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901.
Implementing of photonic sampling and quantizing analog-to-digital converters (ADCs) enable us to extract a single binary word from optical signals without need for extra electronic assisting parts. This would enormously increase the sampling and quantizing time as well as decreasing the consumed power. To this end, based on the concept of successive approximation method, a 4-bit full-optical ADC that operates using the intensity-dependent Kerr-like nonlinearity in a two dimensional photonic crystal (2DPhC) platform is proposed. The Silicon (Si) nanocrystal is chosen because of the suitable nonlinear material characteristic. An optical limiter is used for the clamping and quantization of each successive levels that represent the ADC bits. In the proposal, an energy efficient optical ADC circuit is implemented by controlling the system parameters such as ring-to-waveguide coupling coefficients, the ring’s nonlinear refractive index, and the ring’s length. The performance of the ADC structure is verified by the simulation using finite difference time domain (FDTD) method. 相似文献
902.
We have investigated the influence of an external electric field on the binding energies and polaronic shifts of the ground and some first few excited states of a hydrogenic impurity in a spherical quantum dot by taking into account the image charge effect. By using Landau–Pekar variational method the general analytical expression is obtained for the impurity bound-polaron energies. It has been numerically identified the conditions (electric field, nominal radius of quantum dot, etc.) in which the bound-polaron states can be existence in GaAs quantum dot. We have shown that the polaronic shifts in the binding energy of 1s-like state are the same in cases with and without image charge effect while they for 2s-like state are not coincide and have different monotonic behavior versus confinement potential. Electron–phonon interaction lifts the degeneracy of the 2px-, 2py-, and 2pz-like states of a donor impurity and reduces their binding energies. 相似文献
903.
The photocurrent of surface states of topological insulator due to photon-drag effect is computed, being based on pure Dirac model of surface states. The scattering by disorder is taken into account to provide a relaxation mechanism for the photocurrent. The Keldysh–Schwinger formalism has been employed for the systematic calculation of photocurrent. The helicity dependent photocurrent of sizable magnitude transverse to the in-plane photon momentum is found, which is consistent with experimental data. Other helicity independent photocurrents with various polarization states are also calculated. 相似文献
904.
We investigate the longitudinal optical conductivity of spatially separated few-layer graphene analytically and numerically. Each layer could be monolayer or bilayer graphene. The density–density correlation function has been screened by the dielectric function using the random phase approximation, which includes the inter-layer Coulomb coupling. In the presence of the potential function between the layers, the carrier densities in each layer can be tuned respectively. In these two-dimensional layered structures, the main contributions to the optical conductivity are from the intra- and inter-band transition channels in a same layer. In the infrared region, the Drude optical conductivity was observed by the unscreened intra-band transition process. But in the presence of the inter-layer Coulomb interaction, one peak structure of the optical conductivity is observed which can be modified by the dielectric environment. From the number of turning points and the turning positions, the carrier density, the Fermi wavevector, and the layered structure can be determined. 相似文献
905.
Z. P. Niu Z. M. Zheng D. Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):281-287
Four-component Bogoliubov-de Gennes equations are applied to study
tunneling conductance spectra of ferromagnet/ferromagnet/d-wave
superconductor (F1/F2/d-wave S) tunnel junctions and to find
out signs of spin-triplet pairing correlations induced in the
proximity structure. The pairing correlations with equal spins
arises from the novel Andreev reflection (AR), which requires at
least three factors: the usual AR at the F2/S interface, spin
flip in the F2 layer, and superconducting coherence kept up in
the F2 layer. Effects of angle α between magnetizations of
the two F layers, polarizations of the F1 and F2 layers, the
thickness of the F2 layer, and the orientation of the d-wave S crystal on the tunneling conductance are investigated. A conversion
from a zero-bias conductance dip at α = 0 to a zero-bias
conductance peak at a certain value of α can be seen as a
sign of generated spin-triplet correlations. 相似文献
906.
In this study, the axial flow cyclone used in Tsai et al. (2004) was further tested for the collection efficiency of both
solid (NaCl) and liquid (OA, oleic acid) nanoparticles. The results showed that the smallest cutoff aerodynamic diameters
achieved for OA and NaCl nanoparticles were 21.7 nm (cyclone inlet pressure: 4.3 Torr, flow rate: 0.351 slpm) and 21.2 nm
(5.4 Torr, 0.454 slpm), respectively. The collection efficiencies for NaCl and OA particles were close to each other for the
aerodynamic diameter ranging from 25 to 180 nm indicating there was almost no solid particle bounce in the cyclone. The 3-D
numerical simulation was conducted to calculate the flow field in the cyclone and the flow was found to be nearly paraboloid.
Numerical simulation of the particle collection efficiency based on the paraboloid flow assumption showed that the collection
efficiency was in good agreement with the experimental data with less than 15% of error. A semi-empirical equation for predicting
the cutoff aerodynamic diameter at different inlet pressures and flow rates was also obtained. The semi-empirical equation
is able to predict the cutoff aerodynamic diameter accurately within 9% of error. From the empirical cutoff aerodynamic diameter,
a semi-empirical square root of the cutoff Stokes number, , was calculated and found to be a constant value of 0.241. This value is useful to the design of the cyclone operating in
vacuum to remove nanoparticles. 相似文献
907.
908.
B. Doggett S. Chakrabarti R. OHaire A. Meaney E. McGlynn M.O. Henry J.P. Mosnier 《Superlattices and Microstructures》2007,42(1-6):74
Phosphorus-doped ZnO films were grown by pulsed laser deposition using a ZnO:P2O5-doped target as the phosphorus source with the aim of producing p-type ZnO material. ZnO:P layers (with phosphorus concentrations of between 0.01 to 1 wt%) were grown on a pure ZnO buffer layer. The electrical properties of the films were characterised from temperature dependent Hall-effect measurements. The samples typically showed weak n-type conduction in the dark, with a resistivity of 70 Ω cm, a Hall mobility of μn0.5 cm2 V −1 s−1 and a carrier concentration of n3×1017 cm−3 at room temperature. After exposure to an incandescent light source, the samples underwent a change in conduction from n- to p-type, with an increase in mobility and decrease in concentration for temperatures below 300 K. 相似文献
909.
The electrophoresis and electric conduction of a suspension of charged spherical particles in a salt-free solution are analyzed by using a unit cell model. The linearized Poisson-Boltzmann equation (valid for the cases of relatively low surface charge density or high volume fraction of the particles) and Laplace equation are solved for the equilibrium electric potential profile and its perturbation caused by the imposed electric field, respectively, in the fluid containing the counterions only around the particle, and the ionic continuity equation and modified Stokes equations are solved for the electrochemical potential energy and fluid flow fields, respectively. Explicit analytical formulas for the electrophoretic mobility of the particles and effective electric conductivity of the suspension are obtained, and the particle interaction effects on these transport properties are significant and interesting. The scaled zeta potential, electrophoretic mobility, and effective electric conductivity increase monotonically with an increase in the scaled surface charge density of the particles and in general decrease with an increase in the particle volume fraction, keeping each other parameter unchanged. Under the Debye-Hückel approximation, the dependence of the electrophoretic mobility normalized with the surface charge density on the ratio of the particle radius to the Debye screening length and particle volume fraction in a salt-free suspension is same as that in a salt-containing suspension, but the variation of the effective electric conductivity with the particle volume fraction in a salt-free suspension is found to be quite different from that in a suspension containing added electrolyte. 相似文献
910.
运用多重态计算方法研究了在正八面体对称性的晶体场中Co2+离子的2p电子X射线L2,3吸收边光谱, 研究了Co2+离子和周围的配位离子之间的正八面体(Oh)晶体场效应和相应的电荷转移效应对于吸收光谱的影响. 系统讨论了在多重态计算中起作用的所有物理参数对CoO和CoCl2的X射线吸收光谱特性的特定影响及其物理机制. 将计算得出的光谱数据和同样具有Oh对称性结构Co2+离子的CoO和CoCl2实验光谱数据进行了对比, 在实验光谱数据中发现的特征被确定为来自不同自旋态, 并且光谱强度的变化与晶体场的强度相关, 揭示了其中包含的电荷转移效应. 本文为低对称性复杂系统的多重态计算提供了一个基础的参考标准, 可以适用于含有钴元素或其它过渡金属的复杂体系的X射线吸收光谱的理论计算. 相似文献