Durability of concrete — Degradation phenomena involving detrimental chemical reactions

While interacting with its service environment, concrete often undergoes significant alterations that often have significant adverse consequences on its engineering properties. As a result, the durability of hydrated cement systems and their constituent phases has received significant attention from scientists and engineers. Cement paste deterioration by detrimental chemical reactions is discussed. First, the mechanisms that govern the transport of ions, moisture and gas are described. Then, different chemical degradation phenomena are reviewed. Microstructural alterations resulting from exposure to chlorides and carbon dioxide are discussed. Sulfate attack from external sources is described including processes resulting in the formation of ettringite and thaumasite. The mineralogy of Portland cement is sensitive to temperature and thermal cycling, particularly during the early hydration period.     

Control of nonlinear chained systems: from the Routh-Hurwitzstability criterion to time-varying exponential stabilizers

We show how any linear feedback that stabilizes the origin of a linear chain of integrators induces a simple, continuous time-varying feedback that exponentially stabilizes the origin of a nonlinear chained-form system. The design method is related to a method developed by M'Closkey and Murray (1997) to transform smooth feedback yielding slow polynomial convergence into continuous homogeneous ones that give exponential convergence     

MIQR Active Learning on a Continuous Function and a Discontinuous Function

Active learning balances the cost of data acquisition against its usefulness for training. We select only those data points which are the most informative about the system being modelled. The MIQR (Maximum Inter-Quartile Range) criterion is defined by computing the inter-quartile range of the outputs of an ensemble of networks, and finding the input parameter values for which this is maximal. This method ensures data selection is not unduly influenced by ‘outliers’, but is principally dependent upon the ‘mainstream’ state of the ensemble. MIQR is more effective and efficient than contending methods¹ . The algorithm automatically regulates the training threshold and the network architecture as necessary. We compare active learning methods by applying them to a continuous function and a discontinuous function. Training is more difficult for a discontinuous function than a continuous function, and the volume of data for active learning is substantially less than for passive learning.     

Progress of quantum electronics and the future of wireless technologies

Research in quantum electronics over several decades has fueled the creation and rapid growth of today's wireless communications market. Sales of electronic components into this market exceeded $25 billion in 2006. Nearly all cellular handsets sold today include integrated circuits (ICs) based on energy gap engineered transistors—high-electron mobility transistors (HEMTs) and heterojunction base transistors (HBTs). The success of these technologies notwithstanding, future wireless communications systems will require even more demanding IC performance, especially in the areas of linearity and low noise. We propose that a new concept in transistor design, wave-function engineering, offers un-tapped opportunities to realize these needed performance improvements.     

Usage-based comparison of ESI techniques

A comparative study of equivalent-step-index (ESI) techniques is performed on the basis of the ESI fiber's ability to predict the bend, transition, microbending and splice loss, waveguide dispersion, launching efficiency, and second-mode cutoff wavelength. Theoretical and experimental investigations were performed to determine the accuracy of the predictions. It was found that none of the present ESI techniques can be used to characterize all features of interest for a single-mode fiber with great accuracy. However, for the purpose of producing specifications on the behavior of single-mode fiber systems, it may be adequate to specify bounds on parameters such as bend loss within a factor of two.     

Simulated annealing-based fitting of CAD models to point clouds of mechanical parts’ assemblies

Engineering with Computers - This paper introduces a new fitting approach to allow an efficient part-by-part reconstruction or update of editable CAD models fitting the point cloud of a digitized...     

Safety Watchdog for universally safe gaseous high pressure hydrogen fillings

The fast filling time for hydrogen fuel cell vehicles makes them a user-friendly zero emission alternative to fossil fuel powered vehicles. The filling, by compressing gas into the vehicle tanks, produces heat that can be damaging. There are different protocols, standardized or the intellectual property of station operators, dedicated for different specific applications taking into account the specificity of the vessel and customer requirements. Standard protocols are developed for worst case conditions across a broad range of vehicle tank sizes and configurations. These worst case conditions do not result in the most economical equipment solution for hydrogen fueling. To ensure safety for different existing and future potential protocols a new “Safety Watchdog” approach is suggested in the current paper. This “Safety Watchdog” monitors the fueling process boundary conditions independently from the main process controls. The decoupling between the watchdog and the protocol allows use of protocols that are more economically beneficial while ensuring full safety conditions. The current paper provides a mathematical formulation of the Safety Watchdog as well as its validation versus modeling and field experimental data.