Two-way Tunnel Research Articles

Enhanced combustion performance of Al–Zn alloys with property optimization inspired by “two-way tunneling” strategy

Fluorinated polymers (PVDF) are widely used due to their pre-ignition reaction with Al2O3 to improve the combustion of Al. In this study, a homogeneous PVDF coating layer was constructed on the surface of Al–Zn alloys by solvent evaporation, and Al-Zn@PVDF composites with “two-way tunneling” function during thermal decomposition and combustion were prepared. The constructed PVDF coating layer can react with Al2O3 to destroy the protective layer and promote the oxidation and combustion of Al–Zn from the outside to the inside. At the same time, the energy provided by the Al-Zn@PVDF during the ignition and combustion process also promotes the melting and vaporization of Zn, which achieves the rapid and full combustion of Al–Zn alloy from the inside to outside. The “ two-way tunneling” function of Al-Zn@PVDF composites significantly improves the combustion performance, resulting in a maximum combustion temperature of 1346.9 °C for Al-Zn@PVDF-40 % and a minimum combustion duration of 1.39 s for Al-Zn@PVDF-30 %, which is a significant improvement in combustion performance. The good chemical stability of PVDF also improves the hydrophobicity of Al–Zn and enhances its applicability. In conclusion, the construction of composites with “two-way tunneling” function first proposed in this study can significantly improve the thermal decomposition and combustion properties of Al–Zn, which is expected to further facilitate its application in propellants, explosives and pyrotechnics.

Nonlinear Electronic Transport Behavior of <inline-formula> <tex-math notation="LaTeX">$\Upsilon$ </tex-math> </inline-formula>-Graphyne Nanotubes

In this paper, we have investigated the electronic transport properties and current–voltage characteristics of the armchair and zigzag $\Upsilon $ -graphyne nanotubes by the SIESTA and TRANSIESTA packages including density functional theory and nonequilibrium Green’s function for the four chiral vectors 2, 3, 4, and 5. We foundthat the current in $\Upsilon $ -graphyne nanotubes is very negligible for low bias voltages, but it enhances precipitously for voltages above the thresholdvoltage. Both zigzag and armchair $\Upsilon $ -graphyne nanotubes reveal negative differential resistance, for specific diameters, which is a promising result for nano-based device usages such as switching and memory circuits. Finally, the characteristics of these nanotubes are similar to those of a two-way tunneling diode. Therefore, we can expect a new application that produces oscillation.

Анализ напряженно-деформированного состояния обделки двухпутного тоннеля на различных стадиях размораживания грунтового массива

Анализ напряженно-деформированного состояния обделки двухпутного тоннеля на различных стадиях размораживания грунтового массива

Innovative Engineering Solutions for Improving Operational Safety and Efficiency of Subways with Two-way Tunnels

The paper considers the problems of improving the operational safety of the two-way tunnel subway under weather conditions characteristic of Russian megapolises. A significant difference is indicated between annually mean, monthly mean and extreme outdoor air temperatures affecting thermodynamic parameters of the intra-subway atmosphere in Russia and foreign countries having subways. Comparative characteristics are given for the factors determining temperature regimes of the subway lines with single-way and two-way tunnels in case conventional ventilation schemes are used. The paper also describes alternative ventilation schemes involving constructive elements widely used for venting motor-road tunnels. Based on specific initial data, calculations have been performed whose results characterize temperature distribution in running single-way and two-way tunnels vented by using the ventilation scheme comprising vent ducts and air recirculation. The efficiency of the two-way tunnel ventilation scheme comprising a ventilation duct and air recirculation has been justified. Mathematical simulation of the dynamics of smoke propagation in case of a fire in tunnels and at stations has been accomplished. Efficiency of the emergency ventilation scheme comprising a vent duct in smoke protection of the fire evacuation passages for people and in smoke removal has been proved. The paper presents such station complex layout solutions that, contrary to historical prototypes, imply integrating the station ventilation and smoke removal systems into the general structure of the station space-planning solutions so that they are in close vicinity of all the designed passenger flows with retention of the comfortable space necessary for passengers.

Numerical modeling of the piston effect in longitudinal ventilation systems for subway tunnels

This paper analyzes the influence of the piston effect in the longitudinal ventilation system of subway tunnels using numerical methodologies. This aerodynamic effect, highly complex, three-dimensional and unsteady is modeled using Computational Fluid Dynamics (CFD) in order to simulate and analyze in detail the flow patterns associated to this effect. This approach improves the description provided by typical conventional tools, based on 1-D numerical modeling, and constitutes a useful benchmark for calibrating existing tunnel environment simulation software. For this study, a 3-D computational model for a typical subway line between two consecutive stations has been considered. The implemented geometry is a typical configuration that mimics any modern infrastructure with 100m long stations connected through a two-way tunnel, 500m in length. The ventilation system is longitudinal, composed of two inlet shafts, with mechanical ventilation for each station, and an exhaust shaft in the middle of the tunnel. Additionally, at the tunnel edges, close to the stations, there are also natural ventilation shafts or draught relief shafts (DRSs) – i.e. without mechanical fans – to attenuate possible pressure fluctuations originating from the piston effect.The numerical simulation has been conducted using the commercial code, FLUENT, developing an unsteady numerical model with a dynamic mesh technique to simulate the train displacement between the two stations. Different cases have been studied in detail, including a wide range of ventilation conditions, as well as travel frequencies (single train and two trains crossing halfway). The main objective of this analysis has been the definition and quantification of the different parameters influencing the subway ventilation system. Finally, the impact of the piston effect on the global ventilation performance has also been addressed via numerical estimation.

A Strategy to Join Adaptive and Reputation-Based Social-Collaborative E-Learning, Through the Zone of Proximal Development

The educational concept of “Zone of Proximal Development”, introduced by Vygotskij, stems from the identification of a strong need for adaptation of the learning activities, both traditional classroom and modern e-learning ones, to the present state of learner’s knowledge and abilities. Furthermore, Vygotskij’s educational model includes a strong bent towards social and collaborative learning. The joint answer to these two trends can be concretely implemented through a tight integration between personalized learning paths and collaborative learning activities. Along this line, the authors designed the combination of the functions of two pre-existing prototypes of web-based systems, to investigate how the above integration can merge adaptive and social e-learning. LECOMPS is a web-based e-learning environment for the automated construction of adaptive learning paths. SOCIALX is a web-based system for shared e-learning activities, which implements a reputation system to provide feedback to its participants. The authors propose a two-way tunneling strategy to integrate the above prototypes. The result is twofold: on the one hand the use of the student model supported by LECOMPS in an adaptive e-learning course is extended to support choosing exercise activities delivered through SOCIALX; on the other hand the reputation and the skills gained during social-collaborative activities are used to update the student model. Under the social perspective induced by the integration, the authors present a mapping between the student model and the definition of Vygotskij’s Autonomous Problem Solving and Proximal Development regions, with the aim to provide the learner with better guidance, especially in the selection of available social learning activities.

Two-Way Tunneling Model of Oxide Trap Charging and Discharging in SiC MOSFETs

A two-way tunneling model describing simultaneous oxide trap charging and discharging in SiC MOSFETs is presented, along with a comparison with experimental results. This model can successfully account for the variation in threshold-voltage instability observed as a function of bias-stress time, bias-stress magnitude, and measurement time.

On information process in living matter time and the 4th dimension: exposé of a hypothesis

The hypothesis concerns the nature of the biological information signal. It is envisaged as a unit existing in two different states — dipole and monopole according to its location in the three-dimensional space, respectively in the 4th dimension. The reversible transformation dipole-monopole which marks the crucial phase of the information process in living organisms outlines a two-way functioning tunnel in the space. According to the hypothesis this two-way tunnel in the space fixes the fundamental difference between living and non-living matter.