Exploring a Multicriteria Approach to Production Scheduling

A current problem in production scheduling is related to the multi-criteria nature of the task. No matter how effective a heuristic or algorithm is, there remains a need to use human judgement to find a balance between an organization's conflicting objectives, such as meeting due-dates and minimizing work-in-progress. The problem is that heuristics do not have convenient input parameters that relate to these organizational objectives. In this paper we introduce the concept of a ‘control mechanism’ that would allow the scheduler to direct the search for a schedule on the basis of preferences with respect to multiple performance criteria. The feasibility of such a system is dependent on there being a predictable relationship between the input parameters of the scheduling heuristic and the performance measures. We describe a prototype Visual Interactive implementation of the proposed system, present the results of some initial experimental work, which indicates that the method has some potential, and comment on potentially fruitful areas for further research.     

Gas Flow Dynamics in Inlet Capillaries: Evidence for non Laminar Conditions

In this work, the characteristics of gas flow in inlet capillaries are examined. Such inlet capillaries are widely used as a first flow restriction stage in commercial atmospheric pressure ionization mass spectrometers. Contrary to the common assumption, we consider the gas flow in typical glass inlet capillaries with 0.5 to 0.6 mm inner diameters and lengths about 20 cm as transitional or turbulent. The measured volume flow of the choked turbulent gas stream in such capillaries is 0.8 L·min^?1 to 1.6 L·min^?1 under typical operation conditions, which is in good agreement to theoretically calculated values. Likewise, the change of the volume flow in dependence of the pressure difference along the capillary agrees well with a theoretical model for turbulent conditions as well as with exemplary measurements of the static pressure inside the capillary channel. However, the results for the volume flow of heated glass and metal inlet capillaries are neither in agreement with turbulent nor with laminar models. The velocity profile of the neutral gas in a quartz capillary with an inner diameter similar to commercial inlet capillaries was experimentally determined with spatially resolved ion transfer time measurements. The determined gas velocity profiles do not contradict the turbulent character of the flow. Finally, inducing disturbances of the gas flow by placing obstacles in the capillary channel is found to not change the flow characteristics significantly. In combination the findings suggest that laminar conditions inside inlet capillaries are not a valid primary explanation for the observed high ion transparency of inlet capillaries under common operation conditions.

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A counterexample to the maximality of toric varieties

We present a counterexample to the conjecture of Bihan, Franz, McCrory, and van Hamel concerning the maximality of toric varieties. There exists a six dimensional projective toric variety with the sum of the Betti numbers of strictly less than the sum of the Betti numbers of .

     

Determination of benzene in soft drinks and other beverages by isotope dilution headspace gas chromatography/mass spectrometry

An automated, simple, and reproducible method was developed for the determination of benzene in soft drinks, based on isotope dilution headspace gas chromatography/mass spectrometry in the selected-ion monitoring mode. The method was used to assess benzene levels in samples of 124 soft drinks and beverages. Benzene was not detected in 60% of the 124 products. The average benzene levels in 6 products exceeded the Canadian maximum acceptable concentration of 5 microg/L for benzene in drinking water, and 2 of the 6 products had benzene levels above the World Health Organization guideline of 10 microg/L. The highest level of benzene, 23 microg/L, was found in a soft drink product specifically marketed to children.     

Amyloid-like behavior in abiotic, amphiphilic foldamers

Previously, we reported an abiotic amphiphilic foldamer that, upon heating, undergoes an irreversible conformational change to a highly aggregated state (Nguyen, J.Q.; Iverson, B.L. J. Am. Chem. Soc. 1999, 121, 2639-2640.). Herein, we extend this work through the study of a series of structurally related amphiphilic foldamers and present a more refined model of their conformational switching behavior. Prior to heating, all foldamers of the series exhibited spectral characteristics consistent with folding in the pleated, stacked geometry characteristic of this class of foldamer. Following heating at 80 degrees C, three of the four molecules exhibited irreversible aggregation to produce hydrogels. The hydrogels were characterized by rheology measurements, and circular dichroism spectra revealed that hydrogel formation was dependent on highly ordered intermolecular assembly, conceptually analogous to protein amyloid formation. Hydrogel formation had the effect of amplifying the subtle structural differences between molecules, as the three amphiphilic foldamer constitutional isomers that formed hydrogels upon heating displayed significant differences in hydrogel properties. Taking a global view, our results indicate that amyloid-like behavior is not unique to proteins but may be a relatively general property of amphiphilic folding molecules in aqueous solution.     

Improved liquid chromatography-Online radioactivity detection for metabolite profiling

If very-high-pressure liquid chromatography (VHPLC) is to replace conventional HPLC as the ultimate separation tool for metabolism studies in development, coupling it efficiently with online radioactivity detection (RAD) is needed. We describe the successful combination of VHPLC/RAD, facilitated by improvements in online radioactivity detection, as well as in column loading and peak capacity. The sensitivity of (14)C detection was improved by the use of a variable scintillation flow achieved via a simple modification to the classical online radiochemical detection set-up. A modification of the flow-through cell design in which internal diameter of the tubing was reduced further increased the sensitivity and resolution by decreasing peak tailing. The injection of relatively large injection volumes was made possible by the use of columns packed at ultra-high pressure with 2.2 microm particles. Because of the reduced back pressure generated using these larger particle sizes, two 150 mm x 3 mm columns could be coupled, allowing 4-fold larger injection volumes and a 50% increase in theoretical plate number at a similar back pressure compared to a standard 150 mm x 2.1mm Waters UPLC column. The value of the methodology described was demonstrated by the analysis of in vitro and in vivo metabolism samples of (3)H- and (14)C-labeled compounds and compared with conventional radio-HPLC. We have shown that metabolite separation can be achieved with increased efficiency while maintaining a sensitivity comparable to that of conventional HPLC/RAD.     

Search for fractional-charge particles in meteoritic material

We have used an automated Millikan oil drop method to search for free fractional-charge particles in a sample containing in total 3.9 mg of pulverized Allende meteorite suspended in 259 mg of mineral oil. The average diameter of the drops was 26.5 microm with the charge on about 42 500 000 drops being measured. This search was motivated by the speculation that isolatable, fractional-charge particles produced in the early Universe and present in our Solar System are more likely to be accumulated in asteroids than on Earth's surface. No evidence for fractional-charge particles was found. With 95% confidence, the concentration of particles with fractional-charge more than 0.25 e (e being the magnitude of the electron charge) from the nearest integer charge is less than 1.3 x 10(-21) particles per nucleon in the meteoritic material and less than 1.9 x 10(-23) particles per nucleon in the mineral oil.