617 research outputs found
Proceedings of the 2011 New York Workshop on Computer, Earth and Space Science
The purpose of the New York Workshop on Computer, Earth and Space Sciences is
to bring together the New York area's finest Astronomers, Statisticians,
Computer Scientists, Space and Earth Scientists to explore potential synergies
between their respective fields. The 2011 edition (CESS2011) was a great
success, and we would like to thank all of the presenters and participants for
attending. This year was also special as it included authors from the upcoming
book titled "Advances in Machine Learning and Data Mining for Astronomy". Over
two days, the latest advanced techniques used to analyze the vast amounts of
information now available for the understanding of our universe and our planet
were presented. These proceedings attempt to provide a small window into what
the current state of research is in this vast interdisciplinary field and we'd
like to thank the speakers who spent the time to contribute to this volume.Comment: Author lists modified. 82 pages. Workshop Proceedings from CESS 2011
in New York City, Goddard Institute for Space Studie
Assessment of the performance of the Chilbolton 3-GHz Advanced Meteorological radar for cloud-top height retrieval
The Chilbolton 3-GHz Advanced Meteorological Radar (CAMRa), which is mounted on a
fully steerable 25 metre dish, can provide three-dimensional information on the presence of
hydrometeors. We investigate the potential for this radar to make useful measurements of
low-altitude liquid water cloud structure. In order to assess the cloud-height assignment
capabilities of the 3-GHz radar, low-level cloud-top heights were retrieved from CAMRa
measurements made between May and July 2003 and compared with cloud-top heights
retrieved from a vertically pointing 94-GHz radar that operates alongside CAMRa. The
average difference between 94-GHz and 3-GHz radar derived cloud-top heights is shown to
be -0.1±0.4 km. In order to assess the capability of 3-GHz radar scans to be used for
satellite-derived cloud-top height validation, Multi-angle Imaging SpectroRadiometer
(MISR) cloud-top heights were compared with both 94-GHz and 3-GHz radar retrievals. The
average difference between 94-GHz radar and MISR cloud-top heights is shown to be
0.1±0.3 km while the 3-GHz radar and MISR average cloud-top height difference is shown
to be –0.2±0.6 km. In assessing the value of the CAMRa measurements, the problems
associated with low reflectivity values from stratiform liquid water clouds, ground clutter,
and Bragg scattering resulting from turbulent mixing are all addressed. We show that in
spite of the difficulties, the potential exists for CAMRa measurements to contribute
significantly to liquid water cloud-top height retrievals leading to the production of twodimensional
transects (i.e. maps) of cloud-top height
Assessment of MISR and MODIS cloud top heights through inter-comparison with a back-scattering lidar at SIRTA
One year of back-scattering lidar cloud boundaries and optical depth were analysed for coincident inter-comparison with the latest processed versions of the NASA-TERRA MISR stereo and MODIS CO2-slicing operational cloud top heights. Optically thin clouds were found to be accurately characterised by the MISR cloud top height product as long as no other cloud was present at lower altitude. MODIS cloud top heights were generally found within the cloud extent retrieved by lidar; agreement improved as cloud optical depth increased and when CO2-slicing was the only technique used for the retrieval. The difference between Lidar and MISR cloud top heights was found to lie between −0.1 and 0.4 km for low clouds and between 0.1 and 3.1 km for high clouds. The difference between Lidar and MODIS cloud top heights was found to lie between −1.2 and 1.5 km for low clouds and between −1.4 and 2.7 km for high clouds
Aharonov-Bohm cages in the GaAlAs/GaAs system
Aharonov-Bohm oscillations have been observed in a lattice formed by a two
dimensional rhombus tiling. This observation is in good agreement with a recent
theoretical calculation of the energy spectrum of this so-called T3 lattice. We
have investigated the low temperature magnetotransport of the T3 lattice
realized in the GaAlAs/GaAs system. Using an additional electrostatic gate, we
have studied the influence of the channel number on the oscillations amplitude.
Finally, the role of the disorder on the strength of the localization is
theoretically discussed.Comment: 6 pages, 11 EPS figure
The fractional quantum Hall effect in infinite layer systems
Stacked two dimensional electron systems in transverse magnetic fields
exhibit three dimensional fractional quantum Hall phases. We analyze the
simplest such phases and find novel bulk properties, e.g., irrational braiding.
These phases host ``one and a half'' dimensional surface phases in which motion
in one direction is chiral. We offer a general analysis of conduction in the
latter by combining sum rule and renormalization group arguments, and find that
when interlayer tunneling is marginal or irrelevant they are chiral semi-metals
that conduct only at T > 0 or with disorder.Comment: RevTeX 3.0, 4p., 2 figs with epsf; reference to the detailed
companion paper cond-mat/0006506 adde
Electron states of mono- and bilayer graphene on SiC probed by STM
We present a scanning tunneling microscopy (STM) study of a
gently-graphitized 6H-SiC(0001) surface in ultra high vacuum. From an analysis
of atomic scale images, we identify two different kinds of terraces, which we
unambiguously attribute to mono- and bilayer graphene capping a C-rich
interface. At low temperature, both terraces show
quantum interferences generated by static impurities. Such interferences are a
fingerprint of -like states close to the Fermi level. We conclude that the
metallic states of the first graphene layer are almost unperturbed by the
underlying interface, in agreement with recent photoemission experiments (A.
Bostwick et al., Nature Physics 3, 36 (2007))Comment: 4 pages, 3 figures submitte
Minimal subtraction and the Callan-Symanzik equation
The usual proof of renormalizability using the Callan-Symanzik equation makes
explicit use of normalization conditions. It is shown that demanding that the
renormalization group functions take the form required for minimal subtraction
allows one to prove renormalizability using the Callan-Symanzik equation,
without imposing normalization conditions. Scalar field theory and quantum
electrodynamics are treated.Comment: 6 pages, plain Te
Kerr non-linearity in a superconducting Josephson metamaterial
We present a detailed experimental and theoretical analysis of the dispersion
and non-linear Kerr frequency shifts of plasma modes in a one-dimensional
Josephson junction chain containing 500 SQUIDs in the regime of weak
nonlinearity. The measured low-power dispersion curve agrees perfectly with the
theoretical model if we take into account the Kerr renormalisation of the bare
frequencies and the long-range nature of the island charge screening by a
remote ground plane. We measured the self- and cross-Kerr shifts for the
frequencies of the eight lowest modes in the chain. We compare the measured
Kerr coefficients with theory and find good agreement
Kerr coefficients of plasma resonances in Josephson junction chains
We present an experimental and theoretical analysis of the self- and
cross-Kerr effect of extended plasma resonances in Josephson junction chains.
We calculate the Kerr coefficients by deriving and diagonalizing the
Hamiltonian of a linear circuit model for the chain and then adding the
Josephson non-linearity as a perturbation. The calculated Kerr-coefficients are
compared with the measurement data of a chain of 200 junctions. The Kerr effect
manifests itself as a frequency shift that depends linearly on the number of
photons in a resonant mode. By changing the input power on a low signal level,
we are able to measure this shift. The photon number is calibrated using the
self-Kerr shift calculated from the sample parameters. We then compare the
measured cross-Kerr shift with the theoretical prediction, using the calibrated
photon number.Comment: 10 pages, 9 figure
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