11 research outputs found
Imaging of high-Z material for nuclear contraband detection with a minimal prototype of a Muon Tomography station based on GEM detectors
Muon Tomography based on the measurement of multiple scattering of
atmospheric cosmic ray muons in matter is a promising technique for detecting
heavily shielded high-Z radioactive materials (U, Pu) in cargo or vehicles. The
technique uses the deflection of cosmic ray muons in matter to perform
tomographic imaging of high-Z material inside a probed volume. A Muon
Tomography Station (MTS) requires position-sensitive detectors with high
spatial resolution for optimal tracking of incoming and outgoing cosmic ray
muons. Micro Pattern Gaseous Detector (MPGD) technologies such as Gas Electron
Multiplier (GEM) detectors are excellent candidates for this application. We
have built and operated a minimal MTS prototype based on 30cm \times 30cm GEM
detectors for probing targets with various Z values inside the MTS volume. We
report the first successful detection and imaging of medium-Z and high-Z
targets of small volumes (~0.03 liters) using GEM-based Muon Tomography
Toxicity Testing in the 21st Century: Defining New Risk Assessment Approaches Based on Perturbation of Intracellular Toxicity Pathways
The approaches to quantitatively assessing the health risks of chemical exposure have not changed appreciably in the past 50 to 80 years, the focus remaining on high-dose studies that measure adverse outcomes in homogeneous animal populations. This expensive, low-throughput approach relies on conservative extrapolations to relate animal studies to much lower-dose human exposures and is of questionable relevance to predicting risks to humans at their typical low exposures. It makes little use of a mechanistic understanding of the mode of action by which chemicals perturb biological processes in human cells and tissues. An alternative vision, proposed by the U.S. National Research Council (NRC) report Toxicity Testing in the 21st Century: A Vision and a Strategy, called for moving away from traditional high-dose animal studies to an approach based on perturbation of cellular responses using well-designed in vitro assays. Central to this vision are (a) “toxicity pathways” (the innate cellular pathways that may be perturbed by chemicals) and (b) the determination of chemical concentration ranges where those perturbations are likely to be excessive, thereby leading to adverse health effects if present for a prolonged duration in an intact organism. In this paper we briefly review the original NRC report and responses to that report over the past 3 years, and discuss how the change in testing might be achieved in the U.S. and in the European Union (EU). EU initiatives in developing alternatives to animal testing of cosmetic ingredients have run very much in parallel with the NRC report. Moving from current practice to the NRC vision would require using prototype toxicity pathways to develop case studies showing the new vision in action. In this vein, we also discuss how the proposed strategy for toxicity testing might be applied to the toxicity pathways associated with DNA damage and repair
Gap junction assembly: roles for the formation plaque and regulation by the C-terminus of connexin43
Gap junction (GJ) “formation plaques” are distinct membrane domains with GJ precursors; they assemble by means of a series of defined steps. The C-terminus of Cx43 is required for normal progression of assembly, normal aggregation of 10-nm particles into small GJs, and negative regulation of assembly involving protein kinase C