99 research outputs found
Wakefield generation in magnetized plasmas
We consider wakefield generation in plasmas by electromagnetic pulses
propagating perpendicular to a strong magnetic field, in the regime where the
electron cyclotron frequency is equal to or larger than the plasma frequency.
PIC-simulations reveal that for moderate magnetic field strengths previous
results are re-produced, and the wakefield wavenumber spectrum has a clear peak
at the inverse skin depth. However, when the cyclotron frequency is
significantly larger than the plasma frequency, the wakefield spectrum becomes
broad-band, and simultaneously the loss rate of the driving pulse is much
enhanced. A set of equations for the scalar and vector potentials reproducing
these results are derived, using only the assumption of a weakly nonlinear
interaction.Comment: 6 pages, 8 figure
The St. Petersburg Paradox Despite Risk-seeking Preferences: An Experimental Study
The St. Petersburg Paradox is one of the oldest challenges of expected value theory. Thus far, explanations of the paradox aim at small probabilities being perceived as zero and the boundedness of utility of the outcome. This paper provides experimental results showing that neither diminishing marginal utility of the outcome nor perception of small probabilities can explain the paradox. We find that even in situations where subjects are risk-seeking, and zeroingout small probabilities supports risk-taking, the St. Petersburg Paradox exists. This indicates that the paradox cannot be resolved by the arguments advanced to date
The Influence of Serotonin Deficiency on Choice Deferral and the Compromise Effect
Psychological and physiological states such as mood, hunger, stress, and sleep deprivation are known to affect decision-making processes and therefore crucially influence consumer behavior. A possible biological mechanism underlying the observed variability of consumer behavior is the context-sensitive variation in the levels of neuromodulators in the brain. In a series of four experimental studies, the authors pharmaceutically reduce the levels of the neurotransmitter serotonin in the brain to diminish the availability of subjects’ cognitive resources. In doing so, they study how serotonin brain levels influence (1) subjects’ tendency to avoid buying and (2) consumers' preference for product options positioned as a compromise in a given choice set rather than for more extreme alternatives (i.e., the compromise effect). Using realistic product choice scenarios in a binding decision framework, they find that a reduction of brain serotonin levels leads to choice deferral and decreases the compromise effect, both as a within-subjects and as a between-subjects choice phenomenon. As such, this study provides neurobiological evidence for the assumption that the compromise effect is the result of deliberate and demanding thought processes rather than intuitive decision making
The reflectivity of relativistic ultra-thin electron layers
The coherent reflectivity of a dense, relativistic, ultra-thin electron layer
is derived analytically for an obliquely incident probe beam. Results are
obtained by two-fold Lorentz transformation. For the analytical treatment, a
plane uniform electron layer is considered. All electrons move with uniform
velocity under an angle to the normal direction of the plane; such electron
motion corresponds to laser acceleration by direct action of the laser fields,
as it is described in a companion paper. Electron density is chosen high enough
to ensure that many electrons reside in a volume \lambda_R^3, where \lambda_R
is the wavelength of the reflected light in the rest frame of the layer. Under
these conditions, the probe light is back-scattered coherently and is directed
close to the layer normal rather than the direction of electron velocity. An
important consequence is that the Doppler shift is governed by
\gamma_x=(1-(V_x/c)^2)^{-1/2} derived from the electron velocity component V_x
in normal direction rather than the full \gamma-factor of the layer electrons.Comment: 7 pages, 4 figures, submitted to the special issue "Fundamental
Physics with Ultra-High Fields" in The European Physical Journal
Generation of ultra-short light pulses by a rapidly ionizing thin foil
A thin and dense plasma layer is created when a sufficiently strong laser
pulse impinges on a solid target. The nonlinearity introduced by the
time-dependent electron density leads to the generation of harmonics. The pulse
duration of the harmonic radiation is related to the risetime of the electron
density and thus can be affected by the shape of the incident pulse and its
peak field strength. Results are presented from numerical
particle-in-cell-simulations of an intense laser pulse interacting with a thin
foil target. An analytical model which shows how the harmonics are created is
introduced. The proposed scheme might be a promising way towards the generation
of attosecond pulses.
PACS number(s): 52.40.Nk, 52.50.Jm, 52.65.RrComment: Second Revised Version, 13 pages (REVTeX), 3 figures in ps-format,
submitted for publication to Physical Review E, WWW:
http://www.physik.tu-darmstadt.de/tqe
Ensemble of ultra-high intensity attosecond pulses from laser-plasma interaction
The efficient generation of intense X-rays and -radiation is studied.
The scheme is based on the relativistic mirror concept, {\it i.e.}, a flying
thin plasma slab interacts with a counterpropagating laser pulse, reflecting
part of it in the form of an intense ultra-short electromagnetic pulse having
an up-shifted frequency. In the proposed scheme a series of relativistic
mirrors is generated in the interaction of the intense laser with a thin foil
target as the pulse tears off and accelerates thin electron layers. A
counterpropagating pulse is reflected by these flying layers in the form of an
ensemble of ultra-short pulses resulting in a significant energy gain of the
reflected radiation due to the momentum transfer from flying layers.Comment: 6 pages, 2 figures. Phys. Lett. A, in pres
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