共查询到20条相似文献,搜索用时 62 毫秒
1.
"牛顿由于发现了万有引力定律而创立了科学的天文学,由于进行了光的分解而创立了科学的光学,由于建立了二项式定律和无穷理论而创立了科学的数学,由于认识了力的本性而创立了科学的力学."恩格斯的这段话很好地总结了牛顿的科学业绩.为了纪念牛顿在科学上的伟大建树,许多国家发行了多枚一套的邮票. 相似文献
2.
3.
4.
5.
6.
7.
本文系统地讨论了大统一理论的来龙去脉。回顾了大统一理论的发展历史,讨论了其发展现状及存在问题,指出了进一步发展的方向。本文重点介绍了SU(5)和SO(10)两个模型,讨论了Higgs场、规范等级、渐近自由、重正化等问题。文章进而讨论了一些有趣问题,比如提供了对宇宙重子起源的解释、计算了质子衰变寿命、论述了B-L是否守恒以及讨论了中子和中微子可能有的振荡现象等。 相似文献
8.
本文系统地讨论了大统一理论的来龙去脉。回顾了大统一理论的发展历史,讨论了其发展现状及存在问题,指出了进一步发展的方向。本文重点介绍了SU(5)和SO(10)两个模型,讨论了Higgs场、规范等级、渐近自由、重正化等问题。文章进而讨论了一些有趣问题,比如提供了对宇宙重子起源的解释、计算了质子衰变寿命、论述了B-L是否守恒以及讨论了中子和中微子可能有的振荡现象等。 相似文献
9.
采用控制环量方法设计了一单级涡轮。该方法打破了传统的设计规律,为验证该方法的可靠性进行了模型试验。在宽广的范围内测定了总特性;在设计点附近作了沿叶高效率分布及动叶进、出口速度三角形的测定。本文给出了主要试验结果并作了简要分析。结果表明基本上达到了设计要求,控制环量设计的主要特征得到了验证,该方法基本可行。 相似文献
10.
体内(in Vivo)NMR研究 总被引:1,自引:1,他引:0
本文综述了体内(in Vivo)核磁共振波谱技术的目前概况,简要介绍了这一技术的基本原理。对空间定位技术进行了重点评述,并给出了分类表。同时讨论了化学位移对空间定位精确的影响,介绍了提高定位精确度的实验方法。列举了空间定位波谱技术在生命科学研究中的应用,给出了大量的参考文献。 相似文献
11.
Nordmeyer-Massner JA De Zanche N Pruessmann KP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,210(1):7-15
A method for characterizing the noise figure of preamplifiers at NMR frequencies is presented. The noise figure of preamplifiers as used for NMR and MRI detection varies with source impedance and with the operating frequency. Therefore, to characterize a preamplifier's noise behavior, it is necessary to perform noise measurements at the targeted frequency while varying the source impedance with high accuracy. At high radiofrequencies, such impedance variation is typically achieved with transmission-line tuners, which however are not available for the relatively low range of typical NMR frequencies. To solve this issue, this work describes an alternative approach that relies on lumped-element circuits for impedance manipulation. It is shown that, using a fixed-impedance noise source and suitable ENR correction, this approach permits noise figure characterization for NMR and MRI purposes. The method is demonstrated for two preamplifiers, a generic BF998 MOSFET module and an MRI-dedicated, integrated preamplifier, which were both studied at 128MHz, i.e., at the Larmor frequency of protons at 3 Tesla. Variations in noise figure of 0.01dB or less over repeated measurements reflect high precision even for small noise figures in the order of 0.4dB. For validation, large sets of measured noise figure values are shown to be consistent with the general noise-parameter model of linear two-ports. Finally, the measured noise characteristics of the superior preamplifier are illustrated by SNR measurements in MRI data. 相似文献
12.
An interferometric technique to measure a nontransparent window plate using visible light is proposed. Using this technique,
the relative surface figure of one surface with respect to another can be measured. The relative surface figure also includes
the parallel of both surfaces of the window plate. The optical performance of a nontransparent window plate as an optical
component can be evaluated accurately without using infrared light sources if the relative surface figure of the plate is
measured. 相似文献
13.
14.
二维三维简谐振动的合成是个复杂且抽象的物理问题,使用Python的3D模块Vpython对简谐振动合成进行了可视化模拟,形象直观地展示了简谐振动合成所形成的李萨如图形,并简单讨论了李萨如图形与频率相位的关系. 相似文献
15.
16.
17.
18.
19.
本文讨论了棱镜表面误差(主要是局部误差)对波面面形的影响。给出了计算公式及其证明。并以直角棱镜和列曼棱镜为例进行了计算和讨论 相似文献