A Comparison of Hydrocarbon Vapor Attenuation in the Field with Predictions from Vapor Diffusion Models

This study used field data from three sites in Southern California to evaluate vapor phase transport from: (1) free product (die-sel and gasoline spill) on groundwater; (2) dissolved benzene (gasoline spill) in groundwater; and (3) hydrocarbon-impacted soil (gasoline spill) in the vadose zone. A sampling program to evaluate the vapor pathway included the following: vertical profile data, minimal purging prior to sample collection, field analysis of data, confirmation of field data using a fixed laboratory analysis, and soil physical property data. Comparison of hydrocarbon vapor concentrations measured in this field study with those calculated using vapor diffusion models suggest that an additional attenuation factor of between 500 and 35,000 is needed to account for observed concentrations. Comparison of hydrocarbon profiles with oxygen, carbon dioxide, and methane values is consistent with the interpretation that biodegradation is primarily responsible for the observed attenuation. Therefore, vapor pathway models that do not account for bioattenuation will result in a large overesti-mation of the risk at spill sites and will not be consistent with field data.     

Prediction of yield in the Rothamsted Park Grass Experiment by Ellenberg indicator values

Abstract. The Rothamsted Park Grass Experiment was established in 1856, with experimental plots subjected to annual applications of fertilizer and twice-yearly cutting of hay. There were two major responses to fertilizer, one reflecting high ammonium-nitrogen and increased acidity and the other reflecting high herbage yield without increased acidity. We calculated mean Ellenberg indicator values for N (nitrogen) and R (soil reaction) for the hay harvested between 1948 and 1975, using both unweighted and abundance-weighted means. Plot Ellenberg values were compared with herbage yield and with fertilizer application rates and published soil data. Annual yield of hay varied from 1.5 to 7.4 t/ha and was well predicted by the unweighted mean Ellenberg N-values (r = 0.91). Relatively large negative residuals from the relationship were found in plots whose soil combined low K and low pH. Soil pH was poorly predicted by the unweighted mean R-value, but showed a moderately good relation with weighted mean R (r = 0.73). The fact that Ellenberg N-values correlated better with yield than with applied nitrogen suggests that they might rather be called productivity values.     

Serial manipulator functional calibration for in vitro biomechanical testing

Serial manipulators are often used in biomechanical testing of human joints because they are precise, repeatable instruments that can create interesting loading scenarios. Unfortunately, commercial serial manipulators often do not have acceptable global positional accuracy due to manufacturing tolerances, assembly errors, and other mechanical imperfections. Numerous calibration methods have been reported which calibrate geometric and non-geometric parameters to reduce static position errors under constant loading conditions. However, the manipulator's global accuracy during continuous motion with time-varying external loading conditions is often not addressed but is necessary for joint biomechanical testing. Using the Mitsubishi PA10-6CE as a case study, a novel functional calibration procedure was developed that performs both static and dynamic calibration. The calibration uses optimization techniques to populate a 34-parameter model that accounts for the robot's geometric and non-geometric parameters and significantly reduces the mean/peak static and dynamic position errors to 0.368/0.67 mm and 0.353/0.81 mm, respectively, while externally loaded.     

Propagation of soft tissue artifacts to the center of rotation: A model for the correction of functional calibration techniques

This paper presents a mathematical model for the propagation of errors in body segment kinematics to the location of the center of rotation. Three functional calibration techniques, usually employed for the gleno-humeral joint, are studied: the methods based on the pivot of the instantaneous helical axis (PIHA) or the finite helical axis (PFHA), and the “symmetrical center of rotation estimation” (SCoRE). A procedure for correcting the effect of soft tissue artifacts is also proposed, based on the equations of those techniques and a model of the artifact, like the one that can be obtained by double calibration. An experiment with a mechanical analog was performed to validate the procedure and compare the performance of each technique. The raw error (between 57 and 68 mm) was reduced by a proportion of between 1:6 and less than 1:15, depending on the artifact model and the mathematical method. The best corrections were obtained by the SCoRE method. Some recommendations about the experimental setup for functional calibration techniques and the choice of a mathematical method are derived from theoretical considerations about the formulas and the results of the experiment.     

Evaluation of knee functional calibration with and without the effect of soft tissue artefact

Functional calibration methods were devised to improve repeatability and accuracy of the knee flexion–extension axis, which is used to define the medio-lateral axis of the femur coordinate system in gait analysis. Repeatability of functional calibration methods has been studied extensively in healthy individuals, but not accuracy in the absence of a benchmark knee axis. We captured bi-plane fluoroscopy data of the knee joint in 17 subjects with unilateral total knee arthroplasty during treadmill walking. The prosthesis provided a benchmark knee axis to evaluate the functional calibration methods. Stereo-photogrammetry data of thigh and shank marker clusters were captured simultaneously to investigate the effect of soft tissue artefact (STA). Three methods were tested, the Axis Transformation Technique (ATT) finds the best single fixed axis of rotation, 2DofKnee finds the axis that minimises knee varus–valgus and trajAJC finds the axis perpendicular to the trajectory, in the transverse plane of the femur, of a point located on the longitudinal axis of the tibia. Using fluoroscopy data, functional axes formed an angle of less than 2° in the transverse plane with the benchmark axis. True internal–external range of movement was correlated with decreased accuracy for ATT, while varus–valgus range of movement was correlated with decreased accuracy for 2DofKnee and trajAJC. STA had negative impact on accuracy and variability. Using stereo-photogrammetry data, the accuracy of 2DofKnee was 1.7°(SD: 5.1°), smaller than ATT 2.9°(SD: 5.1°) but not to trajAJC 1.7°(SD: 5.2°). Our results confirm that of previous studies, which utilised the femur condylar axis as reference.     

Stable isotope fractionation of strontium in coccolithophore calcite: Influence of temperature and carbonate chemistry

Marine calcifying eukaryotic phytoplankton (coccolithophores) is a major contributor to the pelagic production of CaCO₃ and plays an important role in the biogeochemical cycles of C, Ca and other divalent cations present in the crystal structure of calcite. The geochemical signature of coccolithophore calcite is used as palaeoproxy to reconstruct past environmental conditions and to understand the underlying physiological mechanisms (vital effects) and precipitation kinetics. Here, we present the stable Sr isotope fractionation between seawater and calcite (Δ^88/86Sr) of laboratory cultured coccolithophores in individual dependence of temperature and seawater carbonate chemistry. Coccolithophores were cultured within a temperature and a pCO₂ range from 10 to 25°C and from 175 to 1,240 μatm, respectively. Both environmental drivers induced a significant linear increase in coccolith stable Sr isotope fractionation. The temperature correlation at constant pCO₂ for Emiliania huxleyi and Coccolithus braarudii is expressed as Δ^88/86Sr = ?7.611 × 10^?3 T + 0.0061. The relation of Δ^88/86Sr to pCO₂ was tested in Emiliania huxleyi at 10 and 20°C and resulted in Δ^88/86Sr = ?5.394 × 10^?5 pCO₂ – 0.0920 and Δ^88/86Sr = ?5.742 × 10^?5 pCO₂ – 0.1351, respectively. No consistent relationship was found between coccolith Δ^88/86Sr and cellular physiology impeding a direct application of fossil coccolith Δ^88/86Sr as coccolithophore productivity proxy. An overall significant correlation was detected between the elemental distribution coefficient (D_Sr) and Δ^88/86Sr similar to inorganic calcite with a physiologically induced offset. Our observations indicate (i) that temperature and pCO₂ induce specific effects on coccolith Δ^88/86Sr values and (ii) that strontium elemental ratios and stable isotope fractionation are mainly controlled by precipitation kinetics when embedded into the crystal lattice and subject to vital effects during the transmembrane transport from seawater to the site of calcification. These results provide an important step to develop a coccolith Δ^88/86Sr palaeoproxy complementing the existing toolbox of palaeoceanography.     

The Geomagnetic Field Is a Compass Cue in Cataglyphis Ant Navigation

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