507 research outputs found

    Site-Directed Spin-Labeling Analysis of Reconstituted Mscl in the Closed State

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    The mechanosensitive channel from Escherichia coli (Eco-MscL) responds to membrane lateral tension by opening a large, water-filled pore that serves as an osmotic safety valve. In an attempt to understand the structural dynamics of MscL in the closed state and under physiological conditions, we have performed a systematic site-directed spin labeling study of this channel reconstituted in a membrane bilayer. Structural information was derived from an analysis of probe mobility, residue accessibility to O2 or NiEdda and overall intersubunit proximity. For the majority of the residues studied, mobility and accessibility data showed a remarkable agreement with the Mycobacterium tuberculosis crystal structure, clearly identifying residues facing the large water-filled vestibule at the extracellular face of the molecule, the narrowest point along the permeation pathway (residues 21ā€“26 of Eco-MscL), and the lipid-exposed residues in the peripheral transmembrane segments (TM2). Overall, the present dataset demonstrates that the transmembrane regions of the MscL crystal structure (obtained in detergent and at low pH) are, in general, an accurate representation of its structure in a membrane bilayer under physiological conditions. However, significant differences between the EPR data and the crystal structure were found toward the COOH-terminal end of TM2

    Far-Term Exploration of Advanced Single-Aisle Subsonic Transport Aircraft Concepts

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    Far-term single-aisle class aircraft concepts for potential entry-into-service of 2045 were investigated using an Interactive Reconfigurable Matrix of Alternatives (IRMA) approach. The configurations identified through this design space exploration were then distilled into three advanced aircraft concepts best characterizing the prominent features identified through the IRMA exploration. These three aircraft concepts were then configured and sized for a 150-passenger capacity and a 3,500 nautical mile design mission. Mission block fuel burn was estimated and compared to a far-term conventional configuration baseline concept and a 2005 l. These comparisons suggest considerable potential improvements in fuel efficiency from the investigated advanced concepts

    Monitoring the process mean when standards are unknown : a classic problem revisited

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    One of the most common applications in statistical process monitoring is the use of control charts to monitor a process mean. In practice, this is often done with a Shewhart X chart along with a Shewhart R (or an S) chart. Thus two charts are typically used together, as a scheme, each using the 3-sigma limits. Moreover, the process mean and standard deviation are often unknown and need to be estimated before monitoring can begin. We show that there are three major issues with this monitoring scheme described in most textbooks. The first issue is not accounting for the effects of parameter estimation, which is known to degrade chart performance. The second issue is the implicit assumption that the charting statistics are both normally distributed and, accordingly, using the 3-sigma limits. The third issue is multiple testing, since two charts are used, in this scheme, at the same time. We illustrate the deleterious effects of these issues on the in-control properties of the (X,R) charting scheme and present a method for finding the correct charting constants taking proper account of these issues. Tables of the new charting constants are provided for some commonly used nominal in-control average run-length (ICARL0) values and different sample sizes. This will aid in implementing the (X,R) charting scheme correctly in practice. Examples are given along with a summary and some conclusions.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1099-16382017-03-31hb2016Statistic
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