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Particle flow code simulation of intact and fissured granitic rock samples 被引量:16
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作者 Uxía Castro-Filgueira Leandro R.Alejano Diego Mas Ivars 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2020年第5期960-974,共15页
This study presents a calibration process of three-dimensional particle flow code(PFC3D)simulation of intact and fissured granite samples.First,laboratory stressestrain response from triaxial testing of intact and fis... This study presents a calibration process of three-dimensional particle flow code(PFC3D)simulation of intact and fissured granite samples.First,laboratory stressestrain response from triaxial testing of intact and fissured granite samples is recalled.Then,PFC3D is introduced,with focus on the bonded particle models(BPM).After that,we present previous studies where intact rock is simulated by means of flatjoint approaches,and how improved accuracy was gained with the help of parametric studies.Then,models of the pre-fissured rock specimens were generated,including modeled fissures in the form of“smooth joint”type contacts.Finally,triaxial testing simulations of 1 t 2 and 2 t 3 jointed rock specimens were performed.Results show that both elastic behavior and the peak strength levels are closely matched,without any additional fine tuning of micro-mechanical parameters.Concerning the postfailure behavior,models reproduce the trends of decreasing dilation with increasing confinement and plasticity.However,the dilation values simulated are larger than those observed in practice.This is attributed to the difficulty in modeling some phenomena of fissured rock behaviors,such as rock piece corner crushing with dust production and interactions between newly formed shear bands or axial splitting cracks with pre-existing joints. 展开更多
关键词 Numerical methods Artificially fissured samples Rock mass behavior Particle flow code Parallel bond Flat-joint Smooth-joint
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Experimental study on the type change of liquid flow in broken coal samples 被引量:6
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作者 Lu-zhen WANG Zhan-qing CHEN Hai-de SHEN 《Journal of Coal Science & Engineering(China)》 2013年第1期19-25,共7页
A test system of the permeability of broken coal samples mainly consists of a CMT5305 electronic universal test machine, crushed rock compaction containing cylinder and a self-designed seepage circuit, which is compos... A test system of the permeability of broken coal samples mainly consists of a CMT5305 electronic universal test machine, crushed rock compaction containing cylinder and a self-designed seepage circuit, which is composed of a gear pump, a reversing valve, a relief valve and other components. By using the steady penetration method, the permeability and non-Darcy flow β factor of broken coal samples under five different porosity levels were measured, the grain diameters of the coal samples were selected as 2.5-5 mm, 5-10 mm, 10-15 mm, 15-20 mm, 20-25 mm and 2.5-25 ram, respectively. After measuring the permeability under each porosity, the overfall pressure of the relief valve continuously increased until the coal sample was broken down. In this way, the flow type of liquid inside the broken coal samples changed from seepage to pipe flow. The correlation between breakdown pressure gradient (BPG) and porosity was analyzed, and the BPG was compared with the pressure gradient when seepage instability occurred. The results show that, ①the non-Darcy flow β factor was negative before broken coal samples with six kinds of diameters were broken down; ②the BPG of coal samples with a grain size of 2.5-25 mm was lower than that of the others; ③ the BPG of coal samples with a single diameter under the same porosity increased as the grain size increased; ④ the BPG could be fitted by an exponential function with porosity, and the exponent decreased as the grain size increased for coal samples with a single diameter; ⑤ the BPG was slightly less than the seepage instability pressure gradient. The change in liquid flow type from seepage to pipe flow could be regarded as the performance of the seepage instability. 展开更多
关键词 broken coal sample permeability parameters breakdown pressure gradient (BPG) seepage instability flow type
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A New Automated Method and Sample Data Flow for Analysis of Volatile Nitrosamines in Human Urine 被引量:1
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作者 James A. Hodgson Tiffany H. Seyler +2 位作者 Ernest McGahee Stephen Arnstein Lanqing Wang 《American Journal of Analytical Chemistry》 2016年第2期165-178,共14页
Volatile nitrosamines (VNAs) are a group of compounds classified as probable (group 2A) and possible (group 2B) carcinogens in humans. Along with certain foods and contaminated drinking water, VNAs are detected at hig... Volatile nitrosamines (VNAs) are a group of compounds classified as probable (group 2A) and possible (group 2B) carcinogens in humans. Along with certain foods and contaminated drinking water, VNAs are detected at high levels in tobacco products and in both mainstream and side-stream smoke. Our laboratory monitors six urinary VNAs—N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), and N-nitrosomorpholine (NMOR)—using isotope dilution GC-MS/ MS (QQQ) for large population studies such as the National Health and Nutrition Examination Survey (NHANES). In this paper, we report for the first time a new automated sample preparation method to more efficiently quantitate these VNAs. Automation is done using Hamilton STAR<sup>TM</sup> and Caliper Staccato<sup>TM</sup> workstations. This new automated method reduces sample preparation time from 4 hours to 2.5 hours while maintaining precision (inter-run CV < 10%) and accuracy (85% - 111%). More importantly this method increases sample throughput while maintaining a low limit of detection (<10 pg/mL) for all analytes. A streamlined sample data flow was created in parallel to the automated method, in which samples can be tracked from receiving to final LIMs output with minimal human intervention, further minimizing human error in the sample preparation process. This new automated method and the sample data flow are currently applied in bio-monitoring of VNAs in the US non-institutionalized population NHANES 2013-2014 cycle. 展开更多
关键词 Volatile Nitrosamines AUTOMATION sample Data flow Gas Chromatography Tandem Mass Spectrometry
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Development of an accurate lateral flow immunoassay for PEDV detection in swine fecal samples with a filter pad design 被引量:7
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作者 Siyi Zou Lei Wu +5 位作者 Gan Li Juan Wang Dongni Cao Tao Xu Aiqing Jia Yong Tang 《Animal Diseases》 2021年第3期150-161,共12页
Porcine epidemic diarrhea virus(PEDV),as the main causative pathogen of viral diarrhea in pigs,has been reported to result in high morbidity and mortality in neonatal piglets and cause significant economic losses to t... Porcine epidemic diarrhea virus(PEDV),as the main causative pathogen of viral diarrhea in pigs,has been reported to result in high morbidity and mortality in neonatal piglets and cause significant economic losses to the swine industry.Rapid diagnosis methods are essential for preventing outbreaks and transmission of this disease.In this study,a paper-based lateral flow immunoassay for the rapid diagnosis of PEDV in swine fecal samples was developed using stable color-rich latex beads as the label.Under optimal conditions,the newly developed latex bead-based lateral flow immunoassay(LBs-LFIA)attained a limit of detection(LOD)as low as 10^(3.60) TCID_(50)/mL and no cross-reactivity with other related swine viruses.To solve swine feces impurity interference,by adding a filtration unit design of LFIA without an additional pretreatment procedure,the LBs-LFIA gave good agreement(92.59%)with RT-PCR results in the analysis of clinical swine fecal samples{n=108),which was more accurate than previously reported colloidal gold LFIA(74.07%)and fluorescent LFIA(86.67%).Moreover,LBs-LFIA showed sufficient accuracy(coefficient of variance[CV]<15%)and stable(room temperature storage life>56 days)performance for PEDV detection,which is promising for on-site analysis and user-driven testing in pig production system. 展开更多
关键词 Porcine epidemic diarrhea virus Latex beads Lateral flow immunoassay sample pretreatment Filter pad
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Spatiotemporal variations in sap flow in a larch plantation:sampling size for stand scale estimates
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作者 Zebin Liu Songping Yu +3 位作者 Lihong Xu Yanhui Wang Mengfei Wang Pengtao Yu 《Journal of Forestry Research》 2025年第1期321-331,共11页
The sap flow method is widely used to estimate forest transpiration.However,at the individual tree level it has spatiotemporal variations due to the impacts of environmental conditions and spatial relationships among ... The sap flow method is widely used to estimate forest transpiration.However,at the individual tree level it has spatiotemporal variations due to the impacts of environmental conditions and spatial relationships among trees.Therefore,an in-depth understanding of the coupling effects of these factors is important for designing sap flow measurement methods and performing accurate assessments of stand scale transpiration.This study is based on observations of sap flux density(SF_(d))of nine sample trees with different Hegyi’s competition indices(HCIs),soil moisture,and meteorological conditions in a pure plantation of Larix gmelinii var.principis-rupprechtii during the 2021 growing season(May to September).A multifactorial model of sap flow was developed and possible errors in the stand scale sap flow estimates associated with sample sizes were determined using model-based predictions of sap flow.Temporal variations are controlled by vapour pressure deficit(VPD),solar radiation(R),and soil moisture,and these relationships can be described by polynomial or saturated exponential functions.Spatial(individual)differences were influenced by the HCI,as shown by the decaying power function.A simple SF_(d)model at the individual tree level was developed to describe the synergistic influences of VPD,R,soil moisture,and HCI.The coefficient of variations(CV)of the sap flow estimates gradually stabilized when the sample size was>10;at least six sample trees were needed if the CV was within 10%.This study improves understanding of the mechanisms of spatiotemporal variations in sap flow at the individual tree level and provides a new methodology for determining the optimal sample size for sap flow measurements. 展开更多
关键词 Sap flow Environmental conditions COMPETITION MODELLING Optimal sample size
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Comparison of different sampling strategies for debris flow susceptibility mapping: A case study using the centroids of the scarp area, flowing area and accumulation area of debris flow watersheds 被引量:3
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作者 GAO Rui-yuan WANG Chang-ming LIANG Zhu 《Journal of Mountain Science》 SCIE CSCD 2021年第6期1476-1488,共13页
The quality of debris flow susceptibility mapping varies with sampling strategies. This paper aims at comparing three sampling strategies and determining the optimal one to sample the debris flow watersheds. The three... The quality of debris flow susceptibility mapping varies with sampling strategies. This paper aims at comparing three sampling strategies and determining the optimal one to sample the debris flow watersheds. The three sampling strategies studied were the centroid of the scarp area(COSA), the centroid of the flowing area(COFA), and the centroid of the accumulation area(COAA) of debris flow watersheds. An inventory consisting of 150 debris flow watersheds and 12 conditioning factors were prepared for research. Firstly, the information gain ratio(IGR) method was used to analyze the predictive ability of the conditioning factors. Subsequently, 12 conditioning factors were involved in the modeling of artificial neural network(ANN), random forest(RF) and support vector machine(SVM). Then, the receiver operating characteristic curves(ROC) and the area under curves(AUC) were used to evaluate the model performance. Finally, a scoring system was used to score the quality of the debris flow susceptibility maps. Samples obtained from the accumulation area have the strongest predictive ability and can make the models achieve the best performance. The AUC values corresponding to the best model performance on the validation dataset were 0.861, 0.804 and 0.856 for SVM, ANN and RF respectively. The sampling strategy of the centroid of the scarp area is optimal with the highest quality of debris flow susceptibility maps having scores of 373470, 393241 and 362485 for SVM, ANN and RF respectively. 展开更多
关键词 Debris flow Artificial neural network Support vector machine Random forest SUSCEPTIBILITY sampling strategy
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Two Pass Port Scan Detection Technique Based on Connection Pattern and Status on Sampled Data 被引量:1
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作者 Sunil Kumar Kamlesh Dutta Ankit Asati 《Journal of Computer and Communications》 2015年第9期1-8,共8页
Anomaly detection is now very important in the network because the increasing use of the internet and security of a network or user is a main concern of any network administrator. As the use of the internet increases,... Anomaly detection is now very important in the network because the increasing use of the internet and security of a network or user is a main concern of any network administrator. As the use of the internet increases, so the chances of having a threat or attack in the network are also increasing day by day and traffic in the network is also increasing. It is very difficult to analyse all the traffic data in network for finding the anomaly in the network and sampling provides a way to analyse the anomalies in network with less traffic data. In this paper, we propose a port scan detection approach called CPST uses connection status and pattern of the connections to detect a particular source is scanner or benign host. We also show that this approach works efficiently under different sampling methods. 展开更多
关键词 PORT SCAN TRW TAPS CPST PACKET sampling flow sampling
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Factors Associated with Sample Rejection for CD4+/CD8+ T Cell Count Analyses at the Kenyatta National Hospital Comprehensive Care Center Laboratory, Kenya
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作者 Moherai Wilfred Felix Joshua Nyagol Walter Mwanda 《World Journal of AIDS》 2021年第4期181-188,共8页
<strong><em>Background: </em></strong>The appropriate time to initiate antiretroviral therapy (ART) in HIV/AIDS patients is determined by measurement of CD4+/CD8+ T cell count. The CD4/CD8+ T c... <strong><em>Background: </em></strong>The appropriate time to initiate antiretroviral therapy (ART) in HIV/AIDS patients is determined by measurement of CD4+/CD8+ T cell count. The CD4/CD8+ T cell count is also useful, together with viral load, in monitoring disease progression and effectiveness treatment regimens. Several factors may contribute to sample rejection during the CD4+/CD8+ T cells count, resulting in negative effects on patient management. <strong> <em>Objective: </em></strong>Evaluate the causes for CD4+CD8+ T cell count sample rejection at the Kenyatta National Hospital Comprehensive Care Center Laboratory. <strong><em>Method:</em></strong> A retrospective cross-sectional study was conducted between 2018 and 2020. Data was obtained from the “rejected samples” for Partec<sup>R</sup> FlowCyp flow cytometry file. Designed data collection sheet was used for data capture. A total of 3972 samples were submitted for CD4+/CD8+ T cell count during the study period. Causes for sample rejection were numbered 1 to 12, each representing a reason for sample rejection. Number 1 was sub-categorized into clotted, hemolyzed, short-draw and lipemic. Data was analyzed using excel, and presented using tables, graphs and pie charts. Approval to conduct the study was obtained from KNH/UoN ERC. <strong> <em>Results:  </em></strong>In the study period, 81/3972 (2.0%) samples were rejected. Samples submitted more than 48 hours after collection were mostly rejected. Other factors included improper collection technique, delayed testing, patient identification error and incorrect use of vacutainer. A combination of clotted samples, specimen submission more than 48 hours caused the most frequent sample rejection, followed with combination of specimen submission more than 48 hours, delayed testing and delayed specimen processing. Together, clotted samples, incorrect vacutainer and poor specimen label caused the least sample rejection. <strong><em>Conclusion:</em></strong> Sample rejection rate for CD4/CD8+ T cell count was relatively low, and multiple factors contributed to rejection. However, improved quality assurance will enable more benefit to patients who seek this test in the laboratory. 展开更多
关键词 sample REJECTION Causes CD4/CD8+ T Cell Count flow Cytometry
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我国烟豆种质资源搜集取样策略研究
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作者 王克晶 时英喆 +1 位作者 王浩辰 李向华 《植物遗传资源学报》 北大核心 2026年第1期87-99,共13页
大豆属(Glycine Willd.)多年生亚属(Subgenus Glycine)的烟豆[G. tabacina(Labill.)Benth.]是我国福建省特有物种,为国家二级保护野生植物。合理的居群取样可以最大程度维持样本的遗传多样性,对物种的种质资源搜集具有重要意义。本研究... 大豆属(Glycine Willd.)多年生亚属(Subgenus Glycine)的烟豆[G. tabacina(Labill.)Benth.]是我国福建省特有物种,为国家二级保护野生植物。合理的居群取样可以最大程度维持样本的遗传多样性,对物种的种质资源搜集具有重要意义。本研究使用物种特异SSR引物对13个居群和1个单居群分别进行地理空间居群和居群内的遗传结构分析。结果显示,居群在地理空间上显示极低基因地理分化(F_(st)=0.056)、高期望杂合度(H_(e)=0.741)和多态性信息指数(PIC=0.70)、高基因流(N_(m)=4.445),居群内遗传变异(H_(s)占总变异的78.0%)大于居群间遗传变异(D_(st)占总变异的22.0%)。说明虽然烟豆是自花授粉植物,但是地理空间居群的遗传变异特性表现类似于异花授粉植物,其原因可能是烟豆的多年生特性使该物种存在高的遗传异质性和广泛的长距离扩散,导致地理空间上的高基因流。对高程度扰动的龙海单居群内植株空间遗传结构分析显示,植株空间遗传斑块范围约为5.0 m;当取样样本为20~25株时,达到居群95%的遗传多样性。依据本研究结果,提出了烟豆种质资源搜集策略:在居群层次,居群内取样单株至少20~25株,植株距离至少间隔9~15 m;在居群地理空间层次,由于我国烟豆仅分布在福建省一段狭窄的海岸地带,建议尽可能搜集多的居群。 展开更多
关键词 烟豆 遗传结构 SSR分析 基因流 取样策略
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双流中间包单流改造的流场优化和夹杂物去除效果
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作者 唐爱华 王多刚 江中块 《炼钢》 北大核心 2026年第2期39-45,53,共8页
为了降低高品质低碳钢铸轧界面能耗,上海梅山钢铁股份有限公司2号连铸机实施了双流中间包单流改造,将连铸机拉速由1.2 m/min提升为2.4 m/min,进行单流高拉速的生产。针对改造后中包流场和夹杂物去除效率等问题,通过物理和数值模拟相结... 为了降低高品质低碳钢铸轧界面能耗,上海梅山钢铁股份有限公司2号连铸机实施了双流中间包单流改造,将连铸机拉速由1.2 m/min提升为2.4 m/min,进行单流高拉速的生产。针对改造后中包流场和夹杂物去除效率等问题,通过物理和数值模拟相结合的方法,研究了不同工况下中间包内钢水的流动行为和夹杂物运动轨迹。研究结果表明:单流改造后,原双流中间包的控流装置不再适合单流浇铸,其堵流侧死区较大,包内混匀性差。使用新型的湍流控制器和挡墙后,堵流侧流动情况得到改善,包内死区体积下降12.2%,响应时间延长了96.7%,平均停留时间增加了11.2%,峰值浓度降低了45.3%,表明优化后的中间包具有更好的流场。另外,优化后的中包夹杂物的去除率相比原来均有明显的提升。大样电解结果表明,优化前夹杂物平均含量较高,达到了0.78 mg/kg,优化后显著降低至0.29 mg/kg。该研究通过在中间包内引入新型控流装置组合,有效改善了包内流场,提升了夹杂物的去除效率和钢水洁净度,使得连铸机拉速显著提升,助力炼钢节能减碳。 展开更多
关键词 双流中间包 单流浇铸 夹杂物 流场 大样电解
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基于改进时间全卷积网络的中短期树干液流预测
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作者 姚琴娟 王伟博 +4 位作者 胡云昊 任桢 罗煦钦 张培松 邬嘉豪 《中南林业科技大学学报》 北大核心 2026年第1期104-114,共11页
[目的]为准确预测短期至中期的树干液流速率,提出一种基于CEEMDAN-SE-CE-UnetTSF的混合预测模型,用于实现树干液流的中短期精准预测,对于评估森林水分利用效率以及实现树木健康状况的早期诊断具有重要意义。[方法]首先,采用完全集成自... [目的]为准确预测短期至中期的树干液流速率,提出一种基于CEEMDAN-SE-CE-UnetTSF的混合预测模型,用于实现树干液流的中短期精准预测,对于评估森林水分利用效率以及实现树木健康状况的早期诊断具有重要意义。[方法]首先,采用完全集成自适应噪声经验模态分解与样本熵分析,提取树干液流序列的内在模态特征;其次,利用交叉熵算法筛选关键环境变量,最终确定4个主要环境因子作为模型输入;最后,在此基础上,构建基于UnetTSF架构的预测框架,分别对未来24~168 h的液流速率进行预测。研究采用来自SAPFLUXNET的公开数据集,包含2013—2015年间以30 min间隔采集的49 660条树干液流与环境因子记录。[结果]在不同预测时间尺度下所提出的模型性能均优于Transformer、Informer、Autoformer和PatchTST等主流时序预测模型。该模型在不同时间跨度的数据集上均表现出良好的预测精度与鲁棒性,具有较强的泛化能力。[结论]构建的树干液流预测模型不仅方法上有创新,还为智慧林业管理中的水分监测与生理诊断提供了有效的技术支持,在水资源优化与森林健康管理领域具有广泛的应用前景。 展开更多
关键词 完全集成自适应噪声经验模态分解 样本熵 交叉熵 UnetTSF 树干液流
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流奖赏引导的基于模型学习的策略优化方法
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作者 王义 钟珊 龚声蓉 《计算机工程与设计》 北大核心 2026年第2期528-535,共8页
针对基于模型的强化学习中模型误差累积与探索效率低下的问题,提出耦合标准化流的动态奖励优化方法。通过构建双流网络区分真实环境与模型生成分布,利用分布差异动态重构奖励函数:训练阶段最小化差异提升预测精度,策略在线交互阶段根据... 针对基于模型的强化学习中模型误差累积与探索效率低下的问题,提出耦合标准化流的动态奖励优化方法。通过构建双流网络区分真实环境与模型生成分布,利用分布差异动态重构奖励函数:训练阶段最小化差异提升预测精度,策略在线交互阶段根据差异强度自适应调节探索范围。该方法突破传统静态奖励机制限制,在连续控制任务中有效抑制多步预测误差传播,显著提升样本效率与累积回报,同时增强策略收敛稳定性,为开放环境中的智能体学习提供新范式。 展开更多
关键词 强化学习 模型学习 策略优化 标准化流 样本效率 奖赏函数 探索与利用
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基于归一化流退火重要性抽样的安全关键场景生成
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作者 曾昭汰 石晴 +2 位作者 余国宽 范萱 马智文 《计算机工程与应用》 北大核心 2026年第4期344-352,共9页
自动驾驶系统测试与评估的主流方法是虚拟仿真测试,而测试场景是虚拟仿真测试的关键。为了同时解决测试场景生成的“维度诅咒”和安全关键事件的罕见性问题,提出了归一化流退火重要性抽样(normalizing flow-annealed importance samplin... 自动驾驶系统测试与评估的主流方法是虚拟仿真测试,而测试场景是虚拟仿真测试的关键。为了同时解决测试场景生成的“维度诅咒”和安全关键事件的罕见性问题,提出了归一化流退火重要性抽样(normalizing flow-annealed importance sampling,NF-AIS)方法。从HighD数据集提取车辆动作数据,通过归一化流(normalizing flow,NF)模型训练生成自然驾驶行为动作分布;将该分布作为退火重要性抽样(annealed importance sampling,AIS)的初始分布,灵活调整抽样权重以增大危险动作的比例;以最小化α=2散度为目标,使得最终生成的危险动作分布尽可能拟合真实数据分布。实验结果表明,所提方法在保证场景真实性的同时,能大量生成安全关键场景用于自动驾驶系统测试,与自然驾驶场景相比,NF-AIS方法生成的安全关键场景的测试效率提高了约7700倍,且碰撞率达到了8.03%,远高于自然驾驶场景的碰撞率,从而能更高效地测试自动驾驶系统。 展开更多
关键词 自动驾驶系统测试 场景生成 归一化流 退火重要性抽样
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Super point detection based on sampling and data streaming algorithms
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作者 程光 强士卿 《Journal of Southeast University(English Edition)》 EI CAS 2009年第2期224-227,共4页
In order to improve the precision of super point detection and control measurement resource consumption, this paper proposes a super point detection method based on sampling and data streaming algorithms (SDSD), and... In order to improve the precision of super point detection and control measurement resource consumption, this paper proposes a super point detection method based on sampling and data streaming algorithms (SDSD), and proves that only sources or destinations with a lot of flows can be sampled probabilistically using the SDSD algorithm. The SDSD algorithm uses both the IP table and the flow bloom filter (BF) data structures to maintain the IP and flow information. The IP table is used to judge whether an IP address has been recorded. If the IP exists, then all its subsequent flows will be recorded into the flow BF; otherwise, the IP flow is sampled. This paper also analyzes the accuracy and memory requirements of the SDSD algorithm , and tests them using the CERNET trace. The theoretical analysis and experimental tests demonstrate that the most relative errors of the super points estimated by the SDSD algorithm are less than 5%, whereas the results of other algorithms are about 10%. Because of the BF structure, the SDSD algorithm is also better than previous algorithms in terms of memory consumption. 展开更多
关键词 super point flow sampling data streaming
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双球面无相位近远场变换方法研究
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作者 李建煌 贾云飞 《电子测量技术》 北大核心 2026年第3期111-118,共8页
针对高频天线近场测量中相位信息缺失导致的远场重构精度下降问题,提出一种基于双球面采样的无相位近远场变换方法。基于等效磁流近远场变换理论,通过双球面截断幅值流算法实现等效磁流重构与远场反演。首先对测量矩阵实施预处理以保证... 针对高频天线近场测量中相位信息缺失导致的远场重构精度下降问题,提出一种基于双球面采样的无相位近远场变换方法。基于等效磁流近远场变换理论,通过双球面截断幅值流算法实现等效磁流重构与远场反演。首先对测量矩阵实施预处理以保证算法的收敛性;其次在迭代过程中引入Armijo线搜索策略优化步长选择,提升等效磁流解的逼近效率;通过双球面交替采样机制有效降低测量矩阵相关性,增强幅值信息的空间采样维度。仿真实验表明:对于不同类型大小的天线,在仅获取双球面近场幅值的条件下,所提方法可实现主瓣±60°范围内的精确远场重构,其幅度误差控制在0.5dB以内。在实际近场测量中计算结果吻合良好。该方法为无相位近场测量提供了有效解决方案,具有工程实用价值。 展开更多
关键词 近远场变换 相位恢复 等效磁流法 截断幅值流算法 双球面采样
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一种基于Netflow机制的大流抽样算法设计
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作者 李川 李岷 《火力与指挥控制》 CSCD 北大核心 2015年第8期127-130,135,共5页
在网络测量中,如何在快速存储器容量一定的条件下提高对大流的测量精度是目前研究的一个热点问题。首先在不影响应用需求的前提下,提出了对双向流进行抽样测量的思想。然后对流抽样算法进行了一定的数学分析,证明了测量双向流能有效提... 在网络测量中,如何在快速存储器容量一定的条件下提高对大流的测量精度是目前研究的一个热点问题。首先在不影响应用需求的前提下,提出了对双向流进行抽样测量的思想。然后对流抽样算法进行了一定的数学分析,证明了测量双向流能有效提高流表的利用率,较好地提高大流测量精度。为实现基于Netflow机制的抽样算法,详细设计了哈希函数,流表表项结构,重点解决了将双向流映射到同一个流表表项的问题。最后利用网络实测数据对该算法进行了仿真验证,结果表明,当存储资源一定时,该算法的大流测量精度要优于单向流测量算法。 展开更多
关键词 大流抽样 双向流 NETflow 测量精度
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基于时移多尺度等概率符号化样本熵的气液两相流动态特性分析
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作者 孙庆明 张玉玮 +3 位作者 巴頔 李振谭 夏雨蒙 杜洋 《大连理工大学学报》 北大核心 2026年第2期111-118,共8页
为了揭示气液两相流动结构间复杂性和不稳定性的差异,提出一种基于时移多尺度等概率符号化样本熵(TMESSE)的分析方法.在对7种典型时间序列进行分析的基础上,充分验证了所提方法的可行性与有效性;进而对垂直上升管内气液两相流压差波动... 为了揭示气液两相流动结构间复杂性和不稳定性的差异,提出一种基于时移多尺度等概率符号化样本熵(TMESSE)的分析方法.在对7种典型时间序列进行分析的基础上,充分验证了所提方法的可行性与有效性;进而对垂直上升管内气液两相流压差波动时间序列展开深入分析.结果表明,TMESSE熵值分布趋势能够跨多尺度表征不同流型演化特性,TMESSE均值与复杂性指数联合分布可以在定性刻画不同条件下流动不稳定性之间差异的基础上,跨多尺度定量映射气液两相流动结构的综合不稳定程度. 展开更多
关键词 时移多尺度 符号化 样本熵 两相流 动态特性
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抽样情况下复杂LDoS攻击检测方法研究
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作者 徐一凡 程光 周余阳 《信息网络安全》 北大核心 2026年第1期79-90,共12页
低速率拒绝服务(LDoS)攻击借助网络协议的自适应机制缺陷,以合法方式致使网络自适应机制失效,显著降低带宽利用率和服务质量。因此,LDoS攻击的高隐蔽性和强破坏性使其成为网络安全领域的重要研究课题。针对复杂LDoS攻击在多网络层次中... 低速率拒绝服务(LDoS)攻击借助网络协议的自适应机制缺陷,以合法方式致使网络自适应机制失效,显著降低带宽利用率和服务质量。因此,LDoS攻击的高隐蔽性和强破坏性使其成为网络安全领域的重要研究课题。针对复杂LDoS攻击在多网络层次中的隐蔽性及传统检测方法在抽样场景下的局限性,文章提出一种基于HLD-Sketch的LDoS攻击检测方法。文章涵盖在抽样情况下传输层LDoS攻击、应用层LDoS攻击及混合层次攻击场景。首先,通过改进的CM-Sketch结构实现动态流长估计,基于流长自适应调整抽样概率,优先对短流实施细粒度采样,减少长流背景噪声对攻击特征提取的干扰;其次,利用CM-Sketch的轻量级特性,在抽样流量中高效提取多维时序统计特征,包括流速率、上下行数据包个数及端口散布值等特征;最后,采用机器学习分类器对传输层、应用层及混合攻击进行层次化检测。实验结果表明,文章方法在3%的抽样率以及在混合攻击场景中,6 s内的检测准确率可以达到99.94%。该方法为高速网络环境下多维度LDoS攻击的实时检测提供了轻量化解决方案,尤其适用于大规模流量环境中的资源受限场景。 展开更多
关键词 低速率拒绝服务攻击 SKETCH 动态流抽样 多维时序特征 轻量化检测
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火星探测器发动机羽流高速冲击下的火壤侵蚀特性
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作者 周炳康 朱阳 +1 位作者 杨志 黄生洪 《宇航学报》 北大核心 2026年第2期426-435,共10页
针对火星探测任务中着陆器发动机出口高速羽流与火壤相互干扰的复杂流动问题,采用数值模拟方法,研究了天问一号着陆器高度对火壤侵蚀坑形态的影响规律。建立了一套考虑高速羽流、气固两相流和固体颗粒沉积的可压缩双流体模拟方法和程序... 针对火星探测任务中着陆器发动机出口高速羽流与火壤相互干扰的复杂流动问题,采用数值模拟方法,研究了天问一号着陆器高度对火壤侵蚀坑形态的影响规律。建立了一套考虑高速羽流、气固两相流和固体颗粒沉积的可压缩双流体模拟方法和程序,将计算结果与已有文献测算结果进行对比,结果表明所建立的算法可靠。基于所发展的算法,分析了羽流结构、气动参数、火尘扩散特性随着陆器高度的演化过程,阐明了羽流扩散范围增大、火壤上方压力降低是诱导侵蚀坑宽度增大而深度降低的原因。进而建立了侵蚀坑形态的工程预测模型,可用于指导火星探测器软着陆、火星取样等任务的方案设计。 展开更多
关键词 深空探测 火星取样 变推力发动机 高速羽流 气固两相流
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流动注射化学发光法测定环境水样中邻苯二酚的实验分析
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作者 王清清 赵培杏 《环境科学导刊》 2026年第1期86-90,共5页
采用文献研究法总结了流动注射化学发光法的基本原理,此方法具有分析速度快、检测精密度高、检测过程自动化、检测过程噪音小、检测成本低等技术特征,并通过实验分析了流动注射化学发光法测定邻苯二酚的过程。结果表明,在鲁米诺-六氰铁... 采用文献研究法总结了流动注射化学发光法的基本原理,此方法具有分析速度快、检测精密度高、检测过程自动化、检测过程噪音小、检测成本低等技术特征,并通过实验分析了流动注射化学发光法测定邻苯二酚的过程。结果表明,在鲁米诺-六氰铁酸钾化学发光体系中加入纳米银,能增强化学发光强度,邻苯二酚检测的线性范围在5.0×10^(-5)~1.0×10^(-2) mg/L,检出限为4.8×10^(-5) mg/L,连续测定8.0×10^(-4) mg/L邻苯二酚时偏差仅为2.3%,能满足环境水样中邻苯二酚的高精度检测需求,证实了流动注射化学发光法在水环境检测方面的适用性。 展开更多
关键词 流动注射 化学发光 水样检测 邻苯二酚
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