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Search Results: 1 - 10 of 58049 matches for " Cheng Zhou "
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Figure of Merit Analysis of a Hybrid Solar-geothermal Power Plant  [PDF]
Cheng Zhou, Elham Doroodchi, Behdad Moghtaderi
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.51B005
Abstract: Figure of merit analysis is a general methodology used to evaluate whether a hybrid power plant could produce more power than two stand-alone power plants. In this paper, the assessment methodology using figure of merit analysis was re-examined for a hybrid solar-geothermal power plant. A new definition of the figure of merit was introduced specifically for a solar boosted geothermal plant to include both the technical and economic factors. The new definition was then applied in a case study of a hypothetical demonstration hybrid solar-geothermal power plant in Australia. The power plant was considered to have a typical net power output of 2.2 MW with a solar energy fraction of 27%. The analysis was performed to compare the power output and capital cost of the hybrid plant with the state-of-the-art (SoA) and existing stand-alone solar and geothermal plants. Based on the new definition, the hybrid plant was found to generally outperform the two existing stand-alone plants. Moreover, at an ambient temperature of 5 °C, the hybrid plant was found to outperform the SoA stand-alone plants when the geothermal temperature was greater than 150 °C. For geothermal temperature of 180 °C on the other hand, the hybrid plant outperformed the SoA stand-alone plants at ambient temperatures lower than 33 °C.
Planar Dual-Band Electrically Small Antenna Based on Double-Negative Metamaterials  [PDF]
Cheng Zhou, Guangming Wang, Yu Xiao
Journal of Computer and Communications (JCC) , 2015, DOI: 10.4236/jcc.2015.33005
Abstract:

A coaxially fed dual-band electrically small antenna based on double-negative metamaterials is presented in this letter. The antenna consists of a microstrip patch antenna as driven element and a double-negative metamaterials shell as parasitic element. Nearly complete matching of the entire system to a 50 Ω source without any matching network is achieved at 299 MHz and 837 MHz, with ka = 0.444 and 1.242 respectively. Measured performance agrees with simulations, and the proposed antenna has considerable radiation efficiency and is suitably employed for VHF and UHF applications.

On-Line Scheduling for Jobs with Arbitrary Release Times on Parallel Related Uniform Machines  [PDF]
Xiayan Cheng, Rongheng Li, Yunxia Zhou
Intelligent Information Management (IIM) , 2016, DOI: 10.4236/iim.2016.84008
Abstract: A parallel related uniform machine system consists of m machines with different processing speeds. The speed of any machine is independent on jobs. In this paper, we consider online scheduling for jobs with arbitrary release times on the parallel uniform machine system. The jobs appear over list in terms of order. An order includes the processing size and releasing time of a job. For this model, an algorithm with competitive ratio of 12 is addressed in this paper.
Theoretical analysis and experimental research on thermal focal length of a YVO4/Nd:YVO4 composite crystal

Zhou Cheng,

中国物理 B , 2009,
Abstract: This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.
The Analysis of Several Models of Investment Value of Logistics Project Evaluation
Ke Qiu Cheng Zhou
Economics Research International , 2013, DOI: 10.1155/2013/412725
Abstract:
The Analysis of Several Models of Investment Value of Logistics Project Evaluation
Ke Qiu Cheng Zhou
Economics Research International , 2013, DOI: 10.1155/2013/412725
Abstract: The study of the logistics project evaluation model features reviews the traditional value evaluation model. On the basis of this, using the fuzzy theory, we establish several logistics project evaluation models under fuzzy environment. The analysis of the respective characteristics and the comparison of the calculated results of the three models show that these models are important methods of investment value of logistics evaluation. 1. Introduction With the use of information technology and e-commerce and other modern technology, the investment in logistics industry has high uncertainty, irreversibility, and fuzziness. The application of NPV and other traditional methods of logistics project valuation is easy to cause the enterprise objective and actual value deviation. Giving full consideration to market volatility, uncertainty, irreversibility, and real option is of great practicality. The application of the real option to evaluate logistics project investment value is widely used. Schwartz and moon [1] believe that real option in venture capital evaluation can make better explanation. Dayanik [2] and so forth solved the one-dimensional diffusion process of optimal stopping problems, and the results for American option pricing, control, and so on are suitable. At the same time, in view of logistics project investment also having the characteristic of fuzziness, fuzzy factors with real option theory to carry on the research is very important. Carlsson and fullér [3] considered the rates of fuzzy-relation-fuzzy-option formula and used the optimization theory to build the project investment decision model of R&D optimization. The fuzzy process, mixing process, and uncertain process proposed by Liu [4] can well explain the fuzzy financial market. Qin and Li [5] also presented the option pricing problem under fuzzy environment. Although most of the distribution function of a random variable can be obtained by statistical method, but in actual, because of the incomplete logistics project information and prior knowledge, we often fail to accurately collect and measure these data and cannot depict or control the various factors of the logistics project, which increase the logistics project management fuzzy. Thinking about these factors of the logistics project completely, many scholars are considering the classical option pricing theory on how to be improved. This paper reviews the logistics project evaluation model under traditional situation, then, on this foundation, it puts forward a few other value evaluation models and discusses and finally compares
Transport properties for a Luttinger liquid wire with Rashba spin-orbit coupling and Zeeman splitting
Fang Cheng,Guanghui Zhou
Physics , 2006, DOI: 10.1088/0953-8984/19/13/136215
Abstract: We study the transport properties for a Luttinger-liquid (LL) quantum wire in the presence of both Rashba spin-orbit coupling (SOC) and a weak external in-plane magnetic field. The bosonized Hamiltonian of the system with an externally applied longitudinal electric field is established. And then the equations of motion for the bosonic phase fields are solved in the Fourier space, with which the both charge and spin conductivities for the system are calculated analytically based on the linear response theory. Generally, the ac conductivity is an oscillation function of the strengths of electron-electron interaction, Rashba SOC and magnetic field, as well as the driving frequency and the measurement position in the wire. Through analysis with some examples it is demonstrated that the modification on the conductivity due to electron-electron interactions is more remarkable than that due to SOC, while the effects of SOC and Zeeman splitting on the conductivity are very similar. The spin-polarized conductivities for the system in the absence of Zeeman effect or SOC are also discussed, respectively. The ratio of the spin-polarized conductivities $\sigma_\uparrow/\sigma_\downarrow$ is dependent of the electron-electron interactions for the system without SOC, while it is independent of the electron-electron interactions for the system without Zeeman splitting.
Rigidity for nearly umbilical hypersurfaces in space forms
Xu Cheng,Detang Zhou
Mathematics , 2012,
Abstract: Perez proved some $L^2$ inequalities for closed convex hypersurfaces immersed in the Euclidean space $\mathbb{R}^{n+1}$, more generally, for closed hypersurfaces with non-negative Ricci curvature, immersed in an Einstein manifold. In this paper, we discuss the rigidity of these inequalities when the ambient manifold is $\mathbb{R}^{n+1}$, the hyperbolic space $\mathbb{H}^{n+1}$, or the closed hemisphere $\mathbb{S}_+^{n+1}$. We also obtain a generalization of the Perez's theorem to the hypersurfaces without the hypothesis of non-negative Ricci curvature.
Manifolds with weighted Poincaré inequality and uniqueness of minimal hypersurfaces
Xu Cheng,Detang Zhou
Mathematics , 2008,
Abstract: In this paper, we obtain results on rigidity of complete Riemannian manifolds with weighted Poincar\'e inequality. As an application, we prove that if $M$ is a complete $\frac{n-2}{n}$-stable minimal hypersurface in $\mathbb{R}^{n+1}$ with $n\geq 3$ and has bounded norm of the second fundamental form, then $M$ must either have only one end or be a catenoid.
Eigenvalues of the drifted Laplacian on complete metric measure spaces
Xu Cheng,Detang Zhou
Mathematics , 2013,
Abstract: I In this paper, first we study a complete smooth metric measure space $(M^n,g, e^{-f}dv)$ with the ($\infty$)-Bakry-\'Emery Ricci curvature $\textrm{Ric}_f\ge \frac a2g$ for some positive constant $a$. It is known that the spectrum of the drifted Laplacian $\Delta_f$ for $M$ is discrete and the first nonzero eigenvalue of $\Delta_f$ has lower bound $\frac a2$. We prove that if the lower bound $\frac a2$ is achieved with multiplicity $k\geq 1$, then $k\leq n$, $M$ is isometric to $\Sigma^{n-k}\times \mathbb{R}^k$ for some complete $(n-k)$-dimensional manifold $\Sigma$ and by passing an isometry, $(M^n,g, e^{-f}dv)$ must split off a gradient shrinking Ricci soliton $(\mathbb{R}^k, g_{can}, \frac{a}{4}|t|^2)$, $t\in \mathbb{R}^k$. This result has an application to gradient shrinking Ricci solitons. Secondly, we study the drifted Laplacian $\mathcal{L}$ for properly immersed self-shrinkers in the Euclidean space $\mathbb{R}^{n+p}$, $p\geq1$ and show the discreteness of the spectrum of $\mathcal{L}$ and a logarithmic Sobolev inequality.
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