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Confined states and spin polarization on a topological insulator thin film modulated by an electric potential

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Chinese Physics B 2013年第7期22卷 478-483页

作者：刘一曼邵怀华周小英周光辉 Department of Physics and Key laboratory for Low-Dimensional structures and quantum Manipulation (Ministry of Education) Hunan Normal University

We study the electronic structure and spin polarization of the surface states of a three-dimensional topological insulator thin film modulated by an electrical potential well. By routinely solving the low-energy surface Dirac equation for the system, we demonstrate that confined surface states exist, in which the electron density is almost localized inside the well and exponentially decayed outside in real space, and that their subband dispersions are quasilinear with respect to the propagating wavevector. Interestingly, the top and bottom surface confined states with the same density distribution have opposite spin polarizations due to the hybridization between the two surfaces. Along with the mathematical analysis, we provide an intuitive, topological understanding of the effect.

关键词： topological insulator thin film electronic structure spin polarization electric potential

Thermodynamics of charged AdS black hole surrounded by quintessence in restricted phase space

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Chinese Physics B 2024年第10期33卷 205-212页

作者： Siyu Jian Siying Long Juhua Chen Yongjiu Wang Department of Physics Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Educationand Synergetic Innovation Center for Quantum Effects and ApplicationsHunan Normal UniversityChangsha 410081China

We study thermodynamics of charged AdS black hole surrounded by quintessence in a new formalism which is called the restricted phase space *** context is based on Visser’s holographic thermodynamics with a fixed antide Sitter radius and a variable Newton *** conjugate variables,central charge C and the chemical potential m,are introduced as a new pair of thermodynamic *** find that the iso-e-charge T-S curve becomes non-monotonic when Qenergy density of Kiselev’s fluid becomes larger,the critical temperature T_(c)will ***,the van derWaals-like phase transition will occur at lower *** is always a non-quilibrium transition from a small unstable black hole to a large stable black hole state in the isocoltage T-S *** exist a maximum and a Hawking-Page phase transition points in theμ-C *** the value of b related to Kiselev’s fluid becomes larger,the Hawking-Page phase transition will occur at lower temperature in the isovoltageμ-T *** other values of the state parameterω,there also exists van der Waals-like phase transition.

关键词： Reissner-Nordstrom qAdS black hole restricted phase space variable Newton constant

Transparently manipulating spin-orbit qubit via exact degenerate ground states

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Chinese Physics B 2020年第8期29卷 217-227页

作者： Kuo Hai Wenhua Zhu Qiong Chen Wenhua Hai Department of Physics and Key laboratory of Low-dimensional quantum structures and quantum Control of Ministry of Education and Synergetic Innovation Center for Quantum Effects and ApplicationsHunan Normal UniversityChangsha 410081China

By investigating a harmonically confined and periodically driven particle system with spin-orbit coupling(SOC)and a specific controlled parameter,we demonstrate an exactly solvable two-level model with a complete set of spin-motion entangled Schrödinger kitten(or cat)*** the undriven case,application of a modulation resonance results in the exact stationary *** show a decoherence-averse effect of SOC and implement a transparent coherent control by exchanging positions of the probability-density wavepackets to create transitions between the different degenerate ground *** expected energy consisting of quantum and continuous parts is derived,and the energy deviations caused by the exchange operations are much less than the quantum *** results could be directly extended to a weakly coupled single-particle chain for transparently encoding spin-orbit qubits via the robust spin-motion entangled degenerate ground states.

关键词： transparent coherent control spin-orbit qubit exact degenerate ground state spin-orbit coupling spin-motion entanglement

quantum speed limit time of a non-Hermitian two-level system

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Chinese Physics B 2020年第3期29卷 89-94页

作者： Yan-Yi Wang Mao-Fa Fang Synergetic Innovation Center for quantum Effects and Application and Key Laboratory of Low-dimensional Quantum Structures and Quantum Control of Ministry of EducationSchool of Physics and ElectronicsHunan Normal UniversityChangsha 410081China

We investigated the quantum speed limit time of a non-Hermitian two-level system for which gain and loss of energy or amplitude are present. Our results show that, with respect to two distinguishable states of the non-Hermitian system, the evolutionary time does not have a nonzero lower bound. The quantum evolution of the system can be effectively accelerated by adjusting the non-Hermitian parameter, as well as the quantum speed limit time can be arbitrarily small even be zero.

关键词： quantum speed limit time non-Hermitian dynamics quantum optics

A high-performance biochar produced from bamboo pyrolysis with in-situ nitrogen doping and activation for adsorption of phenol and methylene blue

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Chinese Journal of Chemical Engineering 2020年第11期28卷 2872-2880页

作者： Zhenhao Li Bo Xing Yan Ding Yunchao Li Shurong Wang State Key laboratory of clean energy Utilization Zhejiang UniversityHangzhou 310027China

Nitrogen doping is a promising method for the preparation of functional carbon *** this study,a nitrogen-doped porous coral biochar was prepared by using bamboo as raw material,urea as nitrogen source,and KHCO3 as green activator through in-situ *** structure of the obtained biochar was characterized by various techniques including nitrogen adsorption and desorption,Raman spectroscopy,X-ray photoelectron spectrometer,and *** adsorption properties of nitrogen-doped biochar were evaluated with phenol and methylene blue *** results showed that the nitrogen source ratio had a significant effect on the evolution of pore structure of *** urea addition ratio was beneficial to the development of pore *** optimum specific surface area of nitrogen-doped biochar could be up to 1693 m^2·g^-*** doping can effectively improve the adsorption capacity of biochar to phenol and methylene *** prepared at 973.15 K with low urea addition ratio exhibited the highest adsorption capacity for phenol and methylene blue,and the equilibrium adsorption capacity was 169.0 mg·g^-1 and 499.3 mg·g^-1,*** comparing the adsorption capacity of various adsorbents in related fields,it is proved that the nitrogen-doped biochar prepared in this study has a good adsorption effect.

关键词： In-situ pyrolysis Nitrogen doping Green activator Biochar Adsorption

Characterization of pyrolytic lignins with different activities obtained from bio-oil

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Chinese Journal of Chemical Engineering 2017年第3期25卷 324-329页

作者： Furong Leng Yurong Wang Junhao Chen Shurong Wang Jinsong Zhou Zhongyang Luo State Key laboratory of clean energy Utilization Zhejiang UniversityHangzhou 310027China

Pyrolytic lignin, the water-insoluble fraction in bio-oil, often shows a high content and has strong intermolecular interactions with other compounds in bio-oil. In order to obtain pure pyrolytic lignin and facilitate the utilization of aqueous phase obtained from water extraction of bio-oil, methanol–water extraction method was employed to further separate the bio-oil water-insoluble phase in this paper. Different technologies, including Fourier transform infrared spectroscopy, gel permeation chromatography, and nuclear magnetic resonance, were adopted to characterize the structures of pyrolytic lignins with different activities obtained through this method. Both the heating value and the polymerization degree of high-molecular-weight pyrolytic lignin were higher than those of low-molecular-weight pyrolytic lignin. The molecular weight distribution of high-molecular-weight pyrolytic lignin was relatively wider, among which the contents of dimers to pentamers all accounted for 12% –18%,while the low-molecular-weight pyrolytic lignin mainly consisted of trimers(75.38%). The pyrolytic lignins had similar basic structures, both of which contained syringyl and guaiacyl units, whereas the low-molecular-weight pyrolytic lignin had more abundant syringyl units, reactive carbonyl groups and hydroxyl groups. Meanwhile,thermogravimetric study revealed that the final char residue yield of low-molecular-weight pyrolytic lignin was lower than that of high-molecular-weight pyrolytic lignin.

关键词： Bio-oil Pyrolytic lignin Separation Characterization

Catalytic hydrodeoxygenation of pyrolysis bio-oil to jet fuel: A review

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Frontiers in energy 2024年第5期18卷 550-582页

作者： Zhongyang Luo Wanchen Zhu Feiting Miao Jinsong Zhou State Key laboratory of clean energy Utilization Zhejiang UniversityHangzhou 310027China

Bio-oil from biomass pyrolysis cannot directly substitute traditional fuel due to compositional *** hydrodeoxygenation(HDO)is the critical and efficient step to upgrade crude bio-oil to high-quality bio-jet fuel by lowering the oxygen content and increasing the heating ***,the hydrocracking reaction tends to reduce the liquid yield and increase the gas yield,causing carbon loss and producing hydrocarbons with a short *** obtain high-yield bio-jet fuel,the elucidation of the conversion process of biomass catalytic HDO is important in providing guidance for metal catalyst design and optimization of reaction *** the complexity of crude bio-oil,this review aimed to investigate the catalytic HDO pathways with model compounds that present typical bio-oil ***,it provided a comprehensive summary of the impact of physical and electronic structures of both noble and non-noble metals that include monometallic and bimetallic supported catalysts on regulating the conversion pathways and resulting product *** subsequent first principle calculations further corroborated reaction pathways of model compounds in atom-level on different catalyst surfaces with the experiments above and illustrated the favored C-O/C-O scission orders thermodynamically and ***,it discussed hydrogenation effects of different H-donors(such as hydrogen and methane)and catalysts deactivation for economical and industrial *** on the descriptions above and recent researches,it also elaborated on catalytic HDO of biomass and bio-oil with multi-functional ***,it presented the challenges and future prospective of biomass catalytic HDO.

关键词： biomass pyrolysis oil bio-jet fuel catalytic hydrodeoxygenation(HDO) metal catalyst reaction pathways

Experimental Study on Coal Partial Gasification Coproducing Char,Tar,and Gas

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Journal of Thermal Science 2023年第6期32卷 2297-2309页

作者： SONG Xue WANG Qinhui ZHU Yao XIE Guilin ZHU Deao CEN Jianmeng LUO Zhongyang State Key laboratory of clean energy Utilization Zhejiang UniversityHangzhou310027China

The coal partial gasification process produces a large number of *** have similar combustion characteristics to anthracite and can be utilized as a material manufacturing clean briquette to replace residential coal to achieve clean ***,the coal partial gasification produced more tar at relatively low temperature,which can be applied as naphtha or diesel after purification and ***,experiments of coal partial gasification coproducing char,tar,and gas are carried out on a bench-scale fluidized bed reactor during the temperature range of 625–762℃.The effect of equivalence ratio on the characteristics of coal partial gasification products is *** results show that the equivalence ratio increasing from 0.06 to 0.13 leads to a higher partial gasification temperature and lower char yield,and tar yield reaches a maximum value and the lower calorific value of gas reaches as high as 6.14 MJ/m^(3).When the gasification temperature is lower than 643℃,the increase in temperature promotes the generation of oxygen-containing functional groups and aromatic compounds in coal particles,and the microstructures of char become more *** combustion stability of char is getting worse,whereas the pore structures in char become abundant at high *** the analysis of the tar chromatography column,it is observed that asphaltene and non-hydrocarbon account for 77%–88%of the total amount of tar.

关键词： coal partial gasification cascading utilization product characteristics

A quantum chemistry study on reaction mechanisms of SO_2 with O_3 and H_2O_2

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第9期10卷 1327-1333页

作者： Shu-dong JIANG Zhi-hua WANG Jun-hu ZHOU Zheng-cheng WEN Ke-fa CEN State Key laboratory of clean energy Utilization Zhejiang University Hangzhou 310027 China

Reaction mechanisms of SO2 with O3 and H2O2 were investigated using quantum chemistry ab initio methods. structures of all reactants, products, and transition states were optimized at the B3LYP/6-311G＋（3df,2p） level, and energy calculations were made at the G2M level. SO2 reactions with O3 and H2O2 occurred by O-abstraction and OH-abstraction by SO2, respectively, at length forming SO3＋O2 （3Eg） and H2SO4. For SO2＋O3 reactions the barrier height was predicted to be 9.68 kcal/mol with a rate constant of 3.61 × 10^-23 cm^3/（molecule.s） at 300 K, which is below the experimental upper limit. The rate constant predicted for this reaction accords well with the one provided by National Institute for Standards and Technology （NIST） in 250-500 K. For SO2＋H2O2 reactions the barrier height was predicted to be 62.39 kcal/mol with a rate constant of 2.48× 10^-61 cm^3/（molecule.s） at 300 K.

关键词： Sulfur dioxide Ozone Hydrogen peroxide Reaction mechanism Rate constant quantum chemistry