通海地磁台(L=1.03)Pc3地磁脉动的出现率

利用通海地磁台(L=1．03)1999年SMALL磁通门磁力仪记录资料，对Pc3脉动出现率的统计结果表明，日出现频次有两个峰值，即清晨06：00-07：00LT(地方时)出现频次最高，午后14：00～15：00LT为次峰值。Pc3脉动月出现频率最高的是4月和12月，其次是8月和9月；最少的是6月和7月。按季节统计结果为春秋季出现频次最高，冬季次之，夏季最低。     

Predicting channel patterns

The proposed distinction between meandering and braided river channel patterns, on the basis of bankfull specific stream power and bed material size, is analysed and rejected. Only by using regime-based estimates of channel widths (rather than actual widths) has discrimination been achieved, and it is argued that this procedure is unacceptable.An alternative is to explore the patterning processes underlying the marked pattern scatter on bankfull stream power/bed material size plots. Of the five sets of patterning processes, large-scale bedform development and stability is seen as especially important for meandering and braiding. For gravel-bed rivers, bedforms developed at around or above bankfull stage appear important for pattern generation, with braiding relating to higher excess shear stress and Froude number. There seems to be an upper threshold to both meandering and braiding which is achieved at extreme discharges and steep gradients, as on steep alluvial fans, rather than for the rivers with available flow data here considered. For sand-bed rivers with greater excess shear stress, the equivalent upper plane bed threshold may occur below bankfull, with bed material mobility and bedform modification occurring over a wider range of sub-bankfull discharges. Sand-bed channel margin outlines appear to be less perturbed by bedform effects than gravel bed planforms, and they may have naturally straight or sinuous planforms. Bedform relief may nevertheless lead to some being designated as braided when viewed at low flows.It is concluded that the use of a single-stage stream power measure and bed material size alone is unlikely to achieve meandering/braiding discrimination.     

Centralized power and divided space: `Fractured regions' in the Israeli `ethnocracy'

This paper uses a critical political-geographical perspective to account for the high centrality of power found in Israel. It suggests that the concentration of power have not been solely caused by national solidarity and integration or by metropolitan development, as commonly explained, but also by the territorial `fracturing' of the main social and ethnic groups in Israel/Palestine. This has prevented the emergence of effective pressure for regional devolution. Israel's character as a settler and settling state, and its central project of Judaizing contested territories, enabled the Israeli `ethnocracy' and its (mainly Ashkenazi and secular) elites to create a political geography of `fractured ethnic and social regions'. Dispersing minorities and legitimizing segregation and inequality, all in the name of the `national interest', achieved this. The Israeli political landscape is therefore organized as `fractured regions', each representing a distinct and interconnected, yet geographically dispersed, set of localities, and resembling a `chain of beads'. The logic of dispersal and segregation, in turn, has also influenced patterns of development and residential separation within Israel's main urban areas. Thus, ethnic and social fragmentation and conflict, and not a putative process of national or metropolitan integration, can explain much of Israel's highly centralized power structure.     

Assessment of Geomagnetic Hazard to Power Systems in Canada

This paper presents an assessment ofgeomagnetic hazard on the five largest power systemsin Canada. From east to west these are: Nova ScotiaPower, Hydro-Quebec, Ontario Hydro West System, Manitoba Hydro, and the northern B.C. Hydro system. The aim of this study was to determine howfrequently, and where in a system, largegeomagnetically induced currents (GIC) could beexpected. To do this, an analysis was made of thespectral characteristics of the magnetic fieldvariations that cause GIC, and a review was made ofpublished magnetotelluric soundings in order todetermine conductivity models for different parts ofthe country. The magnetic field spectra and theconductivity information were then used to determinethe electric fields produced during geomagneticdisturbances. A relation was determined betweenelectric field magnitudes and the magnetic activityindex, Kp so that statistics for Kp could be used todetermine the occurrence rates of large electricfields. Power system models were used to determinethe GIC produced by the `1-year' and `10-year'electric fields experienced by each power system.     

Power-laws and applications to earthquake populations

In this paper we study the rooted tree model applying the concepts of probability to obtain results of importance in understanding power-law distributions in pure populations and also in an ensemble of pure populations. The well-known Gutenberg-Richter relation, which is an empirical relation providing the number of earthquakes whose magnitude exceeds a given value, is shown to be an asymptotic form of survivor function of earthquake magnitudes. The implications of this model are briefly discussed in relation to other branches of sciences where power-law distributions are encountered.     

River incision and vegetation dynamics in cut-off channels

The consequences of river incision on ecosystems dynamics in cut-off channels were hypothesized to be 1) the reduction of river backflows and overflows of the river in the former channels; 2) the reduction of seepage flows from the river and drainage into the channels; 3) the drainage of the hillslope aquifer by the former channels. The subsequent changes of aquatic plant communities should be 1) the terrestrialization of the higher part of former channels and 2) their change into more oligotraphent ones if the hillslope aquifer is poorer in nutrients than the river. In those reaches where the river bed is aggraded, river backflows in the cut-off channel should increase, as should overflows and seepage, and more eutraphent species should develop. Changes in aquatic vegetation were studied over a ten-year period in four cut-off channels supplied by a nutrient-poor hillslope aquifer and a nutrient-rich river. Two of them were located in an incised reach of the river, one in an aggraded reach and one (reference) in a reach that was neither aggraded nor incised. The vegetation of the reference channel exhibited only minor changes over the ten-year period, indicating that the successional trend is not perceptible at the time scale of the study, and thus that any change observed in the other channels can be ascribed to river incision or aggradation. Terrestrialization expected in the channels located in the incised reach clearly progressed in the downstream parts, but was inhibited by groundwater supplies in the upper parts. As expected, oligotraphent communities progressed or remained dominant in the upper part. The channel located in the aggraded reach of the river exhibited the highest floristic changes. As expected, eutraphent communities progressed in this channel, but unexpectedly, terrestrialization also progressed in the upstream part. Alternative explanations are: 1) aggradation could have instigated more backflows and overflows without modifying significantly the mean water-level and 2) more frequent water overflows could have favoured alluvial deposition and thus terrestrialization.     

A diffusion approximation for a network of reservoirs with power law release rule

A diffusion approximation for a network of continuous time reservoirs with power law release rules is examined. Under a mild assumption on the inflow processes, we show that for physically reasonable values of the power law constants, the system of processes converges to a multi-dimensional Gaussian diffusion process. We also illustrate how the limiting Gaussian process may be used to compute approximations to the original system of reservoirs. In addition, we study the quality of our approximations by comparing them to results obtained by simulations of the original watershed model. The simulations offer support for the use of the approximation developed here.     

浙江天目山自然保护区珍稀濒危植物及其利用与保护

天目山是浙江省珍稀濒危植物最丰富的地区，共有国家保护的珍稀濒危植物２５科、３４属、３７种，其中属二级保护１３种，三级保护２４种．论述了天目山珍稀濒危植物的区系特点、类型及地理分布，列举了它们的一些利用价值，最后提出了保护天目山珍稀濒危植物的一系列建议．     

等高活篱笆试验研究的若干问题*

本文讨论了等高活篱笆技术在设计、管理和效益分析等方面的原则与方法,指出应结合当地的自然条件和社会经济需求,围绕一两种主要功用来应用这种坡地持续利用技术。植物种类选择和篱笆的管理应以篱笆植物的属性、篱笆的形成及农林复合系统中各组分的和谐关系为依据。活篱笆改善生态的功能、社会经济效益宜采用费用-效益分析的方法进行评价。     

Exploring nonlinear characteristics in seismogenic process

Power spectral characteristics of the seismic activities before and after the seven large earthquake — Haicheng, Tangshan, Lancang, Longling, Mabian, Puer and Songpan are studied by spectrum analysis method. The results show that they all have continuous power spectrum and aperiodic behaviour. When the time away from the large earthquake occurrence, the characteristics of the seismic activities are obviously accompanied by stochastic components. About one year before main shock, the moving orbits constructed by spectrum amplitudes showed the contracting tendency. And the properties during that time may display as flicker noise. One’s another time almost mixed whole phase space. But the essence of seismic activities after main shocks is a chaotic state accompanied with much noises. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 276–281, 1993. This subject is supported by the Chinese Joint Seismological Foundation.