RELATIVE RATES OF EVAPORATIVE WATER LOSSES FROM OPEN AND VEGETATION COVERED WATER BODIES1

ABSTRACT: A review of literature pertaining to the relative rates of evaporation from vegetation covered and open water bodies is presented. The review indicates that the only reliable experiments capable of correctly addressing this question are those conducted in situ. Experiments of this nature show the ratio of vegetation covered (swamp) evaporation to open water evaporation to generally be less than unity over extensive surfaces and to only approach unity for vegetation that is young and vigorous. Recent experimental evidence presented within a theoretical context, however, indicates that even in the latter situation the ratio may never reach unity. Consequently, over large lakes and reservoirs, the presence of vegetation may actually be a water conservation mechanism, with the eradication of the vegetation leading to significantly increased evaporative water losses.     

Dynamics of Ammonia Exchange in Response to Cutting and Fertilising in an Intensively-Managed Grassland

Continuous micrometorological measurements of ammonia (NH₃)exchange were made for a period of 19 months (May 1998–November 1999) over intensively managed grassland in southern Scotland. This study focused on the influence of management activities, such as cutting and fertilising, on vegetation-atmosphere exchange of NH₃. Measurements were conducted within the European project GRAMINAE (GRassland AMmonia INteractions Across Europe) within which the Scottish site forms one of 6 sites in an E–W transect across Europe. NH₃ emissions were enhanced (up to 300 ng m^-2 s^-1) after cutting followed by larger emissions after fertilising (up to 1400 ng m^-2 s^-1). Annual budget calculations show the intensive grassland acted as a net source (1.8 kg N ha^-1 yr¹) although fluxes were bi-directional with deposition dominating in the winter and emission in the summer. Initial modelling of the NH₃ exchange using a `canopy compensation point' model has been conducted for key periods. The dynamics of the fluxes during these key periods, such as before and after cutting and fertilising, may be reproduced by introducing different values of the apoplastic ratio, = [NH₄ ⁺]/[H⁺].     

环境物探技术在岩溶勘察中的应用及其效果

将高密度电阻率法及工程地震映像法两种环境物探技术同时应用于实际的地质灾害(岩溶)勘察中,结果表明:对于岩溶这样的地质灾害,单一环境物探技术虽然能清楚反映其埋深、规模和发育情况,但各有缺陷。而多种环境物探技术的综合使用,相互补充,将能大大提高岩溶勘察的准确性,提高勘察效果和效率。     

Method of Testing the Penetration of Acid Solutions Through Safety Gloves

Because they cause burns that are difficult to heal, acids are dangerous, and steps should be taken to ensure that the human skin does not come into contact with them. For this purpose safety gloves are generally used by workers who have to handle acids. Such gloves need to be tested to ensure that they are acid resistant. Standard EN 374 (European Committee for Standardization [CEN], 1993c) specifies a method of testing the permeation of liquid chemicals, on a molecular level, through glove material, but it may be difficult to ensure the fitness of the joints of a two-compartment cell, when gloves are lined with jersey. To deal with this a simple pH-meter method to test the permeation of acid and alkali solutions through safety gloves has been developed. The permeation of H₂S0₄, HCI, HN0₃, and CH₃COOH through gloves made from neoprene, nitrile, and PVC was tested. This method seems to be simple and economical.     

Identification of a multixenobiotic resistance mechanism in Xenopus laevis embryos

In the '90's a membrane-associated transport protein, discovered in aquatic organisms, was considered to be expressed in response to environmental xenobiotics. Like the multidrug resistance protein found in mammalian tumor cell lines, this protein confers resistance in organisms in polluted areas by binding xenobiotics and transporting them out of the cells in an energy-dependent manner.This study investigates the expression and the activity of a P-glycoprotein (Pgp) involved in a multixenobiotic resistance mechanism (MXRW) during the early developmental stages and in tissues of adult Xenopus laevis.     

Structural-temporal organization of a rodent community in the Teletskaya Taiga,Altai Mountains

The structural-temporal organization of a murine rodent community in the taiga has been studied near Lake Teletskoe, Mountain Altai. The results show that the long-term dynamics of indices characterizing community diversity depend mainly on changes in the structure of dominance rather than on the population dynamics of species. The distribution of species in the factor space corresponds to their preference for certain biotopes, from dry to relatively moist. An analysis of relationships within the rodent community has revealed the synchronous dynamics of species abundance and antiphase pattern of changes in the structural indices of dominant species.     

确定岩体斜坡滑动面抗剪强度的动态反分析方法

滑动结构面的抗剪强度在岩体滑坡的稳定性计算中是最重要的参数,也是最难以确定的。基于岩体抗剪强度是多种因素影响下的随机变量这一认识前提下,本文以西柏坡“中共中央解放军总部”旧址滑坡为例提出了确定岩体斜坡滑动面抗剪强度的动态反分析方法,并对该方法获得的抗剪强度的实用性进行了分析。结果表明,反分析方法是获得岩体斜坡滑动面抗剪强度的最经济、合理的途径。     

L型钢管混凝土芯柱耐火极限研究

火灾高温对结构安全有显著影响,为研究等肢L形钢管混凝土芯柱的耐火极限及其影响因素,利用ABAQUS软件建立合理的高温反应分析模型,在验证模型可靠性基础上,分析了荷载比、截面边长、长细比、荷载偏心率、含钢率等对L形钢管混凝土芯柱耐火极限的影响。研究结果表明:在一定参数范围内,荷载比和截面边长是构件耐火极限的主要影响参数,荷载比越小,截面边长越大,构件的耐火极限越高;长细比和荷载偏心率对其影响较大,长细比和荷载偏心率越小,构件的耐火极限越高;含钢率对其影响不显著。结果可为异形钢管混凝土芯柱的抗火安全设计提供参考。     

综放工作面沿空留巷支护阻力研究

为了计算综放工作面沿空留巷支护阻力,以结构力学理论为基础,分析综放工作面沿空留巷支护阻力计算模型,建立沿空留巷围岩和支护体的结构力学模型,应用超静定结构和静定结构分析支护体与沿空留巷围岩相互作用机制,推导出巷旁支护阻力的计算公式.结果表明,进行沿空留巷支护阻力力学分析时,要考虑顶板极限断裂前和断裂后两种状态下的受力情况,支护阻力与岩层厚度、容重、煤体极限平衡区宽度、跨距、支护体宽度和巷道宽度等因素密切相关.工业性试验表明,该技术的应用是成功而有效的.因此,综放巷内沿空留巷围岩结构力学模型和支护阻力计算公式是合理的,可在类似条件的综放工作面中应用.