51 results on '"Xiaoqun Wang"'
Search Results
2. Cellular and molecular properties of neural progenitors in the developing mammalian hypothalamus
- Author
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Ruiguo Chen, Qian Wu, Qiang Ma, Le Sun, Xin Zhou, Suijuan Zhong, Wenyu Ding, Xiaoqun Wang, Jing Liu, Zeyuan Liu, and Honghai Peng
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0301 basic medicine ,Neurogenesis ,Science ,Hypothalamus ,Regulator ,General Physics and Astronomy ,Developmental neurogenesis ,02 engineering and technology ,In situ hybridization ,Biology ,Article ,General Biochemistry, Genetics and Molecular Biology ,Mice ,03 medical and health sciences ,Neural Stem Cells ,Pregnancy ,Animals ,Cluster Analysis ,Humans ,E2F1 ,Genes, Tumor Suppressor ,Progenitor cell ,lcsh:Science ,Gene ,In Situ Hybridization ,Progenitor ,Mammals ,Multidisciplinary ,Mantle zone ,HMGA2 Protein ,Membrane Proteins ,Nuclear Proteins ,General Chemistry ,021001 nanoscience & nanotechnology ,Neural progenitors ,Cell biology ,030104 developmental biology ,nervous system ,Female ,lcsh:Q ,0210 nano-technology - Abstract
The neuroendocrine hypothalamus is the central regulator of vital physiological homeostasis and behavior. However, the cellular and molecular properties of hypothalamic neural progenitors remain unexplored. Here, hypothalamic radial glial (hRG) and hypothalamic mantle zone radial glial (hmRG) cells are found to be neural progenitors in the developing mammalian hypothalamus. The hmRG cells originate from hRG cells and produce neurons. During the early development of hypothalamus, neurogenesis occurs in radial columns and is initiated from hRG cells. The radial glial fibers are oriented toward the locations of hypothalamic subregions which act as a scaffold for neuronal migration. Furthermore, we use single-cell RNA sequencing to reveal progenitor subtypes in human developing hypothalamus and characterize specific progenitor genes, such as TTYH1, HMGA2, and FAM107A. We also demonstrate that HMGA2 is involved in E2F1 pathway, regulating the proliferation of progenitor cells by targeting on the downstream MYBL2. Different neuronal subtypes start to differentiate and express specific genes of hypothalamic nucleus at gestational week 10. Finally, we reveal the developmental conservation of nuclear structures and marker genes in mouse and human hypothalamus. Our identification of cellular and molecular properties of neural progenitors provides a basic understanding of neurogenesis and regional formation of the non-laminated hypothalamus., The hypothalamus performs a wide range of vital physiological functions, including growth and reproductive behaviors, and circadian rhythms. The authors identify and characterize hypothalamic radial glial and hypothalamic mantle zone radial glial cells as the neural progenitors in the hypothalamus.
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- 2020
3. Broadband and strong electromagnetic wave absorption of epoxy composites filled with ultralow content of non-covalently modified reduced graphene oxides
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Xu Zhang, Chen Jiajun, Shanyi Du, Fanbo Meng, and Xiaoqun Wang
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Materials science ,Small-angle X-ray scattering ,Graphene ,Reflection loss ,02 engineering and technology ,General Chemistry ,Epoxy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Polymerization ,law ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,Small-angle scattering ,Composite material ,0210 nano-technology ,Porosity ,Microwave - Abstract
High-efficiency microwave absorption epoxy nanocomposites filled with ultralow content of non-covalently modified reduced graphene oxides (rGO) are prepared via an in-situ polymerization method. Here, the porous and folded rGO nanosheets are successfully functionalized by strong π-π interaction between conjugated imidazole and graphene sheets. The combination of electron microscope and synchronous radiation X-ray small angle scattering (SAXS) techniques unambiguously illustrates that the non-covalently modified graphene nanosheets in the epoxy composites are well-dispersed and extensively winkle. Hence, compared with pristine rGO/epoxy composites, the composites containing the highly dispersed rGO demonstrate more ideal impedance matching and stronger microwave dissipation based on the experimental and simulated results. The composites remarkably achieve excellent microwave absorptions (minimum reflection loss of −65 dB, with a matching thickness of 1.8 mm), an extremely broad absorbing bandwidth of 7.48 GHz (RL
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- 2019
4. High-performance microwave absorption of hierarchical graphene-based and MWCNT-based full-carbon nanostructures
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Ruifeng Zhang, Xu Zhang, Xiaofang Liu, Fanbo Meng, Ran Wei, Ya Li, Xiaoqun Wang, Shanyi Du, and Zhongheng Fu
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Nanostructure ,Materials science ,Graphene ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Exfoliation joint ,0104 chemical sciences ,Surfaces, Coatings and Films ,law.invention ,chemistry ,law ,Dielectric loss ,Graphite ,Composite material ,0210 nano-technology ,Absorption (electromagnetic radiation) ,Carbon ,Microwave - Abstract
A creative fabrication strategy is proposed for synthesizing two kinds of hierarchical graphene-based and MWCNT-based full-carbon nanostructures (FCNS), both of which are excellent microwave absorption (MA) fillers. Through using precursor graphite and MWCNTs, the FCNSs are prepared by simple ultrasonic exfoliation/dispersion and exothermal erosion methods. The hierarchical carbon nanostructures (carbon nanoparticles, carbon nanofilms and carbon hollow hemispheres) and abundant interfaces in FCNSs generate strong dielectric loss. Consequently, the FCNSs present ideal microwave impedance match, attenuation characteristics and excellent MA properties. Results show that the MWCNT-based FCNS and graphene-based FCNS composites achieve extremely strong absorption with minimum microwave reflection loss (RL) values of −58 dB with a thickness of 2.6 mm and −54 dB with a thickness of only 1.2 mm, respectively. And the effective absorption bandwidth (RL
- Published
- 2019
5. Quasi-Monte Carlo method for calculating X-ray scatter in CT
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Xiaoqun Wang, Guiyuan Lin, and Shiwo Deng
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Physics ,business.industry ,Monte Carlo method ,Detector ,Sampling (statistics) ,Sobol sequence ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Imaging phantom ,010309 optics ,Optics ,Rate of convergence ,0103 physical sciences ,Range (statistics) ,Quasi-Monte Carlo method ,0210 nano-technology ,business ,Algorithm - Abstract
In this paper we transform the trajectories of X-ray as it interacts with a phantom into a high-dimensional integration problem and give the integral formula for the probability of photons emitted from the X-ray source through the phantom to reach the detector. We propose a superior algorithm called gQMCFRD, which combines GPU-based quasi-Monte Carlo (gQMC) method with forced random detection (FRD) technique to simulate this integral. QMC simulation is deterministic versions of Monte Carlo (MC) simulation, which uses deterministic low discrepancy points (such as Sobol’ points) instead of the random points. By using the QMC and FRD technique, the gQMCFRD greatly increases the simulation convergence rate and efficiency. We benchmark gQMCFRD, GPU based MC tool (gMCDRR), which performs conventional simulations, a GPU-based Metropolis MC tool (gMMC), which uses the Metropolis-Hasting algorithm to sample the entire photon path from the X-ray source to the detector and gMCFRD, that uses random points for sampling against PENELOPE subroutines: MC-GPU. The results are in excellent agreement and the Efficiency Improvement Factor range 27 ∼ 37 (or 1.09 ∼ 1.16, or 0.12 ∼ 0.15, or 3.62 ∼ 3.70) by gQMCFRD (or gMCDRR, or gMMC, or gMCFRD) with comparison to MC-GPU in all cases. It shows that gQMCFRD is more effective in these cases.
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- 2021
6. Unveiling the phase diagram of a bond-alternating spin- 12 K−Γ chain
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Xiaoqun Wang, Jize Zhao, Qiang Luo, and Hae-Young Kee
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Physics ,Phase transition ,Condensed matter physics ,Magnetism ,Multicritical point ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Universality (dynamical systems) ,Phase (matter) ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Mirror symmetry ,Spin (physics) ,Phase diagram - Abstract
The quantum spin chain with bond-directional interactions can host fascinating phenomena. Here, the authors study such a spin chain, built of a Kitaev interaction and an off-diagonal exchange (dubbed the $\mathrm{\ensuremath{\Gamma}}$ term). This model possesses a self-dual relation and a mirror symmetry, and is found to exhibit a multicritical point, two topological phase transitions of distinct universality classes, three magnetically ordered states, and four disordered phases including the preeminent Haldane phase. These findings demonstrate a fertile playground to study quantum magnetism and topological phase transitions.
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- 2021
7. Raman interrogation of the ferroelectric phase transition in polar metal LiOsO3
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Jiandi Zhang, E. W. Plummer, Anmin Zhang, Xiaoqun Wang, Le Wang, Feng Jin, Youguo Shi, Qingming Zhang, Jianting Ji, and Rong Yu
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Phase transition ,Materials science ,Phonon ,02 engineering and technology ,Dielectric ,Electron ,01 natural sciences ,Condensed Matter::Materials Science ,symbols.namesake ,0103 physical sciences ,010306 general physics ,Anisotropy ,Raman ,Multidisciplinary ,itinerant electrons ,polar metal ,Condensed matter physics ,Physics ,Fermi level ,021001 nanoscience & nanotechnology ,Ferroelectricity ,ferroelectric phase transition ,Physical Sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Raman spectroscopy - Abstract
Significance Electric polarization due to polar structural distortion is a central characteristic of an ferroelectric (FE) material, which is normally unattainable in a metallic system because itinerant electrons screen the internal electric field. A possible exception for a polar metal is if the itinerant electrons are decoupled with FE distortion, as proposed by Anderson and Blount. Here, we reveal an unusual FE phase transition in recently discovered polar metal LiOsO3, different from the typical transition in insulating FEs, with dramatic temperature-dependent electron−phonon coupling. Our results provide a look at models for FE transitions with the interplay between FE dipoles and itinerant electrons, suggesting that an improvement of the Anderson and Blount model is needed., Ferroelectric (FE) distortions in a metallic material were believed to be experimentally inaccessible because itinerant electrons would screen the long-range Coulomb interactions that favor a polar structure. It has been suggested by Anderson and Blount [P. W. Anderson, E. I. Blount, Phys. Rev. Lett. 14, 217−219 (1965)] that a transition from paraelectric phase to FE phase is possible for a metal if, in the paraelectric phase, the electrons at the Fermi level are decoupled from the soft transverse optical phonons, which lead to ferroelectricity. Here, using Raman spectroscopy combined with magnetotransport measurements on a recently discovered FE metal LiOsO3, we demonstrate active interplay of itinerant electrons and the FE order: Itinerant electrons cause strong renormalization of the FE order parameter, leading to a more gradual transition in LiOsO3 than typical insulating FEs. In return, the FE order enhances the anisotropy of charge transport between parallel and perpendicular to the polarization direction. The temperature-dependent evolution of Raman active in-plane 3Eg phonon, which strongly couples to the polar-active out-of-the-plane A2u phonon mode in the high-temperature paraelectric state, exhibits a deviation in Raman shift from the expectation of the pseudospin−phonon model that is widely used to model many insulating FEs. The Curie−Weiss temperature (θ ≈ 97 K) obtained from the optical susceptibility is substantially lower than Ts, suggesting a strong suppression of FE fluctuations. Both line width and Fano line shape of 3Eg Raman mode exhibit a strong electron−phonon coupling in the high-temperature paraelectric phase, which disappears in the FE phase, challenging Anderson/Blount’s proposal for the formation of FE metals.
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- 2019
8. An importance sampling-based smoothing approach for quasi-Monte Carlo simulation of discrete barrier options
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Fei Xie, Zhijian He, and Xiaoqun Wang
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050210 logistics & transportation ,021103 operations research ,Information Systems and Management ,General Computer Science ,Computer science ,05 social sciences ,0211 other engineering and technologies ,Estimator ,02 engineering and technology ,Management Science and Operations Research ,Classification of discontinuities ,Effective dimension ,Industrial and Manufacturing Engineering ,Rate of convergence ,Modeling and Simulation ,0502 economics and business ,Quasi-Monte Carlo method ,Algorithm ,Variance gamma process ,Importance sampling ,Smoothing ,Curse of dimensionality - Abstract
Handling discontinuities in financial engineering is a challenging task when using quasi-Monte Carlo (QMC) method. This paper develops a so-called sequential importance sampling (SIS) method to remove multiple discontinuity structures sequentially for pricing discrete barrier options. The SIS method is a smoothing approach based on importance sampling, which yields an unbiased estimate with reduced variance. However, removing discontinuities still may not recover the superiority of QMC when the dimensionality of the problem is high. In order to handle the impact of high dimensionality on QMC, one promising strategy is to reduce the effective dimension of the problem. To this end, we develop a good path generation method with the smoothed estimator under the Black–Scholes model and models based on subordinated Brownian motion (e.g., Variance Gamma process). We find that the order of path generation influences the variance of the SIS estimator, and show how to choose optimally the first generation step. As confirmed by numerical experiments, the SIS method combined with a carefully chosen path generation method can significantly reduce the variance with improved rate of convergence. In addition, we show that the effective dimension is greatly reduced by the combined method, explaining the superiority of the proposed procedure from another perspective. The SIS method is also applicable for general models (with the Euler discretization). The smoothing effect of the SIS method facilitates the use of general dimension reduction techniques in reclaiming the efficiency of QMC.
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- 2019
9. Retracted Article: Development of functional hydrogels for heart failure
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Yanxin Han, Wenguo Cui, Xiaoqun Wang, Wei Jin, Wenbo Yang, Ke Yang, Yuanjin Zhao, Yanjia Chen, and Lianfu Deng
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business.industry ,Regeneration (biology) ,Bioactive molecules ,Biomedical Engineering ,02 engineering and technology ,General Chemistry ,General Medicine ,010402 general chemistry ,021001 nanoscience & nanotechnology ,medicine.disease ,Bioinformatics ,01 natural sciences ,Controlled release ,0104 chemical sciences ,Tissue engineering ,Heart failure ,Self-healing hydrogels ,medicine ,General Materials Science ,Functional studies ,0210 nano-technology ,business - Abstract
Although some advanced treatments of heart failure (HF) have experienced great development in recent decades, morbidity and mortality associated with HF have not improved significantly. Hydrogels have some unique advantages for the delivery and controlled release of bioactive molecules, drugs, and cells, which can directly affect the heart locally. Many studies have shown that hydrogels represent a new approach for the treatment of HF. In this review, we present a current perspective of hydrogel-based approaches for cardiac tissue engineering and myocardial regeneration in ischemia-induced HF, with an emphasis on functional studies, translation, and clinical advancements.
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- 2019
10. Clusterization transition between cluster Mott insulators on a breathing kagome lattice
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Xiao-Tian Zhang, Xu-Ping Yao, Yong Baek Kim, Xiaoqun Wang, and Gang Chen
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Condensed Matter::Quantum Gases ,Physics ,Condensed Matter - Materials Science ,Hubbard model ,Condensed matter physics ,Mott insulator ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Partial filling ,Lattice (order) ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
Motivated by recent experimental progress on various cluster Mott insulators, we study an extended Hubbard model on a breathing Kagom\'{e} lattice with a single electron orbital and $1/6$ electron filling. Two distinct types of cluster localization are found in the cluster Mott regime due to the presence of the electron repulsion between neighboring sites, rather than from the on-site Hubbard interaction in the conventional Mott insulators. We introduce a unified parton construction framework to accommodate both type of cluster Mott insulating phase as well as a trivial Ferm liquid metal and discuss the phase transitions in the phase diagram. It is shown that, in one of the cluster localization phases, the strong inter-site repulsion results into locally metallic behavior within one of two triangular clusters on the breathing Kagom\'{e} lattice. We further comment on experimental relevance to existing Mo-based cluster magnets., Comment: 9 pages, 3 figures. Abstracted partly from arXiv:1408.1963
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- 2020
11. A single-cell transcriptome atlas of the aging human and macaque retina
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Mengdi Wang, Suijuan Zhong, Ziqin Yao, Yufeng Lu, Min Wei, Qian Wu, Jing Hong, Xiaoqun Wang, Wei Wang, Zeyuan Liu, Hao Dong, Haohuan Xie, Rong-Mei Peng, Qiang Ma, Yuqian Ma, Yunyun Tong, Hongqiang Qu, Chonghai Yin, Le Sun, Jianwei Liu, Mei Zhang, Tian Xue, Wenyang Yi, Shouzhen Li, and Chao Ma
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genetic structures ,AcademicSubjects/SCI00010 ,cell heterogeneity ,Cell ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Macaque ,single-cell RNA sequencing ,Transcriptome ,chemistry.chemical_compound ,Foveal ,biology.animal ,Gene expression ,medicine ,Primate ,cell-cell communication ,Retina ,age-related disease ,Multidisciplinary ,biology ,Molecular Biology & Genetics ,aging ,Retinal ,primate retina ,021001 nanoscience & nanotechnology ,eye diseases ,0104 chemical sciences ,medicine.anatomical_structure ,chemistry ,sense organs ,0210 nano-technology ,AcademicSubjects/MED00010 ,Neuroscience ,Research Article - Abstract
The human retina is a complex neural tissue that detects light and sends visual information to the brain. However, the molecular and cellular processes that underlie aging primate retina remain unclear. Here, we provide a comprehensive transcriptomic atlas based on 119,520 single cells of the foveal and peripheral retina of humans and macaques covering different ages. The molecular features of retinal cells differed between the two species, suggesting the distinct regional and species specializations of the human and macaque retinae. In addition, human retinal aging occurred in a region- and cell-type- specific manner. Aging of human retina exhibited a foveal to peripheral gradient. MYO9A− rods and a horizontal cell subtype were greatly reduced in aging retina, indicating their vulnerability to aging. Moreover, we generated a dataset showing the cell-type- and region- specific gene expression associated with 55 types of human retinal disease, which provides a foundation to understand the molecular and cellular mechanisms underlying human retinal diseases. Together, these datasets are valuable for understanding the molecular characteristics of primate retina, as well as the molecular regulation of aging progression and related diseases.
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- 2020
12. Bethe-Slater-curve-like behavior and interlayer spin-exchange coupling mechanisms in two-dimensional magnetic bilayers
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Linwei Zhou, Yuhao Pan, Xieyu Zhou, Wei Ji, Zhong-Yi Lu, Cong Wang, Xiaoqun Wang, and Xiangang Wan
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Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Magnetism ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Bethe–Slater curve ,Inductive coupling ,symbols.namesake ,Pauli exclusion principle ,Ferromagnetism ,0103 physical sciences ,symbols ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,van der Waals force ,010306 general physics ,0210 nano-technology ,Wave function - Abstract
Layered magnets have recently received tremendous attention, however spin-exchange coupling mechanism across their interlayer regions is yet to be revealed. Here, we report a Bethe-Slater-curve (BSC)-like behavior in nine transition metal dichalcogenide bilayers ($M{X}_{2}$, $M=\mathrm{V}$, Cr, Mn; $X=\mathrm{S}$, Se, Te) and established interlayer spin-exchange coupling mechanisms at their van der Waals gaps using first-principle calculations. The BSC-like behavior offers a distance-dependent interlayer antiferromagnetic (AFM) to ferromagnetic (FM) transition. This phenomenon is explained with the spin-exchange coupling mechanisms established using bilayer $\mathrm{CrS}{\mathrm{e}}_{2}$ as a prototype in this work. The Se ${p}_{\mathrm{z}}$ wave functions from two adjacent interfacial Se sublayers overlap at the interlayer region. The spin alignment of the region determines interlayer magnetic coupling. At a shorter interlayer distance, Pauli repulsion at the overlapped region dominates and thus favors antiparallel oriented spins leading to interlayer AFM. For a longer distance, kinetic-energy gain of polarized electrons across the bilayer balances the Pauli repulsion and the bilayer thus prefers an interlayer FM state. In light of this, the AFM-FM transition is a result of competition between Pauli and Coulomb repulsions and kinetic-energy gain. All these results open a route to tune interlayer magnetism and the revealed spin-exchange coupling mechanisms are paramount additions to those previously established ones.
- Published
- 2020
13. Entanglements and correlations of one-dimensional quantum spin-1/2 chain with anisotropic power-law long range interactions
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Wen-Long You, Xiaoqun Wang, and Jie Ren
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Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Density matrix renormalization group ,FOS: Physical sciences ,02 engineering and technology ,Quantum entanglement ,021001 nanoscience & nanotechnology ,01 natural sciences ,Wigner crystal ,Condensed Matter - Strongly Correlated Electrons ,Continuous symmetry ,0103 physical sciences ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Anisotropy ,Spin (physics) ,Phase diagram - Abstract
The correlations, entanglement entropy, and fidelity susceptibility are calculated for a one-dimensional spin-1/2 XXZ chain with anisotropic power-law long range interactions by employing the density matrix renormalization group method. In particular, this long-range interaction is assigned to ferromagnetic for transversal components, while it can be either ferro- or antiferromagnetic for the longitudinal spin component. Two ground-state phase diagrams are established versus the anisotropy of the interactions which not only changes the phase boundaries of the counterparts with short-range interactions, but also leads to the emergence of exotic phases. We found that the long-range interactions of the z-component results in a Wigner crystal phase, whereas the transversal one may break a continuous symmetry, resulting in a continuous symmetry breaking phase., 8 pages, 9 figures
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- 2020
14. Crystalline Electric-Field Excitations in Quantum Spin Liquids Candidate $NaYbSe_{2}$
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Jianting Ji, Xiaoqun Wang, Qingming Zhang, Zheng Zhang, D. T. Adroja, Xiaoli Ma, Yoshitomo Kamiya, Jie Ma, Jianshu Li, Weiwei Liu, Yimeng Wang, Feng Jin, T. P. Perring, and Guohua Wang
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Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences ,Charge (physics) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Spectral line ,Inelastic neutron scattering ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,010306 general physics ,0210 nano-technology ,Excitation ,Raman scattering ,Spin-½ - Abstract
Very recently we revealed a large family of triangular lattice quantum spin liquid candidates named rare-earth chalcogenides, which features a high-symmetry structure without structural/charge disorders and spin impurities, and may serve as an ideal platform exploring spin liquid physics. The knowledge of crystalline electric-field (CEF) excitations is an essential step to explore the fundamental magnetism of rare-earth spin systems. Here we employed inelastic neutron scattering (INS) and Raman scattering (RS) to carry out a comprehensive CFE investigation on $NaYbSe_{2}$, a promising representative of the family. By comparison with its nonmagnetic compound $NaLuSe_{2}$, we are able to identify the CEF excitations at 15.8, 24.3 and 30.5 meV at 5K. The selected cuts of the INS spectra are well re-produced with a large anisotropy of $g$ factors ($g_{ab}:g_{c}\sim3:1$). Further, the CEF excitations are explained well by our calculations based on the point charge model. Interestingly, $NaYbSe_{2}$ exhibits an unusual CEF shift to higher energies with increasing temperatures, and the Raman mode close to the first CEF excitation shows an anomalously large softening with decreasing temperatures. The absence of the anomalies in $NaLuSe_{2}$ clearly demonstrates a CEF-phonon coupling not reported in the family. It can be understood in term of the weaker electronegativity of Se. The fact that the smallest first CEF excitation in the sub-family of $NaYbCh_{2}$ is $\sim$ 180K (Ch=O, S, Se), guarantees that the sub-family can be strictly described with an effective S=1/2 picture at sufficiently low temperatures. Interestingly the CEF-phonon coupling revealed here may present alternative possibilities to manipulate the spin systems., 7 pages, 4 figures, supplementary material provided, error corrected in Figure 4
- Published
- 2020
15. Improvement to the sources selection to identify the low frequency noise induced by flood discharge
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Dongming Liu, Xiaoqun Wang, Bin Ma, and Jijian Lian
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0209 industrial biotechnology ,Computer science ,Mechanical Engineering ,Infrasound ,Aerospace Engineering ,Improved method ,02 engineering and technology ,Human judgment ,01 natural sciences ,Blind signal separation ,Computer Science Applications ,Flood discharge ,020901 industrial engineering & automation ,Control and Systems Engineering ,0103 physical sciences ,Signal Processing ,Principal component analysis ,Entropy (information theory) ,010301 acoustics ,Algorithm ,Civil and Structural Engineering - Abstract
Recent studies indicate that low frequency noise (LFN) is generated by flood discharge of high dam. For prototype observation of the LFN, the observed data usually contain multiple sources induced by different mechanisms. To separate and identify the LFN generated by flood discharge from the multiple sources, an improved version of single-channel blind source separation (SCBSS) is proposed. In this study, the source number estimation is improved by a singular entropy (SE) method based on the eigenvalues calculated by principal components analysis (PCA). Then an SCBSS algorithm with no interruption is proposed. Both traditional method and PCA-SE method may result in extra sources that do not exist actually and are introduced by SCBSS due to the misconduct of human judgment or underestimation of threshold. Therefore, a cross-correlation procedure is proposed to identify and eliminate the extra sources and other sources that we are not really concerned about. The proposed method is first applied to a pre-determined signal to validate its effectiveness. Then the LFN data observed during the flood discharge of the Jin’anqiao hydropower station are analyzed and separated using this improved method. Two components, with dominant frequencies about 0.7 Hz and 0.95 Hz respectively, are successfully recognized as the actual acoustic sources induced by the flood discharge.
- Published
- 2018
16. Probing the direct factor for superconductivity in FeSe-Based Superconductors by Raman Scattering
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Xiaoli Ma, Qingming Zhang, Shanshan Sun, Xiaoqun Wang, Changfeng Chen, B. Lei, Animin Zhang, Hechang Lei, Yimeng Wang, and Xianhui Chen
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Superconductivity ,Materials science ,Electronic correlation ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Phonon ,Condensed Matter - Superconductivity ,Anharmonicity ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Superconductivity (cond-mat.supr-con) ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Superconductivity ,0103 physical sciences ,symbols ,Density of states ,010306 general physics ,0210 nano-technology ,Raman spectroscopy ,Raman scattering - Abstract
The FeSe-based superconductors exhibit a wide range of critical temperature Tc under a variety of material and physical conditions, but extensive studies to date have yet to produce a consensus view on the underlying mechanism. Here we report on a systematic Raman scattering work on intercalated FeSe superconductors Lix(NH3)yFe2Se2 and (Li,Fe)OHFeSe compared to pristine FeSe. All three crystals show an anomalous power-law temperature dependence of phonon linewidths, deviating from the standard anharmonic behavior. This intriguing phenomenon is attributed to electron-phonon coupling effects enhanced by electron correlation, as evidenced by the evolution of the A1g Raman mode. Meanwhile, an analysis of the B1g mode, which probes the out-of-plane vibration of Fe, reveals a lack of influence by previously suggested structural parameters, and instead indicates a crucial role of the joint density of states in determining Tc. These findings identify carrier doping as the direct factor driving and modulating superconductivity in FeSe-based compounds., 6 pages, 4 figures
- Published
- 2019
17. The Strategy of Constructing an Interdisciplinary Knowledge Center
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Shunpeng Zou, Xiaohui Zou, and Xiaoqun Wang
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Knowledge management ,Standardization ,Machine translation ,business.industry ,Computer science ,05 social sciences ,Natural language understanding ,050301 education ,Information technology ,02 engineering and technology ,computer.software_genre ,Formal system ,Knowledge acquisition ,Expert system ,Text mining ,Social system ,0202 electrical engineering, electronic engineering, information engineering ,Domain knowledge ,020201 artificial intelligence & image processing ,business ,0503 education ,computer - Abstract
This paper aims to explain the construction strategy of interdisciplinary knowledge centers from the perspective of expert systems, knowledge management and educational information technology. The method is: Firstly, it explores how to construct the strategy of interdisciplinary knowledge centers sharing, and then makes necessary explorations from computer assisted knowledge management, expert knowledge acquisition and educational autonomous learning. Finally, establish the foundation of natural language understanding in the domain knowledge base which is the basis of the interdisciplinary knowledge center. It is characterized by the application of the wisdom system studied strategy, with machine translation, machine learning and human-computer interaction, starting from the excellent courses in research universities, with the combination of intelligent text analysis and knowledge module finishing, and with the application of “seven-stapes pass” and “eight-persons group” as the education management innovation paradigm. The result is the new paradigm with both standardization and individuality, namely the construction of an interdisciplinary knowledge center that combines large production with small production. The significance lies in the combination of “language, knowledge, software, hardware formal system engineering” and “education, management, learning, application social system engineering”, that help to promote the interdisciplinary knowledge center and its systems engineering talents training. It is more efficient to build the smart systems studied for serving the society.
- Published
- 2019
18. Effect of surface treatment on the interfacial adhesion performance of aluminum foil/CFRP laminates for cryogenic propellant tanks
- Author
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Ran Wei, Xuehong Xu, Chen Chen, Xiaoqun Wang, Shanyi Du, and Xu Zhang
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Carbon fiber reinforced polymer ,Propellant ,Propellant tank ,Materials science ,Mechanical Engineering ,Interfacial adhesion ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermal expansion ,0104 chemical sciences ,Corrosion ,Mechanics of Materials ,lcsh:TA401-492 ,lcsh:Materials of engineering and construction. Mechanics of materials ,General Materials Science ,Composite material ,0210 nano-technology ,Layer (electronics) ,FOIL method - Abstract
In this study, an aluminum foil with a thickness of 0.08 mm was inserted between plies of carbon fiber reinforced polymer (CFRP) composites to manufacture Al foil/CFRP laminates. Two kinds of surface treatments, including corrosion method with NaOH or H2SO4/CrO3 solution and addition of flexible layer composed of polyether triamine, were carried out successively on the surface of Al foil to improve the interfacial adhesion strength between Al foil and CFRP under cryogenic cycles. The results showed that, both corrosion methods could improve the interfacial adhesion strength between Al foil and CFRP obviously. The flexible layer applied was verified to be bonded to the surface of Al foil via OAl…N and AlOH…N. The interfacial adhesion performance of Al foil/CFRP laminates after cryogenic cycles improved significantly attributable to the surface treatments applied, which indicated that the flexible layer could adjust the thermal expansion coefficient mismatch between Al foil and CFRP as expected. Furthermore, the Al foil/CFRP laminates exhibit excellent gas barrier property, which is about 15 times higher than that of CFRP laminates. Consequently, the Al foil/CFRP laminates have great potential as cryogenic propellant tank material for aerospace craft. Keywords: Al foil, Carbon fiber reinforced polymer, Interfacial adhesion, Cryogenic cycling, Gas barrier property
- Published
- 2017
19. Microwave curing process and mechanical properties study of epoxy mortars for repairing concrete pavement rapidly
- Author
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Xu Zhang, Yueqing Zhao, Xiaoqun Wang, and Xuehong Xu
- Subjects
chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Mechanical Engineering ,0211 other engineering and technologies ,02 engineering and technology ,Polymer ,Epoxy ,021001 nanoscience & nanotechnology ,Compressive strength ,Microwave curing ,chemistry ,Flexural strength ,Mechanics of Materials ,Scientific method ,visual_art ,021105 building & construction ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Mortar ,Composite material ,0210 nano-technology - Abstract
Polymer mortars are used frequently to repair pavement owing to their excellent properties (mix flexural strength ≥5.75 MPa, compressive strength ≥25 MPa). To repair concrete pavement with polymer mortars rapidly, uniform microwave energy can be used to reduce hardening time of polymer mortars. In this study, the distribution of electromagnetic fields in an industrial microwave facility was optimized, and an area AG with uniform and intensive electric field was obtained. Then microwave curing process of epoxy mortars containing fly ash in the area AG was optimized, and mechanical strengths of the epoxy mortars cured in the optimum process were tested. The results show that, although the distribution of electromagnetic fields in the microwave facility is non-uniform overall, there still are some brush-fire areas, where electric field distribution is relatively uniform. Epoxy mortars added with 10 wt% fly ash can be cured rapidly (approximately 20 min) in the area AG and exhibit outstanding mechanical strengths, which can be used to repair concrete pavement rapidly.
- Published
- 2016
20. Interplay of Dirac electrons and magnetism in CaMnBi2 and SrMnBi2
- Author
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Anmin Zhang, Youguo Shi, Guihua Zhao, Jianting Ji, Xiaoqun Wang, Changle Liu, Tian-Long Xia, Rong Yu, Changjiang Yi, Qingming Zhang, and Changfeng Chen
- Subjects
Magnetism ,High Energy Physics::Lattice ,Science ,Dirac (software) ,General Physics and Astronomy ,02 engineering and technology ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,symbols.namesake ,Dirac electron ,Quantum mechanics ,0103 physical sciences ,010306 general physics ,Physics ,Multidisciplinary ,Condensed matter physics ,Macroscopic quantum phenomena ,General Chemistry ,021001 nanoscience & nanotechnology ,Dirac system ,Coupling (physics) ,symbols ,0210 nano-technology ,Carrier dynamics ,Raman scattering - Abstract
Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin–Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices., The interplay between the low-energy carriers in Dirac materials and magnetism is likely to reveal many novel physical phenomena. Here, the authors use two-magnon Raman scattering to determine the exchange energies of two prototypical magnetic Dirac systems, CaMnBi2 and SrMnBi2.
- Published
- 2016
21. An auto-realignment method in quasi-Monte Carlo for pricing financial derivatives with jump structures
- Author
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Chengfeng Weng, Xiaoqun Wang, and Zhijian He
- Subjects
Surface (mathematics) ,Mathematical optimization ,021103 operations research ,Information Systems and Management ,General Computer Science ,0211 other engineering and technologies ,010103 numerical & computational mathematics ,02 engineering and technology ,Function (mathematics) ,Management Science and Operations Research ,Classification of discontinuities ,01 natural sciences ,Industrial and Manufacturing Engineering ,QR decomposition ,Discontinuity (linguistics) ,Modeling and Simulation ,Jump ,Applied mathematics ,Quasi-Monte Carlo method ,0101 mathematics ,Cluster analysis ,Mathematics - Abstract
Discontinuities are common in the pricing of financial derivatives and have a tremendous impact on the accuracy of quasi-Monte Carlo (QMC) method. While if the discontinuities are parallel to the axes, good efficiency of the QMC method can still be expected. By realigning the discontinuities to be axes-parallel, [Wang & Tan, 2013] succeeded in recovering the high efficiency of the QMC method for a special class of functions. Motivated by this work, we propose an auto-realignment method to deal with more general discontinuous functions. The k-means clustering algorithm, a classical algorithm of machine learning, is used to select the most representative normal vectors of the discontinuity surface. By applying this new method, the discontinuities of the resulting function are realigned to be friendly for the QMC method. Numerical experiments demonstrate that the proposed method significantly improves the performance of the QMC method.
- Published
- 2016
22. Intrinsic jump character of first-order quantum phase transitions
- Author
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Xiaoqun Wang, Jize Zhao, and Qiang Luo
- Subjects
Quantum phase transition ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Statistical Mechanics (cond-mat.stat-mech) ,FOS: Physical sciences ,02 engineering and technology ,Renormalization group ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Character (mathematics) ,Transition point ,Quantum critical point ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Central charge ,Quantum ,Condensed Matter - Statistical Mechanics ,Mathematical physics ,Spin-½ - Abstract
We find that the first-order quantum phase transitions~(QPTs) are characterized by intrinsic jumps of relevant operators while the continuous ones are not. Based on such an observation, we propose a bond reversal method where a quantity $\mathcal{D}$, the difference of bond strength~(DBS), is introduced to judge whether a QPT is of first order or not. This method is firstly applied to an exactly solvable spin-$1/2$ \textit{XXZ} Heisenberg chain and a quantum Ising chain with longitudinal field where distinct jumps of $\mathcal{D}$ appear at the first-order transition points for both cases. We then use it to study the topological QPT of a cross-coupled~($J_{\times}$) spin ladder where the Haldane--rung-singlet transition switches from being continuous to exhibiting a first-order character at $J_{\times, I} \simeq$ 0.30(2). Finally, we study a recently proposed one-dimensional analogy of deconfined quantum critical point connecting two ordered phases in a spin-$1/2$ chain. We rule out the possibility of weakly first-order QPT because the DBS is smooth when crossing the transition point. Moreover, we affirm that such transition belongs to the Gaussian universality class with the central charge $c$ = 1., 6+epsilon + 4 pages, 6 + 9 figures
- Published
- 2019
23. Smart System Studied
- Author
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Xiaohui Zou, Xiaoqun Wang, and Shunpeng Zou
- Subjects
0209 industrial biotechnology ,Smart system ,business.industry ,Computer science ,Learning environment ,Natural language understanding ,02 engineering and technology ,computer.software_genre ,Knowledge acquisition ,Field (computer science) ,Terminology ,020901 industrial engineering & automation ,Software ,Human–computer interaction ,0202 electrical engineering, electronic engineering, information engineering ,020201 artificial intelligence & image processing ,business ,computer - Abstract
This paper aims to focus on the smart system as optimized expert knowledge acquisition system as new approaches to natural language understanding system. This method can finish fine processing for any text segment instantly. The module's precision machining can adopt big production method that combines on the line first, complete coverage and accurate grasp each language point and knowledge point and original point even their respective combination. Its characteristics are teachers and students can use the text analyzed method to do the fine processing of the same knowledge module, and only in Chinese or English, through the selection of keywords and terminology and knowledge modules that can be used as the menu to be selected as the way to achieve knowledge with the system. The result is the learning environment that enables human-computer collaboration system namely smart system to optimize the expert knowledge acquisition and the natural language understanding as a research field that has great significance to human beings. Its significance is that this learning environment software based on the National Excellent Courses by using the language chess with the feature of the introduction on the knowledge big production mode for the textual knowledge module finishing at Peking University.
- Published
- 2019
24. New Approach of Big Data and Education
- Author
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Shunpeng Zou, Xiaohui Zou, and Xiaoqun Wang
- Subjects
Information retrieval ,business.industry ,Computer science ,Process (engineering) ,Data management ,Matrix (music) ,Big data ,02 engineering and technology ,Construct (python library) ,Reuse ,Term (time) ,03 medical and health sciences ,0302 clinical medicine ,Text mining ,020204 information systems ,0202 electrical engineering, electronic engineering, information engineering ,business ,030217 neurology & neurosurgery ,Word (computer architecture) - Abstract
The purpose of this paper is to introduce a new approach that must cover all the terms. Therefore, people's educational process is like making a variety of choices in a super-chessboard of language or a matrix composed of words formally. The method of redemption is: First, construct the chessboard, and then, through human-computer interaction and collaboration, generate massive amounts of big data, including various terms representing knowledge, and finally, through machine learning and man-machine interactive to analyze, compare, and query or reuse any of these terms. The result: an accurate query of terms, which can be automatically queried in multiple ways through bilingual or multi-lingual converters. The significance is that the method and its results can be used not only for machine-assisted instruction in the network environment, but also for machine-assisted intelligent text analysis and knowledge module finishing in the network environment, thus opening up view of big data and education. The new approach, because any term must be in the word matrix, each user and its agents query them very accurately and efficiently.
- Published
- 2019
25. An Improved Empirical Model for Flood Discharge Atomization and Its Application to Optimize the Flip Bucket of the Nazixia Project
- Author
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He Junling, Wang Chang, Fang Liu, Jijian Lian, Danjie Ran, and Xiaoqun Wang
- Subjects
010504 meteorology & atmospheric sciences ,Health, Toxicology and Mutagenesis ,0208 environmental biotechnology ,lcsh:Medicine ,02 engineering and technology ,Wind ,Edge (geometry) ,01 natural sciences ,Article ,Flood discharge ,trajectory nappe ,atomization ,nappe wind ,flip bucket ,0105 earth and related environmental sciences ,Splash ,stochastic splash model ,lcsh:R ,Public Health, Environmental and Occupational Health ,Ranging ,Models, Theoretical ,Floods ,020801 environmental engineering ,two-phase flow ,Model test ,Environmental science ,Two-phase flow ,Intensity (heat transfer) ,Left wall ,Marine engineering - Abstract
Flood discharge atomization is a serious challenge that threatens the daily lives of the residents around the dam area as well as the safety of the water conservancy project. This research aims to improve the prediction accuracy of the stochastic splash model. A physical model test with four types of flip bucket is conducted to obtain the hydraulic parameters of the impinging outer edge of the water jet, the relationship of the splashing droplet diameter with its corresponding velocity, and the spatial distribution of the downstream nappe wind. The factors mentioned above are introduced to formulate the empirical model. The rule obtained from the numerical analyses is compared with the results of the physical model test and the prototype observations, which yields a solid agreement. The numerical results indicate that the powerhouse is no longer in the heavy rain area when adopting the flip bucket whose curved surface is attached to the left wall. The rainfall intensity of the powerhouse is significantly weaker than that of other types under the designed condition, so we choose it as the recommended bucket type. Meanwhile, we compare the rainfall intensity distribution of the original bucket and the recommended bucket under different discharge which rates ranging from 150.71 to 1094.9 m3/s. It is found that the powerhouse and the owner camp are no longer in the heavy rain area under all of the working conditions. Finally, it is shown that the atomization influence during the flood discharge can be reduced by using the recommended bucket.
- Published
- 2019
26. Topological phase transition between distinctWeyl semimetal states in MoTe2
- Author
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Lei Zhang, Tian-Long Xia, Changfeng Chen, Yi-Yan Wang, Yimeng Wang, Rui Lou, Anmin Zhang, Qingming Zhang, Xiaoqun Wang, Changle Liu, Shancai Wang, Xiaoli Ma, and Qiao-He Yu
- Subjects
Physics ,Condensed Matter - Materials Science ,Phase transition ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Phonon ,Weyl semimetal ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,symbols.namesake ,Phase (matter) ,0103 physical sciences ,symbols ,Topological order ,010306 general physics ,0210 nano-technology ,Raman spectroscopy - Abstract
We present experimental evidence of an intriguing phase transition between distinct topological states in the type-II Weyl semimetal MoTe2. We observe anomalies in the Raman phonon frequencies and linewidths as well as electronic quasielastic peaks around 70 K, which, together with structural, thermodynamic measurements, and electron-phonon coupling calculations, demonstrate a temperature-induced transition between two topological phases previously identified by contrasting spectroscopic measurements. An analysis of experimental data suggests electron-phonon coupling as the main driving mechanism for the change of key topological characters in the electronic structure of MoTe2.We also find the phase transition to be sensitive to sample conditions distinguished by synthesis methods. These discoveries of temperature and material condition-dependent topological phase evolutions and transitions in MoTe2 advance the fundamental understanding of the underlying physics and enable an effective approach to tuning Weyl semimetal states for technological applications., Comment: 6 pages, 4 figures
- Published
- 2019
- Full Text
- View/download PDF
27. On the competition between the Kondo effect and the exchange interaction in a parallel double quantum dot system
- Author
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Fei Ye, Guo-Hui Ding, and Xiaoqun Wang
- Subjects
Physics ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Exchange interaction ,FOS: Physical sciences ,Conductance ,Scalar potential ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,Spectral line ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Coulomb ,General Materials Science ,Condensed Matter::Strongly Correlated Electrons ,Kondo effect ,010306 general physics ,0210 nano-technology ,Effective action - Abstract
We study the competition between the Kondo effect and the exchange interaction in the parallel double quantum dot(DQDs) system within an effective action field theory. The strong on-site Coulomb interactions in DQDs are treated by using the Hubbard-Stratonovich transformation and the introduction of scalar potential fields. We show that a self-consistent perturbation approach, which takes into account the statistical properties of the potential fields acting on the electrons in DQDs, describes well the crossover from the Kondo regime to the spin-singlet state in this system. The linear conductance and the intradot/interdot spin excitation spectra of this system are obtain, 5 pages, 5 figures
- Published
- 2018
28. Microwave curing of carbon fiber/bismaleimide composite laminates: Material characterization and hot pressing pretreatment
- Author
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Xiaoqun Wang, Xu Zhang, Zhenzhong Li, Shanyi Du, Liu Weiping, and Xuehong Xu
- Subjects
Materials science ,Mechanical Engineering ,Vacuum pressure ,02 engineering and technology ,Composite laminates ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Hot pressing ,01 natural sciences ,0104 chemical sciences ,Electric arc ,Microwave curing ,Mechanics of Materials ,Thermal ,lcsh:TA401-492 ,General Materials Science ,lcsh:Materials of engineering and construction. Mechanics of materials ,Composite material ,0210 nano-technology ,Microwave ,Curing (chemistry) - Abstract
Microwave curing is proposed as an alternative cost-effective process to thermal curing for composite materials. Carbon fiber/bismaleimide composite laminates were fabricated by vacuum assisted microwave processing without arcing. The physical and mechanical properties of cured composites were compared to those produced using autoclave and conventional oven curing. To compensate for the lower vacuum pressure and further improve part quality, hot pressing pretreatment and subsequent microwave radiation were studied. The results indicated that microwave cured samples with 37% of the thermal manufacturing cycle time, obtained basically identical molecular structure and exhibited full curing. Uniformity and consistency of microwave curing was verified by assessing the mechanical strength at different positions in a laminate. The microwave processed panel properties showed a noticeable enhancement as compared with those cured in a traditional oven. A slightly superior performance to autoclave laminates was observed for the composites manufactured with the hot-pressing pretreatment followed by microwave processing. Keywords: Carbon fiber, Polymer-matrix composites, Cure, Mechanical properties, Microwave processing
- Published
- 2016
29. Improvement of the Compressive Strength of Carbon Fiber/Epoxy Composites via Microwave Curing
- Author
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Cai Qun, Wang Xu, Xuehong Xu, Ran Wei, Xiaoqun Wang, and Shanyi Du
- Subjects
010302 applied physics ,Materials science ,Polymers and Plastics ,Interfacial bonding ,Scanning electron microscope ,Mechanical Engineering ,Metals and Alloys ,02 engineering and technology ,Epoxy ,021001 nanoscience & nanotechnology ,01 natural sciences ,Electric arc ,Compressive strength ,Microwave curing ,Mechanics of Materials ,visual_art ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Composite material ,0210 nano-technology ,Glass transition ,Microwave - Abstract
Microwave processing was used to cure the carbon fiber/epoxy composites and designed for improving the compressive strength of the materials. By controlling the power of microwave heating, vacuum bagged laminates were fabricated under one atmosphere pressure without arcing. The physical and mechanical properties of composites produced through vacuum bagging using microwave and thermal curing were compared and the multistep (2-step or 3-step) microwave curing process for improved compressive properties was established. The results indicated that microwave cured samples had somewhat differentiated molecular structure and showed slightly higher glass transition temperature. The 2-step process was found to be more conducive to the enhancement of the compressive strength than the 3-step process. A 39% cure cycle time reduction and a 22% compressive strength increment were achieved for the composites manufactured with microwave radiation. The improvement in specific compressive strength was attributed to better interfacial bonding between resin matrix and the fibers, which was also demonstrated via scanning electron microscopy analysis.
- Published
- 2016
30. Effect of microwave curing process on the flexural strength and interlaminar shear strength of carbon fiber/bismaleimide composites
- Author
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Ran Wei, Xiaoqun Wang, Xuehong Xu, and Shanyi Du
- Subjects
0209 industrial biotechnology ,Materials science ,Composite number ,General Engineering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Electric arc ,020901 industrial engineering & automation ,Flexural strength ,Volume fraction ,Thermal ,Ceramics and Composites ,Composite material ,0210 nano-technology ,Material properties ,Microwave ,Curing (chemistry) - Abstract
Microwave heating has been conceived as a rapid and cost-effective method for curing carbon fiber composites. In this paper, microwave radiation was used to cure carbon fiber/bismaleimide composites aiming at shortening the production cycle time. Through controlling the microwave power, vacuum bagged laminates were fabricated under one atmosphere pressure without arcing. Degree of cure, void content and fiber volume fraction were measured to evaluate part quality. Three-point flexure and short beam shear testing were employed for mechanical assessment. Variation in the microwave cure cycle had a significant effect on the material properties. The optimum processing parameters for microwave curing were established based on analysis of the mechanical performance. A cycle time reduction of nearly 63% was obtained compared to thermal processing. The physical and mechanical properties of microwave cured samples were found to be superior to those cured in a conventional oven. The composite panels manufactured by the optimized microwave cure process exhibited a slight decrease in flexural strength but equivalent interlaminar shear strength in comparison with those produced by autoclave curing.
- Published
- 2016
31. High-efficiency electromagnetic wave absorption of epoxy composites filled with ultralow content of reduced graphene/carbon nanotube oxides
- Author
-
Bendong Wang, Xiaoqun Wang, Xu Zhang, Peng Sha, Ding Yi, and Shanyi Du
- Subjects
chemistry.chemical_classification ,Materials science ,Graphene ,Reflection loss ,General Engineering ,chemistry.chemical_element ,02 engineering and technology ,Dielectric ,Carbon nanotube ,Polymer ,Epoxy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,chemistry ,law ,visual_art ,Ceramics and Composites ,visual_art.visual_art_medium ,Composite material ,0210 nano-technology ,Absorption (electromagnetic radiation) ,Carbon - Abstract
Graphene or carbon nanotube filled polymer materials with strong electromagnetic wave absorption, broad absorption band, thinness, low filler loading and facile fabricating technique are highly desirable in daily life and areas of electronics. However, there are still many obstacles to simultaneously satisfy the above critical requirements by utilizing the sole carbon absorbers. Herein, first, reduced graphene/CNT oxides (rGTO) are synthetized via simple modified Hummers and chemical reduction methods. Then we fabricate rGTO/epoxy nanocomposites by an in-suit polymerization method. Benefitting from the π-stacking interactions and mutual supporting between graphene and carbon nanotubes, good dispersion and interfacial interactions are formed between rGTO and the polymer matrix within ultralow filling content (1 wt%). Also, the defects and residual oxygen-containing groups in rGTO not only achieve ideal impedance matching but also introduce remarkable dielectric polarization loss. Thus, the rGTO/epoxy nanocomposites exhibit excellent microwave absorption performance with strong absorption (reflection loss is −61.8 dB), thinness (1.9 mm), broad bandwidth (effective absorption bandwidth is 5.38 GHz) and ultralow filler loading (1 wt%). More importantly, minimum RL value below −30 dB is obtained almost over the thickness range of 1.5–4.5 mm and the frequency of 4.2–18 GHz.
- Published
- 2020
32. Experimental Study on the Flow-Induced Motion and Hydrokinetic Energy of Two T-section Prisms in Tandem Arrangement
- Author
-
Zheng Zheng, Heng Deng, Xiaoqun Wang, Nan Shao, Yan Xiang, Guobin Xu, and Fang Liu
- Subjects
020209 energy ,flow induced motion ,tandem ,Geometry ,02 engineering and technology ,Interference (wave propagation) ,lcsh:Technology ,lcsh:Chemistry ,0202 electrical engineering, electronic engineering, information engineering ,Energy transformation ,General Materials Science ,Upstream (networking) ,t-section prism ,lcsh:QH301-705.5 ,Instrumentation ,spacing ratio ,Fluid Flow and Transfer Processes ,Physics ,Tandem ,lcsh:T ,Oscillation ,Process Chemistry and Technology ,General Engineering ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,Computer Science Applications ,Amplitude ,lcsh:Biology (General) ,lcsh:QD1-999 ,lcsh:TA1-2040 ,Prism ,lcsh:Engineering (General). Civil engineering (General) ,0210 nano-technology ,lcsh:Physics ,Energy (signal processing) - Abstract
The advantageous performance in terms of energy conversion for the flow-induced motion (FIM) of T-section prisms has been experimentally reported recently. In order to further understand the oscillation and energy conversion of multiple T-section prisms, a series of tests of two T-section prisms arranged in tandem with five different spacing ratios (3 &le, L/D &le, 15) and seven load resistances (8 &Omega, &le, RL &le, 41 &Omega, ) were conducted. The effects of the spacing ratio and load resistances on energy conversion were discussed. The main conclusions can be summarized as follows. For most tests, the amplitudes of the upstream T-section prism (UTP) and downstream T-section prism (DTP) were both lower than the amplitude of the single T-section prism (STP) due to the mutual interference of the two prisms. Because of the mutual interference, the active powers of UTP and DTP were both less than that of STP, but at some special spacing ratios or load resistances, the mutual interference benefited the energy converted by the two prisms. In the presented tests, the total optimal active power of the upstream T-section prism and downstream T-section prism (UTP + DTP) was 30.12 W, which was 1.5 times that of STP (20.12 W).
- Published
- 2020
33. Fabrication of High Gas Barrier Epoxy Nanocomposites: An Approach Based on Layered Silicate Functionalized by a Compatible and Reactive Modifier of Epoxy-Diamine Adduct
- Author
-
Ran Wei, Shanyi Du, Xu Zhang, Chen Chen, and Xiaoqun Wang
- Subjects
Materials science ,gas barrier property ,Pharmaceutical Science ,02 engineering and technology ,Diamines ,010402 general chemistry ,01 natural sciences ,Article ,Analytical Chemistry ,Nanocomposites ,lcsh:QD241-441 ,chemistry.chemical_compound ,Structure-Activity Relationship ,lcsh:Organic chemistry ,X-Ray Diffraction ,Diamine ,Drug Discovery ,epoxy-diamine adduct ,Physical and Theoretical Chemistry ,layered silicate ,nanocomposite ,small-angle neutron scattering ,Nanocomposite ,Calorimetry, Differential Scanning ,Epoxy Resins ,Silicates ,Organic Chemistry ,Epoxy ,021001 nanoscience & nanotechnology ,Exfoliation joint ,0104 chemical sciences ,Monomer ,Montmorillonite ,chemistry ,Chemical engineering ,Chemistry (miscellaneous) ,Thermography ,visual_art ,visual_art.visual_art_medium ,Bentonite ,Molecular Medicine ,Surface modification ,0210 nano-technology ,Dispersion (chemistry) - Abstract
To solve the drawbacks of poor dispersion and weak interface in gas barrier nanocomposites, a novel epoxy-diamine adduct (DDA) was synthesized by reacting epoxy monomer DGEBA with curing agent D400 to functionalize montmorillonite (MMT), which could provide complete compatibility and reactivity with a DGEBA/D400 epoxy matrix. Thereafter, sodium type montmorillonite (Na-MMT) and organic-MMTs functionalized by DDA and polyether amines were incorporated with epoxy to manufacture nanocomposites. The effects of MMT functionalization on the morphology and gas barrier property of nanocomposites were evaluated. The results showed that DDA was successfully synthesized, terminating with epoxy and amine groups. By simulating the small-angle neutron scattering data with a sandwich structure model, the optimal dispersion/exfoliation of MMT was observed in a DDA-MMT/DGEBA nanocomposite with a mean radius of 751 Å, a layer thickness of 30.8 Å, and only two layers in each tactoid. Moreover, the DDA-MMT/DGEBA nanocomposite exhibited the best N2 barrier properties, which were about five times those of neat epoxy. Based on a modified Nielsen model, it was clarified that this excellent gas barrier property was due to the homogeneously dispersed lamellas with almost exfoliated structures. The improved morphology and barrier property confirmed the superiority of the adduct, which provides a general method for developing gas barrier nanocomposites.
- Published
- 2018
34. How to Do Knowledge Module Finishing
- Author
-
Xiaohui Zou, Shunpeng Zou, and Xiaoqun Wang
- Subjects
0209 industrial biotechnology ,Information retrieval ,Interpretation (logic) ,Computer science ,Character (computing) ,Corporate governance ,010401 analytical chemistry ,02 engineering and technology ,Knowledge module ,01 natural sciences ,0104 chemical sciences ,020901 industrial engineering & automation ,Simple (abstract algebra) ,Feature (machine learning) - Abstract
The aim is to introduce a simple and unique tool to realize the ergonomics of man-machine collaborative research on “governance of the country”. This method: First, the original text is imported, and then, a Chinese character board is generated, and then the language points, knowledge points, and original points are matched. The feature is human-machine collaboration. The result is that the Chinese character is tessellated, the Chinese chess spectrum is made, and the original chess is played. The knowledge module can be used for finishing. Its significance is: the language board, the knowledge game, and the original board game are digital, structured, and formal indirect ways to achieve automatic calculation: language points, knowledge points, and original points. The five menu-based knowledge modules of this example can be layered and distributed, and at least sixteen knowledge modules can be finished. Man-machine can be repeated calls. This is a contribution to the interpretation or understanding of texts.
- Published
- 2018
35. Ground-state phase diagram of the frustrated spin-1/2 two-leg honeycomb ladder
- Author
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Shijie Hu, Sebastian Eggert, Alexandros Metavitsiadis, Xiaoqun Wang, Jize Zhao, and Qiang Luo
- Subjects
Physics ,Phase transition ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,media_common.quotation_subject ,Frustration ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Phase (matter) ,0103 physical sciences ,Ising model ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Ground state ,media_common ,Phase diagram - Abstract
We investigate a spin-$1/2$ two-leg honeycomb ladder with frustrating next-nearest-neighbor (NNN) coupling along the legs, which is equivalent to two $J_1$-$J_2$ spin chains coupled with $J_\perp$ at odd rungs. The full parameter region of the model is systematically studied using conventional and infinite density-matrix renormalization group as well as bosonization. The rich phase diagram consists of five distinct phases: A Haldane phase, a NNN-Haldane phase and a staggered dimer phase when $J_{\perp} < 0$; a rung singlet phase and a columnar dimer phase when $J_{\perp} > 0$. An interesting reentrant behavior from the dimerized phase into the Haldane phase is found as the frustration $J_2$ increases. The universalities of the critical phase transitions are fully analyzed. Phase transitions between dimerized and disordered phases belong to the two-dimensional Ising class with central charge $c=1/2$. The transition from the Haldane phase to NNN-Haldane phase is of a weak topological first order, while the continuous transition between the Haldane phase and rung singlet phase has central charge $c=2$., 14 pages, 17 figures, for latest version and additional information see https://www.physik.uni-kl.de/eggert/papers/index.html
- Published
- 2018
- Full Text
- View/download PDF
36. High-Performance and Low-Cost Sodium-Ion Anode Based on a Facile Black Phosphorus-Carbon Nanocomposite
- Author
-
Xiaoqun Wang, Yaolin Xu, Fokko M. Mulder, Kai Liu, and Bo Peng
- Subjects
Nanocomposite ,Materials science ,Sodium ,Phosphorus ,Inorganic chemistry ,chemistry.chemical_element ,Black phosphorus ,02 engineering and technology ,Carbon black ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Anode ,Anode materials ,Nanocomposites ,Chemical engineering ,chemistry ,Chemical stability ,0210 nano-technology ,Carbon ,Sodium-ion batteries - Abstract
Black phosphorus (BP) has received increasing research attention as an anode material in sodium-ion batteries (SIBs), owing to its high capacity, electronic conductivity, and chemical stability. However, it is still challenging for BP-based SIB anodes to achieve a high electrochemical performance utilizing cost-effective materials and synthetic methods. This work presents a sodium-ion anode based on a BP-carbon nanocomposite synthesized from commercial red phosphorus and low-cost super P carbon black. Intimate interactions between BP and carbon are present, which helps to maintain the electrical conduction during cycling and, therefore, a high cycling stability is achieved. It exhibits a high capacity retention of 1381mAhg-1 for sodium-ion storage after 100 cycles, maintaining 90.5% of the initial reversible capacity. Such high performance/materials cost ratio may provide direction for future phosphorus-based anodes in high energy density SIBs.
- Published
- 2017
37. The electrochemical performance of super P carbon black in reversible Li/Na ion uptake
- Author
-
Bo Peng, Fokko M. Mulder, Yaolin Xu, Xiaoqun Wang, and Xinghua Shi
- Subjects
Materials science ,Graphene ,Na ion batteries ,Intercalation (chemistry) ,General Physics and Astronomy ,02 engineering and technology ,Electrolyte ,Carbon black ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Carboxymethyl cellulose ,law.invention ,super P carbon black ,Chemical engineering ,law ,medicine ,Li ion batteries ,Graphite ,0210 nano-technology ,Faraday efficiency ,medicine.drug - Abstract
Super P carbon black (SPCB) has been widely used as a conducting additive in Li/Na ion batteries to improve the electronic conductivity. However, there has not yet been a comprehensive study on its structure and electrochemical properties for Li/Na ion uptake, though it is important to characterize its contribution in any study of active materials that uses this additive in non-negligible amounts. In this article the structure of SPCB has been characterized and a comprehensive study on the electrochemical Li/Na ion uptake capability and reaction mechanisms are reported. SPCB exhibits a considerable lithiation capacity (up to 310 mAh g–1) from the Li ion intercalation in the graphite structure. Sodiation in SPCB undergoes two stages: Na ion intercalation into the layers between the graphene sheets and the Na plating in the pores between the nano-graphitic domains, and a sodiation capacity up to 145 mAh g–1 has been achieved. Moreover, the influence of the type and content of binders on the lithiation and sodiation properties has been investigated. The cycling stability is much enhanced with sodium carboxymethyl cellulose (NaCMC) binder in the electrode and fluoroethylene carbonate (FEC) in the electrolyte; and a higher content of binder improves the Coulombic efficiency during dis-/charge.
- Published
- 2017
38. Ground-state phase diagram of an anisotropic spin-12model on the triangular lattice
- Author
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Jize Zhao, Shijie Hu, Xiaoqun Wang, Qiang Luo, and Bin Xi
- Subjects
Quantum phase transition ,Density matrix ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,FOS: Physical sciences ,02 engineering and technology ,Quantum entanglement ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Quantum mechanics ,0103 physical sciences ,Hexagonal lattice ,Quantum spin liquid ,010306 general physics ,0210 nano-technology ,Ground state ,Quantum ,Phase diagram - Abstract
Motivated by the recent experiment on a rare-earth material YbMgGaO$_4$ [Y. Li \textit{et al.}, Phys. Rev. Lett. \textbf{115}, 167203 (2015)], which found that the ground state of YbMgGaO$_4$ is a quantum spin liquid, we study the ground-state phase diagram of an anisotropic spin-$1/2$ model that was proposed to describe YbMgGaO$_4$. Using the density-matrix renormalization group method in combination with the exact diagonalization, we calculate a variety of physical quantities, including the ground-state energy, the fidelity, the entanglement entropy and spin-spin correlation functions. Our studies show that in the quantum phase diagram there is a $120^{\circ}$ phase and two distinct stripe phases. The transitions from the two stripe phases to the $120^{\circ}$ phase are of the first order. However, the transition between the two stripe phases is not the first order, which is different from its classical counterpart. Additionally, we find no evidence for a quantum spin liquid in this model. Our results suggest that additional terms may be also important to model the material YbMgGaO$_4$. These findings will stimulate further experimental and theoretical works in understanding the quantum spin liquid ground state in YbMgGaO$_4$., Comment: minor changes
- Published
- 2017
39. Spin-wave approach to the two-magnon Raman scattering in aJ1x−J1y−J2−Jcantiferromagnetic Heisenberg model
- Author
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Anmin Zhang, Xiaoqun Wang, Qingming Zhang, Rong Yu, and Changle Liu
- Subjects
Physics ,Condensed matter physics ,Heisenberg model ,Magnon ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Tetragonal crystal system ,Spin wave ,Lattice (order) ,0103 physical sciences ,symbols ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Raman spectroscopy ,Raman scattering - Abstract
We study the two-magnon non-resonant Raman scattering in the (pi,pi) and (pi,0) ordered antiferromagnetic phases of a J1x-J1y-J2-Jc Heisenberg model on the tetragonal lattice within the framework of the spin-wave theory. We discuss the effects of various tuning factors to the two-magnon Raman spectra. We find that both the magnetic frustration J2/J1 and the interlayer exchange coupling Jc may significantly affect the spectra in both the B1g and A1g' channels in the (pi,pi) Neel ordered phase. Moreover, we find a splitting of the two-magnon peak in the (pi,0) antiferromagnetic phase. We further discuss the implications of our results to the BaMnBi2 and iron pnictide systems.
- Published
- 2017
40. Rare-Earth Chalcogenides: A Large Family of Triangular Lattice Spin Liquid Candidates
- Author
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Jianshu Li, Weiwei Liu, Jianting Ji, Hechang Lei, Yixuan Liu, Xiaoqun Wang, Zheng Zhang, Qingming Zhang, and Gang Chen
- Subjects
Physics ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Condensed Matter - Superconductivity ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Physics and Astronomy ,Charge (physics) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic susceptibility ,Ion ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Coupling (physics) ,Magnet ,0103 physical sciences ,Hexagonal lattice ,Quantum spin liquid ,010306 general physics ,0210 nano-technology ,Quantum - Abstract
Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid (QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO$_4$ stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh$_2$ (A = alkali or monovalent ions, Re = rare earth, Ch = O, S, Se). The family compounds share the same structure (R$\bar{3}$m) as YbMgGaO$_4$, and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the $c$-axis. Specific heat and magnetic susceptibility measurements on NaYbO$_2$, NaYbS$_2$ and NaYbSe$_2$ single crystals and polycrystals, reveal no structural or magnetic transition down to 50mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO$_4$. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages. This makes the family an ideal platform for fundamental research of QSLs and its promising applications., Comment: 8 pages, 4 figures; The updated supplementary materials (10 pages) can be found at http://cpl.iphy.ac.cn/fileup/0256-307X/PDF/0256-307X-2018-35-11-117501-Suppl.pdf
- Published
- 2018
41. Quantum spin ice on the breathing pyrochlore lattice
- Author
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Gang Chen, Yue Yu, Hae-Young Kee, Yong Baek Kim, Xiaoqun Wang, Lucile Savary, Department of Physics [MIT Cambridge], and Massachusetts Institute of Technology (MIT)
- Subjects
Quantum phase transition ,Pyrochlore ,FOS: Physical sciences ,02 engineering and technology ,engineering.material ,01 natural sciences ,7. Clean energy ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,Phase (matter) ,0103 physical sciences ,Spin model ,010306 general physics ,Quantum ,ComputingMilieux_MISCELLANEOUS ,Phase diagram ,Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,021001 nanoscience & nanotechnology ,3. Good health ,13. Climate action ,engineering ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,[PHYS.COND.CM-SCE]Physics [physics]/Condensed Matter [cond-mat]/Strongly Correlated Electrons [cond-mat.str-el] ,0210 nano-technology ,Hamiltonian (quantum mechanics) - Abstract
The Coulombic quantum spin liquid in quantum spin ice is an exotic quantum phase of matter that emerges on the pyrochlore lattice and is currently actively searched for. Motivated by recent experiments on the Yb-based breathing pyrochlore material Ba$_3$Yb$_2$Zn$_5$O$_{11}$, we theoretically study the phase diagram and magnetic properties of the relevant spin model. The latter takes the form of a quantum spin ice Hamiltonian on a breathing pyrochlore lattice, and we analyze the stability of the quantum spin liquid phase in the absence of the inversion symmetry which the lattice breaks explicitly at lattice sites. Using a gauge mean-field approach, we show that the quantum spin liquid occupies a finite region in parameter space. Moreover, there exists a direct quantum phase transition between the quantum spin liquid phase and featureless paramagnets, even though none of theses phases break any symmetry. At nonzero temperature, we show that breathing pyrochlores provide a much broader finite temperature spin liquid regime than their regular counterparts. We discuss the implications of the results for current experiments and make predictions for future experiments on breathing pyrochlores., Published. Update the author list. 10 pages, 3 figures
- Published
- 2016
42. Thermodynamics of a spin-1/2 XYZ Heisenberg chain with a Dzyaloshinskii-Moriya interaction
- Author
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Jize Zhao, Xiaoqun Wang, Qiang Luo, Bin Xi, and Shijie Hu
- Subjects
Physics ,Specific heat ,Strongly Correlated Electrons (cond-mat.str-el) ,Thermodynamics ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Entropy (classical thermodynamics) ,Condensed Matter - Strongly Correlated Electrons ,Quantum mechanics ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Phase diagram - Abstract
We study the thermodynamics of an XYZ Heisenberg chain with Dzyaloshinskii-Moriya interaction, which describes the low-energy behaviors of a one-dimensional spin-orbit-coupled bosonic model in the deep insulating region. The entropy and the specific heat are calculated numerically by the quasi-exact transfer-matrix renormalization group. In particular, in the limit $U^\prime/U\rightarrow\infty$, our model is exactly solvable and thus serves as a benchmark for our numerical method. From our data, we find that for $U^\prime/U>1$ a quantum phase transition between an (anti)ferromagnetic phase and a Tomonaga-Luttinger liquid phase occurs at a finite $\theta$, while for $U^\prime/U, Comment: accepted by Phys. Rev. B, title changed
- Published
- 2016
43. Giant magneto-optical Raman effect in a layered transition metal compound
- Author
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Xiaoqun Wang, Yuesheng Li, Jianting Ji, Qingming Zhang, Jiahe Fan, Anmin Zhang, Jiandi Zhang, and E. W. Plummer
- Subjects
Multidisciplinary ,Materials science ,Condensed matter physics ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Light scattering ,Magnetic field ,symbols.namesake ,X-ray Raman scattering ,0103 physical sciences ,Physical Sciences ,Perpendicular ,symbols ,Symmetry breaking ,010306 general physics ,0210 nano-technology ,Raman spectroscopy ,Intensity (heat transfer) ,Raman scattering - Abstract
Significance Raman scattering is a powerful technique to probe optical phonons in solids. It usually involves an electron-mediated three-step process, involving photon–electron, electron–phonon, and electron–photon interactions. In principle, manipulating electrons, for instance by applying a magnetic field, should affect Raman phonon intensity, yet there is no direct experimental measurement to demonstrate this. In this work we report the first realization to our knowledge of the idea in a prototype material, MoS 2 . From monolayer and bilayer to bulk MoS 2 we observe a dramatic modification of Raman phonon intensity induced by magnetic field. Such a giant magneto-optical effect appearing at a monoatomic layer level and its technological implications for magnetic-optical devices should inspire a new branch of inelastic light scattering.
- Published
- 2016
44. An anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets
- Author
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Yaodong Li, Xiaoqun Wang, and Gang Chen
- Subjects
Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,media_common.quotation_subject ,Frustration ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Spin wave ,0103 physical sciences ,Spin model ,Antiferromagnetism ,Hexagonal lattice ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Quantum fluctuation ,Phase diagram ,media_common ,Spin-½ - Abstract
Motivated by the recent experimental progress on the strong spin-orbit-coupled rare earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120-degree state and two distinct stripe ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3, RZn3P3, RCd3As3, RZn3As3, and R2O2CO3., 12 pages, 10 figures, 1 table. Add two families of triangular antiferromagnets (RCd3P3, RZn3P3, RCd3As3, RZn3As3, R2O2CO3) that were discovered recently
- Published
- 2015
45. A Novel Method for Manufacturing High-Performance Layered Silicate/Epoxy Nanocomposites Using an Epoxy-Diamine Adduct to Enhance Compatibility and Interfacial Reactivity
- Author
-
Ran Wei, Shanyi Du, Shijie Wang, Xu Zhang, Shouyu Zhu, and Xiaoqun Wang
- Subjects
Materials science ,Polymers and Plastics ,General Chemical Engineering ,Organic Chemistry ,Compatibility (geochemistry) ,02 engineering and technology ,Epoxy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Epoxy nanocomposites ,01 natural sciences ,Silicate ,0104 chemical sciences ,Adduct ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Diamine ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Reactivity (chemistry) ,0210 nano-technology - Published
- 2018
46. Electronic transport through graphene nanoribbons with Stone-Wales reconstruction at edges and interfaces
- Author
-
Fei Ye, Jing Wang, Guiping Zhang, and Xiaoqun Wang
- Subjects
010302 applied physics ,Range (particle radiation) ,Materials science ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Transfer-matrix method (optics) ,Biomedical Engineering ,FOS: Physical sciences ,Conductance ,Bioengineering ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Amplitude ,Zigzag ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,Ribbon ,General Materials Science ,Negative energy ,0210 nano-technology ,Graphene nanoribbons - Abstract
In this paper, we study the conductance of the graphene nanoribbons(GNRs) in the presence of the Stone-Wales(S-W) reconstruction, using the transfer matrix method. The ribbon is connected with semi-infinite quantum wires as the leads. The S-W reconstruction occurs on the edges and the interfaces between the electrodes and ribbon. When the reconstruction occurs on the edges, the conductance is suppressed considerably if the gate voltage $V_g$ takes intermediate values around $|V_{g}|\sim t_0$($t_0$ being the hopping amplitude of grahene) in both positive and negative energy regions. In contrast, if $V_g$ is close to the Dirac point or the band edges, the conductance is relatively insensitive to the edge reconstruction. The effect of edge reconstruction become less important with increasing ribbon width as expected. The S-W reconstruction occurs also possibly at the interfaces. In this case, the reconstruction suppresses identically the conductance in the entire range of $V_g$ for armchair GNRs. For the zigzag GNRs, the conductance is strongly suppressed in the negative energy region however the change of the conductance is relatively small in the positive energy region. We also analyze the transmission coefficients as functions of the channel index(the transverse momentum $k_y$ of the leads) for the neutral armchair GNRs with interface defects. Interestingly, there are two transmission peaks appearing at $k_{y}=\pi/3$ and $k_{y}=2\pi/3$ due to the unit cell doubling., Comment: 5 pages, 6 figures
- Published
- 2015
47. Ultralow-frequency collective compression mode and strong interlayer coupling in multilayer black phosphorus
- Author
-
Xiaoqun Wang, X. G. Luo, Changfeng Chen, Kai Liu, Qingming Zhang, Xianhui Chen, Xiaoli Ma, Jianting Ji, Anmin Zhang, Y. G. Ye, Shan Dong, and Yinghao Jie
- Subjects
Imagination ,Chemical substance ,Phonon ,media_common.quotation_subject ,General Physics and Astronomy ,FOS: Physical sciences ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,symbols.namesake ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,media_common ,Coupling ,Physics ,Frequency analysis ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Semiconductor ,Chemical physics ,symbols ,0210 nano-technology ,Science, technology and society ,business ,Raman spectroscopy - Abstract
The recent renaissance of black phosphorus (BP) as a two-dimensional 2D layered material has generated tremendous interest in its tunable electronic band gap and highly anisotropic transport properties that offer new opportunities for device applications. Many of these outstanding properties are attributed to its unique structural characters that still need elucidation. Here we show Raman measurements that reveal an ultralow-frequency collective compression mode (CCM), which is unprecedented among similar 2D layered materials. This novel CCM indicates an unusually strong interlayer coupling in BP, which is quantitatively supported by a phonon frequency analysis and first-principles calculations. Moreover, the CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of the thickness up to tens of atomic layers, which is considerably higher than those previously achieved by using high-frequency Raman modes. These results offer fundamental insights and practical tools for exploring multilayer BP in new device applications., Comment: 19 pages, 4 figures, 1 table, 30 references, supplementary information included
- Published
- 2015
- Full Text
- View/download PDF
48. Thermodynamics of the spin-flop transition in a quantumXYZchain
- Author
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Xiaoqun Wang, Xenophon Zotos, Nikos Papanicolaou, and J. Karadamoglou
- Subjects
Surface (mathematics) ,Physics ,Condensed matter physics ,Condensed Matter (cond-mat) ,FOS: Physical sciences ,Thermodynamics ,Condensed Matter ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Chain (algebraic topology) ,Quantum mechanics ,0103 physical sciences ,Flop-transition ,Thermodynamic limit ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Limit (mathematics) ,010306 general physics ,0210 nano-technology ,Quantum ,Spin-½ - Abstract
A special limit of an antiferromagnetic XYZ chain was recently shown to exhibit interesting bulk as well as surface spin-flop transitions at T=0. Here we provide a complete calculation of the thermodynamics of the bulk transition using a transfer-matrix-renormalization-group (TMRG) method that addresses directly the thermodynamic limit of quantum spin chains. We also shed some light on certain spinwave anomalies at low temperature predicted earlier by Johnson and Bonner., Comment: 4 pages, 6 Postscript figures
- Published
- 2000
49. Multistep Approach to Microscopic Models for Frustrated Quantum Magnets: The Case of the Natural Mineral Azurite
- Author
-
Roser Valentí, Hem C. Kandpal, Harald Olaf Jeschke, Ingo Opahle, Shijie Hu, Helge Rosner, Hena Das, Bernd Wolf, Johannes Richter, Tanusri Saha-Dasgupta, Andreas Honecker, Xiaoqun Wang, Michael Lang, Oleg Janson, A. Brühl, Robert Peters, Thomas Pruschke, Institut für Theoretische Physik [Frankfurt am Main] (ITP), Goethe-Universität Frankfurt am Main, Institut für Theoretische Physik [Göttingen], and Georg-August-University [Göttingen]
- Subjects
FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,engineering.material ,01 natural sciences ,Inelastic neutron scattering ,Condensed Matter - Strongly Correlated Electrons ,Magnetization ,0103 physical sciences ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,010306 general physics ,Quantum ,ComputingMilieux_MISCELLANEOUS ,Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Azurite ,Diamond ,021001 nanoscience & nanotechnology ,Magnetic susceptibility ,visual_art ,Magnet ,engineering ,visual_art.visual_art_medium ,Density functional theory ,0210 nano-technology - Abstract
The natural mineral azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$ is a frustrated magnet displaying unusual and controversially discussed magnetic behavior. Motivated by the lack of a unified description for this system, we perform a theoretical study based on density functional theory as well as state-of-the-art numerical many-body calculations. We propose an effective generalized spin-1/2 diamond chain model which provides a consistent description of experiments: low-temperature magnetization, inelastic neutron scattering, nuclear magnetic resonance measurements, magnetic susceptibility as well as new specific heat measurements. With this study we demonstrate that the balanced combination of first principles with powerful many-body methods successfully describes the behavior of this frustrated material., Comment: final version to appear in Phys. Rev. Lett.; 10 pages, 9 figures, 4 tables (including supplementary material)
- Published
- 2011
50. Accurate determination of the Gaussian transition in spin-1 chains with single-ion anisotropy
- Author
-
Shijie Hu, Xiaoqun Wang, B. Normand, and Lu Yu
- Subjects
Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Magnetism ,Gaussian ,FOS: Physical sciences ,02 engineering and technology ,Renormalization group ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Condensed Matter - Strongly Correlated Electrons ,Transverse plane ,symbols.namesake ,Transition point ,0103 physical sciences ,symbols ,010306 general physics ,0210 nano-technology ,Anisotropy ,Critical exponent ,Quantum - Abstract
The Gaussian transition in the spin-one Heisenberg chain with single-ion anisotropy is extremely difficult to treat, both analytically and numerically. We introduce an improved DMRG procedure with strict error control, which we use to access very large systems. By considering the bulk entropy, we determine the Gaussian transition point to 4-digit accuracy, $D_{c}/J = 0.96845(8)$, resolving a long-standing debate in quantum magnetism. With this value, we obtain high-precision data for the critical behavior of quantities including the ground-state energy, gap, and transverse string-order parameter, and for the critical exponent, $\nu = 1.472(2)$. Applying our improved technique at $J_{z} = 0.5$ highlights essential differences in critical behavior along the Gaussian transition line., Comment: 4 pages and 4 figures
- Published
- 2011
- Full Text
- View/download PDF
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