19,733 research outputs found
The Background Field Method as a Canonical Transformation
We construct explicitly the canonical transformation that controls the full
dependence (local and non-local) of the vertex functional of a Yang-Mills
theory on a background field. After showing that the canonical transformation
found is nothing but a direct field-theoretic generalization of the Lie
transform of classical analytical mechanics, we comment on a number of possible
applications, and in particular the non perturbative implementation of the
background field method on the lattice, the background field formulation of the
two particle irreducible formalism, and, finally, the formulation of the
Schwinger-Dyson series in the presence of topologically non-trivial
configurations.Comment: 11 pages, REVTeX. References added, some explanations extended. Final
version to appear in the journa
Report on the first binary black hole inspiral search in LIGO data
The LIGO Scientific Collaboration is currently engaged in the first search
for binary black hole inspiral signals in real data. We are using the data from
the second LIGO science run and we focus on inspiral signals coming from binary
systems with component masses between 3 and 20 solar masses. We describe the
analysis methods used and report on preliminary estimates for the sensitivities
of the LIGO instruments during the second science run.Comment: 10 pages, 2 figures. Added references for section 2, corrected figure
1. To appear in CQG, in a special issue on the proceedings of the 9th Annual
Gravitational Wave Data Analysis Workshop (GWDAW), Annecy, France, Dec. 200
Comparison of the noise characteristics of two low pressure ratio fans with a high throat Mach number inlet
Acoustics data obtained in experiments with two low pressure ratio 50.8 cm (20 in.) diameter model fans differing in design tip speed were compared. Determination of the average throat Mach number used to compare high Mach inlet noise reduction characteristics was based on a correlation of inlet wall static pressure measurements with a flow field calculation. The largest noise reductions were generally obtained with the higher tip speed fan. At a throat Mach number of 0.79, the difference in noise reduction was about 3.5 db with static test conditions. Although the noise reduction increased for the lower tip speed fan with a simulated flight velocity of 41 m/sec (80 knots), it was still about 2 db less than that of the high tip speed fan which was only tested at the static condition. However, variations in acoustic performance could not be absolutely attributed to the different fan designs because of differences in inlet lip contours which resulted in small variations of peak wall Mach number and axial extend of supersonic and near-sonic flow
Simulated flight effects on noise characteristics of a fan inlet with high throat Mach number
An anechoic wind tunnel experiment was conducted to determine the effects of simulated flight on the noise characteristics of a high throat Mach number fan inlet. Comparisons were made with the performance of a conventional low throat Mach number inlet with the same 50.8 cm fan noise source. Simulated forward velocity of 41 m/sec reduced perceived noise levels for both inlets, the largest effect being more than 3 db for the high throat Mach number inlet. The high throat Mach number inlet was as much as 7.5 db quieter than the low throat Mach number inlet with tunnel airflow and about 6 db quieter without tunnel airflow. Effects of inlet flow angles up to 30 deg were seemingly irregular and difficult to characterize because of the complex flow fields and generally small noise variations. Some modifications of tones and directivity at blade passage harmonics resulting from inlet flow angle variation were noted
Reheating and thermalization in a simple scalar model
We consider a simple model for the Universe reheating, which consists of a
single self--interacting scalar field in Minkowskian space--time. Making use of
the existence of an additional small parameter proportional to the amplitude of
the initial spatially homogeneous field oscillations, we show that the behavior
of the field can be found reliably. We describe the evolution of the system
from the homogeneous oscillations to the moment when thermalization is
completed. We compare our results with the Hartree--Fock approximation and
argue that some properties found for this model may be the common features of
realistic theories.Comment: Some changes in Introduction and Discussion, comparison with the
Hartree--Fock results added. 37 pages, 2 postscript figures attache
High-frequency transmission line transitions
© 2005 COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. Copyright 2005 Society of Photo-Optical Instrumentation Engineers. This paper was published in Smart Structures, Devices, and Systems II, edited by Said F. Al-Sarawi, Proceedings of SPIE Vol. 5649 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.This paper demonstrates the use of modern electromagnetic simulation software to design and develop a selection of three novel transmission line transitions, for operation at mm-wavelengths, and an improvement in the performance of existing transitions. Specifically, our three case studies analyse (i) a microstrip-to-stripline transition, (ii) an inverted microstrip transition, and (iii) a mtripline-to-finline transition. The important concepts are described and the tools available are explained. A number of novel and effective designs are presented as examples.Leonard T. Hall, Hedley J. Hansen, and Derek Abbot
2D scanning Rotman lens structure for smart collision avoidance sensors
Although electronically scanned antenna arrays can provide effective mm-wave search radar sensors, their high cost and complexity are leading to the consideration of alternative beam-forming arrangements. Rotman lenses offer a compact, rugged, reliable, alternative solution. This paper considers the design of a microstrip based Rotman lens for high-resolution, frequency-controlled scanning applications. Its implementation in microstrip is attractive because this technology is low-cost, conformal, and lightweight. A sensor designed for operation at 77 GHz is presented and an ∼ 80° azimuthal scan over a 30 GHz bandwidth is demonstrated.Leonard T. Hall, Hedley J. Hansen, and Derek Abbot
Helicopter simulation validation using flight data
A joint NASA/Army effort to perform a systematic ground-based piloted simulation validation assessment is described. The best available mathematical model for the subject helicopter (UH-60A Black Hawk) was programmed for real-time operation. Flight data were obtained to validate the math model, and to develop models for the pilot control strategy while performing mission-type tasks. The validated math model is to be combined with motion and visual systems to perform ground based simulation. Comparisons of the control strategy obtained in flight with that obtained on the simulator are to be used as the basis for assessing the fidelity of the results obtained in the simulator
QED in external fields, a functional point of view
A functional partial differential equation is set for the proper graphs
generating functional of QED in external electromagnetic fields. This equation
leads to the evolution of the proper graphs with the external field amplitude
and the external field gauge dependence of the complete fermion propagator and
vertex is derived non-perturbativally.Comment: 8 pages, published versio
Evaluation of bistable systems versus matched filters in detecting bipolar pulse signals
This paper presents a thorough evaluation of a bistable system versus a
matched filter in detecting bipolar pulse signals. The detectability of the
bistable system can be optimized by adding noise, i.e. the stochastic resonance
(SR) phenomenon. This SR effect is also demonstrated by approximate statistical
detection theory of the bistable system and corresponding numerical
simulations. Furthermore, the performance comparison results between the
bistable system and the matched filter show that (a) the bistable system is
more robust than the matched filter in detecting signals with disturbed pulse
rates, and (b) the bistable system approaches the performance of the matched
filter in detecting unknown arrival times of received signals, with an
especially better computational efficiency. These significant results verify
the potential applicability of the bistable system in signal detection field.Comment: 15 pages, 9 figures, MikTex v2.
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