The RadioAstron ground–space interferometer has been used to measure the angular sizes of the scattering disks of the three distant pulsars B1641–45, B1749–28, and B1933+16. The observations were carried out with the participation of the Westerbork Synthesis Radio Telescope; two 32-m telescopes at Torun, Poland and Svetloe, Russia (the latter being one antenna of the KVAZAR network); the Saint Croix VLBA antenna; the Arecibo radio telescope; the Parkes, Narrabri (ATCA), Mopra, Hobart, and Ceduna Australian radio telescopes; and the Hartebeesthoek radio telescope in South Africa. The full widths at half maximum of the scattering disks were 27 mas at 1668 MHz for B1641–45, 0.5 mas at 1668 MHz for B1749–28, and 12.3 at 316 MHz and 0.84 mas at 1668 MHz for B1933+16. The characteristic time scales for scatter-broadening of the pulses on inhomogeneities in the interstellar plasma τsc were also measured for these pulsars using various methods. Joint knowledge of the size of the scattering disk and the scatter-broadening time scale enables estimation of the distance to the effective scattering screen d. For B1641–45, d = 3.0 kpc for a distance to the pulsar D = 4.9 kpc, and for B1749–28, d = 0.95 kpc for D = 1.3 kpc. Observations of B1933+16 were carried out simultaneously at 316 and 1668 MHz. The positions of the screen derived using the measurements at the two frequencies agree: d1 = 2.6 and d2 = 2.7 kpc, for a distance to the pulsar of 3.7 kpc. Two screens were detected for this pulsar from an analysis of parabolic arcs in the secondary dynamic spectrum at 1668 MHz, at 1.3 and 3.1 kpc. The scattering screens for two of the pulsars are identified with real physical objects located along the lines of sight toward the pulsars: G339.1–04 (B1641–45) and G0.55–0.85 (B1749–28). 相似文献
The spatiotemporal distribution of harp seal pups around breeding grounds in the White Sea is considered. It is shown that spatial localization of groups of females with different terms of mass pup birth takes place. This somewhat confirms the data on the gregarious structure of White Sea harp seal population. It is possible to explain the structure of this adaptation of the seal population to different living conditions in different feeding areas. 相似文献
Using a well-known method for calculating the propagation of waves in an inhomogeneous medium, we have managed to reduce the
problem of wave propagation in pulsar magnetospheres to a system of two ordinary differential equations that allow the polarization
characteristics of the radio emission to be quantitatively described for any magnetic field structure and an arbitrary density
profile of the outflowing plasma. We confirm that for ordinary pulsars (period P ∼ 1 s, magnetic field B0 ∼ 1012 G, particle production multiplicity parameter λ ∼ 104), the polarization is formed inside the light cylinder at a distance of the order of a thousand neutron star radii. For reasonable
magnetic field strengths and plasma densities on the emission propagation path, the degree of circular polarization is found
to be ∼5–20%, in good agreement with observations. 相似文献
Data on the white whale distribution in Onega Bay of the White Sea obtained during route and stationary observations in the summer of 2003–2006 are given. The presence of three regions of summer habitation of local “nonmigratory” white whale reproductive schools is confirmed. The minimum abundance of the “zhizhginskoe” (northeastern) school is 60 individuals, and the minimum abundance of the “myagostrovskoe” (western) is 50 individuals. The abundance of the best studied “southern” school is close to 120–130 individuals. One more region of white whale concentration (with an abundance of up to 40 individuals) (the eastern one; Cape Letniy Orlov-Cape Chesmenskiy) was found. The localization of single reproductive schools (RS) is due to a number of factors: the morphometry of the shores and bottom, the hydrological regime, and the character of the coastal tidal currents. The white whale distribution in the southern part of Onega Bay in the summer (June–July) is of discontinuous character with concentrations near cape Glubokiy and some other adjacent parts. The coefficient of the white whale attendance in the Cape Glubokiy area varied from 42.5 to 67.4% during the years of the studies (2003–2006). The character of the distribution, the direction of the relocations, and the animals’ behavior peculiarities indicate that the white whales of the southern part of Onega Bay of the White Sea form a rather stable school community of a few (5–6) locally distributed small family groups during the summer. 相似文献
Oceanology - The OCP and PCB contents in the tissues of beluga whales (Delphinapterus leucas) from the Russian Arctic have been studied for the first time. Skin and subcutaneous adipose tissue... 相似文献
Fluctuations of the electric and magnetic field are studied in collisionless shock formed during plasma flow over a terrella. Spectra of magnetic fluctuations in the laboratory experiment and in space appear to coincide in dimensionless units. Electric field fluctuations appear at the shock wave formation, with frequencies in the hybrid Larmor frequency range. The appearance of noise is preceeded by the formation of positive potential maxima. The reflection of ions from the potential maxima must lead to two stream motion in a plasma with magnetized electrons. Such motion is unstable and excites longitudinal waves. Dissipation of energy of the directional motion after damping of electrical noises apparently occurs only through microfluctuations of the magnetic field. 相似文献
The RadioAstron ground-space interferometer provides the highest angular resolution achieved now in astronomy. The detection of interferometric fringes from quasars with this angular resolution on baselines of 100–200 thousand km suggests the brightness temperatures which exceed the Compton limit by two orders of magnitude. Polarimetric measurements on ground-space baselines have revealed fine structure testifying to recollimation shocks on scales of 100–250 μas and a helical magnetic field near the base of radio emission in BL Lacertae. Substructure within a the scattering disk of pulsar emission on interferometer baselines (from 60000 to 250000 km) was discovered. This substructure is produced by action of the interstellar interferometer with an effective baseline of about 1 AU and the effective angular resolution of better than 1 μas. Diameters of scattering disks were measured for several pulsars, and distances to diffusing screens were evaluated. The ground-space observations of sources of the maser radiation in lines of water and hydroxyl have shown that the maser sources in star-forming regions remain unresolved on baselines, which considerably exceed the Earth diameter. These very compact and bright features with angular sizes of about 20–60 μas correspond to linear sizes of about 5–10 million km (several solar diameters). 相似文献
Upscaling methods such as the dual porosity/dual permeability (DPDP) model provide a robust means for numerical simulation of fractured reservoirs. In order to close the DPDP model, one needs to provide the upscaled fracture permeabilities and the parameters of the matrix-fracture mass transfer for every fractured coarse block in the domain. Obtaining these model closures from fine-scale discrete fracture-matrix (DFM) simulations is a lengthy and computationally expensive process. We alleviate these difficulties by pixelating the fracture geometries and predicting the upscaled parameters using a convolutional neural network (CNN), trained on precomputed fine-scale results. We demonstrate that once a trained CNN is available, it can provide the DPDP model closures for a wide range of modeling parameters, not only those for which the training dataset has been obtained. The performance of the DPDP model with both reference and predicted closures is compared to the reference DFM simulations of two-phase flows using a synthetic and a realistic fracture geometries. While the both DPDP solutions underestimate the matrix-fracture transfer rate, they agree well with each other and demonstrate a significant speedup as compared to the reference fine-scale solution.
The current ecological crisis in the Aral basin is a result of a number of factors, including specific features of the history of economic activity of the local population. Interaction of sedentory farmers of oases and nomads of steppes and deserts was of the most importance. Periods of political centralization coincided with the rise and spread of irrigation-based farming, and vice versa, the reduction of irrigated areas occurred in troubled war and crises time. In modern times the total area of ancient irrigation lands in the lower reaches of Amu Darya and Syr Darya has mounted to 4,5 mln hectares. Complex archaeological study of these areas has made possible the reconstruction of complicated history of the development of irrigation and irrigation-based farming. 相似文献
Very Long Baseline Interferometry (VLBI) observations of the pulsar B0833–45 have been carried out as part of the scientific program of the RadioAstron mission. Ground support was provided by the Long Baseline Array, which includes radio telescopes in Australia and other countries in the southern hemisphere. The VLBI observations of the pulsar are analyzed in order to derive the parameters characterizing the scattering of the pulsar radio emission: the angular size of the scattering disk, the spatial scale of the diffraction pattern, the drift velocity of this pattern relative to the observer, the pulse scattering time scale, and the characteristic scintillation time and frequency scales, as well as the index of the electrondensity fluctuation spectrum. Comparison of these values with the predictions of the theory of scattering on a thin screen enables the determination of the position of the effective screen along the line of sight. Estimates made using various methods give distances to the screen from the observer of 0.79 to 0.87 times the total distance to the pulsar. Although the position of the screen is beyond the boundary of the Vela supernova remnant, this object may play the dominant role in the scattering. The scattering disk is an ellipse with a 2:1 axis ratio and with the inferred position angle of the major axis being ≈ 50°, based on the changes in the visibility-function amplitude for various orientations of the projected baseline. This conclusion is supported by the shape of the visibility-function amplitude as a function of the delay.
