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Search Results: 1 - 10 of 241945 matches for " X. G. Wu "
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The Optimal Sensing Coverage for Road Surveillance  [PDF]
X. F. Cheng, P. Liu, Z. G. Chen, H. B. Wu, X. H. Fan
Wireless Sensor Network (WSN) , 2010, DOI: 10.4236/wsn.2010.24043
Abstract: So far path coverage problem has been studied widely to characterize the properties of the coverage of a path or a track in an area induced by a sensor network, in which the path or track is usually treated as a curve and the width of it can be ignored. However, sensor networks often are employed to carry out road surveillance or target tracking, in which the interesting area is only the surface of the road, thus the width of the road must be considered. This paper analyzes the optimal sensing coverage of the road in this kind of applications, assuming that sensor nodes are deployed along both sides of the road determinately. The optimal position of sensor nodes is studied considering the sensing range of sensors and the width of the road, and the purpose is to cover the road surface completely with minimal nodes. The isosceles triangle model is proposed and proved to be the most suitable, that is to say all sensors get the maximal available sensing area if any three nearest sensors located on both sides of the road form an isosceles triangle. Comparing with the equilateral triangle model proposed in other articles, this model increases the coverage rate and supplies complete coverage of the road.
Effects of genetically modified herbicide-tolerant (GMHT) rice on biodiversity of weed in paddy fields
X Jiang, X Wu, G Xiao
African Journal of Biotechnology , 2010,
Abstract: To detect potential changes in properties of weed communities in fields of GMHT rice Bar68-1, trials were carried out from 2007-2008 at Changsha, China with conventional indica rice D68 served as control. The average richness of weed community measured by species accumulation curve tended to be identical in the fields of Bar68-1 and D68 as the number of sampling points increased. There were no significant differences (p > 0.05) in diversity indices which included numbers of species(S), Shannon- Wiener (H’), Pielou evenness (J’), Simpson diversity (D) and evenness (E) indices. Species composition for these two weed communities was roughly comparable. The top four weed species, sorted by individual abundance, were Monochoria vaginalis (Burm. f.) Presl ex Kunth, Lindernia procumbens (Krock.) Philcox, Cyperus diformis L. and Juncellus serotinus (Rottb.) .B. Clarke in the fields of Bar68-1 and D68. ABC curves showed that the weed communities were “unpolluted”. The data above confirm the hypothesis that the difference between the effect of GMHT rice Bar68-1 on biodiversity of weed in paddy fields and that of non-GM rice D68 was not significant.
Influence of bulk inversion asymmetry on the magneto-optical spectrum of a HgTe topological insulator
M. Pang,X. G. Wu
Physics , 2013, DOI: 10.1103/PhysRevB.88.235309
Abstract: The influence of bulk inversion asymmetry in [001] and [013] grown HgTe quantum wells is investigated theoretically. The bulk inversion asymmetry leads to an anti-crossing gap between two zero-mode Landau levels in a HgTe topological insulator, i.e., the quantum well with inverted band structure. It is found that this is the main contribution to the anti-crossing splitting observed in recent experimental magneto spectroscopic measurements. The relevant optical transitions involve different subbands, but the electron-electron interaction induced depolarization shift is found to be negligibly small. It is also found that the splitting of this anti-crossing only depends weakly on the tilting angle when the magnetic field is tilted away from the perpendicular direction to the quantum well. Thus, the strength of bulk inversion asymmetry can be determined via a direct comparison between the theoretical calculated one-electron energy levels and experimentally observed anti-crossing energy gap.
Efficiency of electrical manipulation on two-dimensional topological insulators
M. Pang,X. G. Wu
Physics , 2013,
Abstract: We investigate the efficiency of electrical manipulation on two-dimensional topological insulators by considering a lateral potential superlattice on the system. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. This indicates that the electric manipulation efficiency on two-dimensional topological insulators is not as high as expected, which should be carefully considered in designing a device application that bases on two-dimensional topological insulators. These features can be attributed to the coupled multiple-band nature of the topological insulator model. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model.
Exact wave functions for the edge state of a disk-shaped two dimensional topological insulator
M. Pang,X. G. Wu
Physics , 2013,
Abstract: We report the exact wave functions for the eigen state of a disk-shaped two dimensional topological insulator. The property of the edge state whose energy lies inside the bulk gap is studied. It is found that the edge state energy is affected by the radius of the disk. For a fixed angular momentum index, there is a critical disk radius below which there exists no edge state. The value of this critical radius increases as the angular momentum index increases. In the limit of large disk radius, the energy of the edge state approaches a limiting value determined by the system parameters and independent of the angular momentum index. The derivation from this limiting value is inversely proportional to the radius with a coefficient proportional to the angular momentum index. In the general case, the energy differences between two edge states with adjacent angular momentum indexes are not equal. The exact and analytical wave functions also facilitates the investigation of electronic state in other structures of the two dimensional topological insulator.
Landau level transitions in InAs/AlSb/GaSb quantum wells
X. G. Wu,M. Pang
Physics , 2015, DOI: 10.1088/1674-1056/24/9/097301
Abstract: The electronic structure of InAs/AlSb/GaSb quantum wells embedded in AlSb barriers and in the presence of a perpendicular magnetic field is studied theoretically within the $14$-band ${\bf k}\cdot{\bf p}$ approach without making the axial approximation. At zero magnetic field, for a quantum well with a wide InAs layer and a wide GaSb layer, the energy of an electron-like subband can be lower than the energy of hole-like subbands. As the strength of the magnetic field increases, the Landau levels of this electron-like subband grow in energy and intersect the Landau levels of the hole-like subbands. The electron-hole hybridization leads to a series of anti-crossing splittings of the Landau levels. The energies of some Landau level transitions and their corresponding transition strengthes are calculated. The magnetic field dependence of some dominant transitions is shown with their corresponding initial-states and final-states indicated. This information should be useful in analyzing an experimentally measured magneto-optical spectrum. At high magnetic fields, multiple transitions due to the initial-state splitting can be observed. The dominant transitions at high fields can be roughly viewed as two spin-split Landau level transitions with many electron-hole hybridization induced splittings. The energy separations between the dominant transitions may decrease or increase versus the magnetic field locally, or may be almost field independent. The separations can be tuned by changing the width of InAs layer or the width of middle AlSb layer. When the magnetic field is tilted, the electron-like Landau level transitions show additional anti-crossing splittings due to the subband-Landau level coupling.
Adsorption, Segregation and Magnetization of a Single Mn Adatom on the GaAs (110) Surface
J. X. Cao,X. G. Gong,R. Q. Wu
Physics , 2005, DOI: 10.1103/PhysRevB.72.153410
Abstract: Density functional calculations with a large unit cell have been conducted to investigate adsorption, segregation and magnetization of Mn monomer on GaAs(110). The Mn adatom is rather mobile along the trench on GaAs(110), with an energy barrier of 0.56 eV. The energy barrier for segregation across the trenches is nevertheless very high, 1.67 eV. The plots of density of states display a wide gap in the majority spin channel, but show plenty of metal-induced gap states in the minority spin channel. The Mn atoms might be invisibl in scanning tunneling microscope (STM) images taken with small biases, due to the directional p-d hybridization. For example, one will more likely see two bright spots on Mn/GaAs(110), despite the fact that there is only one Mn adatom in the system.
Fractional Quantum Hall States in Low-Zeeman-Energy Limit
X. G. Wu,J. K. Jain
Physics , 1993, DOI: 10.1103/PhysRevB.49.7515
Abstract: We investigate the spectrum of interacting electrons at arbitrary filling factors in the limit of vanishing Zeeman splitting. The composite fermion theory successfully explains the low-energy spectrum {\em provided the composite fermions are treated as hard-core}.
Hund's Rule for Composite Fermions
J. K. Jain,X. G. Wu
Physics , 1993, DOI: 10.1103/PhysRevB.49.5085
Abstract: We consider the ``fractional quantum Hall atom" in the vanishing Zeeman energy limit, and investigate the validity of Hund's maximum-spin rule for interacting electrons in various Landau levels. While it is not valid for {\em electrons} in the lowest Landau level, there are regions of filling factors where it predicts the ground state spin correctly {\em provided it is applied to composite fermions}. The composite fermion theory also reveals a ``self-similar" structure in the filling factor range $4/3>\nu>2/3$.
Skyrmions in Higher Landau Levels
X. -G. Wu,S. L. Sondhi
Physics , 1995, DOI: 10.1103/PhysRevB.51.14725
Abstract: We calculate the energies of quasiparticles with large numbers of reversed spins (``skyrmions'') for odd integer filling factors 2k+1, k is greater than or equals 1. We find, in contrast with the known result for filling factor equals 1 (k = 0), that these quasiparticles always have higher energy than the fully polarized ones and hence are not the low energy charged excitations, even at small Zeeman energies. It follows that skyrmions are the relevant quasiparticles only at filling factors 1, 1/3 and 1/5.
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