ABSTRACT. A performance evaluation was conducted on a differential mobility classi er that separates bers according to length using dielectrophoresis. The classi er had been constructed and used for several applications in previous studies. The performance of the classi er was predicted using a two-dimensional axisymmetric model of the ow eld and then calculating particle trajectories for a variety of conditions. Based on the ow calculations, several regions of the classi er were improved to reduce likelihood of turbulent losses. For a given total ow through the classi er and a maximum voltage across the electrodes, the performance of the classi er was found to depend on the ratios of the aerosol ow to the inner and the outer sheath ows. It was found that the minimum classi able length, the minimum length distribution width, and the throughput of classi ed bers can each be optimized, but not independently. Several approaches to testing the resolution of the classi er were tried. The rst was to measure the length distribution of bers passing through the classi er under different conditions using electron microscopy. However, this was a slow and imprecise measure of performance. Two approaches using monodisperse latex spheres were used; one operated the instrument as an electrical mobility (electrophoresis) analyzer and the other evaluated only the ow system accuracy. All measures indicate that the classi er operates close to theoretical performance, but improvements are still possible. Suggested improvements require redesign of the ow system and improved electrode alignment.
Researchers in the disciplines of both Operations and Accounting have studied Inventory Management, though in relative isolation. In this paper, one of our goals is to help inform researchers in Operations Management about an extensively debated question in inventory accounting: whether to repeal the LIFO (Last-In-First-Out) inventory accounting choice? This question has received extensive scrutiny from various stakeholders including academics, businesses, and different levels of governmental agencies such as US Congress. Specifically, we provide a literature review on how LIFO affects and is affected by inventory management. This is done by first reviewing the potential determinants of LIFO inventory accounting choice and then reviewing potential interactions between LIFO and inventory management. It is our hope that this review will help stakeholders have a more comprehensive understanding of LIFO before making their decisions.
The transfer function of TSI's widely used 3071 Differential Mobility Analyzer (DMA) widens drastically when the flow rate Q of sheath gas exceeds 30-40 lit/min, limiting its ability to resolve very small particles. This flow instability is unexpected at the prevailing relatively small Reynolds number (Re < 400). Here, we note that the rings holding the laminarization screens penetrate into the flow channel, generating unsteady vortices. A screen step exists not only on the outer screen region, but also on the inner screen region. Using a new step-free screen, no critical transition is observed up to the highest flow rate achieved of Q D 103 lit/min. The original DMA widens the flow cross-section in the mixing region where the aerosol joins the sheath gas. The flow deceleration then arising at small aerosol input flow rates introduces another source of transfer function broadening, which, however, has negative resolution effects only at Q > 60 lit/min. This feature is suppressed here by modifying a single inlet piece. Although the two flow improvements implemented increase the resolving power in the analysis of very small particles, a substantial nonideality of unclear origin remains: the best resolving power R found with electrosprayed ions of the protein Immunoglobulin is R D 13.9 for the trimer (IgG) 3 , and 12 for the monomer, even at a sheath/ aerosol flow ratio of 100.
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