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991.
Numerical simulation based on first-principle calculations is applied to study the wurtzite AlxIn1-xN. Simulation results suggest that the Vegard’s law deviation parameter is 0.063 ± 0.014 Å for the a lattice constant, and -0.160 ± 0.015 Å for the c lattice constant. The band gap bowing parameter is 3.668 ± 0.147 eV with the lattice constants by means of the minimized equilibrium energy, and 3.457 ± 0.152 eV with the lattice constants derived from Vegard’s law. PACS 71.15.-m; 71.20.Nr; 81.05.Ea  相似文献   
992.
Given a graph G, a proper labeling f of G is a one-to-one function . The bandwidth sum of a graph G, denoted by Bs(G), is defined by Bs(G)=min∑uvE(G)|f(u)-f(v)|, where the minimum is taken for all proper labelings f of G. In this paper, we give some results for the bandwidth sum problem for the join of k graphs G1,G2,…,Gk, where each Gi is a path, cycle, complete graph, or union of isolated vertices. We also discuss the bandwidth sum for the composition of two graphs G and H, where G and H are path, cycle, or union of isolated vertices.  相似文献   
993.
X‐ray diffraction and differential scanning calorimeter (DSC) methods have been used to investigate the crystallization behavior and crystalline structure of hexamethylenediamine (HMDA)‐modified maleic‐anhydride‐grafted polypropylene/clay (PP‐g‐MA/clay) nanocomposites. These nanocomposites have been prepared by using HMDA to graft the PP‐g‐MA (designated as PP‐g‐HMA) and then mixing the PP‐g‐HMA polymer in hot xylene solution, with the organically modified montmorillonite. Both X‐ray diffraction data and transmission electron microscopy images of PP‐g‐HMA/clay nanocomposites indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into PP‐g‐HMA matrix. DSC isothermal results revealed that introducing 5 wt % of clay into the PP‐g‐HMA structure causes strongly heterogeneous nucleation, which induced a change of the crystal growth process from a three‐dimensional crystal growth to a two‐dimensional spherulitic growth. Mechanical properties of PP‐g‐HMA/clay nanocomposites performed by dynamic mechanical analysis show significant improvements in the storage modulus when compared to neat PP‐g‐HMA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3242–3254, 2005  相似文献   
994.
The carrier capture and relaxation of type II ZnTe/ZnSe quantum dots have been investigated with ultrafast time-resolved photoluminescence upconversion. The carrier capture times were 7 and 38 ps for the Volmer–Weber mode and Stranski–Krastanow mode, respectively. We found that the carrier relaxation of QDs exhibits faster decay under the Volmer–Weber growth mode than under the Stranski–Krastanow growth mode. We attribute the difference of carrier relaxation to the wetting layer formed in the Stranski–Krastanow growth mode.  相似文献   
995.
A series of first-principles Monte Carlo simulations in the isobaric-isothermal ensemble were carried out for liquid water at ambient conditions (T=298 K and p=1 atm). The Becke-Lee-Yang-Parr (BLYP) exchange and correlation energy functionals and norm-conserving Goedecker-Teter-Hutter (GTH) pseudopotentials were employed with the CP2 K simulation package to examine systems consisting of 64 water molecules. The fluctuations in the system volume encountered in simulations in the isobaric-isothermal ensemble require a reconsideration of the suitability of the typical charge-density cutoff and the regular grid-generation method previously used for the computation of the electrostatic energy in first-principles simulations in the microcanonical or canonical ensembles. In particular, it is noted that a much higher cutoff is needed and that the most computationally efficient method of creating grids can result in poor simulations. Analysis of the simulation trajectories using a very large charge-density cutoff at 1200 Ry and four different grid-generation methods point to a significantly underestimated liquid density of about 0.8 g cm-3 resulting in a somewhat understructured liquid (with a value of about 2.7 for the height of the first peak in the oxygen-oxygen radial distribution function) for BLYP-GTH water at ambient conditions. In addition, a simulation using a charge-density cutoff at 280 Ry yields a higher density of 0.9 g cm-3, showing the sensitivity of the simulation outcome to this parameter.  相似文献   
996.
Mono‐polyhedral oligomeric sillsesquioxane‐end capped poly(ε‐caprolactone) (mPPCL) can form inclusion complexes (ICs) with α‐ and γ‐cyclodextrins (CDs) but not with β‐CD. These CD ICs have been characterized with X‐ray diffraction, solid‐state 13C cross‐polarization/magic‐angle‐spinning NMR spectroscopy, 1H NMR spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. The poly(ε‐caprolactone) (PCL) chain of mPPCL is included within the channel provided by the CDs to form a columnar, crystalline structure. The PCL/CD ratios determined by 1H NMR spectroscopy for the ICs with α‐ or γ‐CDs are higher than the stoichiometries because of the steric hindrance of the bulky polyhedral oligomeric silsesquioxane chain end and result in a fraction of the ε‐caprolactone units free from complexation with the CDs. On the basis of these analyses, we propose some possible structures for these CD/mPPCL ICs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 125–135, 2007  相似文献   
997.
Response characteristics of bilinear hysteretic systems are investigated under two-frequency excitation. The excitation involves a predominate frequency component superimposed by a weaker high-frequency component having an integer frequency ratio. Depending on the frequency ratio, the long-term solutions show various forms of asymmetric response besides a symmetric steady-state response. In the limiting case of zero post-yielding stiffness, the displacement solution may exhibit a periodic-like response characterized by a constant drift increment occurring in each response cycle. To analyze the drift, two solution schemes, respectively, assuming uni-frequency and two-frequency response shapes are presented. Analytical results indicate that the frequency ratio and the phase difference of the two-frequency excitation highly influence not only the drift increment but also the direction of drift response. The effects associated with the addition of viscous damping are also investigated and discussed.  相似文献   
998.
We investigate the optimal management problem of an M/G/1/K queueing system with combined F policy and an exponential startup time. The F policy queueing problem investigates the most common issue of controlling the arrival to a queueing system. We present a recursive method, using the supplementary variable technique and treating the supplementary variable as the remaining service time, to obtain the steady state probability distribution of the number of customers in the system. The method is illustrated analytically for exponential service time distribution. A cost model is established to determine the optimal management F policy at minimum cost. We use an efficient Maple computer program to calculate the optimal value of F and some system performance measures. Sensitivity analysis is also investigated.  相似文献   
999.
A cost‐effective and environmentally friendly method to dissolve microcrystalline cellulose (MCC) has been utilized. A detailed investigation of the effects of cellulose amount and solvent (aqueous NaOH) concentration on MCC solubility has been presented. In the experiments, NaOH solutions with concentrations ranging from 3.7 to 18.6 wt% have been employed to dissolve MCC with various weights. The results show that an optimal NaOH concentration range can always be found to give the best solubility of MCC having a certain weight. The solubility monotonically decreases with either the decreasing or increasing of NaOH concentration away from the optimal concentration range. In addition, the optimal concentration range of NaOH for dissolving cellulose has been shown to shrink as the amount of MCC increases. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
1000.
For a bounded linear injectionCon a Banach spaceXand a closed linear operatorA : D(A) XXwhich commutes withCwe prove that (1) the abstract Cauchy problem,u″(t) = Au(t),t R,u(0) = Cx,u′(0) = Cy, has a unique strong solution for everyx,y D(A) if and only if (2)A1 = AD(A2) generates aC1-cosine function onX1(D(A) with the graph norm), if (and only if, in caseAhas nonempty resolvent set) (3)Agenerates aC-cosine function onX. HereC1 = CX1. Under the assumption thatAis densely defined andC−1AC = A, statement (3) is also equivalent to each of the following statements: (4) the problemv″(t) = Av(t) + C(x + ty) + ∫t0 Cg(r) dr,t R,v(0) = v′(0) = 0, has a unique strong solution for everyg L1locandx, y X; (5) the problemw″(t) = Aw(t) + Cg(t),t R,w(0) = Cx,w′(0) = Cy, has a unique weak solution for everyg L1locandx, y X. Finally, as an application, it is shown that for any bounded operatorBwhich commutes withCand has range contained in the range ofC,A + Bis also a generator.  相似文献   
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