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201.
建立了考虑空间效应的无质量基础-地基-结构相互作用模型,将模型简化为三个自由度体系,得到了考虑结构水平侧移和扭转位移相耦合的振动方程,用多尺度法研究了体系在强激励下的超谐共振和亚谐共振行为,通过算例分析得到了一些不同于线性体系的结论,为结构非线性分析提供了更深刻的理论依据。 相似文献
202.
S. Ferraz-Mello 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):275-289
Explicit construction of the solutions of the Hamiltonian system given by H = H
0(J) – A(J) cos (ideal resonance problem), two orders of approximation beyond the well-known pendulum approximation. The given solutions are valid for libration amplitudes of order
. The procedure used is extended to allow the construction of the solutions of Hamiltonians with perturbations involving two degrees of freedom; the post-pendulum solution of an example of this kind is constructed. 相似文献
203.
204.
小肝癌的MR诊断:几种序列FMPPGR动态增强及延迟扫描的特点刘爱莲,郎志谨,袁越,傅维利大连医科大学附属一院放射科,116011大连市友谊医院外科摘要:本文总结了36例经病理及临床证实的小肝癌的MR征象,探讨了小肝癌的T1MI,T2WI抑脂SE序列... 相似文献
205.
Electron spin resonance (ESR) is evaluated as a method to study the thermal degradation of sedimentary organic matter which consists mainly of kerogen. Whole rock and separated kerogen samples were pyrolysed stepwise (ambient to 700°C at 50°C increments), extracted and analysed for elemental composition and ESR spectra at each step. Whole rock samples give rise to complex spectra which include those of paramagnetic metals and are therefore unsuitable in most cases for this purpose.The ESR parameters g value, ΔH and Ng differ for different types of immature organic matter. An increase in Ng,shift of g value to 2.0026–2.0028 and reduction in h are the main trends during pyrolysis and in natural heating of sedimentary organic matter.The peak generations of liquid and gaseous hydrocarbons coincide with maxima of free radical density. ESR spectroscopy in combination with complementary geochemical characterization of the sedimentary organic matter can serve to indicate maturity with respect to peak oil-gas generation. 相似文献
206.
A cryogenic system for the airborne and ground based sampling of ambient radicals by matrix isolation is described. The trapped radicals, e.g., NO2 and RO2, are analyzed by ESR. The technique has been improved, mainly by addition of water vapor to the sampled air, to yield a collection efficiency of (90±10)% and a lower detection limit of about 20 ppt, but it still does not distinguish between the different RO2. Careful calibration reduced the measurement error (1 ) to ±10% for NO2 and ±15% for HO2. Two diurnal variations of RO2 and NO2 at ground level and vertical profiles in the lower troposphere are presented. 相似文献
207.
13C- and 1H-NMR spectra were obtained for humic substances isolated from a coastal marine environment and also for the intracellular and extracellular extracts of a marine diatom. Phaeodactylum tricornutum Bohlin. Highly branched alkyl chains constitute a large proportion of the structure of the marine humic material, whereas aromatic components are less important. Carbohydrate-type materials, possibly uronic acids, are also present in appreciable amounts. Furans (derived from carbohydrates). pyrroles and nitriles (derived from proteins, nucleic acids and/or tetrapyrroles) and phenols and methylphenols (non-lignin derived) are pyrolysis products derived from pyrolysis-gas chromatography-mass spectrometry of the extracts. The results indicate the similarities in chemical structure of P. tricornutum exudate and dissolved marine humic material. 相似文献
208.
A study has been made of solid and solution electron paramagnetic resonance (EPR) spectra of humic acids from different horizons in a podzolic soil. Hyperfine splitting was observed in the solution spectra of humic acids from all horizons and depended on the strength of alkali and the period of dissolution. The upper organic horizons L, F and O1 contained humic acids with some spectral characteristics in common with lignin. Humic acid from the lower horizons showed different spectra. At least 5 different radical signals were present. 相似文献
209.
D. Mihelcic D. Klemp P. Müsgen H. W. Pätz A. Volz-Thomas 《Journal of Atmospheric Chemistry》1993,16(4):313-335
We present simultaneous field measurements of NO3 and peroxy radicals made at night in a forested area (Schauinsland, Black Forest, 48° N, 8° N, 1150 ASL), together with measurements of CO, O3, NO
x
, NO
y
, and hydrocarbons, as well as meteorological parameters. NO2, NO3, HO2, and (RO2) radicals are detected with matrix isolation/electron spin resonance (MIESR). NO3 and HO2 were found to be present in the range of 0–10 ppt, whilst organic peroxy radicals reached concentrations of 40 ppt. NO3, RO2, and HO2 exhibited strong variations, in contrast to the almost constant values of the longer lived trace gases. The data suggest anticorrelation between NO3 and RO2 radical concentrations at night.The measured trace gas set allows the calculation of NO3 and peroxy radical concentrations, using a chemical box model. From these simulations, it is concluded that the observed anthropogenic hydrocarbons are not sufficient to explain the observed RO2 concentrations. The chemical budget of both NO3 and RO2 radicals can be understood if emissions of monoterpenes are included. The measured HO2 can only be explained by the model, when NO concentrations at night of around 5 ppt are assumed to be present. The presence of HO2 radicals implies the presence of hydroxyl radicals at night in concentrations of up to 105 cm–3. 相似文献
210.
卫星热红外温度异常点是天线附近背景噪声与地球信息随机共振的结果。温度异常点是卫星热红外图像新的信息源,温度异常点在利用卫星热红外信息和研究地球脉搏方面可以发挥重要作用。卫星热红外温度异常点的发现开拓了随机共振应用的新领域。 相似文献