1,237 research outputs found
Tunable Circularly Polarized Terahertz Radiation from Magnetized Gas Plasma
It is shown, by simulation and theory, that circularly or elliptically
polarized terahertz radiation can be generated when a static magnetic (B) field
is imposed on a gas target along the propagation direction of a two-color laser
driver. The radiation frequency is determined by
, where is the
plasma frequency and is the electron cyclotron frequency. With the
increase of the B field, the radiation changes from a single-cycle broadband
waveform to a continuous narrow-band emission. In high-B-field cases, the
radiation strength is proportional to . The B field
provides a tunability in the radiation frequency, spectrum width, and field
strength.Comment: 6 pages, 5 figure
Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects
We investigate how next-generation laser pulses at 10 PW 200 PW interact
with a solid target in the presence of a relativistically underdense preplasma
produced by amplified spontaneous emission (ASE). Laser hole boring and
relativistic transparency are strongly restrained due to the generation of
electron-positron pairs and -ray photons via quantum electrodynamics
(QED) processes. A pair plasma with a density above the initial preplasma
density is formed, counteracting the electron-free channel produced by the hole
boring. This pair-dominated plasma can block the laser transport and trigger an
avalanche-like QED cascade, efficiently transfering the laser energy to
photons. This renders a 1--scalelength, underdense preplasma
completely opaque to laser pulses at this power level. The QED-induced opacity
therefore sets much higher contrast requirements for such pulse in solid-target
experiments than expected by classical plasma physics. Our simulations show for
example, that proton acceleration from the rear of a solid with a preplasma
would be strongly impaired.Comment: 5 figure
A discussion and plans for remodeling the hydraulic lighting plant at Chapman, Kansas
Citation: Gibbon, C. T. and Simpson, Jay W. A discussion and plans for remodeling the hydraulic lighting plant at Chapman, Kansas. Senior thesis, Kansas State Agricultural College, 1908.Introduction: When a hydro-electric generating plant it to be designed and installed the problem must be taken up with the greatest possible tact and detailed consideration. The first item of importance which must be taken into consideration is the probable amount of power that can be sold and the competition which is to be met in the sale
Lagrangian analysis of alignment dynamics for isentropic compressible magnetohydrodynamics
After a review of the isentropic compressible magnetohydrodynamics (ICMHD)
equations, a quaternionic framework for studying the alignment dynamics of a
general fluid flow is explained and applied to the ICMHD equations.Comment: 12 pages, 2 figures, submitted to a Focus Issue of New Journal of
Physics on "Magnetohydrodynamics and the Dynamo Problem" J-F Pinton, A
Pouquet, E Dormy and S Cowley, editor
Relativistic Attosecond Electron Bunches from Laser-Illuminated Droplets
The generation of relativistic attosecond electron bunches is observed in
three-dimensional, relativistic particle-in-cell simulations of the interaction
of intense laser light with droplets. The electron bunches are emitted under
certain angles which depend on the ratios of droplet radius to wavelength and
plasma frequency to laser frequency. The mechanism behind the multi-MeV
attosecond electron bunch generation is investigated using Mie theory. It is
shown that the angular distribution and the high electron energies are due to a
parameter-sensitive, time-dependent local field enhancement at the droplet
surface.Comment: 4 pages, 5 figures, REVTeX-styl
Lagrangian particle paths and ortho-normal quaternion frames
Experimentalists now measure intense rotations of Lagrangian particles in
turbulent flows by tracking their trajectories and Lagrangian-average velocity
gradients at high Reynolds numbers. This paper formulates the dynamics of an
orthonormal frame attached to each Lagrangian fluid particle undergoing
three-axis rotations, by using quaternions in combination with Ertel's theorem
for frozen-in vorticity. The method is applicable to a wide range of Lagrangian
flows including the three-dimensional Euler equations and its variants such as
ideal MHD. The applicability of the quaterionic frame description to Lagrangian
averaged velocity gradient dynamics is also demonstrated.Comment: 9 pages, one figure, revise
Sistemas GuÃa regionales en funcionamiento para crecidas repentinas. Casos prácticos: Croacia y Zimbabwe
ILIAS Ion and Laser beam Interaction and Application Studies : A scientific portrait of the PHELIX theory group
Is overweight and obesity in 9–10-year-old children in Liverpool
Objectives: To determine whether weight problems in children (overweight, obesity and overweight or obesity) were related to deprivation indices when attributed only according to electoral ward of the school attended. To determine whether children
with weight problems were more likely to be found in some wards rather than others, and to compare the distribution for boys and girls.
Design: Retrospective, cross-sectional, observational study.
Setting: One hundred and six primary schools from all parts of Liverpool city.
Subjects: Five cohorts of 9–10-year-old children between 1998 and 2003.
Main outcome measures: Body mass index (BMI) for each child to estimate proportions overweight, obese and overweight or obese according to international criteria.
Results: Between January 1998 and March 2003, the heights and weights of 7902 boys and 7514 girls were measured and BMI calculated. The prevalence of boys and girls categorised as overweight or obese was very high (1620, 20.6% and 1909, 25.7%,
respectively). Prevalence was not related to deprivation and varied between wards only for the girls; some wards had very different prevalence rates for boys and girls (Picton: 59 boys, 23.4%; 106 girls, 36.6%). The most deprived ward did not have a
remarkable prevalence of overweight or obesity (Speke: 32 boys, 15.3%; 40 girls, 19.8%).
Conclusions: Obesity is a major problem and requires urgent action but targeting intervention on the basis of administrative areas may be very wasteful. Different factors seem to lead to obesity in boys and girls, and attention should be paid to the
role of the physical environment
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