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991.
992.
We analyze observations of the compact GHZ-peaked-spectrum radio source in the nucleus of the weakly active galaxy NGC 1052,
assuming that the low-frequency turnover in its spectrum is due to synchrotron self-absorption. The analysis is based on a
model for an inhomogeneous source of synchrotron radiation. It is shown that the magnetic field is not uniform, but the change
in the field strength from the center to the edge of the compact radio source does not exceed an order of magnitude. The maximum
magnetic-field strength in the nucleus of NGC 1052 is 20 G < H
⊥ < 200 G, and the density of relativistic electrons is 0.018 cm−3 < n
e
< 0.18 cm−3 on scales of 0.1 pc; everywhere in the radio source, the energy density of the magnetic field exceeds the energy density
of the relativistic electrons. The physical conditions are similar to those in the nuclei of the nearby radio galaxies 3C
111 and 3C 465, and differ strongly from those in the nucleus of the radio galaxy 0108+388, which is a compact GHz-peaked-spectrum
source (these three galaxies were studied by the authors earlier using the same method). 相似文献
993.
Ajith G. Nair D.S. Suresh Babu K.T. Damodaran R. Shankar C.N. Prabhu 《Journal of Asian Earth Sciences》2009,34(2):115-122
The magnetic fractions of ilmenite from the beach placer deposit of Chavara, southwest India have been studied for mineralogical and chemical composition to assess the range of their physical and chemical variations with weathering. Chavara deposit represents a highly weathered and relatively homogenous concentration. Significant variation in composition has been documented with alteration. The most magnetic of the fractions of ilmenite, separated at 0.15 Å, and with a susceptibility of 3.2 × 10?6 m3 kg?1, indicates the presence of haematite–ilmenite intergrowth. An iron-poor, titanium-rich component of the ilmenite ore has been identified from among the magnetic fractions of the Chavara ilmenite albeit with an undesirably high Nb2O5 (0.28%), Cr2O3 (0.23%) and Th (149 ppm) contents. The ilmenite from Chavara is compared with that from the nearby Manavalakurichi deposit of similar geological setting and provenance. The lower ferrous iron oxide (2.32–14.22%) and higher TiO2 (56.31–66.45%) contents highlight the advanced state of alteration of Chavara. This is also evidenced by the relatively higher Fe3+/Fe2+ ratio compared to Manavalakurichi ilmenite. In fact, the ilmenite has significantly been converted to pseudorutile/leucoxene. 相似文献
994.
Picard SODISM, a Space Telescope to Study the Sun from the Middle Ultraviolet to the Near Infrared 总被引:1,自引:0,他引:1
M. Meftah J.-F. Hochedez A. Irbah A. Hauchecorne P. Boumier T. Corbard S. Turck-Chièze S. Abbaki P. Assus E. Bertran P. Bourget F. Buisson M. Chaigneau L. Damé D. Djafer C. Dufour P. Etcheto P. Ferrero M. Hersé J.-P. Marcovici M. Meissonnier F. Morand G. Poiet J.-Y. Prado C. Renaud N. Rouanet M. Rouzé D. Salabert A.-J. Vieau 《Solar physics》2014,289(3):1043-1076
995.
Parvaiz A. Khan Sharad C. Tripathi O. A. Troshichev Malik A. Waheed A. M. Aslam A. K. Gwal 《Astrophysics and Space Science》2014,349(2):647-656
Geomagnetic field variations during five major Solar Energetic Particle (SEP) events of solar cycle 23 have been investigated in the present study. The SEP events of 1 October 2001, 4 November 2001, 22 November 2001, 21 April 2002 and 14 May 2005 have been selected to study the geomagnetic field variations at two high-latitude stations, Thule (77.5° N, 69.2° W) and Resolute Bay (74.4° E, 94.5° W) of the northern polar cap. We have used the GOES proton flux in seven different energy channels (0.8–4 MeV, 4–9 MeV, 9–15 MeV, 15–40 MeV, 40–80 MeV, 80–165 MeV, 165–500 MeV). All the proton events were associated with geoeffective or Earth directed CMEs that caused intense geomagnetic storms in response to geospace. We have taken high-latitude indices, AE and PC, under consideration and found fairly good correlation of these with the ground magnetic field records during the five proton events. The departures of the H component during the events were calculated from the quietest day of the month for each event and have been represented as ΔH THL and ΔH RES for Thule and Resolute Bay, respectively. The correspondence of spectral index, inferred from event integrated spectra, with ground magnetic signatures ΔH THL and ΔH RES along with Dst and PC indices have been brought out. From the correlation analysis we found a very strong correlation to exist between the geomagnetic field variation (ΔHs) and high-latitude indices AE and PC. To find the association of geomagnetic storm intensity with proton flux characteristics we derived the correspondence between the spectral indices and geomagnetic field variations (ΔHs) along with the Dst and AE index. We found a strong correlation (0.88) to exist between the spectral indices and ΔHs and also between spectral indices and AE and PC. 相似文献
996.
We assess the predictive capabilities of various classes of avalanche models for solar flares. We demonstrate that avalanche models cannot generally be used to predict specific events because of their high sensitivity to the embedded stochastic process. We show that deterministically driven models can nevertheless alleviate this caveat and be efficiently used for predictions of large events. Our results suggest a new approach for predictions of large (typically X-class) solar flares based on simple and computationally inexpensive avalanche models. 相似文献
997.
This article continues our study of spacecraft guidance and control for a soft Moon landing (see our article “Main braking phase for a soft Moon landing as a form of trajectory correction”). Rationale is given for the objectives of the subsequent (final touchdown) phases. Analytical relations for the main parameters are obtained, and the impact of various disturbing factors is estimated. A methodology is proposed for calculating the main parameters for the whole braking sequence from the sighting altitude of the main braking phase termination to braking engine thrust and its throttle range. 相似文献
998.
999.
Calibration of cosmogenic noble gas production based on 36Cl‐36Ar ages. Part 2. The 81Kr‐Kr dating technique 下载免费PDF全文
I. Leya N. Dalcher N. Vogel R. Wieler M. W. Caffee K. C. Welten K. Nishiizumi 《Meteoritics & planetary science》2015,50(11):1863-1879
We calibrated the 81Kr‐Kr dating system for ordinary chondrites of different sizes using independent shielding‐corrected 36Cl‐36Ar ages. Krypton concentrations and isotopic compositions were measured in bulk samples from 14 ordinary chondrites of high petrologic type and the cosmogenic Kr component was obtained by subtracting trapped Kr from phase Q. The thus‐determined average cosmogenic 78Kr/83Kr, 80Kr/83Kr, 82Kr/83Kr, and 84Kr/83Kr ratiC(Lavielle and Marti 1988; Wieler 2002). The cosmogenic 78Kr/83Kr ratio is correlated with the cosmogenic 22Ne/21Ne ratio, confirming that 78Kr/83Kr is a reliable shielding indicator. Previously, 81Kr‐Kr ages have been determined by assuming the cosmogenic production rate of 81Kr, P(81Kr)c, to be 0.95 times the average of the cosmogenic production rates of 80Kr and 82Kr; the factor Y = 0.95 therefore accounts for the unequal production of the various Kr isotopes (Marti 1967a). However, Y should be regarded as an empirical adjustment. For samples whose 80Kr and 82Kr concentrations may be affected by neutron‐capture reactions, the shielding‐dependent cosmogenic (78Kr/83Kr)c ratio has been used instead to calculate P(81Kr)/P(83Kr), as for some lunar samples, this ratio has been shown to linearly increase with (78Kr/83Kr)c (Marti and Lugmair 1971). However, the 81Kr‐Kr ages of our samples calculated with these methods are on average ~30% higher than their 36Cl‐36Ar ages, indicating that most if not all the 81Kr‐Kr ages determined so far are significantly too high. We therefore re‐evaluated both methods to determine P(81Kr)c/P(83Kr)c. Our new Y value of 0.70 ± 0.04 is more than 25% lower than the value of 0.95 used so far. Furthermore, together with literature data, our data indicate that for chondrites, P(81Kr)c/P(83Kr)c is rather constant at 0.43 ± 0.02, at least for the shielding range covered by our samples ([78Kr/83Kr]c = 0.119–0.185; [22Ne/21Ne]c = 1.083–1.144), in contrast to the observations on lunar samples. As expected considering the method used, 81Kr‐Kr ages calculated either directly with this new P(81Kr)c/P(83Kr)c value or with our new Y value both agree with the corresponding 36Cl‐36Ar ages. However, the average deviation of 2% indicates the accuracy of both new 81Kr‐Kr dating methods and the precision of the new dating systems of ~10% is demonstrated by the low scatter in the data. Consequently, this study indicates that the 81Kr‐Kr ages published so far are up to 30% too high. 相似文献
1000.