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Search Results: 1 - 10 of 3354 matches for " Xiaoming Pang "
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2,3,4-Tri-O-acetyl-β-d-xylosyl 2,4-dichlorophenoxyacetate
Xiaoming Wang,Xinyuan Li,Yale Yin,Yanjun Pang
Acta Crystallographica Section E , 2008, DOI: 10.1107/s1600536808005837
Abstract: In the title compound, C19H20Cl2O10, the hexopyranosyl ring adopts a chair conformation. The four substituents are in equatorial positions. The molecules arelinked via C—H...O contacts along the a axis.
Magneto-structural coupling and harmonic lattice dynamics in CaFe$_2$As$_2$ probed by M?ssbauer spectroscopy
Zhiwei Li,Xiaoming Ma,Hua Pang,Fashen Li
Physics , 2010, DOI: 10.1088/0953-8984/23/25/255701
Abstract: In this paper we present detailed M\"ossbauer spectroscopy study of structural and magnetic properties of the undoped parent compound CaFe$_2$As$_2$ single crystal. By fitting the temperature dependence of the hyperfine magnetic field we show that the magneto-structural phase transition is clearly first-order in nature and we also deduced the compressibility of our sample to be $1.67\times10^{-2}\,GPa^{-1}$. Within the Landau's theory of phase transition, we further argue that the observed phase transition may stem from the strong magneto-structural coupling effect. Temperature dependence of the Lamb-M\"ossbauer factor show that the paramagnetic phase and the antiferromagnetic phase exhibit similar lattice dynamics in high frequency modes with very close Debye temperatures, $\Theta_D \sim$270\,K.
Charge redistribution at the antiferromagnetic phase transition in SrFeAsF compound
Zhiwei Li,Yang Fang,Xiaoming Ma,Hua Pang,Fashen Li
Physics , 2011, DOI: 10.1103/PhysRevB.84.134509
Abstract: The relationship between spin, electron, and crystal structure has been one of the foremost issues in understanding the superconducting mechanism since the discovery of iron-based high temperature superconductors. Here, we report M\"ossbauer and first-principles calculations studies of the parent compound SrFeAsF with the largest temperature gap ($\sim$50\,K) between the structural and antiferromagnetic (AFM) transitions. Our results reveal that the structural transition has little effect on the electronic structure of the compound SrFeAsF while the development of the AFM order induces a redistribution of the charges near the Fermi level.
Spin excitations in K$_{0.84}$Fe$_{1.99}$Se$_2$ superconductor as studied by M?ssbauer spectroscopy
Zhiwei Li,Xiaoming Ma,Hua Pang,Fashen Li
Physics , 2011, DOI: 10.1088/1674-1056/21/4/047601
Abstract: M\"ossbauer spectroscopy was used to probe the site specific information of the $K_{0.84}Fe_{1.99}Se_2$ superconductor. Possibility of coexistence of superconductivity and magnetism is discussed. A spin excitation gap, $\Delta E \approx$5\,meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field (HMF) at the iron site within the spin wave theory. Using a simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the iron-selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.
A M?ssbauer study of the magneto-structural coupling effect in SrFe$_2$As$_2$ and SrFeAsF
Zhiwei Li,Xiaoming Ma,Hua Pang,Fashen Li
Physics , 2011, DOI: 10.1007/s10751-011-0425-2
Abstract: In the present paper, we report a comparison study of SrFe$_2$As$_2$ and SrFeAsF using M\"ossbauer spectroscopy. The temperature dependence of the magnetic hyperfine field is fitted with a modified Bean-Rodbell model. The results give much smaller magnetic moment and magneto-structural coupling effect for SrFeAsF, which may be understood as due to different inter-layer properties of the two compounds.
An Overview on Piezoelectric Power Generation System for Electricity Generation  [PDF]
Xiaoming Sun
Journal of Power and Energy Engineering (JPEE) , 2017, DOI: 10.4236/jpee.2017.52002
Abstract: Coal, petroleum and natural gas will still be the basis of economic development for a long time. However, with a rapider consumption speed, these fossil fuels will be exhausted in the near future. In addition, the usage of these fossil fuels can also cause environmental pollution and greenhouse effect. To deal with energy security and environmental crisis, it is wise to work towards three directions: energy saving and emission reduction, energy recovery, exploration of new renewable energy. Currently, the electricity generation technology using piezoelectric material to recover the compressional or vibrational energy begins to draw attention. However, most of the researches are devoted to designing small self-powered devices. This paper presents an overview of the feasibility of piezoelectric power generation system for electric power system, in which the fundamentals of piezoelectric power generation and the feasible structure of the system are discussed.
Adaptive Quasi-PID Control Method for Switching Power Amplifiers  [PDF]
Xiaoming Sun
Journal of Power and Energy Engineering (JPEE) , 2017, DOI: 10.4236/jpee.2017.52003
Abstract: Quasi-PID control method that is able to effectively inhibit the inherent tracking error of PI control method is proposed on the basis of a rounded theoretical analysis of a model of switching power amplifiers (SPAs). To avoid the harmful impacts of the circuit parameter variations and the random disturbances on quasi-PID control method, a single neuron is introduced to endow it with self-adaptability. Quasi-PID control method and the single neuron combine with each other perfectly, and their formation is named as single-neuron adaptive quasi-PID control method. Simulation and experimental results show that single-neuron adaptive quasi-PID control method can accurately track both the predictable and the unpredictable waveforms. Quantitative analysis demonstrates that the accuracy of single-neuron adaptive quasi-PID control method is comparable to that of linear power amplifiers (LPAs) and so can fulfill the requirements of some high-accuracy applications, such as protective relay test. Such accuracy is very difficult to be achieved by many modern control methods for converter controls. Compared with other modern control methods, the programming realization of single-neuron adaptive quasi-PID control method is more suitable for real-time applications and realization on low-end microprocessors for its simple structure and lower computational complexity.
Analysis on Sensitivity of Power System Stability to Generator Parameters  [PDF]
Xiaoming Sun
Journal of Power and Energy Engineering (JPEE) , 2019, DOI: 10.4236/jpee.2019.71009
Abstract: The sensitivity of power system stability (including transient and dynamic stabilities) to generator parameters (including parameters of generator model, excitation system and power system stabilizer) is analyzed in depth by simulations. From the tables and plots of the resultant simulated data, a number of useful rules are revealed. These rules can be directly applied to the engineering checking of generator parameters. Because the complex theoretical analyses are circumvented, the checking procedure is greatly simplified, remarkably promoting the working efficiency of electrical engineers on site.
Fault Waveform Regenerator and Its Digital Closed-Loop Modification Technique  [PDF]
Xiaoming Sun
Journal of Power and Energy Engineering (JPEE) , 2019, DOI: 10.4236/jpee.2019.72002
Abstract: In order to provide a novel and more effective alternative to the commonly used relay protection testing device that outputs only the sinusoidal testing signals, the concept of fault waveform regenerator is proposed in this paper, together with its hardware structure and software flow chart. Fault waveform regenerator mainly depends on its power amplifiers (PAs) to regenerate the fault waveforms recorded by digital fault recorder (DFR). To counteract the PA’s inherent nonlinear distortions, a digital closed-loop modification technique that is different from the predistortion technique is conceived. And the experimental results verify the effectiveness of the fault waveform regenerator based on the digital closed-loop modification technique.
Multiallelic epistatic model for an out-bred cross and mapping algorithm of interactive quantitative trait loci
Chunfa Tong, Bo Zhang, Zhong Wang, Meng Xu, Xiaoming Pang, Jingna Si, Minren Huang, Rongling Wu
BMC Plant Biology , 2011, DOI: 10.1186/1471-2229-11-148
Abstract: Here we have formulated a general framework to model and define the epistasis between multiallelic QTLs. Based on this framework, we have derived a statistical algorithm for the estimation and test of multiallelic epistasis between different QTLs in a full-sib family of outcrossing species. We used this algorithm to genomewide scan for the distribution of mul-tiallelic epistasis for a rooting ability trait in an outbred cross derived from two heterozygous poplar trees. The results from simulation studies indicate that the positions and effects of multiallelic QTLs can well be estimated with a modest sample and heritability.The model and algorithm developed provide a useful tool for better characterizing the genetic control of complex traits in a heterozygous family derived from outcrossing species, such as forest trees, and thus fill a gap that occurs in genetic mapping of this group of important but underrepresented species.Approaches for quantitative trait locus (QTL) mapping were developed originally for experimental crosses, such as the backcross, double haploid, RILs or F2, derived from inbred lines [1-3]. Because of the homozygosity of inbred lines, the Mendelian (co)segregation of all markers each with two alternative alleles in such crosses can be observed directly. In practice, there is also a group of species of great economical and environmental importance - out-crossing species, such as forest trees, in which traditional QTL mapping approaches cannot be appropriately used. For these species, it is difficult or impossible to generate inbred lines due to long generation intervals and high heterozygosity [4], although experimental hybrids have been commercially used in practical breeding programs.For a given outbred line, some markers may be heterozygous, whereas others may be homozygous over the genome. All markers may, or may not, have the same allele system between any two outbred lines used for a cross. Also, for a pair of heterozygous loci, their allel
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