Incoherent cerenkov radiation and its amplification via the landau instability     

Manoranjan Rao Lalmani  V.V. Somayajulu  B.A.P. Tantry 《Planetary and Space Science》1973,21(6):1076-1079

Quite often the VLF hiss powers recorded by space probes are some orders of magnitude greater than those predicted by the theory of incoherent Cerenkov radiation. In this note we suggest that the wavegrowth via the Landau instability might satisfactorily account for the disparity between the theory and experiment.  相似文献   

Palaeomagnetism of Dhar traps and drift of the subcontinent during the Deccan volcanism     

G. V. S. Poornachandra Rao  M. S. Bhalla 《Geophysical Journal International》1981,65(1):155-164

Summary. Palaeomagnetic investigations were carried out on nine lava flows around the Dhar region, which constitute the northern part of the Deccan traps. The stability of remanent magnetism of these specimens was analysed by an alternating magnetic field, thermal demagnetization and memory tests. Six flows exhibited characteristic components of magnetization, with a mean direction of D =143°, I =+46° ( K = 107.1, α₉₅=5.5°). This gives a VGP located at 29° N, 67° W (δ_p=4.5°, δ_m= 7.0°). The lower site with normal magnetization and the upper five sites with reverse magnetization indicate a geomagnetic field reversal during the initial phases of Deccan volcanism in the Early Tertiary period. A rapid northward migration of about 18° in latitude and a simultaneous anticlockwise rotation of 37° is calculated for the subcontinent.  相似文献   

Anisotropy characteristics of low energy cosmic ray population of solar origin     

U. R. Rao  K. G. McCracken  F. R. Allum  R. A. R. Palmeira  W. C. Bartley  I. Palmer 《Solar physics》1971,19(1):209-233

Comparison of Explorer 34 observations on solar protons in the energy range 0.7–55 MeV with similar observations from other spacecrafts show that the large field aligned anisotropies which are observed during the rise time of a flare event change to an equilibrium anisotropy coming radially from the sunward direction due to the convective removal of the solar particles. At very late times during the decay (T 4 days) the anisotropy is observed to be from a direction 45° E of the satellite-Sun line which is interpreted as indicative of positive density gradient of solar cosmic ray population. The dependence of both types of equilibrium anisotropies on the energy and the velocity of the particles and on plasma velocity are shown to be in agreement with the theoretical predictions. The amplitude of the large field aligned anisotropies observed earlier in the event is found to be independent of the rise time of the event and to vary as (Vt)^–1.Interplanetary magnetic sector crossings during a flare event, cause abrupt changes in both the amplitude and phase of the non-equilibrium anisotropy whereas they have no significant effect on equilibrium anisotropy. The effect of azimuthal density gradients on the decay time constants of flare enhancements are also examined in an attempt to understand the complicated structures, often observed, in the time intensity profiles at low energies.Part of this work was done while the author was at the University of Texas as Dallas, U.S.A.Now at the National Academy of Sciences, Washington, D.C.  相似文献   

Possibility of continuous monitoring of celestial X-ray sources through their ionization effects in the nocturnal D-region ionosphere     

D. P. sharma  A. K. Jain  S. C. Chakravarty  K. Kasturirangan  K. R. Ramanathan  U. R. Rao 《Astrophysics and Space Science》1972,17(2):409-425

The electron production rates in the night-time D-region arising from the transit of strong celestial X-ray sources Sco X-1, Tau X-1 and Galactic Center are estimated and compared with the ambient electron production rates resulting from other known stable agencies. Using the experimentally measured values of the night-time electron densities, the number of additional electrons/cc expected from the passage of these sources is computed. For the 164 kHz transmission from Tashkent, received at Ahmedabad, the associated enhancement in the attenuation is calculated using the full wave admittance technique of Barron and Budden. Reasonable agreement is shown to exist between the calculated values of the attenuation and those of direct observations.  相似文献   

Evidence for short term changes in the intensity and spectrum of hard X-rays from Cyg X-1     

A. K. Jain  U. B. Jayanthi  K. Kasturirangan  U. R. Rao 《Astrophysics and Space Science》1976,45(2):433-438

The paper presents experimental evidence for the existence of fast intensity fluctuations with time scales of the order of a minute in the X-ray emission from Cyg X-1 at energies greater than 29 keV. Spectral variations over time intervals of 20–25 min are also observed in the same energy range. Whereas, similar intensity and spectral fluctuations have been reported earlier at lower energies the observations presented here is the first evidence for the existence of similar fluctuations at high energies.  相似文献   

Rare gases on the Earth and in meteorites     

M. N. Rao 《Astrophysics and Space Science》1970,6(2):315-320

Analysis of abundance patterns of rare gases Ne²², Ar³⁶, Kr⁸⁴ and Xe¹³⁰ on Earth and in ordinary and carbonaceous chondrites is presented. A mechanism of chemical adsorption of rare gases at the planetesimal stage during their accretion is proposed to generate the abundance pattern of the heavy rare gases on the Earth. The calculated values for Xe and Kr agree well with the observed values whereas for Ar, the agreement is poor.  相似文献   

Palaeomagnetic results from two basic volcanic formations in the western Himalayas and a Phanerozoic polar wandering curve for India     

R. N. Athavale  G. V. S. P. Rao  M. S. Rao 《Geophysical Journal International》1980,60(3):419-433

Summary. We present palaeomagnetic results from the Durgapipal and Rudraprayag formations, which are basic volcanic formations in the Lesser Himalayas of Uttar Pradesh State. NRM measurements and AF demagnetization stability tests were made on specimens cored from oriented block samples collected at representative sites. Mean stable remanent magnetic directions were used for calculating the Virtual Geomagnetic Pole (VGP) positions; where necessary tectonic corrections were applied.
The virtual geomagnetic north poles were found to be located at:

• (a). 

  Durgapipal (Permian): λ _p = 10° S, L_p = 42° W;
• (b). 

  Rudraprayag (Silurian-Devonian): λ _p = 30° S, L_p = 12° W.

A new, continuous Phanerozoic apparent polar wandering curve for the Indian subcontinent has been plotted from the available palaeomagnetic data and the VGP positions reported in this paper. As a result, the gap in the Indian palaeomagnetic data from the Lower Carboniferous to the Cambrian has been partially filled. The locations of the pole positions for the two formations on the Phanerozoic polar wandering curve for the Indian subcontinent, have been found to coincide with the stratigraphic ages assigned to them on the basis of rather limited geological and palaeontological evidence.
The Cambrian and Permian poles for the Salt Range in the NW Himalayas and the Permian pole for the Kumaon Himalayas are grouped along with the pole positions of contemporaneous formations of the Peninsular Shield. The palaeomagnetic data thus suggests that the two formations are autochthonous in nature.  相似文献   

Diffuse X-ray background measurements in the energy range 2–18 keV     

A. S. Prakasarao  D. P. Sharma  U. B. Jayanthi  U. R. Rao 《Astrophysics and Space Science》1971,10(1):150-155

Rocket measurements, of the diffuse X-ray background in the energy range 2–18 keV, conducted from Thumba Equatorial Rocket Launching Station (TERLS), India, are presented. The estimates of the cosmic background are derived by the method which employs the Earth and its atmosphere as a shutter to intercept the celestial X-rays. The results are shown to be consistent with a power law photon spectrum.13.6 _–3.3 ^+4.3 E ^{–1.73±0.15} photons/cm²-sec-keV-ster the spectrum being much flatter than that observed at higher energies.  相似文献   

中西部地区高温炎热 台风引发致洪暴雨   总被引：1，自引：0，他引：1  

饶晓琴 《气象》2006,32(10):117-123

7月份，黄淮南部、江淮、江南南部、华南、西北中东部降水偏多，皖、苏、湘、赣、闽、桂、粤等省（区）出现暴雨洪涝灾害；东北中南部、华北东南部、西南地区大部降水偏少，四川、重庆等地出现严重伏旱。全国大部地区月平均气温接近常年或偏高，江南大部、华南北部、四川东部、重庆、新疆东南部、内蒙古西部等地出现多日高温酷热天气。西北太平洋及南海有3个热带气旋活动，其中0604号强热带风暴碧利斯和0605号台风格美先后在福建省登陆西行，使江南、华南暴雨成灾。  相似文献   

Estimation and comparison of leaf area index of agricultural crops using irs liss-III and EO-1 hyperion images     

N. Rama Rao  P. K. Garg  S. K. Ghosh 《Journal of the Indian Society of Remote Sensing》2006,34(1):69-78

Motivated by the increasingly availability and importance of hyperspectral remote sensing data, this study aims to determine whether current generation narrowband hyperspectral remote sensing data could be used to estimate vegetation Leaf Area Index (LAI) accurately than the traditional broadband multispectral data. A comparative study has been carried out to evaluate the performance of the narrowband Normalized Difference Vegetation Index (NDV1) derived from Hyperion hyperspectral sensor with that of derived from IRS LISS-III for the estimation of LAI of some major agricultural crops (e.g. cotton, sugarcane and rice) in part of Guntur district, India. It has been found that the narrowband NDVI derived from Hyperion has shown better results over its counterpart derived from broadband LISS-III. Linear regression models have been used which with selected subsets of individual Hyperion bands performed better to predict LAI than those based on the broadband datasets, although the potential to overfit models using the large number of available Hyperion bands is a concern for further research.  相似文献