783 research outputs found
Two-Stream Instability Model With Electrons Trapped in Quadrupoles
We formulate the theory of the two-stream instability (e-cloud instability)
with electrons trapped in quadrupole magnets. We show that a linear instability
theory can be sensibly formulated and analyzed. The growth rates are
considerably smaller than the linear growth rates for the two-stream
instability in drift spaces and are close to those actually observed
First record of the Mediterranean Gecko (Hemidactylus turcicus) from Hudspeth County, Texas, USA, with an updated statewide distribution map for the species
Interspecific amplexus of a Gulf Coast Toad, Incilius nebulifer (Girard 1854), and a Hurter's Spadefoot, Scaphiopus hurterii (Strecker 1910), in Bastrop County, Texas, USA)
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Prevention of anxiety among at-risk children: a systematic review and meta-analysis
Background
Anxiety disorders are common, often start in childhood and run a chronic course. As such there is a need for effective prevention.
Methods
We conducted a systematic review and meta-analyses of randomized, controlled trials to prevent the onset of anxiety disorders in ‘at risk’ young people. Diagnostic and symptom outcomes were examined. Putative moderators were tested as was publication bias.
Results
We included 16 trials (2545 young people). Two trials reported diagnostic outcomes, and significant effects were found for these at end-of-programme (RR = .09, 95%CI = .02 to .16), 6- (RR = .17, 95%CI = .06 to .27) and 12-month (RR = .31, 95%CI .17 to .45) follow-ups. Based on 16 trials, improved anxiety symptoms were significant compared to nonattention controls only, with small effect sizes reported by young people at the end-of-programmes, 6- and 12-month follow-ups; and by parents at the end of the programmes and 12-, but not 6-, month follow-ups. There was no evidence of significant moderation or publication bias.
Conclusions
Fourteen studies included children and young people who presented with elevated anxiety symptoms, but anxiety disorder was not ruled out in the participants in these studies. Hence, these studies might be reporting results of mixed prevention/early intervention programmes. Prevention programmes that target developmental risk factors, not only disorder maintaining factors, appear most promising. The clinically meaningful impact of anxiety disorder prevention programmes remains unknown
Observed Effect of Magnetic Fields on the Propagation of Magnetoacoustic Waves in the Lower Solar Atmosphere
We study Hinode/SOT-FG observations of intensity fluctuations in Ca II H-line
and G-band image sequences and their relation to simultaneous and co-spatial
magnetic field measurements. We explore the G-band and H-line intensity
oscillation spectra both separately and comparatively via their relative phase
differences, time delays and cross-coherences. In the non-magnetic situations,
both sets of fluctuations show strong oscillatory power in the 3 - 7 mHz band
centered at 4.5 mHz, but this is suppressed as magnetic field increases. A
relative phase analysis gives a time delay of H-line after G-band of 20\pm1 s
in non-magnetic situations implying a mean effective height difference of 140
km. The maximum coherence is at 4 - 7 mHz. Under strong magnetic influence the
measured delay time shrinks to 11 s with the peak coherence near 4 mHz. A
second coherence maximum appears between 7.5 - 10 mHz. Investigation of the
locations of this doubled-frequency coherence locates it in diffuse rings
outside photospheric magnetic structures. Some possible interpretations of
these results are offered.Comment: 19 pages, 6 figure
Classical aspects of Hawking radiation verified in analogue gravity experiment
There is an analogy between the propagation of fields on a curved spacetime
and shallow water waves in an open channel flow. By placing a streamlined
obstacle into an open channel flow we create a region of high velocity over the
obstacle that can include wave horizons. Long (shallow water) waves propagating
upstream towards this region are blocked and converted into short (deep water)
waves. This is the analogue of the stimulated Hawking emission by a white hole
(the time inverse of a black hole). The measurements of amplitudes of the
converted waves demonstrate that they appear in pairs and are classically
correlated; the spectra of the conversion process is described by a
Boltzmann-distribution; and the Boltzmann-distribution is determined by the
determined by the change in flow across the white hole horizon.Comment: 17 pages, 10 figures; draft of a chapter submitted to the proceedings
of the IX'th SIGRAV graduate school: Analogue Gravity, Lake Como, Italy, May
201
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