5,668 research outputs found
A relativistic coupled-channel formalism for the pion form factor
The electromagnetic form factor of a confined quark-antiquark pair is
calculated within the framework of point-form relativistic quantum mechanics.
The dynamics of theexchanged photon is explicitly taken into account by
treating theelectromagnetic scattering of an electron by a meson as a
relativistic two-channel problem for a Bakamjian-Thomas type mass operator.
This approach guarantees Poincare invariance. Using a Feshbach reduction the
coupled-channel problem can be converted into a one-channel problem for the
elastic electron-meson channel. By comparing the one-photon-exchange optical
potential at the constituent and hadronic levels, we are able to unambiguously
identify the electromagnetic meson form factor. Violations of
cluster-separability properties, which are inherent in the Bakamjian-Thomas
approach, become negligible for sufficiently large invariant mass of the
electron-meson system. In the limit of an infinitely large invariant mass, an
equivalence with form-factor calculations done in front-form relativistic
quantum mechanics is established analytically.Comment: 3 pages, 1 figure, submitted to EPJ Web of Conference
Effect of a rotating propeller on the separation angle of attack and distortion in ducted propeller inlets
The present study represents an extension of an earlier wind tunnel experiment performed with the P&W 17-in. Advanced Ducted Propeller (ADP) Simulator operating at Mach 0.2. In order to study the effects of a rotating propeller on the inlet flow, data were obtained in the UTRC 10- by 15-Foot Large Subsonic Wind Tunnel with the same hardware and instrumentation, but with the propeller removed. These new tests were performed over a range of flow rates which duplicated flow rates in the powered simulator program. The flow through the inlet was provided by a remotely located vacuum source. A comparison of the results of this flow-through study with the previous data from the powered simulator indicated that in the conventional inlet the propeller produced an increase in the separation angle of attack between 4.0 deg at a specific flow of 22.4 lb/sec-sq ft to 2.7 deg at a higher specific flow of 33.8 lb/sec-sq ft. A similar effect on separation angle of attack was obtained by using stationary blockage rather than a propeller
Visualisation of ectomycorrhizal rhizomorph structure using laser scanning confocal microscopy
A method for the observation of the three-dimensional structure of intact ectomycorrhizal rhizomorphs is described. The method is based on a combination of clearing the material with KOH followed by staining with congo red and subsequent imaging under a laser scanning confocal microscope (LSCM). The images obtained are of a much higher three-dimensional resolution than those obtained previously by use of conventional light microscopical techniques. The structure of highly differentiated and undifferentiated rhizomorphs is described. Applications of the method are briefly discussed
Tiefenverteilung von Wurzeln bei Winterweizen
The production and distribution of roots was examined for two winter wheat cultivars
(Capo and Saturnus). Plants were grown in PVC tubes of 150 cm length that were
placed in a field. The length of roots in 20 cm soil sections was measured at three
times. Mean root length densities decreased from 7-15 cm cm-3 soil in the top 20 cm
soil to 2 cm cm-3 at soil depths below 80 cm. Only slight differences were obtained for
the two cultivars and between harvests. Saturnus produced relatively greater root
lengths in upper soil horizons, while Capo spread its roots further down the soil profile.
Maximum rooting depth was between 150 to 160 cm
Electromagnetic meson form factor from a relativistic coupled-channel approach
Point-form relativistic quantum mechanics is used to derive an expression for
the electromagnetic form factor of a pseudoscalar meson for space-like momentum
transfers. The elastic scattering of an electron by a confined quark-antiquark
pair is treated as a relativistic two-channel problem for the and
states. With the approximation that the total velocity of the
system is conserved at (electromagnetic) interaction vertices this
simplifies to an eigenvalue problem for a Bakamjian-Thomas type mass operator.
After elimination of the channel the electromagnetic meson
current and form factor can be directly read off from the one-photon-exchange
optical potential. By choosing the invariant mass of the electron-meson system
large enough, cluster separability violations become negligible. An equivalence
with the usual front-form expression, resulting from a spectator current in the
reference frame, is established. The generalization of this
multichannel approach to electroweak form factors for an arbitrary bound
few-body system is quite obvious. By an appropriate extension of the Hilbert
space this approach is also able to accommodate exchange-current effects.Comment: 30 pages, 5 figure
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