A fuzzy multicriteria evaluation system for the assessment of tunnels vis-à-vis surface roads: the WPMA case—part II

The Fuzzy Multicriteria Evaluation System (FUMES) is applied on a real evaluation problem such as the Western Peripheral Motorway of Athens (WPMA). The lack of a formal development model of the study area suggested an evaluation strategy, which is characterized by the high uncertainty of the evaluation environment. This has resulted in using judgments when quantitative information on the performance of the tunnel or the surface road was not available. It also resulted in employing a relatively large number of alternative scenarios to deal with the different policy goals. The attempted impact analysis generated crisp and fuzzy scores for each competing alternative. The different scenarios under which the various alternatives were evaluated are of two types: socio-economic and policy scenarios. Subsequently, the criteria weights were computed using the Fuzzy Hierarchical Analysis and the different CBA and MCA methods were applied. Finally, the output of the evaluation determined that the surface road is the most ‘stable’ solution for all the ‘extrovert’ development scenarios, while the tunnel is more preferable for all the ‘introvert’ development scenarios.     

MPLS-VPN技术的探讨

随着Internet的发展,以及企业内部网络之间、不同企业网络之间信息交流的日益频繁,基于MPLS的VPN技术成为许多大型企业的首选方式。本文介绍了,VPN和MPLS的产生背景和技术优势,还涉及到隧道技术,MPLSVPN的技术实现以及现存的缺点,最后展望了MPLSVPN广阔的发展前景。     

IPv4向IPv6的过渡策略

IPv6是解决IPv4局限性和缺陷的关键技术,但IPv6不可能在一夜之间代替IPv4,IPv4和IPv6将会有一个很长的共存期。怎样使得IPv4向IPv6平稳的过度是目前积焦点。文章将对双栈机制、隧道机制、转换机制这三种策略进行分析。     

Contribution of electron tunneling transport in semiconductor gas sensor

It was found that thin film devices derived from SnO₂ sols by spin-coating method showed unique thermal behavior of electric resistance in air involving a temperature region where resistance was independent of temperature. The temperature independent resistance region extended up to 400 °C, replacing a region of temperature-conventionally dependent resistance, as film thickness increased. Such unique behavior of resistance was observed also for a brush-coated device but not for screen-coated thick film devices or disk-type device, suggesting that the absence of mechanical forces applied during device fabrication favored the occurrence of the unique behavior. It was shown that the unique behavior could be well accounted for by postulating a combination of electron tunneling transport and conventional migration transport. Calculation of tunneling probability based on a simple model allowed estimating that electron tunneling transport can take place between oxide grains with a probability of 0.01 or larger if a gap in between is narrower than 0.01 nm.     

Theory of dislocation tunneling through a pinning point

We have calculated the transition rate for a string unpinning from a point barrier, using a truncated parabolic potential. In this approximation, it was shown that the result for this N-dimensional system has the one-dimensional form R=ν_effexp (−ΔU/kT_eff), where ν_eff is an effective frequency, ΔU the barrier height, T_eff the effective temperature. There is a crossover temperature T* separating the high temperature classical behavior from the low temperature quantum rate and given by T*=ω_eff/2k. The effective temperature is given by the actual temperature above T*, while below it, is given by the ground state energy, calculated using the effective frequency. The important point is that if one knows the transition rate at high T, then the crossover temperature and the low T transition rate may be calculated. The effective frequency has been calculated for dislocations in the classical regime: ν_eff0.26 (U₀/Gb³) ν_D, where U₀ is the binding energy with a pinning atom, G the shear modulus, b the Burgers vector, and ν_D is the Debye frequency. The predicted crossover temperature of a few tenths Kelvin for an Al crystal is in good agreement with our recent experimental results.     

Gas breakdown limit and maximum acceleration gradient for inverse Cherenkov laser accelerator

Laser intensity thresholds for CO₂ laser-induced gas breakdown, such as tunneling, multiphoton, and cascade ionization have been estimated for the inverse Cherenkov accelerator experiment at the Brookhaven Accelerator Test Facility. The gas breakdown is dominated by cascade ionization and the maximum acceleration gradient is up to 300 MeV/m for a 3 ps CO₂ laser.     

Probabilistic assessment of tunnel construction performance based on data

A probabilistic model for estimating tunnel construction time is learnt with data from past tunnel projects. The model is based on the Dynamic Bayesian Network technique. The model inputs are determined through an analysis of data from three tunnels built by means of the conventional tunneling method. The data motivate the development of a novel probability distribution to describe the excavation performance. In addition, the probability of construction failure events and the delay caused by such failures are estimated using databases available in the literature. The model is applied to a case study, in which it is demonstrated how observations from the tunnel construction process can be included to continuously update the prediction of construction time.     

Reactions on Inverse Model Catalyst Surfaces: Atomic Views by STM

Planar “inverse catalyst” model systems, i.e. noble metal single crystal surfaces decorated by oxide nanostructures, have been used to visualise surface processes in the STM with atomic level precision. The processes chosen for their prototypical relevance in heterogeneous catalysis systems comprise the oxidation-reduction of surface oxide phases, the effects of the metal-oxide phase boundary in promoting the CO oxidation reaction and the O₂+H₂ water reaction, and the mass transport processes of oxide materials over metal surfaces via the diffusion of oxide clusters.     

Capacitance theory of open quantum systems with classical contacts

We consider semiconductor devices composed of a small quantum structure as the active device region and two classical environments constituting the source- and the drain contact. The contacts are taken as free electron gases with infinite conductivity defining the chemical potentials in the contacts. The transport through the quantum structure is described in the Landauer–Büttiker formalism using electronic scattering wave functions which determine the electron density in the quantum system. In our Hartree approximation these charges and the induced charges in the contacts are the sources of the self-consistent Coulomb field. As a particular quantum structure we study a GaAs heterostructure device consisting of a two-dimensional electron gas sandwiched between a gate contact and an AlGaAs blocking barrier [see V.T. Dolgopolov et al., Phys. Low-Dim. Struct. 6 (1996) 1]. We demonstrate the quantitative agreement of our theory with the experimental results.     

A method for assessing adhesion of clays to tunneling machines

Tunnel boring machines passing through cohesive soils sometimes experience significant clogging, leading to delays and increased costs. The paper describes a test to assess the likelihood of adhesion problems occurring, simulating the situation where a clay sticks to the cutting wheel of the machine. The results of tests using kaolin clay suggest that the adhesion changes with the compression force. Further studies are being undertaken to elucidate the factors which influence this, including clay mineralogy and roughness of the face of the cutting wheel. It is hoped that the work will lead to an industrial standard method of assessing adhesion which can be used in site investigation and on site.