scholarly journals A Relationship Between the Brightness Temperatures for Type III Bursts

1974 ◽  
Vol 57 ◽  
pp. 285-287
Author(s):  
D. B. Melrose
Keyword(s):  
Fundamental Frequency ◽  
Solar Phys ◽  
Second Harmonic ◽  
Intermediate Stage ◽  
Langmuir Waves ◽  
Type Iii ◽  
Brightness Temperatures ◽  
Two Stages

(Solar Phys.). The widely accepted emission mechanisms for type III bursts involve at least two stages. The first stage is the generation of Langmuir waves by the inferred stream of electrons. Emission at the fundamental frequency arises when these waves are scattered by thermal ions. Emission at the second harmonic arises when two Langmuir waves coalesce; however, the coalescence is possible only after an intermediate stage in which the distribution of Langmuir waves evolves towards isotropy due to scattering by thermal ions.

scholarly journals Polarization and Position Measurements of Type III Bursts

1980 ◽  
Vol 86 ◽  
pp. 315-322 ◽  
Author(s):  
S. Suzuki ◽  
G.A. Dulk ◽  
K. V. Sheridan
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Open Field ◽  
Langmuir Waves ◽  
Type Iii ◽  
Brightness Temperatures ◽  
Polarization Characteristics ◽  
Field Lines ◽  
Cosine Law ◽  
The Magnetic Field

We report on the positional and polarization characteristics of Type III bursts in the range 24–220 MHz as measured by the Culgoora radioheliograph, spectrograph and spectropolarimeter. Our study includes 997 bursts which are of two classes: fundamental-harmonic (F-H) pairs and “structureless” bursts with no visible F-H structure. In a paper published elsewhere (Dulk and Suzuki, 1979) we give a detailed description and include observations of source sizes, heights and brightness temperatures. Here we concentrate on the polarization of the bursts and the variation of polarization from centre to limb. The observed centre-to-limb decrease in polarization approximately follows a cosine law. This decrease is not as predicted by simple theory but is consistent with other observations which imply that open field lines from an active region diverge strongly. The observed o-mode polarization of harmonic radiation implies that the wave vectors of Langmuir waves are always parallel, within about 20°, to the magnetic field, while the constancy of H polarization with frequency implies that the ratio fB/fP, the Alfvén speed vA and the plasma beta are constant with height on the open field lines above an active region. Finally, we infer that some factor, in addition to the magnetic field strength, controls the polarization of F radiation.

scholarly journals Detection of Langmuir Solitons: Implications for Type III Burst Emission Mechanisms at 2ωPE

1996 ◽  
Vol 154 ◽  
pp. 195-198
Author(s):  
G. Thejappa ◽  
R.G. Stone ◽  
M.L. Goldstein
Keyword(s):  
Second Harmonic ◽  
Theoretical Models ◽  
Burst Source ◽  
Langmuir Waves ◽  
Type Iii ◽  
Source Regions ◽  
Envelope Solitons ◽  
Turbulence Regime ◽  
Solar Type ◽  
Langmuir Solitons

AbstractWe present the experimental verification of existing theoretical models of emission mechanisms of solar type III bursts at the second harmonic of the plasma frequency, ωpe. This study is based on the detection of Langmuir and envelope solitons by the Ulysses spacecraft inside three type III burst source regions. We show that the oscillating-two-stream instability, coherent radiation by Langmuir solitons and stochastic phase mixing of the Langmuir waves in the strong turbulence regime are the appropriate emission mechanisms at 2ωpe.

scholarly journals Evidence for four- and three-wave interactions in solar type III radio emissions

2013 ◽  
Vol 31 (8) ◽  
pp. 1417-1428 ◽  
Author(s):  
G. Thejappa ◽  
R. J. MacDowall ◽  
M. Bergamo
Keyword(s):  
Wave Packet ◽  
Second Harmonic ◽  
Wave Packets ◽  
Spectral Peak ◽  
Wave Number ◽  
Radio Bursts ◽  
Langmuir Waves ◽  
Type Iii ◽  
Primary Peak ◽  
Solar Type

Abstract. The high time resolution observations obtained by the STEREO/WAVES experiment show that in the source regions of solar type III radio bursts, Langmuir waves often occur as intense localized wave packets with short durations of only few ms. One of these wave packets shows that it is a three-dimensional field structure with WLneTe ~ 10−3, where WL is the peak energy density, and ne and Te are the electron density and temperature, respectively. For this wave packet, the conditions of the oscillating two-stream instability (OTSI) and supersonic collapse are satisfied within the error range of determination of main parameters. The density cavity, observed during this wave packet indicates that its depth, width and temporal coincidence are consistent with those of a caviton, generated by the ponderomotive force of the collapsing wave packet. The spectrum of each of the parallel and perpendicular components of the wave packet contains a primary peak at fpe, two secondary peaks at fpe ± fS and a low-frequency enhancement below fS, which, as indicated by the frequency and wave number resonance conditions, and the fast Fourier transform (FFT)-based tricoherence spectral peak at (fpe, fpe, fpe + fS, fpe − fS), are coupled to each other by the OTSI type of four-wave interaction (fpe is the local electron plasma frequency and fS is the frequency of ion sound waves). In addition to the primary peak at fpe, each of these spectra also contains a peak at 2fpe, which as indicated by the frequency and wave number resonance conditions, and the wavelet-based bicoherence spectral peak at (fpe, fpe), appears to correspond to the second harmonic electromagnetic waves generated as a result of coalescence of oppositely propagating sidebands excited by the OTSI. Thus, these observations for the first time provide combined evidence that (1) the OTSI and related strong turbulence processes play a significant role in the stabilization of the electron beam, (2) the coalescence of the oppositely propagating up- and down-shifted daughter Langmuir waves excited by the OTSI probably is the emission mechanism of the second harmonic radiation, and (3) the Langmuir collapse follows the route of OTSI in some of the type III radio bursts.

scholarly journals 'Plasma Emission' without Langmuir Waves

1982 ◽  
Vol 35 (1) ◽  
pp. 67 ◽  
Author(s):  
DB Melrose
Keyword(s):  
Second Harmonic ◽  
Parametric Instability ◽  
The Other ◽  
Plasma Emission ◽  
Sound Waves ◽  
S Wave ◽  
Langmuir Waves ◽  
Transverse Waves ◽  
Type Iii ◽  
T Wave

Recent observations have confirmed that the level of Langmuir waves associated with type III streams of electrons in the interplanetary medium is usually too low to account for the observed radio emission by the accepted 'plasma emission' processes, and it has been suggested that emission mechanisms which do not require Langmuir waves should be explored. Four such mechanisms are discussed. One is a parametric instability leading directly to second-harmonic emission; it is found inapplicable under conditions of interest here. The other three processes all involve ion-sound turbulence. One which is known in a different context is turbulent bremsstrahlung. Turbulent bremsstrahlung of transverse waves is found to compare unfavourably with the other two processes, which are scattering of an ion-sound (s) wave into a transverse (t) wave and double emission of both waves simultaneously. These latter two processes are related by a crossing symmetry and are treated together with the following results: (i) The processes become greatly enhanced when the beat (w�w', k�k') between the t wave and the s wave nearly satisfies the dispersion relation for Langmuir (I) waves. (ii) A bump-in-the-tail instability (due to electrons with dF(v)/dv > 0) can cause the transverse waves to grow due to double emission; this growth has been likened to a freeelectron maser. (iii) The familiar bump-in-the-tail instability for resonant I waves can be suppressed by the ion-sound waves, and the double-emission instability then takes over with about the same growth rate as the original I-wave instability. (iv) The conditions for the double-emission instability to occur are probably satisfied at least some of the time for type III streams. It is concluded that although 'plasma emission' without Langmuir waves may be possible in principle, it is unlikely to play any role in type III bursts.

scholarly journals Receptivity of Boundary Layer over a Blunt Wedge due to Freestream Pulse Disturbances at Mach 6

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Jianqiang Shi ◽  
Xiaojun Tang ◽  
Zhenqing Wang ◽  
Mingfang Shi ◽  
Wei Zhao
Keyword(s):  
Boundary Layer ◽  
Fundamental Frequency ◽  
High Frequency ◽  
Pulse Wave ◽  
Second Harmonic ◽  
Acoustic Pulse ◽  
Disturbance Wave ◽  
Acoustic Disturbances ◽  
Disturbance Frequency ◽  
Harmonic Components

Direct numerical simulation (DNS) of a hypersonic compressible flow over a blunt wedge with fast acoustic disturbances in freestream is performed. The receptivity characteristics of boundary layer to freestream pulse acoustic disturbances are numerically investigated at Mach 6, and the frequency effects of freestream pulse wave on boundary layer receptivity are discussed. Results show that there are several main disturbance mode clusters in boundary layer under acoustic pulse wave, and the number of main disturbance clusters decreases along the streamwise. As disturbance wave propagates from upstream to downstream direction, the component of the modes below fundamental frequency decreases, and the component of the modes above second harmonic components increases quickly in general. There are competition and disturbance energy transfer between different boundary layer modes. The nose boundary layer is dominated by the nearby mode of fundamental frequency. The number of the main disturbance mode clusters decreases as the freestream disturbance frequency increases. The frequency range with larger growth narrows along the streamwise. In general, the amplitudes of both fundamental mode and harmonics become larger with the decreasing of freestream disturbance frequency. High frequency freestream disturbance accelerates the decay of disturbance wave in downstream boundary layer.

scholarly journals Second-Order Nonlinearity in Triangular Lattice Perforated Gold Film due to Surface Plasmas Resonance

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
Renlong Zhou ◽  
Xiaoshuang Chen ◽  
Yingyi Xiao ◽  
Bingju Zhou ◽  
Lingxi Wu ◽  
...  
Keyword(s):  
Fundamental Frequency ◽  
Triangular Lattice ◽  
Gold Film ◽  
Second Harmonic ◽  
Resonance Effect ◽  
Second Order ◽  
Square Lattice ◽  
Frequency Wave ◽  
Surface Plasmas ◽  
Second Order Nonlinearity

We have studied the excitation second-order nonlinearity through a triangular lattice perforated gold film instead of square lattice in many papers. Under the excitation of surface plasmas resonance effect, the second order nonlinearity exists in the noncentrosymmetric split-ring resonators arrays. Reflection of fundamental frequency wave through a triangular lattice perforated gold film is obtained. We also described the second harmonic conversion efficiencies in the second order nonlinear optical process with the spectra. Moreover, the electric field distributions of fundamental frequency above the gold film region are calculated. The light propagation through the holes results in the enhancement of the second order nonlinearity including second harmonic generation as well as the sum (difference) frequency generation.

A Phase Controlled Technology on Fundamental Frequency and Second-Harmonic Generation Laser Wavefront

2009 ◽  
Vol 36 (8) ◽  
pp. 2099-2103
Author(s):  
雷亮 Lei Liang ◽  
陈丽 Chen Li ◽  
胡正发 Hu Zhengfa ◽  
周金运 Zhou Jinyun ◽  
胡义华 Hu Yihua
Keyword(s):  
Second Harmonic Generation ◽  
Fundamental Frequency ◽  
Harmonic Generation ◽  
Second Harmonic

scholarly journals Source Structure in Metre-Wave Type V Solar Bursts

1974 ◽  
Vol 57 ◽  
pp. 235-238
Author(s):  
N. R. Labrum ◽  
R. A. Duncan
Keyword(s):  
Second Harmonic ◽  
Magnetic Loop ◽  
Plasma Waves ◽  
Trapping Region ◽  
Type Iii ◽  
Coronal Magnetic Loop ◽  
Field Lines ◽  
Set Up ◽  
Type V ◽  
Open Magnetic Field

(Astrophys. Letters). The type V burst has been defined as a wideband continuum which sometimes appears for a minute or so following a type III burst (Wild et al., 1959b). It is now generally accepted that type III bursts arise from plasma waves set up by electrons escaping with velocity ~c/3 along open magnetic field lines (Wild et al., 1959a; Stewart, 1965); the most widely accepted explanation of type V continua is that they arise from plasma waves set up by electrons of similar velocity which have become trapped in a coronal magnetic loop (Weiss and Stewart, 1975). On this hypothesis the plasma waves are set up by two opposing electron streams in the trapping region, and from this consideration Zheleznyakov and Zaitsev (1968) have concluded that type V emission should be predominantly at the second harmonic of the local plasma frequency. In this paper we describe and discuss some two-dimensional observations of source positions of type III–V events which were obtained at 80 MHz on the Culgoora radioheliograph.

Efficient two-stage sequential arrays of proof of concept studies for pharmaceutical portfolios

2020 ◽  
pp. 096228022095817
Author(s):  
Linchen He ◽  
Linqiu Du ◽  
Zoran Antonijevic ◽  
Martin Posch ◽  
Valeriy R Korostyshevskiy ◽  
...  
Keyword(s):  
Cost Effectiveness ◽  
Cost Benefit ◽  
Cost Effective ◽  
Cost Ratio ◽  
Proof Of Concept ◽  
Type Iii ◽  
Benefit Cost Ratio ◽  
Stage 1 ◽  
Two Stages ◽  
Benefit Cost

Previous work has shown that individual randomized “proof-of-concept” (PoC) studies may be designed to maximize cost-effectiveness, subject to an overall PoC budget constraint. Maximizing cost-effectiveness has also been considered for arrays of simultaneously executed PoC studies. Defining Type III error as the opportunity cost of not performing a PoC study, we evaluate the common pharmaceutical practice of allocating PoC study funds in two stages. Stage 1, or the first wave of PoC studies, screens drugs to identify those to be permitted additional PoC studies in Stage 2. We investigate if this strategy significantly improves efficiency, despite slowing development. We quantify the benefit, cost, benefit-cost ratio, and Type III error given the number of Stage 1 PoC studies. Relative to a single stage PoC strategy, significant cost-effective gains are seen when at least one of the drugs has a low probability of success (10%) and especially when there are either few drugs (2) with a large number of indications allowed per drug (10) or a large portfolio of drugs (4). In these cases, the recommended number of Stage 1 PoC studies ranges from 2 to 4, tracking approximately with an inflection point in the minimization curve of Type III error.

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