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331.
E. N. Vinyaikin 《Astronomy Reports》2018,62(2):130-137
The radio spectrum of Tycho’s Supernova Remnant is constructed at frequencies 12.6–143 000 MHz for epoch 2010.3, taking into account the secular decrease in the radio flux density of the remnant at the rate d = ?(0.46 ± 0.03)%/year: The spectrum has positive curvature. The presence of a low-frequency turnover in the spectrum of the radio source 3C10 with its maximum at 7.7 MHz is predicted, due to absorption in the interstellar medium in the direction toward the source.
相似文献
$$S_\nu ^{3C10} (t = 2010.3) = (43.1 \pm 1.8 Jy)(\nu [GHz])^{ - (0.592 \pm 0.019) + (0.041 \pm 0.012)\log (\nu [GHz])} .$$
332.
Geraint J. A. Harker Saleem Zaroubi Rajat M. Thomas Vibor Jeli Panagiotis Labropoulos Garrelt Mellema Ilian T. Iliev Gianni Bernardi Michiel A. Brentjens A. G. de Bruyn Benedetta Ciardi Leon V. E. Koopmans V. N. Pandey reas H. Pawlik Joop Schaye Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,393(4):1449-1458
Detecting redshifted 21-cm emission from neutral hydrogen in the early Universe promises to give direct constraints on the epoch of reionization (EoR). It will, though, be very challenging to extract the cosmological signal (CS) from foregrounds and noise which are orders of magnitude larger. Fortunately, the signal has some characteristics which differentiate it from the foregrounds and noise, and we suggest that using the correct statistics may tease out signatures of reionization. We generate mock data cubes simulating the output of the Low Frequency Array (LOFAR) EoR experiment. These cubes combine realistic models for Galactic and extragalactic foregrounds and the noise with three different simulations of the CS. We fit out the foregrounds, which are smooth in the frequency direction, to produce residual images in each frequency band. We denoise these images and study the skewness of the one-point distribution in the images as a function of frequency. We find that, under sufficiently optimistic assumptions, we can recover the main features of the redshift evolution of the skewness in the 21-cm signal. We argue that some of these features – such as a dip at the onset of reionization, followed by a rise towards its later stages – may be generic, and give us a promising route to a statistical detection of reionization. 相似文献
333.
A general mixing equation with applications to Icelandic basalts 总被引:4,自引:0,他引:4
Charles H. Langmuir Robert D. Vocke Gilbert N. Hanson Stanley R. Hart 《Earth and Planetary Science Letters》1978,37(3):380-392
The mixing equation applied by Vollmer [1] to Pb and Sr isotope ratios is shown to be a general equation applicable to consideration of element and isotope ratios. The mixing equation is hyperbolic and has the form:Ax + Bxy + Cy + D = 0where the coefficients are dependent on the type of plot considered: i.e. ratio-ratio, ratio-element, or element-element. Careful use of this equation permits testing whether mixing is a viable process, places constraints on end member compositions, allows distinction between mixing of sources and mixing of magmas, and should allow distinction between recent mixing and long-term evolution of sources.The available chemical data for postglacial basalts from Iceland and along the Reykjanes Ridge are not consistent with either mixing of magmas or simple mixing of an enriched ocean island source with a depleted ocean ridge source. If the available analyses for basalts are representative of the source regions, the data are consistent with at least two models neither of which can be properly tested with the available data.(1) There are two separate mixing trends: one beneath Iceland with the alkali basalt source and a depleted Iceland source as end members; the second along the Reykjanes Ridge with a heterogeneous ocean ridge basalt source and a source similar to that for intermediate basalts on Iceland as end members. The depleted Iceland source and the depleted ocean ridge source are not the same.(2) The chemistry of the basalts is not determined by mixing. Instead the basalts are derived from a multiplicity of sources with a similar history which have been isolated for hundreds of millions of years. 相似文献
334.
Influence of the Atlantic Multidecadal Oscillation on the winter climate of East China 总被引:11,自引:0,他引:11
The Atlantic Multidecadal Oscillation (AMO), the multidecadal variation of North Atlantic sea surface temperature (SST), exhibits an oscillation with a period of 65-80 years and an amplitude of 0.4℃. Observational composite analyses reveal that the warm phase AMO is linked to warmer winters in East China, with enhanced precipitation in the north of this region and reduced precipitation in the south, on multidecadal time scales. The pattern is reversed during the cold phase AMO. Whether the AMO acts as a forcing of the multidecadal winter climate of East China is explored by investigating the atmospheric response to warm AMO SST anomalies in a large ensemble of atmospheric general circulation model (AGCM) experiments. The results from three AGCMs are consistent and suggest that the AMO warmth favors warmer winters in East China. This influence is realized through inducing negative surface air pressure anomalies in the hemispheric-wide domain extending from the midlatitude North Atlantic to midlatitude Eurasia. These negative surface anomalies favor the weakening of the Mongolian Cold High, and thus induce a weaker East Asian Winter Monsoon. 相似文献
335.
G. N. Baturin 《Doklady Earth Sciences》2006,407(1):330-334
336.
I. González M. M. Jordán T. Sanfeliu M. Quiroz C. de la Fuente 《Environmental Geology》2007,52(7):1243-1251
In southern Chile, with a mild and rainy climate, high levels of heavy metals have been detected in many gold placer deposits.
Many of the contaminants pose risks to human life, and consequently damage the trofic chain in this environment. The study
zones selected correspond to the handicraft gold-bearing sands of Rio Gato (Los Muermos), Carelmapu and Cucao. These are all
located in the X Region of “Los Lagos” in Chile. The type of methodology used in the characterization of the associated mineralization
consists of testing each representative sample with a grain size distribution, statistical parameter analysis and a mineralogical
analysis, using a binocular magnifying glass, a petrographic microscope, XRD and SEM/EDX. The chemical composition was defined
by means of X ray fluorescence and micro-chemical analysis. The results of the study about sediments in southern Chile are
presented. The major concentrations of heavy minerals are generally located in areas of dynamic river energy. In the samples,
more than 70% of the heavy minerals were distributed among grain sizes corresponding to thin sand with good grain selection
(meshes of 0.25–0.06 mm). The main mineral phases present in the analysed samples were gold, zircon, olivine, ilmenite, hornblende,
hypersthene, hematite, garnet, chromite, chlorite, augite, amphibolitic-epidote, etc. The main heavy metals found as a result
of the study were mercury, lead, cadmium, chrome, tellurium, indium, zinc, cobalt, copper, platinum, gold, etc., and as well
some less common elements like cerium, praseodymium, gadolinium, neodymium, samarium and lanthanum. This research work is
only a starting point for carrying out a risk probability mapping of heavy metals and the mineralogy of the Cucao, Carelmapu
and Rio Gato gold-bearing sands. 相似文献
337.
Simulation of the Holocene climate evolution in Northern Africa: The termination of the African Humid Period 总被引:2,自引:0,他引:2
The Holocene climate evolution in Northern Africa is studied in a 9000-yr-long transient simulation with a coupled atmosphere–ocean–vegetation model forced by changes in insolation and atmospheric greenhouse gas concentrations. The model simulates in the monsoonal domains a significant decrease in precipitation under influence of the orbitally forced reduction in summer insolation. In the Western Sahara region, the simulated mid-Holocene transition from humid to arid conditions (the termination of the African Humid Period) is highly non-linear with the occurrence of centennial-scale climate fluctuations due to the biogeophysical feedback between precipitation and vegetation cover. This result is in agreement with proxy data from the Western Sahara region. The other monsoonal regions experience a more gradual climate evolution that linearly follows the insolation forcing, which appears in disagreement with available lake level records. 相似文献
338.
A. N. Opanasenko N. V. Opanasenko Yu. G. Shkuratov V. G. Kaidash Yu. I. Velikodskii V. V. Korokhin 《Kinematics and Physics of Celestial Bodies》2011,27(1):38-41
Polarimetric observations of the moon have been carried out at λeff = 0.48 and 0.63 μm using the 50 cm telescope of the Maidanak (Middle Asia) observatory. Imaging has been performed using
a Canon-350D camera with a CMOS array and rotating polaroid. The investigation covered the north-western part of the lunar
disk comprising the northern part of Ocean Procellarum and obtained the images representing the albedo, polarization degree, color index, and polarimetric color ratio at a phase
angle of 96°. It is the first time that the latter parameter has been imaged with a resolution of approximately 1 km. Its
pattern has proved to resemble that of the color index, although some important differences can be seen. This shows that spectropolarimetric
observations of the moon can give new information on the composition and optical properties of the lunar regolith. 相似文献
339.
A calculation procedure using the modulation transfer function approach is presented to estimate the distortions to the values of the peak ocean wavelength and direction derived from SAR images of these waves. The distortions are calculated for ranges of SAR parameters which are typical for aircraft and satellites, and ocean wave parameters which reflect sea states which can be imaged by these SARs. The calculated distortions are discussed in terms of overall trends, effect of particular SAR and wave parameters, and qualitatively compared with observed differences between SAR and in situ measurements. 相似文献
340.