从生态学角度复原元代滦河上游的景观与物候   总被引：5，自引：0，他引：5  

崔海亭  王文江 《地理学报》2003,58(1):101-108

运用自然地理学和生态学的方法,根据元代古籍中的景观与物候信息复原了13~14世纪滦河上游及其邻近地区的自然景观：(1) 坝下的落叶阔叶林景观;(2) 坝缘和坝上东部的草甸草原景观;(3) 坝上西部的典型草原景观;(4) 北部的沙地疏林草原景观;(5) 河湖湿地景观。事实表明：从宏观上看,元代的景观结构与现代基本一致。另外,通过物候现象的古今对比,发现14世纪30年代夏季芍药的始花期比现代约提早10天,而14世纪中叶初雪较现代约提早10天。  相似文献   

MULTIPLE ISLAND ARC-BASIN SYSTEM AND ITS EVOLUTION IN GANGDISE TECTONIC BELT,TIBET     

Li Guangming  Feng Xiaolian  Pan Guitang WT  ”BX 《地学前缘》2000,(Z1)

MULTIPLE ISLAND ARC-BASIN SYSTEM AND ITS EVOLUTION IN GANGDISE TECTONIC BELT,TIBET  相似文献   

Quasi-harmonic faraday-rotation fluctuations of radio waves when sounding the outer solar corona     

A. I. Efimov  L. N. Samoznaev  V. E. Andreev  I. V. Chashei  M. K. Bird 《Astronomy Letters》2000,26(8):544-552

A statistical analysis of the Faraday-rotation fluctuations (FRFs) of linearly polarized radio signals from the Helios 1 and Helios 2 spacecraft shows that the FRF time power spectra can be of three types. Spectra of the first type are well fitted by a single power law in the range of fluctuation frequencies 1–10 mHz. Spectra of the second type are a superposition of a power law and two quasi-harmonic components with fluctuation frequencies of about v₁=4 mHz (fundamental frequency) and v₂=8 mHz (second harmonic). Spectra of the third type exhibit only one of the two quasi-harmonic components against the background of a power law. The spectral density of the quasi-harmonic components can be represented by a resonance curve with a fairly broad [Δυ ≈ (0.5–1.3)υ_1,2] distribution relative to the v=v_{1, 2} peak. The intensity of the quasi-harmonic FRF has a radial dependence that roughly matches the radial dependence for the background FRF, while their period at the fundamental frequency is approximately equal to the period of the wellknown 5-min oscillations observed in the lower solar atmosphere. The fluctuations with 5-min periods in FRF records can be explained by the presence in the outer corona of isolated trains of Alfvén waves generated at the base of the chromosphere-corona transition layer and by acoustic waves coming from deeper layers.  相似文献   

应用爆破检验KM-n程序定位精度的研究   总被引：1，自引：0，他引：1  

李桂华  刘国华  王力平  何家斌  卫爱民  颜其中  叶建庆 《地震研究》2006,29(4):355-359

采用云南区域数据地震遥测台网近震定位程序“KM—n”,分别测定了2005年1月11～27日进行的“04昆深工程”中18个点位的人工地震参数,以此检验台网近震定位程序“KM—n”的可靠性及台网的地震监测能力。洲定结果表明,对于记录波形初动清晰的人工地震,如果台站位置分布较好,参与定位的台站选择适当,用“KM—n”定位,结果相当准确可靠,误差在2km范围内。  相似文献   

Are Io's Alfvén wings filamented? Galileo observations     

T. Chust  A. Roux  D.A. Gurnett  K.K. Khurana 《Planetary and Space Science》2005,53(4):395-412

The interaction of Io with the Jovian magnetosphere generates auroral and radio emissions. The underlying electron acceleration process is not understood and few observations exist to constrain the theoretical models. The source of energy for the electron acceleration is in all likelihood supplied from the Alfvén wings that stretch out from both poles of Io into the two Jovian hemispheres. The form of the current system associated with the Alfvén wings has been disputed, some suggesting that the greatly slowed flow near Io implies that a steady current loop links Io to Jupiter's ionosphere, others arguing that the return waves appear only downstream of Io and others suggesting that both forms develop. Given the finite inclination of the Alfvén wings implied by the finite value of the Alfvén Mach number and the strong reflection that occurs at the boundary of the Io torus, we argue that no steady current loop can be invoked between Io and Jupiter's ionosphere. However, the energetics of the auroral and radio emissions imply that most of the energy in the Alfvén wings is transformed into electron acceleration at high-latitudes, that is, outside the Io torus. The dilemma then is to understand how a large fraction of the power penetrates the reflecting boundary. We present data from Galileo's multiple flybys of Io that suggest that the coupling with the Jovian ionosphere is mediated by filamentary Alfvén wings associated with electromagnetic waves propagating out of the torus. In particular, we report on the systematic observation, within the cross-section of Io's Alfvén wings and in their immediate vicinity, of intense electromagnetic waves at frequencies up to several times the proton gyrofrequency. We interpret these “high-frequency/small-scale” waves as the signature of a strong filamentation/fragmentation of the Alfvén wings before they reflect off of the sharp boundary gradient of the Io torus. As a consequence, we suggest that most of the primary energy is converted into “high-frequency/small-scale” electromagnetic waves that can propagate out from the torus toward Jupiter's ionosphere. Reaching high-latitudes, these waves are able to accelerate electrons to almost relativistic speeds.  相似文献   

Dolomitic marbles and associated calc-silicates, Tandilia belt, Argentina: Geothermobarometry, metamorphic evolution, and P–T path     

Sergio H. Delpino  Jorge A. Dristas   《Journal of South American Earth Sciences》2008,25(4):501-525

The metamorphic evolution of dolomitic marbles and associated calc-silicate rocks from Punta Tota (NE Tandilia belt, Buenos Aires province, Argentina) has been evaluated through petrographic, geothermobarometric, and fluid inclusion studies. Thin beds of dolomitic marble are intercalated in amphibolites and constitute the upper part of a stratified basement sequence, which starts at the base with garnet migmatites showing a great abundance of pegmatitic segregates, overlain by biotite–garnet gneisses. Peak metamorphic conditions are estimated at 750–800 °C and 5–6 kb, followed by near isobaric cooling to about 500–450 °C and 5.5–6.5 kb. Anhydrous progressive metamorphic assemblages in both marbles (Fo + Cal + Dol + Cpx + Spl) and adjacent calc-silicate rocks (Cpx + An + Cal + Qtz) strongly retrogressed to hydrous minerals (Tr, Tlc, Grs, Czo, Srp) with decreasing temperatures and increasing water activities. The intense rehydration of the rocks relates to the emplacement of volatile-rich pegmatitic bodies (Qtz + Pl + Kfs + Bt + Grt), which also resulted in the crystallization of clinochlore + phlogopite in the marble and biotite + muscovite in the adjacent calc-silicate rocks. Metamorphic reactions based on textural relations and evaluated on a suitable petrogenetic grid, combined with geothermobarometric results and fluid inclusion isochores, indicate a metamorphic evolution along a counterclockwise P–T path. Two probable geotectonic settings for the determined P–T trajectory are proposed: (1) thinning of the crust and overlying supracrustal basin in an ensialic intraplate tectonic setting and (2) development of a marginal back-arc basin, associated with an oceanic–continental convergent plate margin. In both models, the initial extensional regime is followed by a compressional stage, with overthickening of the basement and supracrustal rocks, during the climax of the Transamazonian cycle at approximately 1800 Ma ago. Continuous convergence and blockage of structures produce transition to transcurrent tectonics (transpression) with a consequent moderate uplift.  相似文献   

多目标遗传算法改进的加权多点灰色模型     

马龙  张献州  段海东  吴开岩  张拯  张正国  罗奕 《测绘科学》2017,42(4)

针对传统多点灰色预测模型MGM(1,n)白化背景值构造方法不合理性导致模型往往不符合变形体实际情况的问题,该文提出了一种基于遗传算法的加权MGM(1,n)模型。引入白化背景值最佳生成权值矩阵替换传统模型背景值构造公式中的紧邻均值生成权阵,较好地顾及变形区域内多监测点变形趋势的突变性与不规则性,弥补了线性系统MGM(1,n)模型在非线性动力学系统变形预测分析应用中的不足;建立多目标优化实数编码遗传算法,实现背景值最优构造权阵的迭代搜索。基于仿真和工程实例数据的建模结果表明:改进模型较传统MGM(1,n)模型预测精度提高,抗噪声干扰能力增强。  相似文献   

Construction and assessment of a logistic regression model applied to short-term forecasting of thunderstorms in León (Spain)     

Jos Luis Snchez  Eduardo García Ortega  Jos Luis Marcos 《Atmospheric Research》2001,56(1-4)

Forecasting thunderstorms is one of the most difficult tasks in weather prediction due to the scarce knowledge on how to characterise the mechanisms taking part in the formation of thunderstorms. New tools based upon the objective recognition of appropriate conceptual models have been developed in the last years. A good example of this are the statistical models, based on variables that characterise the preconvective atmospheric conditions.This paper presents the results obtained by applying a short-term forecast model to thunderstorms during the summer periods in León (Spain). This model makes use of the logistic function as a binary forecasting technique determining storm/no storm. The logistic function used was a combination of 15 previously selected meteorological variables. The model has been constructed with the data collected on 152 occasions, and it has been verified on 77 other occasions.The skill scores obtained show that the use of statistical models combining the data, provided by variables characterizing the preconvective conditions and the triggering mechanisms, represent an important step in the difficult task of short-term thunderstorm forecasting.  相似文献   

关于优化n条线段求交算法的研究     

程昌秀  严泰来 《测绘工程》2001,10(3):29-31

首先分析了n条线段相交算法的不足，然后系统地阐述利用扫视法缩小求交线段的范围，利用点位判别法高效判断两线段是否相交的理论，从而提出了一套较为优化的n条线段求交算法。本文对其算法给出详细的分析和讨论，最后指出此算法的适用范围。  相似文献   

Active and laboratory experiments in space plasma physics     

Walter Gekelman 《Surveys in Geophysics》1995,16(3):457-485

This report focuses on active experiments in space as well as laboratory experiments which are directly related to space phenomena. The active experiments involve particle releases in the CRESS and AMPTE missions. Unexpected results such as the motion of the plasma triggered several interesting computer simulations and a laboratory experiment which will be reviewed. Critical Ionization Phenomena will be discussed in this context. A recent release over Arecibo was used to create a ntent/jx710h4527071k63/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">plasma lensntent/jx710h4527071k63/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> to focus radiation from the HF heater beam. The higher power triggered several nonlinear processes. Advances in plasma sources and diagnostics have made it possible to scale many laboratory experiments. Discussed here are experiments on Alfvén waves generated by a localized source, 3D magnetic field line reconnection, three dimensional magnetized double layers and simulations of a tethered satellite.  相似文献