Atmospheric effects and spurious signals in GPS analyses

Improvements in the analyses of Global Positioning System (GPS) observations yield resolvable millimeter to submillimeter differences in coordinate estimates, thus providing sufficient resolution to distinguish subtle differences in analysis methodologies. Here we investigate the effects on site coordinates of using different approaches to modeling atmospheric loading deformation (ATML) and handling of tropospheric delays. The rigorous approach of using the time-varying Vienna Mapping Function 1 yields solutions with lower noise at a range of frequencies compared with solutions generated using empirical mapping functions. This is particularly evident when ATML is accounted for. Some improvement also arises from using improved a priori zenith hydrostatic delays (ZHD), with the combined effect being site-specific. Importantly, inadequacies in both mapping functions and a priori ZHDs not only introduce time-correlated noise but significant periodic terms at solar annual and semiannual periods. We find no significant difference between solutions where nontidal ATML is applied at the observation level rather than as a daily averaged value, but failing to model diurnal and semidiurnal tidal ATML at the observation level can introduce anomalous propagated signals with periods that closely match the GPS draconitic annual (351.4 days) and semiannual period (175.7 days). Exacerbated by not fixing ambiguities, these signals are evident in both stacked and single-site power spectra, with each tide contributing roughly equally to the dominant semiannual peak. The amplitude of the propagated signal reaches a maximum of 0.8 mm with a clear latitudinal dependence that is not correlated directly with locations of maximum tidal amplitude

An assessment of theICE6G_C(VM5a)glacial isostatic adjustment model

The recent release of the next-generation global ice history model, ICE6G_C(VM5a), is likely to be of interest to a wide range of disciplines including oceanography (sea level studies), space gravity (mass balance studies), glaciology, and, of course, geodynamics (Earth rheology studies). In this paper we make an assessment of some aspects of the ICE6G_C(VM5a) model and show that the published present-day radial uplift rates are too high along the eastern side of the Antarctic Peninsula (by ∼8.6 mm/yr) and beneath the Ross Ice Shelf (by ∼5 mm/yr). Furthermore, the published spherical harmonic coefficients—which are meant to represent the dimensionless present-day changes due to glacial isostatic adjustment (GIA)—contain excessive power for degree ≥90, do not agree with physical expectations and do not represent accurately the ICE6G_C(VM5a) model. We show that the excessive power in the high-degree terms produces erroneous uplift rates when the empirical relationship of Purcell et al. (2011) is applied, but when correct Stokes coefficients are used, the empirical relationship produces excellent agreement with the fully rigorous computation of the radial velocity field, subject to the caveats first noted by Purcell et al. (2011). Using the Australian National University (ANU) groups CALSEA software package, we recompute the present-day GIA signal for the ice thickness history and Earth rheology used by Peltier et al. (2015) and provide dimensionless Stokes coefficients that can be used to correct satellite altimetry observations for GIA over oceans and by the space gravity community to separate GIA and present-day mass balance change signals. We denote the new data sets as ICE6G_ANU

A New Facility to Enhance Australian GPS-geodetic Research

The Australian Research Council recently awarded a grant to a consortium of five Australian universities to purchase ten geodetic-quality GPS receivers and peripherals. This cooperative approach will enhance new and existing GPS-geodetic research opportunities for Australian academic geodesists. These research projects include the monitoring of deformation of man-made structures and natural features, global and regional plate tectonics, measurement of sea-level change, mapping of Antarctic ice sheets and their flow, sounding of the Earth's atmosphere, and experiments in kinematic and rapid-static GPS-geodesy

Intranasal immunisation with Outer Membrane Vesicles (OMV) protects against airway colonisation and systemic infection with Acinetobacter baumannii.

OBJECTIVES: The multi-drug resistant bacteria Acinetobacter baumannii is a major cause of hospital associated infection; a vaccine could significantly reduce this burden. The aim was to develop a clinically relevant model of A. baumannii respiratory tract infection and to test the impact of different immunisation routes on protective immunity provided by an outer membrane vesicle (OMV) vaccine. METHODS: BALB/c mice were intranasally challenged with isolates of oxa23-positive global clone GC2 A. baumannii from the lungs of patients with ventilator associated pneumonia. Mice were immunised with OMVs by the intramuscular, subcutaneous or intranasal routes; protection was determined by measuring local and systemic bacterial load. RESULTS: Infection with A. baumannii clinical isolates led to a more disseminated infection than the prototype A. baumannii strain ATCC17978; with bacteria detectable in upper and lower airways and the spleen. Intramuscular immunisation induced an antibody response but did not protect against bacterial infection. However, intranasal immunisation significantly reduced airway colonisation and prevented systemic bacterial dissemination. CONCLUSION: Use of clinically relevant isolates of A. baumannii provides stringent model for vaccine development. Intranasal immunisation with OMVs was an effective route for providing protection, demonstrating that local immunity is important in preventing A. baumannii infection

Antibodies to Chlamydia trachomatis in patients presenting with ectopic pregnancy at Groote Schuur hospital

Objectives. To detennine the prevalence of antibodies to Chlamydia trachomatis in women presenting with ectopic pregnancies to Groote Schuur Hospital.Methods. C. trachomatis antibody titres were measured using a modified micro-immunofluorescence test in women presenting with ectopic pregnancy. Control subjects were drawn from women with term pregnancies and an uneventful reproductive history.Results. Seventy-four patients and controls were studied. Demographic variables were controlled for at time of entry into the study. A significant association between the number of lifetime sexual partners and exposure to C. trachomatis was noted (P = 0.001). Patients with ectopic pregnancies had significantly higher antibody titres than control subjects (P = 0.001), and in both groups the prevalence of background antichlamydial antibody was high (ectopic pregnancies 59%, pregnant controls 32%).Conclusions. While the role of C. trachomatis infection in women who develop ectopic pregnancies needs to be explored further, it seems wise to treat them all with empirical antibiotics at the time of presentation