21 research outputs found
Experimental observation of nonlinear Thomson scattering
A century ago, J. J. Thomson showed that the scattering of low-intensity
light by electrons was a linear process (i.e., the scattered light frequency
was identical to that of the incident light) and that light's magnetic field
played no role. Today, with the recent invention of ultra-high-peak-power
lasers it is now possible to create a sufficient photon density to study
Thomson scattering in the relativistic regime. With increasing light intensity,
electrons quiver during the scattering process with increasing velocity,
approaching the speed of light when the laser intensity approaches 10^18
W/cm^2. In this limit, the effect of light's magnetic field on electron motion
should become comparable to that of its electric field, and the electron mass
should increase because of the relativistic correction. Consequently, electrons
in such high fields are predicted to quiver nonlinearly, moving in figure-eight
patterns, rather than in straight lines, and thus to radiate photons at
harmonics of the frequency of the incident laser light, with each harmonic
having its own unique angular distribution. In this letter, we report the first
ever direct experimental confirmation of these predictions, a topic that has
previously been referred to as nonlinear Thomson scattering. Extension of these
results to coherent relativistic harmonic generation may eventually lead to
novel table-top x-ray sources.Comment: including 4 figure
Pacific island regional preparedness for El Niño
The El Niño Southern Oscillation (ENSO) cycle is often blamed for disasters in Pacific island communities. From a disaster risk reduction (DRR) perspective, the challenges with the El Niño part of the ENSO cycle, in particular, are more related to inadequate vulnerability reduction within development than to ENSO-induced hazard influences. This paper analyses this situation, filling in a conceptual and geographic gap in El Niño-related research, by reviewing El Niño-related preparedness (the conceptual gap) for Pacific islands (the geographic gap). Through exploring El Niño impacts on Pacific island communities alongside their vulnerabilities, resiliences, and preparedness with respect to El Niño, El Niño is seen as a constructed discourse rather than as a damaging phenomenon, leading to suggestions for El Niño preparedness as DRR as part of development. Yet the attention which El Niño garners might bring resources to the Pacific region and its development needs, albeit in the short term while El Niño lasts. Conversely, the attention given to El Niño could shift blame from underlying causes of vulnerability to a hazard-centric viewpoint. Instead of focusing on one hazard-influencing phenomenon, opportunities should be created for the Pacific region to tackle wider DRR and development concerns
Fast multidimensional ensemble empirical mode decomposition for the analysis of big spatio-temporal datasets
Distribution and statistics of African mesoscale convective weather systems based on the ISCCP Meteosat imagery
This paper provides for the first time an objective short-term (8
yr) climatology of African convective weather systems based on satellite
imagery. Eight years of infrared International Satellite Cloud Climatology
Project-European Space Agency's Meteorological Satellite (ISCCP-Meteosat)
satellite imagery has been analyzed using objective feature identification,
tracking, and statistical techniques for the July, August, and September
periods and the region of Africa and the adjacent Atlantic ocean.
This allows various diagnostics to be computed and used to study
the distribution of mesoscale and synoptic-scale convective weather
systems from mesoscale cloud clusters and squall lines to tropical
cyclones. An 8-yr seasonal climatology (1983-90) and the seasonal
cycle of this convective activity are presented and discussed. Also
discussed is the dependence of organized convection for this region,
on the orography, convective, and potential instability and vertical
wind shear using European Centre for Medium-Range Weather Forecasts
reanalysis data
Spray deposition process study of SnO 2 silicon solar cells using orthogonal experimental design
With the "orthogonal experimental design" (OED), the dependence of conductivity and transparency of tin oxide films and open circuit voltage V oc of SIS solar cells on the spray deposition process factors was studied. The OED technique was found to be a powerful method for realizing the best factor combination. Using OED, curves were obtained which clearly depict the effects of each factor on the SIS characteristics. The results of the experiments also illustrate exactly which variation in fabrication technique most affects the sheet resistance, V oc, and film transparency. Under the optimal combination of conditions, a thin film doped with NH 4F was obtained, with about 90% transmission and a sheet resistance of about 80 Ω/□, along with an SIS structure with a V oc of about 0.61 V. © 1985.link_to_subscribed_fulltex