The temporal instability of parallel viscous two-phase mixing layers is extended to current-fluid mud by considering a composite error function velocity profile. The influence of viscosity ratio, Reynolds number, and ...The temporal instability of parallel viscous two-phase mixing layers is extended to current-fluid mud by considering a composite error function velocity profile. The influence of viscosity ratio, Reynolds number, and Froude number on the instability of the system are discussed and a new phenomenon never discussed is investigated based on our numerical results. It is shown that viscosity can enlarge the unstable wave number range, cause new instability modes, and certainly reduce the growth rate of Kelvin-Helmholtz （K-H） instability.展开更多
Liver transplantation is an effective treatment for patients with end-stage liver disease. Accurate imaging evaluation of the transplanted patient is critical for ensuring that the limited donor liver is functioning a...Liver transplantation is an effective treatment for patients with end-stage liver disease. Accurate imaging evaluation of the transplanted patient is critical for ensuring that the limited donor liver is functioning appropriately. Ultrasound contrast agents(UCAs), in combination with contrastspecific imaging techniques, are increasingly accepted in clinical use for the assessment of the hepatic vasculature, bile ducts and liver parenchyma in pre-, intra- and posttransplant patients. We describe UCAs, their technical requirements, the recommended clinical indications, image interpretation and the limitations for contrastenhanced ultrasound applications in liver transplantation.展开更多
乙烯裂解炉是乙烯生产的核心装置,烃类原料在裂解炉中发生复杂的高温裂解反应,及时识别裂解炉运行工况变化对设备安全高效运行非常重要。裂解炉运行过程中产生大量的过程数据,这些数据通常具有多变量、高维度特性,增加了数据处理和分析...乙烯裂解炉是乙烯生产的核心装置,烃类原料在裂解炉中发生复杂的高温裂解反应,及时识别裂解炉运行工况变化对设备安全高效运行非常重要。裂解炉运行过程中产生大量的过程数据,这些数据通常具有多变量、高维度特性,增加了数据处理和分析的复杂性,如何基于过程数据及时检测乙烯裂解炉工况变化成为亟需解决的问题。借鉴对比学习算法在图片分类中的优秀性能,提出一类基于对比学习的裂解炉运行工况识别方法。首先,将乙烯裂解炉工业数据经归一化后,使用不同长度的时间窗动态提取数据,将其转化为灰度图片。根据图片中的信息,将图片进行数据增强后输入编码器,得到图片的全局语义、类别、内容不变性等特征。将这些特征应用于计算对比学习的损失函数,通过最小化对比损失函数,实现对灰度图片的分类。通过本文方法,可以根据过程数据快速发现工况变化,其分类准确度较通用时间序列表示学习的自监督对比学习(self-supervised contrastive learning for universal time series representation learning,TimesURL)方法有明显提升,可有效实现乙烯裂解炉工况识别。展开更多
基金supported by the National Nature Science Foundation of China(11172307 and11232012)973 Program(2014CB046200)
文摘The temporal instability of parallel viscous two-phase mixing layers is extended to current-fluid mud by considering a composite error function velocity profile. The influence of viscosity ratio, Reynolds number, and Froude number on the instability of the system are discussed and a new phenomenon never discussed is investigated based on our numerical results. It is shown that viscosity can enlarge the unstable wave number range, cause new instability modes, and certainly reduce the growth rate of Kelvin-Helmholtz （K-H） instability.
基金Supported by National Natural Science Foundation of ChinaNo.81371554+1 种基金Science and Technology Planning Project of Guangdong Province of ChinaNo.2013B021800092
文摘Liver transplantation is an effective treatment for patients with end-stage liver disease. Accurate imaging evaluation of the transplanted patient is critical for ensuring that the limited donor liver is functioning appropriately. Ultrasound contrast agents(UCAs), in combination with contrastspecific imaging techniques, are increasingly accepted in clinical use for the assessment of the hepatic vasculature, bile ducts and liver parenchyma in pre-, intra- and posttransplant patients. We describe UCAs, their technical requirements, the recommended clinical indications, image interpretation and the limitations for contrastenhanced ultrasound applications in liver transplantation.
文摘乙烯裂解炉是乙烯生产的核心装置,烃类原料在裂解炉中发生复杂的高温裂解反应,及时识别裂解炉运行工况变化对设备安全高效运行非常重要。裂解炉运行过程中产生大量的过程数据,这些数据通常具有多变量、高维度特性,增加了数据处理和分析的复杂性,如何基于过程数据及时检测乙烯裂解炉工况变化成为亟需解决的问题。借鉴对比学习算法在图片分类中的优秀性能,提出一类基于对比学习的裂解炉运行工况识别方法。首先,将乙烯裂解炉工业数据经归一化后,使用不同长度的时间窗动态提取数据,将其转化为灰度图片。根据图片中的信息,将图片进行数据增强后输入编码器,得到图片的全局语义、类别、内容不变性等特征。将这些特征应用于计算对比学习的损失函数,通过最小化对比损失函数,实现对灰度图片的分类。通过本文方法,可以根据过程数据快速发现工况变化,其分类准确度较通用时间序列表示学习的自监督对比学习(self-supervised contrastive learning for universal time series representation learning,TimesURL)方法有明显提升,可有效实现乙烯裂解炉工况识别。
文摘数字图像后处理流程带来的非唯一性人造(Non-Unique Artifacts,NUAs)噪声掺杂在具有唯一性、稳定性的光响应非均质性(Photo-Response Non-Uniformity,PRNU)指纹中,极大地影响了下游成像设备溯源任务的精确性。然而,现有NUAs抑制方案主要针对实验环境,不仅需要额外的超参数设定,而且需额外的算力和存储空间,难以在开放环境中实际应用。为解决该问题,提出了一种面向开放环境的PRNU指纹提纯算法。首先,对现有PRNU指纹相关性度量指标即峰值相关能量比(Peak-to-Correlation Energy Ratio,PCE)进行改进,提出了基于归一化的PCE_norm和PCE_denuas,以实现开放环境下的自适应相关性度量。然后,通过构建对比学习机制缩小同一指纹和放大不同指纹的距离,实现NUAs离线抑制,从而在溯源任务中不需额外计算和存储成本进行在线抑制。最后,通过在Dresden和Daxing数据集上的实验证明了所提算法的有效性和鲁棒性。
