669 research outputs found
Studies of an orbital gradiometer mission
The goal of using an orbital gradiometer mission to provide an accurate (1 to 2 mgal), high resolution (1 by 1 deg), global map of the earth's geopotential is currently being investigated. This investigation involves the simulation of the satellite ephemeris and the corresponding gradiometer measurements which can be used in the study of various techniques and methodologies that were proposed to recover the parameters used in modeling the geopotential. Also, the effects on the mission of various time varying forces acting on the spacecraft were included in the studies
On the Lense-Thirring test with the Mars Global Surveyor in the gravitational field of Mars
I discuss some aspects of the recent test of frame-dragging performed by me
by exploiting the Root-Mean-Square (RMS) orbit overlap differences of the
out-of-plane component N of the orbit of the Mars Global Surveyor (MGS)
spacecraft in the gravitational field of Mars. A linear fit of the full time
series of the entire MGS data (4 February 1999-14 January 2005) yields a
normalized slope 1.03 +/- 0.41 (with 95% confidence bounds). Other linear fits
to different data sets confirm the agreement with general relativity. The huge
systematic effects induced by the mismodeling in the martian gravitational
field claimed by some authors are absent in the MGS out-of-plane record. The
non-gravitational forces affect at the same level of the gravitomagnetic one
the in-plane orbital components of MGS, not the out-of-plane one. Moreover,
they experience high-frequency variations which does not matter in the present
case in which secular effects are relevant.Comment: LaTex2e, 8 pages, no figures, no tables, 17 references. It refers to
K. Krogh, Class. Quantum Grav., 24, 5709-5715, 2007 based on
astro-ph/0701653. Final version to appear in CEJP (Central European Journal
of Physics
First results from the GPS atmosphere sounding experiment TOR aboard the TerraSAR-X satellite
GPS radio occultation events observed between 24 July and 17 November 2008 by the IGOR occultation receiver aboard the TerraSAR-X satellite are processed and analyzed. The comparison of 15 327 refractivity profiles with collocated ECMWF data yield a mean bias between zero and −0.30 % at altitudes between 5 and 30 km. Standard deviations decrease from about 1.4 % at 5 km to about 0.6 % at 10 km altitude, however, increase significantly in the upper stratosphere. At low latitudes mean biases and standard deviations are larger, in particular in the lower troposphere. The results are consistent with 15 159 refractivity observations collected during the same time period by the BlackJack receiver aboard GRACE-A and processed by GFZ's operational processing system. The main difference between the two occultation instruments is the implementation of open-loop signal tracking in the IGOR (TerraSAR-X) receiver which improves the tropospheric penetration depth in terms of ray height by about 2 km compared to the conventional closed-loop data acquired by BlackJack (GRACE-A)
A sustainable future for Chinese giant salamanders: Chinese giant salamander field survey manual. Technical report, Zoological Society of London.
On the possibility of measuring relativistic gravitational effects with a LAGEOS-LAGEOS II-OPTIS-mission
In this paper we wish to preliminary investigate if it would be possible to
use the orbital data from the proposed OPTIS mission together with those from
the existing geodetic passive SLR LAGEOS and LAGEOS II satellites in order to
perform precise measurements of some general relativistic
gravitoelectromagnetic effects, with particular emphasis on the Lense-Thirring
effect.Comment: Abridged version. 16 pages, no figures, 1 table. First results from
the GGM01C Earth gravity model. GRACE data include
Indication, from Pioneer 10/11, Galileo, and Ulysses Data, of an Apparent Anomalous, Weak, Long-Range Acceleration
Radio metric data from the Pioneer 10/11, Galileo, and Ulysses spacecraft
indicate an apparent anomalous, constant, acceleration acting on the spacecraft
with a magnitude cm/s, directed towards the Sun.
Two independent codes and physical strategies have been used to analyze the
data. A number of potential causes have been ruled out. We discuss future
kinematic tests and possible origins of the signal.Comment: Revtex, 4 pages and 1 figure. Minor changes for publicatio
Iron-coated Komodo dragon teeth and the complex dental enamel of carnivorous reptiles.
Komodo dragons (Varanus komodoensis) are the largest extant predatory lizards and their ziphodont (serrated, curved and blade-shaped) teeth make them valuable analogues for studying tooth structure, function and comparing with extinct ziphodont taxa, such as theropod dinosaurs. Like other ziphodont reptiles, V. komodoensis teeth possess only a thin coating of enamel that is nevertheless able to cope with the demands of their puncture-pull feeding. Using advanced chemical and structural imaging, we reveal that V. komodoensis teeth possess a unique adaptation for maintaining their cutting edges: orange, iron-enriched coatings on their tooth serrations and tips. Comparisons with other extant varanids and crocodylians revealed that iron sequestration is probably widespread in reptile enamels but it is most striking in V. komodoensis and closely related ziphodont species, suggesting a crucial role in supporting serrated teeth. Unfortunately, fossilization confounds our ability to consistently detect similar iron coatings in fossil teeth, including those of ziphodont dinosaurs. However, unlike V. komodoensis, some theropods possessed specialized enamel along their tooth serrations, resembling the wavy enamel found in herbivorous hadrosaurid dinosaurs. These discoveries illustrate unexpected and disparate specializations for maintaining ziphodont teeth in predatory reptiles
Immediate and delayed antibiotic prescribing strategies used by Australian early-career GP: A cross-sectional analysis
BACKGROUND: Antibiotics are overused for non-pneumonia acute respiratory tract infections (ARTIs). AIM: To establish prevalence and explore associations of delayed and immediate antibiotic prescribing strategies of Australian early-career GPs (specialist GP vocational trainees, also known as GP registrars) for non-pneumonia ARTIs. DESIGN AND SETTING: Cross-sectional analysis of data collected between September 2016 and December 2017 from the Registrar Clinical Encounters in Training cohort (ReCEnT) study, an ongoing cohort study of GP registrars’ in-practice clinical experiences in four Australian states and territories. METHOD: Multinomial logistic regression with outcome antibiotic prescribing (no prescribing, immediate prescribing, and delayed prescribing). RESULTS: Of 7156 new ARTI diagnoses, no antibiotics were prescribed for 4892 (68%); antibiotics were prescribed for immediate use for 1614 diagnoses (23%) and delayed antibiotics were used for 650 diagnoses (9%). Delayed prescribing was used in 22% of otitis media, 16% of sinusitis, 13% of sore throat, 11% of acute bronchitis/bronchiolitis, and 5% of upper respiratory tract infection (URTI) diagnoses. Delayed prescribing was used for 29% of all prescriptions written. Delayed prescribing and immediate prescribing were associated with markers of clinical concern. Delayed prescribing was associated with longer duration of consultation and with fewer diagnoses/problems dealt with in the consultation. CONCLUSION: Australian early-career GPs use no prescribing for ARTIs substantially more than established GPs; however, except where URTIs are concerned, they still prescribe antibiotics in excess of validated benchmarks. Australian early-career GPs may use delayed prescribing more often than European established GPs, and may use it to manage diagnostic uncertainty and, possibly, conflicting influences on prescribing behaviour. The use of delayed prescribing may enable a transition to an environment of more-rational antibiotic prescribing for ARTIs
- …