An efficient method is presented to determine precision and accuracy of multichannel liquid-handling systems under conditions near to application. The method consists of gravimetrical determination of accuracy and optical determination of precision based on the dilution of absorbing and fluorescent dye solutions in microplates. Mean delivery volume per well can be determined with precision better than a 0.04% coefficient of variation (CV). Optical signal precision, CV(S), is improved by multiwavelength measurements. Precision of absorbance measurement yields a better resolution than precision of fluorescence measurement (0.3% and 1.5%, respectively), indicating that absorbance measurements should be preferred. From CV(S), an upper bound of the precision of the volumes delivered is derived. Method performance is demonstrated with the dispenser CyBi™-Drop and the pipettor CyBi™-Well using different ejection principles; with commonly used fluids; with 96-, 384-, and 1536-well microplates; and with photometric and fluorometric indicators. Precision of the volumes delivered, as obtained with optimized methods, all plate formats, and both devices, is better than 2% CV with 2 µL set volume and about 1% CV with higher set volumes. (Journal of Biomolecular Screening 2004:726-733)

The onset of surface fluidization of granular material in a vertically vibrated container, z = A cos (ωt), is studied experimentally. Recently, for a column of spheres it has been theoretically found (see T. Pöschel, T. Schwager, C. Salueña, Phys. Rev. E 62, 1361 (2000)) that the particles lose contact if a certain condition for the acceleration amplitudez ≡ Aω 2 /g = f (ω) holds. This result is in disagreement with other findings where the criterionz =zcrit = const was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not a proper criterion for fluidization and compare the results with theory.

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