665 research outputs found
Implementation of a GNU Radio and Python FMCW radar toolkit
Abstract: The use of GNU Radio in order to explore FMCW radar is growing rapidly, where it is used for radar signal processing. In this paper we implement FMCW surveillance radar for drone detection on SDR using GNU Radio and the USRP B210. The requirement was to design and implement an FMCW surveillance radar to detect a drone with a radar cross-section of 0.1 m2 and a maximum range of 150 m for the purpose of point detection..
Rapid Profiling of Marine Notches Using a Handheld Laser Distance Meter
A rapid, single-user profiling method for rocky shores is described. The Leica Disto D8 handheld laser distance meter
measures distance up to 100 m and inclination in 360 degrees. It automatically calculates horizontal distance and vertical elevation. Memory storage accommodates data for 30 measurement points, allowing easy plotting of shore profiles. This technique allows even inaccessible, dangerous, and overhanging cliff faces to be evaluated faithfully and within minutes. It is a major improvement over standard methods that often involve risky coasteering and climbing. Examples are given from marine notches in Thailand
BoGSy:ein Informationssystem fĂŒr Botanische GĂ€rten
Botanische GĂ€rten bieten den Botanischen Instituten die Grundlage fĂŒr deren Forschungen und Besuchern einen Einblick in die Pflanzenwelt. Die mit dem Wissenschaftszweig der Botanik entstanden UniversitĂ€tsgĂ€rten haben ihren Mittelpunkt in der Botanischen Forschung und Lehre, vor allem in den Bereichen Taxonomie und Ăkologie. Die Grundlagen und der Inhalt der Botanischen Arbeit sind demnach insbesondere Sammlungen. DarĂŒber hinaus erfordert die Teilnahme im IPEN (International Plant Exchange Network) seit einigen Jahren die Einhaltung strenger Kriterien der CBD (Convention on Biological Diversity) beim Austausch von Samen und Pflanzenmaterial. Die Entwicklung eines Datenbank gestĂŒtzten Informationssystems fĂŒr Botanische GĂ€rten wird durch eine Reihe von Beobachtungen motiviert und muss diverse Randbedingungen beachten. Dies wird im Folgenden genauer erlĂ€utert. Sodann werden der Entwurf und eine erste Realisierung des Informationssystems BoGSy beschrieben, welches an der UniversitĂ€t MĂŒnster entwickelt wird und diesen Bedingungen genĂŒgt.<br/
USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550-564
We report on timing and spectral observations of the 2000 outburst of XTE
J1550-564 made by the Unconventional Stellar Aspect (USA) Experiment on board
the Advanced Research and Global Observation Satellite (ARGOS). We observe a
low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that
tends to increase with increasing flux and a fractional rms amplitude which is
correlated with the hardness ratio. The evolution of the hardness ratio (4--16
keV/1--4 keV) with time and source flux is examined. The hardness-intensity
diagram (HID) shows a cyclical movement in the clockwise direction and possibly
indicates the presence of two independent accretion flows. We observe a
relationship between the USA 4--16 keV count rate and radio observations and
discuss this in the context of previously observed correlations between X-ray,
radio, optical and IR data. We examine our results in the context of models
invoking two accretion flows: a thin disk and a hot sub-Keplerian flow.Comment: 11 pages, 2 figure
On the nature of the first transient Z-source XTE J1701-462: its accretion disk structure, neutron star magnetic field strength, and hard tail
Using the data from the Rossi X-Ray Timing Explorer satellite, we investigate
the spectral evolution along a "Z" track and a "v" track on the
hardness-intensity diagrams of the first transient Z source XTE J1701-462. The
spectral analyses suggest that the inner disk radius depends on the mass
accretion rate, in agreement with the model prediction, R_in \propto
((dM/dt)_disk)^{2/7}, for a radiation pressure dominated accretion disk
interacting with the magnetosphere of a neutron star (NS). The changes in the
disk mass accretion rate (dM/dt)_disk are responsible for the evolution of the
"Z" or "v" track. The radiation pressure thickens the disk considerably, and
also produces significant outflows. The NS surface magnetic field strength,
derived from the interaction between the magnetosphere and the radiation
pressure dominated accretion disk, is ~(1--3)X10^9 G, which is possibly between
normal atoll and Z sources. A significant hard tail is detected in the
horizontal branches and we discuss several possible origins of the hard tail
Defining Meyer's loop-temporal lobe resections, visual field deficits and diffusion tensor tractography
Anterior temporal lobe resection is often complicated by superior quadrantic visual field deficits (VFDs). In some cases this can be severe enough to prohibit driving, even if a patient is free of seizures. These deficits are caused by damage to Meyer's loop of the optic radiation, which shows considerable heterogeneity in its anterior extent. This structure cannot be distinguished using clinical magnetic resonance imaging sequences. Diffusion tensor tractography is an advanced magnetic resonance imaging technique that enables the parcellation of white matter. Using seed voxels antero-lateral to the lateral geniculate nucleus, we applied this technique to 20 control subjects, and 21 postoperative patients. All patients had visual fields assessed with Goldmann perimetry at least three months after surgery. We measured the distance from the tip of Meyer's loop to the temporal pole and horn in all subjects. In addition, we measured the size of temporal lobe resection using postoperative T1-weighted images, and quantified VFDs. Nine patients suffered VFDs ranging from 22% to 87% of the contralateral superior quadrant. In patients, the range of distance from the tip of Meyer's loop to the temporal pole was 24â43 mm (mean 34 mm), and the range of distance from the tip of Meyer's loop to the temporal horn was â15 to +9 mm (mean 0 mm). In controls the range of distance from the tip of Meyer's loop to the temporal pole was 24â47 mm (mean 35 mm), and the range of distance from the tip of Meyer's loop to the temporal horn was â11 to +9 mm (mean 0 mm). Both quantitative and qualitative results were in accord with recent dissections of cadaveric brains, and analysis of postoperative VFDs and resection volumes. By applying a linear regression analysis we showed that both distance from the tip of Meyer's loop to the temporal pole and the size of resection were significant predictors of the postoperative VFDs. We conclude that there is considerable variation in the anterior extent of Meyer's loop. In view of this, diffusion tensor tractography of the optic radiation is a potentially useful method to assess an individual patient's risk of postoperative VFDs following anterior temporal lobe resection
Initial low/hard state, multiple jet ejections and X-ray/radio correlations during the outburst of XTE J1859+226
We have studied the 1999 soft X-ray transient outburst of XTE J1859+226 at
radio and X-ray wavelengths. The event was characterised by strong variability
in the disc, corona and jet - in particular, a number of radio flares
(ejections) took place and seemed well-correlated with hard X-ray events.
Apparently unusual for the `canonical soft' X-ray transient, there was an
initial period of low/hard state behaviour during the rise from quiescence but
prior to the peak of the main outburst - we show that not only could this
initial low/hard state be an ubiquitous feature of soft X-ray transient
outbursts but that it could also be extremely important in our study of
outburst mechanisms.Comment: 12 pages, Accepted for publication in MNRA
Temporal Properties of Cygnus X-1 During the Spectral Transitions
We report the results from our timing analysis of 15 RXTE observations of
Cygnus X-1 throughout its 1996 spectral transitions. The entire period can be
divided into 3 distinct phases: (1) transition from the hard to soft state, (2)
soft state, and (3) transition from the soft state back to the hard state. The
observed X-ray properties in phases 1 and 3 are remarkably similar, suggesting
that the same physical processes are likely involved in triggering such
transitions. The power density spectrum (PDS) during the transition can be
characterized by a red noise component, followed by a white noise component
which extends to roughly 1-3 Hz where it is cut off, and a steeper power law at
higher frequencies. The X-ray flux also exhibits apparent quasi-periodic
oscillation (QPO) with the centroid frequency varying in the range of 4-12 Hz.
The QPO shows no correlation with the source flux, but becomes more prominent
at higher energies. This type of PDS bears resemblance to that of other black
hole candidates often observed in a so-called very high state, although the
origin of the observed QPO may be very different. The low-frequency red noise
has not been observed in the hard state, thus seems to be positively correlated
with the disk mass accretion rate which is presumably low in the hard state and
high in the soft state; in fact, it completely dominates the PDS in the soft
state. In the framework of thermalComptonization models, Cui et al. (see
astro-ph/9610071 and astro-ph/9610072) speculated that the difference in the
observed spectral and timing properties between the hard and soft states is due
to the presence of a ``fluctuating'' Comptonizing corona during the transition.
Here we present the measured hard X-ray time lags and coherence functions
between various energy bands, and show that the results strongly support such a
scenario.Comment: AASTex file. 29 pages including 11 figures. To appear in Ap
Cortical thickness, surface area and volume measures in Parkinson's disease, multiple system atrophy and progressive supranuclear palsy
OBJECTIVE
Parkinson's disease (PD), Multiple System Atrophy (MSA) and Progressive Supranuclear Palsy (PSP) are neurodegenerative diseases that can be difficult to distinguish clinically. The objective of the current study was to use surface-based analysis techniques to assess cortical thickness, surface area and grey matter volume to identify unique morphological patterns of cortical atrophy in PD, MSA and PSP and to relate these patterns of change to disease duration and clinical features.
METHODS
High resolution 3D T1-weighted MRI volumes were acquired from 14 PD patients, 18 MSA, 14 PSP and 19 healthy control participants. Cortical thickness, surface area and volume analyses were carried out using the automated surface-based analysis package FreeSurfer (version 5.1.0). Measures of disease severity and duration were assessed for correlation with cortical morphometric changes in each clinical group.
RESULTS
Results show that in PSP, widespread cortical thinning and volume loss occurs within the frontal lobe, particularly the superior frontal gyrus. In addition, PSP patients also displayed increased surface area in the pericalcarine. In comparison, PD and MSA did not display significant changes in cortical morphology.
CONCLUSION
These results demonstrate that patients with clinically established PSP exhibit distinct patterns of cortical atrophy, particularly affecting the frontal lobe. These results could be used in the future to develop a useful clinical application of MRI to distinguish PSP patients from PD and MSA patients
Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT
Galaxy clusters are one of the prime sites to search for dark matter (DM)
annihilation signals. Depending on the substructure of the DM halo of a galaxy
cluster and the cross sections for DM annihilation channels, these signals
might be detectable by the latest generation of -ray telescopes. Here
we use three years of Fermi Large Area Telescope (LAT) data, which are the most
suitable for searching for very extended emission in the vicinity of nearby
Virgo galaxy cluster. Our analysis reveals statistically significant extended
emission which can be well characterized by a uniformly emitting disk profile
with a radius of 3\deg that moreover is offset from the cluster center. We
demonstrate that the significance of this extended emission strongly depends on
the adopted interstellar emission model (IEM) and is most likely an artifact of
our incomplete description of the IEM in this region. We also search for and
find new point source candidates in the region. We then derive conservative
upper limits on the velocity-averaged DM pair annihilation cross section from
Virgo. We take into account the potential -ray flux enhancement due to
DM sub-halos and its complex morphology as a merging cluster. For DM
annihilating into , assuming a conservative sub-halo model
setup, we find limits that are between 1 and 1.5 orders of magnitude above the
expectation from the thermal cross section for
. In a more optimistic scenario, we
exclude
for for the same channel. Finally, we
derive upper limits on the -ray-flux produced by hadronic cosmic-ray
interactions in the inter cluster medium. We find that the volume-averaged
cosmic-ray-to-thermal pressure ratio is less than .Comment: 15 pages, 11 figures, 4 tables, accepted for publication in ApJ;
corresponding authors: T. Jogler, S. Zimmer & A. Pinzk
- âŠ