Properties of train traffic flow in a moving block system

The development direction of railways is toward the improvement of capacity and service quality, where the service quality includes safety, schedule, high speed, and comfort. In light of the existing cellular automaton models, in this paper, we develop a model to analyze the mixed running processes of trains with maximal speeds of 500 km/h and 350 km/h respectively in the moving block system. In the proposed model, we establish some sound rules to control the running processes of a train, where the rules include the departure rules in the intermediate stations, the overtaking rules, and the conditions of speed limitation for a train stopping at a station or passing through a station. With the consideration of the mixed ratio and the distance between two adjacent stations, the properties of the train traffic flow (including capacity and average speed) are simulated. The numerical results show that the interactions among different trains will affect the capacity, and a proper increase of the spatial distance between two adjacent stations can enhance the capacity and the average speed under the moving block.     

Photon-counting chip-interleaved iterative PIC detector over atmospheric turbulence channels

A photon-counting-based iterative parallel interference cancellation (PIC) scheme for free-space optical communications in the presence of multiple-access interference,shot noise,background radiation,and turbulence fading is designed.An efficient chip-level iterative equivalent noise estimation algorithm is also derived.Simulation results show that the proposed scheme can achieve a single-user performance,bound with the fast convergence property.More importantly,it can eliminate the bit-error rate floor of the conventional optical code-division multiple-access system with the aid of a relatively short spreading code length.     

Enhanced microwave magnetic and attenuation properties of composites with free-standing spinel ferrite thick films as fillers

Free-standing thick films of spinel ferrite, Ni_0.89−xCu_0.11Zn_xFe₂O₄ with x=0.55 and 0.60, were prepared as fillers to fabricate electromagnetic composites. Compared to those made with conventional spherical fillers, the composites made with thick film fillers showed enhanced static permeability (μ′₀) and maximum imaginary permeability (μ″_max). At the same time, complex permittivity (ε′ and ε″) were almost unchanged. A relative bandwidth W_R of 7–8 was achieved, which is about 75% of the theoretical maximum relative bandwidth. These composites are potential candidates as electromagnetic attenuation materials with ultrabroad absorption bandwidth in L and S bands.     

Mixed traffic flow model considering illegal lane-changing behavior: Simulations in the framework of Kerner’s three-phase theory

This paper studies the mixed motorized vehicle (m$m$-vehicle) and non-motorized vehicle (nm$nm$-vehicle) traffic flow in the m$m$-vehicle lane. We study the formation mechanism of the nm$nm$-vehicle illegal lane-changing behavior (NILB) by considering the overtaking motivation and the traffic safety awareness. In the framework of Kerner’s three-phase theory, we propose a model for the mixed traffic flow by introducing a new set of rules. A series of simulations are carried out in order to reveal the formation, travel process and influence of the mixed traffic flow. The simulation results show that the proposed model can be used to study not only the travel characteristic of the mixed traffic flow, but also some complex traffic problems such as traffic breakdown, moving synchronized flow pattern (MSP) and moving jam. Moreover, the results illustrate that the proposed model reflects the phenomenon of the mixed flow and the influence of the MSP caused by the NILB, which is consistent with the actual traffic system, and thus this work is helpful for the management of the mixed traffic flow.     

A two-component geodesic equation on a space of constant positive curvature

We propose a new two-component geodesic equation with the unusual property that the underlying space has constant positive curvature. In the special case of one space dimension, the equation reduces to the two-component Hunter–Saxton equation.     

High-performance ZnO nanoflake moisture sensor

Humidity control is an important issue across variety of industries. In this study, a novel zinc oxide (ZnO) flake-based humidity sensor was fabricated and characterized. It was found that fast response sensor can be achieved by substituting conventional sputter ZnO thin films with nano-flakes. It is proposed that the enhancement in dynamic performance originate from the high surface area offered by the nanoflakes.     

Blue–green and red luminescence from ZnO/porous silicon and ZnO:Cu/porous silicon nanocomposite films

Both ZnO and Cu doped ZnO films with strong c-axis preferred orientation have been successfully prepared on porous silicon substrate, formed by electrochemical anodization, using radio frequency reactive magnetron sputtering method. X-ray diffraction measurements showed that the intensity of (0 0 2) diffraction peak first decreased and then increased with the Cu doping content increasing. Meanwhile new weak (1 0 0), (1 0 1), (1 0 2) and (1 1 0) diffraction peaks appeared after doping. The optical band edge of ZnO:Cu films, deduced from the optical absorption spectra, shifted to a longer wavelength comparing with the undoped sample and we attributed this red shift phenomenon to the decreasing of carrier concentration. The broad light emission from 350 to 800 nm was obtained by combining the blue–green emission from ZnO with red–orange emission from porous silicon. This could be used as a source of white light emitting diode chips underlying the importance of our work. The variation and origin of the emission peaks were discussed through the Gaussian deconvolution, and the Raman scattering spectral revealed the characteristics of porous silicon and multiphonon processes.     

Pressure‐induced incompressibility and point singularity of mechanical properties of TaC in NiAs‐type structure

The structural and elastic properties of TaC in NiAs‐type structure under high pressure have been investigated using first principles calculations based on density functional theory. Results indicate that the incompressibility along the c‐axis of TaC exceeds that of diamond under higher pressure. Particularly, an interesting point singularity exists in its mechanical properties as the pressure increases from 20 GPa to 40 GPa. The minimal shear modulus, Young's modulus, Debye temperature, and maximum Poisson ratio of TaC are simultaneously obtained at 28 GPa. The calculations of hardness indicate that the NiAs‐type TaC crystal possesses excellent mechanical properties. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controlled synthesis of luminescent CuInS2 nanocrystals and their optical properties

Luminescent CuInS₂ nanocrystals have been synthesized in dodecanethiol using air-stable precursors. The nanocrystals were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The optical properties of the CuInS₂ nanocrystals can be controlled by changing the reaction conditions, such as reaction time, temperature, and addition of ligands. It was found that the steady-state photoluminescence spectrum of the close-packed CuInS₂ nanocrystals on glass substrate peaked at longer wavelength than that of the colloidal ones and the close-packed nanocrystals possessed a shorter luminescence decay time. This behavior was explained on the basis of Förster resonant energy transfer due to the shorter distance between nanocrystals on substrate.     

Investigation of luminescence properties in SiO2: Tb,Yb upconversion inverse opal

The SiO₂: Tb, Yb inverse opals with photonic band gap at 465 or 543 nm were prepared, and an effect of photonic band gap on upconversion spontaneous emission from Tb³⁺ was investigated. The results show that the photonic band gap has a significant influence on the upconversion emission of the SiO₂: Tb, Yb inverse opals. The upconversion luminescence of the Tb³⁺ ions is suppressed in the inverse opal compared with the luminescence of that of the reference sample.