Miller定理的推论及其在小信号负反馈放大器分析中的应用     

滕军 《成都信息工程学院学报》1988,(2)

本文对电路分析理论中的Miller对定理进行了新的延拓,推导出的另外三个推论使得Miller,定理的应用范围大大地扩展了,它不仅适用于并——并相连的二端对网络分析,而且还适用于串——串相连、并——串相连及串——并相连的二端对网络分析,从而使常规二端对网络的分析更加简化了。从给出的应用举例分析可知,这些推论用于小信号负反馈放大器的分析之中尤其简便。  相似文献   

基于低压核磁共振(LF-NMR)技术对东海带鱼(Trichiurus lepturus)保鲜品质及水分迁移特性的研究     

周卓颖  谢超  俞群娣  张家玮  郑霖波  郑炜  叶常青 《海洋与湖沼》2022,53(2):440-447

为探究东海带鱼(Trichiurus lepturus)在低压核磁共振(LF-NMR)技术下的品质变化及水分迁移特性,以挥发性盐基氮(TVB-N)含量、pH、水分含量为指标,并分析NMR横向弛豫时间T₂反演谱图和MRI成像,研究不同电场强度(DY₁~DY₄分别为0,2,2.5,3kV/m)对带鱼内部水分迁移及品质的影响。分析TVB-N数据发现,DY₃(E=2.5kV/m)、DY₄(E=3kV/m)在贮藏后期表现出更佳的保鲜优势。在0~40d贮藏期内,不同电场强度条件下的带鱼pH值均呈先降后升趋势。电场的添加能降低自由水的流动性,抑制微生物生长,减少带鱼体内水分流失。分析NMR横向弛豫时间T₂反演谱图发现,T₂₁、T₂₂、T₂₃峰面积均有不同程度减小,其中T₂₂信号幅度变化最大,表明电场的添加能改变带鱼体内水分迁移路径,维持较高的水分含量,增加带鱼持水性和保水性。MRI成像图表明在贮藏期间,电场处理后带鱼水分保有率得到了提升,保鲜效果优于未施加电场带鱼,且电场强度越大,体外迁移水分越少。实验表明低压核磁共振(LF-NMR)技术对东海带鱼具有良好的保鲜效果,对低压核磁共振(LF-NMR)技术的保鲜应用提供一定的理论指导作用。<  相似文献   

大气CO2浓度非均匀分布及其对地表升温影响的研究进展与展望     

张帆  宣鑫  邓祥征 《地球信息科学学报》2021,23(8):1362-1371

在气候变化和全球治理挑战日益严峻的背景下,CO₂排放及代价评估日益受到学术界和决策者的关注。当前全球范围包括联合国政府间气候变化专门委员会（IPCC）评估在内的几乎所有研究都是基于全球平均CO₂浓度来驱动气候模式的,但基于全球CO₂平均分布设定开展模拟影响评估在学术界多有争议。首先,综述了大气CO₂非均匀分布的证据,评述了大气CO₂浓度非均匀分布与地表升温过程的互馈机制。其次,从自然和人为2个维度,梳理了大气CO₂浓度非均匀分布形成的原因,并评估了其对地表升温的影响。最后,评述了当前大气CO₂浓度非均匀分布研究中存在的问题,进一步展望了其发展趋势,为把握全球与区域碳排放现状及气候变化影响提供科学判据。  相似文献   

Feedback Concept in the Ore-forming Systems     

Jamshid Shahabpour 《Resource Geology》2010,60(1):109-115

Feedback, one of the most fundamental processes existing in nature, is present in almost all dynamic systems. Feedback concepts have been utilized almost exclusively by engineers. Nevertheless, this theory is applicable to formulating and solving problems in geology, particularly in the ore-forming systems. Feedback is distinctly operative in the generation of two groups of mineral deposits: (i) Mineral deposits showing rhythmic structures/textures, such as layered chromite deposits, re-opened veins with banded structure/texture, Mississippi Valley-type deposits with alternate bands/crusts of barite and galena, proximal volcanogenic massive sulfide deposits with mineralized layers of breccia clasts, and banded iron formations with alternate silica and magnetite and/or hematite bands, and (ii) mineral deposits lacking visible rhythmic structures/textures, but showing evidence of rhythmic process(es), such as in porphyry base metal deposits. There is an alternation of positive and negative feedback mechanisms in the ore-forming systems discussed here, which implies the involvement of feedback loops of negative sign.  相似文献   

Nonlinear coherent four‐wave interaction in space plasma     

A.V. Volosevich  C.‐V. Meister 《Astronomische Nachrichten》2000,321(4):263-272

According to a widespread point of view, intensive electrostatic structures in the E‐region of the auroral ionosphere can be a consequence of the excitation of the modified two‐stream or Farley‐Buneman (FB) plasma turbulence. But in spite of the successes of the theoretical and experimental research of the auroral radar scattering, it is impossible to explain the existence of auroral echoes with large aspect angles (> 2 deg.), the wave propagation perpendicular to the electron drift velocity and wave scales less than 1 m. In this paper the coherent nonlinear interactions of three and four electrostatic FB‐waves are considered analytically and numerically. The evolution of the nonlinear waves is described by a system of magnetohydrodynamic equations. 1) It is shown that the interaction of three and four coherent waves is the main physical mechanism which leads to the saturation of the FB‐instability. 2) If no dissipative and dispersive effects occur, an explosive instability may be excited. 3) The main result of the interaction of coherent waves is the generation of nonlinear waves and nonlinear structures when the waves are damped linearly and propagate perpendicular to the electron drift velocity. This region corresponds to large aspect angles of the small‐scale waves. 4) Further, the wave interaction causes a nonlinear stabilization of the growth of the high‐frequency waves and a formation of local density structures of the charged particles. The results of the numerical models allow to analyse the possibility of scenarios of the two‐stream plasma instability in the collisional auroral E‐region.  相似文献