The Exposome in Toxicologic Pathology

The “exposome” is an individual’s lifetime spectrum of chemical exposures beginning at conception. An exposome includes general external influences such as pollution and weather; external individual-specific factors (diet, infections, self-selected chemical intake); and internal individual-specific constituents (metabolic byproducts, microbiome derivatives, inflammatory mediators, stress hormones, etc). The exposome paradigm is inherent in animal toxicity testing because laboratory studies are designed so that subjects share a common exposure history encompassing not only exposure(s)/treatment(s) but also other chemical sources (eg, air, bedding, food, water). Toxicologic pathologists should remember that some differences in responsiveness to a test article may reflect subtle differences in individual exposomes of seemingly equivalent test animals. Translation of toxicity data obtained in tests of genetically inbred animals maintained under controlled environmental conditions to produce quasi-identical exposomes at best offers only approximate guidance regarding potential responses in genetically heterogeneous human populations who live in many environmental settings and thus have divergent, complex exposomes.

Effect of TiO2 Doping on Microdefects and Electrical Properties of ZnO-Based Varistors

Positron lifetime spectrum and electrical property measurements were performed on ZnO-based ceramics doped with different contents of TiO2. For ZnO-based ceramics with TiO2 content less than 1.8 mol%, the mean positron lifetime of the ZnO-based ceramic decreases with increasing in TiO2 content, and reaches a minimum value at 1.8 mol% TiO2. As the TiO2 content higher than 1.8 mol%, the mean positron lifetime increases with TiO2 content. The ZnO-based varistor with 1.8 mol% TiO2 exhibites an optimized varistor property; it has a relatively low leakage current IL, a relatively low breakdown voltage VB, and a relatively high nonlinear coefficient α. The effects of TiO2 doping on microdefects and electrical properties of ZnO-based varistors were discussed.

Sealed 22Na Sources for Positron Annihilation Lifetime Spectroscopy

Sealed radioactive sources of 22Na for positron annihilation lifetime spectroscopy (PALS), free from the legal regulations, are commercially available from an American company. However, thick foils are used to seal 22Na in these sources and large fractions of the positrons annihilate in the sealing materials. Further, it is pointed out that a long lifetime component over 1 ns appears in the positron lifetime spectrum acquired with the Kapton sealed source (POSK-22, IPL Inc.). In this research, attempts were made to develop high quality sealed positron sources, potentially free from regulations, for ubiquitous application of PALS. The sources prepared in the present work are of high quality and applicable to our new PALS, which does not require sample cutting and is potentially applicable to truly nondestructive, onsite inspection of various materials

Production and Applications of Intense Pulsed, Slow Positron Beams

Positron annihilation lifetime spectroscopy (PALS) is an experimental technique whereby the lifetime spectrum of positrons injected into a material is measured. Analysis of this spectrum can be used to characterize defects in the material. While radioisotope positron sources are often used for PALS, there are several advantages of using mono-energetic, slow positron beams. In order to measure lifetime spectra with such beams it is necessary to produce a pulsed beam with an extremely short pulse length (~ 200 ps). In this article we discuss the advantages of using pulsed, slow-positron beams, the various methods of beam production and pulsing methods. We focus in particular on intense beams generated by electron accelerators and describe the current status and future plans for the accelerator based facility at AIST.

The Effect of Impact Pressure on Positron Lifetime in Ultra High Molecular Weight Polyethylene (PE-UHMW)Chirulen®1120

The paper presents the results of investigations of the effect of impact pressure (in the range of both elastic and plastic deformations) on the parameters of the positron lifetime spectra in PE-UMHW polymer known under the trade mark Chirulen1120. The changes in the long-living component of the positron lifetime spectrum, connected with the annihilation of o-Ps in the pick-off process, are analyzed in dependence on the impact energy. The impact duration in the Charpy’s tests depending on the impact energy was measured, too. The dependencies of the radius of the volume of empty spaces in which the positronium annihilates, on the impact pressure were determined applying the Eldrup-Tao model.

Micromechanism of Plastic Deformation on Elastic Modulus

The key to enhance the precision of sheet metal stamping parts is accurate prediction and control of the springback. And one of the dominant factors of springback is the elastic modulus. The change of elastic modulus with plastic deformation was experimentally studied for the annealed LY12 and the annealed LF21 aluminum alloy respectively, and the changing role of elastic modulus with plastic deformation was obtained. By inverse pole figure from the X-ray diffraction analysis, the effects of the material original textures and their changing with plastic deformation on the elastic modulus were studied. And by positron annihilation lifetime spectrum , the influence of lattice distortion caused by crystal defect during plastic deformation on the elastic modulus was investigated. The micromechanism of the elastic modulus changing with plastic deformation for aluminum alloy is revealed, which lays a foundation for improving the stamping parts’ precision.