47 results on '"Zhiwei Shi"'
Search Results
2. Multi-Sensor Information Fusion Algorithm for Night Driving Vehicle Detection
- Author
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Yingqian Chen, Zhiwei Shi, Haowen Luo, Weiye Li, and Yaohua Deng
- Published
- 2023
3. Virtual flight test techniques to predict a blended-wing-body aircraft in-flight departure characteristics
- Author
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Zheng Gong, Zhiwei Shi, Mark H Lowenberg, Lijun Pan, Junquan Fu, and Dawei Wu
- Subjects
0209 industrial biotechnology ,Wing ,Elevator ,Angle of attack ,Computer science ,Mechanical Engineering ,System identification ,Open-loop controller ,Aerospace Engineering ,02 engineering and technology ,01 natural sciences ,Flight test ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Deflection (engineering) ,0103 physical sciences ,Simulation ,Wind tunnel - Abstract
As one of the promising configurations of the next generation of commercial aircraft, research on departure characteristics of the Blended-Wing-Body (BWB) is of great signification to safe flight limits. A three-degree-of-freedom (3-DOF) virtual flight test in a wind tunnel has been implemented for a candidate configuration to predict the departure characteristics. The support mechanism, the test model and the control law of the virtual flight test are introduced. In order to show the relationship between virtual flight test and actual flight test, the similarity criterion is also given. In open loop, the model has mild oscillations in the longitudinal and lateral directions, which are stable in closed-loop. The effect of flight control has been verified in virtual flight and actual subscale flight test. The analysis of system identification results indicate that the model has a good response to the excitation signal, and the response is in reasonable agreement with the flight test. Finally, the virtual flight departure test results are compared with the flight test. It shows that there is a good correspondence between the angle of attack and the elevator deflection at departure. This gives promising evidence of the practicability of virtual flight testing to predict departure of a BWB.
- Published
- 2022
4. Improvement of thermal performance and energy efficiency of micro-thermophotovoltaic with the dual-inlet combustor at appropriate equivalence ratio
- Author
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Zhiwei Shi, Qingguo Peng, Zhuang Kang, Zhixin Huang, Hao Wang, Xinghua Tian, Depeng Wei, and Xianhua Li
- Subjects
Fuel Technology ,General Chemical Engineering ,Organic Chemistry ,Energy Engineering and Power Technology - Published
- 2023
5. Experimental investigation of the interaction between a curved-surface jet and the mainstream on an airfoil at Mach 8
- Author
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Zhikun Sun, Zhiwei Shi, Xi Geng, Zheng Li, Quanbing Sun, Sinuo Chen, and Chuanhong Zhang
- Subjects
Aerospace Engineering - Published
- 2023
6. Experimental and numerical investigation on H2-fueled thermophotovoltaic micro tube with multi-cavity
- Author
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Shihao Tang, Jia Wei, Bo Xie, Zhiwei Shi, Hao Wang, Xinghua Tian, Biao He, and Qingguo Peng
- Subjects
General Energy ,Mechanical Engineering ,Building and Construction ,Electrical and Electronic Engineering ,Pollution ,Industrial and Manufacturing Engineering ,Civil and Structural Engineering - Published
- 2023
7. Flight trajectory optimization of sun-tracking solar aircraft under the constraint of mission region
- Author
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Haisong Ang, Mingjian Wu, Zhiwei Shi, and Tianhang Xiao
- Subjects
0209 industrial biotechnology ,Computer science ,business.industry ,Payload ,Mechanical Engineering ,Solar azimuth angle ,Aerospace Engineering ,ComputerApplications_COMPUTERSINOTHERSYSTEMS ,02 engineering and technology ,Radius ,Trajectory optimization ,01 natural sciences ,010305 fluids & plasmas ,Power (physics) ,020901 industrial engineering & automation ,Loiter ,Range (aeronautics) ,Physics::Space Physics ,0103 physical sciences ,Trajectory ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Aerospace engineering ,business - Abstract
The optimal yawing angle of sun-tracking solar aircraft is tightly related to the solar azimuth angle, which results in a large arc flight path to dynamically track the sun position. However, the limited detection range of payload usually requires solar aircraft to loiter over areas of interest for persistent surveillance missions. The large arc sun-tracking flight may cause the target area on the ground to be outside the maximum coverage area of payload. The present study therefore develops an optimal flight control approach for planning the flight path of sun-tracking solar aircraft within a mission region. The proposed method enables sun-tracking solar aircraft to maintain the optimal yawing angle most of the time during daylight flight, except when the aircraft reverses its direction by turning flight. For a circular region with a mission radius of 50 km, the optimal flight trajectory and controls of an example Λ-shaped sun-tracking solar aircraft are investigated theoretically. Results demonstrate the effectiveness of the proposed approach to optimize the flight path of the sun-tracking aircraft under the given circular region while maximizing the battery input power. Furthermore, the effects of varying the mission radius on energy performance are explored numerically. It has been proved that both net energy and energy balance remain nearly constant as the radius constraint varies, which enables the solar aircraft to achieve perpetual flight at almost the same latitude as the large arc flight. The method and results presented in this paper can provide reference for the persistent operation of sun-tracking solar aircraft within specific mission areas.
- Published
- 2021
8. Investigation of CH4 and porous media addition on thermal and working performance in premixed H2/air combustion for micro thermophotovoltaic
- Author
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Bo Xie, Qingguo Peng, Zhiwei Shi, Jia Wei, Zhuang Kang, Depeng Wei, Xinghua Tian, and Guang Fu
- Subjects
Fuel Technology ,General Chemical Engineering ,Organic Chemistry ,Energy Engineering and Power Technology - Published
- 2023
9. Surface wetting kinetics of water soluble organic film
- Author
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Katarzyna Majerczak, Joseph R.H. Manning, Zhiwei Shi, Zhanping Zhang, and Zhenyu Jason Zhang
- Subjects
General Chemical Engineering ,Organic Chemistry ,Materials Chemistry ,Surfaces, Coatings and Films - Published
- 2023
10. Investigation of heat and mass transfer of flow structures generated by a pulsed surface arc discharge actuator in quiescent air
- Author
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Zhikun Sun, Zhiwei Shi, Xi Geng, Zheng Li, and Qijie Sun
- Subjects
Aerospace Engineering - Published
- 2023
11. The optimization of photoinitiation system for holography by receiving the protection from dithiothreitol
- Author
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Zhiwei Shi, Weiping Li, Huishi Pi, Huicong Liu, Haining Chen, Yuzhe Wang, Pei Li, and Xiaoyu Jiang
- Subjects
Polymers and Plastics ,Organic Chemistry ,Materials Chemistry ,General Physics and Astronomy - Published
- 2023
12. Investigation of Heat and Mass Transfer by Surface Arc Discharge in Quiescent Air
- Author
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ZhiKun Sun, Zhiwei Shi, Xi Geng, and Qijie Sun
- Published
- 2022
13. Investigation on the H2 fueled combustion with CH4 and C3H8 blending in a micro tube with/without fins
- Author
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Jia Wei, Qingguo Peng, Zhiwei Shi, Bo Xie, Zhuang Kang, Jiahao Ye, and Guang Fu
- Subjects
Fuel Technology ,General Chemical Engineering ,Organic Chemistry ,Energy Engineering and Power Technology - Published
- 2022
14. Study on propagation mechanisms of the actuations generated by plasma synthetic jet actuator in a supersonic flow
- Author
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Weilin Zhang, Zhiwei Shi, Zheng Li, Xi Geng, Chuanhong Zhang, and Quanbing Sun
- Subjects
Aerospace Engineering - Published
- 2022
15. Energy optimization and investigation for Z-shaped sun-tracking morphing-wing solar-powered UAV
- Author
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Tianhang Xiao, Zhiwei Shi, Mingjian Wu, and Haisong Ang
- Subjects
0209 industrial biotechnology ,Wing ,business.industry ,Energy conversion efficiency ,Aerospace Engineering ,02 engineering and technology ,Energy minimization ,Tracking (particle physics) ,Solar energy ,01 natural sciences ,010305 fluids & plasmas ,Latitude ,020901 industrial engineering & automation ,0103 physical sciences ,Environmental science ,Daylight ,Electricity ,Aerospace engineering ,business - Abstract
To achieve perpetual flight, solar-powered UAVs (SPUAVs) need to convert sufficient solar energy into electricity during daylight flight. However, perpetual flight at middle and high latitude regions in winter days still poses great challenges for gaining enough solar energy due to the low sun elevation angle and short daylight duration. Among measures for flight endurance enhancement, tracking the sun through changing geometry of wing and orienting flight direction may be an effective design scheme for gaining more solar energy. In this paper, the energy optimization method for Z-shaped sun-tracking morphing-wing SPUAV is developed and used to investigate the advantages on energy performance of the optimal Z-shaped wing over the conventional planar wing. Energy optimization for a whole year's flight shows that the optimal Z-shaped wing is capable of achieving longer flight endurance, improving perpetual flight latitude and extending perpetual flight date efficiently compared with the planar wing, especially for the middle and high latitude regions during winter days. The investigation on implications of conversion efficiency of solar cells indicates that, with higher conversion efficiency of solar cells, the optimal Z-shaped wing is more effective to collect more net energy, retain more energy margin and achieve perpetual flight at higher latitude. The Z-shaped sun-tracking morphing-wing design combined with the energy optimization method proposed is helpful to increase flight endurance and improve perpetual flight latitude for SPUAVs.
- Published
- 2019
16. Design of LED free form lens based on improved mesh method
- Author
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Neng-you Le, Zhiwei Shi, and Xin-gang Shi
- Subjects
Materials science ,Plane (geometry) ,business.industry ,Near and far field ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Refraction ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,Lens (optics) ,LED lamp ,Optics ,law ,0103 physical sciences ,Reflection (physics) ,Point (geometry) ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Light-emitting diode - Abstract
Aiming at the LED (Light Emitting Diode) point sources with Lambertian distribution, we propose an improved mesh method to design a free form lens. For this method, a free-form surface is divided into two parts. A part is designed to be a refraction surface by using mesh method. Based on the refraction, the other part is designed to be a reflection surface. The combination of two parts forms a free-form surface lens. To take a petal-shaped lens as an example, simulation results show that the lens designed by using the improved mesh method can be higher illumination uniformity by comparing our method with the tradition method. When the radius of the light shape increases, the illumination uniformity increases, but the efficiency has no obvious change. When the distance between the point light source and the target plane increases, the illumination uniformity does not change significantly and the efficiency increases. Thus, the improved method can realize the limited illumination of light shape in the far and near field, so it will has broad application prospects in LED lighting.
- Published
- 2019
17. Pyrolytic behavior of coal-related model compounds connected with C–C bridged linkages by in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry
- Author
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Lijun Jin, Yang Zhou, Yang Li, Haoquan Hu, Jian Zhou, Zhiwei Shi, and Lu Li
- Subjects
chemistry.chemical_classification ,Steric effects ,Hydrogen bond ,020209 energy ,General Chemical Engineering ,Radical ,Organic Chemistry ,Energy Engineering and Power Technology ,Aromaticity ,02 engineering and technology ,Photochemistry ,Fuel Technology ,020401 chemical engineering ,chemistry ,Covalent bond ,Intramolecular force ,0202 electrical engineering, electronic engineering, information engineering ,0204 chemical engineering ,Pyrolysis ,Alkyl - Abstract
Coal pyrolysis is generally considered to initiate by cleavage of weak covalent bonds bridged between aromatic rings. The C–C covalent bonds are predominant bridged linkages among the framework of coal, which have a critical influence on coal pyrolysis reaction but lack of direct online observation. Five representative coal-related model compounds containing C–C bridged bonds, polypropylene (PP), polyvinylpyrrolidone (PVP), poly-4-vinylpyridine (P4VP), polystyrene (PS) and poly-4-vinylphenol, were selected to pyrolyze in an in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry (Py-VUV-PIMS). The soft ionized mass spectral detection can provide product distribution and evolved information of original products and intermediates, which are the key evidence to understand the initiation, recombination and reaction routes during pyrolysis process. Online analysis of pyrolysis reaction was found to be priority with cracking of C–C bond in the five polymer samples, and homologous free radicals and original products, which mainly include monomers, dimers and their alkyl and alkenyl radicals, were detected. The results reveal the cleavage temperature of C–C covalent bond is deeply related to its chemical environment, and obvious conjugation effect and steric effect for the bridged linkage were observed. In addition, the effect of hydrogen bond was also observed during the pyrolysis of model compounds containing hydroxyl groups, and intramolecular or intermolecular hydrogen bonding reduced the temperature at which C–C bridged bonds break. The analogous fracture mode and pyrolysis behavior of coal-related model compounds, which are beneficial to understand the reaction route and mechanism of coal pyrolysis, were discussed based on the experimental observations and theoretical calculation.
- Published
- 2019
18. Nonlocal surface solitons in two-dimensional PT-symmetric optical lattices
- Author
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Wanchun Lu, Xing Zhu, Zhiwei Shi, and Huagang Li
- Subjects
Surface (mathematics) ,02 engineering and technology ,01 natural sciences ,Stability (probability) ,010309 optics ,symbols.namesake ,Optics ,Linear stability analysis ,Quantum mechanics ,0103 physical sciences ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,Nonlinear Sciences::Pattern Formation and Solitons ,Physics ,business.industry ,Function (mathematics) ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Nonlinear system ,Fourier transform ,Step function ,symbols ,0210 nano-technology ,business ,Refractive index - Abstract
We investigate the existence and stability of nonlocal surface solitons at the interface between linear media and nonlocal nonlinear media with two-dimensional (2D) parity-time ( PT )-symmetric optical lattices. We analytically obtain the nonlinearity-induced change of the refractive index by introducing a reasonable step function with the method of Fourier transform, and carry out the linear stability analysis for the surface solitons based on the response function of the infinite nonlocal medium. Numerical results show that nonlocal PT surface solitons can exist and be stable in 2D PT -symmetric optical lattices.
- Published
- 2019
19. In-situ analysis of catalytic pyrolysis of Baiyinhua coal with pyrolysis time-of-flight mass spectrometry
- Author
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Heng Li, Yang Zhou, Zhiwei Shi, Yang Li, Haoquan Hu, and Lijun Jin
- Subjects
business.industry ,020209 energy ,General Chemical Engineering ,Organic Chemistry ,Inorganic chemistry ,Energy Engineering and Power Technology ,chemistry.chemical_element ,02 engineering and technology ,Mass spectrometry ,Oxygen ,Catalysis ,chemistry.chemical_compound ,Fuel Technology ,020401 chemical engineering ,chemistry ,0202 electrical engineering, electronic engineering, information engineering ,Coal ,Phenols ,0204 chemical engineering ,Time-of-flight mass spectrometry ,Benzene ,business ,Pyrolysis - Abstract
Baiyinhua coal was subjected to catalytic pyrolysis over HZSM-5 and Ni-modified HZSM-5 (Ni/HZSM-5) with a novel pyrolysis time-of-flight mass spectrometers (Py-TOF-MS) equipped with vacuum ultraviolet photoionization (VUVPI). The soft ionization of VUVPI allowed the detection of volatile organic compounds. The effect of HZSM-5 and Ni/HZSM-5 on distribution of coal pyrolysis products was online investigated. The coal pyrolysis products including alkanes, phenols, aromatics and sulfur containing compounds (H2S and CH3SH) were detected. In the presence of HZSM-5 and Ni/HZSM-5, the products from coal pyrolysis have higher content of substituted benzene and alkenes and lower content of phenols in comparison with that without catalyst. The catalysts promote the conversion of phenols products to aromatic hydrocarbons via dehydroxylation reaction. Ni/HZSM-5 exhibits better catalytic performance for generating products with higher aromatic content and less oxygen species than HZSM-5 alone. Temperature-evolved profiles of pyrolysis products were also measured. It was found that the peak temperature of alkenes and substituted benzene of catalytic pyrolysis shifts to lower temperature region while that of dihydroxybenzenes moves to higher temperature. This work demonstrates the good performance of Py-TOF-MS for the online study of the coal catalytic pyrolysis process.
- Published
- 2018
20. Stall flutter suppression of NACA 0012 airfoil based on steady blowing
- Author
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Zhen Chen, Zhiwei Shi, Sinuo Chen, and Zhangyi Yao
- Subjects
Mechanical Engineering - Published
- 2022
21. Multi-degree-of-freedom beam rotation based on multi-beam vector superposition
- Author
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Huagang Li and Zhiwei Shi
- Subjects
Physics ,business.industry ,Phase (waves) ,Plane wave ,Elliptical polarization ,Polarization (waves) ,Rotation ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Superposition principle ,Optics ,Optical tweezers ,Physics::Accelerator Physics ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business ,Beam (structure) - Abstract
A method for the generation of tunable multi-degree-of-freedom rotations of vector beams on demand along a propagation direction is theoretically proposed. This generation can be achieved by a suitable vector superposition of three monochromatic non-coplanar beams, including a plane wave with elliptical polarization and two Bessel–Hermite–Gauss (BHG) beams with orthogonal polarization, the parameters of which were systematically chosen to obtain the different longitudinal characteristics of the field, i.e., the state of polarization (SoP), phase, and intensity. On one hand, both the incidence angles of the two BHG beams and the additional phase of the plane wave affect the rotation of the beam intensity and phase, but the incidence angle does not affect the rotation of the SoP. Moreover, the additional phase can lead to a change of the rotation angle of the SoP. On the other hand, the weight coefficients of the two BHG beams periodically change the beam intensity distribution along the propagation direction. Interestingly, the beam is non-diffracting, which means that energy is only exchanged internally and is conserved as a whole. This approach may find applications in dynamic multi-beam optical tweezers, atom guiding, materials processing, microscopy, and optical communications.
- Published
- 2022
22. Influence of selenium on root morphology and photosynthetic characteristics of winter wheat under cadmium stress
- Author
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Xiaoming Qin, Hongen Liu, Shiyu Qin, Zhiwei Shi, Zhaojun Nie, and Peng Zhao
- Subjects
0106 biological sciences ,Cadmium ,Stomatal conductance ,food and beverages ,chemistry.chemical_element ,Plant Science ,010501 environmental sciences ,Photosynthesis ,Hydroponics ,01 natural sciences ,Animal science ,chemistry ,Shoot ,Dry matter ,Agronomy and Crop Science ,Ecology, Evolution, Behavior and Systematics ,Selenium ,010606 plant biology & botany ,0105 earth and related environmental sciences ,Transpiration - Abstract
To explore the feasibility of reducing cadmium (Cd) concentrations and alleviating Cd toxicity via selenium (Se), this study investigated the effects of Se on the root morphology, photosynthetic parameters, and Se, and Cd concentrations in winter wheat under different Cd stress levels. Three Cd levels (0, 5 and 10 μM) and three Se levels (0, 1 and 5 μM) were applied in a hydroponics test. The results showed that increases in Cd stress significantly decreased the shoot and root dry matter weight, root length, root volume, root effective surface area, root total surface area, Se concentration, Se accumulation, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and intercellular CO2 concentration (Ci). Increases in Cd stress significantly increased the Cd concentration and accumulation in shoots and roots, the root average diameter, and the stomatal limiting value (Ls). There were significant relationships between the root Cd concentrations and the root morphology parameters, shoot Cd concentrations and photosynthetic characteristics of winter wheat. The Se1 and Se5 treatments effectively increased the shoot dry matter weight, root length, root volume, root effective surface area and root total surface area and decreased the shoot Cd concentration, when Cd stress was at the medium level (Cd5). Only the Se1 treatment effectively increased the Gs, Tr and Ci under the Cd5 treatment. When Cd stress was at the high level (Cd10), the Se5 treatment had greater effects on root growth than the Se1 treatment, the Se levels had no pronounced effect on the shoot dry weight and Cd concentration in winter wheat. Meanwhile, the root Se concentration was closely related to each root morphology parameter. Cd stress inhibited the root growth and leaf photosynthesis of winter wheat, and a high enough Se supply reduced the Cd toxicity by enhancing the root growth of winter wheat.
- Published
- 2018
23. Self-learned suppression of roll oscillations based on model-free reinforcement learning
- Author
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Zhiwei Shi, Zhangyi Yao, Kun Chen, and Yizhang Dong
- Subjects
0209 industrial biotechnology ,Computer science ,Counterintuitive ,Aerospace Engineering ,02 engineering and technology ,Model free ,Space (mathematics) ,01 natural sciences ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Control theory ,0103 physical sciences ,Reinforcement learning ,Current sensor - Abstract
The high-angle-of-attack uncommanded roll oscillations are dangerous and cause significant challenges in flight control. This paper focuses on investigating the feasibility and performance of an artificial-intelligence method - “model-free reinforcement learning” (MFRL) on this issue, in both simulation and experiment. In simulation, two algorithms TD3 and SAC were used to learn the policies to suppress the roll oscillations of a widely used mathematical model. The agents only utilized current states as observation vector, and achieved perfect results. In the experiments, these two algorithms were used to learn the policies to suppress the roll oscillations of a flying-wing model which utilized spanwise blowing as its roll effectors. It is worth noting that unlike in simulation, the experiments investigated the influence of the observation vectors' memory size on training results. The results show that for both algorithms, the agents cannot learn good-enough policies when their observation spaces were constructed only by the current sensor data. This phenomenon, which is a big difference between experiments and simulations of MFRL, is due to the non-Markovian characteristic of the real-world dynamics caused by inevitable latencies. However, constructing the observation space using current and past sensor data help both the TD3 and SAC agents to learn great policies to suppress the oscillations using spanwise blowing in real world. Surprisingly, the trained agents showed some counterintuitive “smart” behaviors in tests.
- Published
- 2021
24. Effect of hydrothermal treatment on structure and liquefaction behavior of Baiyinhua coal
- Author
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Lijun Jin, Yang Zhou, Zhiwei Shi, Yang Li, and Haoquan Hu
- Subjects
020209 energy ,General Chemical Engineering ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Mineralogy ,02 engineering and technology ,Coal liquefaction ,complex mixtures ,Autoclave ,020401 chemical engineering ,0202 electrical engineering, electronic engineering, information engineering ,Coal ,0204 chemical engineering ,Fourier transform infrared spectroscopy ,Chemistry ,business.industry ,technology, industry, and agriculture ,Liquefaction ,respiratory system ,respiratory tract diseases ,Thermogravimetry ,Fuel Technology ,Chemical engineering ,Atomic ratio ,business ,Carbon - Abstract
Baiyinhua (BYH) coal, a kind of lignite, was hydrothermally treated in an autoclave reactor at 200–350 °C for 30 min and the liquefaction behavior of the treated samples were investigated. To uncouple the complex behavior of the changes in structural characteristics and functional groups of treated samples, the structural change in BYH coal was investigated by thermogravimetry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Results reveal that oxygen content and volatile matter in treated sample reduce and carbon content increases. The decrease in atomic ratio of oxygen to carbon and hydrogen to carbon of treated sample indicates the improvement in coalification degree. CO 2 and CO account for the overwhelming majority of gaseous products from hydrothermal treatment, which can be attributed to the significantly decrease of carboxyl and carbonyl content. The hydrothermal treatment involves the breakup of some weak bonds within coal structure, and the main structure of BYH coal does not change significantly. A desirable upgraded coal was obtained by hydrothermal treatment of BYH raw coal at 250 °C. The liquefaction behavior of coal can be improved by hydrothermal treatment at 250 °C, and the oil yield increases from 32.9 wt% (dry ash-free basis) of raw coal to 37.8 wt% (dry ash-free basis). This work illustrates that hydrothermal treatment is a promising approach for upgrading of low rank coal.
- Published
- 2017
25. Isotope analysis for understanding the hydrogen transfer mechanism in direct liquefaction of Bulianta coal
- Author
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Yang Li, Lijun Jin, Zhiwei Shi, Haoquan Hu, and Ben Niu
- Subjects
Hydrogen ,Chemistry ,020209 energy ,General Chemical Engineering ,Organic Chemistry ,Inorganic chemistry ,Energy Engineering and Power Technology ,Liquefaction ,chemistry.chemical_element ,02 engineering and technology ,Electrophilic aromatic substitution ,Coal liquefaction ,chemistry.chemical_compound ,Fuel Technology ,Deuterium ,Kinetic isotope effect ,0202 electrical engineering, electronic engineering, information engineering ,Proton NMR ,Tetralin - Abstract
Direct coal liquefaction (DCL) was investigated using a deuterium tracer method which makes it possible to determine which structural positions in the coal react with H 2 or hydrogen-donor solvents, i.e. hydrogen-transfer mechanism. D 2 and/or 1,2,3,4-d 4 -tetralin (tetralin-d 4 ) were used in DCL of Bulianta coal at 7.0 MPa (initial charge pressure) and 445 °C for 0 or 60 min in a tubing-bomb microreactor. 2 H NMR and isotope ratio mass spectrometry (IRMS) were used to determine the distribution of deuterium in liquefaction solvent and products qualitatively and quantitatively. The 2 H NMR of solvents after DCL under a variety of conditions showed that the α-radical of tetralin is an important intermediate in hydrogen transfer to and exchange with coal, and the de/re-hydrogenation cycle of tetralin is not a dominating approach of hydrogen transfer in DCL. The distribution of deuterium in each structural position and the D/ 1 H in preasphaltenes and asphaltenes (PAA) under a variety of conditions showed that both hydrogen atoms in tetralin and H 2 could enter alkyl groups remote from aromatic nucleus of PAA in preference to aromatic nucleus and α to aromatic groups of PAA. The hydrogen atoms in tetralin are more easily to stabilize radicals from coal cracking to form PAA than those in H 2 during the heating-up stage of DCL. Both the kinetic isotope effect and electrophilic aromatic substitution reaction in DCL, indicating the existence of ionic reaction process besides a radical reaction process in DCL.
- Published
- 2017
26. Propagation of an Airy-Gaussian vortex beam in defected photonic lattices
- Author
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Zhiwei Shi, Yongtao Xu, Huagang Li, Xing Zhu, and Yang Li
- Subjects
Physics ,Condensed matter physics ,Self-focusing ,Soliton (optics) ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Vortex ,Intensity (physics) ,010309 optics ,Amplitude modulation ,Nonlinear system ,Lattice (module) ,0103 physical sciences ,Physics::Accelerator Physics ,Electrical and Electronic Engineering ,010306 general physics ,Beam (structure) - Abstract
We investigate numerically the propagation of an Airy-Gaussian vortex (AiGV) beam in the defected photonic lattices. The propagation properties of the AiGV beam are affected by positive and negative defects. Interestingly, we find that the intensity distribution of the AiGV beam focuses on the position of the defect and then forms a lattice soliton for the positive defect. On the contrary, the AiGV beam is diffused for the negative defect. The higher value the defected depth is, the more energy can be constrained by the positive defect and the shorter transmission distance for the beam forming a lattice soliton is. And the effect of nonlinear is smaller than the effect of defects. Moreover, by changing the effects of nonlinearity, the lattice modulation depth, the defect depth and the distribution factor, we can control the propagation distance for the AiGV beam focusing for the positive defect.
- Published
- 2017
27. Inverted solitons in a spin-orbit-coupled Bose-Einstein condensate
- Author
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Zhiwei Shi, Xing Zhu, and Huagang Li
- Subjects
Field (physics) ,01 natural sciences ,010305 fluids & plasmas ,law.invention ,symbols.namesake ,Optics ,law ,Position (vector) ,0103 physical sciences ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,010306 general physics ,Nonlinear Sciences::Pattern Formation and Solitons ,Spin-½ ,Condensed Matter::Quantum Gases ,Physics ,Zeeman effect ,business.industry ,Spin–orbit interaction ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Nonlinear Sciences::Exactly Solvable and Integrable Systems ,symbols ,Orbit (dynamics) ,Soliton ,business ,Bose–Einstein condensate - Abstract
We investigate the “inverted” solitons in spin-orbit-coupled Bose-Einstein condensate with one-dimensional spatially periodic Zeeman field. Soliton existence depends on the exact invert for the condensate components in the spatially periodic Zeeman field. And the position and the total pseudomagnetization density of the solitons can be controlled by the spatially periodic Zeeman field. Simulated results show that the inverted solitons can be stable for the interatomic attractive interactions.
- Published
- 2017
28. Mechanism of hydrogen transfer and role of solvent during heating-up stage of direct coal liquefaction
- Author
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Ben Niu, Yang Li, Zhiwei Shi, Lijun Jin, Yueting Li, and Haoquan Hu
- Subjects
business.industry ,020209 energy ,General Chemical Engineering ,Inorganic chemistry ,Energy Engineering and Power Technology ,Liquefaction ,02 engineering and technology ,Coal liquefaction ,Catalysis ,Solvent ,chemistry.chemical_compound ,Fuel Technology ,020401 chemical engineering ,Decalin ,chemistry ,0202 electrical engineering, electronic engineering, information engineering ,Coal ,Tetralin ,0204 chemical engineering ,business ,Dissolution - Abstract
In this paper, the liquefaction of a Bulianta coal, from China Shenhua Group, was carried out in a hydrogen donor solvent, tetralin, or a non-hydrogen donor solvent, 1-methylnaphthalene, with or without catalyst to clarify the mechanism of hydrogen transfer. And roles of solvent and a nano-size iron catalyst from Shenhua Group in the heating-up stage of DCL were also investigated by using mixed solvent of decalin, phenanthrene, pyrene or fluoranthene and tetralin. The results show that tetralin inhibits the reaction of coal macromolecule to oil and the transfer of H2. The major transfer approach of H2 may be directly from H2 to coal rather than via the hydrogen donor solvents in the presence of the nano-sized iron catalyst. In the heating-up stage of DCL, the major role of solvent is to provide activated hydrogen for coal. High dissolving capability of the liquefaction solvent that has high enough hydrogen donor capacity is beneficial for improving liquefaction performance. The dominant function of the catalyst is to promote the activation of H2, which can improve coal liquefaction performance in the heating-up stage of DCL.
- Published
- 2017
29. Gap solitons in parity-time-symmetric mixed linear-nonlinear optical lattices with fourth-order diffraction
- Author
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Xing Zhu, Zhiwei Shi, and Huagang Li
- Subjects
Diffraction ,Physics ,Coupling constant ,Condensed matter physics ,business.industry ,Parity (physics) ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,Nonlinear optical ,Dipole ,Nonlinear Sciences::Exactly Solvable and Integrable Systems ,Fourth order ,Optics ,Quantum mechanics ,0103 physical sciences ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,010306 general physics ,business ,Nonlinear Sciences::Pattern Formation and Solitons - Abstract
We report on the existence and stability of fundamental and out-of-phase dipole gap solitons in parity-time (PT)-symmetric mixed linear-nonlinear optical lattices with a fourth-order diffraction. These solitons exist in the semi-infinite gap. For fundamental gap solitons, they can bifurcate from the higher edge of the first Bloch band, solitons are stable in the low power region. For dipole gap solitons, they cannot bifurcate from the higher edge of the first Bloch band, they can stably exist in the moderate power region. The coupling constant of the fourth-order diffraction can influence the stability of these gap solitons.
- Published
- 2017
30. Experimental investigation of influence of strake wings on self-induced roll motion at high angles of attack
- Author
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Keming Cheng, Xi Geng, and Zhiwei Shi
- Subjects
Engineering ,Strake wing ,Aerospace Engineering ,02 engineering and technology ,01 natural sciences ,Trim ,010305 fluids & plasmas ,Flow separation ,Missile ,0203 mechanical engineering ,0103 physical sciences ,Cruciform fins ,020301 aerospace & aeronautics ,Wing ,business.industry ,Mechanical Engineering ,Structural engineering ,Mechanics ,Aerodynamics ,Strake ,Vortex ,PIV ,Nonlinear system ,High angle of attack ,Roll motion ,business - Abstract
The modern high performance air vehicles are required to have extreme maneuverability, which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the self-induced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at α = 60°. The free-to-roll results show that the model with whole strake wings (baseline), the model assembled with three strake wings (Case A) and the model assembled with two opposite strake wings (Case C) experience the spinning, while the model assembled with two adjacent strake wings (Case B), the model assembled with one strake wing (Case D) and the model with no strake wing (Case E) trim or slightly vibrate at a certain “×” rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at α = 60°.
- Published
- 2016
- Full Text
- View/download PDF
31. Defect matter-wave gap solitons in spin–orbit-coupled Bose–Einstein condensates in Zeeman lattices
- Author
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Zhiwei Shi, Xing Zhu, and Huagang Li
- Subjects
Physics ,Zeeman effect ,Condensed matter physics ,General Physics and Astronomy ,01 natural sciences ,law.invention ,010309 optics ,Coupling (physics) ,Nonlinear system ,symbols.namesake ,law ,Quantum mechanics ,0103 physical sciences ,symbols ,Even and odd functions ,Matter wave ,Orbit (control theory) ,010306 general physics ,Nonlinear Sciences::Pattern Formation and Solitons ,Bose–Einstein condensate ,Spin-½ - Abstract
We report on the properties of fundamental defect matter-wave gap solitons in spin–orbit-coupled Bose–Einstein condensates in one-dimensional Zeeman lattices with attractive nonlinearity. One component of these solitons is a real even function, and the other is an imaginary odd function. When the defect is repulsive, these solitons can be stable in the semi-infinite, first, and second gaps. Increasing the strength of spin–orbit coupling, stable defect gap-stripe solitons in the semi-infinite and first gaps are found. However, for an attractive defect, the solitons only stably exist in the semi-infinite gap and cannot be close to the lower edge of the first Bloch band.
- Published
- 2016
32. Effect of wingtip connection on the energy and flight endurance performance of solar aircraft
- Author
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Tianhang Xiao, Zhiwei Shi, Mingjian Wu, and Haisong Ang
- Subjects
Battery (electricity) ,0209 industrial biotechnology ,Lift-induced drag ,business.industry ,Aerospace Engineering ,02 engineering and technology ,Energy consumption ,01 natural sciences ,Aspect ratio (image) ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Solar cell efficiency ,Range (aeronautics) ,Physics::Space Physics ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Environmental science ,Daylight ,Astrophysics::Earth and Planetary Astrophysics ,Aerospace engineering ,business ,Oswald efficiency number ,Physics::Atmospheric and Oceanic Physics - Abstract
This study explores the effects of wingtip connection on decreasing energy consumption and increasing flight endurance for solar aircraft. The Oswald efficiency factor, induced drag coefficient and power consumption are derived as the models of the number of wingtip connected aircraft. As the energy margin model is related to the number of connected solar aircraft, a flight endurance margin model is proposed to evaluate the advantages of wingtip connection quantitatively. With the numerical method developed, researches on the energy and flight endurance performance for a given example wingtip-connected solar aircraft are performed. Moreover, the impacts of solar cell efficiency, flight date and latitude on the advantages of wingtip connection for solar aircraft are explored. The results suggest that the wingtip connection design enables solar aircraft to decrease induced drag coefficient, increase flight endurance and range effectively when the aircraft is only powered by battery. The wingtip connection design is more effective to increase the flight endurance and improve the maximum perpetual flight latitude with more connected solar aircrafts and higher solar cell efficiency, especially in the flight condition with high solar elevation angle and more daylight hours. However, as the number of connected solar aircraft increases, the effect of one more connected aircraft on these advantages decreases because the effect of wingtip connection on decreasing induced drag coefficient decreases with increasing aspect ratio.
- Published
- 2021
33. Study on inner characteristics of plasma synthetic jet actuator and geometric effects
- Author
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Weilin Zhang, Shoulin Jin, Zhiwei Shi, and Xi Geng
- Subjects
0209 industrial biotechnology ,Jet (fluid) ,Materials science ,Computer simulation ,Turbulence ,Oscillation ,Flow (psychology) ,Aerospace Engineering ,02 engineering and technology ,Plasma ,Mechanics ,01 natural sciences ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Speed of sound ,0103 physical sciences ,Body orifice - Abstract
In order to further study the inner characteristics of the plasma synthetic jet actuator (PSJA) which consists of a cavity, two electrodes and a lid with orifice, a two-dimensional numerical simulation is carried out with SST k-ω turbulence model. The evolutions of the flow parameters inside the cavity with a single pulse, such as pressure, density, temperature and velocity, are analyzed in detail. The oscillation mechanisms of the flow parameters at the orifice of the cavity is also investigated. To study the effects of geometric factors on the performance of the PSJA, five widths and heights of the cavities are considered. The results suggest that the base frequencies are inversely proportional to the width and height of the cavity respectively. The proportional constant is equal to the sound speed. Besides, shortening the width or height of the cavity can obtain a faster peak velocity of the jet. The peak of the jet velocity occurs earlier with a shorter height of the cavity.
- Published
- 2020
34. The study of flow separation control by a nanosecond pulse discharge actuator
- Author
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Zhiwei Shi, Keming Cheng, Lu Jichun, Zheng Li, Hai Du, Hu Liang, and Ganniu Li
- Subjects
010302 applied physics ,Fluid Flow and Transfer Processes ,Leading edge ,Materials science ,Mechanical Engineering ,General Chemical Engineering ,Aerospace Engineering ,Dielectric barrier discharge ,Mechanics ,Nanosecond ,01 natural sciences ,010305 fluids & plasmas ,Vortex ,Flow control (fluid) ,Flow separation ,Nuclear Energy and Engineering ,Inviscid flow ,0103 physical sciences ,Plasma actuator - Abstract
The basic dynamic characteristic of a nanosecond (NS) pulse discharge actuator in still air is investigated, which introduces viscid and inviscid effects to the flow, namely, heated air and pressure waves, respectively. The efficacy of a dielectric barrier discharge plasma actuator driven by a nanosecond pulse for active flow separation control is investigated experimentally on a NASA SC(2)-0712 aerofoil at Re = 0.5 × 10 6 (25 m/s). The pressure distribution on the aerofoil surface is measured, and the result indicates that the separation is well controlled at a high angle of attack. The PIV test result shows that the forcing frequency selectively affects the flow over the aerofoil, and a higher forcing frequency has a better influence on the leading edge shear layer. Schlieren imaging experiments at Re = 0.1 × 10 6 (5 m/s) show that the main disturbance factor for the nanosecond pulse plasma actuator is the heating effect, which changes the local temperature and density and induces several vortex structures. The vortex structures entrain the outer high-momentum fluid into the shear layer, thereby strengthening the mixing of the shear layer with the main flow and delaying separation or even reattaching a separated flow. The research reveals the major disturbance factor introduced by NS discharge applied to flow separation control. Furthermore, the spatiotemporal disturbance process induced by the pulse discharge is investigated.
- Published
- 2016
35. Zinc oxide Chemical Bath Deposition on Functionalized organic thin films: Formation of nanorods, nanorockets and nanoflowers
- Author
-
Zhiwei Shi and Amy V. Walker
- Subjects
Materials science ,Inorganic chemistry ,Metals and Alloys ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,Zinc ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Nanomaterials ,law.invention ,chemistry ,law ,Reagent ,Materials Chemistry ,Nanorod ,Thin film ,Crystallization ,0210 nano-technology ,Dissolution ,Chemical bath deposition - Abstract
Controlling the morphology of nanostructured materials is critical for their use in technological applications including in sensing, electronics and energy harvesting. In this paper we investigate the reaction pathways involved and their dependence on reactant concentrations in the formation of ZnO nanomaterials on –COOH terminated self-assembled monolayers using a simple chemical bath deposition process which employs zinc acetate, which acts as the Zn source, and ethylenediamine, which acts as both the O source and a complexing agent for Zn2 +. At a deposition temperature of 318 K (45 °C) our data shows that the concentration of Zn2 + as well as the deposition bath pH, which is controlled by the ethylenediamine concentration, is critical in determining the ZnO morphology. Above 0.01 M zinc acetate at low bath pH (~ 7.7–8.5), nanorods and nanorockets are observed to form. The nanorods exhibit a clear interface in the middle indicating that they are composed of two crystals. At lower zinc acetate concentrations over a wide pH range (~ 8.0–10.5) nanoflowers form. The nanorockets and nanoflowers grow via a modified La Mer mechanism in which there are multiple nucleation and crystallization steps. The initial nuclei are sphelurites (nanoflowers) or nanocrystallites (nanorockets). Since the reagent concentrations limit the reaction, for these initial precursor crystallites to increase in size, it is required dissolution and re-precipitation must occur. Thus at later times nanorockets or nanoflowers develop.
- Published
- 2016
36. Nonlocal gray solitons in parity-time-symmetric potentials with spatially modulated nonlinearity
- Author
-
Huagang Li, Xing Zhu, and Zhiwei Shi
- Subjects
Physics ,business.industry ,Parity (physics) ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Nonlinear system ,Quantum nonlocality ,Nonlinear Sciences::Exactly Solvable and Integrable Systems ,Optics ,Computer Science::Computer Vision and Pattern Recognition ,Quantum mechanics ,Computer Science::Multimedia ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business ,Nonlinear Sciences::Pattern Formation and Solitons - Abstract
We investigate the nonlocal gray solitons in parity-time (PT)-symmetric potentials with spatially modulated nonlinearity. If the nonlinear modulated function (nonlinear potential) is real, the coefficient of the function can control the grayness and the existence domain of these gray solitons. Especially, if the coefficient of the nonlinear modulated function is below a threshold, the gray solitons will be changed into anti-dark solitons. The effects of the degree of the nonlocality and the imaginary part of the PT-symmetric potentials on the grayness and the existence of the gray solitons are also discussed. If the nonlinear modulated function is also PT symmetric, the imaginary part of the function will obviously affect the existence and stability of the nonlocal gray solitons.
- Published
- 2015
37. The suppression of flying-wing roll oscillations with open and closed-loop spanwise blowing
- Author
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Yizhang Dong, Dechen Wei, Zhiwei Shi, Shengxiang Tong, and Kun Chen
- Subjects
Flow control (data) ,Physics ,0209 industrial biotechnology ,Wing ,Angle of attack ,Control variable ,Aerospace Engineering ,02 engineering and technology ,Mechanics ,01 natural sciences ,Trim ,010305 fluids & plasmas ,Vortex ,020901 industrial engineering & automation ,Duty cycle ,0103 physical sciences ,Order of magnitude - Abstract
Uncommanded self-induced roll oscillations cause significant challenges in flight control and are ubiquitous in high-attack-angle flights in the flying-wing configuration. Spanwise blowing slots were designed in this article to suppress these roll oscillations with nonzero mean angles of a 53° swept flying-wing model. Three flow control strategies were proposed and studied successively. The open-loop symmetric blowing successfully suppressed oscillations below the nominal angle of attack of 24° before losing its effectiveness. Subsequently, adaptive continuous blowing using the proportion-integral-differential algorithm was performed with symmetric pre-blowing to eliminate the ineffective region with a small blowing coefficient. Using this strategy, roll oscillations under all tested nominal angles of attack were successfully addressed as the nonzero trim angles were eliminated and the oscillations were suppressed. However, the air consumption needed to maintain the model balance was too large, which necessitated the development of pulsed blowing. Static force measurements showed that the blowing-induced rolling moment had a linear relationship with the duty cycle of blowing. The results from the particle-image-velocimetry tests revealed that the mechanism of the linear relationship was the increased duration of coherent vortices over a period at longer duty cycles. Based on the static experimental results, the model was stabilized via proportion-integral-differential adaptive blowing, which utilized the duty cycle as the control variable. Compared to the second strategy, the last one reduced the required mean blowing momentum coefficient by two orders of magnitude while maintaining a great control effect.
- Published
- 2020
38. Design of a CHMSL based on Fresnel lens
- Author
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Xin-gang Shi, Neng-you Le, and Zhiwei Shi
- Subjects
Physics ,business.industry ,Fresnel lens ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Collimated light ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,Optical axis ,Optics ,law ,0103 physical sciences ,Perpendicular ,Light beam ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Layer (electronics) ,Beam (structure) ,Diode - Abstract
We propose a design of a center high mounted stop lamp (CHMSL) based on Fresnel lens. The Fresnel lens is divided into four layers. The first layer collimates the beam of Light Emitting Diode (LED) along the direction perpendicular to optical axis; The second layer makes the output light uniformly distributed; The third layer collimates the beam along the optical axis direction; The fourth layer scatters the collimating light to make the last light distribution meet the relevant regulations. The simulation and test results show that the efficient of this CHMSL is 38.3 % and the uniformity is about 92.4 %. This CHMSL is practical and can applicable to vehicle lighting.
- Published
- 2020
39. Discrete solitons in saturable nonlinearity media with parity-time symmetric lattices
- Author
-
Huagang Li, Zhiwei Shi, Yang Li, and Qianggui Song
- Subjects
Physics ,Nonlinear system ,Nonlinear Sciences::Exactly Solvable and Integrable Systems ,Optics ,business.industry ,Quantum mechanics ,Parity (physics) ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business ,Nonlinear Sciences::Pattern Formation and Solitons ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials - Abstract
We study the existence of discrete solitons in saturable nonlinearity media with parity-time symmetric lattices. We find that there exist two kinds of discrete solitons, they share the same parameters but different energy flows. The degree of saturable nonlinearity can influence the properties of such discrete solitons. Stable discrete solitons are found near the anti-continuum limit.
- Published
- 2014
40. Bioaccumulation and biomarker responses of cubic and octahedral Cu2O micro/nanocrystals in Daphnia magna
- Author
-
Hong Liu, Dongfeng Zhang, Lin Guo, Wenhong Fan, Xiuping Yang, Zhiwei Shi, Xiaolong Wang, and Minming Cui
- Subjects
Environmental Engineering ,Daphnia magna ,Nanotechnology ,Nanomaterials ,medicine ,Animals ,Waste Management and Disposal ,Dissolution ,reproductive and urinary physiology ,Water Science and Technology ,Civil and Structural Engineering ,biology ,Chemistry ,Ecological Modeling ,fungi ,Copper toxicity ,medicine.disease ,biology.organism_classification ,Pollution ,Bioavailability ,Daphnia ,Nanocrystal ,Nanotoxicology ,Bioaccumulation ,Nanoparticles ,Metallothionein ,Copper ,Water Pollutants, Chemical ,Nuclear chemistry - Abstract
Great progress has been made in the controlled fabrication of nanomaterials with given sizes, shapes, and geometries. However, how such changes in structure potentially affect the bioavailability and toxicity of metal nanoparticles to aquatic organisms remains mostly unknown. The present study reports the different behaviors of two types of Cu2O micro/nanocrystals (micro/nano-Cu2O) with different shapes (cubic and octahedral) and crystallographies (with exposed surfaces as {100} or {111}). The bioaccumulation, median lethal concentration, and biomarker responses of Daphnia magna exposed to the two micro/nanocrystals are also investigated. The Cu accumulation, production of metallothionein (MT), and inhibition ratio of D. magna increased gradually with increasing micro/nano-Cu2O concentration. The two crystals showed slight Cu accumulation differences toward D. magna, and their biomarker responses and toxicities to D. magna differed significantly as well. The octahedral Cu2O micro/nanocrystals were more toxic to D. magna compared with the cubic micro/nanocrystals probably because of the higher surface activities of the {111} facets compared with those of the {100} facets for cuprites. Food ingestion was the main entry pathway of the micro/nanocrystals into organisms, and toxicity was consequently determined based on the dissolution behavior of the micro/nanocrystals in vivo.
- Published
- 2012
41. Multipole surface solitons supported by the interface between linear media and nonlocal nonlinear media
- Author
-
Huagang Li, Zhiwei Shi, and Qi Guo
- Subjects
Surface (mathematics) ,Physics ,Nonlinear system ,Quantum nonlocality ,Classical mechanics ,Degree (graph theory) ,Quantum mechanics ,Nonlinear medium ,General Physics and Astronomy ,Propagation constant ,Multipole expansion ,Nonlinear Sciences::Pattern Formation and Solitons ,Linear medium - Abstract
We address multipole surface solitons occurring at the interface between a linear medium and a nonlocal nonlinear medium. We show the impact of nonlocality, the propagation constant, and the linear index difference of two media on the properties of the surface solitons. We find that there exist a threshold value of the degree of the nonlocality at the same linear index difference of two media, only when the degree of the nonlocality goes beyond the value, the multipole surface solitons can be stable.
- Published
- 2012
42. Two-dimensional stationary nonlinear surface solitons in nonlocal nonlinear media
- Author
-
Zhiwei Shi, Guodong Yan, and Huagang Li
- Subjects
Physics ,Surface (mathematics) ,Degree (graph theory) ,Critical value ,Atomic and Molecular Physics, and Optics ,Linear medium ,Electronic, Optical and Magnetic Materials ,Quantum nonlocality ,Nonlinear system ,Dipole ,Nonlinear Sciences::Exactly Solvable and Integrable Systems ,Classical mechanics ,Quantum mechanics ,Nonlinear medium ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,Nonlinear Sciences::Pattern Formation and Solitons - Abstract
We address two-dimensional surface solitons occurring at the interface between a semi-infinite linear medium and a semi-infinite nonlocal nonlinear medium. We find that there exist stable single and dipole surface solitons. The properties of the surface solitons can be affected by the degree of nonlocality. Interestingly, only when the degree of nonlocality is greater than a critical value, the surface solitons can exist.
- Published
- 2012
43. Surface solitons at the interface between semi-infinite linear and thermal nonlinear optical media
- Author
-
Xiujuan Jiang, Dongmei Deng, Huagang Li, Zhiwei Shi, and Xing Zhu
- Subjects
Physics ,Kerr effect ,business.industry ,Nonlinear optics ,Threshold energy ,Atomic and Molecular Physics, and Optics ,Linear medium ,Electronic, Optical and Magnetic Materials ,Dipole ,Optics ,Nonlinear medium ,Soliton ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business ,Refractive index - Abstract
We investigate numerically surface-wave solitons occurring at the interface between semi-infinite linear and thermal nonlinear optical media, with the refractive index of the linear medium being greater than that of the nonlinear medium (in the absence of light). We find that the threshold energy flows of the existence of the surface solitons depend on the linear refractive index difference of the two media. Their fitting empirical formula has been obtained. Furthermore, we elucidate that the optical beams propagating in thermal nonlinear optical media, either as a single surface soliton or as a dipole surface soliton, can be attracted to the surface, even when launched from far away.
- Published
- 2011
44. Influence of laser wavelength on target irradiation uniformity
- Author
-
Xiujuan Jiang, Zunqi Lin, Zhiwei Shi, and Shenlei Zhou
- Subjects
Materials science ,business.industry ,Physics::Optics ,Plasma ,medicine.disease_cause ,Laser ,Thermal conduction ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Wavelength ,Optics ,law ,medicine ,Optoelectronics ,Irradiation ,Electrical and Electronic Engineering ,business ,Smoothing ,Ultraviolet ,Lens array - Abstract
Target irradiation uniformity is very important in laser-produced plasmas experiments. The wavelength dependence of the irradiation uniformity is investigated in the joint scheme using a lens array (LA) and the technique of smoothing by spectral dispersion (SSD). It is proved that, for the long wavelength laser, lateral thermal conduction smoothing within the target is quite effective, while for the ultraviolet laser, SSD is the main smoothing mechanism. So SSD and other temporal smoothing methods are very necessary in producing uniform irradiation with laser beam of short wavelength.
- Published
- 2011
45. Selective formation of monodisperse CdSe nanoparticles on functionalized self-assembled monolayers using chemical bath deposition
- Author
-
Zhiwei Shi, Amy V. Walker, and Peng Lu
- Subjects
Chemistry ,General Chemical Engineering ,Analytical chemistry ,Nucleation ,Nanoparticle ,Self-assembled monolayer ,chemistry.chemical_compound ,Chemical engineering ,Monolayer ,Electrochemistry ,Self-assembly ,Carboxylate ,Deposition (chemistry) ,Chemical bath deposition - Abstract
Using CdSe chemical bath deposition (CBD) we demonstrate the selective growth and deposition of monodisperse nanoparticles on functionalized self-assembled monolayers (SAMs) using time-of-flight secondary ion mass spectrometry and scanning electron microscopy. We show that the deposition mechanism involves both ion-by-ion growth and cluster-by-cluster deposition. On –COOH terminated SAMs strongly adherent CdSe nanoparticles form via a mixed ion-by-ion and cluster-by-cluster mechanism. Initially, Cd 2+ ions form complexes with the terminal carboxylate groups. The Cd 2+ -carboxylate complexes then act as the nucleation sites for the ion-by-ion growth of CdSe. After a sufficient concentration of Se 2− has formed in solution via the hydrolysis of selenosulfate ions, the deposition mechanism switches to cluster-by-cluster deposition. On –OH and –CH 3 terminated SAMs monodisperse CdSe nanoparticles are deposited via cluster-by-cluster deposition and they do not bind strongly to the surface. Finally, under the appropriate experimental conditions we demonstrate the selective deposition of CdSe nanoparticles on patterned –CH 3 /–COOH SAMs.
- Published
- 2010
46. γ–C plane and robustness in static reservoir for nonlinear regression estimation
- Author
-
Zhiwei Shi and Min Han
- Subjects
Mathematical optimization ,Cognitive Neuroscience ,Feature vector ,MathematicsofComputing_NUMERICALANALYSIS ,Reservoir computing ,Computer Science Applications ,Robust regression ,Support vector machine ,Kernel method ,Artificial Intelligence ,Outlier ,Algorithm ,Extreme learning machine ,Mathematics ,Cholesky decomposition - Abstract
Reservoir method is applied to the feed-forward learning machines for nonlinear regression estimation. Inspired by the existing experience from extreme learning machine (ELM), the new method inherits the basic idea from support vector echo-state machines, but eliminates the internal feedback matrix to adapt for the feed-forward usage. Based on the analysis of nonlinearity in reservoir and regularization in readout weights, the parameters of input scaling and penalty regularization are taken as the hyper-parameters to characterize a static reservoir (ELM), and then a proper reservoir is identified on the @c-C plane based on a generalization error criterion. For outlier suppression, the regularized robust regression is applied in the reservoir feature space, and it leads to an efficient algorithm for large-scale problems, which can be solved by Cholesky decomposition. The proposed method is compared with the classical kernel method and ELM method on several benchmark nonlinear regression datasets, and the results indicate the method is comparable with the existing methods.
- Published
- 2009
47. Application of multimode fiber optical sensor in optical tomography technology
- Author
-
Zhiwei, Shi, primary, Huan, Zhou, additional, Yang, Li, additional, and Yanhua, Zeng, additional
- Published
- 2005
- Full Text
- View/download PDF
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