省投资;在不考虑其他作业干扰的理想条件下,悬挂式单轨交通车辆基地运用库最多可采用1线5列位,实际设计过程中需结合车辆基地条件、综合考虑列车出库的便捷性、扣除其他作业干扰等因素选择合适的运用库单线列位数。

不同铺层数平纹碳纤维力学特性分析

为明确面密度为200g/m^(2)的3K平纹碳纤维的力学特性,分别进行不同铺层数下碳纤维树脂基复合材料的拉伸、弯曲和冲压式剪切实验。结果表明:试样的损伤形式为断口处的分层、纤维从基体中拔出和断裂、垂直于载荷方向上的纤维束撕裂、基体之间的挤压、纤维的剪切断裂、基体的挤压变形。拉伸和弯曲试样的位移载荷曲线的起始阶段是线性的,弯曲试样的位移载荷曲线的起始阶段是非线性的。在2—12层的铺层数变化范围内,所有试样的铺层数载荷曲线呈现线性变化,试样承受弯曲载荷的能力较弱。

基于中智数的突发事件网络舆情辅助决策方法研究

为解决当前应急决策研究大多侧重于数学模型构建且决策数据偏主观假定,导致客观性、实用性及智能性不足的问题,提出基于深度学习和情感倾向分析的单值中智数智能获取方法,并将其应用于突发事件应急决策。首先,利用Python编程技术对突发事件网络舆情数据进行抓取、预处理、统计分析和可视化,得到量化的单值中智数;其次,利用中智数本身具有的不确定性特点,基于精确函数和信息熵客观确定属性权重;最后,利用案例推理(CBR)方法对备选方案进行排序和择优。研究结果表明:所提方法能够对突发事件网络舆情进行实时监测,可以客观智能获取决策数据从而实现对台风灾害的量化评估。研究结果可为相关部门有效应对突发事件网络舆情提供智能辅助决策支持。

基于ClinicalTrials.gov的全球数字疗法临床试验注册现状研究

目的研究全球数字疗法临床试验注册现状,为数字疗法的临床研究及应用提供参考。方法在ClinicalTrials.gov中检索数字疗法相关临床试验,运用文献计量学方法,分析全球数字疗法临床试验的注册数量和年度变化趋势、国家/地区分布及合作情况、申办者类型及构成情况、研究类型及试验分期、适应证分类和特征。结果全球数字疗法相关临床试验共2960项,其中美国最为活跃,远超其他国家/地区,与德国同处国际合作的中心,申办者中64.79%是高校/医院,美国高校/医院表现突出。85.44%是干预性研究,大多数属于设备和行为干预,适应证集中于精神疾病、慢性病和神经系统疾病领域,包括焦虑症(109项)、抑郁症(103项)和肥胖(101项)。截至检索日期,我国数字疗法相关临床试验为143项,与美国存在较大差距。结论全球数字疗法临床试验呈现逐年增长趋势,受COVID-19大流行影响,2020年后增长显著。我国数字疗法尚处于起步阶段,全面推广及应用尚需时间。

填充密度和轮廓层数对浆料挤出3D打印型壳性能的影响

目的采用浆料挤出3D打印工艺直接制备具有中空网络结构的铸造型壳,研究填充密度和轮廓层数对型壳性能的影响,以优化型壳制备工艺。方法选择直线填充模式,设置填充密度从60%~100%、轮廓层数从1~3,采用铝矾土浆料制备型壳试样,并测试孔隙率、收缩率、弯曲强度和导热性。结果随着填充密度的增加,孔隙率从49.4%持续降低到36.7%,但是降幅不断缩窄;收缩率逐渐减小并具有明显的各向异性,大部分收缩率在1.5%~2.5%;弯曲强度从6.15 MPa迅速提高到9.48 MPa,但填充密度超过80%后增幅很小;铝合金液浇注实验显示导热性呈现增加的趋势。随着轮廓层数增加,孔隙率和导热性逐渐降低;弯曲强度从9.48 MPa逐渐降低到7.61 MPa;轮廓层数为1和2时收缩率相近,轮廓层数为3时收缩率大大提高,尤其是在打印高度方向。结论填充密度和轮廓层数通过改变型壳的内部网格结构和外壁厚度来影响型壳性能,当填充密度为80%和轮廓层数为1时型壳综合性能最优,浆料挤出3D打印工艺制备的型壳经铝合金试铸,验证效果良好。

Effect of Free-Stream Mach Number on the Base Thermal Environment of LaunchVehicle

Convective heating of the rocket base caused by high-temperature reverse flow has long been a focus of thermal protection research.With distinctive structural characteristics,the base thermal environment of a twin-nozzle engine proves more susceptible to the recirculation region than its multi-nozzle counterparts.During the transonic stage,significant alterations in the flow field structure at the rocket base strongly influence the recirculation region.This study investigated the thermal environment of the rocket base with a twin-nozzle configuration in freestream at Mach numbers of 0.6 to 3.0.Results indicate that the freestream Mach number significantly affects the thermal environment at the rocket base during the transonic stage.The increase of Mach number from 0.6 to 1.0 causes the convective heating of the rocket base to increase by 7.7 times.This phenomenon arises due to the plume-induced shock wave caused by the impact of the supersonic free shear layer and plume shear layer while the flight speed exceeds the sound speed.The interaction between the shock wave and the shear layer amplifies turbulence in the recirculation region and at the inflection point,resulting in a stronger high-temperature reverse flow.In addition,the cause of low-altitude base heating was analyzed,and it was found that the mechanism is different from the high-temperature countercurrent effect caused by plume interaction.

固体磷酸催化竹屑液化的反应机理

固体磷酸为催化剂液化竹屑制备生物基多元醇,利用FT-IR、GC-MS、NMR等技术和方法对液化产物组成进行了表征,研究其反应机理。研究结果表明:Vinyl ethyl carbitol等烯烃类的生成主要是通过固体磷酸催化PEG400一端脱去羟基形成的,而戊二酸物质等物质主要是由固体磷酸催化纤维素等生物质通过氧化重排而形成,除此之外,固体磷酸还解决液化产物酸值高的问题。

融媒体时代宁夏主流媒体抖音号融合发展现状及优化路径

宁夏主流媒体抖音号短时期内呈现出规模化发展态势,但同时也面临着区域媒体原创性内容供给不足、账号尚未形成品牌和口碑、与用户无法建立强连接和深互动等结构性难题。要想成为意识形态的主阵地、舆论宣传的主战场和区域媒体发展的领跑者,宁夏主流媒体抖音号需要借鉴其他媒体抖音号的成功经验,深度融合抖音短视频平台的规则,实现硬新闻内容和短视频视觉化、故事化、情感化等软传播的兼容发展。

红外光谱法测定柴油中硝酸酯型十六烷值改进剂的含量

本文主要研究硝酸酯型十六烷值改进剂提升柴油的十六烷值效果,含不同浓度的硝酸酯型十六烷值改进剂的定性结果;利用红外光谱法原理研究一种柴油中该类型改进剂的定量方法,校正曲线的相关系数为0.9999,0.025%的精密度为7.7%,0.050%的精密度为9.9%,绝对偏差在0.000%~0.005%之间;比较不同方法测定硝酸酯型十六烷值改进剂,红外光谱法和分光光度计法。

广义b-基超立方体网络的符号全控制数

该文研究了广义b-基超立方体网络GC_(n)(b)的符号全控制数γst(GC_(n)(b))的问题.首先给出了当n=2k+1,b=3时,网络GC_(n)(b)的符号全控制数的上下界,然后利用数学归纳递推和反证法,确定了当b=3,n=1,2,3时,网络GC_(n)(b)符号全控制数的精确值.

阔叶箬竹母竹和鞭段育苗效果分析

【目的】揭示阔叶箬竹(Indocalamus latifolius)母竹和鞭段育苗对育苗数量和质量的影响,探索阔叶箬竹有效的无性繁育技术,为阔叶箬竹推广应用提供优质种苗。【方法】以阔叶箬竹母竹移栽和鞭段移栽为研究对象,对比分析母竹不同留枝节数(1、2、3、4、自然株)和不同鞭段长度(30、40、50 cm)繁育的存活率、新竹数量和基径粗度的差异。【结果】随着留枝节数的增多,母竹移栽存活率逐渐降低,3节枝成活率87.4%,4节枝成活率83%处于造林技术标准的临界点,但新竹数量和基径逐渐增大,3~4个节枝新竹数量达2.5株以上,新竹基径达0.87 cm以上。鞭段长度在30~50 cm之间新竹数量和基径粗度没有明显变化,成活率40、50 cm的明显高于30 cm的。【结论】采用留养3~4个节枝的母竹和长度为40~50 cm的鞭段进行阔叶箬竹无性繁育均可以取得较好的育苗效果。