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Search Results: 1 - 10 of 10250 matches for " Qian Xuemin "
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Field Emission Properties and Fabrication of CdS Nanotube Arrays
Qian Xuemin,Liu Huibiao,Guo Yanbing,Zhu Shiqun
Nanoscale Research Letters , 2009,
Abstract: A large area arrays (ca. 40 cm2) of CdS nanotube on silicon wafer are successfully fabricated by the method of layer-by-layer deposition cycle. The wall thicknesses of CdS nanotubes are tuned by controlling the times of layer-by-layer deposition cycle. The field emission (FE) properties of CdS nanotube arrays are investigated for the first time. The arrays of CdS nanotube with thin wall exhibit better FE properties, a lower turn-on field, and a higher field enhancement factor than that of the arrays of CdS nanotube with thick wall, for which the ratio of length to the wall thickness of the CdS nanotubes have played an important role. With increasing the wall thickness of CdS nanotube, the enhancement factorβdecreases and the values of turn-on field and threshold field increase.
Effect of Aspect Ratio on Field Emission Properties of ZnO Nanorod Arrays
Qian Xuemin,Liu Huibiao,Guo Yanbing,Song Yinglin
Nanoscale Research Letters , 2008,
Abstract: ZnO nanorod arrays are prepared on a silicon wafer through a multi-step hydrothermal process. The aspect ratios and densities of the ZnO nanorod arrays are controlled by adjusting the reaction times and concentrations of solution. The investigation of field emission properties of ZnO nanorod arrays revealed a strong dependency on the aspect ratio and their density. The aspect ratio and spacing of ZnO nanorod arrays are 39 and 167 nm (sample C), respectively, to exhibit the best field emission properties. The turn-on field and threshold field of the nanorod arrays are 3.83 V/μm and 5.65 V/μm, respectively. Importantly, the sample C shows a highest enhancement of factorβ, which is 2612. The result shows that an optimum density and aspect ratio of ZnO nanorod arrays have high efficiency of field emission.
Ultra-Sensitivity Glucose Sensor Based on Field Emitters
Liu Huibiao,Qian Xuemin,Wang Shu,Li Yuliang
Nanoscale Research Letters , 2009,
Abstract: A new glucose sensor based on field emitter of ZnO nanorod arrays (ZNA) was fabricated. This new type of ZNA field emitter-based sensor shows high sensitivity with experimental limit of detection of 1 nM glucose solution and a detection range from 1 nM to 50 μM in air at room temperature, which is lower than that of glucose sensors based on surface plasmon resonance spectroscopy, fluorescence signal transmission, and electrochemical signal transduction. The new glucose sensor provides a key technique for promising consuming application in biological system for detecting low levels of glucose on single cells or bacterial cultures.
Joint Scheduling and Power Allocations for Traffic Offloading via Dual-Connectivity
Yuan Wu,Yanfei He,Liping Qian,Jianwei Huang,Xuemin,Shen
Computer Science , 2015,
Abstract: With the rapid growth of mobile traffic demand, a promising approach to relieve cellular network congestion is to offload users' traffic to small-cell networks. In this paper, we investigate how the mobile users (MUs) can effectively offload traffic by taking advantage of the capability of dual-connectivity, which enables an MU to simultaneously communicate with a macro base station (BS) and a small-cell access point (AP) via two radio-interfaces. Offloading traffic to the AP usually reduces the MUs' mobile data cost, but often at the expense of suffering increased interferences from other MUs at the same AP. We thus formulate an optimization problem that jointly determines each MU's traffic schedule (between the BS and AP) and power control (between two radio-interfaces). The system objective is to minimize all MUs' total cost, while satisfying each MU's transmit-power constraints through proper interference control. In spite of the non-convexity of the problem, we design both a centralized algorithm and a distributed algorithm to solve the joint optimization problem. Numerical results show that the proposed algorithms can achieve the close-to-optimum results comparing with the ones achieved by the LINGO (a commercial optimization software), but with significantly less computational complexity. The results also show that the proposed adaptive offloading can significantly reduce the MUs' cost, i.e., save more than 75% of the cost without offloading traffic and 65% of the cost with a fixed offloading.
Baryon QCD sum rules in an external isovector-scalar field and baryon isospin mass splittings
Xuemin Jin
Physics , 1995, DOI: 10.1103/PhysRevD.52.2964
Abstract: Within the QCD sum-rule approach in an external field, we calculate the baryon matrix element of isovector-scalar current, $H_{\rm B}=\langle B|\overline{u}u- \overline{d}d|B\rangle/2M_{\rm B}$, for octet baryons, which appears in the response of the correlator of baryon interpolating fields to a constant isovector-scalar external field. The sum rules are obtained for a general baryon interpolating field with an appropriate form for the phenomenological ansatz of the spectral density. The key phenomenological input is the response of the quark condensates to the external field. To first order in the quark mass difference $\delta m=m_d-m_u$, the non-electromagnetic part of the baryon isospin mass splitting is given by the product of $\delta m$ and $H_{\rm B}$. Therefore, QCD sum-rule calculation of $H_{\rm B}$ leads to an estimate of the octet baryon isospin mass splittings. The resulting values are comparable to the experimental values; however, the sum-rule predictions for $H_{\rm B}$ are sensitive to the values of the response of the quark condensates to the external source, which are not well determined.
A Note on the External-Field Method in QCD Sum Rules
Xuemin Jin
Physics , 1996, DOI: 10.1103/PhysRevD.55.1693
Abstract: The external-field method has been used extensively in the QCD sum-rule approach to explore various hadron static properties. In the traditional formalism of this method, the transitions from the ground state hadron to excited states are not exponentially suppressed relative to the ground state term and thus contaminate the ground state hadron property to be extracted. In this paper, we suggest a modified formalism, in which the transition terms are exponentially suppressed relative to the ground state term. As such, the pole plus continuum spectral model, traditionally invoked in QCD sum-rule approach, can be adopted. Thus, this modified formalism has potential to improve the predictability and reliability of external-field sum-rule calculations, which is illustrated in an explicit example.
QCD sum rules for $Δ$ isobar in nuclear matter
Xuemin Jin
Physics , 1994, DOI: 10.1103/PhysRevC.51.2260
Abstract: The self-energies of $\Delta$ isobar propagating in nuclear matter are calculated using the finite-density QCD sum-rule methods. The calculations show that the Lorentz vector self-energy for the $\Delta$ is significantly smaller than the nucleon vector self-energy. The magnitude of the $\Delta$ scalar self-energy is larger than the corresponding value for the nucleon, which suggests a strong attractive net self-energy for the $\Delta$; however, the prediction for the scalar self-energy is very sensitive to the density dependence of certain in-medium four-quark condensate. Phenomenological implications for the couplings of the $\Delta$ to the nuclear scalar and vector fields are briefly discussed.
Constraints on the Fiite-Density Spectral Densities of Vector Channel
Xuemin Jin
Physics , 1994,
Abstract: Sum rules for the variation of finite-density spectral density of vector channel with baryon density are derived based on dispersion relations and the operator product expansion. These sum rules may serve as constraints on the phenomenological models for the finite-density spectral densities used in the approaches motivated from QCD. Applying these sum rules to the rho meson in nuclear medium with a simple pole-plus-continuum ansatz for the spectral densities, we found that the qualitative features of the QCD sum-rule predictions for the spectral parameters are consistent with these sum rules; however, the quantitative QCD sum-rule results violate the sum rules to certain degree.
Isospin Breaking in the Nucleon Isovector Axial Charge from QCD Sum Rules
Xuemin Jin
Physics , 1996,
Abstract: The isospin breaking in the nucleon isovector axial charge, $g_A^3$, are calculated within the external field QCD sum-rule approach. The isospin violations arising from the difference in up and down current quark masses and in up and down quark condensates are included; electromagnetic effects are not considered. We find $\delta g^3_A/g^3_A \approx (0.5-1.0)\times 10^{-2}$, where $\delta g^3_A = (g^3_A)_p + (g^3_A)_n$ and $ g^3_A = [(g^3_A)_p - (g^3_A)_n]/2$. Using the Goldberger-Treiman relation, we also obtain an estimate of the isospin breaking in the pion-nucleon coupling constant, $(g_{pp\pi_0}-g_{nn\pi_0})/g_{NN\pi} \approx (2-7) \times 10^{-3}$.
Electromagnetic Anomalies around The Wenchuan Earthquake and Their Relationship with Earthquake Preparation
Xuemin Zhang,Xuhui Shen
International Journal of Geophysics , 2011, DOI: 10.1155/2011/904132
Abstract: Electromagnetic precursors before the Wenchuan earthquake on May 12, 2008 were collected and summarized on the basis of related published papers. The relationship between electromagnetic anomalies and different earthquake preparation stages was analyzed, and an entire seismic preparation process was constructed according to corresponding anomalies in different electromagnetic parameters. It is illustrated that stereo electromagnetic observation is useful in the understanding of earthquake preparation mechanism. It is inevitable that a lot of problems exist in anomaly distinguishing and coupling mechanism analysis, which needs further studies in future.
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