High-Resolution Simulations of Nonhelical MHD Turbulence

According to the kinematic theory of nonhelical dynamo action, the magnetic energy spectrum increases with wavenumber and peaks at the resistive cutoff wavenumber. It has previously been argued that even in the dynamical case, the magnetic energy peaks at the resistive scale. Using high resolution simulations (up to 1024³ meshpoints) with no large-scale imposed field, we show that the magnetic energy peaks at a wavenumber that is independent of the magnetic Reynolds number and about five times larger than the forcing wavenumber. Throughout the inertial range, the spectral magnetic energy exceeds the kinetic energy by a factor of two to three. Both spectra are approximately parallel. The total energy spectrum seems to be close to k ^?3/2, but there is a strong bottleneck effect and we suggest that the asymptotic spectrum is instead k ^?5/3. This is supported by the value of the second-order structure function exponent that is found to be ζ₂ = 0.70, suggesting a k ^?1.70 spectrum. The third-order structure function scaling exponent is very close to unity,—in agreement with Goldreich–Sridhar theory. Adding an imposed field tends to suppress the small-scale magnetic field. We find that at large scales the magnetic energy spectrum then follows a k ^?1 slope. When the strength of the imposed field is of the same order as the dynamo generated field, we find almost equipartition between the magnetic and kinetic energy spectra.     

USE OF SPACE PHOTOGRAPHS IN THE MAKING AND REVISION OF SMALL-SCALE MAPS

A brief review paper focuses on Soviet strategies for the use of space imagery, particularly photographic products (1:2,000,000 to 1:4,200,000 scale) from manned spaceflights, in the revision of small-scale general reference maps. Principles for the interpretation and mapping of basic map elements appearing on space photographs are outlined. Space photographs provide for reduction in time spent in map editing and the more correct analysis of the reliability of information and its generalization. A technology of map revision based on the joint use of original photographs and photomaps, with the transfer of revisions from photomaps to map originals, is proposed. Translated from: Geodeziya i kartografiya, 1986, No. 8, pp. 29-33.     

Far-infrared contribution to interstellar extinction from graphite whiskers

A mass contribution of graphite whiskers as small as 0.1% to the population of interstellar grains could dramatically change their far-infrared extinction properties. With varying mass fractions of graphite whiskers, and for different size parameters, the infrared extinction could vary from a ^-2 dependence to ⁰, consistent with the requirements of some astronomical observations.     

Geophysical and geodetic observations in the messina straits

The present note is intended as a contribution to the clarification of the collision process, generally assumed to be active between the African and the Eurasian plates in the area of the Messina Straits.For this purpose detailed analyses are made of the surveys carried out in the Straits of Messina in order to investigate the 1908 earthquake. The magnitude and intensity are established; limits are set for the linear dimension of the fault and of the dislocation that gave rise to the earthquake and an estimate is then given of these parameters. The results are then set out of the investigation into the focal mechanism of the earthquake of 1908. The results are also studied of geodetic surveys carried out at the time for the purpose of measuring the variations in height that occurred during the earthquake.A study is also made of the results of geodetic surveys (some of which are still under way) designed to measure the horizontal movements of Sicily with respect to Calabria in order to study locally the continental collision process in the area of the Messina Straits.It is found that the old and recent geodetic measurements as well as the fault-plane solution of the old and recent earthquakes of that area and the slips associated with those earthquakes indicate a motion towards the north of Sicily with respect to Calabria.     

Behavior of Titan's atmosphere during a total eclipse

The edge-on presentation of Saturn's rings and satellites system has provided a rare opportunity to observe total eclipses of Titan. During its emersion from the Saturnian shadow (1980, June 28), Titan has been observed simultaneously in the visible and the infrared ranges (6000–9000 Å, 11.8 μm and 20 μm). No change has been recorded in these three spectral ranges. Our observations tend to support the thick-atmosphere model, which has been shown to be valid by Voyager a few months later.     

Geochronology and geochemistry of Grenvillian igneous suites in the northern Oaxacan Complex, southern Mexico: tectonic implications

Chemical and U–Pb isotopic analyses of metaigneous rocks in the northern Oaxacan Complex in southern Mexico indicate that they form part of two granitic–gabbroic suites intruded at 1157–1130 and 1012 Ma, which were metamorphosed under granulite facies conditions between 1004 and 980 Ma. Although the older suite has both within-plate and arc geochemical signatures, the arc characteristics (enrichment of La and Ce relative to Nb, Ta, and Th) are inferred to result from crustal contamination, a conclusion consistent with their negative _Nd signatures. The younger suite is spatially associated with anorthosites (from which we were unable to acquire a protolith age), suggesting that collectively it forms part of anorthosite–mangerite–charnockite–granite (AMCG) suites. The tholeiitic nature of the mafic rocks along with the within-plate character of the felsic rocks suggests that they were intruded during extension related to either farfield backarc rifting, rifting above a slab window, or anorogenic intercontinental rifting. Potentially correlative AMCG suites are widespread in Mexico, the Grenville Province of eastern Canada and northeastern USA, and the Andean massifs of Colombia, however, Pb isotopic data most closely resemble those in South America. These data are consistent with published hypotheses that suggest Oaxaquia represents an exotic terrane derived from Amazonia.     

基于综合指标法的中国生态系统服务保护有效性评价研究

将生态系统服务保护纳入到传统的以保护区为基础的自然保护之中是生态保护研究的新领域。利用综合指标方法,分析了中国从2000-2010年的4种生态系统服务时空变化特征;并对中国的七大生态保护和恢复区域的服务空间保护成效进行评价,提出了国家尺度上的生态系统服务保护优先性分级。主要结论为：① 中国的生态系统服务自西北向东南逐渐增加,显著增加区主要分布在黄土高原地区,显著减少区主要分布在东北及华北地区。黄土高原的生态系统服务提高主要是农田向草地和林地、草地向林地的转换引的;华北地区的降低主要是耕地的减少以及人工用地的增加引起的;东北地区是由于林地向耕地草地、耕地向湿地与人工用地的转换引起的。② 七大生态保护和恢复区的生态系统服务均为增加趋势而且显著增加面积大于减少面积;显著增加面积最大的为三北防护林工程区、最小的为重点生态功能区;显著减少最大为重要生态功能区、最小的为三北防护林工程区。而且,对服务的保护成效在重要生态功能区最高,其次为天然林保护工程区,其余区域均小于全国平均水平。③ 提出的生态系统服务保护优先性等级中,极高级别占到了国土面积的26.18%,保护的生态系统服务量占到全国总量的64.19%,保护成效为全国平均水平的2.47倍。