Transit times through hydrologic systems vary in time, but the nature of that variability is not well understood. Transit times variability was investigated in a 1 m3 sloping lysimeter, representing a simplified model of a hillslope receiving periodic rainfall events for 28 days. Tracer tests were conducted using an experimental protocol that allows time‐variable transit time distributions (TTDs) to be calculated from data. Observed TTDs varied with the storage state of the system, and the history of inflows and outflows. We propose that the observed time variability of the TTDs can be decomposed into two parts: “internal” variability associated with changes in the arrangement of, and partitioning between, flow pathways; and “external” variability driven by fluctuations in the flow rate along all flow pathways. These concepts can be defined quantitatively in terms of rank StorAge Selection (rSAS) functions, which is a theory describing lumped transport dynamics. Internal variability is associated with temporal variability in the rSAS function, while external is not. The rSAS function variability was characterized by an “inverse storage effect,” whereby younger water is released in greater proportion under wetter conditions than drier. We hypothesize that this effect is caused by the rapid mobilization of water in the unsaturated zone by the rising water table. Common approximations used to model transport dynamics that neglect internal variability were unable to reproduce the observed breakthrough curves accurately. This suggests that internal variability can play an important role in hydrologic transport dynamics, with implications for field data interpretation and modeling.

Serum samples from 317 patients with patients with severe acute respiratory syndrome (SARS) were tested for the nucleocapsid (N) protein of SARS-associated coronavirus, with sensitivities of 94% and 78% for the first 5 days and 6–10 days after onset, respectively. The specificity was 99.9%. N protein can be used as an early diagnostic maker for SARS.

Rapid diagnosis and serotyping of dengue virus (DV) infections are important for timely clinical management and epidemiological control in areas where multiple flaviviruses are endemic. However, the speed and accuracy of diagnosis must be balanced against test cost and availability, especially in developing countries. We developed a specific antigen capture enzyme-linked immunosorbent assay (ELISA) for early detection and serotyping of DV serotype 1 (DV1) by using well-characterized monoclonal antibodies (MAbs) specific to nonstructural protein 1 (NS1) of DV1. With this assay, a total of 462 serum specimens from clinically probable DV1-infected patients during the DV1 epidemic in Guangdong, China, in 2002 and 2003 were analyzed. DV1 NS1 was detectable in blood circulation from the first day up to day 18 after onset of symptoms, with a peak at days 6 to 10. The sensitivity of DV1 NS1 detection in serum specimens with reference to results from reverse transcriptase PCR was 82%, and the specificity was 98.9% with reference to 469 healthy blood donors. No cross-reactions with any of the other three DV serotypes or other closely related members of the genus Flavivirus (Japanese encephalitis virus and Yellow fever virus) were observed when tested with the clinical specimens or virus cultures. These findings suggest that the serotype-specific MAb-based NS1 antigen capture ELISA may be a valuable tool for early diagnosis and serotyping of DV infections, while also providing a standardized assay for the analysis of a great number of clinical samples with convenience and cost-effectiveness.

Sub-second liquid chromatography in very short packed beds is demonstrated as a broad proof of concept for chiral, achiral, and HILIC separations of biologically important molecules. Superficially porous particles (SPP, 2.7 μm) of different surface chemistries, namely, teicoplanin, cyclofructan, silica, and quinine, were packed in 0.5-cm-long columns for separating different classes of compounds. Several issues must be addressed to obtain the maximum performance of 0.5 cm columns with reduced plate heights of 2.6 to 3.0. Modified UHPLC hardware can be used to obtain sub-second separations provided extra-column dispersion is minimized and sufficient data acquisition rates are used. Further, hardware improvements will be needed to take full advantage of faster separations. The utility of power transform, which is already employed in certain chromatography detectors, is shown to be advantageous for sub-second chromatography. This approach could prove to be beneficial in fast screening and two-dimensional liquid chromatography.