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991.
Theoretical study of N-doped TiO2 rutile crystals 总被引:1,自引:0,他引:1
The N-doping effects on the electronic and optical properties of TiO2 rutile crystal have been studied using density functional theory (DFT). The calculations of several possible N-doped structures show that band gaps have little reduction but some N 2p states lie within the band gap in the substitutional N to O structure and interstitial N-doped rutile supercell, which results in the reduction of the photon-transition energy and absorption of visible light. In contrast, substitutional N to Ti doped model has a significant band-gap narrowing. The results maybe clarify confusions in nitrogen-doped TiO2 rutile crystal. 相似文献
992.
We report first-principles calculations on the electrical transport properties of two kinds of one-dimensional nanowires: (a) a carbon nanowire (CNW) with alternating single and triple bonds and (b) a boron-nitrogen nanowire (BNNW) with equidistant bonds. We demonstrate the similarity and difference between the carbon nanowire and its boron-nitrogen analogue in the molecular orbital and transport properties, and then explore the potential innovations. The effects of molecular orbitals and nanowire-electrode coupling on the transport properties are analyzed. The cases of the nanowires sandwiched between both nanoscale and bulk electrodes are considered. It suggests that the characteristics of the transmission spectra and the current-voltage characteristics (I-V curves) are determined both by the electrodes and by the molecule as well as their coupling. In particular, the negative differential resistance (NDR) phenomenon is more apparent when the nanowires are positioned between two nanoscale electrodes. The tuning of the transport properties is also probed through the changes of nanowire-electrode separation and the inclusion of a gate voltage. These lead to dramatic variations in the equilibrium conductance, which can be understood from the shift and alignment of the molecular orbital relative to the Fermi level of the electrodes. In the analysis of the effects of nanowire-electrode separation, it shows that the equilibrium conductance has the same variation behavior as that of the projected density of states (PDOS) for CNW, while the localized molecular orbitals of BNNW result in its conductance varies differently from its PDOS. The different molecular orbital characteristics near the Fermi level of these two kinds of nanowires underlie their different transport properties. 相似文献
993.
Ablikim M Bai JZ Ban Y Bian JG Cai X Chang JF Chen HF Chen HS Chen HX Chen JC Chen J Chen J Chen ML Chen YB Chi SP Chu YP Cui XZ Dai HL Dai YS Deng ZY Dong LY Du SX Du ZZ Fang J Fang SS Fu CD Fu HY Gao CS Gao YN Gong MY Gong WX Gu SD Guo YN Guo YQ Guo ZJ Harris FA He KL He M He X Heng YK Hu HM Hu T Huang GS Huang L Huang XP Ji XB Jia QY Jiang CH Jiang XS Jin DP Jin S Jin Y Lai YF Li F Li G Li HB Li HH Li J Li JC Li QJ Li RB Li RY Li SM Li WG Li XL Li XQ Li XS Liang YF Liao HB Liu CX Liu F Liu F 《Physical review letters》2006,97(6):062001
The decay J/psi-->NNpi provides an effective isospin 1/2 filter for the piN system due to isospin conservation. Using 58x10(6) J/psi decays collected with the Beijing Electromagnetic Spectrometer at the Beijing Electron Positron Collider, more than 100 thousand J/psi-->ppi-n+c.c. events are obtained. Besides the two well-known N* peaks at around 1500 MeV/c2 and 1670 MeV/c2, there are two new, clear N* peaks in the ppi invariant mass spectrum around 1360 MeV/c2 and 2030 MeV/c2 with statistical significance of 11sigma and 13sigma, respectively. We identify these as the first direct observation of the N*(1440) peak and a long-sought missing N* peak above 2 GeV/c2 in the piN invariant mass spectrum. 相似文献
994.
995.
We study three types of practical optimization problems faced by a firm that can control its liquid reserves by paying dividends
and by issuing new equity. In the first problem, we consider the classical dividend problem without equity issuance. The second
problem aims at maximizing the expected discounted dividend payments minus the expected discounted costs of issuing new equity
over strategies associated with positive reserves at all times. The third problem has the same objective as the second one,
but with no constraints on the reserves. Under the assumption of proportional transaction costs, we identify the value functions
and the optimal strategies. We also present the relationship between three problems. 相似文献
996.
In this paper, an impulsive delay predator–prey model with stage structure and Beddington-type functional response is established. By using the discrete dynamical system determined by the stroboscopic map, we obtain the existence and global attractivity of the predator-extinction periodic solution. By use of the theory on delay and impulsive differential equation, we study the permanence of the system. Finally, an example is given to show the effectiveness of the main results. 相似文献
997.
Considering the effects of changing environments, delays, impulses and functional response, a one-prey multi-predators system is established in this paper. Using comparison theorem and some analysis techniques, sufficient conditions ensuring the global attractivity of the prey-extinction positive periodic solution and the permanence of the system are obtained. Finally, examples and numerical simulations are given to show the effectiveness of the main results. 相似文献
998.
A refinable spline in ℝ
d
is a compactly supported refinable function whose support can be decomposed into simplices such that the function is a polynomial
on each simplex. The best-known refinable splines in ℝ
d
are the box splines. Refinable splines play a key role in many applications, such as numerical computation, approximation
theory and computer-aided geometric design. Such functions have been classified in one dimension in Dai et al. (Appl. Comput.
Harmon. Anal. 22(3), 374–381, 2007), Lawton et al. (Comput. Math. 3, 137–145, 1995). In higher dimensions Sun (J. Approx. Theory 86, 240–252, 1996) characterized those splines when the dilation matrices are of the form A=mI, where m∈ℤ and I is the identity matrix. For more general dilation matrices the problem becomes more complex. In this paper we give a complete
classification of refinable splines in ℝ
d
for arbitrary dilation matrices A∈M
d
(ℤ). 相似文献
999.
We study the smooth LU decomposition of a given analytic functional A-matrix A(A) and its block-analogue. Sufficient conditions for the existence of such matrix decompositions are given, some differentiability about certain elements arising from them are proved, and several explicit expressions for derivatives of the specified elements are provided. By using these smooth LU decompositions, we propose two numerical methods for computing multiple nonlinear eigenvalues of A(A), and establish their locally quadratic convergence properties. Several numerical examples are provided to show the feasibility and effectiveness of these new methods. 相似文献
1000.
Analytical study for electromagnetothermoelastic behaviors of a hollow cylinder composed of functionally graded piezoelectric material (FGPM), placed in a uniform magnetic field, subjected to electric, thermal and mechanical loads are presented. For the case that the electric, magnetic, thermal and mechanical properties of the material obey an identical power law in the radial direction, exact solutions for electric displacement, stresses, electric potential and perturbation of magnetic field vector in the FGPM hollow cylinder are determined by using the infinitesimal theory of electromagnetothermoelasticity. Some useful discussions and numerical examples are presented to show the significant influence of material inhomogeneity, and adopting a certain value of the inhomogeneity parameter β and applying suitable electric, thermal and mechanical loads can optimize the FGPM hollow cylindrical structures. This will be of particular importance in modern engineering design. 相似文献