排序方式： 共有47条查询结果，搜索用时 375 毫秒
11.
M. V. Popov A. D. Kuz’min O. M. Ul’yanov A. A. Deshpande A. A. Ershov V. V. Zakharenko V. I. Kondrat’ev S. V. Kostyuk B. Ya. Losovskiĭ V. A. Soglasnov 《Astronomy Reports》2006,50(7):562-568
The results of simultaneous multifrequency observations of giant radio pulses from the Crab pulsar, PSR B0531+21, at 23, 111, and 600 MHz are presented and analyzed. Giant pulses were detected at a frequency as low as 23 MHz for the first time. Of the 45 giant pulses detected at 23 MHz, 12 were identified with counterparts observed simultaneously at 600 MHz. Of the 128 giant pulses detected at 111 MHz, 21 were identified with counterparts observed simultaneously at 600 MHz. The spectral indices for the power-law frequency dependence of the giant-pulse energies are from ?3.1 to ?1.6. The mean spectral index is ?2.7 ± 0.1 and is the same for both frequency combinations (600–111 MHz and 600–23 MHz). The large scatter in the spectral indices of the individual pulses and the large number of unidentified giant pulses suggest that the spectra of the individual giant pulses do not actually follow a simple power law. The observed shapes of the giant pulses at all three frequencies are determined by scattering on interstellar plasma inhomogeneities. The scatter-broadening of the pulses and its frequency dependence were determined as τ sc = 20(ν/100)?3.5±0.1 ms, where frequency ν is in MHz. 相似文献
12.
Barbro Ulén 《Aquatic Sciences - Research Across Boundaries》1978,40(1):104-118
Aerobic decomposition of algae is studied in view of their biochemical composition, and the process is mathematically described. 相似文献
13.
This paper is devoted to the study of static axially symmetric spacetime with anisotropic fluid by means of structure scalars in the presence of electromagnetic field. The structure scalars in terms of physical variables are evaluated through the Einstein-Maxwell field equations and the inhomogeneity factors are identified. We also explore analytic solutions for isotropic as well as anisotropic fluids. It is found that isotropic solution turns out to be a charged solution which has no correspondence with the Weyl metrics while the anisotropic solution has the correspondence with the Weyl metrics. 相似文献
14.
The objective of this study was to determine and discuss field‐scale phosphorus losses via subsurface tile drains. A total phosphorous (Tot‐P) export, which averaged 0·29 kg ha−1 year−1, was measured over a six‐year period from the 4·43 ha drainage system of a Eutric Cambisol in Central Sweden. The main part (63%) was in particulate form (PP) while the remainder was either in phosphate form (PO4‐P) or in other dissolved or colloidal forms. A very small area, less than 1% of the soil surface, was demonstrated to be hydraulically active by using a staining technique in soil monoliths taken from the field. The stained macropores were few, but were continuous downward, and were relatively evenly distributed among the eight 7 dm2 areas that were investigated. The transport from the field mainly occurred in episodes during which the relationship between phosphorus concentration and discharge was characterized by hysteresis loops. On average, half of the yearly P transport occurred in 140 hours. Compared with flow‐proportional and frequent sampling, manual and fortnightly sampling underestimated the transport of Tot‐P and suspended solids (SS) by 59 and 42%, respectively, during the six years studied. Amounts of different phosphorus forms exported through the tile drains were very similar to those reported from other clay soils in Northern Europe and North America. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
15.
The distribution of trace elements in sulfide minerals from the Broken Spur hydrothermal vent field (MAR) suggests the presence
of nanomineral phases for some trace elements, including Au and Ag. 相似文献
16.
Barbro Uln 《水文研究》2003,17(4):747-758
During a 16 day period with pronounced snowmelt via surface runoff, high water concentrations (usually 0·4–0·5 mg l?1) of dissolved molybdate‐reactive phosphorus (MRP) were detected in surface runoff water from a clay soil of illite type. Other phosphorus fractions defined were: phosphorus in particles with a higher settling coefficient than 80 000 S (SPP); colloidal phosphorus caught on filters with a pore size of 0·2 µm but with a smaller settling coefficient (CPP); and dissolved phosphorus not reacting with molybdate (DUP). The order of concentrations was MRP > SPP > CPP > DUP. Nearly identical amounts of MRP, CPP, and DUP (in total 0·3 kg ha?1) were lost from a grass–clover ley and a ploughed soil. However, more of the heavier phosphorus‐containing material was lost from the ploughed area. In drainpipe water, CPP was the largest fraction (28%), and in stream water from mixed arable/forest land, MRP dominated (33%). Loss on ignition of the settling material slowly decreased from 10 to 8% (dry weight) during the snowmelt period. Total phosphorus concentrations in the material followed the runoff pattern, with slightly higher phosphorus concentrations during fast runoff. The large amounts of readily dissolved or colloidal‐bound phosphorus (70–80%) transported from this clay soil during snowmelt are discussed with regard to the use of grass buffer strips as a measure against phosphorus losses from arable land. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
17.
This paper is devoted to study spherically symmetric shearfree charged gravitational collapse with radial heat flux and isotropic pressure. For the matching of the interior spacetime, we take Vaidya-Reissner-Nordström metric outside the spherical system. We solve the field equations numerically by taking ansatz on the metric functions and using Darmois junction conditions. The behavior of density, pressure, radial heat flux, luminosity and the mass function is analyzed. Finally, we check validity of the energy conditions through plots. 相似文献
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19.
V. F. Gopka O. M. Ul’yanov S. M. Andrievskii 《Kinematics and Physics of Celestial Bodies》2008,24(1):36-43
Many unidentified lines in the spectrum of Przybylski’s star (HD 101065) match well the spectral lines of radioactive elements, including the lines of short-lived isotopes. The origin of such isotopes in the atmosphere of the star remains unknown. We discuss a scenario in which some heavy nuclei of radioactive elements are produced in Przybylski’s star atmosphere as a result of its permanent exposure to the gamma flux (photon-nuclear reactions) or of the direct interaction of the free neutrons which arise in the atmosphere with seed nuclei of lighter elements (r-process). In both cases the gamma quanta and the free neutrons originate due to the presence of the neutron star which forms a close binary system with Przybylski’s star. This neutron star is the source of the fast electrons and positrons which produce gamma quanta when they are decelerated in their interaction with the atomic nuclei of the atmospheric plasma, while free neutrons can originate in the reactions of the direct capture of fast electrons by atmospheric protons (nuclei of hydrogen atoms). 相似文献
20.
Seston and sediment in Lake Norrviken 总被引：2，自引：0，他引：2
Barbro Ulén 《Aquatic Sciences - Research Across Boundaries》1978,40(2):262-286
Seston and sedimenting material were measured over several years in a lake in central Sweden. The origin of the material is
discussed on basis of the chemical composition and the amounts in terms of successively changing environmental conditions
(mainly phosphorus). Assimilation of N and P by phytoplankton is calculated from the elemental composition of net plankton
combined with C-14 data of C assimilation. Changes in the amount of seston are small compared to production, mineralization
and sedimentation. 相似文献