The first geocenter estimation results using GPS measurements

The center of mass of the Earth is the natural and unambiguous origin of a geocentric satellite dynamical system. A geocentric reference frame assumes that the origin of its coordinate axes is at the geocenter, in which all relevant observations and results can be referred and in which geodynamic theories or models for the dynamic behavior of Earth can be formulated. In practice, however, a kinematically obtained terrestrial reference frame may assume an origin other than the geocenter. A fast and accurate method of determining origin offset from the geocenter is highly desirable. Global Positioning System (GPS) measurements, because of their abundance and broad distribution, provide a powerful tool to obtain this origin offset in a short period of time. Two effective strategies have been devised. Data from the first Central and South America (Casa Uno) global GPS experiment were studied to demonstrate the ability of recovering the geocenter location with present-day GPS satellites and receivers

Deriving a geocentric reference frame for satellite positioning and navigation

With the advent of Earth-orbiting geodetic satellites, nongeocentric datums or reference frames have become things of the past. Accurate geocentric three-dimensional positioning is now possible and is of great importance for various geodetic and oceanographic applications. While relative positioning accuracy of a few centimeters has become a reality using very long baseline interferometry (VLBI), the uncertainty in the offset of the adopted coordinate system origin from the geocenter is still believed to be on the order of 1 meter. Satellite laser ranging (SLR), however, is capable of determining this offset to better than 10 cm, but this is possible only after years of measurements. Global Positioning System (GPS) measurements provide a powerful tool for an accurate determination of this origin offset. Two strategies are discussed. The first strategy utilizes the precise relative positions that were predetermined by VLBI to fix the frame orientation and the absolute scaling, while the offset from the geocenter is determined from GPS measurements. Three different cases are presented under this strategy. The reference frame thus adopted will be consistent with the VLBI coordinate system. The second strategy establishes a reference frame by holding only the longitude of one of the tracking sites fixed. The absolute scaling is determined by the adopted gravitational constant (GM) of the Earth; and the latitude is inferred from the time signature of the Earth rotation in the GPS measurements. The coordinate system thus defined will be a geocentric Earth-fixed coordinate system

Application of GPS tracking techniques to orbit determination for TDRS

In this paper, we evaluate two fundamentally different approaches to TDRS orbit determination utilizing Global Positioning System (GPS) technology and GPS-related techniques. In the first, a GPS flight receiver is deployed on the TDRSS spacecraft. The TDRS ephemerides are determined using direct ranging to the GPS spacecraft, and no ground network is required. In the second approach, the TDRSS spacecraft broadcast a suitable beacon signal, permitting the simultaneous tracking of GPS and TDRSS satellites from a small ground network. Both strategies can be designed to meet future operational requirements for TDRS-2 orbit determination

An Economic Comparison between Grid Based and Isolated Rural Electrification in Nepal

This paper presents a methodology for financial analysis that compares costs and benefits of rural electrification by grid expansion with isolated micro hydro schemes. Financial analysis of three existing isolated micro hydro schemes in different parts of Nepal are compared against the alternative option of grid expansion. Case study results are tabulated and discussed

Synthesis of multifunctional nanocomposite material: tungstate-pillared Mg-Al hydrotalcite-like compound

Hydrotalcite-like compounds (HTLC) with different cationic ratios (Mg/AI) and charge-balancing inter layer anions were prepared and characterized. The surface areas of HTLCs were found to increase with increasing Mg/AI ratio. Pure HTLCs were obtained when the Mg/AI ratio was below 7. Water adsorption properties of HTLCs show that they are microporous. BET surface areas with water and nitrogen are dependent on the Mg/AI ratio of HTLC. Tungstate-pillared HTLC (synthesized from Mg/AI=7) was prepared and characterized, resulting in higher gallery height and surface area

Use of global positioning system measurements to determine geocentric coordinates and variations in Earth orientation

Geocentric tracking station coordinates and short-period Earth-orientation variations can be measured with Global Positioning System (GPS) measurements. Unless calibrated, geocentric coordinate errors and changes in Earth orientation can lead to significant deep-space tracking errors. Ground-based GPS estimates of daily and subdaily changes in Earth orientation presently show centimeter-level precision. Comparison between GPS-estimated Earth-rotation variations, which are the differences between Universal Time 1 and Universal Coordinated Time (UT1-UTC), and those calculated from ocean tide models suggests that observed subdaily variations in Earth rotation are dominated by oceanic tidal effects. Preliminary GPS estimates for the geocenter location (from a 3-week experiment) agree with independent satellite laser-ranging estimates to better than 10 cm. Covariance analysis predicts that temporal resolution of GPS estimates for Earth orientation and geocenter improves significantly when data collected from low Earth-orbiting satellites as well as from ground sites are combined. The low Earth GPS tracking data enhance the accuracy and resolution for measuring high-frequency global geodynamical signals over time scales of less than 1 day

Head injury at a tertiary referral centre in the Eastern Region of Nepal

Background: The purpose of this epidemiologic study was to determine the pattern and characteristics of head injuries and to establish an epidemiologic data bank for designing preventive strategies for head injuries in the eastern region of Nepal.Patients and Methods: This retrospective review was done at B.P.Koirala institute of Health Sciences, Dharan, Nepal. All the patients with head injury admitted to the Department of Surgery between the periods January 2005 to December 2005 were included in the study.Results: The study population consisted of 334 patients who sustained head injuries. Their ages ranged from 1 to 88 with a mean age of 28.53 years. The majority (66.3%), were young adults in the 2nd to 5th decades The male to female sex ratio was 2.6:1. Road traffic crushes were the most common cause (43.4%) followed by fall from heights (30.8%). X-ray of skull showed lesions in 114 cases (49.8%) such as depressed fracture (11.4%) and linear fracture (24.0%). Common lesions on CT scan included cerebral contusion (21.6%), extradural haematoma (20.9%), linear fracture (23.8%), subarachnoid haemorrhage (18.5%) and pnemocephalus (11.2%). Forty patients (12.0%) sustained moderate head injury. There were 15 deaths. One patient had associated intra-abdominal injury (splenic rupture) and two patient sustained pulmonary trauma and succumbed to haemothorax and aspiration.Conclusion: A clearer understanding of the patterns of head injuries will assist health care providers to plan and manage the treatment of traumatic facial injuries. Such epidemiological information can also be used to guide the future funding of public health programs geared toward prevention

Lower urinary tract symptoms and sexual functions after endorectal pull-through for Hirschsprung disease : controlled long-term outcomes

Background/purpose: To define the prevalence of lower urinary tract symptoms (LUTS) and outcomes for sexual function after endorectal pull-through (EPT) for Hirschsprung disease (HD) compared to controls. To date, similar controlled studies are lacking. Methods: Patients aged = 4 years (n= 123) operated on forHDat our center between 1987 and 2011were invited to answer questionnaires on LUTS and sexual function (aged = 16 years). Patients with an intellectual disability and patients with a definitive endostomy were excluded. Patients were matched to three controls and also invited to a clinical follow-up for urological investigations including urine flow measurement, renal tract ultrasound, and urinalysis. Results: Altogether, 59 responses concerning LUTS and 24 responses concerning sexual functions were analyzed. No significant differences were demonstrated in the overall prevalence of LUTS between patients (67%) and controls (80%), nor in the prevalence of frequent LUTS (14% vs. 16%; P = NS for both). One patient (2%) had a urethral stricture after laparotomy-assisted EPT. Male patients reported sexual satisfaction and erectile function similar to controls (P N 0.10). Female patients were currently less in stable relationships compared to controls (25% vs. 83%, P= 0.005). Conclusions: Our results support the safety of EPT in patientswith HDwith regard to preservation of the integrity and functioning of the genitourinary tract. (C) 2017 Elsevier Inc. All rights reserved.Peer reviewe