Blast resistance of FRP composites and polymer strengthened concrete and masonry structures – A state-of-the-art review

Recent world events such as bombings in London, Madrid and Istanbul have highlighted the susceptibility of many civilian structures to terrorist attack. Explosives directed towards vulnerable structures may cause considerable damage and loss of life. As a result, there is now a desire to increase the blast resistance of many types of existing structures. This has led to experimental and finite element (FE) research in retrofitting concrete and masonry structures with fibre reinforced polymer (FRP) composites for blast protection. This paper presents a review of the publicly available literature and highlights areas where research is lacking.     

A novel silicon Schottky diode for NLTL applications

The design and simulation of a novel silicon Schottky diode for nonlinear transmission line (NLTL) applications is discussed in this paper. The Schottky diode was fabricated on a novel silicon-on-silicide-on-insulator (SSOI) substrate for minimized series resistance. Ion implantation technology was used as a low-cost alternative to molecular beam epitaxy to approximate the delta (/spl delta/) doping profile, which results in strong nonlinear CV characteristics. The equivalent circuit model of the Schottky diode under reverse bias conditions was extracted from the S-parameter measurement performed on the diode. The measured CV characteristics show strong nonlinearity, the junction capacitance varies from 182 to 47.5 fF as the reverse bias voltage is varied from 0 to -5 V. A parasitic inductance of 40 pH was measured for the silicon Schottky diode, which is much smaller than a comparable sized GaAs Schottky diode. This small inductance is an advantage for the silicon Schottky diode offering improvement in the silicon NLTL performance.     

Sensor fault tolerant control using sliding mode observers

Previous work has considered the use of sliding mode observers for fault detection and isolation (FDI) in uncertain linear systems whereby the unknown faults are reconstructed by appropriate processing of the so-called equivalent output error injection. The paper builds on this work and considers such a scheme within the broader context of fault tolerant control. Specifically, by correcting the faulty measurement by an estimate of the fault obtained from the sliding mode FDI scheme, good closed-loop performance is still maintained. An example of such a scheme, which has been implemented in real-time on a laboratory dc motor rig, is described.     

Influence of curing at different relative humidities upon compound reactions and porosity in Portland cement paste

The reduction in relative humidity within drying concrete depends mainly on the depth from the exposed surface, exposure duration, temperature and environmental humidity; this limits hydration and coarsens pore structure, thus impairing durability. OPC paste, of 0.59 water/cement ratio, was cured for 2 days and then exposed to controlled relative humidity environments. After 14 and 90 days exposure, hydration of the individual compounds was measured using quantitative X-ray diffraction and thermogravimetry. Methanol adsorption was used to monitor porosity and gel formation. Even a small drop in relative humidity below 95% r.h. significantly limited cement hydration. Gel porosity increased with amount of hydration and, for a given level of hydration, decreased with drying. Curing below 80% r.h. produced a coarsened pore structure with a large-diameter porosity three times greater than that obtained with saturated curing.     

Effect of temperature and salt on the maturation of white-salted cheese

White-salted cheeses were prepared from ultrafiltered (UF) cows' milk and salted to give final salt-in-moisture (SM) levels of 2.5, 3.2 and 4.0%. The cheeses were stored at 5°C and 10°C for up to 15 weeks. The microflora was dominated by lactic acid bacteria (LAB) but some mould growth was evident within 15 weeks at all SM levels and both temperatures. Levels of water-soluble nitrogen (WSN), attributed to chymosin activity, increased significantly with time, the rate being inversely proportional to the SM level and increasing with storage temperature. Similar effects were noted for trichloroacetic acid-soluble nitrogen (TCA-SN) and free amino acid (FAA) levels, both of which would also be affected by bacterial protease activity. The proteolytic activity was reflected by changes in the hardness and fracturability of the cheeses.     

Desktop inkjet printer as a tool to print conducting polymers

In order to exploit mechanical flexibility of organic-based electronic devices, conducting polymer anodes, such as polyaniline or poly(3,4-ethylenedioxy)-thiophene-poly(styrene sulfonate) (PEDOT-PSS), have been extensively studied. Along with the use of solution based processing techniques, conducting polymers can simplify the device fabrication procedure and yield themselves easily to printing techniques. In this paper, we present the results of utilizing desktop inkjet printer as a tool for direct printing and patterning of conducting polymer. Design of printable patterns and adjustment of printing parameters can be performed using any software such as Power Point. PEDOT-PSS suspension can be loaded into an inkjet cartridge and deposited on a given substrate in any designed pattern. The gray-scale color scheme can be employed to control the layer thickness and sheet resistivity of the inkjet printed layers. These layers are then used as anodes in organic light-emitting devices (OLEDs).     

Optical analysis of crack tip stress fields: a comparative study

Four optical techniques for evaluating stress intensity factors in opaque specimens are described in outline, and compared for both an artificial crack and a fatigue crack. The results are compared to a standard solution for the geometry considered. All the techniques gave acceptable results over a range of stress levels and crack lengths. The methods of caustics and strain gauges were less good, whilst photoelasticity gave consistent results over a wide range of stress levels. Comments on the ease of application and the resource implications are also made in order to assist practitioners.     

Two methods for sensitivity analysis of coagulation processes in population balances by a Monte Carlo method

We consider two stochastic simulation algorithms for the calculation of parametric derivatives of solutions of a population balance equation, namely, forward and adjoint sensitivity methods. The dispersed system is approximated by an N-particle stochastic weighted ensemble. The infinitesimal deviations of the solution are accounted for through infinitesimal deviation of the statistical weights that are recalculated at each coagulation. In the forward method these deviations of the statistical weights immediately give parametric derivatives of the solution. In the second method the deviations of the statistical weights are used to calculate a finite-mode approximation of the linearized version of the population balance equation. The linearized equation allows for the calculation of the eigenmodes and eigenvalues of the process, while the parametric derivatives of the solution are given by a Lagrange formalism.     

Word-specific precoding of contention bursts for broadband wireless networks

A precoding technique for pre-equalising contention bursts in a slotted-ALOHA access request scheme, for use in single-carrier broadband fixed wireless access (FWA) networks is presented. Multipath channel distortion is compensated for at the transmitter, so that the contention burst arrives undistorted at the receiver.     

Current gasket standards development in Europe

There are a large number of standards concerned with gasketed joints in the UK that are derived from the applications and practice of different industries. Many other countries also have equivalent standards. John Hoyes, technical director of Flexitallic and chairman of the British Standards Committee concerned with gaskets describes the European initiatives to rationalize the standards and improve the technical basis by which they will lead a user to select the joint design and material.