A mechanistic model of GPS collar location data: Implications for analysis and bias mitigation

Global positioning system (GPS) collars have revolutionized the collection of animal location data; however, it is well-recognized that considerable bias can be present in these data due to habitat or behavior-induced obstruction of satellite signals resulting in inaccurate or missing locations. To date, no explicit theoretical framework of GPS fix acquisition specific to animal telemetry has been presented, and studies make differing assumptions regarding factors influencing GPS fix acquisition and how these data should be analyzed. Inappropriate statistical models have been used, interaction effects have been misunderstood, and the implementation of bias mitigation techniques has been problematic. Herein we outline current conceptual and analytical problems in the GPS animal telemetry literature, and subsequently present a theoretical model-based framework for GPS fix acquisition that clarifies the single and interactive effects of habitat and behavioral obstruction, fix interval, and collar model on GPS collar performance. By recognizing that GPS fix acquisition is a Bernoulli process, it becomes apparent that all forms of obstruction inherently interact with each other, making generalizations across study areas, study species, and collar models problematic. Stationary collar tests to determine the probability of fix acquisition (PFA), location accuracy, and the response to sources of obstruction are thus of limited applicability to animal-deployed collars. Bias mitigation techniques that extrapolate PFA models across samples, especially those using stationary collar tests to correct animal-deployed collars, are theoretically unsound. It is also demonstrated that nonlinearities in the relationships between sources of obstruction and PFA complicate PFA modeling with limited data and that even slight model misspecification can lead to considerable errors in correction factors, especially when using inverse weighting to mitigate bias. By emphasizing the importance of GPS collar sensitivity and ephemeris retention, the theoretical framework predicts that newer, more sensitive GPS collars will be less severely biased by sources of obstruction than reported for the older, less sensitive collars that have been used in the majority of GPS performance studies to date and we expect this trend to continue. This heuristic modeling exercise should be of value to researchers planning and analyzing studies using GPS collars and it also establishes a starting point for future theoretical investigations into GPS collar performance and bias mitigation.     

Terbuthylazine persistence in an organic amended soil

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N²-tert-butyl-6-chloro-N⁴-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha^{? 1}. Terbuthylazine was applied to both plots at a rate of 2 kg ha^{? 1} a.i. Triplicates from each plot were sampled at 3 depths (0–10, 10–20 and 20–30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.     

A conceptual cost estimate for remediation activities at a multisite federal facility

The Sandia National Laboratories Environmental Restoration Project is in the process of determining the nature and extent of environmental contamination at numerous potential release sites. Sites found to be contaminated above certain action levels must be remediated. Sandia is responsible for preparing preliminary cost estimates for remediation activities in order to meet Department of Energy planning requirements for future funding. Sandia used the ENVEST parametric cost-estimating model to prepare conceptual cost estimates for remediation prior to having definitive knowledge of the nature and extent of contamination. This article describes the estimating approach and the results achieved at Sandia.     

The use of passive sampling to monitor forest exposure to O3, NO2 and SO2: a review and some case studies

The use of passive sampler systems is reviewed and discussed. These devices are able to determine both spatial and temporal differences in canopy exposure, as is demonstrated by their use in extensive monitoring of air-pollution exposure in forest health plots. Categorising forest health monitoring plots according to air-pollution exposure permits cause-effect analysis of certain forest health responses. In addition, passive sampling may identify areas affected by interaction between different gaseous pollutants. Passive samplers at the stand level can be used to resolve vertical profiles of ozone within the stand, and edge effects, which are important in exposure of understorey and ground flora. Recent case studies using passive samplers to determine forest exposure to gaseous pollutants indicate a potential for the development of spatial models on regional-, landscape-, and stand-level scales and the verification of atmospheric transport models.     

A comparative study of prenatal ultrasound findings and post-mortem examination in a tertiary referral centre

This retrospective study compares the findings of prenatal ultrasound, performed in a tertiary fetal medicine centre, with the results of post-mortem examination in pregnancies complicated by suspected fetal abnormality that results in fetal loss. The study was carried out over a year at a teaching hospital, Fetal Medicine Centre and Regional Centre for Perinatal Pathology. Results were directly compared and the level of agreement between the ultrasound and post-mortem findings described. These were classified as having complete agreement; major agreement or major disagreement. The group of cases with major agreement between findings was further divided into those with significant, or minor, additional findings at post-mortem examination. Over the 12-month period, 153 ultrasound cases were identified, of which 47 were also examined by autopsy and were thus suitable for comparison in this study (30.7%). Complete agreement between ultrasound and post-mortem findings was found in 22 cases (46.8%). In 24 cases (51.1%), major agreement between ultrasound and post-mortem findings was seen. Of these, 11 had minor additional findings at post-mortem examination and 13 were found to have significant additional findings at post-mortem (27.7%), adding to the eventual diagnosis. In 12.8% of cases, post-mortem examination provided a definitive diagnosis. Only in one case was there complete discordance in the findings of the ultrasound examination and the autopsy (2.1%). No major disagreement between ultrasound and post-mortem findings was seen in 98% of cases. This study confirms the accuracy of prenatal ultrasound diagnosis in specialist centres, whilst emphasising the continuing importance of post-mortem examination in cases of fetal malformation to refine and, in some cases, define the diagnosis. Copyright © 2004 John Wiley & Sons, Ltd.     

A low cost instrument based on a solid state sensor for balloon-borne atmospheric O(3) profile sounding

The design of an instrument based on a solid state tungsten oxide sensor for making profile measurements of atmospheric ozone from balloon platforms is described. The sensor is operated at a constant temperature, typically 530 [degree]C. The importance of a detailed consideration of the electronic design is demonstrated, with particular reference to the circuit to control the sensor heater. Calibration methods which are straightforward to implement are illustrated, and the results of a test flight alongside an electrochemical ozonesonde are shown. Quantitative agreement within 25% for most of the profile demonstrates the potential of this type of sensor for ozone sounding. Future improvements from manufacture to analysis are expected to improve on this.     

Using gypsum to reduce phosphorus in runoff from subcatchments in South Australia

Concentrations of phosphorus (P) in runoff from agricultural catchments in southern Australia are high and well above national and international limits. Phosphorus was found to exit two subcatchments of 3.6 and 4.2 ha in the Adelaide hills via both overland flow and interflow. The subcatchments had texture-contrast soils with high inputs of superphosphate and were openly grazed by cattle all year. Interflow at the boundary of the B and C soil horizons accounted for as much as half the total water flow that was measured (overland flow, A-B interflow, and B-C interflow). The average flow-weighted concentration of total P within overland flow was as high as 0.25 mg L(-1), and 0.05 mg L(-1) in B-C interflow. In most years P loss was in the dissolved (<0.45 microm) form. In some years, interflow was the major pathway for P loss off these catchments. The B-C interflow cannot be discounted when searching for management options to reduce P loss from texture-contrast soils to waterways. Preliminary laboratory experiments showed promise that gypsum could modify agricultural soils and reduce the concentrations of P (and dissolved organic C) in runoff before it enters public water supply reservoirs. In this study, gypsum, applied at a rate of 15 Mg ha(-1) to the 4.2-ha subcatchment, substantially modified the soil chemistry, and thereby soil structure. The size and stability of structural aggregates increased markedly and this change affected not only the A but also the upper B horizons, to a profile depth of approximately 50 cm. However, the impact of these physicochemical changes on P concentrations in runoff was not marked. Average profile P concentrations were only slightly lower in the runoff from the subcatchment following treatment. The high subsoil macroporosity of the gypsum-treated subcatchment caused an increase in the proportion of runoff by interflow.     

Spontaneous cessation of umbilical blood flow in the acardiac fetus of a twin pregnancy

The acardiac fetus is a rare entity found only in monozygotic multiple pregnancy. Although the acardiac fetus is non-viable, the perinatal mortality rate for the normal fetus may be as high as 50 per cent, and is usually associated with fetal heart failure and hydrops fetalis, or as the result of prematurity. In this communication, we describe a case of spontaneous cessation of blood flow to an acardiac fetus and discuss the management of this condition with special reference to optimizing the outcome for the normal fetus.     

Rapid detection of aneuploidy in uncultured chorionic villus cells using fluorescence in situ hybridization

Rapid detection of aneuploidy using chromosome-specific repetitive DNA probes and the potential diagnostic accuracy of fluorescence in situ hybridization (FISH) on interphase cells of chorionic villus samples (CVS) are presented. Analyses demonstrated the ability to correctly identify aneuploidy using FISH in uncultured CVS. Our preliminary investigation suggests that this technique offers a significant clinical potential to circumvent problems of culture, time, and cost in cytogenetic analysis.