共查询到20条相似文献,搜索用时 15 毫秒
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针对正交频分复用(OFDM)系统,提出了一种适用于时变信道的信道估计算法。该方法利用频域导频,经离散傅立叶变换(DFT),获得的信道冲击响应等效于利用频域导频对应的时域序列和接收信号进行循环相关获得的信道冲击响应。因此,避免了在时域采用复杂的循环相关运算。同时,通过消除频域导频时域序列的自相关误差,能有效降低由DFT谱泄漏导致的信道估计误差。仿真和分析表明,在时变多径衰落信道下,提出的信道估计方法的性能比传统的基于DFT的算法和频域维纳滤波算法有明显提高。 相似文献
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D. E. Oates 《Journal of Superconductivity and Novel Magnetism》2007,20(1):3-12
The linear surface resistance of the HTS materials is low enough to support a variety of applications that can surpass conventional
technology. However, nonlinearity in the form of intermodulation distortion (IMD) is a serious limiting effect for some applications.
The nonlinear effects are only weakly correlated with the low-power surface impedance, and considerable material variation
has been the hallmark of IMD. With improvement in film quality, the intrinsic nonlinearity now seems to be the most important
source of IMD. Presented here is a brief review of the experimental situation and a comparison with the theories of intrinsic
nonlinearity. Suggestions for further work are given. 相似文献
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根据自适应天线阵列理论,结合给定的参考波束的误差,引入虚拟干扰的概念,对目标波束图形状进行调整,提出一种新的可以应用于任意类型天线阵列的波束综舍算法.应用提出的新算法,在主辩和旁瓣位置都可以对波束进行有效的调节.最终获得阵列的最优权矢量,能够最小化目标波束图与参考波束图间的差异.理论分析与仿真结果表明,与现有的同类算法相比,该算法能更有效地获得与参考波束基本相符的波束.应用于OFDM智能天线系统时,对不同子载波频率上信号进行单独处理,利用该算法进行波束综合,能够在整个有效频段,使所有子载波上获得基本一致的阵列输出. 相似文献
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Sultan Noman Qasem Amar Nazar Attia Qamar Shahaboddin Shamshirband Ahmad Karim 《计算机、材料和连续体(英文)》2019,59(3):713-727
Brain tumor is one of the most dangerous disease that causes due to uncontrollable and abnormal cell partition. In this paper, we have used MRI brain scan in comparison with CT brain scan as it is less harmful to detect brain tumor. We considered watershed segmentation technique for brain tumor detection. The proposed methodology is divided as follows: pre-processing, computing foreground applying watershed, extract and supply features to machine learning algorithms. Consequently, this study is tested on big data set of images and we achieved acceptable accuracy from K-NN classification algorithm in detection of brain tumor. 相似文献
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光电摆角测量系统中CCD信号检测与处理电路设计 总被引:2,自引:0,他引:2
本文介绍了在光电摆角测量系统中,采用多片CCD同步采样实现物体空间摆角实时测量的方法。给出了CCD工作参数和输出信号处理电路的设计,讨论了工程中的有关问题。 相似文献
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本文介绍了一套基于西门子S7-1200 PLC开发的、以触摸屏为人机交互界面的真空泵性能参数自动检测系统。该系统可实现真空度、抽速、温度、转速、电流电压等性能参数的自动测量、采集、处理、储存,并在人机界面以参数、图表等多种形式进行显示等功能。系统在运行过程中可自动判断设备运行安全性并报警,同时上传相关数据至上位机。本文从该系统的总体方案设计、硬件组成和软件编程三方面进行了深入探讨。 相似文献
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Since the web service is essential in daily lives, cyber security becomes more
and more important in this digital world. Malicious Uniform Resource Locator (URL) is
a common and serious threat to cybersecurity. It hosts unsolicited content and lure
unsuspecting users to become victim of scams, such as theft of private information,
monetary loss, and malware installation. Thus, it is imperative to detect such threats.
However, traditional approaches for malicious URLs detection that based on the
blacklists are easy to be bypassed and lack the ability to detect newly generated malicious
URLs. In this paper, we propose a novel malicious URL detection method based on deep
learning model to protect against web attacks. Specifically, we firstly use auto-encoder to
represent URLs. Then, the represented URLs will be input into a proposed composite
neural network for detection. In order to evaluate the proposed system, we made
extensive experiments on HTTP CSIC2010 dataset and a dataset we collected, and the
experimental results show the effectiveness of the proposed approach. 相似文献
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Qi Bao Jiadi Sun Xuran Fu Lina Sheng Yongli Ye Jian Ji Yinzhi Zhang Jiasheng Wang Jianfeng Ping Xiulan Sun 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(29):2207343
Drug resistance in pathogenic bacteria has become a major threat to global health. The misuse of antibiotics has increased the number of resistant bacteria in the absence of rapid, accurate, and cost-effective diagnostic tools. Here, an amplification-free CRISPR-Cas12a time-resolved fluorescence immunochromatographic assay (AFC-TRFIA) is used to detect drug-resistant Salmonella. Multi-locus targeting in combination crRNA (CcrRNA) is 27-fold more sensitive than a standalone crRNA system. The lyophilized CRISPR system further simplifies the operation and enables one-pot detection. Induction of nucleic acid fixation via differentially charged interactions reduced the time and cost required for flowmetric chromatography with enhanced stability. The induction of nucleic acid fixation via differentially charged interactions reduces the time and cost required for flowmetric chromatography with enhanced stability. The platform developed for the detection of drug-resistant Salmonella has an ultra-sensitive detection limit of 84 CFU mL−1 within 30 min, with good linearity in the range of 102–106 CFU mL−1. In real-world applications, spiked recoveries range from 76.22% to 145.91%, with a coefficient of variation less than 10.59%. AFC-TRFIA offers a cost-effective, sensitive, and virtually equipment-independent platform for preventing foodborne illnesses, screening for drug-resistant Salmonella, and guiding clinical use. 相似文献
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旅游业是福建省的生态效益型产业之一。本文基于福建生态省建设的战略定位,通过对原有的旅游标准体系的问题剖析,提出了福建省旅游业标准体系的优化建议。 相似文献
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本文根据《水质监测》(第四版)等资料提供的操作方法,对水样预处理、不同的提取时间等几方面提出了自己试验中的心得体会,采用三色分光法来计算水中叶绿素a的含量。并就质控措施提出建议。 相似文献
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Rongrong Huang Lei He Yanyan Xia Hongpan Xu Chang Liu Hui Xie Su Wang Lijun Peng Yufeng Liu Yuan Liu Nongyue He Zhiyang Li 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(19)
Emerging evidence indicates that exosomes derived from gastric cancer cells enhance tumor migration and invasion through the modulation of the tumor microenvironment. However, it remains a major problem to detect cancer‐specific exosomes due to technical and biological challenges. Most of the methods reported could not achieve efficient detection of tumor‐derived exosomes in the background of normal exosomes. Herein, a label‐free electrochemical aptasensor is presented for specific detection of gastric cancer exosomes. This platform contains an anti‐CD63 antibody modified gold electrode and a gastric cancer exosome specific aptamer. The aptamer is linked to a primer sequence that is complementary to a G‐quadruplex circular template. The presence of target exosomes could trigger rolling circle amplification and produce multiple G‐quadruplex units. This horseradish peroxidase mimicking DNAzyme could catalyze the reduction of H2O2 and generate electrochemical signals. This aptasensor exhibits high selectivity and sensitivity toward gastric cancer exosomes with a detection limit of 9.54 × 102 mL?1 and a linear response range from 4.8 × 103 to 4.8 × 106 exosomes per milliliter. Therefore, this electrochemical aptasensor is expected to become a useful tool for the early diagnosis of gastric cancer. 相似文献
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基于机器视觉的安瓿溶液异物检测系统 总被引:1,自引:0,他引:1
针对1~20 mL安瓿瓶装溶液的在线异物检测,本文分析并设计了基于机器视觉的安瓿溶液在线异物检测系统,介绍了检测系统硬件结构和图像采集卡等配置.根据应用要求,对溶液中的不同异物类型,分别设计了合理有效的成像方法,并设计高速旋转急停法成功地区分异物与瓶壁上的干扰.鉴于溶液中异物在图像上的呈现的弱目标性质,设计了一种快速方便的区域分割方法,并在融合传统目标检测方法的基础上,重点提出基于机器视觉的有效的目标检测方法,文章最后给出实验结果并进行分析,证明了算法的有效性和该系统的实用性. 相似文献
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目的 针对凹版印刷以镭射光柱纸作为承印物,镭射光柱对色标检测传感器产生干扰,致使镭射光柱纸不能使用传统套印工艺进行印刷,提出一种可直接在镭射光柱区域直接印刷套准色标的新工艺与技术方案。方法 对色标传检测感器检测原理进行分析,分析镭射光柱纸的特点以及对色标传感器造成的干扰。根据镭射光柱光谱反射率曲线来进行滤光镜片的选取,同时也加入衰减镜片以及消光膜进行组合实验测量电压,实验使用松德凹印机组进行。以白卡纸套印电压作为参考,选取不同镜片组合进行生产打样。结果 镜片组合可以滤除镭射光柱,色标传感器能准确检测色标光信号,上机打样满足高精度多色套印,且不需要复杂的镂空、遮盖工艺,节省了一组色序,并节省了2%的承印物原材料。结论 对色标检测传感器检测原理的分析以及对镭射光柱纸的光谱反射率曲线的测量,实现了使用滤光镜片组合对镭射光柱的滤除,证明了套准标记可直接印刷在镭射光柱区域的可行性。同时,提高了承印物的利用率,减低了油墨使用量。 相似文献