A combined statistical approach and ground movement model for improving taxi time estimations at airports

With the expected continued increases in air transportation, the mitigation of the consequent delays and environmental effects is becoming more and more important, requiring increasingly sophisticated approaches for airside airport operations. Improved on-stand time predictions (for improved resource allocation at the stands) and take-off time predictions (for improved airport-airspace coordination) both require more accurate taxi time predictions, as do the increasingly sophisticated ground movement models which are being developed. Calibrating such models requires historic data showing how long aircraft will actually take to move around the airport, but recorded data usually includes significant delays due to contention between aircraft. This research was motivated by the need to both predict taxi times and to quantify and eliminate the effects of airport load from historic taxi time data, since delays and re-routing are usually explicitly considered in ground movement models. A prediction model is presented here that combines both airport layout and historic taxi time information within a multiple linear regression analysis, identifying the most relevant factors affecting the variability of taxi times for both arrivals and departures. The promising results for two different European hub airports are compared against previous results for US airports.     

Die Bestimmung von Kodein

Ohne Zusammenfassung     

Development, validation, and standardization of polymerase chain reaction-based detection of E. coli O157

A diagnostic polymerase chain reaction assay was developed for the detection of E. coli O157 as the first part of a multicenter validation and standardization project. The assay is based on amplification of sequences of the rfbE O157 gene and includes an internal amplification control. The selectivity of the assay was evaluated against 155 strains, including 32 E. coli O157, 38 E. coli non-O157, and 85 non-E. coli. It was shown to be highly inclusive (100%) and exclusive (100%). The assay has a 100% detection probability of approximately 2 x 10(3) cells per reaction.     

Increased adhesion of Enterococcus faecalis strains with bimodal electrophoretic mobility distributions

Initial adhesion is a determinant in the development of microbial biofilms. It is influenced, amongst others, by the surface hydrophobicity and the electrostatic characteristics of the substratum and adhering organisms. Enterococcus faecalis strains, grown in pure cultures, generally display subpopulations with different electrokinetic features, reflected in a bimodal electrophoretic mobility distribution. Here, the initial adhesion kinetics of five heterogeneous and five homogeneous E. faecalis strains were followed in a parallel-plate flow chamber. After 4h of flow, heterogeneous strains adhered in significantly higher numbers than homogeneous strains (7.3 x 10(6) and 1.9 x 10(6)cm(-2), respectively), but the initial deposition rates were not significantly influenced (740 and 600 cm(-2)s(-1), respectively). Apparently, initial deposition of bacteria is mainly governed by attractive Lifshitz-Van der Waals forces that overwhelm the electrostatic repulsion energy barrier, thus resulting in similar initial deposition rates for the various bacterial populations investigated. In contrast, during later stages of adhesion, bacteria in heterogeneous cultures likely experience a lower electrostatic repulsion from already adhering bacteria than bacteria in homogeneous cultures, thus allowing a closer proximity of the bacteria with respect to each other, which ultimately leads to increased adhesion after 4 h.     

Bioconversion of red ginseng saponins in the gastro-intestinal tract in vitro model studied by high-performance liquid chromatography–high resolution Fourier transform ion cyclotron resonance mass spectrometry

A high-performance liquid chromatography–high resolution Fourier transform ion cyclotron resonance mass spectrometry (HPLC–FTICR-MS) method was developed to investigate the metabolism of ginsenosides in in vitro models of the gastro-intestinal tract. The metabolites were identified by high-resolution tandem mass spectrometry. Degradation and bioconversion routes of the different ginsenosides at acidic (gastric) conditions and in the presence of intestinal microbiota were elaborated. Besides hydrolysis (deglycosylation) also hydration reactions occurred at acidic conditions. The results illustrate the value of metabolite profiling by HPLC–FTICR-MS for understanding of the mechanisms in bioavailability of herbal drugs and their metabolites.     

Synthesis of pH-activatable red fluorescent BODIPY dyes with distinct functionalities

A series of tunable pH-dependent BODIPY dyes were synthesized and further functionalized in a Knoevenagel condensation reaction with various aldehydes. In this fashion, monofunctional dyes containing an alkyne, azide, or carboxylic acid (masked as its methyl ester) as ligation sites as well as asymmetrical bifunctional dyes were obtained, without compromising their pH-dependency. In addition, fluorescence excitation and emission maxima for these dyes were shown to be significantly red-shifted in comparison to their tetramethyl precursors.