Limited sensitivity analysis of ARAIM availability for LPV-200 over Australia using real data

Current availability of Advanced Receiver Autonomous Integrity Monitoring (ARAIM) for LPV-200 in aviation is experimentally investigated using real navigation data and GPS measurements collected at 60 stations across Australia. ARAIM algorithm and fault probabilities were first discussed. Availability sensitivity analysis due to changes in the elevation mask angle and the error model parameters URA, URE, and nominal biases for integrity and accuracy used for computation of the protection level is presented. It is shown that incorporation of other GNSS constellation with GPS in ARAIM is needed to achieve LPV-200 Australia wide. The inclusion of BeiDou with GPS at two tests sites in Western and Eastern Australia demonstrates the promising potential of achieving this goal

Performance evaluation of different troposphere delay models and mapping functions

Tropospheric delay is a major error source in positioning by Global Navigation Satellite Systems (GNSSs). System users often apply one of the available troposphere models without giving sufficient background on their performance. In this study, the performance of different known hydrostatic and wet troposphere delay models and mapping functions are internally and externally compared and analysed at selected sites around the globe. International GNSS Service (IGS) products were used as a reference. The best performing models are presented. Results showed that small discrepancies are present between different models. All models perform significantly better at the mid-latitudes than at the Equator

Maintaining real-time precise point positioning during outages of orbit and clock corrections

The precise point positioning (PPP) is a popular positioning technique that is dependent on the use of precise orbits and clock corrections. One serious problem for real-time PPP applications such as natural hazard early warning systems and hydrographic surveying is when a sudden communication break takes place resulting in a discontinuity in receiving these orbit and clock corrections for a period that may extend from a few minutes to hours. A method is presented to maintain real-time PPP with 3D accuracy less than a decimeter when such a break takes place. We focus on the open-access International GNSS Service (IGS) real-time service (RTS) products and propose predicting the precise orbit and clock corrections as time series. For a short corrections outage of a few minutes, we predict the IGS-RTS orbits using a high-order polynomial, and for longer outages up to 3 h, the most recent IGS ultra-rapid orbits are used. The IGS-RTS clock corrections are predicted using a second-order polynomial and sinusoidal terms. The model parameters are estimated sequentially using a sliding time window such that they are available when needed. The prediction model of the clock correction is built based on the analysis of their properties, including their temporal behavior and stability. Evaluation of the proposed method in static and kinematic testing shows that positioning precision of less than 10 cm can be maintained for up to 2 h after the break. When PPP re-initialization is needed during the break, the solution convergence time increases; however, positioning precision remains less than a decimeter after convergence

Investigating the ability of high-rate GNSS-PPP for determining the vibration modes of engineering structures: small scale model experiment

This study evaluates the performance of the Precise Point Positioning method using Global Navigation Satellite System measurements (GNSS-PPP) for monitoring vibration modes of shear type buildings excited by harmonic ground motions and hammer tests. For experimental testing, the shear type lumped-mass building system is represented by a specially designed metal frame model, resembling a three story building, which was excited on a small scale shaking table. The excitation protocols applied were harmonic motions with different frequencies and amplitudes. The metal model has special deformation plates at the column tips to prevent the nonlinear rotations and out-of-plane motions for the entire system. The fundamental vibration periods of the model structure were computed by a Finite Element Mathematical (FEM) model, which were compared with the position variations determined by GNSS-PPP. Two GNSS receivers were mounted on top of the model structure on the line perpendicular to the motion axis to measure the rotation motion. The GNSS data comprised dual-frequency observations with a 10 Hz sampling rate. GNSS-derived positioning was obtained by processing the data using a post-mission kinematic PPP method with fixed phase ambiguities. Analysis of the characteristics of the vibration frequencies showed that the high-rate GNSS PPP method can capture the frequencies of first motion mode of shear type structural response when compared with the FEM output. Results demonstrate the efficiency of the high-rate GNSS PPP method in monitoring first motion mode of a natural frequency

Quorum sensing inhibitory activity of sub-inhibitory concentrations of β-lactams

Introduction: The virulence factors of Pseudomonas aeruginosa are under the control of quorum sensing (QS) signals. Hence, interference with QS prevents its pathogenesis.Objective: The aim of the present research is to assess the influence of some β-lactam antibiotics on cell communication and the release of different virulence factors.Methods: The minimal inhibitory concentrations of ceftazidime, cefepime and imipenem were evaluated by microbroth dilution method. The effect of sub-inhibitory concentration of the tested antibiotics on QS signals was investigated using reporter strain assay. In addition, different virulence factors (elastase, protease, pyocyanin and hemolysin) were estimated in the presence of their sub-inhibitory concentrations.Results: Low concentrations of ceftazidime, cefepime and imipenem caused significant elimination of the QS signals 3OHC12- HSL and C4-HSL up to 1/20 MIC. Furthermore, low concentrations of the tested antimicrobials suppressed virulence factors elastase and hemolysin. Moreover, 1/20 of their MICs reduced elastase, protease, pyocyanin and hemolysin.Conclusion: Utilization of β-lactam antibiotics at low concentrations could be an effective approach for prevention and treatment of P. aeruginosa infection.Keywords: Quorum sensing inhibition, β-lactams, Pseudomonas aeruginos

Crustal deformation across and beyond Central Europe and its impact on the boundaries

Land is a critical and limited natural resource. The Land Administration System (LAS) has been developed to resolve and adjudicate over any disputes that might arise concerning the rights and boundaries of land. Land registration and cadastre are types of land recording that need to be established. To secure the property rights, we must be sure of accuracy of the boundary points determining the size of the property. However, in addition to typical factors considered when determining the boundary point positions, such as accuracy of geodetic networks and measurement errors, the global and local crustal deformation, resulting, e.g., from the movement of tectonic plates, should be considered. In this work, the focus is on the movement of points inside the European plate due to tectonic movement, without taking into account local events caused by erosion, landslides, etc. The study area is Europe, and particular attention was paid to Poland, which is located in the centre of the European continent and does not have significant anomalous sub-areas, making it an authoritative research object. In this study, we analysed the velocity of point displacements and the boundary deformation, using GPS observations. For this reason, we used both global (IGS) and regional (ETRF) reference frames, to show differences in point velocities for the studied areas. Overall, for the needs of the real estate cadastre in Poland, information about parcel boundary points must be obtained with an accuracy better than 0.30 m. Within 25 years, the border mark may be shifted by 0.13 m due to tectonic plate movement, which is within the required accuracy. Pursuant to the current legal regulations, the measurements of the boundary points can be performed with any method, ensuring the required accuracy (0.30 m). The most commonly used are direct measurements (GNSS and tacheometry) and photogrammetric measurements. It is recommended that periodic verifications and update of the cadastre data in Poland be carried out at least once every 15 years. In the case of such relatively frequent verification and possible modernisation of data, the potential impact of tectonic plate movement on the relative boundary point displacement can be ignored, particularly in the short term. However, for a long time period it has an influence. We suggest “relatively frequent” cadastral boundary verification to be able to ignore such influence

Brain Natriuretic Peptide is a Predictor of Cardiac Thrombus in Critically Ill Acute Ischemic Stroke Patients

CONTEXT: Plasma brain natriuretic peptide (BNP) levels are elevated in patients with acute ischemic stroke, particularly when accompanied by atrial fibrillation (AF). Plasma BNP might be a useful marker of vulnerability to thromboembolism in non-valvular AF patients. AIM: The aim of the present study was to assess whether the BNP level can serve as a biomarker of the left atrial (LA) thrombus in AF patients with acute ischemic stroke. SETTINGS AND DESIGN: This was a multicenter prospective cohort study. PATIENTS AND METHODS: Thirty AF patients with acute ischemic stroke were included in the study. Their transesophageal echocardiography (TEE) and BNP were assessed. RESULTS: There was a positive significant relation between serum BNP levels and LA thrombus detection by TEE. BNP with a cutoff value >498 pg/l can be used as a diagnostic biomarker for the presence of the LA thrombus. A significant positive correlation existed between serum BNP and LA diameter. Furthermore, a statistically significant positive correlation between serum BNP and AF rate and duration was found in all patients. In addition, a statistically significant inverse correlation was detected between serum BNP and direct bilirubin, international normalized ratio, and albumin. A statistically significant positive correlation existed between serum BNP and prothrombin concentration. CONCLUSION: BNP can be a good diagnostic biomarker for the detection of the LA thrombus in chronic AF patients with acute ischemic stroke