592,532 research outputs found
Structure, spectra and variability of some GPS radio sources
We report the results of multifrequency-VLBI observations of
GHz-Peaked-Spectrum (GPS) radio sources. The VLBI structure and component
spectra of some GPS sources are presented. Our VLBI results show that about 80%
of the GPS galaxies exhibit a compact double or CSO-like structure, while the
GPS quasars tend to show a core-jet. The component spectra of the GPS galaxies
are often steep/convex, and the core has a flat spectrum but it is usually
hidden or weak. In addition, we studied the variability of GPS sources by
comparing new flux density measures, acquired with the Urumqi 25m telescope at
4.85 GHz, with previous 87GB data. The results show that 44% of the GPS quasars
varied higher than 10% in passed 20 years, while the fraction is only 12% for
the GPS galaxies meaning that the GPS quasars are much more variable than GPS
galaxies. In total, 25% of GPS sources show >10% variability at 4.85 GHz in our
sample.Comment: 4 pages, 7 figure
A Giant Sample of Giant Pulses from the Crab Pulsar
We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a
timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and
seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses
(GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken
with the same telescope and backend and analyzed as one data set. We calculated
power-law fits to amplitude distributions for main pulse (MP) and interpulse
(IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz
and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also
correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank
Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9
GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2
GHz and 39900 GPs from the GBT were recorded during these contemporaneous
observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at
8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP
GPs were detected within one spin period of high-frequency IP GPs, with a
chance probability of 9%. This indicates that the emission processes at high
and low radio frequencies are related, despite significant pulse profile shape
differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to
see if increased pair production in the magnetosphere is the mechanism
responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons
were used in this correlation analysis. No significant correlations were found
between GPs and gamma-ray photons. This indicates that increased pair
production in the magnetosphere is likely not the dominant cause of GPs.
Possible methods of GP production may be increased coherence of synchrotron
emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap
Improving the accuracy of estimates of animal path and travel distance using GPS drift-corrected dead reckoning
Route taken and distance travelled are important parameters for studies of animal locomotion. They are often measured using a collar equipped with GPS. Collar weight restrictions limit battery size, which leads to a compromise between collar operating life and GPS fix rate. In studies that rely on linear interpolation between intermittent GPS fixes, path tortuosity will often lead to inaccurate path and distance travelled estimates. Here, we investigate whether GPSâcorrected dead reckoning can improve the accuracy of localization and distance travelled estimates while maximizing collar operating life. Customâbuilt tracking collars were deployed on nine freely exercising domestic dogs to collect high fix rate GPS data. Simulations were carried out to measure the extent to which combining accelerometerâbased speed and magnetometer heading estimates (dead reckoning) with low fix rate GPS drift correction could improve the accuracy of path and distance travelled estimates. In our study, median 2âdimensional rootâmeanâsquared (2DâRMS) position error was between 158 and 463Â m (median path length 16.43Â km) and distance travelled was underestimated by between 30% and 64% when a GPS position fix was taken every 5Â min. Dead reckoning with GPS drift correction (1 GPS fix every 5Â min) reduced 2DâRMS position error to between 15 and 38Â m and distance travelled to between an underestimation of 2% and an overestimation of 5%. Achieving this accuracy from GPS alone would require approximately 12 fixes every minute and result in a battery life of approximately 11Â days; dead reckoning reduces the number of fixes required, enabling a collar life of approximately 10Â months. Our results are generally applicable to GPSâbased tracking studies of quadrupedal animals and could be applied to studies of energetics, behavioral ecology, and locomotion. This lowâcost approach overcomes the limitation of low fix rate GPS and enables the longâterm deployment of lightweight GPS collars
Where do we go from here? An assessment of navigation performance using a compass versus a GPS unit
The Global Positioning System (GPS) looks set to replace the traditional map and
compass for navigation tasks in military and civil domains. However, we may ask
whether GPS has a real performance advantage over traditional methods. We present
an exploratory study using a waypoint plotting task to compare the standard magnetic
compass against a military GPS unit, for both expert and non-expert navigators.
Whilst performance times were generally longer in setting up the GPS unit, once
navigation was underway the GPS was more efficient than the compass. For mediumto
long-term missions, this means that GPS could offer significant performance
benefits, although the compass remains superior for shorter missions.
Notwithstanding the performance times, significantly more errors, and more serious
errors, occurred when using the compass. Overall, then, the GPS offers some clear
advantages, especially for non-expert users. Nonetheless, concerns over the
development of cognitive maps remain when using GPS technologies
Recommended from our members
The GPS Assimilator: a Method for Upgrading Existing GPS User Equipment to Improve Accuracy, Robustness, and Resistance to Spoofing
Preprint of the 2010 ION GNSS Conference
Portland, OR, September 21â24, 2010A conceptual method is presented for upgrading existing GPS user equipment, without requiring hardware or software modifications to the equipment, to improve the equipmentâs position, velocity, and time (PVT) accuracy, to increase its PVT robustness in weak-signal or jammed environments, and to protect the equipment from counterfeit GPS signals (GPS spoofing). The method is embodied in a device called the GPS Assimilator that couples to the radio frequency (RF) input of an existing GPS receiver. The Assimilator extracts navigation and timing information from RF signals in its environmentâincluding non-GNSS signalsâand from direct baseband aiding provided, for example, by an inertial navigation system, a
frequency reference, or the GPS user. The Assimilator optimally fuses the collective navigation and timing information to produce a PVT solution which, by virtue of the diverse navigation and timing sources on which it is based, is highly accurate and inherently robust to GPS signal obstruction and jamming. The Assimilator embeds the PVT solution in a synthesized set of GPS signals and injects
these into the RF input of a target GPS receiver for which an accurate and robust PVT solution is desired. A prototype software-defined Assimilator device is presented with three example applications.Aerospace Engineerin
GPS Seismology for a moderate magnitude earthquake: Lessons learned from the analysis of the 31 October 2013 ML6.4 Ruisui (Taiwan) earthquake
The 31 October 2013 ML 6.4 Ruisui earthquake was well recorded by twelve 50-Hz, four 20-Hz and thirteen 1-Hz GPS receivers, and twenty-five strong motion stations located within the epicentral distance of 90 km in eastern Taiwan. Kinematic positioning solutions estimated by four GNSS software (TRACK, RTKLIB, GIPSY, VADASE) are used to derive the seismic waveforms and the co-seismic displacements for this event; strong motion accelerometers are used to verify the capability of high rate GPS to detect seismic waves generated by this earthquake. Results show that the coordinate repeatability of the GPS displacements time series are ~6 mm and ~20 mm standard deviation in the horizontal and vertical components respectively, after applying spatial filtering. The largest co-seismic displacement derived from high-rate GPS is nearly 15 centimeter at 5 km northeast of the epicenter. S waves and surface waves are successfully detected by motions of high-rate GPS and double-integrated accelerometers within the 15 km epicentral distance. For the first time twelve 50-Hz and four 20 Hz GPS observations for seismological study were used and analyzed in Taiwan; a clear benefit was evidenced with regard to the seismic waves features detection, with respect to the 1-Hz GPS data, so that ultra-high rate (> 1-Hz) observations can compensate the sparse coverage of seismic data, provided proper monuments for the GPS permanent stations are realized. Spectra analysis between co-located GPS and strong motion data further suggests that the optimal sampling rate for high-rate GPS Seismology study is 5 Hz. The 2013 Ruisui Taiwan earthquake recorded by the high-rate GPS permanent stations network in Taiwan demonstrates the benefits of GPS Seismology for a moderate size earthquake at a local scale
GPsâ strategies in exploring the preschool childâs wellbeing in the paediatric consultation
Background:
Although General Practitioners (GPs) are uniquely placed to identify children with emotional, social, and behavioural problems, they succeed in identifying only a small number of them. The aim of this article is to explore the strategies, methods, and tools employed by GPs in the assessment of the preschool childâs emotional, mental, social, and behavioural health. We look at how GPs address parental care of the child in general and in situations where GPs have a particular awareness of the child.
Method:
Twenty-eight Danish GPs were purposively selected to take part in a qualitative study which combined focus-group discussions, observation of child consultations, and individual interviews with GPs.
Results:
Analysis of the data suggests that GPs have developed a set of methods, and strategies to assess the preschool child and parental care of the child. They look beyond paying narrow attention to the physical health of the child and they have expanded their practice to include the relations and interactions in the consultation room. The physical examination of the child continues to play a central role in doctor-child communication.
Conclusion:
The participating GPsâ strategies helped them to assess the wellbeing of the preschool child but they often find it difficult to share their impressions with parents
Quasi-simultaneous multi-frequency observations of inverted-spectrum GPS candidate sources
Gigahertz-Peaked Spectrum (GPS) sources are probably the precursors of local
radio galaxies.Existing GPS source samples are small (<200). It is necessary to
extend the availabe sample of the Gigahertz-Peaked Spectrum (GPS) and High
Frequency Peaker (HFP) sources in order to study their nature with greater
details and higher statistical significance. A sample of 214 radio sources,
which were extracted from the SPECFIND catalog and show an inverted radio
spectrum, were observed quasi-simultaneously at 4.85, 10.45, and 32GHz with the
100-m Effelsberg radio telescope. Using the VLBA calibrator survey (VCS) we
have investigated the parsec-scale morphology of the sources. About 45% of the
sources in our sample are classified as GPS or HFP candidates. We add 65 new
GPS/HFP candidates to existing samples. We confirm the expected tendency that
HFP are more compact on milliarcsecond scale than the 'classical' GPS sources,
which peak at lower frequencies. The data mining of the SPECFIND database
represents a promising tool for the discovery of new GPS/HFP sources.Comment: 16 pages, 7 figures, accepted for publication in A&
MRI Tracking of Macrophages Labeled with Glucan Particles Entrapping a Water Insoluble Paramagnetic Gd-Based Agent.
PURPOSE: This study is aimed at demonstrating the in vivo potential of Gd(III)-loaded glucan particles (Gd-GPs) as magnetic resonance imaging (MRI)-positive agents for labeling and tracking phagocytic cells.
PROCEDURE: GPs were obtained from Saccharomyces cerevisae and loaded with the water-insoluble complex Gd-DOTAMA(C18)2. The uptake kinetics of Gd-GPs by murine macrophages was studied in vitro and the internalization mechanism was assessed by competition assays. The in vivo performance of Gd-GPs was tested at 7.05 T on a mouse model of acute liver inflammation.
RESULTS: The minimum number of Gd-GPs-labeled J774.A1 macrophages detected in vitro by MRI was ca. 300 cells/Îźl of agar, which is the lowest number ever reported for cells labeled with a positive T1 agent. Intravenous injection of macrophages labeled with Gd-GPs in a mouse model of liver inflammation enabled the MRI visualization of the cellular infiltration in the diseased area.
CONCLUSIONS: Gd-GPs represent a promising platform for tracking macrophages by MRI as a T1 alternative to the golden standard T2-based iron oxide particles
Survey of general practitioners' knowledge about Helicobacter pylori infection
BACKGROUND: Helicobacter pylori, occurring throughout the world and causing gastroduodenal diseases, is one of the most common chronic bacterial agents in humans. The purpose of this study was to measure the general practitioners' (GPs) knowledge and practices pertaining to H. pylori infection. METHODS: A cross-sectional type questionnaire survey was conducted in all of 19 primary health care centres (PHCC) in Samsun, Turkey, between November 1 and December 31, 2003. The questionnaire was sent to 124 GPs and 109 (87.9 %) of those filled in. They were requested to answer the questions on the knowledge, sources of medical information, diagnostic tests and treatment to H. pylori. RESULTS: Medical journals were the most frequently used source of information on H. pylori, being cited by 86 (78.9%) of GPs. Ninety-two (84.4%) of the GPs reported having used one or more tests and 17 (15.6%) never used any test for the diagnosis of H. pylori infection. Only 9.8% had used stool antigen test for diagnosis. GPs reported that they would prescribe symptomatic treatment without ordering diagnostic tests for 29 (26.6%). 54.1% of the GPs explain that they sent patients with H. pylori infection to a specialist, and most used a triple drug regimen containing a PPI. Treatment duration varies between 7 to 28 days. 80.7 of the GPs treat patients for 14 days. CONCLUSION: GPs may not have enough knowledge about the importance of stool antigen test or possibility of usage of this test. GPs have not sufficient knowledge about the difference between symptomatic and asymptomatic individuals. It is thought that GPs preferred to treat the patients with suspected ulcer empirically or to send them to a specialist because of the limited diagnostic conditions. The efforts to educate the GPs about the algorithms regarding the management of H. pylori infection during post-graduation period should be improved in PHCCs
- âŚ