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311.
Density functional theory (DFT) calculations have been performed to investigate the availabilities and properties of boron nitride nanotubes (BNNTs) with quadrangular cross sections. To achieve the purposes, the original structure of a representative BNNT was individually decorated by the carbon and silicon atoms to make the C-BNNT and Si-BNNT models. The sp3 hybridizations were set for the C and Si atoms to make possible the formation of the quadrangular cross sections for the BNNTs. The optimized results indicated that the investigated models could be stabilized; however, they showed different properties. The atomic scale properties based on computations of quadrupole coupling constants (CQ) also approved different properties for the C-BNNT and Si-BNNT models. Moreover, the CQ parameters indicated that the properties of C-BNNT could be considered similar to the original BNNT; however, more discrepancies were observed for the Si-BNNT. 相似文献
312.
Sanaa Kholfi Hosam M. Mahmoud 《Statistics & probability letters》2012,82(1):49-57
In Kholfi and Mahmoud (2011) the class of tenable irreducible nondegenerate zero-balanced Pólya urn schemes is introduced and its asymptotic behavior in various phases is studied. In the absence of an initially dominant subset of colors, the counts of balls of all the colors satisfy multivariate central limit theorems. It is reported there that the case of an initially dominant subset of colors poses challenges requiring finer asymptotic analysis. In the present investigation we follow up on this. Indeed, we characterize noncritical cases with an initially dominant subset of colors in which not all ball counts satisfy one multivariate central limit theorem, but rather a subset of the ball counts satisfies a singular multivariate central limit theorem. The rest of the cases are critical, in which all the ball counts satisfy a multivariate central limit theorem, but under a different scaling. However, for these critical cases the Gaussian phases are delayed considerably. 相似文献
313.
An integrated model for optimum weight design of symmetrically laminated composite plates subjected to dynamic excitation is presented in this work. Optimum design procedure based on flexibility and strength criteria is presented. The objective is to determine the optimum thicknesses of the laminate layers and its optimum orientations without exhibiting any failure according to Tsai-Wu failure criterion. The finite element method, based on Mindlin plate theory, is used in conjunction with an optimization method in order to determine the optimum design. Newmark algorithm, as an implicit time integration scheme, is used to discretize the time domain and calculate the transient response of the laminated composite plate. Exterior penalty method is exploited for the constrained minimization procedure. Fletcher-Powell algorithm is used for the unconstrained minimization process. To verify the capability and efficiency of the proposed model, three examples are solved. The examples deal with flexibility and stress constraints for different boundary conditions under various dynamic excitations. 相似文献
314.
Background model updating is a vital process for any background subtraction technique. This paper presents an updating mechanism that can be applied efficiently to any background subtraction technique. This updating mechanism exploits the color and spatial features to characterize each detected object. Spatial and color features are used to classify each detected object as a moving background object, a ghost, or a real moving object. The starting position of each detected object is the cue for updating background images. In addition, this paper presents a hybrid scheme to detect and remove cast shadows based on texture and color features. The robustness of the proposed method and its effectiveness in overcoming challenging problems such as gradual and sudden illumination changes, ghost appearance, non-stationary background objects, the stability of moving objects most of the time, and cast shadows are verified quantitatively and qualitatively. 相似文献
315.
Abstract
Arylaminotetrazoles were efficiently synthesized from secondary arylcyanamides by application of ZnCl2/AlCl3/silica as a reusable heterogeneous Lewis acid catalyst. 5-Arylamino-1H-tetrazoles can be obtained from arylcyanamides carrying electron-withdrawing substituents on the aryl ring, while with electron-releasing groups 1-aryl-5-amino-1H-tetrazoles will be produced. The former isomer is also produced within longer reaction times (~20 h) even with electron-releasing groups. 相似文献316.
Light is used to 'gate' the Diels-Alder reaction using a photoresponsive dithienylfuran backbone and turn the reversibility of the Diels-Alder reaction 'off' and 'on' at 100 °C. These features make the reported system an excellent candidate for developing the next generation of self-healing polymers and photothermal drug delivery vehicles. 相似文献
317.
The potential energy curves have been investigated for the 13 lowest sextet electronic states in the representation below 53,000 cm?1 of the molecule CrCl via CASSCF and MRCI (single and double excitation with Davidson correction) calculations. The harmonic frequency ωe, the internuclear distance re, the rotational constant Be, the electronic energy with respect to the ground state Te, and the permanent dipole moment μ have been calculated. By using the canonical functions approach, the eigenvalues Ev, the rotational constant Bv, and the abscissas of the turning points rmin and rmax have been calculated for the considered electronic states up to the vibrational level v = 16. Nine electronic states have been studied theoretically here for the first time. The comparison of these values with the theoretical and experimental results available in the literature shows a good agreement. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
318.
We consider the relativistic Euler equations in isentropic fluids with the equation of state , which is the ultra-relativistic limit. We analyze the single shocks. We study the shock interaction, and give explicit example for the non-backward uniqueness. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
319.
On the hyperchaotic complex Lü system 总被引:1,自引:0,他引:1
The aim of this paper is to introduce the new hyperchaotic complex Lü system. This system has complex nonlinear behavior which
is studied and investigated in this work. Numerically the range of parameter values of the system at which hyperchaotic attractors
exist is calculated. This new system has a whole circle of equilibria and three isolated fixed points, while the real counterpart
has only three isolated ones. The stability analysis of the trivial fixed point is studied. Its dynamics is more rich in the
sense that our system exhibits both chaotic and hyperchaotic attractors, as well as periodic and quasi-periodic solutions
and solutions that approach fixed points. The nonlinear control method based on Lyapunov function is used to synchronize the
hyperchaotic attractors. The control of these attractors is studied. Different forms of hyperchaotic complex Lü systems are
constructed using the state feedback controller and complex periodic forcing. 相似文献
320.
Bottom rack intake is one of the most popular structures for diverting water in steep rivers. The problems of corrosion, deformity,
and clogging of the bottom racks in long term inspire a new system of bottom intake in which a filled trench of porous media
replaces the bottom racks. Diversion of a specified amount of water through the porous media, when the void space in the granular
material is filled with fine sediments in comparison to the bottom racks, requires much larger structure. For the proposed
water intake, lower cost of construction and maintenance and higher compatibility with the river morphology are considered
as major advantages. This research deals with an experimental model with two-story channel, the lower one is used to convey
diverted water through the porous media and the upper one is used to carry the remained flow to downstream. Measurements of
the diverted discharge were performed for different rates of flow, grain, and sediment size distributions as well as surface
slopes of intake. Results show that despite clogging of the suspended sediments in porous media, using appropriate grain size
with a surface slope of the porous media increases the discharge coefficient of system. In comparison to the clear water flow,
the diverted discharge reduction induced by clogging is not significant and the efficiency of system in long term with no
operation effort is confirmed. An empirical formulation has been proposed based on the concept of Darcy’s law for surface
infiltration. The equation is found to be dependent on size ratio, Reynolds number, and hydraulic gradient. The theoretical
predictions in comparison with the experimental results have shown a good consistency. 相似文献