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991.
The configurational sequences of 1,2-unit in a series of hydrogenated syndiotactic 1,2-polybutadienes were investigated in relation to the sequence distribution of 1,2- and 1,4-units. The signals at 10.20–10.94 ppm were assigned to the methyl carbons in the isolated 1,2-unit, the 1,2-1,2 dyad sequence flanked by 1,4-unit, and the 1,2-1,2-1,2 triad sequence, in order of increasing magnetic field. The splittings due to the configurational sequences were observed in the signals, reflecting the dyad and triad sequences of the 1,2-unit, which were assigned by considering the relative intensity of the signals and also the chemical shifts of model polymers. 相似文献
992.
In industrial motor drive systems such as industrial plants and industrial robots, a torsional vibration often is generated because of the elastic elements in torque transmission. This vibration makes it difficult to achieve quick responses of speed and may result in damage to the plant. Such systems simply are modeled as a two mass system. The shaft torque feedback system with the disturbance observer, which is called “resonance ratio control,” is proposed to suppress the vibration for the two-mass system. In this paper, the design of controller gains in the shaft torque feedback system is examined considering not only the control performance such as the vibration suppression and dynamic responses, but also the robust stability against the noise and the model uncertainties. This paper shows the validity of the control system and the examinations by several experiments. 相似文献
993.
CaiYan-Huang ZhuZhi-Yuan 《核技术(英文版)》1998,9(4):231-234
A microscopic semiclassical Vlasov equation approach is used to investigate the dipole giant resonances of spherical cluster Na14.The main strength distributions of collective response function are located around 2eV region,with a fair agreement with the experiment ones.The results are quite independent of the choice of parameters of the mean field. 相似文献
994.
Chemical preparation, crystal structure, calorimetric and spectroscopic investigations (IR and RMN) are given for a new non-centrosymmetric organic-cation dihydrogen phosphate-arsenate [H2(C4H10N2)][H2(As, P)O4]2. This compound is triclinic P1 with the following unit-cell parameters: a = 7.082(2) Å, b = 7.796(1) Å, c = 12.05(3) Å, α = 95.37(2)°, β = 98.38(3)°, γ = 62.98(1)°, Z = 2, V = 586.2(1) Å3 and Dx = 1.836 g cm−3. The crystal structure has been solved and refined to R = 0.03 using 2328 independent reflections. The structure can be described as infinite (H2XO)n chains spreading parallel to the b direction. These chains are themselves interconnected by a set of NH?O hydrogen bonds generated by the organic entities, alternating with the chains. Solid-state 13C, 15N and 31P MAS NMR spectroscopies are in agreement with the X-ray structure. 相似文献
995.
A new crystal of 2-amino-3-methylpyridinium dihydrogenomonoarsenate has been prepared and characterized by X-ray crystallography, thermal analysis and spectroscopic studies. This compound crystallizes in the triclinic space group with a = 7.2689 (2) Å, b = 8.0975 (2) Å, c = 8.3969 (4) Å, α = 77.09 (3)°, β = 79.20 (3)°, γ = 88.16 (2)°, V = 473.19 (3) Å3, Z = 2. The crystal structure was solved and refined to R = 0.027 with 3375 independent reflections. The atomic arrangement can be described as (H2AsO4−)n polymeric chains anchoring the 2-amino-3-methylpyridinium cations through short hydrogen bonds. All the ring atoms of the organic entity are coplanar. The exocyclic N atom is an electron receiving center, which is consistent with features of imino resonance evidenced by bond lengths and angles. Solid-state 13C and 15N CP-MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of carbons and nitrogen to the independent crystallographic sites. 相似文献
996.
Generalized system function analysis of resonant behavior of electromagnetic open systems 总被引:1,自引:0,他引:1
LI Long LIU Haixia SHI Yan & LIANG Changhong . National Laboratory of Antennas Microwave Technology Xidian University Xi’an China . Institute of Signal Data Processing Xidian University Xi’an China 《中国科学F辑(英文版)》2005,48(5):615-631
1 Introduction A severe challenge for the electromagnetic compatibility (EMC) of a complex elec-tromagnetic system has been given with the increasingly complicated electromagnetic environment and dense electric devices. In particular, there are a lot of various antennas and scattering bodies on the large electromagnetic objects, such as airplane, ship, car, etc., and the interaction and mutual coupling between antennas and scatterers become more and more severe, which sometimes gives rise to … 相似文献
997.
Liu?Yadong Zhou?Zongtan Hu?Dewen?Email author Yan?Lirong Tan?Changlian Wu?Daxing Yao?Shuqiao 《中国科学F辑(英文版)》2005,48(2):151-160
1 Introduction Functional magnetic resonance imaging (fMRI) is a non-invasive brain imaging technique which has been utilized in brain function researches since the early 1990s[1]. However, it is often difficult to do analysis in fMRI data because of the low signal to noise ratio (SNR) (about 2%—4% with 1.5T magnetic field strength) and the delay within the true neural activity and the stimuli-induced signal dynamic responses. The prevalent methods applied to fMRI data could be divided i… 相似文献
998.
变压器局部放电试验“大脉冲”的消除 总被引:3,自引:0,他引:3
通过实例,介绍了变压器局部放电试验出现的“大脉冲”现象及消除过程,并提出了大脉冲产生的三大原因——绕组局部谐振、参数匹配及铁心剩磁。 相似文献
999.
1000.
The woodchuck is one of the only lab animal models of chronic viral hepatitis infection and the development of hepatocellular
carcinoma. Using this model, changes in tissue energetics in the liver due to the development of hepatocellular carcinoma
can be monitored by repeated magnetic resonance imaging and localized phosphorus spectroscopy. Age- and sex-matched control
(n=5) and chronically infected (n=5) adult woodchucks were imaged four times in a six-month period in a 7-T horizontal-bore magnet. Using a custom-built doubly
tunable quadrature volume coil, sagittal and axial FLASH images (128×128, slice thickness = 5 mm, TR/TE=1000/4.1, 8 averages)
were acquired to locate the largest portion of the liver with the least amount of signal contamination from surrounding abdominal
muscle. Two-dimensional 31P chemical-shift imaging (2D-CSI) was acquired (16×16 data matrix, 24×24×2 cm3, 1024 data points, 16 averages) for all animals. The extent of liver injury was determined using serum gamma glutamyltransferase
(GGT). The livers of infected woodchucks showed a significant increase (p=0.01) in phosphomonoesters (PME):β-adenosine triphosphate (NTP). Chronically infected woodchucks had higher levels of serum GGT compared to uninfected woodchucks
(p=0.002). An increase in the PME:β-NTP ratio indicates cellular proliferation within the malignant tumor. 相似文献