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71.
Symmetrical dynamics of peak current-mode and valley current-mode controlled switching dc-dc converters with ramp compensation 下载免费PDF全文
The discrete iterative map models of peak current-mode
(PCM) and valley current-mode (VCM) controlled buck converters, boost
converters, and buck--boost converters with ramp compensation are
established and their dynamical behaviours are investigated by using
the operation region, parameter space map, bifurcation diagram, and
Lyapunov exponent spectrum. The research results indicate that ramp
compensation extends the stable operation range of the PCM controlled
switching dc--dc converter to D>0.5 and that of the VCM controlled switching
dc--dc converter to D<0.5. Compared with PCM controlled switching
dc--dc converters with ramp compensation, VCM controlled
switching dc--dc converters with ramp compensation exhibit
interesting symmetrical dynamics. Experimental results are given to
verify the analysis results in this paper. 相似文献
73.
采用正电子湮没技术研究了NiTi合金在降温和升温过程中缺陷和电子密度随温度的变化.在降温过程中,当温度从295K降至225K时,合金的电子密度nb随温度的降低而下降,在225K时降至最小;随后,nb随温度的降低而升高.当温度从295K降至221K时,合金缺陷的开空间随温度的下降而升高,在221K时达到最大值;随后,缺陷的开空间随温度的下降而下降.在升温过程中,当温度从25K升至253K时,合金的电子密度nb随温度的升高而降低,并在253K时达到最小;当温度从253K升至295K时,合金电子密度nb随温度的升高而升高.在相变临界温度点Ms=222K,Mf=197.2K,As=237.5K,Af=255.5K附近,合金的电子密度nb及合金缺陷的开空间均有异常的变化. 相似文献
74.
We report on a theoretical study of the commensurability oscillations in a quasi-two-dimensional electron gas modulated by a unidirectional periodic potential and subject to tilted magnetic fields with a strong in-plane component. As a result of coupling of the in-plane field component and the confining potential in the finite-width quantum well, the originally circular cyclotron orbits become anisotropic and tilted out of the sample plane. A quasi-classical approach to the theory, that relates the magneto-resistance oscillations to the guiding-center drift, is extended to this case. 相似文献
75.
The paper introduces the preparation of floating TiO2/beads photocalyst attached to the hollow glass micro-beads surface by sol-gel technique using tetrabutyl titanate as material and the preparation of floating CoPcS/TiO2/beads by dip-coatig technique. The optimal factor of degradation of vegetable oil floating on water using CoPcS/TiO2/beads was studied. The result showed that the removal rate of vegetable oil floating on water can highly reach 90% at the optimal condition (acidity or neutrality, 375W medium-pressure mercury vapour lamp, illumination 2h-3h, lg CoPcS/TiO2/beads). The photocatalytic removal efficiency causing by CoPcS/TiO2/beads was increased rapidly by adding a trace amount of H2O2. 相似文献
76.
以焦脱镁叶绿酸-a甲酯(1)为起始原料, 通过E环保护和3-位乙烯基的氧化反应得到卟吩醛2, 与长链烷基溴化镁的Grignard反应将3-位甲酰基转化为1-羟长链烷基, 选用TPAP和N-甲基吗啉N-氧化物混合氧化剂对卟吩仲醇3的羟基进行氧化, 生成3-位烷酰基焦脱镁叶绿酸-a衍生物4, 再与长链烷基溴化镁进行Grignard反应, 得到亲核加成产物卟吩叔醇5和还原产物3; 以对甲苯磺酸催化, 卟吩醇3和5在干燥苯中回流脱水, 分别给出反式结构的3-位长链烷基单或者双取代的焦脱镁叶绿酸-a甲酯衍生物6和7. 所合成的叶绿酸衍生物均经UV, IR, 1H NMR及元素分析证明其结构. 相似文献
77.
Pu Su Zhao Ji Ming Xu Wei Guang Zhang Fang Fang Jian Lan Zhang 《Structural chemistry》2007,18(6):993-1000
The title compound of 3-p-methylphenyl-4-amino-1, 2, 4-triazole-5-thione was synthesized and characterized by elemental analysis, IR, electronic spectra,
and X-ray single crystal diffraction. Quantum chemical calculations of the structure, natural bond orbital, and thermodynamic
functions of the title compound were performed by using B3LYP/6-311G** and HF-6-311G** methods. Both the methods can well
simulate the molecular structure. Vibrational frequencies were predicted, assigned and compared with the experimental values,
and B3LYP/6-311G** method is superior to HF/6-311G** method to predict the vibrational frequencies. Electronic absorption
spectra calculated by B3LYP/6-311G** method have some red shifts compared with the experimental ones and natural bond orbitals
analyses indicate that the two absorption bands are mainly derived from the contribution of n → π* and π → π* transitions. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures
have been calculated, revealing the correlations between C
0
p,m
, S
0
m
, H
0
m
, and temperatures. 相似文献
78.
Ab initio calculations of the structure, atomic charges, natural bond orbital and thermodynamic functions have been performed at HF/6-311G** and B3LYP/6-311G** levels of theory for the title compound of 4-phenyl-1-(1-phenylethylidene) thiosemicarbazide. The calculated results show
that the sulfur atom and all of the nitrogen atoms have bigger negative charges and that they are the potential sites to react
with the metallic ions, which make the title compound a multidentate ligand. The coordination ability of the sulfur atom and
the nitrogen atom of C=N double bond increases with the increase of polarity of the solvent. Electronic absorption spectra
have been calculated by time-dependent density functional theory (TD-DFT) method. The calculation of the second-order optical
nonlinearity has also been carried out with the PM3 semi-empirical method, resulting in the molecular hyperpolarisability
is 5.477×10−30 esu. 相似文献
79.
We investigate a mechanism for cooling a lead based on a process that replaces hot electrons by cold ones. The central idea is that a double quantum dot with an inhomogeneous Zeeman splitting acts as energy filter for the transported electrons. The setup is such that hot electrons with spin up are removed, while cold electrons with spin down are added. The required non-equilibrium condition is provided by the capacitive coupling of one quantum dot to the shot noise of a strongly biased quantum point contact in the tunneling limit. Special attention is paid to the identification of an operating regime in which the net electrical current vanishes. 相似文献
80.
We have studied the electronic structure and magnetism of the single transitional metal element X=Sc, V, Cr, Mn, Fe, Ni, Cu-doped CoO systems by first-principles calculations. At X=Sc, Cr, Cu, the binding energy of the doped systems is lower than pure CoO, suggesting that these systems are energetically stable. In the Sc, V, Cr, Mn, Fe, Ni, Cu-doped 2×2×2 CoO supercells, the total magnetic moments are 3.03, 5.64, 6.80, 7.70, 6.93, 2.30 and 1.96 μB, respectively. At X=Cr and Fe, the doped CoO systems are half-metallic with a high spin polarization. The large magnetic moment and high spin polarization in the Cr and Fe-doped CoO are important for the design of the spintronic devices. 相似文献