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关键词： Absorption   Heat transfer   Wave function   Defects   Materials  

摘要： We present a theoretical approach to understanding the role of defect states in hole localization in chalcopyrite quantum dots. The total energy of the electron-phonon coupled system is modeled using harmonic oscillators. The model successfully explains results from a number of separate experimental studies using a single set of parameters. The hole transfer rate from the valence band to a defect state is calculated to be 3.3 ps. Our analysis, in conjunction with the emission line width and the Stokes shift observed in these quantum dots, suggests that along with the vibronic coupling, the copper d-orbital participation to the valence band needs to be considered. In addition, we explain the radiative lifetime observed in these systems in terms of fine-structure. We furthermore study the temporal evolution of spontaneous emission rates in these quantum dots. Our results (change of radiative lifetime over similar to 10 ps) match extremely well with the experimentally reported values (similar to 15 ps).

关键词： zigzag graphene nanoribbon   quantum entanglement   quantum dynamics  

摘要： We study the dynamics of entanglement between two edge spins in a zigzag graphene nanoribbon (ZGNR) which is thermalized with a reservoir at temperature T. The results show that the entanglement evolution displays oscillating behaviors in the presence of an external magnetic field. Such oscillating behaviors of entanglement strongly depend on the field frequency and relative location between two inter-edge coupled spins. At some critical field frequencies, the entanglement exhibits a periodic structure. When the temperature is low, the oscillating patterns of entanglement are quite regular and symmetrical. When the temperature is high, the patterns of entanglement evolution occur irregular distortions due to the thermal fluctuations. However, the entanglement between two inter-edge coupled spins in ZGNR still exists a nontrivial value even at room temperature.

关键词： 高校   篮球运动训练   表象训练法   策略  

摘要： 随着社会的不断发展,对高校体育教学提出了越来越高的要求.表象训练法主要是对学生进行心理训练的有效方法,不仅可以提升学生的身体素质以及心理素质,还能加强学生头脑以及四肢的配合性.因此,在以往教学中存在的很多问题都可利用表象训练法来解决.本文通过对高校篮球运动训练的"表象训练法"进行深度探究,并提出相应的策略,为之后的高校篮球教学提供有效的参考.

关键词： Salvatore Leonardi   Eigenvalues   spherically symmetric manifolds   the drifting Laplacian   p-Laplacian   warped products  

摘要： In this paper, we investigate minimal submanifolds M immersed into warped products of type N-n x (f) Q(q), where f is an element of C-infinity (N) is positive, and can give lower bounds for the weighted fundamental tone of the drifting Laplacian, the first eigenvalue of the p-Laplacian on open domains in M. This achievement enables us to deal with spectral estimates for minimal submanifolds bounded by cylinders, cones, spheres and pseudo-hyperbolic spaces, and meanwhile some interesting byproducts can be obtained. For instance, we can show that the fundamental tone of any cylindrically bounded minimal hypersurface in the Euclidean m-space R-m (m >= 3) is positive.

关键词： Kirchhoff-type problem   variable-order fractional Laplacian  

摘要： In this paper, we show the existence of infinitely many solutions for Kirchhoff-type variable-order fractional Laplacian problems involving variable exponents. More precisely, we consider {(M([u]s(-)2)(-Delta))(u=0)s()u+V(x) u = lambda vertical bar u vertical bar(p(x)-2) u + mu vertical bar mu vertical bar q((x)-2)u in Omega, in R-N backslash Omega, where [u](s(.)):= (integral integral(R2N) vertical bar u(x) - u(y)vertical bar(2) / vertical bar x - y vertical bar(N+2s(x,y)) dxdy)(1/2), N >= 1, s(.) : R-N x R-N -> (0, 1) is a continuous function, Omega is a bounded domain in R-N with N > 2s(x, y) for all (x, y). is an element of Omega x Omega, (-Delta)(s(.)) is the variable-order fractional Laplace operator, M : R-0(+) -> R-0(+) and V : Omega -> [0,infinity) are two continuous functions, alpha, beta > 0 are two parameters and p, q is an element of C(Omega). In addition to using the new version of Clark's theorem due to Liu and Wang to prove the existence of infinitely many solutions for the above problem, we also apply the symmetric mountain pass theorem, fountain theorem and dual fountain theorem to obtain the same conclusion. The main feature, as well as the main difficulty, of our problem is the fact that the Kirchhoff term M could be zero at zero.

关键词： Applied and Technical Physics   Theoretical   Mathematical and Computational Physics   Complex Systems   Condensed Matter Physics   Atomic   Molecular   Optical and Plasma Physics  

摘要： We discuss the time evolution of entanglement, purity, and coherence of two non-interacting maximally entangled qubits in two different classical environmental configurations: bipartite and independent system-environment configuration. Gaussian noises, such as fractional Gaussian (F-G) and power-law (P-L) noise, are considered characterizing these environments. In particular, we are interested in exploring the dephasing effects in two qubits caused by the Gaussian noises in pure and mixed situations using entanglement witness, concurrence, purity, and decoherence measures. We notice both the noises in pure and in mixed forms are highly dephasing, and the bipartite quantum correlation, purity, and coherence eventually disappear after a finite interaction time. We notice that the current quantum phenomena decay faster under F-G noise than under P-L noise. Also, in independent system-environment configuration, the bipartite state is found to have slightly longer quantum correlation, purity, and coherence preservation than common environments, suggesting it more favourable for such quantum operations. For increasing values of the memory parameter of the F-G noise, the entanglement, purity, and coherence become initially robust, defying the dephasing character of parameters of nearly all the noises. The wide spectrum of the pure P-L noise can be readily exploited to design long preservation effects, especially by fixing the noise parameters to utmost low values. Also, the decay outlook induced by both noises is a monotonous function of time, with no entanglement sudden death and births observed.

关键词： Cryogenics   Electroluminescence   Nonequilibrium thermodynamics   Photoluminescence spectroscopy   Charge transport   Light emitting diodes   Exciton dynamics   Charge recombination   Quantum dots   Optoelectronic devices  

摘要： Exploring the temperature-dependent electroluminescence (EL) properties of quantum dots (QDs) is not only critical for the fundamental understanding of charge recombination processes in quantum dot light-emitting diodes (QLEDs) but also important to expand their particular applications at cryogenic temperatures. Herein, the temperature-dependent EL properties of typical CdSe/ZnS core/shell QDs were systematically studied for both the standard and inverted QLEDs in the temperature range of 100-300 K. It was found that EL intensity and efficiency were gradually enhanced and exhibited a pronounced blue shifting in EL spectra with the decrease in temperature. We demonstrated that temperature-dependent EL behaviors mainly originated from the inherent properties of QDs, while the different device structures could induce some fine temperature-dependent behaviors on this basis. Moreover, the effective Joule heat dissipation at low temperatures protects the charge transport and QD layers from thermal decomposition and damage, which prolongs the operational lifetime of devices.

摘要： The biosynthesis of R-phenylacetylcarbinol (R-PAC) by the acetohydroxy acid synthase, (AHAS) is addressed by molecular dynamics simulations (MD), hybrid quantum mechanics/molecular mechanics (QM/MM), and QM/MM free energy calculations. The results show the reaction starts with the nucleophilic attack of the C2α atom of the HEThDP intermediate on the Cβ atom of the carbonyl group of benzaldehyde substrate via the formation of a transition state (TS1) with the HEThDP intermediate under 4′-aminopyrimidium (APH+) form. The calculated activation free energy for this step is 17.4 kcal mol−1 at 27 °C. From this point, the reaction continues with the abstraction of Hβ atom of the HEThDP intermediate by the Oβ atom of benzaldehyde to form the intermediate I. The reaction is completed with the cleavage of the bond C2α-C2 to form the product R-PAC and to regenerate the ylide intermediate under the APH+ form, allowing in this way to reinitiate to the catalytic cycle once more. The calculated activation barrier for this last step is 15.9 kcal mol−1 at 27 °C.