Durability of FRP Composite Bridge Deck Materials under Freeze-Thaw and Low Temperature Conditions

Fiber-reinforced polymer (FRP) composites, especially lightweight sandwich structures, are rapidly finding their way into civil infrastructure application. FRP composite panels are particularly attractive as bridge deck systems due to their high strength, low density, and durability, which are of importance to the bridge industry. Most of the vast amount of durability data for FRP has been generated for aerospace and automotive applications, which involve very different service conditions than civil infrastructure. For civil engineering applications, it is essential to examine the durability performance of FRP materials under weathering conditions. The ultimate goal of this research is to develop a reliable framework for durability assessment of FRP decks, including laboratory testing procedure and finite-element simulation capability. Such a framework should be applicable to all types of FRP deck construction. In this paper, specimens of typical FRP bridge deck skin materials are subjected to freeze-thaw cycling between 4.4 and ?17.8°C in media of dry air, distilled water, and saltwater, and constant freeze at ?17.8°C . The selected deck is used as an example for demonstration purposes. In addition, selected specimens are subjected to simultaneous environmental exposure conditions and sustained loading of 25% ultimate strain. It should be emphasized that most of the environmental conditions reported in the literature produce minor deterioration of a single composite property, and the assessment of such effect on this single property becomes unreliable because of a large property variation. Therefore, in this paper we use multiple mechanical properties as performance indices for damage evaluation. Based on findings from this work, it is concluded that freeze-thaw cycling between 4.4 and ?17.8°C alone and up to 1,250 h and 625 cycles caused very insignificant or no change in the flexural strength, storage modulus, and loss factor of the FRP specimens conditioned in dry air, distilled water, and saltwater. Small reductions in storage modulus (about 1% or less) were observed when specimens were prestrained and subjected to 250 freeze-thaw cycles in distilled water and saltwater. Changes in flexural strength were statistically insignificant, since they were within the data scatter.     

Recent advances in brain cholesterol dynamics: Transport, domains, and Alzheimer's disease

Major advances in understanding cholesterol dynamics and the role that cholesterol plays in vascular disease have recently been made. The brain is an organ that is highly enriched in cholesterol, but progress toward understanding brain cholesterol dynamics has been relatively limited. This review examines recent contributions to the understanding of brain cholesterol dynamics, focusing on extracellular and intracellular lipid carrier proteins, membrane cholesterol domains, and emerging evidence linking an association between cholesterol dynamics and Alzheimer's disease.     

Dispersion-free transient-grating frequency-resolved optical gating

We have developed a compact dispersion-free TG (transient-grating) FROG (frequency-resolved optical gating) by utilizing a mask that separates the input beam into three distinct beams focused into fused silica to create the FROG signal. Two of the beams are reflected off the same set of mirrors to ensure identical optical paths, eliminating the difficulty in establishing zero time delay between the beams. In addition, the use of only reflective optics avoids material dispersion in the FROG except for the mixing crystal. This TG FROG is capable of operating with an intensity of 1 x 10(11) W/cm(2) and has resolutions less than 0.5 and 1.3 fs for 25- and 10-fs input pulses, respectively.     

Visual quality and attentional capture: A challenge to the special role of abrupt onsets.

This article investigates the nature of stimulus-driven attentional capture. Previous studies (e.g., J. Jonides & S. Yantis, see record 1989-03735-001) have suggested that only a single visual feature—abrupt visual onset—can elicit stimulus-driven attentional capture. Two experiments are reported that challenge the special status of abrupt onsets in attentional capture. In particular, this evidence suggests that abrupt onsets appear to attenuate display-size effects only in certain experimental contexts that inadvertently increase the ease with which they are perceived. Consequently, the special status attributed to abrupt onsets is argued to derive from their higher visual quality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An investigation into the effects of forestry plantations on the water quality of upland reservoirs in northern ireland

A study was made of a wide range of Northern Ireland lakes to determine the effect of the fertilisation of forestry plantations. Lakes with fertilised forest catchments contained very high phosphorus levels. Bioassay with Selenastrum suggested that nitrogen and phosphorus were the only elements limiting growth and the supply of iron and trace metals was sufficient for large crops in nearly all cases.     

Basic dyeability and acid content of high-conversion polyacrylonitrile

Previous data have shown that the basic dyeability of acrylic polymers increases at a given specific viscosity as the peroxydisulfate-to-bisulfite ratio, that is, the catalyst-toactivator (C/A) ratio, is increased. This study represents an effort to understand better the role of the initiator system on the basic dyeability, the acid group composition, and the chain composition of acrylic polymers by preparing model polymers with radioactive initiators. As the C/A ratio is increased, the molecular weight distribution broadens as measured by the M?_v/M?_n ratio, the latter obtained by osmometry. There is also a significant effect of both C/A ratio and molecular weight on the sulfate group content per molecule, but there is no effect of C/A ratio on the number of basic dye sites per molecule, the number of sulfonate groups per molecule, or the weak acid groups per molecule. These effects can be explained by invoking a chain transfer to activator reaction in addition to the usual method of chain termination by recombination. The basic dyeability is found to correlate with the number-average molecular weight and with the number of strong acid groups plus the nonchromophoric weak acid groups.     

Chiral discrimination of basic and hydrophobic molecules by chemical force spectroscopy

Chemical force spectroscopy (CFS) is becoming a powerful technique with which to measure intermolecular forces. The prime advantage over other techniques is the ability to map spatial distribution of ligands on the surface. We have used CFS to explore the binding force of a variety of different chiral molecules in order to understand more about the nature of what is a fundamental aspect of chemical biology and of central importance in pharmacology.     

Atom pair persistence in disordered materials from fluctuation microscopy

We show that the kinematical theory of fluctuation microscopy for a disordered specimen can be reformulated in terms of an atom pair-pair correlation function. Resolution and coherence are two experimental variables which yield a two-dimensional fluctuation map. This map is a transformation of the pair-pair correlation function, but can be directly interpreted in terms of a pair persistence function (PPF). We show that the PPF reveals the correlation length and structure for a simple paracrystalline model.