876 research outputs found
4D Tropospheric Tomography using GPS Estimated Slant Delays
Tomographic techniques are successfully applied to obtain 4D images of the
tropospheric refractivity in a local dense network. In the lower atmosphere
both the small height and time scales and the non-dispersive nature of
tropospheric delays require a more careful analysis of the data. We show how
GPS data is processed to obtain the tropospheric slant delays using the
GIPSY-OASIS II software and define the concept of pseudo-wet delays, which will
be the observables in the tomographic software. We then discuss the inverse
problem in the 3D stochastic tomography, using simulated refractivity fields to
test the system and the impact of noise. Finally, we use data from the Kilauea
network in Hawaii and a local 4x4x41-voxel grid on a region of 400 Km and
15 Km in height to produce 4D refractivity fields. Results are compared with
ECMWF forecast.Comment: 9 pages, 6 figures (2 color
Differential Regularization of a Non-relativistic Anyon Model
Differential regularization is applied to a field theory of a
non-relativistic charged boson field with
self-interaction and coupling to a statistics-changing Chern-Simons
gauge field. Renormalized configuration-space amplitudes for all diagrams
contributing to the 4-point function, which
is the only primitively divergent Green's function, are obtained up to 3-loop
order. The renormalization group equations are explicitly checked, and the
scheme dependence of the -function is investigated. If the
renormalization scheme is fixed to agree with a previous 1-loop calculation,
the 2- and 3-loop contributions to vanish, and
itself vanishes when the ``self-dual'' condition relating
to the gauge coupling is imposed.Comment: 22 pages in ReVTEX (with a plaintext PostScript figure appended at
end), MIT CTP #221
4D tropospheric tomography using GPS slant wet delays
International audienceTomographic techniques are successfully applied to obtain 4D images of the tropospheric refractivity in a local dense network of global positioning system (GPS) receivers. We show here how GPS data are processed to obtain the tropospheric slant wet delays and discuss the validity of the processing. These slant wet delays are the observables in the tomographic processing. We then discuss the inverse problem in 4D tropospheric tomography making extensive use of simulations to test the system and define the resolution and the impact of noise. Finally, we use data from the Kilauea network in Hawaii for February 1, 1997, and a local 4×4×40 voxel grid on a region of 400 km2 and 15 km in height to produce the corresponding 4D wet refractivity fields, which are then validated using forecast analysis from the European Center for Medium Range Weather Forecast (ECMWF). We conclude that tomographic techniques can be used to monitor the troposphere in time and space
Gravity-mediated Scalar Dark Matter in Warped Extra-Dimensions
We revisit the case of scalar dark matter interacting just gravitationally
with the Standard Model (SM) particles in an extra-dimensional Randall-Sundrum
scenario. We assume that both, the dark matter and the Standard Model, are
localized in the TeV brane and only interact via gravitational mediators,
namely the graviton Kaluza-Klein modes and the radion. We analyze in detail the
dark matter annihilation channel into two on-shell KK-gravitons, and contrary
to previous studies which overlooked this process, we find that it is possible
to obtain the correct relic abundance for dark matter masses in the range [1,
10] TeV even after taking into account the strong bounds from LHC Run II. We
also consider the impact of the radion contribution (virtual exchange leading
to SM final states as well as on-shell production), which does not
significantly change our results. Quite interestingly, a sizeable part of the
currently allowed parameter space could be tested by LHC Run III and by the
High-Luminosity LHC.Comment: 43 pages, 9 figure
Rapid extracellular acidification induced by glucose metabolism in non-proliferating cells of Serratia marcescens
The addition of glucose or other sugars to resting cells of Serratia marcescens induced rapid acidification of the extracellular medium. This acidification was due to the catabolism of sugars. The rate of acidification depended on the carbon source and its concentration. HPLC analysis of the supernatants demonstrated that the progressive fall in pH resulted from the rapid production of lactic, acetic, pyruvic and citric acids. Other microorganisms were tested for their ability to produce this rapid acidification of the medium. This study may provide a rapid and simple method for metabolism studies
Selective epitaxial growth of graphene on SiC
We present an innovative method of selective epitaxial growth of few layers
graphene (FLG) on a pre-patterned SiC substrate. The methods involves,
successively, the sputtering of a thin AlN layer on top of a mono-crystalline
SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet
etching. The sublimation of few atomic layers of Si from the SiC substrate
occurs only through the selectively etched AlN layer. The presence of the Raman
G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it
gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace
The Eddy Experiment: accurate GNSS-R ocean altimetry from low altitude aircraft
During the Eddy Experiment, two synchronous GPS receivers were flown at 1 km
altitude to collect L1 signals and their reflections from the sea surface for
assessment of altimetric precision and accuracy. Wind speed (U10) was around 10
m/s, and SWH up to 2 m. A geophysical parametric waveform model was used for
retracking and estimation of the lapse between the direct and reflected signals
with a 1-second precision of 3 m. The lapse was used to estimate the SSH along
the track using a differential model. The RMS error of the 20 km averaged
GNSS-R absolute altimetric solution with respect to Jason-1 SSH and a GPS buoy
measurement was of 10 cm, with a 2 cm mean difference. Multipath and retracking
parameter sensitivity due to the low altitude are suspected to have degraded
accuracy. This result provides an important milestone on the road to a GNSS-R
mesoscale altimetry space mission.Comment: All Starlab authors have contributed significantly; the Starlab
Author list has been ordered randoml
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