895 research outputs found
Optimal Cantilever Dynamic Vibration Absorbers
This work considers the use of a double-ended cantilever beam as a distributed parameter dynamic vibration absorber applied to a single-degree-of-freedom system in the presence of sinusoidal forces. The problem is analyzed exactly and by an energy approach using a single mode approximation for the cantilever beam. The results for both techniques compare favorably and damping is introduced in the form of a complex beam modulus. Optimal tuning and optimal damping parameters are found for a given ratio of absorber mass to main mass. © 1977 by ASME
Relations entre les productions animales et l'Ă©quilibre nutritif des populations humaines
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Modelling of the ICRF induced E x B convection in the scrape-off-layer of ASDEX Upgrade
In magnetic controlled fusion devices, plasma heating with radio-frequency (RF) waves in the ion cyclotron (IC) range of frequency relies on the electric field of the fast wave to heat the plasma. However, the slow wave can be generated parasitically. The electric field of the slow wave can induce large biased plasma potential (DC potential) through sheath rectification. The rapid variation of the rectified potential across the equilibrium magnetic field can cause significant convective transport (E x B drifts) in the scrape-off layer (SOL). In order to understand this phenomenon and reproduce the experiments, 3D realistic simulations are carried out with the 3D edge plasma fluid and kinetic neutral code EMC3-Eirene in ASDEX Upgrade. For this, we have added the prescribed drift terms to the EMC3 equations and verified the 3D code results against the analytical ones in cylindrical geometry. The edge plasma potential derived from the experiments is used to calculate the drift velocities, which are then treated as input fields in the code to obtain the final density distributions. Our simulation results are in good agreement with the experiments
Sending femtosecond pulses in circles: highly non-paraxial accelerating beams
We use caustic beam shaping on 100 fs pulses to experimentally generate
non-paraxial accelerating beams along a 60 degree circular arc, moving
laterally by 14 \mum over a 28 \mum propagation length. This is the highest
degree of transverse acceleration reported to our knowledge. Using diffraction
integral theory and numerical beam propagation simulations, we show that
circular acceleration trajectories represent a unique class of non-paraxial
diffraction-free beam profile which also preserves the femtosecond temporal
structure in the vicinity of the caustic
Low density instability in a nuclear Fermi liquid drop
The instability of a Fermi-liquid drop with respect to bulk density
distortions is considered. It is shown that the presence of the surface
strongly reduces the growth rate of the bulk instability of the finite
Fermi-liquid drop because of the anomalous dispersion term in the dispersion
relation. The instability growth rate is reduced due to the Fermi surface
distortions and the relaxation processes. The dependence of the bulk
instability on the multipolarity of the particle density fluctuations is
demonstrated for two nuclei and .Comment: 12 pages, latex, 3 ps-figures, submitted to Phys. Rev.
Numerical Simulations of Ion Cyclotron Range of Frequency (ICRF) Wave Fields in a Linear Plasma Device
Effect of fiber dispersion on broadband chaos communications implemented by electro-optic nonlinear delay phase dynamics
We investigate theoretically and experimentally
the detrimental e ect of ber dispersion on the synchroniza-
tion of an optoelectronic phase chaos cryptosystem. We
evaluate the root-mean square synchronization error and
the cancellation spectra between the emitter and the re-
ceiver in order to characterize the quality of the optical
ber communication link. These two indicators explicitly
show in temporal and spectral domain how ber dispersion
does negatively a ect the phase chaos cancellation at the re-
ceiver stage. We demonstrate that the dispersion manage-
ment techniques used in conventional optical ber networks,
such as dispersion-compensating modules/ bers or disper-
sion shifted bers, are also e cient to strongly reduce the
detrimental e ects of ber propagation in phase chaos com-
munications. This compatibility therefore opens the way to
a successful integration of more than 10-Gb/s phase chaos
communications systems in existing networks, even when
the ber link spans over more than 100 km.Peer reviewe
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