Alterations of the Nitrogen Mineralization Rates in Soils of Forest Community Depending on the Ski Run Construction (Mount Uludag,Bursa,Turkey)

Since 1940s,Mount Uludag(Bithynian Olympus) has been considered famous with winter sports center in Turkey.In addition,it is one of the rare places because of its plant diversity and is also one of the important plant areas of Turkey.The ski run constructions are rapidly increased in the past decades in the alpine and subalpine belts of the mountain.Rate of nitrogen mineralization and some properties of soil were investigated in the soils of the three ski runs and undisturbed neighborhood forest sites.These...     

Studying the post-fire performance of tussock grasses in Patagonia: Survival, biomass production and early competition

Patagonia grasslands are subjected to two main disturbances, fire and grazing, but little information is available about its effects on vegetation. We studied post-fire survival and resprouting ability of two dominant grass species, Stipa speciosa and Festuca pallescens, for four years; evaluated the effect of early post-fire defoliation on both species; and tested whether competition is important in post-fire recovery in San Ramón Ranch, NW Patagonia (Argentina). To simulate grazing, a clipping treatment was applied at the beginning and end of growing seasons. Survival rates were high (>60%) and, after three years, biomass of both species in the burned area was similar to the unburned area. Competition seems to play an important role in the early post-fire recovery of both species, particularly in the case of F. pallescens that increased 87% the biomass production without competition. Fire may improve forage quality by eliminating the standing dead material, but early post-fire grazing might endanger the persistence of F. pallescens. We suggest requiring a resting period before livestock introduction and controlling grazing intensity.     

Pile and pile group response to tunnelling using a large diameter slurry shield – Case study in Shanghai

The study investigates the disturbance to piles and pile groups caused by multiple nearby drives of a large diameter slurry shield-driven tunnelling machine in Shanghai. The minimum distance between the slurry shield tunnel (with diameter D = 15.43 m) and the adjacent pile groups of Metro Line 3 and Yixian Elevated Road is 1 m. The nonlinear finite element (FE) software program ABAQUS was used to analyse the movement of the pile groups caused by the process of shield tunnelling. A field investigation was conducted before the multiple crossings to study the impact (movement and excess pore water pressure) on the surrounding soil and piles caused by the tunnelling process. The field investigation is divided into two sections: (i) free-field tunnelling, and (ii) tunnelling close to trial piles pre-installed in the section. For the full-scale test, tunnelling variable, including slurry pressure and grouting pressure, are adjusted during construction to reduce the disturbance during tunnelling close to pile groups supporting two elevated bridges. The FE simulation of the multiple crossings includes two steps: (a) shield tunnelling along the south bound tunnel approaching the working shaft at the western bank of the Huangpu River, and passing separately between two adjacent pile groups of each bridge; (b) return tunnel passing again between the pile groups of the two bridges along the north bound tunnel. Three different FE models are generated: (1) free-field tunnelling process, (2) tunnelling close to trial piles, and (3) multiple tunnel passes adjacent to pile groups supporting the two elevated bridges. Most of the relevant factors in tunnelling are taken into consideration in the FE models including (a) slurry pressure, (b) grouting pressure, (c) grouting material hardening, and (d) soil-pile interaction.     

Cold fronts induce changes in phycoperiphyton structure in a shallow lake: Wind forces drive algae succession and nutrient availability

We evaluated wind as the main structuring force in driving phycoperiphyton structure, community composition and succession in a warm, polymictic shallow lake in southern Brazil. Mangueira Lake is continuously mixed due to its exposure to wind, and during cold fronts the wind changes from the dominant NE direction to a SSW direction. Our question was: could changes in wind forces induce phycoperiphyton succession and determine population structure? To answer this question, we studied the phycoperiphyton successional response to a change in wind forces under three different situations: on clean macrophyte leaves in an open site (Open) and in an enclosed site protected from the wind (Enclosure), and the Natural community growing on uncleaned macrophyte leaves in an open site. Cold fronts improved nutrient availability and changed the algal community. The phycoperiphyton natural community was dominated by Epithemia spp bound in gross masses of green filaments during cold fronts. However, the wind direction typically changes when cold fronts are over (NE-E) and wind blowing from the off-shore direction dislodged the attached algae biomass and pushed it toward to lake shore, inducing community changes. The macrophyte bank exhibited rapid colonization and acted as a refuge for phycoperiphyton, providing habitat heterogeneity, whereas the enclosure acted as a buffer against wind forces, delaying the succession derived from settlement of loosely adhered algae. Furthermore, in the enclosure, the succession only started after a strong disturbance (rain and wind > 10 m s⁻¹) in which lake water flooded the mesocosm inducing colonization. Phycoperiphyton showed resilience and recovered rapidly after the disturbance, when the rain supplied inocula and wind favored colonization with growth forms that take advantage of local conditions, depending of wind dynamics.     

激发态氮分子N*2在电离层中的作用的模拟研究

激发态氮分子N*2在电离层F区中起着重要的作用,它使F区占主导地位的O+离子的损失率增大,从而使该区的电子浓度减少. 本文利用理论电离层数值模型,通过考虑与不考虑N*2的作用,对包括1990年6月、1997年5月、1998年5月以及2000年4月磁暴事件在内的时间区间的电离层响应情形进行模拟研究,并与实测结果进行对比. 结果表明,N*2对电离层电子浓度的影响在太阳活动高年非常明显,在太阳活动低年虽有些影响,但效果并不明显,其程度远不如高年. 在太阳活动高年,不仅是磁暴期间,在较宁静期间也必须考虑N*2的影响. 而且,在考虑N*2的作用时,还与激发态振动温度Tν有关,在采用Tν=Tn（其中Tn为背景中性大气的温度）的简化处理时,所得结果与观测结果的符合程度不如对Tν进行精确计算时所得的结果好. 模拟结果还表明,太阳活动高年,N*2作用的结果主要是使150km高度以上的F区电离层电子浓度减少,而对150km以下高度的电离层电子浓度则影响不大. 另外,N*2基本不影响F2层峰高hmF2的值.     

倾斜观测载荷干扰源最小"安静"距离理论分析

作为一种高精度的形变观测,钻孔倾斜观测点必须尽可能避开干扰源。河流、湖泊、仓库(货场、列车编组站)和铁路,是几种主要的影响钻孔倾斜观测的地面载荷变化干扰源。中对这些地面载荷变化干扰影响分别建立了不同的模型,提出了针对一定的干扰限定指标,估计观测点到干扰源的最小“安静”距离的方法。     

Paleoecological analyses of lake sediments reveal prehistoric human impact on forests at Anthony Island UNESCO World Heritage Site, Queen Charlotte Islands (Haida Gwaii), Canada

Pollen and plant macrofossil analyses of lake sediments from Anthony Island in the southern Queen Charlotte Islands (Haida Gwaii), British Columbia, reveal 1800 yr of relatively stable temperate rainforest vegetation. Cupressaceae (cedar) pollen percentages and accumulation rates decline about 1000 cal yr BP, coincident with occupation of the island by Haida peoples, who use Thuja plicata (western red cedar) almost exclusively for house construction, dugout canoes, monumental poles, and many other items. Anthropogenic disturbance offers the most likely explanation for the decline of T. plicata.     

地面脉动分析

本文概述了地面脉动的特性及其分析方法，指出了实际应用中应注意的问题。     

断层土壤气的观测与地震短临预报

地震前兆的干扰现象是无时不在的,各种因素的干扰是影响前兆异常定论的一个重要因素,只有在最大限度地降低人为干扰的基础上,进行自然因素的干扰排除,才有可能大大提高异常的可信度,以近十年发展起来的断层土壤气观测为研究对象,对断导土壤气的观测方法,干扰因素以及在地震短临预报中的作用等方面进行系统总结。     

A STORABE PROCESS OF THE MAGNETIC ENERGY RESULTS FROM THE UNSTEADY PLASMA FLOW FIELD IN THE DISTURBANCE REGIONS OF COMETARY TAIL AND ATMOSPHERE

In this paper we discuss coupling processes between a magnetic field and an unsteady plasma motion, and analyze the features of energy storage and conversions in the cometary disturbance regions.