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81.
Using ab initio calculations on Zn0.975? x Fe0.025Cu x O (x = 0, 0.01, 0.02, 0.05), we study the variations of magnetic moments vs Cu concentration. The electronic structure is calculated by using the Korringa-Kohn-Rostoker (KKR) method combined with coherent potential approximation (CPA). We show that the total magnetic moment and magnetic moment of Fe increase on increasing Cu content. From the density of state (DOS) analysis, we show that Cu-induced impurity bands can assure, by two mechanisms, the enhancement of Fe magnetic moment in Zn0.975? x Fe0.025Cu x O. 相似文献
82.
M Waqas Iqbal M Zahir Iqbal M Farooq Khan Xiaozhan Jin Chanyong Hwang 《Science and Technology of Advanced Materials》2014,15(5)
The properties of graphene are strongly affected by metal adsorbates and clusters on graphene. Here, we study the effect of a thin layer of platinum (Pt) metal on exfoliated single, bi- and trilayer graphene and on chemical vapor deposition-grown single-layer graphene by using Raman spectroscopy and transport measurements. The Raman spectra and transport measurements show that Pt affects the structure as well as the electronic properties of graphene. The shift of peak frequencies, intensities and widths of the Raman bands were analyzed after the deposition of Pt with different thicknesses (1, 3, 5 nm) on the graphene. The shifts in the G and 2D peak positions of the Raman spectra indicate the n-type doping effect by the Pt metal. The doping effect was also confirmed by gate-voltage dependent resistivity measurements. The doping effect by the Pt metal is stable under ambient conditions, and the doping intensity increases with the increasing Pt deposition without inducing a severe degradation of the charge carrier mobility. 相似文献
83.
The aerodynamic characteristics of wind turbines are closely related to the geometry of their blades. The innovation and the technological development of wind turbine blades can be centred on two tendencies. The first is to improve the shape of existing blades; the second is to design new shapes of blades. The aspiration in the two cases is to achieve an optimal circulation and hence enhancing some more ambitious aerodynamic characteristics. This paper presents an inverse design procedure, which can be adapted to both thin and thick wind turbine blade sections aiming to optimise the geometry for a prescribed distribution of bound vortices. A method for simulating the initial contour of the blade section is exposed, which simultaneously satisfy the aerodynamic and geometrical constraints under nominal conditions. A detailed definition of the function characterising the bound vortex distribution is presented. The inviscid velocity field and potential function distributions are obtained by the singularities method. In the design method implemented, these distributions and the circulation of bound vortices on the camber line of the blade profile, are used to rectify its camber in an iterative calculation leading to the final and optimal form of the blade section once convergence is attained. The scheme proposed has been used to design the entire blade of the wind turbine for a given span-wise distribution of bound circulation around the blade contour. 相似文献
84.
Corfdir P Abid M Mouti A Stadelmann PA Papa E Ansermet JP Ganière JD Deveaud-Plédran B 《Nanotechnology》2011,22(28):285710
The design of cost-effective standards for the quality of nano-objects is currently a key issue toward their massive use for optoelectronic applications. The observation by photoluminescence of narrow excitonic and biexcitonic emission lines in semiconductor nanowires is usually accepted as evidence for high structural quality. Here, we perform time-resolved cathodoluminescence experiments on isolated ZnO nanobelts grown by chemical vapor deposition. We observe narrow emission lines at low temperature, together with a clear biexciton line. Still, drastic alterations in both the CL intensity and lifetime are observed locally along the nano-object. We attribute these to non-radiative recombinations at edge dislocations, closing basal plane stacking faults, inhomogeneously distributed along the NB length. This leads us to the conclusion that the observation of narrow excitonic and biexcitonic emission lines is far from sufficient to grade the quality of a nano-object. 相似文献
85.
The electronic parameters and photovoltaic properties of the Au/methylene blue/n-Si diodes were investigated by current-voltage and capacitance-conductance-frequency techniques. The diode exhibits a non-ideal behavior due the series resistance, organic layer and oxide layer. The barrier height (1.04 eV) of the Au/methylene blue/n-Si is higher than that of Au/n-Si Schottky diode (0.83 eV) due to an excess barrier formed by organic layer. The interface state density of the diode was determined using a conductance technique and was found to be 3.25 × 1012 eV−1 cm−2. The diode shows a photovoltaic behavior with a maximum open circuit voltage Voc of 0.23 V and short-circuit current Isc of 20.8 μA under 100 mW/cm2. It is evaluated that Au/methylene blue/n-Si is an organic-on-inorganic photodiode with the obtained electronic parameters and methylene blue organic dye controls the interface and electrical properties of conventional metal/n-type silicon junction. 相似文献
86.
Mehmet Enver Ayd?nMurat Soylu Fahrettin Yakuphanoglu W.A. Farooq 《Microelectronic Engineering》2011,88(6):867-871
The electronic properties of metal-organic semiconductor-inorganic semiconductor structure between GaAs and poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic film have been investigated via current-voltage and capacitance-voltage methods. The Au/PEDOT/n-GaAs contact exhibits a rectification behavior with the barrier height of 0.69 eV and ideality factor value of 3.94. The barrier height of the studied diode (0.67 eV) is lower than that of Ni/n-GaAs/In (0.85 eV) and Au/n-GaAs/In Schottky diodes. The decrease in barrier height of Au/n-GaAs/In Schottky diode is likely to be due to the variation in the space charge region in the GaAs. The obtained results indicate that control of the interfacial potential barrier for metal/n-GaAs diode was achieved using thin interlayer of the poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol). 相似文献
87.
The realizability of Reynolds stress models in homogeneous turbulence is critically assessed from a theoretical standpoint. It is proven that a well known second-order closure model formulated using the strong realizability constraints of Schumann (1977) and Lumley (1978) is, in fact, not a realizable model. The problem arises from the failure to properly satisfy the necessary positive second time derivative constraint when a principal Reynolds stress vanishes-a flaw that becomes apparent when the nonanalytic terms in the model are made single-valued as required on physical grounds. More importantly, arguments are advanced which suggest that it is impossible to identically satisfy the strong from of realizability in any version of the present generation of second-order closures. On the other hand, models properly formulated to satisfy the weak form of realizability—wherein states of one or two component turbulence are made inaccessible in finite time via the imposition of a positive first derivative condition—are found to be realizable. However, unlike the simpler and more commonly used second-order closures, these models can be ill-behaved near the extreme limits of realizable turbulence due to the way that higher-degree nonlinearities are often unnecessarily introduced to satisfy realizability. Illustrative computations of homogeneous shear flow are presented to demonstrate these points which can have important implications for turbulence modeling. 相似文献
88.
移动代理技术已经成为设计、实现分布式应用的一种极具前景的技术,现有许多移动代理系统已经在研究及商业领域得以实现.但是移动代理系统至今仍然没有得到很广泛的应用,其原因除了使用移动代理系统所涉及的安全性问题之外,另一个主要因素就是缺少一个对移动代理系统性能进行量化评价的基准.本文对于现有的能够对各种不同移动代理系统进行量化评测的基准进行综述,并且讨论哪些因素会对移动代理架构性能产生根本的影响. 相似文献
89.
90.
Wavelet transform has been found to be an effective tool for the time-frequency analysis of non-stationary and quasi-stationary signals. Recent years have seen wavelet transform being used for feature extraction in speech recognition applications. In the paper a sub-band feature extraction technique based on an admissible wavelet transform is proposed and the features are modified to make them robust to additive white Gaussian noise. The performance of this system is compared with the conventional mel frequency cepstral coefficients (MFCC) under various signal to noise ratios. The recognition performance based on the eight sub-band features is found to be superior under the noisy conditions compared with MFCC features. 相似文献