3,872 research outputs found
Facets of confinement and dynamical chiral symmetry breaking
The gap equation is a cornerstone in understanding dynamical chiral symmetry
breaking and may also provide clues to confinement. A symmetry-preserving
truncation of its kernel enables proofs of important results and the
development of an efficacious phenomenology. We describe a model of the kernel
that yields: a momentum-dependent dressed-quark propagator in fair agreement
with quenched lattice-QCD results; and chiral limit values: f_pi= 68 MeV and
= -(190 MeV)^3. It is compared with models inferred from studies of
the gauge sector.Comment: 5 pages, 3 figures; contribution to the proceedings of Quark Nuclear
Physics (QNP 2002), Juelich, Germany, 9-14 Jun 200
Preliminary test results of a hollow cathode MPD thruster
Performance of four hollow cathode configurations with low work function inserts was evaluated in a steady-state 100 kW class applied magnetic field magnetoplasmadynamic (MPD) thruster. Two of the configurations exhibited stable discharge current attachment to the low work function inserts of the hollow cathodes. A maximum discharge current of 2250 A was attained. While the applied-field increased the performance of the thruster, at high applied fields the discharge current attachment moved from the insert to the cathode body. The first successful hollow cathode performed well in comparison with a conventional rod cathode MPD thruster, attaining a thrust efficiency with argon of close to 20 percent at a specific impulse of about 2000 s. The second successful configuration had significantly lower performance
100-kW class applied-field MPD thruster component wear
Component erosion and material deposition sites were identified and analyzed during tests of various configurations of 100 kW class, applied-field, water-cooled magnetoplasmadynamic (MPD) thrusters. Severe erosion of the cathode and the boron nitride insulator was observed for the first series of tests, which was significantly decreased by reducing the levels of propellant contamination. Severe erosion of the copper anode resulting from sputtering by the propellant was also observed. This is the first observation of this phenomenon in MPD thrusters. The anode erosion indicates that development of long life MPD thrusters requires the use of light gas propellants such as hydrogen, deuterium, or lithium
Emergence of rotational bands in ab initio no-core configuration interaction calculations of light nuclei
The emergence of rotational bands is observed in no-core configuration
interaction (NCCI) calculations for the odd-mass Be isotopes (7<=A<=13) with
the JISP16 nucleon-nucleon interaction, as evidenced by rotational patterns for
excitation energies, quadrupole moments, and E2 transitions. Yrast and
low-lying excited bands are found. The results demonstrate the possibility of
well-developed rotational structure in NCCI calculations using a realistic
nucleon-nucleon interaction.Comment: 7 pages, 6 figures; to be published in Phys. Lett.
Confinement Phenomenology in the Bethe-Salpeter Equation
We consider the solution of the Bethe-Salpeter equation in Euclidean metric
for a qbar-q vector meson in the circumstance where the dressed quark
propagators have time-like complex conjugate mass poles. This approximates
features encountered in recent QCD modeling via the Dyson-Schwinger equations;
the absence of real mass poles simulates quark confinement. The analytic
continuation in the total momentum necessary to reach the mass shell for a
meson sufficiently heavier than 1 GeV leads to the quark poles being within the
integration domain for two variables in the standard approach. Through Feynman
integral techniques, we show how the analytic continuation can be implemented
in a way suitable for a practical numerical solution. We show that the would-be
qbar-q width to the meson generated from one quark pole is exactly cancelled by
the effect of the conjugate partner pole; the meson mass remains real and there
is no spurious qbar-q production threshold. The ladder kernel we employ is
consistent with one-loop perturbative QCD and has a two-parameter infrared
structure found to be successful in recent studies of the light SU(3) meson
sector.Comment: Submitted for publication; 10.5x2-column pages, REVTEX 4, 3
postscript files making 3 fig
Mind the gap
In this summary of the application of Dyson-Schwinger equations to the theory
and phenomenology of hadrons, some deductions following from a nonperturbative,
symmetry-preserving truncation are highlighted, notable amongst which are
results for pseudoscalar mesons. We also describe inferences from the gap
equation relating to the radius of convergence of a chiral expansion,
applications to heavy-light and heavy-heavy mesons, and quantitative estimates
of the contribution of quark orbital angular momentum in pseudoscalar mesons;
and recapitulate upon studies of nucleon electromagnetic form factors.Comment: 7 pages, 3 figures. Contribution to Proceedings of 4th International
Conference on Quarks and Nuclear Physics (QNP06), Madrid, Spain, 5-10 Jun
200
A systematic approach to the Planck LFI end-to-end test and its application to the DPC Level 1 pipeline
The Level 1 of the Planck LFI Data Processing Centre (DPC) is devoted to the
handling of the scientific and housekeeping telemetry. It is a critical
component of the Planck ground segment which has to strictly commit to the
project schedule to be ready for the launch and flight operations. In order to
guarantee the quality necessary to achieve the objectives of the Planck
mission, the design and development of the Level 1 software has followed the
ESA Software Engineering Standards. A fundamental step in the software life
cycle is the Verification and Validation of the software. The purpose of this
work is to show an example of procedures, test development and analysis
successfully applied to a key software project of an ESA mission. We present
the end-to-end validation tests performed on the Level 1 of the LFI-DPC, by
detailing the methods used and the results obtained. Different approaches have
been used to test the scientific and housekeeping data processing. Scientific
data processing has been tested by injecting signals with known properties
directly into the acquisition electronics, in order to generate a test dataset
of real telemetry data and reproduce as much as possible nominal conditions.
For the HK telemetry processing, validation software have been developed to
inject known parameter values into a set of real housekeeping packets and
perform a comparison with the corresponding timelines generated by the Level 1.
With the proposed validation and verification procedure, where the on-board and
ground processing are viewed as a single pipeline, we demonstrated that the
scientific and housekeeping processing of the Planck-LFI raw data is correct
and meets the project requirements.Comment: 20 pages, 7 figures; this paper is part of the Prelaunch status LFI
papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jins
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