Torsional statics of two-dimensionally functionally graded microtubes

A size-dependent governing equation is derived to investigate the torsional static behaviors of two-dimensionally functionally graded microtubes based on the modified couple stress theory. The shear modulus is assumed to vary along the tube’s length direction according to an exponential distribute function, and varies along the tube’s radius direction according to a power-law function. A generalized differential quadrature method is developed to determine the rotational angle and shear stresses. Some illustrative examples are given to investigate the effects of applied torques, the length scale parameter and various material compositions on the torsional angle and shear stresses.     

低渗透率地层渗透率的确定方法

结合大庆油田外围低渗透率地层的地质特点,根椐渗流理论和岩心分析资料,分析了地层渗透率与孔隙度、组成地层的各种矿物含量以及泥质含量之间的关系,建立了不同矿物组合地层的渗透率计算方程。用本方法计算的和岩心分析的渗透率进行了对比,二者之间具有较好的一致性。     

Customer entrepreneurship on digital platforms: Challenges and solutions for platform business models

Drawing on the mixed methods of qualitative research and agent‐based simulation, this study examines: (a) how end‐users use digital platforms to become customer–entrepreneurs undertaking commercial activities on platforms; and (b) how platform providers can convert this customer entrepreneurship into a revenue stream. Considering that end‐users have traditionally been defined as passive and uncharged actors in platform business models, an in‐depth understanding of their commercial activities and the viable revenue model to monetize this emerging customer practice is warranted. Our qualitative study reveals that customer–entrepreneurs make substantial use of platform offerings to advertise their products; communicate with end‐consumers; and accept payments. These commercial activities are largely exercised for free on platforms, even though they could otherwise serve as a source of revenue. On this point, our simulation results identify two pricing models achieving the generation of nearly identical revenues over time. First, platform providers may charge both advertising and transaction fees, which maximize the survival of professional customer–entrepreneurs. Second, platform businesses may levy advertising fees only, which maximizes the survival of informal customer–entrepreneurs operating on a micro‐scale and part‐time basis. This study offers theoretical, methodological, and managerial implications for platform studies.     

NiAl金属间化合物的热爆合成过程研究

以Al粉和Ni粉为主要原料，采用自蔓延高温合成技术，制备Ni—Al基金属间化合物。绘制了热爆反应曲线、描述了热爆反应的过程，分析了热爆反应机理及产物的显微组织特征，研究了热爆反应的边界条件以及各种反应参数对热爆反应的影响。研究结果表明，升温速率和颗粒尺寸对热爆反应均有不同程度的影响。提高升温速率、减小颗粒尺寸均可缩短热爆反应的起始时间，降低热爆反应的起始温度。初步确定了反应起始温度低于Ni—Al系的最低共晶温度（640℃），Ni—A1系的热爆反应是由固一固扩散反应引发的，Ni-32Al的反应产物为单相、均一的NiAl相。     

铝表面改性SiOx薄膜力学性能研究

采用常压化学气相沉积(APCVD)技术在铝基底上成功制备了改性SiOx陶瓷薄膜.通过显微硬度测试与涂层附着力自动划痕测试定量研究了薄膜显微硬度和膜基结合强度,利用光学显微镜(OM)和扫描电子显微镜(SEM)观察了薄膜的原始表面以及压痕、划痕形貌.结果表明,SiOx膜层由大小不均匀的等轴状颗粒团聚堆垛而成,退火处理时长大或融合成片状;SiOx薄膜有效提高纯铝表面的硬度,并能通过SiOx薄膜变形以松弛表层应力,抑制脆性裂纹产生;划痕测试证明基底和薄膜具有很高的结合强度,薄膜与基底发生塑性变形而不剥离.     

铝表面改性SiOx薄膜力学性能研究

采用常压化学气相沉积（APCVD）技术在铝基底上成功制备了改性SiOx陶瓷薄膜。通过显微硬度测试与涂层附着力自动划痕测试定量研究了薄膜显微硬度和膜基结合强度，利用光学显微镜（0M）和扫描电子显微镜（SEM）观察了薄膜的原始表面以及压痕、划痕形貌。结果表明，SiOx膜层由大小不均匀的等轴状颗粒团聚堆垛而成，退火处理时长大或融合成片状；SiOx薄膜有效提高纯铝表面的硬度，并能通过SiOx薄膜变形以松弛表层应力，抑制脆性裂纹产生；划痕测试证明基底和薄膜具有很高的结合强度，薄膜与基底发生塑性变形而不剥离。     

基于正负理想点的导弹武器系统作战效能评估

讨论了目前导弹武器系统作战效能评估中的几点不足,提出用正负理想点法来评估导弹武器系统的作战效能.首先给出评估模型.其次,通过对具有典型意义的5种空舰导弹武器系统作战效能进行分析,给出应用示例,并对评估效果进行分析,得出结论.     

双重JPEG压缩图像篡改区域检测与定位

对JPEG(joint photographic experts group)图像实施篡改往往会产生双重JPEG(double JPEG,DJPE) 压缩痕迹,分析该痕迹有助于揭示图像压缩历史并实现篡改区域定位。现有算法在图像尺寸较小和质量因子(quality factor,QF) 较低的时候性能不佳,对两个QF的组合情况存在限制。本文提出了一种端到端的混合QF双重JPEG压缩图像取证网络,命名为DJPEGNet。首先,使用预处理层从图像头文件中提取表征压缩历史信息的量化表 (quantization table,Qtable) 特征,将图像从空域转换至DCT(discrete cosine transform)域构造统计直方图特征。然后,将两个特征输入到由深度可分离卷积和残差结构堆叠而成的主体结构,输出二分类结果。最后,使用滑动窗口算法自动定位篡改区域并绘制概率分布图。实验结果表明,在使用不同Qtable集生成的小尺寸数据集上,DJPEGNet所有指标均优于现有最先进的算法,其中ACC提高了1.78%,TPR提升了2.00%,TNR提升了1.60%。     

三模混合集成小型化滤波器设计

提出了一种基于LC串联单元的三模混合集成小型化滤波器电路拓扑。该电路拓扑具有对称性,主体由4个LC串联单元所构成的“星型”结构组成,能够通过对其并联于地的LC串联单元中元件参数的调节实现对滤波器双零点的自由调节。基于奇偶模分析方法,给出了所提出滤波器拓扑的综合设计方法,并采用基于商业化硅基表贴电容的低成本混合集成技术研制一款具有明显小型化特性的三模多零点带通滤波器。所研制的滤波器仿真与测试结果吻合良好,其中心频率为2.6 GHz,3 dB带宽为1.34 GHz,插入损耗典型值为1.6 dB,能够在4～12 GHz的频带范围内实现30 dB的抑制能力,其面积尺寸为3.2 mm×1.9 mm(0.03λ0×0.02λ0)。