331 research outputs found
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Validation of the radiation pattern of the VHF MST radar MAARSY by scattering off a sounding rocket's payload
The Middle Atmosphere Alomar Radar System (MAARSY) is a monostatic radar with an active phased array antenna designed for studies of phenomena in the mesosphere and lower thermosphere. Its design, in particular the flexible beam forming and steering capability, makes it a powerful instrument to perform observations with high angular and temporal resolution. For the configuration and analysis of experiments carried out with the radar it is essential to have knowledge of the actual radiation pattern. Therefore, during the time since the radar was put into operation various active and passive experiments have been performed to gain knowledge of the radiation pattern. With these experiments the beam pointing accuracy, the beam width and phase distribution of the antenna array were investigated. Here, the use of a sounding rocket and its payload as a radar target is described which was launched in the proximity of the radar. The analysis of these observations allows the detailed investigation of the two-way radiation pattern for different antenna array sizes and beam pointing positions
The Geminid meteor shower during the ECOMA sounding rocket campaign: specular and head echo radar observations
The ECOMA (Existence of Charge state Of meteoric
smoke particles in the Middle Atmosphere) sounding
rocket campaign was conducted during the Geminid meteor
shower in December 2010 in order to explore whether there
is a change of the properties of meteoric smoke particles due
to the stream. In parallel to the rocket flights, three radars
monitored the Geminid activity located at the launch site in
Northern Norway and in Northern Germany to gain information
about the meteor flux into the atmosphere. The results
presented here are based on specular meteor radar observations measuring the radiant position, the velocity and the meteor flux into the atmosphere during the Geminids. Further, the MAARSY (Middle Atmosphere Alomar Radar System) radar was operated to conduct meteor head echo experiments. The interferometric capabilities of MAARSY permit measuring the meteor trajectories within the radar beam and to determine the source radiant and geocentric meteor velocity, as well as to compute the meteor orbit
Regular networks of Luttinger liquids
We consider arrays of Luttinger liquids, where each node is described by a
unitary scattering matrix. In the limit of small electron-electron interaction,
we study the evolution of these scattering matrices as the high-energy single
particle states are gradually integrated out. Interestingly, we obtain the same
renormalization group equations as those derived by Lal, Rao, and Sen, for a
system composed of a single node coupled to several semi-infinite 1D wires. The
main difference between the single node geometry and a regular lattice is that
in the latter case, the single particle spectrum is organized into periodic
energy bands, so that the renormalization procedure has to stop when the last
totally occupied band has been eliminated. We therefore predict a strongly
renormalized Luttinger liquid behavior for generic filling factors, which
should exhibit power-law suppression of the conductivity at low temperatures
E_{F}/(k_{F}a) >
1. Some fully insulating ground-states are expected only for a discrete set of
integer filling factors for the electronic system. A detailed discussion of the
scattering matrix flow and its implication for the low energy band structure is
given on the example of a square lattice.Comment: 16 pages, 7 figure
A Parallelized Bayesian Approach To Accelerated Gravitational-Wave Background Characterization
The characterization of nanohertz-frequency gravitational waves (GWs) with
pulsar-timing arrays requires a continual expansion of datasets and monitored
pulsars. Whereas detection of the stochastic GW background is predicated on
measuring a distinctive pattern of inter-pulsar correlations, characterizing
the background's spectrum is driven by information encoded in the power spectra
of the individual pulsars' time series. We propose a new technique for rapid
Bayesian characterization of the stochastic GW background that is fully
parallelized over pulsar datasets. This Factorized Likelihood (FL) technique
empowers a modular approach to parameter estimation of the GW background,
multi-stage model selection of a spectrally-common stochastic process and
quadrupolar inter-pulsar correlations, and statistical cross-validation of
measured signals between independent pulsar sub-arrays. We demonstrate the
equivalence of this technique's efficacy with the full pulsar-timing array
likelihood, yet at a fraction of the required time. Our technique is fast,
easily implemented, and trivially allows for new data and pulsars to be
combined with legacy datasets without re-analysis of the latter.Comment: 14 pages, 6 figures. Matches version accepted by PR
Observation of KelvinâHelmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway
We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two KelvinâHelmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Riâ<0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40km, vertical wavelengths between 5 and 10km, and rather high intrinsic phase speeds between 45 and 85msâ1 with intrinsic periods of 5â10min
Globale Strahlungswirkung atmosphÀrischer Aerosolteilchen basierend auf dem Globalen Aerosoldatensatz GADS
Caracterização morfofisiolĂłgica e patogĂȘnica de isolados de Sphaeropsis sapinea e avaliação de resistĂȘncia em Pinus radiata.
Resumo
Bound States and Threshold Resonances in Quantum Wires with Circular Bends
We study the solutions to the wave equation in a two-dimensional tube of unit
width comprised of two straight regions connected by a region of constant
curvature. We introduce a numerical method which permits high accuracy at high
curvature. We determine the bound state energies as well as the transmission
and reflection matrices, and and focus on the nature of
the resonances which occur in the vicinity of channel thresholds. We explore
the dependence of these solutions on the curvature of the tube and angle of the
bend and discuss several limiting cases where our numerical results confirm
analytic predictions.Comment: 24 pages, revtex file, one style file and 17 PostScript figures
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Radar Observation of Extreme Vertical Drafts in the Polar Summer Mesosphere
The polar summer mesosphere is the Earth's coldest region, allowing the formation of mesospheric ice clouds. These ice clouds produce strong polar mesospheric summer echoes (PMSE) that are used as tracers of mesospheric dynamics. Here, we report the first observations of extreme vertical drafts (+/-50 ms [hoch]-1) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles a solitary wave in a varicose mode, narrow along propagation (3â4 km) and elongated (>10 km) transverse to propagation direction, with a relatively large vertical extent (~13 km). These spatial features are similar to previously observed mesospheric bores, but we observe only one crest with much larger vertical extent and higher vertical velocities
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