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Search Results: 1 - 10 of 89137 matches for " Wu Wei "
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Homotopy Continuous Method for Weak Efficient Solution of Multiobjective Optimization Problem with Feasible Set Unbounded Condition  [PDF]
Wei Xing, Boying Wu
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.37114
Abstract: In this paper, we propose a homotopy continuous method (HCM) for solving a weak efficient solution of multiobjective optimization problem (MOP) with feasible set unbounded condition, which is arising in Economical Distributions, Engineering Decisions, Resource Allocations and other field of mathematical economics and engineering problems. Under the suitable assumption, it is proved to globally converge to a weak efficient solution of (MOP), if its x-branch has no weak infinite solution.
A Study on Establishing Low-Carbon Auditing System in China  [PDF]
Wei Zhang, Zhongxin Wu
Low Carbon Economy (LCE) , 2012, DOI: 10.4236/lce.2012.32005
Abstract: This paper establishes the framework of low-carbon auditing based on the current environment of China which is a developing country. A comprehensive system of low-carbon auditing should be composed by low carbon related laws compliance auditing, low-carbon conduct auditing and performance auditing. The functional paths of low-carbon auditing include at least four things: building a comprehensive low-carbon auditing system, establishing sets of indicators, cultivating talents with diverse carbon related knowledge and providing policies step by step.
The Influence Factors Study of Aerosol Particles  [PDF]
Tao Jiang, Wu Wei
Modern Mechanical Engineering (MME) , 2013, DOI: 10.4236/mme.2013.32014
Abstract:

The marine and coastal intake filtration device is mainly used to filter out the salt spray aerosol particles. So, the laboratory studies of the intake filtration device need to simulate the salt spray aerosols state of the ocean environment. But the distribution of ocean salt spray aerosol particle of diameter is very wide, so the simulation device of salt spray aersol should produce a variety of salt spray aerosol particles. The paper is to mainly study the influencing factors of salt spray aerosol device to produce different particles diameter. And the investigation and study mainly include two aspects: numerical simulation and experimental study.

Urban Development and Water Management in the Yangtze River Delta  [PDF]
Yan Wang, Wei Wu
World Journal of Engineering and Technology (WJET) , 2018, DOI: 10.4236/wjet.2018.62B002
Abstract:
Throughout the history of the world, the development of the cities are related to the large water systems and the ocean. Where the river is abundant, the trade and regional centres could be formed. However, along with the prosperity of the water-cities, massive urban construction and environmental issues are enormous challenges in human process. A “scientific” urban planning, “Sponge City”, “Resilient City”, regional and urban culture and characteristics get more and more attention. The theme of “water and city” is clearly of great historical value and practical significance for the new resilient urban and water management strategies. The paper will summarize characteristics of geographical, historical, socio-cultural and political realms in metropolitan deltas and the historical governance as well as the recent developments in the Yangtze River Delta. It will introduce urban development and water management in four water cities: the canal and the city-Yangzhou, the river and the city-Nanjing, the lake and the city-Suzhou and the sea and the city-Shanghai. And then it will analyze the inner motivation of the interaction between water and cities in Yangtze River Delta. Furthermore, learning from successful historical experiences, the paper will provide suggestions for future sustainable urban development.
DC Motor Parameter Identification Using Speed Step Responses
Wei Wu
Modelling and Simulation in Engineering , 2012, DOI: 10.1155/2012/189757
Abstract: Based on the DC motor speed response measurement under a step voltage input, important motor parameters such as the electrical time constant, the mechanical time constant, and the friction can be estimated. A power series expansion of the motor speed response is presented, whose coefficients are related to the motor parameters. These coefficients can be easily computed using existing curve fitting methods. Experimental results are presented to demonstrate the application of this approach. In these experiments, the approach was readily implemented and gave more accurate estimates than conventional methods. 1. Introduction DC motors have wide applications in industrial control systems because they are easy to control and model. For analytical control system design and optimization, sometimes a precise model of the DC motor used in a control system may be needed. In this case, the values for reference of the motor parameters given in the motor specifications, usually provided by the motor manufacturer, may not be considered adequate, especially for cheaper DC motors which tend to have relatively large tolerances in their electrical and mechanical parameters. General system identification methods [1–4] can be applied to DC motor model identification. In particular, various methods have been applied to DC motor parameter identification; that is, [5, 6] used the algebraic identification method, [7] used the recursive least square method, [8] applied the inverse theory, [9] used the least square method, and [10] applied the moments method. Identified DC motor models are often subsequently used for controller design and/or optimization, for example, [6, 9, 11]. Without expensive testing apparatus and a long testing cycle, a quick and effective system identification approach based on the motor input and output is desirable and valuable, especially for the field applications and quick controller prototyping. In this paper, a DC motor parameter identification approach based on the Taylor series expansion of the motor speed response under a constant voltage input is presented. The relationships between the motor parameters and the coefficients of the Taylor series are established. In the implementation, the motor speed response under a constant voltage is sampled, then fit the samples to obtain the coefficients of power terms in the Taylor series. Then, the DC motor mechanical and electrical time constants, back-EMF, and the friction can be computed using these coefficients. With the knowledge of these parameters, a precise motor model is obtained for the
An Investigation of the Nature and Functions of Exercises in Textbooks for Intensive Reading Course for English Majors
Wei Wu
Journal of Language Teaching and Research , 2011, DOI: 10.4304/jltr.2.5.998-1008
Abstract: The qualification of the text exercises directly influences students’ learning effect. This research is conducted reviewing and classifying the referred exercises in the English textbook, the author attempts to present the practical application of the exercises by means of investigation, exploratory research and interview with the nature and functions of the exercises as well. The research makes contributions to the deep understanding of the nature and functions of exercises in textbooks, serving as a reference for teachers to select and apply exercise types appropriately and effectively in their teaching practice. It can be of some significance in exercise design, evaluation, compiling and selection and in other areas of study within EFL.
Electronic structure and magnetic properties of $\mathrm{CaCr}\mathrm{O}_3$: The interplay between spin- and orbital-orderings
Wei Wu
Physics , 2015,
Abstract: The electronic structure and magnetic properties of CaCr$\mathrm{O}_3$ have been calculated by two methods, including hybrid-exchange density-function theory and density-functional theory + $U$. The computed densities of states from both of these methods are in a qualitative agreement with the previous x-ray spectroscopy. On the other hand, the opening of the band gap separates them apart. hybrid-exchange density-functional theory always gives a finite band gap, down to $\sim 1.2$ eV from HSE06 functional, whereas by tuning the Hubbard-$U$ parameter down to $0.5$ eV, a conducting state with AFM-C (defined in the text) spin configuration can be achieved. From hybrid density-functional theory, the computed nearest-neighbouring exchange interaction along the $c$-axis and in the $ab$-plane are $\sim 4$ meV and $\sim 6$ meV (anti-ferromagnetic), respectively, which are qualitatively in agreement with the previous magnetic measurements. These anti-ferromagnetic exchange interaction, together with the in-plane anti-ferro-orbital ordering will induce a spin-orbital frustration, which could play a role for the abnormal electronic properties in CaCrO$_3$. In hybrid-exchange density-functional theory, an abrupt reduction ($\sim 0.2$ eV) of the majority-spin band gap of the ferromagnetic state between 60 K and 100 K has been found as lowering temperature, which shows a strong link to the previous optical conductivity measurements in [A. C. Komarek, et. al., Phys. Rev. B \textbf{84}, 125114 (2011)]. In sharp contrast, the density-functional theory + $U$ methods predicted AFM-C state as the lowest AFM state for the crystal structure measured below 90 K, above which AFM-A is however the lowest. The closely related concepts including electron-hole liquid and surface-plasmon-mediating spin-spin interactions have been discussed as well.
A hybrid-exchange density-functional theory study of the electronic structure of $\mathrm{MnV}_2\mathrm{O}_4$: Exotic orbital ordering in the cubic structure
Wei Wu
Physics , 2015, DOI: 10.1103/PhysRevB.91.195108
Abstract: The electronic structures of the cubic and tetragonal $\mathrm{MnV}_2\mathrm{O}_4$ have been studied by using hybrid-exchange density functional theory. The computed electronic structure of the tetragonal phase shows an anti-ferro orbital ordering on V sites and a ferrimagnetic ground state (the spins on V and Mn are anti-aligned). These results are in a good agreement with the previous theoretical result obtained from the local-density approximation+$U$ methods [S. Sarkar, et. al., Phys. Rev. Lett. 102, 216405 (2009)]. Moreover, the electronic structure, especially the projected density of states of the cubic phase has been predicted with a good agreement with the recent soft x-ray spectroscopy experiment. Similar to the tetragonal phase, the spins on V and Mn in the cubic structure favour a ferrimagnetic configuration. Most interesting is that the computed charge densities of the spin-carrying orbitals on V in the cubic phase show an exotic orbital ordering, i.e., a ferro-orbital ordering along [110] but an anti-ferro-orbital ordering along [$\overline{1}$10].
Modelling the electronic structure and magnetic properties of LiFeAs and FeSe using hybrid-exchange density functional theory
Wei Wu
Physics , 2012, DOI: 10.1016/j.ssc.2013.03.003
Abstract: The electronic structure and magnetic properties of LiFeAs and FeSe have been studied using hybrid exchange density functional theory. The total energies for a unit cell in LiFeAs and FeSe with different spin states including non-magnetic and spin-2 are calculated. The spin-2 configuration has the lower energy for both LiFeAs and FeSe. The computed anti-ferromagnetic exchange interactions between spins on the nearest (next nearest) neighbouring Fe atoms in LiFeAs and FeSe are approximately 14 (17) meV and 6 (13) meV respectively. The total energies of the checkerboard and stripe-type anti-ferromagnetic ordering for LiFeAs and FeSe are compared, yielding that for LiFeAs the checkerboard is lower whereas for FeSe the stripe-type is lower. However, owing to the fact that the exchange interaction of the next nearest neighbour is larger than that of the nearest one, which means that the collinear ordering might be the ground state. These results are in agreement with previous theoretical calculations and experiments. Especially the calculations for LiFeAs indicate a co-existence of conducting d-bands at the Fermi surface and d-orbital magnetism far below the Fermi surface. The theoretical results presented here might be useful for the experimentalists working on the electronic structure and magnetism of iron-based superconductors.
Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine
Wei Wu
Physics , 2014, DOI: 10.1063/1.4881897
Abstract: Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-$\frac{1}{2}$) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localised spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.
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