Pressure wave propagation in a short tunnel caused by passing trains

The aerodynamic behaviour of pressure transients in railway tunnels due to the passage of train are accompanied by the wave reflection between the entrance and exit of the tunnel as well as the tunnel wall and train surface. This study presents a numerical method using the Harten-Yee upwind TVD scheme to simulate compression wave transients and reflection in a railway tunnel. The strength of the compression wave generated by the entrance of a train into a tunnel emerged within the applied calculation procedure, without any special consideration of the boundary condition for the entrance or exit of the tunnel as well as the train nose and tail. Good agreements were obtained when the initial pressure rise at tunnel entrance and the process of pressure variations in a short tunnel, which were calculated by the presented numerical method, were compared with experimental data. The pressure wave reflection at the entrance and exit, the unsteady flow around the train and the transmitted wave at tunnel exit portal were simulated. The transmitted wave at the tunnel exit portal is also discussed. In addition a method to determine the non-reflective boundary condition for multi-dimensional Euler equation is given.     

Use of transfer++factor in allergic bronchial asthma

The therapeutic panorama of immunomodulation and its effects on the modification of the immune reaction is reviewed. Particular reference is made to the transfer factor as a therapeutic element in bronchial asthma, which insures its efficacy or innocuity.     

Peridynamic modeling of concrete structures

The peridynamic model described in Silling (Silling, S.A., 1998. Reformation of Elasticity Theory for Discontinuous and Long-Range Forces, SAND98-2176. Sandia National Laboratories, Albuquerque, NM), being a central-force model, is limited to modeling materials with a Poisson's ratio of 1/4. In this paper, the peridynamic model is generalized by adding pairwise peridynamic moments to simulate linear elastic materials with varying Poisson's ratios. The new model is called the “micropolar peridynamic model”. The micropolar peridynamic model is placed within a finite element context to enable efficacious application of boundary conditions and efficient computational solutions using an implicit, rather than an explicit solution algorithm. The implicit solution algorithm is suitable for quasistatic simulation of damage and cracking in concrete structures. With this new model, very simple tensile damage mechanisms at the micro structural (peridynamic) level are sufficient to explain a great deal of the microcracking (damage) and fracture mechanics observed in concrete structures. The new implementation appears to be computationally efficient.     

Entanglement network and relaxation temperature dependence of single‐site catalyzed ethylene/1‐hexene copolymers

In this work, we investigate the linear viscoelastic response of high molecular weight ethylene/1‐hexene copolymers, characterized by a narrow molecular weight distribution and comonomer content in the range from 0 to 10 mol %. A variation in the entanglement plateau modulus has been found in agreement with the recently developed packing length model. The packing model applied to viscoelastic data suggests decreased values of the characteristic ratio, accordingly with recent computer simulation results. The flow activation energy increases as the side chain content increases. This feature is thought to be related to the mobility of the molecules. The presence of side branches due to the comonomer hinders the mobility of the molecules, and increases the thermal barrier for the segmental motion. Then in the comonomer content range studied, the increase of the flow activation energy goes parallel with a decrease in the characteristic ratio. This result suggests that more parameters than only the stiffness of the chain modulate the thermal dependence of viscoelastic properties. A more refined study is necessary combining experiments with computer simulations in order to elucidate these aspects. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.     

Writing quality, reading skills, and domain knowledge as factors in text comprehension.

103 undergraduates listened to and recalled 3 passages and were given a general reading comprehension test. The passages were presented such that Ss could use general knowledge to understand them or such that no specific world knowledge seemed applicable. The passages were written in 2 different versions, preserving their content but varying their style. All 3 factors (domain knowledge, writing style, and skill) significantly affected reproductive recall, and there were no interactions between these factors. However, while good writing was sufficient to improve the reproduction of the texts, an analysis of the recall elaborations Ss made revealed that the correctness of their elaborations depended strongly on the availability of appropriate domain knowledge. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

North sea oil: Responses to employment opportunities

Britain's new offshore oil industry might have generated much additional employment especially in the building, manning and supply of rigs. But there was a failure at first to take proper advantage; little was done to train people in new skills. Consequently the oil companies brought in equipment and skilled personnel from abroad. Eventually efforts were made to improve matters and the paper examines the steps taken to bring more of the employment benefits to Britain, but finds only partial success.