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High-speed transportation is closely related to people’s livelihood and national economy, so it becomes an important development aspect to the whole country. The safety, comfort and economy of high-speed train are the key consideration during its design process. In the future, new trains and old ones will be used for a long time, and the performance of new trains which run on the old lines may be limited. These situations make the research of high-speed train with asymmetric heads much necessary. Aiming at the feasibility of the train with asymmetric heads, the heads of train CRH3 and another typical train with a similar speed are selected. Based on the two heads, the digital models of the traditional trains with symmetric heads and the new trains with asymmetric heads are built firstly. And then their aerodynamic characteristics are computed by the SIMPLE method. In the numerical part, the performances of the trains are compared on the condition without crosswind, which shows that one of the new trains with asymmetric heads is the best among them. Moreover, the aerodynamic characteristics of this new model under crosswind is analyzed, which demonstrates that the train with asymmetric heads is feasible. The research shows that the train with asymmetric heads can achieve better results through the proper aerodynamic shape optimization design, which presents an idea for the future high-speed train design.

Based on the consideration of grid factors and turbulence model factors, the confluence boundary layer and aerodynamic characteristics of the NHLP-2D airfoil are studied. Compared with the experimental results, the grid distribution near the confluence boundary layer is important for calculating the width of the wake area. The calculation results of the structured and unstructured grids are basically the same when the surface grid distribution is the same. On the basis of the mesh refinement in the wake area, the aerodynamic characteristics calculated by the SA turbulence model and the distribution of the total pressure coefficient in the confluence boundary layer are in good agreement with the experimental results. The width of the confluence boundary layer and the wake strength decrease with the increase of Reynolds number, the lift coefficient increases with the increase of Reynolds number, but the drag and pitching moment have opposite pattern. The maximum lift of the airfoil increases as the Reynolds number increases. As the Reynolds number increases, the stall angle of attack of the airfoil gradually increases and then remains stable with the increase of the Reynolds number.

Static component (SC) generation of guided waves (GWs), which combines the high sensitivity of acoustic nonlinearity to micro-damage and low attenuative effect, has great potential for damage assessment in large composite structures. The present work explores the use of SC generation of GWs for assessing damages in carbon fiber reinforced polymer (CFRP) composite laminates. The features including mode, waveform, and cumulative effect of the generated SC in composites are numerically investigated by three-dimensional finite element modeling and simulation. A dynamic displacement measurement method based on piezoelectric transducers is accordingly proposed and experimentally verified. The cumulative SC pulse generated from primary GW tone-burst with a finite duration, is observed and verified numerically and experimentally. It is found that the magnitude of the generated SC pulse is linearly proportional to the quadratic material nonlinearity. Experimental results demonstrate that the generated SC pulse of GW under group velocity matching condition, is an effective means to assess the hygrothermal damage and low-velocity impact damage in CFRP composite plates. The performed experimental examination validates the feasibility of the proposed approach for damage assessment in CFRP composites.

Supercooled large droplets widely exist in clouds, which have poor aerodynamic follow-up and strong dynamic characteristics, making the relevant experiments and numerical simulation more difficult. Splash is the main influencing factor of droplet collection efficiency, and it is easier to be recorded and quantified. In the LEWICE model, little or no splash happened around stagnation point. Focus on this problem, an improved large droplet splashing model is proposed based on the idea of minimum mass loss ratio. In the numerical simulation part, the advantages and disadvantages of the proposed model are analyzed by comparing with several classical splashing models and experimental data. Based on the experimental data of airfoil MS317, the validity of the model is verified. Moreover, airfoil NACA23012 and ARJ cruise configuration are chosen to obtain the droplet collection efficiency, which shows the feasibility of the proposed model.

In order to improve the activity of monohalide ruthenium oxide, different ratios of BiOBrXCl1-X series samples (X=0, 0.2, 0.4, 0.6, 0.8, 1) were synthesized by solvothermal method. The synthesized BiOBrXCl1-X samples were characterized by X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS) and scanning electron microscopy(SEM). The photocatalytic degradation experiment for Rhodamine B showed that the BiOBr0.2Cl0.8 sample had higher degradation efficiency under visible light and effectively improved photocatalytic activity.

The dynamic process of the evaporation and the desiccation of sessile saline colloidal droplets, and their final deposition are investigated. During the evaporation, the movement of the colloidal particles shows a strong dependence on the salt concentration and the droplet shape. The final deposition pattern indicates a weakened coffee-ring effect in this mixed droplet system. The microscopic observation reveals that as evaporation proceeds, the particle motion trail is affected by the salt concentration of the droplet boundary. The Marangoni flow, which is induced by surface tension gradient originating from the local evaporative peripheral salt enrichment, suppresses the compensation flow towards the contact line of the droplet. The inhomogeneous density and concentration field induced by evaporation or crystallization can be the major reason for various micro-flows. At last stage, the distribution and crystallization of NaCl are affected by the colloidal particles during the drying of the residual liquid film.

We investigate the energy eigenvalues and eigenstates of a resonant field in a Kerr-like medium by an efficient method. All the energy eigenvalues and eigenstates can be obtained for an arbitrary total particle number N and other parameters involved in the system. We show that the eigenstates can be explicitly expressed analytically in terms of a single parameter. whose values are determined by the roots of a polynomial of the order of at most 1+ int( N/2) with int( x) being x's integer part. By studying the spectra, the erratic level crossings appear apparent when N > 40 and. over critical values.

The theory of continuous phase transitions predicts the universal collective properties of a physical system near a critical point, which for instance manifest in characteristic power-law behaviours of physical observables. The well-established concept at or near equilibrium, universality, can also characterize the physics of systems out of equilibrium. The most fundamental instance of a genuine non-equilibrium phase transition is the directed percolation universality class, where a system switches from an absorbing inactive to a fluctuating active phase. Despite being known for several decades it has been challenging to find experimental systems that manifest this transition. Here we show theoretically that signatures of the directed percolation universality class can be observed in an atomic system with long range interactions. Moreover, we demonstrate that even mesoscopic ensembles --- which are currently studied experimentally --- are sufficient to observe traces of this non-equilibrium phase transition in one, two and three dimensions., Comment: 15 pages, 5 figures

We consider a novel system of two-component atomic Bose-Einstein condensate in a double-well potential. Based on the well-known two-mode approximation, we demonstrate that there are obvious avoided level-crossings when both interspecies and intraspecies interactions of two species are increased. The quantum dynamics of the system exhibits revised oscillating behaviors compared with a single component condensate. We also examine the entanglement of two species. Our numerical calculations show the onset of entanglement can be signed as a violation of Cauchy-Schwarz inequality of second-order cross correlation function. Consequently, we use Von Neumann entropy to quantity the degree of entanglement.

We show the formation of slow bistable solitons in a lifetime broadened three-state atomic medium with strong field excitation. We demonstrate, both analytically and numerically, that slow bistable solitons with low peak intensity can exist under appropriate conditions. This work may provide new experimental evidence of bistability of light solitons.

Using a topcolour-assisted multiscale technicolour model, we calculate the corrections of pseudo-Goldstone bosons (technipions, top pions) to the cross section of the process q→t at the Fermilab Tevatron. Our results show that corrections mainly come from top pions. With reasonable values of the parameters, the correction can increase the total t production cross section σt by as much as 17%. This may provide a window to detect top pions.

We calculated the contribution of pseudo-Goldstone bosons (technipions, top pions) to the cross-section of the process e+ e - s in the topcolour-assisted multiscale technicolour model at LEPII. Our results show that the cross-section is of the order of 10-2 fb, for reasonable values of the parameter. This is larger than that predicted by the standard model by about one order of magnitude. Such enhancement might provide an opportunity to detect the new physics at future colliders.

Composite materials which are widely used in the aerospace industry, are usually subjected to frequent variation of temperature. Thermal cyclic loading may induce material degradation. Considering the long-term service of aircraft composites and the importance of safety in the aircraft industry, even a little damage that may be accumulative via thermal fatigue is often of great concern. Therefore, there is a demand to develop non-destructive approaches to evaluate thermal fatigue damage in an early stage. Due to the sensitivity of acoustic nonlinearity to micro-damage, the nonlinear ultrasonic technique has been explored as a promising tool for early detection of micro-damage. This paper investigates an experimental scheme for characterizing thermal fatigue damage in composite laminates using second harmonic Lamb waves. The present results show a monotonic increase of acoustic nonlinearity with respect to thermal fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and thermal fatigue cycles in carbon/epoxy laminates verifies that nonlinear Lamb waves can be used to assess thermal fatigue damage rendering improved sensitivity over conventional linear feature based non-destructive evaluation techniques. Velocity and attenuation based ultrasonic studies are carried out for comparison with the nonlinear ultrasonic approach and it is found that nonlinear acoustic parameters are more promising indicators of thermal fatigue damage than linear ones.

We provide a detailed theoretical and conceptual study of a planned experiment to excite Rydberg states of ions trapped in a Paul trap. The ultimate goal is to exploit the strong state dependent interactions between Rydberg ions to implement quantum information processing protocols and to simulate the dynamics of strongly interacting spin systems. We highlight the promises of this approach when combining the high degree of control and readout of quantum states in trapped ion crystals with the novel and fast gate schemes based on interacting giant Rydberg atomic dipole moments. We discuss anticipated theoretical and experimental challenges on the way towards its realization., submitted to special issue on "Quantum Simulation" in New Journal of Physics