3,131 research outputs found
Multilevel Analysis of Oscillation Motions in Active Regions of the Sun
We present a new method that combines the results of an oscillation study
made in optical and radio observations. The optical spectral measurements in
photospheric and chromospheric lines of the line-of-sight velocity were carried
out at the Sayan Solar Observatory. The radio maps of the Sun were obtained
with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the
sunspots were analyzed to study the oscillation processes in the
chromosphere-corona transition region in the layer with magnetic field B=2000
G. A high level of instability of the oscillations in the optical and radio
data was found. We used a wavelet analysis for the spectra. The best
similarities of the spectra of oscillations obtained by the two methods were
detected in the three-minute oscillations inside the sunspot umbra for the
dates when the active regions were situated near the center of the solar disk.
A comparison of the wavelet spectra for optical and radio observations showed a
time delay of about 50 seconds of the radio results with respect to optical
ones. This implies a MHD wave traveling upward inside the umbral magnetic tube
of the sunspot. Besides three-minute and five-minute ones, oscillations with
longer periods (8 and 15 minutes) were detected in optical and radio records.Comment: 17 pages, 9 figures, accepted to Solar Physics (18 Jan 2011). The
final publication is available at http://www.springerlink.co
How much laser power can propagate through fusion plasma?
Propagation of intense laser beams is crucial for inertial confinement
fusion, which requires precise beam control to achieve the compression and
heating necessary to ignite the fusion reaction. The National Ignition Facility
(NIF), where fusion will be attempted, is now under construction. Control of
intense beam propagation may be ruined by laser beam self-focusing. We have
identified the maximum laser beam power that can propagate through fusion
plasma without significant self-focusing and have found excellent agreement
with recent experimental data, and suggest a way to increase that maximum by
appropriate choice of plasma composition with implication for NIF designs. Our
theory also leads to the prediction of anti-correlation between beam spray and
backscatter and suggests the indirect control of backscatter through
manipulation of plasma ionization state or acoustic damping.Comment: 15 pages, 4 figures, submitted to Plasma Physics and Controlled
Fusio
Critical Strain Region Evaluation of Self-Assembled Semiconductor Quantum Dots
A novel peak finding method to map the strain from high resolution transmission electron micrographs, known as the Peak Pairs method, has been applied to In(Ga) As/AlGaAs quantum dot (QD) samples, which present stacking faults emerging from the QD edges. Moreover, strain distribution has been simulated by the finite element method applying the elastic theory on a 3D QD model. The agreement existing between determined and simulated strain values reveals that these techniques are consistent enough to qualitatively characterize the strain distribution of nanostructured materials. The correct application of both methods allows the localization of critical strain zones in semiconductor QDs, predicting the nucleation of defects, and being a very useful tool for the design of semiconductor device
Dielectric properties of BiB3O6 crystal in the sub-THz range
We present the thorough studies of dielectric properties of BiB3O6 (BIBO) crystal in the sub-THz range. We observe a large birefringence Δn = nZ −nX = 1.5 and the values of absorption coefficients of all three axes to be less than 0.5 cm−1. The difference from visible range in angle ϕ between the axes z and X is found to be more than 6°. The simulated phase-matching curves show the optimal value of the angle θ to be around 25.5°±1° for an efficient millimeter-wave generation under the pump of 1064 nm laser radiation
- …