21,772 research outputs found
Planned improvements to the Owens Valley frequency-agile interferometer
Three small antennas will be added to the OVRO interferometer to form a five-element solar-dedicated array. This would provide up to 7 or 10 baselines (compared to the present 1 or 3). This would be sufficient to apply microwave diagnostics to most active region and burst sources. By using frequency-synthesis it would also provide an imaging capability comparable to that of an approximately 100 baseline interferometer. Expansion of the array is discussed
The Generalized Spectral Kurtosis Estimator
Due to its conceptual simplicity and its proven effectiveness in real-time
detection and removal of radio frequency interference (RFI) from radio
astronomy data, the Spectral Kurtosis (SK) estimator is likely to become a
standard tool of a new generation of radio telescopes. However, the SK
estimator in its original form must be developed from instantaneous power
spectral density (PSD) estimates, and hence cannot be employed as an RFI
excision tool downstream of the data pipeline in existing instruments where any
time averaging is performed. In this letter, we develop a generalized estimator
with wider applicability for both instantaneous and averaged spectral data,
which extends its practical use to a much larger pool of radio instruments.Comment: 5 pages, 2 figures, MNRAS Letters accepte
Flavor-Spin Symmetry and the Tensor Charge
Exploiting an approximate phenomenological symmetry of the
light axial vector mesons and using pole dominance, we calculate the flavor
contributions to the nucleon tensor charge. The result depends on the decay
constants of the axial vector mesons and their couplings to the nucleons.Comment: Talk given at 3rd Circum-Pan-Pacific Symposium on High Energy Spin
Physics (SPIN 2001), Beijing, China, 8-13 Oct 200
Gauges in the Bulk II: Models with Bulk Scalars
Extending previous work in Randall-Sundrum type models, we construct
low-energy effective actions for braneworlds with a bulk scalar field, with
special attention to the case of BPS branes. Holding the branes at fixed
coordinate position with a general ansatz for the bulk metric, and imposing the
Einstein frame as a gauge condition, we obtain a scalar-tensor theory with only
one scalar degree of freedom related to the proper brane separation. The
formalism is applicable even when there is direct coupling of the bulk scalar
and brane matter, as in the Horava-Witten model. We further show that the usual
moduli space approximation actually describes a non-BPS three-brane system.Comment: LaTeX file of 18 page
A computational model for a regenerator
This paper concerns a numerical model of a regenerator running at very low temperatures. The model consists of the usual three equations for a compressible fluid with an additional equation for a matrix temperature. The main difficulty with the model is the very low Mach number (approximately 1.E-3). The divergence of the velocity is not small, the pressure divergence is small, and the pressure fluctuation in time is not small. An asymptotic expansion based on the bounded derivative method of Kreiss is used to give a reduced model which eliminates acoustic waves. The velocity is then determined by a two-point boundary value problem which does not contain a time derivative. The solution obtained from the reduced system is compared with the numerical solution of the original system
New Interactive Solar Flare Modeling and Advanced Radio Diagnostics Tools
The coming years will see routine use of solar data of unprecedented spatial
and spectral resolution, time cadence, and completeness in the wavelength
domain. To capitalize on the soon to be available radio facilities such as the
expanded OVSA, SSRT and FASR, and the challenges they present in the
visualization and synthesis of the multi-frequency datasets, we propose that
realistic, sophisticated 3D active region and flare modeling is timely now and
will be a forefront of coronal studies over the coming years. Here we summarize
our 3D modeling efforts, aimed at forward fitting of imaging spectroscopy data,
and describe currently available 3D modeling tools. We also discuss plans for
future generalization of our modeling tools.Comment: 4 pages; IAU Symposium # 274 "Advances in Plasma Astrophysics"; typo
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