Probabilistic modeling of chloride-induced corrosion in concrete structures using first- and second-order reliability methods

Concrete structures are subjected to chloride-induced corrosion that can lead to shortened service life. Reliable predictions of life cycle performance of concrete structures are critical to the optimization of their life cycle design and maintenance to minimize their life cycle costs. This paper presents two simplified semi-analytical probabilistic models based on the first- and second-order reliability methods to model the uncertainty of the key parameters including surface chloride concentration, chloride threshold, cover depth and diffusion coefficient, which govern the chloride ingress into concrete and corrosion of reinforcing steel. A case study of a reinforced concrete highway bridge deck is used to illustrate the capability and efficiency of these simplified probabilistic models in modeling the uncertainty and predicting the time-dependent probability of corrosion. The models enable to quantify the impact of the different governing parameters on probability of corrosion and service life, which can be used to develop cost-effective management strategies.     

RF transceiver and transmission line behavioral modeling in VHDL-AMS for wired RFNoC

Despite the exceptional progress of MPSoC architectures, on chip communication networks remain a lock for the evolution of their performances due to the power consumption and the delay in data carrying. In this context, the wired radio frequency (RF) network on chip (RFNoC) has emerged. In this paper, we developed a library of RF component models in VHDL-AMS for time domain simulation. This library includes mainly the transmission line (TL) and the RF transceiver components such as the low noise amplifier (LNA), the mixer and the local oscillator (LO). The models consider the conventional parameters describing their performances including the non-linearities, the noise and the bandwidth of the LNA and the mixer. Leakages between ports are also considered for the mixer. The LO model considers the traditional parameters, more importantly its phase noise. The originality of the TL model is the modeling of the skin effect on a wide frequency range for time domain simulations. All the models are validated. Global simulations are performed to demonstrate the interest to accurately model the components of the RFNoC. The developed library is used here for wired RFNoC, however it can be used for all other wired and wireless RF communication system.     

Maximum Lifetime Target Coverage in Wireless Sensor Networks

Wireless Personal Communications - The challenge in the deployment of wireless sensor networks is to ensure the coverage of targets with high energy efficiency, particularly when coverage and...     

Minimization of wiring inductance in high power IGBT inverter

The wiring inductance is one of main causes limiting the use of the inverter in hard commutation mode, particularly when voltage, current and switching frequency are increased. The busbar technology is the means that allows one to reach low wiring inductance between DC source and power switches in spite of relatively long connections. This paper deals with studies of busbar structure applied to the high power inverters in order to improve their performances. Two structures of wiring are tested; the traditional one and busbar technology. Experimental and simulation results show that this last technique permits to obtain very low wiring inductance so that no snubber circuits are needed     

An Engineering Approach to Multicriteria Optimization of Bridge Structures

Abstract: This paper presents an approach to multicriteria optimization of engineering structures and structural systems based on the use of the constraint approach for generating efficient solutions and compromise programming for selecting the "best" or satisficing solution. The criteria of minimax and minimum Euclidian distance provide the designer with a rationale for the choice of the best solution. For system optimization problems, the definition of a dominant criterion and compromise programming lead to a practical approach to the design of large-scale structural systems. The approach is illustrated by two examples of optimizing prestressed concrete highway bridges, including selection of the optimal system.     

Absorption spectroscopy of individual single-walled carbon nanotubes

Current methods for producing single-walled carbon nanotubes (SWNTs) lead to heterogeneous samples containing mixtures of metallic and semiconducting species with a variety of lengths and defects. Optical detection at the single nanotube level should thus offer the possibility to examine these heterogeneities provided that both SWNT species are equally well detected. Here, we used photothermal heterodyne detection to record absorption images and spectra of individual SWNTs. Because this photothermal method relies only on light absorption, it readily detects metallic nanotubes as well as the emissive semiconducting species. The first and second optical transitions in individual semiconducting nanotubes have been probed. Comparison between the emission and absorption spectra of the lowest-lying optical transition reveal mainly small Stokes shifts. Side bands in the near-infrared absorption spectra are observed and assigned to exciton-phonon bound states. No such sidebands are detected around the lowest transition of metallic nanotubes.     

Sensitivity analysis of simplified diffusion-based corrosion initiation model of concrete structures exposed to chlorides

This paper presents the results of a sensitivity analysis of the diffusion-based corrosion initiation model for reinforced concrete structures built in chloride-laden environments. Analytical differentiation techniques are used to determine the sensitivity of the time to corrosion initiation to the four governing parameters of the model, which include chloride diffusivity in concrete, chloride threshold level of steel reinforcement, concrete cover depth, and surface chloride concentration. For conventional carbon steel, the time to corrosion initiation is found to be most sensitive to concrete cover depth, followed by chloride diffusion coefficient, with normalized sensitivity coefficients of about 2 and − 1. For corrosion resistant steels, the time to corrosion initiation is most sensitive to the surface chloride concentration and chloride threshold level followed by the concrete cover depth and chloride diffusion coefficient. The results of this sensitivity analysis are discussed in detail, including the variations in predicted time to corrosion initiation induced by variations of the four model parameters and their implications for the design and maintenance of concrete structures built in corrosive environments.