On the stress-optic law for orthotropic-model materials in biaxial-stress fields

The stress-optic law for othotropic-model materials, proposed by Sampson on the basis of a simple analogy to the isotropic-model materials, is examined for biaxial-stress fields. The stress-optic law is reduced to a simple form for special cases. It is also shown that the zero-order isochromatic fringe corresponds to an isotropic state of stress only in the case of balanced laminates. A glass-fiber-reinforced plastic disk with the glass fibers in only one direction is examined under diametral compression photoelastically and by means of strain-gage rosettes, with the loading direction perpendicular and at 45 deg to the reinforcement direction. The fringe order along the horizontal diameter is computed from the simplified stress-optic law making use of stress values from strain-gage readings and compared with the observed fringe order. Based on a fairly good agreement of the fringe orders, it is shown that a circular-disk specimen can be used to calibrate an orthotropic-model material. The three independent material-fringe values,f _L ,f _T ,f _LT , can be found from measurements of the fringe order and the strains at the center of the disk for the three cases of loading perpendicular, parallel and at 45 deg to the reinforcement direction.     

Application of carbon-powder-polymer composite as a continuous crack-length sensor

This paper explores the application of carbon-powder-impregnated polymeric composites for measuring crack extensions. The strain sensitivity of the gage material is shown to be very small. In the first series of tests, the gage material is characterized by measuring the change in electrical resistance due to machined slits for various gage lengths. The measured response is compared with the response predicted from a very simple electrical model. On the basis of good correlation and repeatability, the usefulness of such gages to measure crack extensions is assessed by a second series of tests. Further work to improve the gage response by optimizing the shape of the gage and making the gage and the adhesive layer thinner is proposed. The presented concept, with improvements, can result in a reliable, inexpensive crack gage requiring inexpensive instrumentation. Paper was presented at the 1990 SEM Spring Conference on Experimental Mechanics held in Albuquerque, NM on June 3–6.     

Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2-Reducing Photocatalytic Liposomes

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium-based CO₂-reduction catalysts [Re(4,4’-(C_nH_2n+1)₂-bpy)(CO)₃Cl] ( ReC_n ; 4,4’-(C_nH_2n+1)₂-bpy=4,4’-dialkyl-2,2’-bipyridine) and ruthenium-based photosensitisers [Ru(bpy)₂(4,4’-(C_nH_2n+1)₂-bpy)](PF₆)₂ ( RuC_n ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuC_n and ReC_n , hereafter noted C_n , to perform photocatalytic CO₂ reduction in the presence of sodium ascorbate. The photocatalytic performance of the C_n liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C₉ liposomes, compared to C₁₉ (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time-resolved spectroscopy, we identified the main reason for this trend: two types of membrane-bound RuC_n species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C₉ system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC₉ and ReC₉ .     

Progress in PET Imaging of Neuroinflammation Targeting COX-2 Enzyme

Neuroinflammation and cyclooxygenase-2 (COX-2) upregulation are associated with the pathogenesis of degenerative brain diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), epilepsy, and a response to traumatic brain injury (TBI) or stroke. COX-2 is also induced in acute pain, depression, schizophrenia, various cancers, arthritis and in acute allograft rejection. Positron emission tomography (PET) imaging allows for the direct measurement of in vivo COX-2 upregulation and thereby enables disease staging, therapy evaluation and aid quantifying target occupancy of novel nonsteroidal anti-inflammatory drugs or NSAIDs. Thus far, no clinically useful radioligand is established for monitoring COX-2 induction in brain diseases due to the delay in identifying qualified COX-2-selective inhibitors entering the brain. This review examines radiolabeled COX-2 inhibitors reported in the past decade and identifies the most promising radioligands for development as clinically useful PET radioligands. Among the radioligands reported so far, the three tracers that show potential for clinical translation are, [11CTMI], [11C]MC1 and [18F]MTP. These radioligands demonstrated BBB permeablity and in vivo binding to constitutive COX-2 in the brain or induced COX-2 during neuroinflammation.     

Response of composite plates to blast loading

The transient response of composite plates, with and without central circular holes, to blast loading is studied. The modal-analysis approach has been used in the computation of numerical results, which have been obtained for isotropic and orthotropic plates, with and without holes. In order to verify the theoretical results, experiments have been conducted on aluminum and unidirectionally reinforced E-glassepoxy plates, using a shock tube as the loading device. The experimental peak dynamic strains (normalized with respect to the pressure) are compared with the theoretical values. The strain-time history is also shown for a particular gage location in the composite plate. Finally, a comparison of dynamic-amplification factors, defined as the ratio of the peak dynamic strains to the static strains, has been made between the isotropic and the composite plates.     

Kinetics and mechanism of oxidation of excited state Tris-(2,2′-bipyridyl)-ruthenium (II) complex by peroxomonosulfate,peroxodisulfate, and peroxodiphosphate

Excitation of Ru(bipy)₃²⁺ ion by visible radiation of wavelength λ = 436 nm in aqueous medium in presence of inorganic peroxides, peroxomonosulfate (PMS), peroxodisulfate (PDS), and peroxodiphosphate (PDP) was found to generate Ru(bipy)₃³⁺. The kinetics of this photochemical oxidation of Ru(bipy)₃²⁺ by each peroxide was followed spectrophotometrically and found to obey a total second-order, first-order each in [Ru(bipy)₃²⁺] and [peroxide]. In the absence of light, thermal reaction of PMS and PDS with Ru(bipy)₃²⁺ occurred but only when at 1.0 M [H⁺] and > 10^?2M [peroxide]. The reaction of PMS with the complex is found to be cyclic, ie., Ru(bipy)₃³⁺ formed oxidizes PMS itself and such a reaction was not observed in the case of PDS and PDP. The effects of pH, [peroxide], and [Ru(bipy)₃²⁺] on the visible light induced oxidation of Ru(bipy)₃²⁺ by these peroxides are investigated. The results are discussed with suitable reaction mechanisms.     

Iron(II) complexes of 1-benzyl-2-phenylbenzimidazole and 2-coumarinylbenzimidazole

Summary Iron(II) complexes of 1-benzyl-2-phenylbenzimidazole (BPBI) and 2-coumarinylbenzimidazole (CBI) have been prepared and characterised. The chloride, bromide, iodide and thiocyanate complexes have the general formula FeL₂X₂ (where L = BPBI or CBI) while the perchlorate complex of CBI has the composition [Fe(CBI)₃](CIO₄)₂. The perchlorate complex behaves as a 1 : 2 electrolyte in nitrobenzene and methanol; Fe(BPBI)₂I₂ shows considerable dissociation in nitrobenzene while the other complexes behave as nonelectrolytes. The i.r. spectra of the complexes suggest that N(3) of BPBI and N(3) together with the CO group of CBI are the coordination sites. The magnetic and spectral evidence suggests a regular octahedral geometry for the perchlorate complex and pseudotetrahedral configuration for the iodide and thiocyanate complexes. The other complexes appear to be distorted octahedral with halide bridging.Author to whom all correspondence should be addressed.     

Compressive Properties of Pultruded Composites

The compressive properties of E-glass fiber/polyester resin matrix pultruded composites were measured using a short-block compression test fixture. Twenty specimens were tested in the pultrusion (longitudinal) direction and twenty more specimens in the transverse direction. Six specimens were tested at 30, 45, and 60° orientations to the pultrusion direction. Compressive properties such as the compressive modulus, compressive strength, Poisson ratio, and compressive failure strain were measured for both 6.3 and 12.7 mm thick pultruded sheet materials. The test specimens were rectangular with a length of 44.4 mm, width of 25.4 mm, and gage length of 25.4 mm. The test fixture was initially validated by measuring the axial strain distribution across the width of the specimen; from the beginning of loading up to the final failure, the distribution of strains across the specimen width was found to be very uniform. Back-to-back strain gages were also mounted on representative specimens. The end shortening was also measured on all specimens. The compressive strength data were analyzed both for the longitudinal and transverse directions using a two-parameter Weibull, lognormal, and normal distributions. The compressive properties are presented as functions of the specimen orientation angle for both thicknesses.     

Plasmonic Au-Metal Oxide Nanocomposites for High-Temperature and Harsh Environment Sensing Applications

Noble metal nanoparticles like Au have long been admired for their brilliant colour, significantly influenced by plasmon resonance. When embedded in metal oxides, they exhibit unique properties which make them an excellent choice for sensing in high-temperature and harsh environment atmospheres. In this review, the various morphologies of Au nanoparticles (AuNPs) used in combination with metal oxides for sensing gases at temperatures greater than 300 °C are discussed. Theoretical discussions on the plasmon resonance properties of AuNPs as well as computational techniques like finite difference time domain (FDTD), are often used for understanding and correlating their extinction spectra and are briefed initially. The sensing properties of AuNPs embedded on a metal oxide matrix (such as TiO₂, SiO₂, NiO etc) for quantifying multiple analytes are then elucidated. The effect of high temperature as well as gas environments including corrosive atmospheres on such nanocomposites, and the different approaches to comprehend them are presented. Finally, techniques and methods to improve on the challenges associated with the realization and integration such Au-metal oxide plasmonic nanostructures for applications such as combustion monitoring, fuel cells, and other applications are discussed.