Calibration of Electret-Based Integral Radon Monitors Using NIST Polyethylene-Encapsulated 226Ra/222Rn Emanation (PERE) Standards

The recently developed ²²²Rn emanation standards that are based on polyethylene-encapsulated ²²⁶Ra solutions were employed for a first field-measurement application test to demonstrate their efficacy in calibrating passive integral radon monitors. The performance of the capsules was evaluated with respect to the calibration needs of electret ionization chambers (E-PERM^®, Rad Elec Inc.). The encapsulated standards emanate well-characterized and known quantities of ²²²Rn, and were used in two different-sized, relatively-small, accumulation vessels (about 3.6 L and 10 L) which also contained the deployed electret monitors under test. Calculated integral ²²²Rn activities from the capsules over various accumulation times were compared to the averaged electret responses. Evaluations were made with four encapsulated standards ranging in ²²⁶Ra activity from approximately 15 Bq to 540 Bq (with ²²²Rn emanation fractions of 0.888); over accumulation times from 1 d to 33 d; and with four different types of E-PERM detectors that were independently calibrated. The ratio of the electret chamber response E_Rn to the integral ²²²Rn activity I_Rn was constant (within statistical variations) over the variables of the specific capsule used, the accumulation volume, accumulation time, and detector type. The results clearly demonstrated the practicality and suitability of the encapsulated standards for providing a simple and readily-available calibration for those measurement applications. However, the mean ratio E_Rn/I_Rn was approximately 0.91, suggesting a possible systematic bias in the extant E-PERM calibrations. This 9 % systematic difference was verified by an independent test of the E-PERM calibration based on measurements with the NIST radon-in-water standard generator.     

High-efficiency generation of narrow bandwidth tunable VUV radiation

Frequency tunable VUV radiation has been generated using excimer lasers and very narrow bandwidth dye lasers by two-photon resonant difference frequency mixing in xenon. Conversion efficiencies of >0.1 percent have been achieved.     

Design of 2-hydroxyethyl methacrylate-functional macromonomer dispersants by semi-batch cobalt chain transfer polymerization

Acrylic resins for automotive coatings are produced in nonaqueous dispersions (NAD) of nanometer size. These must be sterically stabilized by oligomeric dispersants, which are complex reactive oligomers possessing vinyl and hydroxyl functionalities, controlling the size of the nanocolloid. Hence, we have developed a kinetic Monte Carlo (kMC) model to improve the molecular structure of 2-hydroxyethyl methacrylate-functionalized poly (butyl methacrylate) (pBMA) dispersants of ca. 6,000 g/mol produced via semi-batch cobalt chain transfer polymerization (CCTP). The kMC-predicted degree of functionalization is benchmarked against a novel analytic expression suitable for oligomers. Stepwise adjustment of the semi-batch feed program illustrates the successive improvement in molecular structure of the dispersant product, finally arriving at a functionalization degree close to the theoretical maximum for CCTP.     

Derivation of an aquatic predicted no-effect concentration for the synthetic hormone, 17 alpha-ethinyl estradiol

17alpha-Ethinyl estradiol (EE2) is a synthetic estrogen widely used in combination with other steroid hormones in oral contraceptives and in the contraceptive patch. EE2 has been detected in sewage treatment plant effluents in the low nanogram -per-liter range and occasionally in surface waters in the U.S., U.K., Canada, Brazil, Germany, and elsewhere. The mode of action is receptor-mediated, and estrogen receptors exist in mammals and other vertebrates. A large number of studies on the effects of EE2 on aquatic organisms exist. One hundred English language studies published between 1994 and 2007, one as yet unpublished study, and findings published in conference proceedings (in German) were compared to published data quality criteria to identify the most relevant studies for deriving a predicted no-effect concentration (PNEC). Reproduction in fish was identified as the most sensitive end point in aquatic species. A species sensitivity distribution was constructed using no observed effect concentrations (NOECs) for reproductive effects from 39 papers in 26 species, resulting in a median hazardous concentration at which 5% of the species tested are affected (HC5,50) of 0.35 ng/L. After comparing this HC5,50 to all of the laboratory and field-derived toxicity information available for EE2, we recommend using 0.35 ng/L as the PNEC for EE2 in surface water. This PNEC is below 95% of the existing NOECs for effects on reproduction and is also below virtually all of the NOECs for vitellogenin induction in the key fish reproduction studies.     

Coherent imaging with two-dimensional focal-plane arrays: design and applications

Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images.     

Contrast-modified gradient echo imaging using rotary echo preparatory pulses

The use of on-resonance binomial composite pulses in two- or three-dimensional magnetization-prepared gradient-recalled echo magnetic resonance imaging experiments generates rotary echoes, leading to an increase in contrast range that is, in part, determined by the ratio ofT ₂ toT ₁. In comparison with other fast gradient-recalled echo imaging techniques designed for enhancedT ₂ contrast, this method is more robust with respect to radiofrequency field inhomogeneity and less sensitive with respect to motion artifacts. Three-dimensional parametric images may be calculated using least-squares fitting based on a simple model for steady-state longitudinal magnetization during the imaging sequences.     

Plastic intensity factors for cracked plates

An elastic-plastic analysis is performed for two problems relevant to fracture mechanics: a semiinfinite body with an edge crack in a far out-of-plane shearing field and an infinite plate under plane stress conditions containing a finite line crack in a remote tensile field. Amplitudes of the dominant singularity in the plastic region at the crack tip, the plastic stress and strain intensity factors, are calculated for applied stress levels approaching the yield stress. A technique is developed for using the dominant singular solution in conjunction with the finite element method to make accurate calculations for the near-tip fields. Additionally, a comparative study of deformation theory with flow theory is performed for cracks in an anti-plane shear field. Elastic fracture mechanics is extended to high levels of applied stress for which the plastic zone is no longer small compared to the crack length by relating the critical stress for fracture initiation to the plastic intensity factors.     

Intercalation of epoxy resin in organically modified montmorillonite

Various methods of preparation of epoxy resin/clay mixtures, before the addition of the crosslinking agent and curing to form epoxy‐based polymer layered silicate (PLS) nanocomposites, have been investigated to determine their effect on the nanostructure. Organically modified montmorillonite clay was used, and the mixtures were prepared by both simple mixing and solvent‐based methods. X‐ray diffraction shows that intercalation of the resin into the clay galleries occurs for all clay loadings up to 25 wt % and for both preparation methods, but the dispersion of the clay in the resin, observed by optical microscopy, is significantly better for the solvent preparation method. Differential scanning calorimetry (DSC) shows that the intercalated resin has the same molecular mobility as the extra‐gallery resin, but suggests that the intercalated resin does not penetrate completely into the galleries. Prolonged storage of the resin/clay mixtures at room temperature leads to changes in the DSC response, as well as in the response to thermogravimetry, which are interpreted as resulting from homopolymerization of the epoxy resin, catalyzed by the onium ion in the modified clay. This confirms and explains the earlier observation of Benson Tolle and Anderson (J Appl Polym Sci 2004, 91, 89) that “conditioning” of the resin/clay mixtures at ambient temperature has a significant effect when the crosslinking agent is subsequently added, and indicates that the preparation method has important consequences for the nanostructure development in the PLS nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3751–3763, 2006     

Overview of disbonding technologies for adhesive bonded joints

ABSTRACT

The ability to separate adhesive bonded assemblies without causing damage to the substrates is clearly very desirable. There are many applications such as in electronics, medical surgery, dentistry, building and general manufacturing where the opportunity to separate assemblies is important. This may be for repositioning in manufacturing, repair in service or recovery of materials at end of life. Various methods for adhesive reversibility or disbonding have been proposed over the last 40 years but there currently exist no universally accepted solutions for disbond-on-demand bonded applications. This paper considers the motivation for disbonding, the requirements and considerations associated with possible methods, and the overall effectiveness of the various mechanisms in the context of non-structural, semi-structural and structural joints. The range of technologies and mechanisms is reviewed, together with the associated methods for activation. The variety of methods is evaluated for their effectiveness in the context of different applications. Particular attention is given to the adverse effects on the performance of bonded assemblies in service, and the ways of mitigating these effects. It is shown that a total materials system approach must be adopted when seeking a disbonding technology for a particular set of circumstances.