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11.
Here we report the statistical analysis of 160 isolated decimetric type III bursts, a majority of them (74%) having central frequency above 1000 MHz, observed in 8 flares by the spectrometer Phoenix. The most important finding of the detailed analysis is: 67% of all the bursts are reverse slope, 38% normal and 5% bi-directional. Also, we obtained the following results: (a) the best fits for the average half power duration and for the average drift rate as a function of frequency are given by t1/2=1.7×104f–0.60and /df/dt|=(0.09±0.03)f(1.35 ± 0.10), respectively; (b) the frequency range of most of the type III bursts is less than 250 MHz; (c) the number of bursts decreases with increasing starting frequency and flux; (d) peak flux decreases with increasing frequency. The relations obtained fit well for higher frequency observations. Assuming an improved density model and type III emission at 2ndharmonic, the beam parameters of type III bursts are determined. 相似文献
12.
A wide-band digital decimetric spectroscope is in the process of development at INPE (Brazil), in conjunction with a 9-m diameter polar mounted antenna. Initially, this spectroscope was operating over a narrow-band 1.6 ± 0.05 MHz in an analogue mode. Here we report a slow drifting 5.0 MHz s-1, narrow-band 1630-1580 MHz, split frequency solar burst lasting for about 15 s, observed on 15 June, 1991. The separation between the split components is 30 MHz, and the upper split frequency component is more intense than the lower split frequency component. These observed characteristics favour the hypothesis of conversion of plasma waves by combinational scattering on upgoing ion-sound waves in a magnetic loop. Existing strong electron density gradients across the magnetic field in the source region will reduce the free-free absorption of radiation at the fundamental frequency. In order to explain the observed temporal characteristics of the upper and lower split frequency components, the radiation has to propagate at some angle to the electron density gradient in the source region. Estimated physical parameters of the source and exciters are as follows: (i) maximum source size (height) 2 × 107 cm; (ii) velocity and length of ion-sound pulse 3.1 × 106 cm s-1 and 5 × 107 cm, respectively, and (iii) velocity of the exciter of plasma waves (electron or proton beam) 5 × 108 cm s-1.On leave from the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. 相似文献
13.
In previous attempts to show one-to-one correlation between type III bursts and X-ray spikes, there have been ambiguities as to which of several X-ray spikes are correlated with any given type III burst. Here, we present observations that show clear associations of X-ray bursts with RS type III bursts between 16:46 UT and 16:52 UT on July 9, 1985. The hard X-ray observations were made at energies above 25 keV with HXRBS on SMM and the radio observations were made at 1.63 GHz using the 13.7m Itapetinga antenna in R and L polarization with a time resolution of 3 ms. Detailed comparison between the hard X-ray and radio observations shows:
- In at least 13 cases we can identify the associated hard X-ray and decimetric RS bursts.
- On average, the X-ray peaks were delayed from the peak of the RS bursts at 1.6 GHz by ~ 400 ms although a delay as long as 1 s was observed in one case.
14.
Kopparapu Vijaya Kumar Chakradhar Chavan Sariput Sawant K. Naga Raju Prachiti Kanakdande Sangita Patode Krishna Deshpande S. K. G. Krishnamacharyulu T. Vaideswaran V. Balaram 《Contributions to Mineralogy and Petrology》2010,159(6):839-862
Spatial and temporal variations in the geochemistry of an extrusive basaltic section of Deccan traps record progressive changes
in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present
work we have carried out detailed field, petrographic, density and magnetic susceptibility, and geochemical investigations
on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow
magma chambers in CFB magmatism. Four formations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed–Ambajogai
area with increasing elevation. Our studies indicate that: (1) the Karanja Formation represents a major magma addition, as
indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al2O3, Na2O, K2O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimilation fractional crystallization, crystal-laden
magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence
of olivine gabbro–leucogabbro–oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber
within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration
for the Gangakhed–Ambajogai section basalts is ~2 kbar (~6 km depth); (5) petrophysical parameters act as proxies for magmatic
processes; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the
DVP; (7) parental basalts to some of the red boles, considered as formation boundaries, might represent small degree partial
melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber
processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance
of mapping specific stratigraphic intervals in limited areas to understand mantle and magma chamber processes relevant to
CFB magmatism. 相似文献
15.
Zebrafish (Danio rerio) genetic screens allow isolation of a wide array of problems in vertebrate biology. The effects of base analogues 5-bromouracil
and 6-aminopurine on the development of zebrafish embryos are reported for the first time in this study. The early development
of the zebrafish embryos was little affected by 5-bromouracil and 6-aminopurine, while the late development (organogenesis)
was significantly impaired. Embryos exposed to 5-bromouracil mainly showed curled tail, wavy body, golden pigmentation and
the mouth with protruding lower jaw. 6-aminopurine-treated embryos had defective anterior structures, curled tails and wavy
body. RAPD analysis showed that the majority of 5-bromouracil- and 6-aminopurine-treated larvae and fish shared banding patterns
in common with the control, suggesting that most mutagenesis induced by these agents are point mutations. However, some fish
derived from 5-bromouracil-treated embryos had golden (gol) pigmentation; and RAPD analysis revealed that their band patterns differed from those of the control. Possibly, 5-bromouracil
can occasionally cause relatively extensive changes in the fish genome. The results of this study may provide valuable help
for detailed studies of mutagenesis.
This work was supported by Ministry of Science and Technology (MOST) of China (G 1999012005). 相似文献
16.
The mechanism of the double plasma resonance has been applied to the dot-like emission structures observed in the decimetric band. In particular, the existence of dot-emissions on definite trajectories in the dynamic spectra offers a rare opportunity to delineate the details of the double resonance mechanism as well as the diagnostics of the radio source and the ambient corona. The modeling of the chains of dots points to the excitation of the electron Bernstein modes predominantly at the second cyclotron harmonic and their subsequent coalescence to produce the observed dot-emissions. The coalescence process doubles the cyclotron harmonic number and thereby reduces the cyclotron absorption significantly. The discrete nature of the emissions results from the finite extent of the resonant region due to the presence of inhomogeneities. The determination of the relative scales of spatial variation of the magnetic field and the electron density in the region of the decimetric emission is particularly desirable as it has important consequences for the energy release, acceleration processes and the configuration of the participating plasma structures. 相似文献
17.
H. S. Sawant R. Ramesh J. R. Cecatto C. Faria F. C. R. Fernandes R. R. Rosa M. C. Andrade S. Stephany L. B. T. Cividanes C. A. I. Miranda L. C. L. Botti J. W. S. V. Boas J. H. Saito C. E. Moron N. D. Mascarenhas K. R. Subramanian M. S. Sundararajan E. Ebenezer M. R. Sankararaman 《Solar physics》2007,242(1-2):213-220
An East – West, one-dimensional radio interferometer array consisting of five parabolic dish antennas has been set up at Cachoeira
Paulista (longitude 45°0′20″ W, latitude 22°41′19″ S) for observations of the Sun and some of the strong sidereal sources
by the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil. This is Phase-I of the proposed Brazilian Decimetric Array
and can be operated at any frequency in the range 1.2 – 1.7 GHz. The instrument has been in operation since November 2004
onwards at 1.6 GHz. The angular and temporal resolutions at this frequency are ∼3′ and 100 ms, respectively. Details of the
array, analog/digital receiver system, and a preliminary East – West one-dimensional solar image at the 1.6 GHz are presented
in this paper. 相似文献
18.
19.
Sawant H.S. Subramanian K.R. Faria C. Fernandes F.C.R. Sobral J.H.A. Cecatto J.R. Rosa R.R. Vats H.O. Neri J.A.C.F. Alonso E.M.B. Mesquita F.P.V. Portezani V.A. Martinon A.R.F. 《Solar physics》2001,200(1-2):167-176
Digital, decimetric (200–2500 MHz) Brazilian Solar Spectroscope (BSS) with high time (10–1000 ms) and frequency (1–10 MHz) resolution is in regular operation since April, 1998, at National Space Research Institute (INPE) at São José dos Campos, Brazil. BSS operates in conjunction with a 9-m diameter polar mounted antenna. It allows to select suitable observing frequency range, frequency and time resolutions and data can be digitized up to 100 channels. BSS has capabilities of quasi-real time display of the ongoing dynamic spectra of the solar activity that enables the observer to modify observational parameters so as to suit a specific type of activity such as spikes and improve the quality of data acquisition and storage. Minimum detectable flux density of the spectroscope, for different combinations of the observational parameters, is 3 s.f.u. Observations are carried out routinely from 11 UT to 19 UT. Necessary software for data acquisition and reductions has been developed in IDL 5.3 environment. Data are available in FITS and ASCII formats. Absolute timing accuracy of the station is less than 3 ms. Here, we present examples of the bursts which have been recorded by BSS and available display facilities. 相似文献
20.
Short-Term Periodicities in the Time Series of Solar Radio Emissions at Different Solar Altitudes 总被引:1,自引:0,他引:1
A spectral analysis of the time series of daily values of 12 parameters, namely, ten solar radio emissions in the range 275–1755 MHz, 2800 MHz solar radio flux, and sunspot numbers for six continuous intervals of 132 values each during June 1997–July 1999 showed considerable differences from one interval to the next, indicating a nonstationary nature. A 27-day periodicity was noticed in Interval 2 (26.8 days), 3 (27.0 days), 5 (25.5 days), 6 (27.0 days). Other periodicities were near 11.4, 12.3, 13.3, 14.5, 15.5, 16.5, 35, 40, 50–70 days. Periodicities were very similar in a large vertical span of the coronal region corresponding to 670–1755 MHz. Above this region, the homogeneity disappeared. Below this region, there were complications and distortions due to localized solar surface phenomena. 相似文献