2,003 research outputs found
External quality assessment of urinary methylmalonic acid quantification - results of a pilot study
This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work noncommercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http:// creativecommons.org/licenses/by-nc/3.0
An on-line solid phase extraction procedure for the routine quantification of urinary methylmalonic acid by liquid chromatography-tandem mass spectrometry
Background: The goal of this study was to develop and to validate an improved isotope-dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of methylmalonic acid (MMA) in urine. Methods: A previously described sample preparation protocol requires two solvent extraction steps, including evaporation. The first extraction is to extract the analyte from the sample, and second occurs following derivatization of the extract. In the method described here, the second evaporation step was substituted by on-line solid phase extraction employing column-switching and a permanent co-polymer based extraction cartridge. A standard validation protocol was applied to investigate the performance of the method. Results: The method was found to be linear in the clinically relevant range of concentrations (6-100 mu mol/L). Total coefficients of variation were below 10% and inaccuracy was <10% for quality control samples at three concentrations. Conclusions: By omitting one evaporation step, the semi-automated method described in this article enables for more convenient work-flow in the quantification of urinary MMA compared to the previous protocol. This is of relevance for MMA measurement in the routine clinical laboratory setting. Validation demonstrated acceptable analytical performance. Clin Chem Lab Med 2010;48:1647-50
The Complexity of the Simplex Method
The simplex method is a well-studied and widely-used pivoting method for
solving linear programs. When Dantzig originally formulated the simplex method,
he gave a natural pivot rule that pivots into the basis a variable with the
most violated reduced cost. In their seminal work, Klee and Minty showed that
this pivot rule takes exponential time in the worst case. We prove two main
results on the simplex method. Firstly, we show that it is PSPACE-complete to
find the solution that is computed by the simplex method using Dantzig's pivot
rule. Secondly, we prove that deciding whether Dantzig's rule ever chooses a
specific variable to enter the basis is PSPACE-complete. We use the known
connection between Markov decision processes (MDPs) and linear programming, and
an equivalence between Dantzig's pivot rule and a natural variant of policy
iteration for average-reward MDPs. We construct MDPs and show
PSPACE-completeness results for single-switch policy iteration, which in turn
imply our main results for the simplex method
Personalization framework for adaptive robotic feeding assistance
The final publication is available at link.springer.comThe deployment of robots at home must involve robots with pre-defined skills and the capability of
personalizing their behavior by non-expert users. A framework to tackle this personalization is presented and applied
to an automatic feeding task. The personalization involves the caregiver providing several examples of feeding using
Learning-by- Demostration, and a ProMP formalism to compute an overall trajectory and the variance along the path.
Experiments show the validity of the approach in generating different feeding motions to adapt to user’s preferences,
automatically extracting the relevant task parameters. The importance of the nature of the demonstrations is also
assessed, and two training strategies are compared. © Springer International Publishing AG 2016.Peer ReviewedPostprint (author's final draft
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