Improving particle collection efficiency of sampling wipes used for trace chemical detection.

Improvement of the particle collection efficiency of sampling wipes is desirable for optimizing the performance of many wipe-based chemical analysis techniques used for trace chemical screening applications. In this note, commercially available Teflon coated fiberglass and calendered Nomex sampling wipes were modified by mechanically scoring the wipe surface to produce topography that promoted enhanced and localized particle collection. Wipe surface modifications improved particle collection efficiency, relative to unmodified wipes, by factors of 3 to 13 depending on sampling conditions, wipe type, and surface sampled. Improvements were demonstrated for both model polystyrene latex microspheres and inkjet printed explosive particles. The modifications also concentrated particles into pre-defined locations on the wipe which can be engineered to ensure maximum overlap with the thermal desorber of a trace contraband detection system allowing for more effective analysis of collected trace residues.

Mechanisms influencing retrograde flow in the atrioventricular canal during early embryonic cardiogenesis.

Normal development of the heart is regulated, in part, by mechanical influences associated with blood flow during early stages of embryogenesis. Specifically, the potential for retrograde flow at the atrioventricular canal (AVC) is particularly important in valve development. However, the mechanisms causing this retrograde flow have received little attention. In this study, a numerical analysis was performed on images of the embryonic zebrafish heart between 48 and 55hpf. During these stages, normal retrograde flow is prevalent. To manipulate this flow, zebrafish were placed in a centrifuge and subjected to a hypergravity environment to alter the cardiac preload at various six-hour intervals between 24 and 48hpf. Parameters of the pumping mechanics were then analyzed through a spatiotemporal analysis of processed image sequences. We find that the loss of retrograde flow in experimentally manipulated embryos occurs in part because of a greater resistance in the form of atrial and AVC contractile closure. Additionally, during retrograde flow, these embryos exhibit significantly greater pressure difference across the AVC based on calculations of expansive and contractile rates of the atrium and ventricle. These results elucidated that the developing heart is highly sensitive to small changes in pumping mechanics as it strives to maintain normal hemodynamic conditions necessary for later cardiac development.