Geocenter coordinates estimated from GNSS data as viewed by perturbation theory

Time series of geocenter coordinates were determined with data of two global navigation satellite systems (GNSSs), namely the U.S. GPS (Global Positioning System) and the Russian GLONASS (Global’naya Nawigatsionnaya Sputnikowaya Sistema). The data was recorded in the years 2008–2011 by a global network of 92 permanently observing GPS/GLONASS receivers. Two types of daily solutions were generated independently for each GNSS, one including the estimation of geocenter coordinates and one without these parameters. A fair agreement for GPS and GLONASS was found in the geocenter x- and y-coordinate series. Our tests, however, clearly reveal artifacts in the z-component determined with the GLONASS data. Large periodic excursions in the GLONASS geocenter z-coordinates of about 40 cm peak-to-peak are related to the maximum elevation angles of the Sun above/below the orbital planes of the satellite system and thus have a period of about 4 months (third of a year). A detailed analysis revealed that the artifacts are almost uniquely governed by the differences of the estimates of direct solar radiation pressure (SRP) in the two solution series (with and without geocenter estimation). A simple formula is derived, describing the relation between the geocenter z-coordinate and the corresponding parameter of the SRP. The effect can be explained by first-order perturbation theory of celestial mechanics. The theory also predicts a heavy impact on the GNSS-derived geocenter if once-per-revolution SRP parameters are estimated in the direction of the satellite’s solar panel axis. Specific experiments using GPS observations revealed that this is indeed the case. Although the main focus of this article is on GNSS, the theory developed is applicable to all satellite observing techniques. We applied the theory to satellite laser ranging (SLR) solutions using LAGEOS. It turns out that the correlation between geocenter and SRP parameters is not a critical issue for the SLR solutions. The reasons are threefold: The direct SRP is about a factor of 30–40 smaller for typical geodetic SLR satellites than for GNSS satellites, allowing it in most cases to not solve for SRP parameters (ruling out the correlation between these parameters and the geocenter coordinates); the orbital arc length of 7 days (which is typically used in SLR analysis) contains more than 50 revolutions of the LAGEOS satellites as compared to about two revolutions of GNSS satellites for the daily arcs used in GNSS analysis; the orbit geometry is not as critical for LAGEOS as for GNSS satellites, because the elevation angle of the Sun w.r.t. the orbital plane is usually significantly changing over 7 days.

Relative estimate of accuracy in orbit determination from a short tracklet

The Astronomical Institute of the University of Bern (AIUB) is conducting several search campaigns for orbital debris. The debris objects are discovered during systematic survey observations. In general only a short observation arc, or tracklet, is available for most of these objects. From this discovery tracklet a first orbit determination is computed in order to be able to find the object again in subsequent follow-up observations. The additional observations are used in the orbit improvement process to obtain accurate orbits to be included in a catalogue. In this paper, the accuracy of the initial orbit determination is analyzed. This depends on a number of factors: tracklet length, number of observations, type of orbit, astrometric error, and observation geometry. The latter is characterized by both the position of the object along its orbit and the location of the observing station. Different positions involve different distances from the target object and a different observing angle with respect to its orbital plane and trajectory. The present analysis aims at optimizing the geometry of the discovery observation is depending on the considered orbit.

Estimation of satellite antenna phase center offsets for Galileo

Satellite antenna phase center offsets for the GalileoInOrbitValidation(IOV) and FullOperationalCapability (FOC) satellites are estimated by two different analysiscenters based on tracking data of a global GNSS network. The mean x- and y-offsets could be determined with a precision of a few centimeters. However, daily estimates of thex-offsets of the IOV satellites show pronounced systematic effects with a peak-to-peak amplitude of up to 70 cm that depend on the orbit model and the elevation of the Sun above the orbital plane. For the IOV y-offsets, no dependence on the orbit model exists but the scatter strongly depends on the elevation of the Sun above the orbital plane. In general, these systematic effects are significantly smaller for the FOC satellites. The z-offsets of the two analysis centers agree within the 10–15 cm level, and the time series do not show systematic effects. The application of an averaged Galileo satellite antenna model obtained from the two solutions results in a reduction of orbit day boundary discontinuities by up to one third—even if an independent software package is used.

Computer-assisted design and manufacture of implants in the late reconstruction of extensive orbital fractures

To evaluate the use of computer-assisted designed and manufactured (CAD/CAM) orbital wall and floor implants for late reconstruction of extensive orbital fractures.

Mandibula wing osteotomy for correction of the mandibular plane: A case report

We report a new technique for vertical enlargement of the inferior border of the mandible.

Chondrocyte function after osteochondral transfer: comparison of concave and plane punches

An incongruity between instrument and articular surfaces in osteochondral transfer (OCT) results in unevenly distributed impact forces exerted on the cartilage which may cause a loss of functional chondrocytes. We tested whether a plane instead of a concave design of the punch of an osteotome can reduce these cartilage damages.

Repair of orbital floor fractures using bioresorbable poly-L/DL-lactide plates

To assess the long-term clinical and radiologic findings after insertion of a bioresorbable polylactide plates P(L/DL)LA 70/30 implant (PolyMax) in the repair of orbital floor and wall defects, with special focus on stability and clinical signs of foreign-body reaction.

Coronal plane segmental flexibility in thoracic adolescent idiopathic scoliosis assessed by fulcrum-bending radiographs

Knowledge about segmental flexibility in adolescent idiopathic scoliosis is crucial for a better biomechanical understanding, particularly for the development of fusionless, growth-guiding techniques. Currently, there is lack of data in this field. The objective of this study was, therefore, to compute segmental flexibility indices (standing angle minus corrected angle/standing angle). We compared segmental disc angles in 76 preoperative sets of standing and fulcrum-bending radiographs of thoracic curves (paired, two-tailed t tests, p < 0.05). The mean standing Cobb angle was 59.7 degrees (range 41.3 degrees -95 degrees ) and the flexibility index of the curve was 48.6\% (range 16.6-78.8\%). The disc angles showed symmetric periapical distribution with significant decrease (all p values <0.0001) for every cephalad (+) and caudad (-) level change. The periapical levels +1 and -1 wedged at 8.3 degrees and 8.7 degrees (range 3.5 degrees -14.8 degrees ), respectively. All angles were significantly smaller on the-bending views (p values <0.0001). We noted mean periapical flexibility indices of 46\% (+1), 49\% (-1), 57\% (+2) and 81\% (-2), which were significantly less (p < 0.001) than for the group of remote levels 105\% (+3), 149\% (-3), 231\% (+4) and 300\% (-4). The discal and bony wedging was 60 and 40\%, respectively, and mean values 35 degrees and 24 degrees (p < 0.0001). Their relationship with the Cobb angle showed a moderate correlation (r = 0.56 and 0.45). Functional, radiographic analysis of idiopathic thoracic scoliosis revealed significant, homogenous segmental tethering confined to four periapical levels. Future research will aim at in vivo segmental measurements in three planes under defined load to provide in-depth data for novel therapeutic strategies.

Low-profile titanium mesh in the use of orbital reconstruction: A pilot study

The purpose of this study was to share our clinical experience in the use and accuracy of a newly designed, low-profile titanium mesh (Modus OPS 1.5; Medartis, Basel, Switzerland) for primary internal orbital reconstruction.

Collateral Damage-Penetrating Head Injury and Orbital Injury: A Case Report

We report a case of an accidental death or potential suicide by revolver with subsequent injury of another person. A 44-year-old man shot himself in the head while manipulating his.38 caliber special revolver in the kitchen in the presence of his wife, standing approximately 1.5 m next to him. After passing through the husband's head, the lead round-nose bullet entered the region underneath his wife's left eye. When the bullet left the man's head, it retained the energy to penetrate the soft tissue at this distance, including the skin and thin bone plates like the orbital wall. Owing to the low energy of the projectile, the entry wound was of atypical in shape and without loss of tissue. Only a small line-resembling a cut-was externally visible. The man died in the hospital from his injuries; his wife suffered visual loss of her left eye.

Combined bone and soft-tissue augmentation surgery in temporo-orbital contour reconstruction

Temporal hollowing due to temporal muscle atrophy after standard skull base surgery is common. Various techniques have been previously described to correct the disfiguring defect. Most often reconstruction is performed using freehand molded polymethylmethacrylate cement. This method and material are insufficient in terms of aesthetic results and implant characteristics. We herein propose reconstruction of such defects with a polyetheretherketone (PEEK)-based patient-specific implant (PSI) including soft-tissue augmentation to preserve normal facial topography. We describe a patient who presented with a large temporo-orbital hemangioma that had been repaired with polymethylmethacrylate 25 years earlier. Because of a toxic skin atrophy fistula, followed by infection and meningitis, this initial implant had to be removed. The large, disfiguring temporo-orbital defect was reconstructed with a PEEK-based PSI. The lateral orbital wall and the temporal muscle atrophy were augmented with computer-aided design and surface modeling techniques. The operative procedure to implant and adopt the reconstructed PEEK-based PSI was simple, and an excellent cosmetic outcome was achieved. The postoperative clinical course was uneventful over a 5-year follow-up period. Polyetheretherketone-based combined bony and soft contour remodeling is a feasible and effective method for cranioplasty including combined bone and soft-tissue reconstruction of temporo-orbital defects. Manual reconstruction of this cosmetically delicate area carries an exceptional risk of disfiguring results. Augmentation surgery in this anatomic location needs accurate PSIs to achieve satisfactory cosmetic results. The cosmetic outcome achieved in this case is superior compared with previously reported techniques.