排序方式： 共有29条查询结果，搜索用时 31 毫秒
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A. V. Megn S. L. Rashkovskiĭ V. A. Shepelev G. A. Inyutin A. I. Brazhenko V. G. Bulatsen R. V. Vashchishin V. V. Koshevoĭ A. B. Lozinskiĭ N. E. Kassim 《Astronomy Reports》2006,50(9):692-698
Results of radio interferometric observations of the quasar 3C 380 carried out on the URAN interferometers at decameter wavelengths and on the aperture synthesis radio telescope VLA at meter wavelengths are reported. The spectral index of an extended lobe about 10″ in size is considerably lower than at decimeter wavelengths. Below ～ 100 MHz, the ratio of the emission from the compact components associated with hot spots in the radio lobe to the total flux of the source decreases due to synchrotron self-absorption at hot spots, whose flux density at 20 MHz does not exceed 65 Jy. A halo with a full width at a half-maximum of about 40″ was detected, whose angular extent considerably exceeds the total source size measured at shorter wavelengths. 相似文献
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The astrophysical S-factor of the experimental cross section data of the main reactions in the proton–proton chain, i.e. 3He(3He,2p)4He, 3He(4He,γ)7Be and 7Be(p,γ)8B, are reanalyzed by using the exact tunneling probability in nuclear reactions. Our goal is to test this treatment in finding the reaction rate per pair for non-resonant reactions. At low temperatures, the exact treatment is identical to the standard formalism but diverges at higher temperatures. 相似文献
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K.P. Stewart B.C. Hicks P.S. Ray P.C. Crane N.E. Kassim R.F. Bradley W.C. Erickson 《Planetary and Space Science》2004,52(15):1351-1355
We are developing and testing active baluns and electrically short dipoles for possible use as the primary wide band receiving elements in the low-frequency array (LOFAR) for long wavelength radio astronomy. Several dipoles of various designs and dimensions have been built and tested. Their useful range occurs when the dipole arms are approximately to one wavelength long and the feedpoint is less than wavelength above ground. An eight-element NRL LOFAR test array (NLTA) interferometer has been built and fringes have been observed from the brightest celestial sources in the frequency range from 10 to 50 MHz. The antenna temperatures vary from about 10% to 100% of the average brightness temperature of the galactic background. With these parameters it is easy to make the amplifier noise levels low enough that final system temperature is dominated by the galactic background. 相似文献
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N.E. Kassim T.J.W. Lazio P.S. Ray P.C. Crane B.C. Hicks K.P. Stewart A.S. Cohen W.M. Lane 《Planetary and Space Science》2004,52(15):1343-1349
We present an overview of the low-frequency array (LOFAR) that will open a window on one of the last and most poorly explored regions of the electromagnetic spectrum. LOFAR will be a large (baselines up to 400 km), low-frequency aperture synthesis array with large collecting area ( at ) and high resolution (1.5″ at 100 MHz), and will provide sub-mJy sensitivity across much of its operating range. LOFAR will be a powerful instrument for solar system and planetary science applications as reviewed by papers in this monogram. Key astrophysical science drivers include acceleration, turbulence, and propagation in the galactic interstellar medium, exploring the high red-shift universe and transient phenomena, as well as searching for the red-shifted signature of neutral hydrogen from the cosmologically important epoch of re-ionization. 相似文献
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The now-closed Clark Radio Observatory was used in 1984 and 1985 to search for flaring emission from a number of dMe flare stars in the 30.9 to 110.6 MHz frequency range. No emission was found to greatly exceed detection limits which range from about 1 Jy for 1 hr averaging, to about 50 Jy for 1 s averaging, even though flares were often seen to tens of mJy at 20 cm using the VLA for those times when VLA-CLRO observations were coordinated. There are marginal detections of flaring from AD Leo over two periods on December 15, 1985 which mark the beginning and the end of along-lasting, narrow-band flare at 1415 MHz. 相似文献
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Deducing sediment transport direction and the relative importance of rivers on a tropical microtidal beach using the "McLaren model" 总被引：1，自引：0，他引：1
H. Mohd-Lokman Y. Rosnan S. Ejria N. A. M. Shazili K. K. Y. Kassim 《Environmental Geology》1998,34(2-3):128-134
Analyses of the sedimentological trend from 90 samples collected at 1-km intervals along a tropical microtidal coastline
of northern Terengganu indicate that the preferred sediment transport direction was northwards, following the McLaren model.
The extent of disruption to and reestablishment of the sedimentological trend on beaches north of two river mouths within
the study area was used to determine their relative importance in supplying sediment to the beaches. The extent of disruption
to the sedimentological trend was 18 and 14 km for the beaches north of the Terengganu and Setiu River mouths, respectively.
This suggests that the Terengganu River is more important in supplying sediments to the beach than the Setiu River. To a limited
extent this study showed that the McLaren model can be applied to deduce sediment transport direction on a microtidal coastline,
while disruption to the sedimentological trend adjacent to river mouths can be used to compare the relative importance of
rivers in supplying sediments, provided that the disruption to the sedimentological trend is small enough so as to allow for
the trend to be discernible again further along the transport path.
Received: 8 May 1997 · Accepted: 12 August 1997 相似文献