8,897 research outputs found
Characteristics of return stroke electric fields produced by lightning flashes at distances of 1 to 15 kilometers
Electric field derivative signals from single and multiple lightning strokes are presented. For about 25 pct. of all acquired waveforms, produced by return strokes, stepped leaders or intracloud discharges, type and distance of the signal source are known from the observations by an all sky video camera system. The analysis of the electric field derivative waveforms in the time domain shows a significant difference in the impulse width between return stroke signals and those of stepped leaders and intracloud discharges. In addition, the computed amplitude density spectrum of return stroke waveforms lies by a factor of 10 above that of stepped leaders and intracloud discharges in the frequency range from 50 to 500 kHz
The Danger of Stalled Flight and an Analysis of the Factors which Govern It
A definition of "stalled fight" is presented as well as a detailed discussion on the how and why it occurs. Some suggestions are made to prevent its occurrence such as carrying an air speed instrument in the airplane
Was Singapore extraordinary? A comparative view of Singapore's saving performance 1965-99
Although the mere observation of saving aggregates might have us believe differently, this article argues that Singapore's sustained high saving performance was far from extraordinary once the country's particular circumstances are econometrically controlled for. Singapore's saving performance should therefore not be regarded as a mere blip in economic history. As a matter of fact, not the high saving rates in the late 1980s and 1990s, which usually attract the most attention, but rather the speed of transformation of the country's saving behaviour in the first years of independence is shown to be indeed extraordinary. Singapore was able to overcome its low initial saving performance much faster and much more strongly than could have been expected given its circumstances. --Asia,Singapore,saving rate,economic growth
Classical Motion in Random Potentials
We consider the motion of a classical particle under the influence of a
random potential on R^d, in particular the distribution of asymptotic
velocities and the question of ergodicity of time evolution.Comment: 45 pages, 3 figure
Orthospectra of Geodesic Laminations and Dilogarithm Identities on Moduli Space
Given a measured lamination on a finite area hyperbolic surface we consider a
natural measure Mon the real line obtained by taking the push-forward of the
volume measure of the unit tangent bundle of the surface under an intersection
function associated with the lamination. We show that the measure M gives
summation identities for the Rogers dilogarithm function on the moduli space of
a surface.Comment: 21 pages, 2 figure
Within-trial effects of stimulus-reward associations
While a globally energizing influence of motivation has long been appreciated in psychological research, a series of more recent studies has described motivational influences on specific cognitive operations ranging from visual attention, to cognitive control, to memory formation. In the majority of these studies, a cue predicts the potential to win money in a subsequent task, thus allowing for modulations of proactive task preparation. Here we describe some recent studies using tasks that communicate reward availability without such cues by directly associating specific task features with reward. Despite abolishing the cue-based preparation phase, these studies show similar performance benefits. Given the clear difference in temporal structure, a central question is how these behavioral effects are brought about, and in particular whether control processes can rapidly be enhanced reactively. We present some evidence in favor of this notion. Although additional influences, for example sensory prioritization of reward-related features, could contribute to the reward-related performance benefits, those benefits seem to strongly rely on enhancements of control processes during task execution. Still, for a better mechanistic understanding of reward benefits in these two principal paradigms (cues vs. no cues), more work is needed that directly compares the underlying processes. We anticipate that reward benefits can be brought about in a very flexible fashion depending on the exact nature of the reward manipulation and task, and that a better understanding of these processes will not only be relevant for basic motivation research, but that it can also be valuable for educational and psychopathological contexts
Switching dynamics of spatial solitary wave pixels
Separatrices and scaling laws in the switching dynamics of spatial solitary wave pixels are investigated. We show that the dynamics in the full model are similar to those in the plane-wave limit. Switching features may be indicated and explained by the motion of the (complex) solitary wave amplitude in the phase plane. We report generalization, into the domain of transverse effects, of the pulse area theorem for the switching process and a logarithmic law for the transient dynamics. We also consider, for what is the first time to our knowledge, phase-encoded address of solitary pixels and find that a near-square-wave temporal switching pattern is permitted without (transverse) cross switching
Effect of molecular relaxation processes on travelling wave solutions of sonic boom waveforms
Asymptotic and numerical analyses are presented for the travelling wave solution of the one-dimensional acoustic wave associated with the sonic boom, subject to thermoviscous dissipation and two molecular relaxation processes. Examination of how these relaxation processes affect the propagation of a weak shock is discussed in detail
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