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高空电磁脉冲(HEMP)是一种能够通过场线或孔缝耦合到各种电子电气设备内部的暂态电磁波,该电磁能量会对正常工作的电子电气设备造成干扰甚至永久性损伤。为了确保关键部门的安保系统能够在电磁脉冲环境下正常工作,有必要针对安保系统进行电磁脉冲效应试验,分析该种类型系统在电磁脉冲环境下的薄弱环节和生存能力。针对核安保典型系统拓扑结构,搭建了电磁脉冲辐照试验和脉冲电流注入试验平台,并通过试验获取了报警分机、门禁主机、报警中心端等核安保典型系统关键部件的电磁脉冲效应阈值和效应现象。进一步结合各部件的电路原理分析了关键部件的失效机理,总结了核安保典型系统的薄弱环节,为后续安保系统的防护加固设计提供数据支撑。 相似文献
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为研究油气管道数据采集与监视控制(SCADA)系统的电磁脉冲易损性和防护措施,搭建了具有数据采集、数据通信、远程控制等功能的典型油气管道SCADA模拟实验系统,进行了峰值场强最高为50kV/m的典型高功率电磁波形作用下的电磁脉冲效应试验。利用实验数据,对目前油气管道SCADA系统面临强电磁脉冲威胁的机理和规律进行了初步分析,发现电磁脉冲对油气管道SCADA系统具有一定程度的威胁,获得了效应现象和效应阈值结果。 相似文献
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《物理学报》2021,(16)
系统电磁脉冲难以有效屏蔽,会显著影响低轨航天器等重要装置和基础设施的性能.为了评估二次电子对系统电磁脉冲的影响,本文基于粒子云网格方法,建立了三维非稳态系统电磁脉冲模型,计算并比较了不同电流密度、金属材料等条件下,两种典型结构的电磁脉冲响应.结果表明,在计算模型中忽略二次电子发射会使部分位置的峰值电场强度被低估2—3倍,电场响应持续的时间也会被低估10%以上.在各类二次电子中,背散射电子对系统电磁脉冲的影响占主导,而真二次电子的作用约为背散射电子的1/5.二次电子发射对系统电磁脉冲的影响随着系统所用材料原子序数的增高而加大.空间电荷效应较强时,二次电子才会对腔体外系统电磁脉冲产生影响.本研究有助于更好地通过数值模拟来获得具体装置在强辐射环境下的系统电磁脉冲响应. 相似文献
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从能量分布和测量有效性的观点出发,提出了强电磁脉冲的能量有效带宽和动态范围有效带宽的概念。针对IEC61000-4-4,MIL-STD-464,IEC61000-4-2,IEC61312-1等标准规定的核电磁脉冲(NEMP)、雷电电磁脉冲(LEMP)、静电放电电磁脉冲(ESDEMP)等强电磁脉冲,分别计算了它们的能量有效带宽和动态范围有效带宽。通过分析,得知在一定的范围内,上述强电磁脉冲上升时间的变化对两种有效带宽的影响并不明显,在此基础上,确定了它们的测量带宽。计算结果为NEMP,ESD EMP及LEMP的60 dB有效带宽分别是371,786,1 233 MHz与96 kHz;99%能量有效带宽分别是46,95,183 MHz与15 kHz;不失真测量所需的带宽分别是152,307,916 MHz和95 kHz。 相似文献
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MRI of normal and abnormal duodenum using Half-Fourier Single-Shot RARE and gadolinium-enhanced spoiled gradient echo sequences. 总被引:1,自引:0,他引:1
The objective of this research was two-fold: First, to describe the normal and abnormal MR appearances of the duodenum using combined Half-Fourier Acquisition Single Shot RARE (HASTE) and gadolinium-enhanced standard and fat suppressed spoiled gradient echo (SGE) sequences. The second objective was to assess the ability of these combined sequences to detect and characterize duodenal diseases. MR examinations were performed on fifty consecutive patients with no clinical history of duodenal diseases, who were 1) imaged with HASTE and gadolinium-enhanced standard and fat suppressed SGE sequences and 2) referred to MR examination for reasons other than duodenal diseases, and were reviewed retrospectively to determine the normal MR appearances of the duodenum. A second population of patients with abnormal duodenum who were imaged with the same MR sequences were included in the second part of this study. This population was composed of 20 consecutive patients with subsequently proven duodenal abnormalities, including: malrotation (2), diverticula (4), intussusception (1), sprue (1), polyps (2), neurofibroma (1), lymphoma (1), Zollinger Ellison syndrome (1), metastatic disease (1), Crohn's disease (1), and wall thickening and duodenitis (5). Normal measurements of the duodenum are described. Abnormalities of wall thickness and duodenal masses required combined HASTE and gadolinium-enhanced SGE images to evaluate well. Abnormalities of the bowel lumen (e.g., diverticula and intussusception), and developmental variants (e.g., malrotation), were sufficiently visualized on HASTE images alone. Bowel inflammation was best shown on gadolinium-enhanced fat suppressed SGE images. HASTE and gadolinium-enhanced fat suppressed SGE sequences are complementary techniques for the demonstration of normal and abnormal duodenum. The combined use of both sequences allows evaluation of different aspects of bowel diseases; abnormalities of position, lumen, and contents are well shown on HASTE, while inflammation is best shown on gadolinium enhanced fat suppressed SGE, and wall thickening and masses are best evaluated with the combined use of both techniques. 相似文献
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Evaluation of Crohn's disease using half-fourier RARE and gadolinium-enhanced SGE sequences: initial results 总被引:4,自引:0,他引:4
To assess the bowel changes in Crohn's disease, 11 consecutive patients underwent magnetic resonance imaging (MRI) study using T(2)-weighted half-Fourier rapid acquisition with relaxation enhancement (RARE) and gadolinium-enhanced standard and fat suppressed spoiled gradient echo (SGE) sequences. Comparison was made between MR findings of disease extent, severity, and complications and clinical data, endoscopic findings and/or surgical specimens in all patients. We found that the half-Fourier RARE images showed bowel wall thickening, dilatation of bowel and bowel obstruction well in all patients, however severity of bowel disease could not be determined as the signal intensity of diseased bowel was comparable to normal bowel in 10/11 patients. Gadolinium-enhanced fat suppressed SGE demonstrated variations of mural enhancement that correlated well with extent of disease severity in 10/11 patients. Complications such as intraperitoneal (i. p.) abscess (2 patients), gastric outlet obstruction (1 patient), bowel obstruction (2 patients), and fistula formation (3 patient), were accurately shown. We conclude that T(2)-weighted half-Fourier RARE and gadolinium-enhanced fat suppressed SGE sequences are complementary techniques that possess different imaging features that are of value for assessing bowel changes in Crohn's disease. 相似文献
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Nalini Joshi 《Letters in Mathematical Physics》1990,20(4):261-270
The (n+1)-dimensional differential geometric generalization of the sine-Gordon equation (SGE) given by Tenenblat and Terng is solved explicitly in the casen=2 to obtain a one-soliton solution. The solution yields the soliton solution of the (1+1)-dimensional SGE in the limit as one of the three independent variables approaches infinity. However, more than one variable plays the role of time in these limits. 相似文献
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Field equations of the S2 sigma model (“the A3 model”) with spontaneously broken Z(2) symmetry are presented for (D+1)-dimensional space–time. The A3 model is an extension of the sine-Gordon equation (SGE) and supports kink-like U(1) charged solitons which are a generalization of neutral solitons of the SGE. The natural question arises — is the A3 model completely integrable in (1+1)-dimensional space–time? The Lorentz-invariant scalar A3 field can be viewed as a promising alternative to the Higgs field. 相似文献
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N L Kelekis R C Semelka S Worawattanakul P L Molina M A Mauro 《Magnetic resonance imaging》1999,17(5):641-651
This study evaluates a combined protocol consisting of breath hold immediate post gadolinium 3-D gradient echo MR angiography and blood pool phase gadolinium-enhanced breath hold 2-D fat-suppressed spoiled gradient echo (SGE) sequences in the examination of diseases of the abdominal aorta and iliac vessels. Thirty-two patients with suspected disease of the abdominal aorta, major aortic branches, or iliac vessels underwent MR angiographic study from January 1996 to January 1997. Examinations were performed on a 1.5 T MR imager using 2-D axial SGE, coronal 3-D fast imaging in steady state precession (3-D FISP) following bolus administration of 40 mL of gadolinium, and axial and coronal blood pool phase gadolinium-enhanced fat-suppressed SGE. Post-processed data, including 3-D reconstructions using maximum intensity projection (MIP), targeted MIP, and multiplanar reconstruction (MPR) were evaluated. MR findings in all patients were correlated as follows: surgery (13 patients), angiography (11 patients), contrast enhanced CT (3 patients), non-contrast enhanced CT (1 patient), color doppler US (2 patients), and previous MR study (2 patients). MR findings correlated closely with findings at surgery or other imaging studies in 31 of 32 patients. One patient had renal artery occlusion that was misinterpreted as mild stenosis. The following vascular diseases were present: aneurysm disease [10 patients: aortic aneurysm (8 patients), inflammatory aneurysm (2 patients)], thoracoabdominal aortic dissection (2 patients), arteriovenous fistula (1 patient), stenoses and/or occlusion of the abdominal aorta, major aortic branches and iliac vessels [12 patients: stenoses and/or occlusion of the abdominal aorta with stenoses of the iliac vessels (9 patients), renal artery stenosis (2 patients), occlusion of the abdominal aorta (1 patient)], and occluded artery to pancreatic transplant artery (1 patient). Five patients had normal studies. The 3-D FISP technique accurately defined the luminal contours of vessels, allowing precise depiction of vessel stenosis (i.e., renal artery stenosis or common iliac artery stenosis) and clear demonstration of relationship of aortic branch vessels (i.e., renal arteries) to underlying aortic pathology (i.e., aortic aneurysm or dissection). Blood pool phase gadolinium-enhanced fat-suppressed SGE images were useful in the evaluation of the external surface of vessel walls, and providing accurate measurement of aneurysm diameter and other associated vascular entities (i.e., inflammatory aneurysm, left-sided IVC). Targeted MIP or MPR reconstruction were important for assessing stenoses of medium sized vessels such as renal arteries and branches of the iliac arteries, and for identifying accessory arteries. The combination of immediate post gadolinium 3-D FISP and blood pool phase gadolinium-enhanced fat-suppressed SGE is useful in the evaluation of the abdominal aorta, major aortic branches and iliac vessels. Immediate post gadolinium 3-D FISP images provides diagnostically useful information regarding vessel luminal contour, while blood pool phase gadolinium-enhanced fat-suppressed SGE provides ancillary information on the vessel wall and surrounding tissue. 相似文献
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The purpose of this study was to evaluate the appearance of infectious cholangitis on MRI. The MR images of 13 patients (9 women, 4 men; age range, 14-79 years) with clinically confirmed infectious cholangitis, who represent our complete 9.5 year experience with this entity, were retrospectively evaluated. All MR studies were performed at 1.5 T and included: in-phase and out-of-phase T(1)-weighted spoiled gradient echo (SGE), T(2)-weighted fat-suppressed echo train spin echo, single shot T(2)-weighted sequences, and serial postgadolinium T(1)-weighted SGE sequences without and with fat-suppression. The biliary ductal system was evaluated regarding presence of dilatation, stenosis, wall irregularities, wall thickening, and gadolinium enhancement of duct walls. The liver parenchyma was evaluated regarding focal signal abnormalities on precontrast and serial postgadolinium images. Biliary ductal dilatation was observed in 100% of patients. Mild to moderate thickening of bile duct walls combined with increased enhancement on postgadolinium images was observed in 92% of patients. The liver parenchyma showed periportal or wedge-shaped areas of hyperintense signal on T(2)-weighted images in 69% of patients. On T(1)-weighted images, 54% of patients showed areas of hypointense signal and 15% of patients showed wedge-shaped hyperintense areas. Areas with increased enhancement on immediate postgadolinium SGE were observed in 58% of patients, and in 42% of patients increased enhancement persisted on 2 min postgadolinium fat-suppressed images. Distinctive MRI findings on pre- and postgadolinium images are appreciated for infectious cholangitis. 相似文献
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接地设计是光电设备电磁兼容设计的重要组成部分,好的接地能够保护设备和人身的安全,保证光电设备正常可靠工作。地线造成电磁干扰的主要原因是它具有阻抗和感抗特性,这些特性在某些情况下会导致地环路干扰和公共阻抗耦合等电磁骚扰。从地线的特性出发分析地线干扰的成因,提出抑制地线干扰,提高电路电磁兼容性的方法。 相似文献