[1] Pressure equilibrium between inside a soil CO 2 flux chamber and the surrounding air outside the chamber must be maintained during a measurement if measured soil CO 2 flux (F CO2 ) is to accurately represent the rate occurring naturally outside the chamber. In previous studies a simple vent tube connecting to the chamber has often been used to maintain pressure equilibrium. This approach, however, can be effective only under calm conditions. Under windy conditions, negative pressure excursions will occur inside the chamber that are artifacts resulting from wind passing over the vent tube's external open end, a phenomenon known as the Venturi effect. This causes anomalous mass flow of CO 2 -rich air from the soil into the chamber, leading to a significant overestimation of F CO2 . In this present study, we found that negative chamber pressure excursions due to the Venturi effect cannot be observed unless the differential pressure measurement is made with the chamber resting on an impermeable base. Making pressure measurements with a chamber resting on porous soil can lead to the erroneous conclusion that an anomalous mass flow is not a problem precisely when it is causing serious artifacts. We also present a new vent design for a soil CO 2 flux chamber capable of maintaining pressure equilibrium between inside the chamber and the ambient air outside the chamber under both calm and windy conditions. Differential pressure measurements from field experiments show that the pressures inside our newly designed vented chamber equal those outside the chamber when wind speed at a height of 0.5 m is up to 7 m s À1, thus virtually eliminating artifacts due to the Venturi effect. Our field data show that the problem of overestimation in measured F CO2 by a chamber with older vent designs under windy conditions can be avoided with our newly designed vented chamber.

Eddy covariance flux research has relied on open-or closed-path gas analyzers for producing estimates of net ecosystem exchange of carbon dioxide (CO 2 ) and water vapor (H 2 O). The two instruments have had different challenges that have led to development of an enclosed design that is intended to maximize strengths and minimize weaknesses of both traditional designs. Similar to the closed-path analyzer, the enclosed design leads to minimal data loss during precipitation events and icing, and it does not have surface heating issues. Similar to the open-path design, the enclosed design has good frequency response due to small flux attenuation loss in the short intake tube, does not need frequent calibration, has minimal maintenance requirements, and can be used in a very low power configuration. Another important feature of such a design is the ability to output instantaneous mixing ratio, or dry mole fraction, so that instantaneous thermal and pressure-related expansion and contraction, and water dilution of the sampled air have been accounted for. Thus, no density corrections should be required to compute fluxes during postprocessing. Calculations of CO 2 and H 2 O fluxes via instantaneous mixing ratio from the new enclosed CO 2 /H 2 O gas analyzer were tested in nine field experiments during 2009-2010 in a wide range of ecosystems and setups. Fluxes computed via a mixing ratio output from the instrument without applying density corrections were compared to those computed the traditional way using density corrections. The results suggest that with proper temperature, water vapor, and pressure measurements in the cell, gas fluxes can be computed confidently from raw covariance of mixing ratio and vertical wind speed, multiplied by a frequency response correction. This has important implications for future flux measurements, because avoiding hourly density corrections could have the advantages of increasing flux measurement quality and temporal resolution, reducing the magnitude of minimum detectable flux, unifying data processing steps, and assuring better intercomparison between different sites and networks.

A B S T R A C TThis study describes design and field performance of a new enclosed CO 2 /H 2 O gas analyser, LI-7200. Unlike present closed-path analysers, this new instrument is designed for operation with short intake tubes, with the intention to maximize strengths and to minimize weaknesses of both traditional open-path and closed-path approaches. The study provides description of the instrument, shows the principles of its operation, and explains advantages of a new design. Field results are provided from three field experiments with the prototypes, and cover such parameters as high frequency air temperature and pressure fluctuations inside the sampling cell versus ambient conditions, instantaneous concentrations and cospectra for CO 2

Western blotting is a commonly used protein assay that combines the selectivity of electrophoretic separation and immunoassay. The technique is limited by long time, manual operation with mediocre reproducibility, and large sample consumption, typically 10–20 μg per assay. Western blots are also usually used to measure only one protein per assay with an additional housekeeping protein for normalization. Measurement of multiple proteins is possible; however, it requires stripping membranes of antibody and then reprobing with a second antibody. Miniaturized alternatives to Western blot based on microfluidic or capillary electrophoresis have been developed that enable higher-throughput, automation, and greater mass sensitivity. In one approach, proteins are separated by electrophoresis on a microchip that is dragged along a polyvinylidene fluoride membrane so that as proteins exit the chip they are captured on the membrane for immunoassay. In this work, we improve this method to allow multiplexed protein detection. Multiple injections made from the same sample can be deposited in separate tracks so that each is probed with a different antibody. To further enhance multiplexing capability, the electrophoresis channel dimensions were optimized for resolution while keeping separation and blotting times to less than 8 min. Using a 15 μm deep × 50 μm wide × 8.6 cm long channel it is possible to achieve baseline resolution of proteins that differ by 5% in molecular weight, e.g. ERK1 (44 kDa) from ERK2 (42 kDa). This resolution allows similar proteins detected by cross-reactive antibodies in a single track. We demonstrate detection of 11 proteins from 9 injections from a single Jurkat cell lysate sample consisting of 400 ng total protein using this procedure. Thus, multiplexed Western blots are possible without cumbersome stripping and reprobing steps.

To further improve the speed and miniaturization of a complete Western blot, a microscale immunoassay with direct deposition of immunoassay reagents has been developed with the flow deposition of antibodies.